Benzene

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Benzene

Geometry Ball and stick model
Space-filling model
Names
Preferred IUPAC name Benzene
Other names Benzol (historic/German) Cyclohexa-1,3,5-triene; 1,3,5-Cyclohexatriene [6]Annulene (not recommended)
Identifiers
CAS Number	71-43-2
3D model (JSmol)	Interactive image
ChEBI	CHEBI:16716
ChEMBL	ChEMBL277500
ChemSpider	236
ECHA InfoCard	100.000.685
EC Number	200-753-7
KEGG	C01407
PubChem CID	241
RTECS number	CY1400000
UNII	J64922108F
CompTox Dashboard (EPA)	DTXSID3039242

InChI

SMILES
Properties
Chemical formula	C6H6
Molar mass	78.114 g·mol−1
Appearance	Colorless liquid
Odor	sweet aromatic
Density	0.8765(20) g/cm3
Melting point	5.53 °C (41.95 °F; 278.68 K)
Boiling point	80.1 °C (176.2 °F; 353.2 K)
Solubility in water	1.53 g/L (0 °C) 1.81 g/L (9 °C) 1.79 g/L (15 °C) 1.84 g/L (30 °C) 2.26 g/L (61 °C) 3.94 g/L (100 °C) 21.7 g/kg (200 °C, 6.5 MPa) 17.8 g/kg (200 °C, 40 MPa)
Solubility	Soluble in alcohol, CHCl3, CCl4, diethyl ether, acetone, acetic acid
Solubility in ethanediol	5.83 g/100 g (20 °C) 6.61 g/100 g (40 °C) 7.61 g/100 g (60 °C)
Solubility in ethanol	20 °C, solution in water: 1.2 mL/L (20% v/v)
Solubility in acetone	20 °C, solution in water: 7.69 mL/L (38.46% v/v) 49.4 mL/L (62.5% v/v)
Solubility in diethylene glycol	52 g/100 g (20 °C)
log P	2.13
Vapor pressure	12.7 kPa (25 °C) 24.4 kPa (40 °C) 181 kPa (100 °C)
Conjugate acid	Benzenium
UV-vis (λmax)	255 nm
Magnetic susceptibility (χ)	−54.8·10−6 cm3/mol
Refractive index (nD)	1.5011 (20 °C) 1.4948 (30 °C)
Viscosity	0.7528 cP (10 °C) 0.6076 cP (25 °C) 0.4965 cP (40 °C) 0.3075 cP (80 °C)
Structure
Molecular shape	Trigonal planar
Dipole moment	0 D
Thermochemistry
Heat capacity (C)	134.8 J/mol·K
Std molar entropy (So298)	173.26 J/mol·K
Std enthalpy of formation (ΔfH⦵298)	48.7 kJ/mol
Std enthalpy of combustion (ΔcH⦵298)	3267.6 kJ/mol
Hazards
Main hazards	potential occupational carcinogen, flammable
Safety data sheet (SDS)	HMDB
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H225, H304, H315, H319, H340, H350, H372, H410
Precautionary statements	P201, P210, P301+P310, P305+P351+P338, P308+P313, P331
NFPA 704 (fire diamond)	2 3 0
Flash point	−11.63 °C (11.07 °F; 261.52 K)
Autoignition temperature	497.78 °C (928.00 °F; 770.93 K)
Explosive limits	1.2–7.8%
Lethal dose or concentration (LD, LC):
LD50 (median dose)	930 mg/kg (rat, oral)
LCLo (lowest published)	44,000 ppm (rabbit, 30 min) 44,923 ppm (dog) 52,308 ppm (cat) 20,000 ppm (human, 5 min)
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 1 ppm, ST 5 ppm
REL (Recommended)	Ca TWA 0.1 ppm ST 1 ppm
IDLH (Immediate danger)	500 ppm
Related compounds
Related compounds	Toluene Borazine
Supplementary data page
Benzene (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Benzene (also called cyclohexatriene) is an organic chemical compound with the molecular formula C₆H₆. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon.

Benzene is a natural constituent of crude oil and is one of the elementary petrochemicals. Due to the cyclic continuous pi bonds between the carbon atoms, benzene is classed as an aromatic hydrocarbon. It is sometimes abbreviated PhH. Benzene is a colorless and highly flammable liquid with a sweet smell, and is partially responsible for the aroma around petrol (gasoline) stations. It is used primarily as a precursor to the manufacture of chemicals with more complex structure, such as ethylbenzene and cumene, of which billions of kilograms are produced annually. Although a major industrial chemical, benzene finds limited use in consumer items because of its toxicity.

History

Discovery

The word "benzene" derives from "gum benzoin" (benzoin resin), an aromatic resin known to European pharmacists and perfumers since the 16th century as a product of southeast Asia. An acidic material was derived from benzoin by sublimation, and named "flowers of benzoin", or benzoic acid. The hydrocarbon derived from benzoic acid thus acquired the name benzin, benzol, or benzene. Michael Faraday first isolated and identified benzene in 1825 from the oily residue derived from the production of illuminating gas, giving it the name bicarburet of hydrogen. In 1833, Eilhard Mitscherlich produced it by distilling benzoic acid (from gum benzoin) and lime. He gave the compound the name benzin. In 1836, the French chemist Auguste Laurent named the substance "phène"; this word has become the root of the English word "phenol", which is hydroxylated benzene, and "phenyl", the radical formed by abstraction of a hydrogen atom (free radical H•) from benzene.

Kekulé's 1872 modification of his 1865 theory, illustrating rapid alternation of double bonds

In 1845, Charles Mansfield, working under August Wilhelm von Hofmann, isolated benzene from coal tar. Four years later, Mansfield began the first industrial-scale production of benzene, based on the coal-tar method. Gradually, the sense developed among chemists that a number of substances were chemically related to benzene, comprising a diverse chemical family. In 1855, Hofmann used the word "aromatic" to designate this family relationship, after a characteristic property of many of its members. In 1997, benzene was detected in deep space.

Ring formula

Historic benzene structures (from left to right) by Claus (1867), Dewar (1867), Ladenburg (1869), Armstrong (1887), Thiele (1899) and Kekulé (1865). Dewar benzene and prismane are distinct molecules that have Dewar's and Ladenburg's structures. Thiele and Kekulé's structures are used today.

The empirical formula for benzene was long known, but its highly polyunsaturated structure, with just one hydrogen atom for each carbon atom, was challenging to determine. Archibald Scott Couper in 1858 and Johann Josef Loschmidt in 1861 suggested possible structures that contained multiple double bonds or multiple rings, but too little evidence was then available to help chemists decide on any particular structure.

In 1865, the German chemist Friedrich August Kekulé published a paper in French (for he was then teaching in Francophone Belgium) suggesting that the structure contained a ring of six carbon atoms with alternating single and double bonds. The next year he published a much longer paper in German on the same subject. Kekulé used evidence that had accumulated in the intervening years—namely, that there always appeared to be only one isomer of any monoderivative of benzene, and that there always appeared to be exactly three isomers of every disubstituted derivative—now understood to correspond to the ortho, meta, and para patterns of arene substitution—to argue in support of his proposed structure. Kekulé's symmetrical ring could explain these curious facts, as well as benzene's 1:1 carbon-hydrogen ratio.

