THE EFFECT OF ALKALINE NITROBENZENE OXIDATION CONDITIONS ON THE YIELDAND COMPONENTS OF PHENOLIC MONOMERS IN WHEAT-STRAW LIGNIN AND COMPARED TO CUPRIC(II) OXIDATION

A comparative study of degradation of wheat straw lignin by alkaline n itrobenzene and cupric compound (CuO, Cu(OH)(2), CuSO4 5H2(O)) oxidati on was carried out at 170 degrees C for 2.5 h in 2 N NaOH (7 mi) and 6 .8% nitrobenzene. The major products of such a degradation were the ph enolic aldehydes of vanillin and syringaldehyde in both of the reactio ns. A relative high guaiacyl/syringyl ratio value was obtained by nitr obenzene oxidation, whereas a slightly high syringy/guaiacyl ratio app eared in the cupric(II) oxidation. A suite of up to 13 phenols was det ected in the oxidation mixtures except that no acetosyringone appeared in the nitrobenzene oxidation. Gallic acid, protocatechuic acid and a cetovanillone were firstly identified in both of the oxidation product s from wheat straw lignin. The main difference between the two oxidant reagents was twice yield of nitrobenzene oxidation than that of cupri c(II) oxidation. The effects reaction time, temperature, concentration of sodium hydroxide and nitrobenzene, and the amounts of sample used on the reaction yield and components of oxidation products from wheat straw were performed at 38 various conditions and the nature of the al dehyde and acid products determined by high-performance liquid chromat ography (HPLC). The results obtained showed that the percentages of va rious products were dependent on the conditions of alkaline nitrobenze ne oxidation. The reaction condition (0.10 g straw in 2 N NaOH (7 mi) with 6.8% nitrobenzene at 170 degrees C for 4 h in a steel autoclaves) optimised for maximum recovery of products from wheat straw. Meanwhil e, ferulic and p-coumaric acid released in amounts during the nitroben zene oxidation, especially, at 170 degrees C for 2.5 h in 2 N NaOH wit hout nitrobenzene, which suggested that more than 50% of ferulic acid was in the etherified form while p-coumaric acid was predominant in th e esterified bond with lignin in wheat straw.