綿セルロース布のTEMPO触媒酸化反応 : 電子スピン共鳴法による解析

抄録

Suitable amounts of carboxylate groups can be effectively introduced into cotton fabrics by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation under aqueous conditions such as TEMPO/NaBr/NaClO and TEMPO/Na₂SO₄/NaClO systems. Then, the difference in oxidation mechanism of cotton fabrics between the two TEMPO-oxidation systems in water at pH 9-11 were studied by measuring radical concentration in aqueous reaction solutions using electron spin resonance (ESR) technique. In the case of the conventional TEMPO/NaBr/NaClO system, the obtained ESR results well supported a previously proposed mechanism; NaBrO molecules are immediately formed in situ from NaClO and NaBr, and oxidize almost all TEMPO radicals, present in the reaction solution, to cationic oxoammonium-type compounds, which can in turn oxidize C6-primary hydroxyl groups of cellulose to C6-carboxylate groups. Thus, TEMPO-oxidation behavior of cotton fabrics can be monitored in terms of time-dependent changes in radical concentration of reaction solution using ESR technique. In contrast, most of TEMPO radicals were present in reaction solutions as the original radial structure in the TEMPO/Na₂SO₄/NaClO system, indicating that only a small amount of cationic oxoammonium-type compounds were formed from TEMPO radicals in this system, although this oxidation system also can effectively form carboxylate groups in cotton fabrics. Thus, new oxidation mechanism other than the conventional one is needed to explain the ESR results for oxidation of cotton fabrics in the TEMPO/Na₂SO₄/NaClO system. 4-Acetamido-TEMPO had similar results to those of TEMPO in both oxidation systems.