Equilibrium Studies of 5-Substituted 4-Hydroxy-2-methylpyrimidines. IV. Lactim-Lactam Tautomerism in Methanol, n-Butanol and n-Hexane

概要

論文の詳細を見る
Lactim-lactam tautomerism of 5-substituted 4-hydroxy-2-methylpyrimidines (R ; H, CH_3,OCH_3 and COOC_2H_5) was examined in MeOH, n-BuOH and n-hexane. All the compounds existed mainly in the lactam form (4(3H)-pyrimidone, IIb) in the alcohols. No substituent effect at 5-position on the tautomerism in the alcohols was observed. In n-hexane, 5-H and 5-CH_3 derivatives also existed mainly in the lactam form, IIb. 5-Carbethoxy-4-hydroxy-2-methylpyrimidine (4), however, existed mainly in the lactim form (4-pyrimidinol, I). The lactim form of 4 in n-hexane was changed into the lactam form, IIb, on addition of MeOH and n-BuOH to the solution. The conversion to the lactam form may be explained as a result of an association of two molecules of alcohol to 4,i. e., [chemical formula] The association was investigated quantitatively by ultraviolet spectrophotometry : K_1=1483±29 (MeOH-association) and K_1=1279±19 (n-BuOH-association). the tautomeric equilibrium constant (K_t ; K_t=[IIb]/[I]) in pure n-hexane was estimated to be less than 0.02.
公益社団法人日本薬学会の論文
1978-05-25