Reactions between Cr(VI) and wood and its model compounds - Part 2: Characterisation of the reaction products by elemental analysis, magnetic susceptibility and FTIR

Hexavalent chromium solutions at two pH levels (about 1.3 and 7.8) were rea cted with wood, gum ghatti, lignin, cellulose and simple model compounds re presenting wood chemical structures (guaiacol, vanillin, vanillyl alcohol, homovanillyl alcohol, methyl-(beta-D-glucoside, and methyl-beta-cellobiosid e). Reaction products were isolated and characterised by elemental analysis , magnetic susceptibility, and Fourier-transform infrared spectroscopy (FTI R). Data suggest that all the chromium present in the reaction products is in its trivalent oxidation state. After reduction reactions, wood and macro molecular substances generally fixed a relatively low level of chromium, wh ich contrasts with the high level in the products isolated from the reactio n with the model compounds. It appears that the reaction of the simple mode l compounds with Cr(VI) did not produce complex adducts of Cr(III) but inor ganic substances, of the hydrated chromium oxide type. Therefore, under the experimental conditions applied, simple model compounds do not seem to beh ave chemically as wood or as the macromolecular substances investigated. He nce, their significance as model compounds must be object of further assess ment. An exception is the product from the reaction of vanillyl alcohol and K2CrO4 aq. This contains a relatively small amount of chromium and its FTI R spectrum presents rather well defined bands indicating reaction of the ph enolic hydroxyl and secondary alcohol groups. This system must be worthy of further investigation as a model for lignin.