Abstract
The use of 73% sulphuric acid at 41° for 1 hour or less caused the periodate lignin to condense with 32% by weight of formaldehyde, as shown by direct measurement and by employing C14-formaldehyde. Analyses of the product, however, suggested that the elements of water had been expelled during the condensation and that the true yield was about 120%. Up to 106% was recovered as material insoluble in dilute sulphuric acid (Ross–Potter lignin), and about 9% as a more soluble form. The approximate equivalence in weight of the Ross–Potter lignin to the original periodate (or Klason) lignin thus originated in the cancellation of three large errors. Formaldehyde periodate lignin failed to yield vanillin when oxidized in alkali with nitrobenzene or cupric hydroxide. Oxidation with alkaline potassium permanganate, or with iodic acid at not more than 200°, yielded benzenepentacarboxylic acid and perhaps mellitic acid (total, 3.9%) but none of the 1,2,4,5-tetracarboxylic acid recovered (together with the pentacarboxylic acid) from similar oxidations of periodate lignin. Convenient semimicro-scale oxidations with cupric hydroxide and with iodic acid, and the chromatography of the benzene-penta- and -tetra-carboxylic acids on paper, were described.
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