[Effect of oxygen, water and hydrophobic medium in model reactions of thiamine pyrophosphate]

Oxygen and water are inhibitors of acyloin and benzoin condensations. An intermediate paramagnetic compund is formed in the benzoin condensation catalyzed with 3-benzyl-4-methyl thiazolium chloride, 3,4-dimethyl thiazolium iodide, 3-benzyl-4,5-dimethyl thiazolium chloride, 3-methyl-4-phenyl thiazolium perchlorate and 3-methyl-4,5-diphenyl thiazolium perchlorate. The formation of benzoin in dimethyl sulphoxide, when the air oxygen is absent, is an irreversible reaction. The presence of hydrophobic solvent in the reaction medium provides more favourable conditions for benzoin condensation proceeding. The reaction mechanism is suggested.