Reaction of Bleach with Detergent?

      Here’s some more interesting household chemistry, one that I just discovered.  I wrote about the dangers of mixing bleach and ammmonia before, but naïvely thought that bleach and pure detergent (like dishwashing liquid) was perfectly safe.  In fact, it’s not particularly hazardous, but there is some chemistry going on and some precautions one should take.

It’s obvious that chemistry is transpiring because when the mixture is made, there is some some significant foaming and a mild temperature rise that results.  Again, neither is dramatic, and both cease soon, giving you a stable liquid (which is great to use on sinks, pots and pans, and on other kitchen or bathroom surfaces).

Of course, I’ve been trying to squirrel out why all this happens.  What follows doesn’t come from any probing research but are just my own ideas and chemical knowledge.  The first thing that strikes me as that when you mix bleach and detergent, you’re setting up reaction between  bleach, which is a solution of sodium hypochlorite, and detergent (usually), a sulfonic acid:

NaOCl + H₂O ® Na⁺ + OCl^- + ( H₂O) ;

OCl^- + H₂O ® HOCl + H⁺ + Cl^-;

R-(S(=O)₂)-OH  + OCl^- and/ or HOCl ®  ?;

     There are other possible reactions going on too; this is not as straightforward as I thought it was going to be!  There’s another clue to what’s going on, which is that I found the evolved gas odorless and colorless.  Now if it had been something like chlorine or sulfur dioxide, there was enough that I should have picked up the pungency or even color of these two compounds.  That leaves us with hydrogen and oxygen, which are both colorless and odorless.  Now, I’making oxygen the more likely of the two because I espy a straightforward way of evolving it (and one consistent with all observations of the reaction), while a I can’t see too many ways it could be hydrogen.

Take the S(=O)₂)-OH part of the sulfonic acid.  I can easily imagine it reacting with HOCl:

S(=O)₂)-OH + HOCl ↔ S(=O)₂)-Cl + HOOH

The reaction yields the chlorinated version of the sulfonic acid (detergent), the properties of which should not be too strongly altered; and hydrogen peroxide, which in the vigor of an exothermic chemical reaction can break down into water and ogygen, foaming it up and realeasing heat.  That’s right, I’m suggesting the gas is oxygen (this is easy to test, by the way; just stick a smoldering match stick end into it and see if it flares up brightly).

Also, note the ↔ symbol I use for the reaction direction, instead of the single headed arrow.  I’m suggesting that this is a reversible reaction; it can go either way, as long as some other process doesn't contiuously consume one or more of the reactants/products.  Many chemical reactions proceed this way.  In the reaction above, as long as the HOOH is breaking down into H₂O and O₂ then it must keep proeceeding to the right, because both the oxygen escapes the mixture.  Two things to bear in mind here, however; first, the reaction is obviously not very strong (or it would get hot and foam up dramatically, perhaps even explode; concentrated HOOH is most unpleasant stuff), and second, the moment the bottle of bleach + detergent is closed tightly the back pressue of oxygen building up in the bottle essentially brings the breakdown of HOOH to at least a near dead stop, and then the entire reaction can go merrily back in forth in equibrium mode.  That’s why it quickly cools and stops foaming.

So what I am proposing that you end up with an equibrium mixture of bleach, detergent,  chloronated detergent, and HOOH (hydrogen peroxide).  If so, that makes it an especially effecting cleaning/bleaching mixture, as all three components will contribute their share.

At least, this is the best I can make of it on short notice.  I’d be fascinated by alternative hypothesis.