The new understanding of benzene, and hence of all aromatic compounds, proved to be so important for both pure and applied chemistry that in 1890 the German Chemical Society organized an elaborate appreciation in Kekulé's honor, celebrating the twenty-fifth anniversary of his first benzene paper. Here Kekulé spoke of the creation of the theory. He said that he had discovered the ring shape of the benzene molecule after having a reverie or day-dream of a snake seizing its own tail (this is a common symbol in many ancient cultures known as the Ouroboros or Endless knot). This vision, he said, came to him after years of studying the nature of carbon-carbon bonds. This was 7 years after he had solved the problem of how carbon atoms could bond to up to four other atoms at the same time. Curiously, a similar, humorous depiction of benzene had appeared in 1886 in a pamphlet entitled Berichte der Durstigen Chemischen Gesellschaft (Journal of the Thirsty Chemical Society), a parody of the Berichte der Deutschen Chemischen Gesellschaft, only the parody had monkeys seizing each other in a circle, rather than snakes as in Kekulé's anecdote. Some historians have suggested that the parody was a lampoon of the snake anecdote, possibly already well known through oral transmission even if it had not yet appeared in print. Kekulé's 1890 speech in which this anecdote appeared has been translated into English. If the anecdote is the memory of a real event, circumstances mentioned in the story suggest that it must have happened early in 1862.

The cyclic nature of benzene was finally confirmed by the crystallographer Kathleen Lonsdale in 1929.

Nomenclature

The German chemist Wilhelm Körner suggested the prefixes ortho-, meta-, para- to distinguish di-substituted benzene derivatives in 1867; however, he did not use the prefixes to distinguish the relative positions of the substituents on a benzene ring. It was the German chemist Karl Gräbe who, in 1869, first used the prefixes ortho-, meta-, para- to denote specific relative locations of the substituents on a di-substituted aromatic ring (viz, naphthalene). In 1870, the German chemist Viktor Meyer first applied Gräbe's nomenclature to benzene.

Early applications

In the 19th and early 20th centuries, benzene was used as an after-shave lotion because of its pleasant smell. Prior to the 1920s, benzene was frequently used as an industrial solvent, especially for degreasing metal. As its toxicity became obvious, benzene was supplanted by other solvents, especially toluene (methylbenzene), which has similar physical properties but is not as carcinogenic.

In 1903, Ludwig Roselius popularized the use of benzene to decaffeinate coffee. This discovery led to the production of Sanka. This process was later discontinued. Benzene was historically used as a significant component in many consumer products such as Liquid Wrench, several paint strippers, rubber cements, spot removers, and other products. Manufacture of some of these benzene-containing formulations ceased in about 1950, although Liquid Wrench continued to contain significant amounts of benzene until the late 1970s.

Occurrence

Trace amounts of benzene are found in petroleum and coal. It is a byproduct of the incomplete combustion of many materials. For commercial use, until World War II, most benzene was obtained as a by-product of coke production (or "coke-oven light oil") for the steel industry. However, in the 1950s, increased demand for benzene, especially from the growing polymers industry, necessitated the production of benzene from petroleum. Today, most benzene comes from the petrochemical industry, with only a small fraction being produced from coal. Benzene molecules have been detected on Mars.

Structure

Main article: Aromaticity

The various representations of benzene.

X-ray diffraction shows that all six carbon-carbon bonds in benzene are of the same length, at 140 picometres (pm). The C–C bond lengths are greater than a double bond (135 pm) but shorter than a single bond (147 pm). This intermediate distance is caused by electron delocalization: the electrons for C=C bonding are distributed equally between each of the six carbon atoms. Benzene has 6 hydrogen atoms, fewer than the corresponding parent alkane, hexane, which has 14. Benzene and cyclohexane have a similar structure, only the ring of delocalized electrons and the loss of one hydrogen per carbon distinguishes it from cyclohexane. The molecule is planar. The molecular orbital description involves the formation of three delocalized π orbitals spanning all six carbon atoms, while the valence bond description involves a superposition of resonance structures. It is likely that this stability contributes to the peculiar molecular and chemical properties known as aromaticity. To accurately reflect the nature of the bonding, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms.

Derivatives of benzene occur sufficiently often as a component of organic molecules that the Unicode Consortium has allocated a symbol in the Miscellaneous Technical block with the code U+232C (⌬) to represent it with three double bonds, and U+23E3 (⏣) for a delocalized version.

Benzene derivatives

Main articles: Aromatic hydrocarbons and Alkylbenzenes

Many important chemical compounds are derived from benzene by replacing one or more of its hydrogen atoms with another functional group. Examples of simple benzene derivatives are phenol, toluene, and aniline, abbreviated PhOH, PhMe, and PhNH₂, respectively. Linking benzene rings gives biphenyl, C₆H₅–C₆H₅. Further loss of hydrogen gives "fused" aromatic hydrocarbons, such as naphthalene, anthracene, phenanthrene, and pyrene. The limit of the fusion process is the hydrogen-free allotrope of carbon, graphite.

In heterocycles, carbon atoms in the benzene ring are replaced with other elements. The most important variations contain nitrogen. Replacing one CH with N gives the compound pyridine, C₅H₅N. Although benzene and pyridine are structurally related, benzene cannot be converted into pyridine. Replacement of a second CH bond with N gives, depending on the location of the second N, pyridazine, pyrimidine, or pyrazine.

Production

Four chemical processes contribute to industrial benzene production: catalytic reforming, toluene hydrodealkylation, toluene disproportionation, and steam cracking. According to the ATSDR Toxicological Profile for benzene, between 1978 and 1981, catalytic reformates accounted for approximately 44–50% of the total U.S benzene production.

Catalytic reforming

In catalytic reforming, a mixture of hydrocarbons with boiling points between 60 and 200 °C is blended with hydrogen gas and then exposed to a bifunctional platinum chloride or rhenium chloride catalyst at 500–525 °C and pressures ranging from 8–50 atm. Under these conditions, aliphatic hydrocarbons form rings and lose hydrogen to become aromatic hydrocarbons. The aromatic products of the reaction are then separated from the reaction mixture (or reformate) by extraction with any one of a number of solvents, including diethylene glycol or sulfolane, and benzene is then separated from the other aromatics by distillation. The extraction step of aromatics from the reformate is designed to produce aromatics with lowest non-aromatic components. Recovery of the aromatics, commonly referred to as BTX (benzene, toluene and xylene isomers), involves such extraction and distillation steps.

In similar fashion to this catalytic reforming, UOP and BP commercialized a method from LPG (mainly propane and butane) to aromatics.

Toluene hydrodealkylation

Toluene hydrodealkylation converts toluene to benzene. In this hydrogen-intensive process, toluene is mixed with hydrogen, then passed over a chromium, molybdenum, or platinum oxide catalyst at 500–650 °C and 20–60 atm pressure. Sometimes, higher temperatures are used instead of a catalyst (at the similar reaction condition). Under these conditions, toluene undergoes dealkylation to benzene and methane:

C₆H₅CH₃ + H₂ → C₆H₆ + CH₄

This irreversible reaction is accompanied by an equilibrium side reaction that produces biphenyl (aka diphenyl) at higher temperature:

2 C
₆H
₆ ⇌ H
₂ + C
₆H
₅–C
₆H
₅

If the raw material stream contains much non-aromatic components (paraffins or naphthenes), those are likely decomposed to lower hydrocarbons such as methane, which increases the consumption of hydrogen.

A typical reaction yield exceeds 95%. Sometimes, xylenes and heavier aromatics are used in place of toluene, with similar efficiency.

This is often called "on-purpose" methodology to produce benzene, compared to conventional BTX (benzene-toluene-xylene) extraction processes.

Toluene disproportionation

Toluene disproportionation (TDP) is the conversion of toluene to benzene and xylene.

Given that demand for para-xylene (p-xylene) substantially exceeds demand for other xylene isomers, a refinement of the TDP process called Selective TDP (STDP) may be used. In this process, the xylene stream exiting the TDP unit is approximately 90% p-xylene. In some systems, even the benzene-to-xylenes ratio is modified to favor xylenes.

Steam cracking

Steam cracking is the process for producing ethylene and other alkenes from aliphatic hydrocarbons. Depending on the feedstock used to produce the olefins, steam cracking can produce a benzene-rich liquid by-product called pyrolysis gasoline. Pyrolysis gasoline can be blended with other hydrocarbons as a gasoline additive, or routed through an extraction process to recover BTX aromatics (benzene, toluene and xylenes).

