Reactions of lignin model compounds with pulp bleaching chemicals. Reactions of 4-methyltrichlorocatechol

Abstract

Aqueous chlorination of 4-methyltrichlorocatechol 2 gave the tetrachlorohydroxycyclohexenone 4, which crystallized as the hydrate 5. Reaction of 4 with aqueous sodium hydroxide resulted in a benzilic acid rearrangement to the tetrachlorodihydroxycyclopentenecarboxylic acid 6. These reactions have important implications with respect to understanding how lignin is removed during pulp bleaching. Crystals of the tetrachlorotrihydroxycyclohexenone 5 are monoclinic, a = 11.4420(6), b = 7.5873(9), c = 12.6443(6) Å, β = 101.266(4)°, Z = 4, space group P21/c, and those of the methyl tetrachlorodihydroxycyclopentenecarboxylate 7 are monoclinic, a = 28.447(1), b = 6.929(1), c = 12.597(1) Å, β = 103.074(5)°, Z = 8, space group C2/c. The structures were solved by direct methods and were refined by full-matrix least-squares procedures to R = 0.028 and 0.034 for 1716 and 2164 reflections with I ≥ 3σ(I), respectively.