Chronic solvent-induced encephalopathy

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https://en.wikipedia.org/wiki/Chronic_solvent-induced_encephalopathy 

 

Chronic solvent induced encephalopathy (CSE) is a condition induced by long-term exposure to organic solvents, often but not always in the workplace, that lead to a wide variety of persisting sensorimotor polyneuropathies and neurobehavioral deficits even after solvent exposure has been removed. This syndrome can also be referred to as "psycho-organic syndrome", "organic solvent syndrome", "chronic painter's syndrome", "occupational solvent encephalopathy", "solvent intoxication", "toxic solvent syndrome", "painters disease", "psycho-organic syndrome", "chronic toxic encephalopathy", and "neurasthenic syndrome". The multiple names of solvent-induced syndromes combined with inconsistency in research methods makes referencing this disease difficult and its catalog of symptoms vague.

Symptoms

Two characteristic symptoms of CSE are deterioration of memory (particularly short-term memory), and attention impairments. There are, however, numerous other symptoms that accompany to varying degrees. Variability in the research methods studying CSE makes characterizing these symptoms difficult, and some may be questionable regarding whether they are actual symptoms of solvent-induced syndromes, simply because of how infrequently they appear. Characterizing of CSE symptoms is more difficult because CSE is currently poorly defined, and the mechanism behind it is not understood yet.

Neurological

Reported neurological symptoms include difficulty sleeping, decrease in intellectual capacity, dizziness, altered visual perceptive abilities, affected psychomotor skills, forgetfulness, and disorientation. The mechanism behind these symptoms beyond solvent molecules crossing the blood-brain barrier is currently unknown. Neurological signs include impaired vibratory sensation at extremities and an inability to maintain steady motion, a possible effect from psychomotor damage in the brain. Other symptoms that have been seen include fatigue, decreased strength, and unusual gait. One study found that there was a correlation between decreased red blood cell count and level of solvent exposure, but not enough data has been found to support any blood tests to screen for CSE.

Sensory alterations

A 1988 study indicated that some solvent-exposed workers suffered from loss of smell or damage to color vision; however this may or may not have been actually caused by exposure to organic solvents. There is other evidence for subtle impairment of color vision (especially titian or "blue-yellow" losses), synergistic exacerbation of hearing loss, and loss of the sense of smell (anosmia).

Psychological

Psychological symptoms of CSE that have been reported include mood swings, increased irritability, depression, a lack of initiative, uncontrollable and intense displays of emotion such as spontaneous laughing or crying, and a severe lack of interest in sex. Some psychological symptoms are believed to be linked to frustration with other symptoms, neurological, or pathophysiological symptoms of CSE. A case study of a painter diagnosed with CSE reported that the patient frequently felt defensive, irritable, and depressed because of his memory deficiencies.

Causes

Organic solvents that cause CSE are characterized as volatile, blood soluble, lipophilic compounds that are typically liquids at normal temperature. These can be compounds or mixtures used to extract, dissolve, or suspend non-water-soluble materials such as fats, oils, lipids, cellulose derivatives, waxes, plastics, and polymers. These solvents are often used industrially in the production of paints, glues, coatings, degreasing agents, dyes, polymers, pharmaceuticals, and printing inks.

Exposure to solvents can occur by inhalation, ingestion, or direct absorption through the skin. Of the three, inhalation is the most common form of exposure, with the solvent able to rapidly pass through lung membranes and then into fatty tissue or cell membranes. Once in the bloodstream, organic solvents, due to their lipophilic properties, easily cross the blood-brain barrier. The mechanism of effect that these solvents have on the brain that cause CSE, however, is not yet fully understood. Some common organic solvents known to cause CSE include formaldehyde, acetates, and alcohols.

Diagnosis

Due to its non-specific nature, diagnosing CSE requires a multidisciplinary "Solvent Team" typically consisting of a neurologist, occupational physician, occupational hygienist, neuropsychologist, and sometimes a psychiatrist or toxicologist. Together, the team of specialists assess the patient's history of exposure, symptoms, and course of symptom development relative to the amount and duration of exposure, presence of neurological signs, and any existing neuropsychological impairment.

Furthermore, CSE must be diagnosed "by exclusion". This means that all other possible causes of the patient’s symptoms must first be ruled out beforehand. Because screening and assessing for CSE is a complex and time-consuming procedure requiring several specialists of multiple fields, few cases of CSE are formally diagnosed in the medical field. This may, in part, be a reason for the syndrome’s lack of recognition. The solvents responsible for neurological effects dissipate quickly after an exposure, leaving only indirect evidence of their presence, in the form of temporary or permanent impairments.