Other methods

Although of no commercial significance, many other routes to benzene exist. Phenol and halobenzenes can be reduced with metals. Benzoic acid and its salts undergo decarboxylation to benzene. The reaction of the diazonium compound derived from aniline with hypophosphorus acid gives benzene. Alkyne trimerisation of acetylene gives benzene.

Uses

Benzene is used mainly as an intermediate to make other chemicals, above all ethylbenzene, cumene, cyclohexane, nitrobenzene, and alkylbenzene. In 1988 it was reported that two-thirds of all chemicals on the American Chemical Society's lists contained at least one benzene ring. More than half of the entire benzene production is processed into ethylbenzene, a precursor to styrene, which is used to make polymers and plastics like polystyrene and EPS. Some 20% of the benzene production is used to manufacture cumene, which is needed to produce phenol and acetone for resins and adhesives. Cyclohexane consumes around 10% of the world's benzene production; it is primarily used in the manufacture of nylon fibers, which are processed into textiles and engineering plastics. Smaller amounts of benzene are used to make some types of rubbers, lubricants, dyes, detergents, drugs, explosives, and pesticides. In 2013, the biggest consumer country of benzene was China, followed by the USA. Benzene production is currently expanding in the Middle East and in Africa, whereas production capacities in Western Europe and North America are stagnating.

Toluene is now often used as a substitute for benzene, for instance as a fuel additive. The solvent-properties of the two are similar, but toluene is less toxic and has a wider liquid range. Toluene is also processed into benzene.

Major commodity chemicals and polymers derived from benzene. Clicking on the image loads the appropriate article

Component of gasoline

As a gasoline (petrol) additive, benzene increases the octane rating and reduces knocking. As a consequence, gasoline often contained several percent benzene before the 1950s, when tetraethyl lead replaced it as the most widely used antiknock additive. With the global phaseout of leaded gasoline, benzene has made a comeback as a gasoline additive in some nations. In the United States, concern over its negative health effects and the possibility of benzene's entering the groundwater have led to stringent regulation of gasoline's benzene content, with limits typically around 1%. European petrol specifications now contain the same 1% limit on benzene content. The United States Environmental Protection Agency introduced new regulations in 2011 that lowered the benzene content in gasoline to 0.62%. In many European languages, the word for petroleum or gasoline is an exact cognate of "benzene".

Reactions

The most common reactions of benzene involve substitution of a proton by other groups. Electrophilic aromatic substitution is a general method of derivatizing benzene. Benzene is sufficiently nucleophilic that it undergoes substitution by acylium ions and alkyl carbocations to give substituted derivatives.

Electrophilic aromatic substitution of benzene

The most widely practiced example of this reaction is the ethylation of benzene.

Approximately 24,700,000 tons were produced in 1999. Highly instructive but of far less industrial significance is the Friedel-Crafts alkylation of benzene (and many other aromatic rings) using an alkyl halide in the presence of a strong Lewis acid catalyst. Similarly, the Friedel-Crafts acylation is a related example of electrophilic aromatic substitution. The reaction involves the acylation of benzene (or many other aromatic rings) with an acyl chloride using a strong Lewis acid catalyst such as aluminium chloride or Iron(III) chloride.

Friedel-Crafts alkylation of benzene by acetyl chloride

Sulfonation, chlorination, nitration

Using electrophilic aromatic substitution, many functional groups are introduced onto the benzene framework. Sulfonation of benzene involves the use of oleum, a mixture of sulfuric acid with sulfur trioxide. Sulfonated benzene derivatives are useful detergents. In nitration, benzene reacts with nitronium ions (NO₂⁺), which is a strong electrophile produced by combining sulfuric and nitric acids. Nitrobenzene is the precursor to aniline. Chlorination is achieved with chlorine to give chlorobenzene in the presence of a Lewis acid catalyst such as aluminium tri-chloride.

Hydrogenation

Via hydrogenation, benzene and its derivatives convert to cyclohexane and derivatives. This reaction is achieved by the use of high pressures of hydrogen in the presence of heterogeneous catalysts, such as finely divided nickel. Whereas alkenes can be hydrogenated near room temperatures, benzene and related compounds are more reluctant substrates, requiring temperatures >100 °C. This reaction is practiced on a large scale industrially. In the absence of the catalyst, benzene is impervious to hydrogen. Hydrogenation cannot be stopped to give cyclohexene or cyclohexadienes as these are superior substrates. Birch reduction, a non catalytic process, however selectively hydrogenates benzene to the diene.

Metal complexes

Benzene is an excellent ligand in the organometallic chemistry of low-valent metals. Important examples include the sandwich and half-sandwich complexes, respectively, Cr(C₆H₆)₂ and [RuCl₂(C₆H₆)]₂.

Health effects

A bottle of benzene. The warnings show benzene is a toxic and flammable liquid.

Benzene is classified as a carcinogen, which increases the risk of cancer and other illnesses, and is also a notorious cause of bone marrow failure. Substantial quantities of epidemiologic, clinical, and laboratory data link benzene to aplastic anemia, acute leukemia, bone marrow abnormalities and cardiovascular disease. The specific hematologic malignancies that benzene is associated with include: acute myeloid leukemia (AML), aplastic anemia, myelodysplastic syndrome (MDS), acute lymphoblastic leukemia (ALL), and chronic myeloid leukemia (CML).

The American Petroleum Institute (API) stated in 1948 that "it is generally considered that the only absolutely safe concentration for benzene is zero". There is no safe exposure level; even tiny amounts can cause harm. The US Department of Health and Human Services (DHHS) classifies benzene as a human carcinogen. Long-term exposure to excessive levels of benzene in the air causes leukemia, a potentially fatal cancer of the blood-forming organs. In particular, acute myeloid leukemia or acute nonlymphocytic leukemia (AML & ANLL) is not disputed to be caused by benzene. IARC rated benzene as "known to be carcinogenic to humans" (Group 1).

As benzene is ubiquitous in gasoline and hydrocarbon fuels that are in use everywhere, human exposure to benzene is a global health problem. Benzene targets the liver, kidney, lung, heart and brain and can cause DNA strand breaks and chromosomal damage. Benzene causes cancer in animals including humans. Benzene has been shown to cause cancer in both sexes of multiple species of laboratory animals exposed via various routes.

Exposure to benzene

According to the Agency for Toxic Substances and Disease Registry (ATSDR) (2007), benzene is both a man-made and naturally occurring chemical from processes that include: volcanic eruptions, wild fires, synthesis of chemicals such as phenol, production of synthetic fibers, and fabrication of rubbers, lubricants, pesticides, medications, and dyes. The major sources of benzene exposure are tobacco smoke, automobile service stations, exhaust from motor vehicles, and industrial emissions; however, ingestion and dermal absorption of benzene can also occur through contact with contaminated water. Benzene is hepatically metabolized and excreted in the urine. Measurement of air and water levels of benzene is accomplished through collection via activated charcoal tubes, which are then analyzed with a gas chromatograph. The measurement of benzene in humans can be accomplished via urine, blood, and breath tests; however, all of these have their limitations because benzene is rapidly metabolized in the human body.

Exposure to benzene may lead progressively to aplastic anemia, leukaemia, and multiple myeloma.

OSHA regulates levels of benzene in the workplace. The maximum allowable amount of benzene in workroom air during an 8-hour workday, 40-hour workweek is 1 ppm. As benzene can cause cancer, NIOSH recommends that all workers wear special breathing equipment when they are likely to be exposed to benzene at levels exceeding the recommended (8-hour) exposure limit of 0.1 ppm.

