Behavior of lignin models on nitration

Abstract

1. The behavior of eight lignin models under the action of concentrated nitric acid in a carbon tetrachloride medium was studied; the models were derivatives of 1-(3,4-dlmethoxyphenyl)- and 1-(4-hydroxy-3-methoxyphenyl)-propane containing a hydroxy group in various positions in the propane chain. 2. In the nitration of models having an etherified phenolic hydroxyl [(3,4-dimethoxyphenyl)propanols], one nitro group entered the nucleus in the 6-position. The action of nitric acid favored also the condensation of the alcohol in which the OH was in the 1-position of the side chain, and it oxidized the alcohol group of 1-(3,4-dimethoxyphenyl)-2-propanol to a keto group. 3. When treated with nitric acid under similar conditions, models with a free phenolic hydroxyl in the para position to the side chain (derivatives of 4-propylguaiacol) behave differently: 1-(4-hydroxy-3-methoxyphenyl)-1-propanol, treated with excess of nitric acid (3 molecular proportions), loses its side chain and gives 4,6-dinitroguaiacol; under the action of a smaller amount of nitric acid 4,6-dinitroguaiacol is accompanied by some dimeric condensation product. When 3-methoxyphenyl)-1-propanol is nitrated, a light-brown powder containing nitrogen is formed. 4. The behavior of the models in nitration indicates the great variety of the process that occur when lignin is treated with nitric acid, for all the types of models studied are present in lignin as structural units.