by Douglas Roger Sandy Dympnus Christopher Messer

Created on: February 14, 2009   Last Updated: February 27, 2009

What is the difference between bichloracetic acid and dichloroacetic acid? The short answer is that there isn't any difference. These are two different names for the same substance.

To explain the above statement a little, you would first note that neither of these is the "official" name for the compound, according to IUPAC (International Union of Pure and Applied Chemistry) nomenclature rules. That name, which unequivocally describes the structure of the molecule, is "2,2-dichloroacetic acid." When translated into Standard English, this name might be interpreted as saying, "In a molecule of acetic acid, two of the three hydrogens on the methyl group (H3C-) which is attached to the organic acid functional group (-COOH) have been replaced by chlorines." That is to say, ordinary acetic acid, which is the material that gives vinegar its sharp taste, has the structure H3C-COOH, while dichloroacetic acid has the structure Cl2HC-COOH.

Why, then, are there two different names for this substance?

Dichloroacetic acid is an accepted IUPAC name simplification, while bichloracetic acid belongs to a class of names chemists refer to as "semi-trivial names." In one well-known chemical database site on the Internet, a full list of synonyms for this substance is given which includes both trivial and semi-trivial names. It includes such names as C11149, DCA, dichloracetic acid, dichlorethanoic acid, dichloroethanoic acid, DKHUK, MLS000028893, SMR000059158, TF4, and Urner's liquid. Some of these refer to specification or registry designations, while others are simply trade names.

The substance itself may be described as a colorless liquid at room temperature with a molecular weight of 128.9 g/mole, and a density of 1.57g/ml. It melts at 9.7 C (45 F) and boils at 193-194 C (379-381 F). It is soluble in water and miscible with alcohol and ether.

It is toxic, has a pungent odor, and is highly corrosive. It attacks metals and releases hydrochloric acid gas (HCl). It is destructive to skin, and especially to eye and mucous membranes. Because of its corrosive nature, the liquid itself is used medically only in procedures requiring a cauterization agent. Of more common use in current and experimental medical procedures are the sodium and potassium salts of dichloroacetic acid. The chief use of the liquid is as an intermediate in the manufacture of a wide variety of industrial and commercial chemicals.

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