Brain imaging techniques that have been explored in research have shown little promise as alternative methods to diagnose CSE. Neuroradiology and functional imaging have shown mild cortical atrophy, and effects in dopamine-mediated frontostriatal circuits in some cases. Examinations of regional cerebral blood flow in some imaging techniques have also shown some cerebrovascular abnormalities in patients with CSE, but the data were not different enough from healthy patients to be considered significant. The most promising brain imaging technique being studied currently is functional magnetic resonance imaging (fMRI) but as of now, no specific brain imaging techniques are available to reliably diagnose CSE.

Classification

Introduced by a working group from the World Health Organization (WHO) in 1985, WHO diagnostic criteria states that CSE can occur in three stages, organic affective syndrome (type I), mild chronic toxic encephalopathy (type II), and severe chronic toxic encephalopathy (type III). Shortly after, a workshop in Raleigh-Durham, NC (United States) released a second diagnostic criterion which recognizes four stages as symptoms only (type 1), sustained personality or mood swings (type 2A), impairment of intellectual function (type 2B), and dementia (type 3). Though not identical, the WHO and Raleigh criteria are relatively comparable. WHO type I and Raleigh types 1 and 2A are believed to encompass the same stages of CSE, and WHO type II and Raleigh type 2B both involve deficiencies in memory and attention. No other international classifications for CSE have been proposed, and neither the WHO nor Raleigh criteria have been uniformly accepted for epidemiological studies.

Treatment

Like diagnosis, treating CSE is difficult because it is vaguely defined and data on the mechanism of CSE effects on neural tissue are lacking. There is no existing treatment that is effective at completely recovering any neurological or physical function lost due to CSE. This is believed to be because of the limited regeneration capabilities in the central nervous system. Furthermore, existing symptoms of CSE can potentially worsen with age. Some symptoms of CSE, such as depression and sleep issues, can be treated separately, and therapy is available to help patients adjust to any disabilities. Current treatment for CSE involves treating accompanying psychopathology, symptoms, and preventing further deterioration.

History

Cases of CSE have been studied predominantly in northern Europe, though documented cases have been found in other countries such as the United States, France, and China. The first documented evidence for CSE was in the early 1960s from a paper published by Helena Hanninen, a Finnish neuropsychologist. Her paper described a case of workers suffering from carbon disulfide intoxication at a rubber manufacturing company and coined the term "psycho-organic syndrome". Studies of solvent effects on intellectual functioning, memory, and concentration were carried out in the Nordic countries, with Denmark spearheading the research. Growing awareness of the syndrome in the Nordic countries occurred in the 1970s.

To reduce cases of CSE in the workforce, a diagnostic criterion for CSE appeared on information notices in occupational disease records in the European Commission. Following, from 1998 to 2004, was a health surveillance program for CSE cases among construction painters in the Netherlands. By 2000, a ban was put into action against using solvent-based paints indoors, which resulted in a considerable reduction of solvent exposure to painters. As a result, the number of CSE cases dropped substantially after 2002. In 2005–2007, no new CSE cases were diagnosed among construction painters in the Netherlands, and no occupational CSE has been encountered in workers under thirty years of age in Finland since 1995.

Though movements to reduce CSE have been successful, CSE still poses an issue to many workers that are at occupational risk. Statistics published in 2012 by Nicole Cherry et al. claim that at least 20% of employees in Finland still encounter organic solvents at the workplace, and 10% of them experience some form of disadvantage from the exposure. In Norway, 11% of the male population of workers and 7% of female workers are still exposed to solvents daily and as of 2006, the country has the highest rate of diagnosed CSE in Europe. Furthermore, due to the complexity of screening for CSE, there is still a high likelihood of a population of undiagnosed cases.

Occupations that have been found to have higher risk of causing CSE are painter, printer, industrial cleaner, and paint or glue manufacturer. Of them, painters have been found to have the highest recorded incidence of CSE. Spray painters in particular have higher exposure intensities than other painters. Studies of instances of CSE have specifically been carried out in naval dockyards, mineral fiber manufacturing companies, and rayon viscose plants.

Dye

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

Chemical structure of indigo dye, the blue coloration of blue jeans. Once extracted from plants, indigo dye is almost exclusively synthesized industrially.

 

Yarn drying after being dyed in the early American tradition, at Conner Prairie living history museum.

 

A dye is a coloured substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they colour. The dye is generally applied in an aqueous solution, and may require a mordant to improve the fastness of the dye on the fiber.

Both dyes and pigments are colored, because they absorb only some wavelengths of visible light. Dyes are usually soluble in water whereas pigments are insoluble. Some dyes can be rendered insoluble with the addition of salt to produce a lake pigment.

