Catalysis of Organic..

Bianchi, Borzatta, Poluzzi and Vaccari 33738. A New Economical and EnvironmentallyFriendly Synthesis of2,5-Dimethyl-2,4-HexadieneAlessandra O. Bianchi a , Valerio Borzatta a , Elisa Poluzzi a and Angelo Vaccari ba Endura SpA, Viale Pietramellara 5, 40012 Bologna (Italy)b Dipartimento di Chimica Industriale e dei Materiali, Alma Mater StudiorumUniversità di Bologna, Viale del Risorgimento 4, 40136 Bologna (Italy)Abstractangelo.vaccari@unibo.it; +39 051 2093679A new vapour phase process for the synthesis of 2,5-dimethyl-2,4-hexadiene (ortetramethyl-butadiene or TMBD) by dehydration of 2,5-dimethyl-2,5-hexandiolon solid acid catalysts has been developed. Commercial acid catalysts (oxides,zeolites, clays and acid-treated clays) were preliminarily screened by using thereaction condition previously reported in literature. Subsequently, the studyfocused on a detailed set-up of the reaction conditions (temperature, LHSV valueand feed concentration). In the best reaction conditions identified, yield valueshigher than 80% were obtained using some commercial and very inexpensiveclay-based adsorbents (Mega Dry and Granosil 750 JF), with a stable activity ofup to 400 h of time-on-stream. These results were significantly superior to thosealready published. Finally, the clay-based catalysts made it possible to recoverhigh amounts of isomers by converting them to TMBD and may be partiallyregenerated.IntroductionPyrethrins and pyrethroids are probably the best known and safest classes ofnatural or synthetic insecticides, widely used in domestic and agriculturalapplications (1-7). Pyrethrins are natural insecticides derived from theChrysanthemum cineraria flowers: the plant extract, called pyrethrum, is amixture of six isomers (pyrethrin I and II, cinerin I and II, jasmolin I and II) whichwas first used in China in the 1 st century AD, during the Chou Dinasty. The worldpyrethrum market is worth half a billion US dollars [main producers are EastAfrica highlands (Kenia, Tanzania and Rwanda) and Australia]; however, itsavailability is subject to cyclical trends, due to rains and relations with farmers,who face high harvest costs also due to the fact that the flowers have to be