The Effect of the Solvent on the Iodination of a Tyrosine Derivative and its Relation to the Iodination of Wool

A study was made of the rate and extent of reaction of N-acetyltyrosine ethyl ester with iodine, using ethanol, n- propanol, and n-butanol as solvents. In anhydrous ethanol, the reaction became extremely slow when about one-third of the tyrosine had been iodinated. In anhydrous propanol, less than 10% of the tyrosine was iodinated after prolonged treatment. In anhydrous n-butanol, the loss of tyrosine was barely detectable. Addition of traces of water to the solvent increased the rate and extent of iodination in all three solvents. The addition of anhydrous NaOH to the anhydrous alcohols caused marginal increases in iodination, but larger increases were observed in the presence of traces of water. The tyrosine residues were found to be iodinated to about the same extent in the high-sulfur and low-sulfur protein fractions extracted from wool which had been treated for 15 days at 30°C with 0.39 M I 2 in anhydrous n-propanol. The data are discussed in relation to the use of measurements of wool iodination to indicate penetration of the solvent in to the fiber.