Acyloin condensation by polymer supported thiazolium salt: Relation between the catalytic activity and the degree of quarternization

Thiazolium salt polymers were synthesized by the quarternization of thiazole polymers by alkyl halides. It was found that these polymers had high catalytic activities for the acyloin condensation of furfural. The catalytic activities of thiazolium salt polymers increased as the degree of quarternization decreased. This tendency was observed both in the polar solvents such as MeOH and in the nonpolar solvents such as dioxane. From the results of the acyloin condensation catalyzed by more hydrophobic polymer catalyst PTS⁺–St (which had styrene unit instead of free thiazole unit) and CnPTS⁺ (which had a long alkyl chain around the active site), it became clear that the hydrophobicity and the steric hindrance around the active site greatly affected the catalytic activity.