Natural vs synthetic

Dyeing wool cloth, 1482: from a French translation of Bartolomaeus Anglicus

The majority of natural dyes are derived from plant sources: roots, berries, bark, leaves, wood, fungi and lichens. Most dyes are synthetic, i.e., are man-made from petrochemicals. Other than pigmentation, they have a range of applications including organic dye lasers, optical media (CD-R) and camera sensors (color filter array).

History

Textile dyeing dates back to the Neolithic period. Throughout history, people have dyed their textiles using common, locally available materials. Scarce dyestuffs that produced brilliant and permanent colors such as the natural invertebrate dyes Tyrian purple and crimson kermes were highly prized luxury items in the ancient and medieval world. Plant-based dyes such as woad, indigo, saffron, and madder were important trade goods in the economies of Asia and Europe. Across Asia and Africa, patterned fabrics were produced using resist dyeing techniques to control the absorption of color in piece-dyed cloth. Dyes from the New World such as cochineal and logwood were brought to Europe by the Spanish treasure fleets, and the dyestuffs of Europe were carried by colonists to America.

Dyed flax fibers have been found in the Republic of Georgia in a prehistoric cave dated to 36,000 BP. Archaeological evidence shows that, particularly in India and Phoenicia, dyeing has been widely carried out for over 5,000 years. Early dyes were obtained from animal, vegetable or mineral sources, with no to very little processing. By far the greatest source of dyes has been from the plant kingdom, notably roots, berries, bark, leaves and wood, only few of which are used on a commercial scale.

The first synthetic dye, mauve, was discovered serendipitously by William Henry Perkin in 1856. The discovery of mauveine started a surge in synthetic dyes and in organic chemistry in general. Other aniline dyes followed, such as fuchsine, safranine, and induline. Many thousands of synthetic dyes have since been prepared. The discovery of mauve also led to developments within immunology and chemotherapy. In 1891 Paul Ehrlich discovered that certain cells or organisms took up certain dyes selectively. He then reasoned that a sufficiently large dose could be injected to kill pathogenic microorganisms, if the dye did not affect other cells. Erlich went on to use a compound to target syphillis, the first time a chemical was used in order to selectively kill bacteria in the body, he also used methylene blue to target the plasmodium responsible for malaria.

Historical collection of over 10,000 dyes at Technical University Dresden, Germany

Chemistry

The colour of a dye is dependent upon the ability of the substance to absorb light within the visible region of the electromagnetic spectrum (400-700 nm). An earlier theory known as Witt theory stated that a coloured dye had two components, a chromophore which imparts colour by absorbing light in the visible region (some examples are nitro, azo, quinoid groups) and an auxochrome which serves to deepen the colour. This theory has been superseded by modern electronic structure theory which states that the colour in dyes is due to excitation of valence π-electrons by visible light.

Types

RIT brand dye from mid-20th century Mexico, part of the permanent collection of the Museo del Objeto del Objeto

 

A woman dyeing her hair.

Dyes are classified according to their solubility and chemical properties.

Acid dyes are water-soluble anionic dyes that are applied to fibers such as silk, wool, nylon and modified acrylic fibers using neutral to acid dye baths. Attachment to the fiber is attributed, at least partly, to salt formation between anionic groups in the dyes and cationic groups in the fiber. Acid dyes are not substantive to cellulosic fibers. Most synthetic food colors fall in this category. Examples of acid dye are Alizarine Pure Blue B, Acid red 88, etc.

Basic dyes are water-soluble cationic dyes that are mainly applied to acrylic fibers, but find some use for wool and silk. Usually acetic acid is added to the dye bath to help the uptake of the dye onto the fiber. Basic dyes are also used in the coloration of paper.

Direct or substantive dyeing is normally carried out in a neutral or slightly alkaline dye bath, at or near boiling point, with the addition of either sodium chloride (NaCl) or sodium sulfate (Na₂SO₄) or sodium carbonate (Na₂CO₃). Direct dyes are used on cotton, paper, leather, wool, silk and nylon. They are also used as pH indicators and as biological stains.

Mordant dyes require a mordant, which improves the fastness of the dye against water, light and perspiration. The choice of mordant is very important as different mordants can change the final color significantly. Most natural dyes are mordant dyes and there is therefore a large literature base describing dyeing techniques. The most important mordant dyes are the synthetic mordant dyes, or chrome dyes, used for wool; these comprise some 30% of dyes used for wool, and are especially useful for black and navy shades. The mordant potassium dichromate is applied as an after-treatment. It is important to note that many mordants, particularly those in the heavy metal category, can be hazardous to health and extreme care must be taken in using them.

Vat dyes are essentially insoluble in water and incapable of dyeing fibres directly. However, reduction in alkaline liquor produces the water-soluble alkali metal salt of the dye. This form is often colorless, in which case it is referred to as a Leuco dye, and has an affinity for the textile fibre. Subsequent oxidation reforms the original insoluble dye. The color of denim is due to indigo, the original vat dye.