Benzene exposure limits

The United States Environmental Protection Agency has set a maximum contaminant level (MCL) for benzene in drinking water at 0.005 mg/L (5 ppb), as promulgated via the U.S. National Primary Drinking Water Regulations. This regulation is based on preventing benzene leukemogenesis. The maximum contaminant level goal (MCLG), a nonenforceable health goal that would allow an adequate margin of safety for the prevention of adverse effects, is zero benzene concentration in drinking water. The EPA requires that spills or accidental releases into the environment of 10 pounds (4.5 kg) or more of benzene be reported.

The U.S. Occupational Safety and Health Administration (OSHA) has set a permissible exposure limit of 1 part of benzene per million parts of air (1 ppm) in the workplace during an 8-hour workday, 40-hour workweek. The short term exposure limit for airborne benzene is 5 ppm for 15 minutes. These legal limits were based on studies demonstrating compelling evidence of health risk to workers exposed to benzene. The risk from exposure to 1 ppm for a working lifetime has been estimated as 5 excess leukemia deaths per 1,000 employees exposed. (This estimate assumes no threshold for benzene's carcinogenic effects.) OSHA has also established an action level of 0.5 ppm to encourage even lower exposures in the workplace.

The U.S. National Institute for Occupational Safety and Health (NIOSH) revised the Immediately Dangerous to Life and Health (IDLH) concentration for benzene to 500 ppm. The current NIOSH definition for an IDLH condition, as given in the NIOSH Respirator Selection Logic, is one that poses a threat of exposure to airborne contaminants when that exposure is likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment [NIOSH 2004]. The purpose of establishing an IDLH value is (1) to ensure that the worker can escape from a given contaminated environment in the event of failure of the respiratory protection equipment and (2) is considered a maximum level above which only a highly reliable breathing apparatus providing maximum worker protection is permitted [NIOSH 2004]. In September 1995, NIOSH issued a new policy for developing recommended exposure limits (RELs) for substances, including carcinogens. As benzene can cause cancer, NIOSH recommends that all workers wear special breathing equipment when they are likely to be exposed to benzene at levels exceeding the REL (10-hour) of 0.1 ppm. The NIOSH short-term exposure limit (STEL – 15 min) is 1 ppm.

American Conference of Governmental Industrial Hygienists (ACGIH) adopted Threshold Limit Values (TLVs) for benzene at 0.5 ppm TWA and 2.5 ppm STEL.

Toxicology

Biomarkers of exposure

Several tests can determine exposure to benzene. Benzene itself can be measured in breath, blood or urine, but such testing is usually limited to the first 24 hours post-exposure due to the relatively rapid removal of the chemical by exhalation or biotransformation. Most people in developed countries have measureable baseline levels of benzene and other aromatic petroleum hydrocarbons in their blood. In the body, benzene is enzymatically converted to a series of oxidation products including muconic acid, phenylmercapturic acid, phenol, catechol, hydroquinone and 1,2,4-trihydroxybenzene. Most of these metabolites have some value as biomarkers of human exposure, since they accumulate in the urine in proportion to the extent and duration of exposure, and they may still be present for some days after exposure has ceased. The current ACGIH biological exposure limits for occupational exposure are 500 μg/g creatinine for muconic acid and 25 μg/g creatinine for phenylmercapturic acid in an end-of-shift urine specimen.

Biotransformations

Even if it is not a common substrate for metabolism, benzene can be oxidized by both bacteria and eukaryotes. In bacteria, dioxygenase enzyme can add an oxygen to the ring, and the unstable product is immediately reduced (by NADH) to a cyclic diol with two double bonds, breaking the aromaticity. Next, the diol is newly reduced by NADH to catechol. The catechol is then metabolized to acetyl CoA and succinyl CoA, used by organisms mainly in the Citric Acid Cycle for energy production.

The pathway for the metabolism of benzene is complex and begins in the liver. Several enzymes are involved. These include cytochrome P450 2E1 (CYP2E1), quinine oxidoreductase (NQ01 or DT-diaphorase or NAD(P)H dehydrogenase (quinone 1)), GSH, and myeloperoxidase (MPO). CYP2E1 is involved at multiple steps: converting benzene to oxepin (benzene oxide), phenol to hydroquinone, and hydroquinone to both benzenetriol and catechol. Hydroquinone, benzenetriol and catechol are converted to polyphenols. In the bone marrow, MPO converts these polyphenols to benzoquinones. These intermediates and metabolites induce genotoxicity by multiple mechanisms including inhibition of topoisomerase II (which maintains chromosome structure), disruption of microtubules (which maintains cellular structure and organization), generation of oxygen free radicals (unstable species) that may lead to point mutations, increasing oxidative stress, inducing DNA strand breaks, and altering DNA methylation (which can affect gene expression). NQ01 and GSH shift metabolism away from toxicity. NQ01 metabolizes benzoquinone toward polyphenols (counteracting the effect of MPO). GSH is involved with the formation of phenylmercapturic acid.

Genetic polymorphisms in these enzymes may induce loss of function or gain of function. For example, mutations in CYP2E1 increase activity and result in increased generation of toxic metabolites. NQ01 mutations result in loss of function and may result in decreased detoxification. Myeloperoxidase mutations result in loss of function and may result in decreased generation of toxic metabolites. GSH mutations or deletions result in loss of function and result in decreased detoxification. These genes may be targets for genetic screening for susceptibility to benzene toxicity.

Molecular toxicology

The paradigm of toxicological assessment of benzene is shifting towards the domain of molecular toxicology as it allows understanding of fundamental biological mechanisms in a better way. Glutathione seems to play an important role by protecting against benzene-induced DNA breaks and it is being identified as a new biomarker for exposure and effect. Benzene causes chromosomal aberrations in the peripheral blood leukocytes and bone marrow explaining the higher incidence of leukemia and multiple myeloma caused by chronic exposure. These aberrations can be monitored using fluorescent in situ hybridization (FISH) with DNA probes to assess the effects of benzene along with the hematological tests as markers of hematotoxicity. Benzene metabolism involves enzymes coded for by polymorphic genes. Studies have shown that genotype at these loci may influence susceptibility to the toxic effects of benzene exposure. Individuals carrying variant of NAD(P)H:quinone oxidoreductase 1 (NQO1), microsomal epoxide hydrolase (EPHX) and deletion of the glutathione S-transferase T1 (GSTT1) showed a greater frequency of DNA single-stranded breaks.

Biological oxidation and carcinogenic activity

One way of understanding the carcinogenic effects of benzene is by examining the products of biological oxidation. Pure benzene, for example, oxidizes in the body to produce an epoxide, benzene oxide, which is not excreted readily and can interact with DNA to produce harmful mutations.

Routes of exposure

Inhalation

Outdoor air may contain low levels of benzene from automobile service stations, wood smoke, tobacco smoke, the transfer of gasoline, exhaust from motor vehicles, and industrial emissions. About 50% of the entire nationwide (United States) exposure to benzene results from smoking tobacco or from exposure to tobacco smoke. After smoking 32 cigarettes per day, the smoker would take in about 1.8 milligrams (mg) of benzene. This amount is about 10 times the average daily intake of benzene by nonsmokers.

Inhaled benzene is primarily expelled unchanged through exhalation. In a human study 16.4 to 41.6% of retained benzene was eliminated through the lungs within five to seven hours after a two- to three-hour exposure to 47 to 110 ppm and only 0.07 to 0.2% of the remaining benzene was excreted unchanged in the urine. After exposure to 63 to 405 mg/m3 of benzene for 1 to 5 hours, 51 to 87% was excreted in the urine as phenol over a period of 23 to 50 hours. In another human study, 30% of absorbed dermally applied benzene, which is primarily metabolized in the liver, was excreted as phenol in the urine.

Exposure from soft drinks

Main article: Benzene in soft drinks

Under specific conditions and in the presence of other chemicals benzoic acid (a preservative) and ascorbic acid (Vitamin C) may interact to produce benzene. In March 2006, the official Food Standards Agency in Britain conducted a survey of 150 brands of soft drinks. It found that four contained benzene levels above World Health Organization limits. The affected batches were removed from sale. Similar problems were reported by the FDA in the United States.

