2-(Isopropylsulfinyl)-Benzothiazole as a Delayed Action Thiazole Accelerator

Abstract

Abstract At vulcanization temperatures, 2-(isopropylsulfinyl)-benzothiazole(ISB) generates 2-benzothiazole sulfenic acid as a reactive intermediate. In this respect (i.e., formation of a sulfenyl species), ISB is analogous to a benzothiazole sulfenamide, but without the built-in amine activation. Thus, ISB alone is slow, but responds to a variety of activators. The potential to independently select the activator can offer a wider latitude in meeting today's compounding challenges. For example, ISB activated by tetrabenzylthiuram disulfide represents a system devoid of precursors of volatile introsamines ISB with thiophosphoryl sulfides can provide effective, amine-free cure packages. Where nitrosamines are not a factor, tetramethylthiuram monosulfide (TMTM) remains the best general purpose activator. Examples of the effects of ISB/activator systems on cure characteristics and physical properties in a variety of recipes are presented. A unique, practical synthesis of ISB in two steps from MBT, propylene and bleach is outlined, and a more generally adaptable laboratory procedure is described in detail. Diagnostic reactions of ISB and substituent effects of related derivatives, designed to support the postulated acceleration mechanism, are described.