Reactive dyes utilize a chromophore attached to a substituent that is capable of directly reacting with the fiber substrate. The covalent bonds that attach reactive dye to natural fibers make them among the most permanent of dyes. "Cold" reactive dyes, such as Procion MX, Cibacron F, and Drimarene K, are very easy to use because the dye can be applied at room temperature. Reactive dyes are by far the best choice for dyeing cotton and other cellulose fibers at home or in the art studio.

Disperse dyes were originally developed for the dyeing of cellulose acetate, and are water-insoluble. The dyes are finely ground in the presence of a dispersing agent and sold as a paste, or spray-dried and sold as a powder. Their main use is to dye polyester, but they can also be used to dye nylon, cellulose triacetate, and acrylic fibers. In some cases, a dyeing temperature of 130 °C (266 °F) is required, and a pressurized dyebath is used. The very fine particle size gives a large surface area that aids dissolution to allow uptake by the fiber. The dyeing rate can be significantly influenced by the choice of dispersing agent used during the grinding.

Azoic dyeing is a technique in which an insoluble Azo dye is produced directly onto or within the fiber. This is achieved by treating a fiber with both diazoic and coupling components. With suitable adjustment of dyebath conditions the two components react to produce the required insoluble azo dye. This technique of dyeing is unique, in that the final color is controlled by the choice of the diazoic and coupling components. This method of dyeing cotton is declining in importance due to the toxic nature of the chemicals used.

Sulfur dyes are inexpensive dyes used to dye cotton with dark colors. Dyeing is effected by heating the fabric in a solution of an organic compound, typically a nitrophenol derivative, and sulfide or polysulfide. The organic compound reacts with the sulfide source to form dark colors that adhere to the fabric. Sulfur Black 1, the largest selling dye by volume, does not have a well defined chemical structure.

Some dyes commonly used in Staining:

Basic Dyes	Acidic Dyes
Safranin	Eosin
Basic Fuchsin	Acid Fuchsin
Crystal violet	Congo Red
Methylene Blue

Food dyes

One other class that describes the role of dyes, rather than their mode of use, is the food dye. Because food dyes are classed as food additives, they are manufactured to a higher standard than some industrial dyes. Food dyes can be direct, mordant and vat dyes, and their use is strictly controlled by legislation. Many are azo dyes, although anthraquinone and triphenylmethane compounds are used for colors such as green and blue. Some naturally occurring dyes are also used.

Other important dyes

A number of other classes have also been established, including:

• Oxidation bases, for mainly hair and fur
• Laser dyes:rhodamine 6G and coumarin dyes.
• Leather dyes, for leather
• Fluorescent brighteners, for textile fibres and paper
• Solvent dyes, for wood staining and producing colored lacquers, solvent inks, coloring oils, waxes.
• Contrast dyes, injected for magnetic resonance imaging, are essentially the same as clothing dye except they are coupled to an agent that has strong paramagnetic properties.
• Mayhems dye, used in water cooling for looks, often rebranded RIT dye

Chromophoric dyes

By the nature of their chromophore, dyes are divided into:

• Category:Acridine dyes, derivates of acridine
• Category:Anthraquinone dyes, derivates of anthraquinone
• Arylmethane dyes
  • Category:Diarylmethane dyes, based on diphenyl methane
  • Category:Triarylmethane dyes, derivates of triphenylmethane
• Category:Azo dyes, based on -N=N- azo structure
• Phthalocyanine dyes, derivatives of phthalocyanine
• Quinone-imine dyes, derivatives of quinone
  • Category:Azin dyes
    • Category:Eurhodin dyes
    • Category:Safranin dyes, derivates of safranin
  • Indamins
  • Category:Indophenol dyes, derivates of indophenol
  • Category:Oxazin dyes, derivates of oxazin
  • Oxazone dyes, derivates of oxazone
  • Category:Thiazine dyes
• Category:Thiazole dyes
• Category:Safranin dyes
• Xanthene dyes
  • Fluorene dyes, derivatives of fluorene
    • Pyronin dyes
  • Category:Fluorone dyes, based on fluorone
    • Category:Rhodamine dyes, derivatives of rhodamine

Pollution

Dyes produced by the textile, printing and paper industries can end up in waste waters and are therefore a potential source of pollution of rivers and waterways.

Various porous materials, often used to adsorb harmful chemicals in general, have been specifically tested to remove dyes from aqueous environments, especially those who could combine wide availability, fast kinetics and strong adsorption capacities.

Possible examples include nickel oxide nanoplates, clays, activated carbons, composites of hydroxyapatite with organic substrates, graphene oxides.