Contamination of water supply

In 2005, the water supply to the city of Harbin in China with a population of almost nine million people, was cut off because of a major benzene exposure. Benzene leaked into the Songhua River, which supplies drinking water to the city, after an explosion at a China National Petroleum Corporation (CNPC) factory in the city of Jilin on 13 November 2005.

When plastic water pipes are subject to high heat, the water may be contaminated with benzene.

Murder

The Nazis used benzene administered via injection as one of their many methods for killing.

Benzene in soft drinks

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Benzene_in_soft_drinks 

Benzene in soft drinks is of potential concern due to the carcinogenic nature of the benzene molecule. This contamination is a public health concern and has caused significant outcry among environmental and health advocates. Benzene levels are regulated in drinking water nationally and internationally, and in bottled water in the United States, but only informally in soft drinks. The benzene forms from decarboxylation of the preservative benzoic acid in the presence of ascorbic acid (vitamin C) and metal ions (iron and copper) that act as catalysts, especially under heat and light.

Formation in soft drinks

The major cause of benzene in soft drinks is the decarboxylation of benzoic acid in the presence of ascorbic acid (vitamin C, E300) or erythorbic acid (a diastereomer of ascorbic acid, E315). Benzoic acid is often added to drinks as a preservative in the form of its salts sodium benzoate (E211), potassium benzoate (E 212), or calcium benzoate (E 213). Citric acid is not thought to induce significant benzene production in combination with benzoic acid, but some evidence suggests that in the presence of ascorbic or erythorbic acid and benzoic acid, citric acid may accelerate the production of benzene.

The proposed mechanism begins with hydrogen abstraction by the hydroxyl radical, which itself is produced by the Cu²⁺-catalysed reduction of dioxygen by ascorbic acid:

Other factors that affect the formation of benzene are heat and light. Storing soft drinks in warm conditions speeds up the formation of benzene.

Calcium disodium EDTA and sugars have been shown to inhibit benzene production in soft drinks.

The International Council of Beverages Associations (ICBA) has produced advice to prevent or minimize benzene formation.

Limit standards in drinking water

Various authorities have set limits on benzene content in drinking water. The following limits are given in parts per billion (ppb; μg/kg).

• World Health Organization (WHO): 10 ppb (WHO notes that benzene should be avoided whenever technically feasible.)
• Republic of Korea (South Korea): 10 ppb
• Canada: 5 ppb
• United States: 5 ppb
• European Union: 1 ppb
• State limits within the United States: California, Connecticut, New Jersey, and Florida: 1 ppb

The EPA and California have set public health goals for benzene of 0 ppb and 0.15 ppb.

Environmental exposure to benzene

See also: Benzene § Exposure to benzene

Benzene in soft drinks has to be seen in the context of other environmental exposure. Taking the worst example found to date of a soft drink containing 87.9 ppb benzene, someone drinking a 350 ml (12 oz) can would ingest 31 μg (micrograms) of benzene, almost equivalent to the benzene inhaled by a motorist refilling a fuel tank for three minutes. While there are alternatives to using sodium benzoate as a preservative, the casual consumption of such a drink is unlikely to pose a significant health hazard to a particular individual (see, for example, the EPA IRIS document on benzene).

The UK Food Standards Agency has stated that people would need to drink at least 20 litres (5.5 gal) per day of a drink containing benzene at 10 μg to equal the amount of benzene they would breathe from city air every day. Daily personal exposure to benzene is determined by adding exposure from all sources.

• Air: A European study found that people breathe in 220 μg of benzene every day due to general atmospheric pollution. A motorist refilling a fuel tank for three minutes would inhale a further 32 μg. The estimated daily exposure from "automobile-related activities" is 49 μg and for driving for one hour is 40 μg.
• Smoking: For smokers, cigarette smoking is the main source of exposure to benzene. Estimates are 7900 μg per day (smoking 20 cigarettes per day), 1820 μg/day, and 1800 μg/day.
• Passive smoking: Benzene intake from passive smoking is estimated at 63 μg/day (Canada) and 50 μg/day.
• Diet and drinking water: 0.2 to 3.1 μg per day.

History

1990s

In 1990, a study reported having found benzene in bottles of Perrier for sale in the United States, resulting in a voluntary product recall.

In the early 1990s, the soft drink industry initially approached FDA with concerns about benzene formation in soft drinks. Following testing, FDA asked manufacturers to voluntarily reformulate. By 1993, FDA determined that most drinks had little benzene contamination.

In 1993, research showed how benzene can form from benzoic acid in the presence of vitamin C.

In the summer of 1998, a number of well known soft drinks manufacturers had to withdraw large quantities of their products from sale after benzene contamination in some production plants was discovered.

2005

In November 2005, the FDA received test results conducted by private citizens that benzene was forming at low levels in several types of beverages.

In December 2005, Germany's Federal Institute for Risk Assessment (Bundesinstitut für Risikobewertung) published a review of benzene's possible formation in foods and drinks.

2006

In February 2006, an unnamed former chemist at the FDA publicly revealed that benzene may be created as part of a chemical reaction during production of soft drinks, particularly those having an orange flavor. Full-scale investigations immediately started at the Food Standards Agency (UK) and in Germany to reveal exactly which amounts of benzene, if any, were present, with several other organizations awaiting their findings.

The United Kingdom's Food Standards Agency released results on March 31, 2006 for 150 beverages. Its results showed 43 beverages contained benzene, four of which contained levels above the World Health Organization drinking water standards (10 ppb). These four were withdrawn from sale.

In April 2006, the Korea Food & Drug Administration (KFDA) announced that it had detected benzene in 27 out of 30 (90%) vitamin-enriched drinks on sale in South Korea. It said the detected amount of benzene – ranging from 5.7 to 87.8 ppb – was not harmful to humans but advised manufacturers of beverages containing more than 10 ppb of benzene to voluntarily recall their products.

The FDA released preliminary results in May 2006 for 100 beverages showing that many soft drinks contained low levels of benzene (less than 5 ppb, the federal drinking water limit) while four drinks contained amounts above the standard. Two of these drinks contained amounts 15-18 times above the drinking water standard. Many of the products showed large variations in the amount of benzene they contained. The FDA stated that it is working with manufacturers to reformulate products that contain benzene above the federal drinking water standard.

These test results are both lower and more accurate than a previous long-term study by the FDA. In the Total Diet Study that FDA conducted from 1996 - 2001 to determine the amounts of volatile organic compounds in various foods, FDA used an analytical procedure that caused more benzene to form in the drinks during the test.

The FDA emphasized that most beverages contain levels below 5 ppb and pose no risk to consumers. Furthermore, there are no standards for beverages beyond drinking and bottled water.

On 9 June 2006, Health Canada released its study results of benzene levels in beverages. Four products out of 118 had levels above the Canadian guideline of five micrograms per liter for benzene in drinking water (average range 6.0 to 23.0 μg/L). The follow up study the next year found only three samples with marginally higher levels and concluded the average levels were quite low.

On 24 August 2006, two soft drink manufacturers agreed to settle a class-action lawsuit that had been filed by a group of parents in the Superior Court of the District of Columbia. The two companies, Zone Brands Inc., maker of "BellyWashers" products, and TalkingRain Beverage Co., denied that their products were harmful, but agreed to change the ingredients in their drinks.

2008

Coca-Cola announced that it would be phasing out sodium benzoate from many of its drinks, but not Fanta and Sprite. As of August 2012, Coca-Cola Zero and Barq's root beer still contains benzoate (added as potassium salt and sodium salt respectively).

A Belgian study found that plastic packaging may play an important role in the formation of benzene in soft drinks.

