Hydroxyacetic acid, oxidative degradation

Reactions and Uses. The common reactions that a-hydroxy acids undergo such as self- or bimolecular esterification to oligomers or cycHc esters, hydrogenation, oxidation, etc, have been discussed in connection with lactic and hydroxyacetic acid. A reaction that is of value for the synthesis of higher aldehydes is decarbonylation under boiling sulfuric acid with loss of water. Since one carbon atom is lost in the process, the series of reactions may be used for stepwise degradation of a carbon chain. 

Organic acid oxidation in conjugation with oxidation of CaS03 slurry was studied for seven acids. Degradation of adipic acid and other aliphatic and sulfo carboxylic acids was least at pH 4.3 with 1.0 mM dissolved Mn and greatest at pH 5.5 without Mn. Hydroxypropionic and hydroxyacetic acids inhibited sulfite oxidation and were less subject to degradation. Fumaric acid degraded faster than the other alternatives. 

Organic acids are normally stable to oxidation, but laboratory and pilot plant results (18) have shown that adipic acid oxidizes in conjugation with sulfite oxidation in the scrubber. This paper reports oxidative degradation rate of adipic acid as a function of pH and Mn concentration (19). Results are also presented on sulfopropionic, sulfosuccinic, succinic, hydroxypropionic, and hydroxyacetic acids (20). 

Formic and acetic acids are most attractive, but would probably be volatile under scrubber conditions (8). Succinic and lactic acids would not be cost-effective if purchased at market price. Fumaric acid is more subject to oxidative degradation. Phthalic and Benzoic acids may give undesirable aromatic degradation products. Therefore, the most useful buffers appear to be hydroxypropionic, sulfosuccinic, fumaric, sulfopropionic, adipic, and hydroxyacetic. 

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