LIGNIN IN WHEAT INTERNODES .1. THE REACTIVITIES OF LIGNIN UNITS DURING ALKALINE NITROBENZENE OXIDATION

The alkaline nitrobenzene procedure for determining lignin building units has been applied to wheat internodes. The effect of reaction time and temperature on the rate of reaction has been measured and the nature of the aldehyde and acid products determined by gas‐liquid chromatography. Survival factors for individual phenolic compounds were determined and found to be in the range 0.85–4.99, and were constant for each compound under the reaction conditions (c 6 % nitrobenzene in 2 M NaOH, 170°C, 2 h in a stainless steel pressure vessel), optimised for maximum recovery of products using wood and wheat internode meals. The reaction products fiom 24 monomeric and dimeric lignin model compounds were quantitativety determined to provide information on the susceptibility of various lignin structures to alkaline nitrobenzene oxidation. The results of these and earlier studies by other authors suggest that at the higher temperature a heterolytic reaction mechanism is operating on nitrobenzene oxidation conditions. On nitrobenzene oxidation, ferulic and p‐coumaric acids survived in amounts which allowed the procedure to be used, with appropriate correction factors, to determine the nature and amount of these cinnamic acids associated with walls of grasses. Copyright © 1990 John Wiley & Sons, Ltd