Solvent

From Wikipedia, the free encyclopedia

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

A bottle of acetic acid, a liquid solvent

A solvent (from the Latin solvō, "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. The quantity of solute that can dissolve in a specific volume of solvent varies with temperature. Common uses for organic solvents are in dry cleaning (e.g. tetrachloroethylene), as paint thinners (e.g. toluene, turpentine), as nail polish removers and glue solvents (acetone, methyl acetate, ethyl acetate), in spot removers (e.g. hexane, petrol ether), in detergents (citrus terpenes) and in perfumes (ethanol). Water is a solvent for polar molecules and the most common solvent used by living things; all the ions and proteins in a cell are dissolved in water within a cell. Solvents find various applications in chemical, pharmaceutical, oil, and gas industries, including in chemical syntheses and purification processes.

Solutions and solvation

When one substance is dissolved into another, a solution is formed. This is opposed to the situation when the compounds are insoluble like sand in water. In a solution, all of the ingredients are uniformly distributed at a molecular level and no residue remains. A solvent-solute mixture consists of a single phase with all solute molecules occurring as solvates (solvent-solute complexes), as opposed to separate continuous phases as in suspensions, emulsions and other types of non-solution mixtures. The ability of one compound to be dissolved in another is known as solubility; if this occurs in all proportions, it is called miscible.

In addition to mixing, the substances in a solution interact with each other at the molecular level. When something is dissolved, molecules of the solvent arrange around molecules of the solute. Heat transfer is involved and entropy is increased making the solution more thermodynamically stable than the solute and solvent separately. This arrangement is mediated by the respective chemical properties of the solvent and solute, such as hydrogen bonding, dipole moment and polarizability. Solvation does not cause a chemical reaction or chemical configuration changes in the solute. However, solvation resembles a coordination complex formation reaction, often with considerable energetics (heat of solvation and entropy of solvation) and is thus far from a neutral process.

Solvent classifications

Solvents can be broadly classified into two categories: polar and non-polar. A special case is mercury, whose solutions are known as amalgams; also, other metal solutions exist which are liquid at room temperature. Generally, the dielectric constant of the solvent provides a rough measure of a solvent's polarity. The strong polarity of water is indicated by its high dielectric constant of 88 (at 0 °C). Solvents with a dielectric constant of less than 15 are generally considered to be nonpolar. The dielectric constant measures the solvent's tendency to partly cancel the field strength of the electric field of a charged particle immersed in it. This reduction is then compared to the field strength of the charged particle in a vacuum. Heuristically, the dielectric constant of a solvent can be thought of as its ability to reduce the solute's effective internal charge. Generally, the dielectric constant of a solvent is an acceptable predictor of the solvent's ability to dissolve common ionic compounds, such as salts.

Other polarity scales

Dielectric constants are not the only measure of polarity. Because solvents are used by chemists to carry out chemical reactions or observe chemical and biological phenomena, more specific measures of polarity are required. Most of these measures are sensitive to chemical structure.

The Grunwald–Winstein mY scale measures polarity in terms of solvent influence on buildup of positive charge of a solute during a chemical reaction.

Kosower's Z scale measures polarity in terms of the influence of the solvent on UV-absorption maxima of a salt, usually pyridinium iodide or the pyridinium zwitterion.

Donor number and donor acceptor scale measures polarity in terms of how a solvent interacts with specific substances, like a strong Lewis acid or a strong Lewis base.

The Hildebrand parameter is the square root of cohesive energy density. It can be used with nonpolar compounds, but cannot accommodate complex chemistry.

Reichardt's dye, a solvatochromic dye that changes color in response to polarity, gives a scale of E_T(30) values. E_T is the transition energy between the ground state and the lowest excited state in kcal/mol, and (30) identifies the dye. Another, roughly correlated scale (E_T(33)) can be defined with Nile red.

The polarity, dipole moment, polarizability and hydrogen bonding of a solvent determines what type of compounds it is able to dissolve and with what other solvents or liquid compounds it is miscible. Generally, polar solvents dissolve polar compounds best and non-polar solvents dissolve non-polar compounds best: "like dissolves like". Strongly polar compounds like sugars (e.g. sucrose) or ionic compounds, like inorganic salts (e.g. table salt) dissolve only in very polar solvents like water, while strongly non-polar compounds like oils or waxes dissolve only in very non-polar organic solvents like hexane. Similarly, water and hexane (or vinegar and vegetable oil) are not miscible with each other and will quickly separate into two layers even after being shaken well.

Polarity can be separated to different contributions. For example, the Kamlet-Taft parameters are dipolarity/polarizability (π*), hydrogen-bonding acidity (α) and hydrogen-bonding basicity (β). These can be calculated from the wavelength shifts of 3–6 different solvatochromic dyes in the solvent, usually including Reichardt's dye, nitroaniline and diethylnitroaniline. Another option, Hansen's parameters, separate the cohesive energy density into dispersion, polar and hydrogen bonding contributions.

