haloacid

Haloacids are a class of organic acids in which one or more hydrogen atoms on the carbon adjacent to the acidic functional group have been replaced by halogen atoms. The most common haloacids are halogenated acetic acids, often called haloacetic acids (HAAs). Their general structure is X-CH2-COOH, where X is a halogen such as fluorine, chlorine, bromine, or iodine; the number of halogen substituents can range from one to three, giving mono-, di-, or trihaloacetic acids. Well-known examples include fluoroacetic acid, monochloroacetic acid, dichloroacetic acid, and trichloroacetic acid.

Preparation and properties: Haloacids are typically prepared by halogenating acetic acid or its derivatives under conditions that favor substitution on the methyl group. The halogen substituents withdraw electron density from the carboxylate, increasing the acidity of the carboxyl group; acidity generally increases with more halogen substitution. They are highly soluble in water and behave as relatively strong acids compared with acetic acid.

Uses and significance: Haloacetic acids serve as intermediates in organic synthesis. Monochloroacetic acid is used to produce sodium monochloroacetate for cellulose carboxymethylation and other derivatives; trichloroacetic acid is a common strong acid and a protein precipitant in biochemistry. Haloacetic acids also occur as disinfection byproducts in drinking water and are subject to regulatory limits in many jurisdictions due to toxicity concerns.

Safety: Haloacids are typically corrosive and can be harmful if inhaled, ingested, or absorbed. Some haloacids and their byproducts exhibit toxicity, necessitating careful handling and appropriate controls.