Solvent-free dehydrogenation of γ-terpinene in a ball mill: investigation of reaction parameters

Abstract

The present article reports on the solvent-free dehydrogenation of γ-terpinene (1) in a planetary ball mill affording p-cymene (2) as the predominant reaction product. The influence of various reaction parameters and technical variables on the transformation of 1 has been assessed. Thus, it is shown that KMnO4 can be substituted by other, less-toxic and environmentally-benign oxidation agents (Oxone®, NaIO4, I2). In most cases the reaction yielded 2 with high selectivities, whereby conversion can be fine-tuned by variation of the oxidant-to-substrate ratio, the rotation frequency νrot, the number of milling balls nball or the type of grinding auxiliary employed. Contrary to particle refinement processes, the size of the milling balls d (constant mass) has no influence on the conversion and chemical yield.