Nitration of models of lignin containing benzyl alcohol and alkyl benzyl ether groupings

Summary

• 1. Models of lignin-α-ethylveratryl alcohol (II), its methyl ether (VI), andα-ethyl-4-hydroxy-3-methoxy-benzyl alcohol methyl ether (V)-were nitrated with concentrated HNO₃ in CCl₄ and in dry ether.

• 2. In the nitration ofα-ethyl-4-hydroxy-3-methoxybenzyl alcohol methyl ether (V) the side chain in the para position relative to the phenolic hydroxyl is replaced by the nitro group with formation of 4,6 -dinitroguaiacol.

• 3. In the nitration ofα-ethylveratryl alcohol methyl ether (VI) the main factor determining the course of reaction is the molar ratio of the substance being nitrated and HNO₃. With a 1∶ 3 ratio the nitro group enters the 6-position of the aromatic nucleus, with a 1∶6 ratio nitration of the nucleus is accompanied by the replacement of the benzyl ether grouping by a nitric ester grouping, and at ratios of 1∶9 and 1∶12 there are two cmpeting reactions: replacement of the side chain by a nitro group and the formation of the mononitro compound nitrate (IV) in the first case and the dinitro compound nitrate (IX) in the second.

  In the nitration ofα-ethylveratryl alcohol (II) with 6–12 molecular proportions of HNO₃ the same, nitro compounds were obtained as in the nitration of (VI).

• 4. It may be supposed that a) the formation of nitric ester groupings in nitrolignin is due to the esterification of benzyl alcohol hydroxyls and the replacement of benzyl ether groupings by ester groupings, and b) the nitration of lignin with a considerable excess of nitric acid is accompanied by degradation with replacement of side chains containing benzyl alcohol or benzyl ether groupings by nitro groups.