Eastern black spruce,Picea mariana, chips have been treated to high yields, at temperatures from 120#xB0; to 150#xB0;C, with sodium bisulphite solutions of pH 4 and total SO2concentrations from 0.23 to 1.92 mol L#x2212;1. The rate of sulphonation depends on the concentration of sites available for sulphonation and total SO2 concentration to the power of 0.4; it increases by approximately 70 percent for each 10#xB0;C temperature rise. It is postulated that sulphonation at pH 4 occurs by two mechanisms, one which is dependent on total SO2concentration and involves a quinonemethide intermediate and one which is independent of total SO2concentration and involves a carbonium ion intermediate.
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