Nitration of saccharification lignin

Abstract

1. A study was made of the nitration of saccharification lignin with a mixture of nitric and sulfuric acids having various water contents (5–16%), with a mixture of nitric acid and crystalline phosphoric acid, with nitric acid in a medium of acetic anhydride, and with nityric acid of sp.gr. 1.52. The highest yields of nitrolignins were obtained by treatment of lignin with mixtures of nitric and phosphoric acids and of nitric acid and acetic anhydride. The products had total nitrogen contents of 7.50–8.00%. 2. It was found that nitration of saccharification lignin with nitration mixtures of low water content at 10–15∌ or with pure nitric acid at 40° resulted in the highest uptake of nitrogen in the nitric-ester form (6.5%), but was associated with degradation of the lignin. Under all conditions nitration of the nucleus was predominant. If we assume that the structural units of lignin are derivatives of 4-propylguaiacol and take account of the carbohydrate content of the lignin, then the content of nonester nitrogen corresponds to almost one nitro group to each structural unit of the lignin molecule. 3. A study of the functional groups of nitrolignins (COOH, OCH3) showed that, under all the conditions which we tried, the nitration of saccharification lignin results in reduction in the number of methoxy groups and considerable increase in the number of carboxy groups.