Condensation of Spruce Periodate Lignin With Formaldehyde

Abstract

The use of 7 3 y 0 sulphuric acid a t 41' for 1 hour or less caused the periodate lignin t o condense with 32y0 by weight of formaldehyde, a s shown by direct measurement and by employing C1a-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 t o 106% was recovered a s 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 t o the original periodate (or Klason) lignin thus originated in the cancellation of three large errors. Formaldehyde periodate lignin failed t o yield vanillin when oxidized in alliali with nitrobenzene or cupric hydroxide. Oxidation with alkaline potassium permanganate, or with iodic acid a t 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 benzenepenta-and -tetra-carboxylic acids on paper, were described. INTRODUCTIONI t is well kilown that the treatment of wood meal with 72y0 sulphuric acid near 20°, as in the I<lason determination of lignin, soon degrades and dissolves all of the carbohydrates but leaves the lignin as a darli. brown, amorphous powder insoluble in all liquids. In 1929, however, Ross and Hill (1) observed that when the wood meal was first soaked in formalin all dissolved in the sulphuric acid, and this solution had to be diluted with water in order to precipitate "formaldehyde lignin". The yield appeared to be quantitative from softwoods, but not from hardwoods, and the products were soluble in alcohol, acetone, or acetic acid containing a little water. Ross and Potter (2) modified the procedure to determine lignin in paper pulps, but the Klason method proved to be more reproducible (3). Since formaldehyde could be expected to condense freely with lignin (a phenolic material) it seemed anomalous that the yield of Ross-Potter lignin was not substantially greater than that of the Iclason lignin. The solubility of fornlaldehyde lignin suggested (2) that the formaldehyde had substituted active centers in the lignin, which normally condensed with each other to forin the insoluble Klason lignin. The present research was planned to gain information on these possibilities.Boriseli. and Polcin (4) determined the amount of formaldehyde that condensed with sulphite waste liquor solids under various conditions. No condensation occurred in neutral solution, and in alkali the formaldehyde underwent the Cannizzaro reaction. In sulphuric acid, the amount condeilsed increased as the concentration of the acid was increased to 27y0, and 2 hours were sufficient for the reaction. Samples pretreated with sulphurous or sulphuric acid failed to react under the condition...

The Reaction of Formaldehyde with Spruce Lignins

“…The size of specimen used is of significance; ideally the length in the direction of the grain should be less than the mean tracheid length, so that the air does not have to pass through a bordered pit during evacuation. Eisenbraun and Purves (1961), found that formaldehyde lignins probably substituted in the 6 position of the ring and in the alpha position of the side chain and also estimated that about every aryl propane unit of spruce periodate lignin took up one mole of formaldehyde in the ring 6-position. It is well known that the treatment of wood meal with strong acids like hydrochloric and sulphuric acids soon degrades and dissolves all the carbohydrates but leaves the lignin as a dark brown amorphous powder.…”