Soft drink

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Soft_drink 

A glass of cola served with ice cubes

 

Soft drink vending machine in Japan

A soft drink is a drink that usually contains water (often carbonated), a sweetener, and a natural and/or artificial flavoring. The sweetener may be a sugar, high-fructose corn syrup, fruit juice, a sugar substitute (in the case of diet drinks), or some combination of these. Soft drinks may also contain caffeine, colorings, preservatives, and/or other ingredients.

Soft drinks are called "soft" in contrast with "hard" alcoholic drinks. Small amounts of alcohol may be present in a soft drink, but the alcohol content must be less than 0.5% of the total volume of the drink in many countries and localities if the drink is to be considered non-alcoholic. Fruit punch, tea (even kombucha), and other such non-alcoholic drinks are technically soft drinks by this definition, but are not generally referred to as such.

Soft drinks may be served cold, over ice cubes, or at room temperature. They are available in many container formats, including cans, glass bottles, and plastic bottles. Containers come in a variety of sizes, ranging from small bottles to large multi-liter containers. Soft drinks are widely available at fast food restaurants, movie theaters, convenience stores, casual-dining restaurants, dedicated soda stores, vending machines, and bars from soda fountain machines. Soft drinks are usually served in paper or plastic disposable cups in the first three venues. In casual dining restaurants and bars, soft drinks are often served in glasses made from glass or plastic. Soft drinks may be drunk with straws or sipped directly from the cups.

Soft drinks are mixed with other ingredients in several contexts. In Western countries, in bars and other places where alcohol is served (e.g. airplanes, restaurants and nightclubs), many mixed drinks are made by blending a soft drink with hard liquor and serving the drink over ice. One well-known example is the rum and coke, which may also contain lime juice. Some homemade fruit punch recipes, which may or may not contain alcohol, contain a mixture of various fruit juices and a soft drink (e.g. ginger ale). At ice cream parlors and 1950s-themed diners, ice cream floats consisting of a soft drink poured over ice cream, such as root beer floats, are often sold. Some types of soft drinks are lemon-lime drinks, orange soda, cola, grape soda, and root beer.

Within a decade of the invention of carbonated water by Joseph Priestley in 1767 inventors in Britain and in Europe had used his concept to produce the drink in greater quantities, with one such inventor, J. J. Schweppe, forming Schweppes in 1783 and selling the world's first bottled soft drink. Soft drink brands introduced in the 19th century include R. White's Lemonade in 1845, Dr Pepper in 1885, and Coca-Cola in 1886. Subsequent brands include Pepsi, Irn-Bru, Sprite, Fanta, and 7 UP.

Terminology

See also: Names for soft drinks in the United States

While the term "soft drink" is commonly used in product labeling and on restaurant menus, in many countries these drinks are more commonly referred to by regional names, including carbonated drink, cool drink, cold drink, fizzy drink, fizzy juice, lolly water, pop, seltzer, soda, coke, soda pop, tonic, and mineral. Due to the high sugar content in typical soft drinks, they may also be called sugary drinks.

In the United States, the 2003 Harvard Dialect Survey tracked the usage of the nine most common names. Over half of the survey respondents preferred the term "soda", which was dominant in the Northeastern United States, California, and the areas surrounding Milwaukee and St. Louis. The term "pop", which was preferred by 25% of the respondents, was most popular in the Midwest and Pacific Northwest, while the genericized trademark "coke", used by 12% of the respondents, was most popular in the Southern United States. The term "tonic" is distinctive to eastern Massachusetts, although usage is declining.

In the English-speaking parts of Canada, the term "pop" is prevalent, but "soft drink" is the most common English term used in Montreal.

In the United Kingdom and Ireland, the term "fizzy drink" is common. "Pop" and "fizzy pop" are used in Northern England, South Wales, and the Midlands, while "mineral" or "lemonade" (as a general term) are used in Ireland. In Scotland, "fizzy juice" or even simply "juice" is colloquially encountered. In Australia and New Zealand, "soft drink" or "fizzy drink" is typically used. In South African English, "cool drink" is any soft drink.

In other languages, various names are used: descriptive names as "non-alcoholic beverages", equivalents of "soda water", or generalized prototypical names. For example, the Bohemian variant of the Czech language (but not Moravian dialects) uses "limonáda" for all such beverages, not only for those from lemons. Similarly, the Slovak language uses "malinovka" (= "raspberry water") for all such beverages, not only for raspberry ones.

History

The origins of soft drinks lie in the development of fruit-flavored drinks. In the medieval Middle East, a variety of fruit-flavored soft drinks were widely drunk, such as sharbat, and were often sweetened with ingredients such as sugar, syrup and honey. Other common ingredients included lemon, apple, pomegranate, tamarind, jujube, sumac, musk, mint and ice. Middle Eastern drinks later became popular in medieval Europe, where the word "syrup" was derived from Arabic. In Tudor England, 'water imperial' was widely drunk; it was a sweetened drink with lemon flavor and containing cream of tartar. 'Manays Cryste' was a sweetened cordial flavored with rosewater, violets or cinnamon.

Another early type of soft drink was lemonade, made of water and lemon juice sweetened with honey, but without carbonated water. The Compagnie des Limonadiers of Paris was granted a monopoly for the sale of lemonade soft drinks in 1676. Vendors carried tanks of lemonade on their backs and dispensed cups of the soft drink to Parisians.

Carbonated drinks

Bubbles of carbon dioxide float to the surface of a carbonated soft drink.

Carbonated drinks or fizzy drinks are beverages that contain dissolved carbon dioxide. The dissolution of CO₂ in a liquid, gives rise to fizz or effervescence. The process usually involves carbon dioxide under high pressure. When the pressure is removed, the carbon dioxide is released from the solution as small bubbles, which causes the solution to become effervescent, or fizzy. A common example is the dissolving of carbon dioxide in water, resulting in carbonated water. Carbon dioxide is only weakly soluble in water, therefore it separates into a gas when the pressure is released.

Carbonated beverages are prepared by mixing the flavored syrup with carbonated water, both chilled. Carbonation levels range up to 5 volumes of CO₂ per liquid volume. Ginger ale, colas, and related drinks are carbonated with 3.5 volumes. Other drinks, often fruity ones, are carbonated less.

Equipment used by Joseph Priestley in his experiments on gases and the carbonation of water

In the late 18th century, scientists made important progress in replicating naturally carbonated mineral waters. In 1767, Englishman Joseph Priestley first discovered a method of infusing water with carbon dioxide to make carbonated water when he suspended a bowl of distilled water above a beer vat at a local brewery in Leeds, England. His invention of carbonated water (also known as soda water) is the major and defining component of most soft drinks.

Priestley found that water treated in this manner had a pleasant taste, and he offered it to his friends as a refreshing drink. In 1772, Priestley published a paper entitled Impregnating Water with Fixed Air in which he describes dripping oil of vitriol (or sulfuric acid as it is now called) onto chalk to produce carbon dioxide gas, and encouraging the gas to dissolve into an agitated bowl of water.

"Within a decade, inventors in Britain and in Europe had taken Priestley's basic idea—get some "fixed air," mix it with water, shake—and created contraptions that could make carbonated water more quickly, in greater quantities. One of those inventors was named Johann Jacob Schweppe, who sold bottled soda water and whose business is still around today."

—The Great Soda-Water Shake Up, The Atlantic, October 2014.

Another Englishman, John Mervin Nooth, improved Priestley's design and sold his apparatus for commercial use in pharmacies. Swedish chemist Torbern Bergman invented a generating apparatus that made carbonated water from chalk by the use of sulfuric acid. Bergman's apparatus allowed imitation mineral water to be produced in large amounts. Swedish chemist Jöns Jacob Berzelius started to add flavors (spices, juices, and wine) to carbonated water in the late eighteenth century. Thomas Henry, an apothecary from Manchester, was the first to sell artificial mineral water to the general public for medicinal purposes, beginning in the 1770s. His recipe for 'Bewley's Mephitic Julep' consisted of 3 drachms of fossil alkali to a quart of water, and the manufacture had to 'throw in streams of fixed air until all the alkaline taste is destroyed'.

