The formation of monomeric products from lignin by the action of ammonium sulfide

Acetoguaiacone and propioguaiacone were found to be the dominant lignin monomeric products (molar ratio 1.3 to 1) from the spent liquor of hemlock pulped with ammonium sulfide/methanol/water. The combined amounts of the ketones were as high as 3.5% based on wood. This is higher than reported monomer quantities from any other pulping process. The model compounds, guaiacyl glycerol β-(2-methoxyphenyl) ether and coniferyl alcohol, also produced aceto- and propioguaiacone, upon ammonium sulfide treatment at 180°C. The molar conversion to these two ketones was more than 50% in both cases. It was, therefore, concluded that uncondensed β-0-4 lignol structures were the primary lignin precursors of the ketones, and coniferyl alcohol was an intermediate in this conversion. Studies using coniferyl alcohol and wood meal were also conducted at 140°C. An alpha carbonyl intermediate was found which primarily formed propioguaiacone.