Kinetic studies on the vulcanization reaction accelerated with 2-mercaptobenzothiazole

Kinetic data for vulcanization of rubber with sulfur, accelerated with 2‐mercaptobenzothiazole (MBT) are presented. The decrease in concentration of sulfur and MBT during vulcanization under various conditions of temperatures have been determined with a precise amperometric method developed by the authors. The order of reaction for disapperance of sulfur was found to be unity. The energy of activation and frequency factor were 28.8 kcal./mole and 4.0 × 1013, respectively. The kinetics of disapperance of MBT was also first‐order, and the rate of reaction, energy of activation, as well as frequency factor were much lower than those for the disapperance of sulfur. The consumption of sulfur proceeded as long as any free sulfur was present in the sample, indicating that the consumption of MBT is closely tied up with the disapperance of sulfur. It was found that about 133 atoms of sulfur were consumed for the disappearance of one molecule of MBT. The mechanism of ring opening involving an attack by the accelerator radical as proposed by Gordon is supported by the present investigation.