Johann Jacob Schweppe developed a process to manufacture bottled carbonated mineral water. He founded the Schweppes Company in Geneva in 1783 to sell carbonated water, and relocated his business to London in 1792. His drink soon gained in popularity; among his newfound patrons was Erasmus Darwin. In 1843, the Schweppes company commercialized Malvern Water at the Holywell Spring in the Malvern Hills, and received a Royal Warrant from King William IV.

It was not long before flavoring was combined with carbonated water. The earliest reference to carbonated ginger beer is in a Practical Treatise on Brewing. published in 1809. The drinking of either natural or artificial mineral water was considered at the time to be a healthy practice, and was promoted by advocates of temperance. Pharmacists selling mineral waters began to add herbs and chemicals to unflavored mineral water. They used birch bark (see birch beer), dandelion, sarsaparilla, fruit extracts, and other substances.

Mass market and industrialization

An 1883 advertisement for Schweppes Mineral-Waters

Soft drinks soon outgrew their origins in the medical world and became a widely consumed product, available cheaply for the masses. By the 1840s, there were more than fifty soft drink manufacturers in London, an increase from just ten in the 1820s. Carbonated lemonade was widely available in British refreshment stalls in 1833, and in 1845, R. White's Lemonade went on sale in the UK. For the Great Exhibition of 1851 held at Hyde Park in London, Schweppes was designated the official drink supplier and sold over a million bottles of lemonade, ginger beer, Seltzer water and soda-water. There was a Schweppes soda water fountain, situated directly at the entrance to the exhibition.

Mixer drinks became popular in the second half of the century. Tonic water was originally quinine added to water as a prophylactic against malaria and was consumed by British officials stationed in the tropical areas of South Asia and Africa. As the quinine powder was so bitter people began mixing the powder with soda and sugar, and a basic tonic water was created. The first commercial tonic water was produced in 1858. The mixed drink gin and tonic also originated in British colonial India, when the British population would mix their medicinal quinine tonic with gin.

The Codd-neck bottle invented in 1872 provided an effective seal, preventing the soft drinks from going 'flat'

A persistent problem in the soft drinks industry was the lack of an effective sealing of the bottles. Carbonated drink bottles are under great pressure from the gas, so inventors tried to find the best way to prevent the carbon dioxide or bubbles from escaping. The bottles could also explode if the pressure was too great. Hiram Codd devised a patented bottling machine while working at a small mineral water works in the Caledonian Road, Islington, in London in 1870. His Codd-neck bottle was designed to enclose a marble and a rubber washer in the neck. The bottles were filled upside down, and pressure of the gas in the bottle forced the marble against the washer, sealing in the carbonation. The bottle was pinched into a special shape to provide a chamber into which the marble was pushed to open the bottle. This prevented the marble from blocking the neck as the drink was poured. R. White's, by now the biggest soft drinks company in London and south-east England, featured a wide range of drinks on their price list in 1887, all of which were sold in Codd's glass bottles, with choices including strawberry soda, raspberry soda, cherryade and cream soda.

New York in 1890. A street sign "SODA" is visible at the bottom left part of the image

In 1892, the "Crown Cork Bottle Seal" was patented by William Painter, a Baltimore, Maryland machine shop operator. It was the first bottle top to successfully keep the bubbles in the bottle. In 1899, the first patent was issued for a glass-blowing machine for the automatic production of glass bottles. Earlier glass bottles had all been hand-blown. Four years later, the new bottle-blowing machine was in operation. It was first operated by Michael Owens, an employee of Libby Glass Company. Within a few years, glass bottle production increased from 1,400 bottles a day to about 58,000 bottles a day.

In America, soda fountains were initially more popular, and many Americans would frequent the soda fountain daily. Beginning in 1806, Yale University chemistry professor Benjamin Silliman sold soda waters in New Haven, Connecticut. He used a Nooth apparatus to produce his waters. Businessmen in Philadelphia and New York City also began selling soda water in the early 19th century. In the 1830s, John Matthews of New York City and John Lippincott of Philadelphia began manufacturing soda fountains. Both men were successful and built large factories for fabricating fountains. Due to problems in the U.S. glass industry, bottled drinks remained a small portion of the market throughout much of the 19th century. (However, they were known in England. In The Tenant of Wildfell Hall, published in 1848, the caddish Huntingdon, recovering from months of debauchery, wakes at noon and gulps a bottle of soda-water.)

In the early 20th century, sales of bottled soda increased exponentially around the world, and in the second half of the 20th century, canned soft drinks became an important share of the market. During the 1920s, "Home-Paks" was invented. "Home-Paks" is the familiar six-pack cartons made from cardboard. Vending machines also began to appear in the 1920s. Since then, soft drink vending machines have become increasingly popular. Both hot and cold drinks are sold in these self-service machines throughout the world.

Consumption

Per capita consumption of soda varies considerably around the world. As of 2014, the top consuming countries per capita were Argentina, the United States, Chile, and Mexico. Developed countries in Europe and elsewhere in the Americas had considerably lower consumption. Annual average consumption in the United States, at 153.5 liters, was about twice that in the United Kingdom (77.7) or Canada (85.3).

In recent years, soda consumption has generally declined in the West. According to one estimate, per capita consumption in the United States reached its peak in 1998 and has continually fallen since. A study in the journal Obesity found that from 2003 to 2014 the proportion of Americans who drank a sugary beverage on a given day fell from approximately 62% to 50% for adults, and from 80% to 61% for children. The decrease has been attributed to, among other factors, an increased awareness of the dangers of obesity, and government efforts to improve diets.

At the same time, soda consumption has increased in some low or middle income countries such as Cameroon, Georgia, India, and Vietnam as soda manufacturers increasingly target these markets and consumers have increasing discretionary income.

Production

A jug of bottler's flavor for 7-Up. The syrup-like concentrate lacks sugar and is sold to franchisees to refill.

Soft drinks are made by mixing dry or fresh ingredients with water. Production of soft drinks can be done at factories or at home. Soft drinks can be made at home by mixing a syrup or dry ingredients with carbonated water, or by Lacto-fermentation. Syrups are commercially sold by companies such as Soda-Club; dry ingredients are often sold in pouches, in a style of the popular U.S. drink mix Kool-Aid. Carbonated water is made using a soda siphon or a home carbonation system or by dropping dry ice into water. Food-grade carbon dioxide, used for carbonating drinks, often comes from ammonia plants.

Drinks like ginger ale and root beer are often brewed using yeast to cause carbonation.

Of most importance is that the ingredient meets the agreed specification on all major parameters. This is not only the functional parameter (in other words, the level of the major constituent), but the level of impurities, the microbiological status, and physical parameters such as color, particle size, etc.

Some soft drinks contain measurable amounts of alcohol. In some older preparations, this resulted from natural fermentation used to build the carbonation. In the United States, soft drinks (as well as other products such as non-alcoholic beer) are allowed by law to contain up to 0.5% alcohol by volume. Modern drinks introduce carbon dioxide for carbonation, but there is some speculation that alcohol might result from fermentation of sugars in a non-sterile environment. A small amount of alcohol is introduced in some soft drinks where alcohol is used in the preparation of the flavoring extracts such as vanilla extract.

Producers

Further information: List of soft drink producers

 

Hartwall Jaffa soft drinks

Market control of the soft drink industry varies on a country-by-country basis. However, PepsiCo and The Coca-Cola Company remain the two largest producers of soft drinks in most regions of the world. In North America, Keurig Dr Pepper and Jones Soda also hold a significant amount of market share.

