Alkaline Hydrolysis of Nonphenolic α-Carbonyl β-0-4 Lignin Dimers Substituted on the Leaving Phenoxide Ring: Comparison with Benzylic Hydroxyl Analogues

Abstract

Four α-carbonyl nonphenolic β-0-4 lignin models [2-(2-methoxy-3- or 4- substitutedphenoxy)-1-(3,4-dimethoxyphenyl)-ethan-1-one] were synthesized and the alkaline hydrolysis rates determined. The rates were then compared to rates for α-hydroxyl analogues run earlier. The unsubstituted ketone hydrolyzed slightly slower, about 30%, then the alcohol analogue. The 4'-CHO ketone hydrolyzed much faster than the unsubstituted ketone and had essentially the same hydrolysis rate as the alcohol analogue. No definitive mechanistic conclusions could be made about the alkaline hydrolysis reaction of the ketones. Unsubstituted and 4'-Me substituted α-carbonyl models appear to be susceptible, even at room temperature, to competing alkali-initiated oxidative degradation.