A new economical and environmentally friendly synthesis of 2,5-dimethyl-2,4-hexadiene

A new vapour phase process for the synthesis of 2,5-dimethyl-2,4-hexadiene (or tetramethyl-butadiene or TMBD) by dehydration of 2,5-dimethyl-2,5-hexandiol on solid acid catalysts has been developed. Commercial acid catalysts (oxides, zeolites, clays and acid-treated clays) were preliminarily screened by using the reaction condition previously reported in literature. Subsequently, the study focused on a detailed set-up of the reaction conditions (temperature, LHSV value and feed concentration). In the best reaction conditions identified, yield values higher than 80% were obtained using some commercial and very inexpensive clay-based adsorbents (Mega Dry and Granosil 750 JF), with a stable activity of up to 400 h of time-on-stream. These results were significantly superior to those already published. Finally, the clay-based catalysts made it possible to recover high amounts of isomers by converting them to TMBD and may be partially regenerated.