Catalysis of Organic..

3442,5-Dimethyl-2,4-Hexadienereactions to cyclic isomers, while the Mega Dry clay, although less active, causedthe formation of TMBD, thus making it possible to recover a sizable fraction ofisomers and rendering the overall process even more economically appealing (Fig.8).Yield (%)6040200Before regenerationAfter regenerationTMBD Isomers CoalFigure 7. Activity of the Mega Dry clay catalyst, before and after regenerationat 550 °C for 4,5 h. (Cat. = 9 g; T = 290 °C; P = 0.1 MPa; Feed = 2.8 MDMED/CH 3 OH solution in N 2 flow; LHSV = 0.92 h -1 ).ConclusionsThe vapour phase dehydration of 2,5-dimethyl-2,5-hexanediol (DMED) to2,5-dimethyl-2,4-hexadiene (TMBD) - key intermediate for the synthesis ofchrysanthemic acid and, consequently, of pyrethroids (probably the safest andmost used family of insecticides) - is an interesting example of an economical andenvironmentally-friendly process of industrial interest. In fact, it uses a non-toxicor non-hazardous raw material, commercially available at a reasonable price,which is thus supported by many companies. Furthermore, it functions in safereaction conditions with heterogeneous catalysts, while showing high conversionand selectivity in TMBD values. The best results have been obtained by using ascatalyst certain commercial raw clay mixtures, available at very low prices andbeing currently used as adsorbents. The best catalysts (Granosil 750 JF and MegaDry) showed stable physical properties and very interesting catalyticperformances, which remained constant with time-on-stream. Finally, they made itpossible to recover a sizable fraction of isomers by their conversion to TMBD,thus making the overall process even more economically attractive.