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

The present article reports on the solvent-free dehydrogenation of gamma-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 KMnO(4) can be substituted by other, less-toxic and environmentally-benign oxidation agents (Oxone (R), NaIO(4), I(2)). In most cases the reaction yielded 2 with high selectivities, whereby conversion can be. ne-tuned by variation of the oxidant-to-substrate ratio, the rotation frequency v(rot), the number of milling balls n(ball) 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.