Oxidation of a primary alcohol affords a carboxylic acid. There are many reagents to acheive this transformation. Chromic acid (H2CrO4), prepared by dissolving a Cr6+ compound such as chromium trioxide (CrO3), potassium dichromate (K2Cr2O7) or sodium chromate (Na2CrO4) in sulfuric acid, is commonly used. CrO3 in aqueous sulfuric acid and acetone is termed "Jones reagent." The reactions proceeds via an aldehyde intermediate (Section 8.4F).
Oxidation of an aldehyde affords a carboxylic acid. Because the oxidation of a primary alcohol to a carboxylic acid proceeds via an aldehyde, any reagent that acheives this oxidation will also oxidize an aldehyde to a carboxylic acid. Reagents commonly used to convert an aldehyde to a carboxylic acid include K2Cr2O7/H2SO4, Tollen's reagent, and H2O2/O2 (Section 11.9A).
Oxidation of a benzylic carbon bearing at least one hydrogen atom affords an aryl carboxylic acid. Benzylic positions that do not have a hydrogen are inert to these conditions. Chromic acid is also used for this reaction (Section 9.5).
Hydrolysis of carboxylic acid derivatives affords the corresponding carboxylic acid. In general, these reactions involve replacement of some leaving group with HO. All carboxylic acid derivatives are subject to this reaction, although some are much slower to react than others. The relative rates of hydrolysis are: acid chloride (fastest; Section 13.3A) > acid anhydride (Section 13.3B; yields two carboxylic acids) > ester (Section 13.3C) > amide (slowest; section 13.3D). Acid chlorides and acid anhydrides can be hydrolyzed eradily with water, but the hydrolysis of less reactive carboxylic acid derivatives such as esters and amides requires the presence of H3O+ or HO-.
Alcoholysis of an acid anhydride is similar to hydrolysis, except that the an alcohol is the nucleophile. The products are one molecule each of ester and carboxylic acid. The reaction usually requires acid or base catalysis (Section 13.5A).
Decarboxylation (loss of CO2) from a b-dicarboxylic acid yields a carboxylic acid. The reaction proceeds via the enol form of the carboxylic acid product (Section 12.8B).