Polar protic and polar aprotic

Solvents with a dielectric constant (more accurately, relative static permittivity) greater than 15 (i.e. polar or polarizable) can be further divided into protic and aprotic. Protic solvents solvate anions (negatively charged solutes) strongly via hydrogen bonding. Water is a protic solvent. Aprotic solvents such as acetone or dichloromethane tend to have large dipole moments (separation of partial positive and partial negative charges within the same molecule) and solvate positively charged species via their negative dipole. In chemical reactions the use of polar protic solvents favors the S_N1 reaction mechanism, while polar aprotic solvents favor the S_N2 reaction mechanism. These polar solvents are capable of forming hydrogen bonds with water to dissolve in water whereas non-polar solvents are not capable of strong hydrogen bonds.

Multicomponent

Solvents

Name	Composition
Solvent 645	toluene 50%, butyl acetate 18%, ethyl acetate 12%, butanol 10%, ethanol 10%.
Solvent 646	toluene 50%, ethanol 15%, butanol 10%, butyl- or amyl acetate 10%, ethyl cellosolve 8%, acetone 7%[8]
Solvent 647	butyl- or amyl acetate 29.8%, ethyl acetate 21.2%, butanol 7.7%, toluene or pyrobenzene 41.3%[9]
Solvent 648	butyl acetate 50%, ethanol 10%, butanol 20%, toluene 20%[10]
Solvent 649	ethyl cellosolve 30%, butanol 20%, xylene 50%
Solvent 650	ethyl cellosolve 20%, butanol 30%, xylene 50%[11]
Solvent 651	white spirit 90%, butanol 10%
Solvent KR-36	butyl acetate 20%, butanol 80%
Solvent P-4	toluene 62%, acetone 26%, butyl acetate 12%.
Solvent P-10	xylene 85%, acetone 15%.
Solvent P-12	toluene 60%, butyl acetate 30%, xylene 10%.
Solvent P-14	cyclohexanone 50%, toluene 50%.
Solvent P-24	solvent 50%, xylene 35%, acetone 15%.
Solvent P-40	toluene 50%, ethyl cellosolve 30%, acetone 20%.
Solvent P-219	toluene 34%, cyclohexanone 33%, acetone 33%.
Solvent P-3160	butanol 60%, ethanol 40%.
Solvent RCC	xylene 90%, butyl acetate 10%.
Solvent RML	ethanol 64%, ethylcellosolve 16%, toluene 10%, butanol 10%.
Solvent PML-315	toluene 25%, xylene 25%, butyl acetate 18%, ethyl cellosolve 17%, butanol 15%.
Solvent PC-1	toluene 60%, butyl acetate 30%, xylene 10%.
Solvent PC-2	white spirit 70%, xylene 30%.
Solvent RFG	ethanol 75%, butanol 25%.
Solvent RE-1	xylene 50%, acetone 20%, butanol 15%, ethanol 15%.
Solvent RE-2	Solvent 70%, ethanol 20%, acetone 10%.
Solvent RE-3	solvent 50%, ethanol 20%, acetone 20%, ethyl cellosolve 10%.
Solvent RE-4	solvent 50%, acetone 30%, ethanol 20%.
Solvent FK-1 (?)	absolute alcohol (99.8%) 95%, ethyl acetate 5%

Thinners

Name	Composition
Thinner RKB-1	butanol 50%, xylene 50%
Thinner RKB-2	butanol 95%, xylene 5%
Thinner RKB-3	xylene 90%, butanol 10%
Thinner M	ethanol 65%, butyl acetate 30%, ethyl acetate 5%.
Thinner P-7	cyclohexanone 50%, ethanol 50%.
Thinner R-197	xylene 60%, butyl acetate 20%, ethyl cellosolve 20%.
Thinner of WFD	toluene 50%, butyl acetate (or amyl acetate) 18%, butanol 10%, ethanol 10%, ethyl acetate 9%, acetone 3%.

Physical properties

Hansen solubility parameter values

The Hansen solubility parameter values are based on dispersion bonds (δD), polar bonds (δP) and hydrogen bonds (δH). These contain information about the inter-molecular interactions with other solvents and also with polymers, pigments, nanoparticles, etc. This allows for rational formulations knowing, for example, that there is a good HSP match between a solvent and a polymer. Rational substitutions can also be made for "good" solvents (effective at dissolving the solute) that are "bad" (expensive or hazardous to health or the environment). The following table shows that the intuitions from "non-polar", "polar aprotic" and "polar protic" are put numerically – the "polar" molecules have higher levels of δP and the protic solvents have higher levels of δH. Because numerical values are used, comparisons can be made rationally by comparing numbers. For example, acetonitrile is much more polar than acetone but exhibits slightly less hydrogen bonding.

