Oxidation of natural rubber using a sodium tungstate/acetic acid/hydrogen peroxide catalytic system

A catalytic system based on Na(2)WO(4)/CH(3)COOH/H(2)O(2) effectively oxidizes natural rubber (NR) to prepare telechelic epoxidised liquid natural rubber (TELNR). The Na(2)WO(4)/CH(3)COOH/H(2)O(2) catalytic system possesses a much higher epoxidation efficiency than the traditional CH(3)COOH/H(2)O(2) system: the epoxidation degree (X(epoxy)) of products increases from merely 5.6% (CH(3)COOH/H(2)O(2)) to values as high as 52.1% (Na(2)WO(4)/CH(3)COOH/H(2)O(2)) by reacting for 24 h at 60 degrees C. Moreover, this catalytic system also induces hydrolytic degradation so that the weight average molecular weight (M) of NR decreases, e.g., from 14.10 x 10(5) Da (NR) to 0.57 x 10(5) Da (TELNR) after reacting for 30 h. The catalytic process probably proceeds via a mononuclear tungsten peroxo-species with coordinated peracetyl/acetyl group, as suggested by ESI-MS measurements. During oxidation, the tungstic anion [W (CH(3)COOO)(O)(O(2))(2)](-) not only catalyzes NR epoxidation, but also induces a further oxidation of epoxy groups to form ketones and aldehydes. (C) 2010 Elsevier Ltd. All rights reserved.