Mechanistic Study for Cyclization Reaction of 3 (2-Alkoxyphenyl) -3 (4-diethylamino 2-hydroxyphenyl) -1(3H) -isobenzofuranone Derivatives to Corresponding Fluoran Dyes

Abstract

Heating of 3-(2-alkoxyphenyl) -3- (4-diethylamino-2-hydroxyphenyl) -1(3H) -isobenzofuranone or 3- (4-diethylamino-2-alkoxyphenyl) -3- (2-hydroxyphenyl) -1(3H) -isobenzofuranone derivatives (1) under acidic and/or basic media provided fiuoran dyes (2), which have been widely used in pressure or heat sensitive recording system as color forming materials, in high yields. Mechanistic studies using oxygen-18 labeled model compounds as tracers and kinetic measurements of this intramolecular cyclization process revealed that the hydroxyl group in the phenol moiety of 1 attacked the ipso-carbon atom bearing the alkoxyl group via nuclephilic aromatic substitution reaction. Furthermore, in case of 3- (2alkoxy-5-anilinophenyl) substituted isobenzofuranone derivatives, the participation of free-radical pathway was assumed in their ring closure reactions.