Dl. Criss et al., ALKALINE-HYDROLYSIS OF NONPHENOLIC BETA-0-4 MODEL DIASTEREOMERS - SUBSTITUENT EFFECT ON THE LEAVING PHENOXIDE, Holzforschung, 52(2), 1998, pp. 171-174
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.