Solvent	Chemical formula	δD Dispersion	δP Polar	δH Hydrogen bonding
Non-polar solvents

n-Hexane	CH3CH2CH2CH2CH2CH3	14.9	0.0	0.0
Benzene	C6H6	18.4	0.0	2.0
Toluene	C6H5-CH3	18.0	1.4	2.0
Diethyl ether	CH3CH2-O-CH2CH3	14.5	2.9	4.6
Chloroform	CHCl3	17.8	3.1	5.7
1,4-Dioxane	/-CH2-CH2-O-CH2-CH2-O-\	17.5	1.8	9.0
Polar aprotic solvents

Ethyl acetate	CH3-C(=O)-O-CH2-CH3	15.8	5.3	7.2
Tetrahydrofuran (THF)	/-CH2-CH2-O-CH2-CH2-\	16.8	5.7	8.0
Dichloromethane	CH2Cl2	17.0	7.3	7.1
Acetone	CH3-C(=O)-CH3	15.5	10.4	7.0
Acetonitrile (MeCN)	CH3-C≡N	15.3	18.0	6.1
Dimethylformamide (DMF)	H-C(=O)N(CH3)2	17.4	13.7	11.3
Dimethyl sulfoxide (DMSO)	CH3-S(=O)-CH3	18.4	16.4	10.2
Polar protic solvents

Acetic acid	CH3-C(=O)OH	14.5	8.0	13.5
n-Butanol	CH3CH2CH2CH2OH	16.0	5.7	15.8
Isopropanol	CH3-CH(-OH)-CH3	15.8	6.1	16.4
n-Propanol	CH3CH2CH2OH	16.0	6.8	17.4
Ethanol	CH3CH2OH	15.8	8.8	19.4
Methanol	CH3OH	14.7	12.3	22.3
Formic acid	H-C(=O)OH	14.6	10.0	14.0
Water	H-O-H	15.5	16.0	42.3

If, for environmental or other reasons, a solvent or solvent blend is required to replace another of equivalent solvency, the substitution can be made on the basis of the Hansen solubility parameters of each. The values for mixtures are taken as the weighted averages of the values for the neat solvents. This can be calculated by trial-and-error, a spreadsheet of values, or HSP software. A 1:1 mixture of toluene and 1,4 dioxane has δD, δP and δH values of 17.8, 1.6 and 5.5, comparable to those of chloroform at 17.8, 3.1 and 5.7 respectively. Because of the health hazards associated with toluene itself, other mixtures of solvents may be found using a full HSP dataset.

Boiling point

Solvent	Boiling point (°C)
ethylene dichloride	83.48
pyridine	115.25
methyl isobutyl ketone	116.5
methylene chloride	39.75
isooctane	99.24
carbon disulfide	46.3
carbon tetrachloride	76.75
o-xylene	144.42

The boiling point is an important property because it determines the speed of evaporation. Small amounts of low-boiling-point solvents like diethyl ether, dichloromethane, or acetone will evaporate in seconds at room temperature, while high-boiling-point solvents like water or dimethyl sulfoxide need higher temperatures, an air flow, or the application of vacuum for fast evaporation.

• Low boilers: boiling point below 100 °C (boiling point of water)
• Medium boilers: between 100 °C and 150 °C
• High boilers: above 150 °C

Density

Most organic solvents have a lower density than water, which means they are lighter than and will form a layer on top of water. Important exceptions are most of the halogenated solvents like dichloromethane or chloroform will sink to the bottom of a container, leaving water as the top layer. This is crucial to remember when partitioning compounds between solvents and water in a separatory funnel during chemical syntheses. 

Often, specific gravity is cited in place of density. Specific gravity is defined as the density of the solvent divided by the density of water at the same temperature. As such, specific gravity is a unitless value. It readily communicates whether a water-insoluble solvent will float (SG < 1.0) or sink (SG > 1.0) when mixed with water.

Safety

Fire

Most organic solvents are flammable or highly flammable, depending on their volatility. Exceptions are some chlorinated solvents like dichloromethane and chloroform. Mixtures of solvent vapors and air can explode. Solvent vapors are heavier than air; they will sink to the bottom and can travel large distances nearly undiluted. Solvent vapors can also be found in supposedly empty drums and cans, posing a flash fire hazard; hence empty containers of volatile solvents should be stored open and upside down.