Health concerns

The over-consumption of sugar-sweetened soft drinks is associated with obesity, hypertension, type 2 diabetes, dental caries, and low nutrient levels. Experimental studies tend to support a causal role for sugar-sweetened soft drinks in these ailments, though this is challenged by other researchers. According to a 2013 systematic review of systematic reviews, 83.3% of the systematic reviews without reported conflict of interest concluded that sugar-sweetened soft drinks consumption could be a potential risk factor for weight gain.

Obesity and weight-related diseases

From 1977 to 2002, Americans doubled their consumption of sweetened beverages—a trend that was paralleled by doubling the prevalence of obesity. The consumption of sugar-sweetened beverages is associated with weight and obesity, and changes in consumption can help predict changes in weight.

The consumption of sugar-sweetened soft drinks can also be associated with many weight-related diseases, including diabetes, metabolic syndrome, and cardiovascular risk factors.

Dental decay

Soft drinks displayed on grocery store shelves.

Most soft drinks contain high concentrations of simple carbohydrates: glucose, fructose, sucrose and other simple sugars. If oral bacteria ferment carbohydrates and produce acids that may dissolve tooth enamel and induce dental decay, then sweetened drinks may increase the risk of dental caries. The risk would be greater if the frequency of consumption is high.

A large number of soda pops are acidic as are many fruits, sauces, and other foods. Drinking acidic drinks over a long period and continuous sipping may erode the tooth enamel. A 2007 study determined that some flavored sparkling waters are as erosive or more so than orange juice.

Using a drinking straw is often advised by dentists as the drink does not come into as much contact with the teeth. It has also been suggested that brushing teeth right after drinking soft drinks should be avoided as this can result in additional erosion to the teeth due to mechanical action of the toothbrush on weakened enamel.

Bone density and bone loss

A 2006 study of several thousand men and women, found that women who regularly drank cola-based sodas (three or more a day) had significantly lower bone mineral density (BMD) of about 4% in the hip compared to women who did not consume colas. The study found that the effect of regular consumption of cola sodas was not significant on men's BMD.

Benzene

Main article: Benzene in soft drinks

In 2006, the United Kingdom Food Standards Agency published the results of its survey of benzene levels in soft drinks, which tested 150 products and found that four contained benzene levels above the World Health Organization (WHO) guidelines for drinking water.

The United States Food and Drug Administration released its own test results of several soft drinks containing benzoates and ascorbic or erythorbic acid. Five tested drinks contained benzene levels above the Environmental Protection Agency's recommended standard of 5 ppb. As of 2006, the FDA stated its belief that "the levels of benzene found in soft drinks and other beverages to date do not pose a safety concern for consumers".

Kidney stones

A study published in the Clinical Journal of the American Society of Nephrology in 2013 concluded that consumption of soft drinks was associated with a 23% higher risk of developing kidney stones.

Government regulation

Schools

Since at least 2006, debate on whether high-calorie soft drink vending machines should be allowed in schools has been on the rise. Opponents of the soft drink vending machines believe that soft drinks are a significant contributor to childhood obesity and tooth decay, and that allowing soft drink sales in schools encourages children to believe they are safe to consume in moderate to large quantities. Opponents also argue that schools have a responsibility to look after the health of the children in their care, and that allowing children easy access to soft drinks violates that responsibility. Vending machine proponents believe that obesity is a complex issue and soft drinks are not the only cause. A 2011 bill to tax soft drinks in California failed, with some opposing lawmakers arguing that parents—not the government—should be responsible for children's drink choices.

On May 3, 2006, the Alliance for a Healthier Generation, Cadbury Schweppes, The Coca-Cola Company, PepsiCo, and the American Beverage Association announced new guidelines that will voluntarily remove high-calorie soft drinks from all U.S. schools.

On May 19, 2006, the British education secretary, Alan Johnson, announced new minimum nutrition standards for school food. Among a wide range of measures, from September 2006, school lunches will be free from carbonated drinks. Schools will also end the sale of junk food (including carbonated drinks) in vending machines and tuck shops.

In 2008, Samantha K Graff published an article in the Annals of the American Academy of Political and Social Science regarding the "First Amendment Implications of Restricting Food and Beverages Marketing in Schools". The article examines a school district's policy regarding limiting the sale and marketing of soda in public schools, and how certain policies can invoke a violation of the First Amendment. Due to district budget cuts and loss in state funding, many school districts allow commercial businesses to market and advertise their product (including junk food and soda) to public school students for additional revenue. Junk food and soda companies have acquired exclusive rights to vending machines throughout many public school campuses. Opponents of corporate marketing and advertising on school grounds urge school officials to restrict or limit a corporation's power to promote, market, and sell their product to school students. In the 1970s, the Supreme Court ruled that advertising was not a form of free expression, but a form of business practices which should be regulated by the government. In the 1976 case of Virginia State Board of Pharmacy v. Virginia Citizens Consumer Council, the Supreme Court ruled that advertising, or "commercial speech", to some degree is protected under the First Amendment. To avoid a First Amendment challenge by corporations, public schools could create contracts that restrict the sale of certain product and advertising. Public schools can also ban the selling of all food and drink products on campus, while not infringing on a corporation's right to free speech.

On December 13, 2010, President Obama signed the Healthy Hunger Free Kids Act of 2010 (effective in 2014) that mandates schools that receive federal funding must offer healthy snacks and drinks to students. The act bans the selling of soft drinks to students and requires schools to provide healthier options such as water, unflavored low-fat milk, 100% fruit and vegetable drinks or sugar-free carbonated drinks. The portion sizes available to students will be based on age: eight ounces for elementary schools, twelve ounces for middle and high schools. Proponents of the act predict the new mandate it will make it easier for students to make healthy drink choices while at school.

In 2015, Terry-McElarth and colleagues published a study in the American Journal of Preventive Medicine on regular soda policies and their effect on school drink availability and student consumption. The purpose of the study was to determine the effectiveness of a program beginning in the 2014–2015 school year that requires schools participating in federally reimbursable meal programs to remove all competitive venues (a la carte cafeteria sales, vending machines, and stores/snack bars/carts), on the availability of unhealthy drinks at schools and student consumption. The study analyzed state- and school district-level policies mandating soda bans and found that state bans were associated with significantly lower school soda availability but district bans showed no significant associations. In addition, no significant correlation was observed between state policies and student consumption. Among student populations, state policy was directly associated with significantly lower school soda availability and indirectly associated with lower student consumption. The same was not observed for other student populations.

Taxation

Main article: Sugary drink tax

In the United States, legislators, health experts and consumer advocates are considering levying higher taxes on the sale of soft drinks and other sweetened products to help curb the epidemic of obesity among Americans, and its harmful impact on overall health. Some speculate that higher taxes could help reduce soda consumption. Others say that taxes should help fund education to increase consumer awareness of the unhealthy effects of excessive soft drink consumption, and also help cover costs of caring for conditions resulting from overconsumption. The food and drink industry holds considerable clout in Washington, DC, as it has contributed more than $50 million to legislators since 2000.

In January 2013, a British lobby group called for the price of sugary fizzy drinks to be increased, with the money raised (an estimated £1 billion at 20p per litre) to be put towards a "Children's Future Fund", overseen by an independent body, which would encourage children to eat healthily in school.

In 2017, the Kingdom of Saudi Arabia, the United Arab Emirates and the Kingdom of Bahrain imposed a 50% tax on soft drinks and a 100% tax on energy drinks to curb excess consumption of the commodity and for additional revenue.

Bans

In March 2013, New York City's mayor Michael Bloomberg proposed to ban the sale of non-diet soft drinks larger than 16 ounces, except in convenience stores and supermarkets. A lawsuit against the ban was upheld by a state judge, who voiced concerns that the ban was "fraught with arbitrary and capricious consequences". Bloomberg announced that he would be appealing the verdict. The state appellate courts upheld the trial court decision, and the ban remains unenforceable as of 2021.