ALKALINE-HYDROLYSIS OF NONPHENOLIC BETA-0-4 MODEL DIASTEREOMERS - SUBSTITUENT EFFECT ON THE LEAVING PHENOXIDE

Nonphenolic beta-0-4 lignin model diastereomers [erythro or three l)-2 -(4-substituted-2-methoxyphenoxy)-propan-1-ol] were synthesized and th e alkaline hydrolysis rates, and activation parameters for some compou nds, determined. These rates and activation parameters were compared t o rates determined earlier for similar models with 2-carbon side chain s. Unfortunately, the three derivative with an electron-withdrawing fo rmyl substituent could not be synthesized. The unsubstituted and 4'-Me erythro isomers hydrolyzed about one-third faster than the respective three analogue. The unsubstituted and 4'-Me 3-carbon side chain model s, both erythro and three, hydrolyzed slightly faster than the 2-carbo n analogues, white the erythro 4'-CHO diastereomer hydrolyzed approxim ately 8 times faster than the formyl analogue with a 2-carbon side cha in. Both unsubstituted diastereomers had similar activation parameters as the unsubstituted 2-carbon side chain model. The erythro 4'-CHO di astereomer had a similar Delta H double dagger as the 2-carbon side ch ain analogue, but the Delta S double dagger was much smaller for the 3 -than the 2-carbon side chain model. Explanations for the hydrolysis r ate differences are proposed.