CHARACTERIZATION OF THE MONOMERIC COMPOSITION OF IN-SITU WHEAT-STRAW LIGNINS BY ALKALINE NITROBENZENE OXIDATION - EFFECT OF TEMPERATURE ANDREACTION-TIME

The effect of temperature and time on the recovery yield of the produc ts of alkaline nitrobenzene oxidation of in situ lignins in wheat stra w internodes and corresponding leaves were studied. The results showed that significant variations in the yields of aromatic aldehydes (p-hy droxybenzaldehyde, vanillin and syringaldehyde) as well as hydroxycinn amic acids (p-coumaric and ferulic acids) arise from changes in the te mperature and the reaction time. The conditions for maximum yield depe nd on the aldehyde concerned. For example, the yield of p-hydroxybenza ldehyde increases with increasing temperature and reaction time. This phenomenon could be attributed to the low relative reactivity related to the specific electronic structure of the non-methoxylated units and /or to the existence of specific condensation reactions involving the p-hydroxyphenyl aromatic ring. Finally, the results indicate a much hi gher complexity of Gramineae lignins compared to those derived from ha rdwoods and softwoods.