Both diethyl ether and carbon disulfide have exceptionally low autoignition temperatures which increase greatly the fire risk associated with these solvents. The autoignition temperature of carbon disulfide is below 100 °C (212 °F), so objects such as steam pipes, light bulbs, hotplates, and recently extinguished bunsen burners are able to ignite its vapours.

In addition some solvents, such as methanol, can burn with a very hot flame which can be nearly invisible under some lighting conditions. This can delay or prevent the timely recognition of a dangerous fire, until flames spread to other materials.

Explosive peroxide formation

Ethers like diethyl ether and tetrahydrofuran (THF) can form highly explosive organic peroxides upon exposure to oxygen and light. THF is normally more likely to form such peroxides than diethyl ether. One of the most susceptible solvents is diisopropyl ether, but all ethers are considered to be potential peroxide sources.

The heteroatom (oxygen) stabilizes the formation of a free radical which is formed by the abstraction of a hydrogen atom by another free radical. The carbon-centred free radical thus formed is able to react with an oxygen molecule to form a peroxide compound. The process of peroxide formation is greatly accelerated by exposure to even low levels of light, but can proceed slowly even in dark conditions.

Unless a desiccant is used which can destroy the peroxides, they will concentrate during distillation, due to their higher boiling point. When sufficient peroxides have formed, they can form a crystalline, shock-sensitive solid precipitate at the mouth of a container or bottle. Minor mechanical disturbances, such as scraping the inside of a vessel or the dislodging of a deposit, merely twisting the cap may provide sufficient energy for the peroxide to explode or detonate. Peroxide formation is not a significant problem when fresh solvents are used up quickly; they are more of a problem in laboratories which may take years to finish a single bottle. Low-volume users should acquire only small amounts of peroxide-prone solvents, and dispose of old solvents on a regular periodic schedule.

To avoid explosive peroxide formation, ethers should be stored in an airtight container, away from light, because both light and air can encourage peroxide formation.

A number of tests can be used to detect the presence of a peroxide in an ether; one is to use a combination of iron(II) sulfate and potassium thiocyanate. The peroxide is able to oxidize the Fe²⁺ ion to an Fe³⁺ ion, which then forms a deep-red coordination complex with the thiocyanate.

Peroxides may be removed by washing with acidic iron(II) sulfate, filtering through alumina, or distilling from sodium/benzophenone. Alumina does not destroy the peroxides but merely traps them, and must be disposed of properly. The advantage of using sodium/benzophenone is that moisture and oxygen are removed as well.

Health effects

General health hazards associated with solvent exposure include toxicity to the nervous system, reproductive damage, liver and kidney damage, respiratory impairment, cancer, and dermatitis.

Acute exposure

Many solvents can lead to a sudden loss of consciousness if inhaled in large amounts. Solvents like diethyl ether and chloroform have been used in medicine as anesthetics, sedatives, and hypnotics for a long time. Ethanol (grain alcohol) is a widely used and abused psychoactive drug. Diethyl ether, chloroform, and many other solvents e.g. from gasoline or glues are abused recreationally in glue sniffing, often with harmful long term health effects like neurotoxicity or cancer. Fraudulent substitution of 1,5-pentanediol by the psychoactive 1,4-butanediol by a subcontractor caused the Bindeez product recall. If ingested, the so-called toxic alcohols (other than ethanol) such as methanol, propanol, and ethylene glycol metabolize into toxic aldehydes and acids, which cause potentially fatal metabolic acidosis. The commonly available alcohol solvent methanol can cause permanent blindness or death if ingested. The solvent 2-butoxyethanol, used in fracking fluids, can cause hypotension and metabolic acidosis.

Chronic exposure

Some solvents including chloroform and benzene a common ingredient in gasoline are known to be carcinogenic, while many others are considered by the World Health Organization to be likely carcinogens. Solvents can damage internal organs like the liver, the kidneys, the nervous system, or the brain. The cumulative effects of long-term or repeated exposure to solvents are called chronic solvent-induced encephalopathy (CSE).

Chronic exposure to organic solvents in the work environment can produce a range of adverse neuropsychiatric effects. For example, occupational exposure to organic solvents has been associated with higher numbers of painters suffering from alcoholism. Ethanol has a synergistic effect when taken in combination with many solvents; for instance, a combination of toluene/benzene and ethanol causes greater nausea/vomiting than either substance alone.

Many solvents are known or suspected to be cataractogenic, greatly increasing the risk of developing cataracts in the lens of the eye. Solvent exposure has also been associated with neurotoxic damage causing hearing loss and color vision losses.

Environmental contamination

A major pathway to induce health effects arises from spills or leaks of solvents that reach the underlying soil. Since solvents readily migrate substantial distances, the creation of widespread soil contamination is not uncommon; this is particularly a health risk if aquifers are affected. Vapor intrusion can occur from sites with extensive subsurface solvent contamination.