POLYMER-BOUND THIAMINE MODELS .6. FACTORS INFLUENCING THE STABILITY OF MACROPOROUS POLYSTYRENE-BOUND THIAZOLIUM SALTS IN THE CONTINUOUS PRODUCTION OF BENZOIN

Two macroporous polystyrene-bound thiazolium salts (2, 3) were prepared and tested in the benzoin condensation reaction (MeOH, 50-degrees-C, Et3N as cocatalyst) in a continuous stirred-tank reactor. A comparison with the results of two previously examined immobilized thiazolium salts (1, 4) was made. This showed that protecting the hydroxyethyl group of the thiamine model (2 versus 1), as well as providing a stronger linkage between the catalyst and the support (3 versus 1), improved the stability of the polymeric catalyst under these reaction conditions. The relatively high stability of 4, which incorporates both aforementioned features, can now be explained.