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HYDROGENATION OF SOME ALLYLIC ALCOHOLS CATALYSED BY ANCHORED MONTMORILLONITEBIPYRIDINEPALLADIUM(II) ACETATE : A KINETIC STUDY

1999; CSIR-NISCAIR; Volume: 38; Issue: 5 Linguagem: Inglês

0975-0975

B. Ramesh, D Thomas Sadanand, K. Venkata Swamy, P. K. Saiprakash,

Asymmetric Hydrogenation and Catalysis

Hydrogenation of some a llyli c a lcohols like 2-methyl-2-propen- l-ol, 4-penten-3-01 , trtllls -2-buten-l -ol, trtllls-3- penten-2-01 and 4methyl-3-penten-2-01 has been carried out by anchored montmorillonitebipyridinepalladium(ll) acetate in THF medium. Under the reacti on conditions 100% saturation of carbon-carbon doubl e bond is observed and there is neither polymerisation nor isomeri sation. The observed rate ha s been found to be first order each with respect to partial pressure of hydrogen and [substrate] and fr ac ti onal order with respect to [catalyst] . The rat e of hydrogenation follows the order: 2-methyl-2-propen-l-ol > 4-pent en-3-o1 > trtllls-2-b ut e n-l-ol > trGll s-3-penten-2-o l > 4-methyl-3-pent en-2-01. Thermodynamic parameters have been evaluated, rate law and a plausible mechan is m have been proposed. One of the most in tensively investigated research areas in recent years in the field of catalysi s is immobilization of tran sition metal complexes on solid supports like or­ ganic polymers and inorganic oxides ' - 6 . Serious interest in these catalysts originated with efforts to develop in­ du strially competitive-homogeneous catalysts to supplant heterogeneous catalysts, which met with li mited success due to th e separation probl em associated with homoge­ neous sys tems. In addition to providing a solution to this problem, the new anchored catalysts have attractive fea­ tures of being reproducible, allowing control and knowl­ edge of the nature of the incipi e nt species immobilized on the support. Inorganic supports that have been used are silica, alumina, g lasses, zeolites and clay. Of all these, clays are shown to be good catalyst supports. The clay used in our study is montmorillonite, a smectite clay. This clay possesses large amounts of hi ghly reactive species which can be readily exchanged by inorganic complexes. Apart from thi s, the intra-cry stal space can be swelled by various polar solv e nt s? The degree of swellin g depends on the interlayer cations, the substrate and negative charge density on si li cate sheet. Keeping these advantages in mind, Choudary et at synthesized a series of montmorillonite functional ised palladium(IJ) complexes 8 . 9 . Number of attempts we re made to hydro­ genate the olefinic compounds, us ing anchored catalysts, however on ly in few in stances de tailed kinetic study has been undertaken 10-1 8 . We report a detailed kinetic study of hydrogenation of some allylic alcohols catalysed by anchored montmorillonitebipyridine-pa ll adium(II) ac­ etate. The influence of structure on reactivity is a topic of current interest in the study of the mechanism of alk e ne hydrogenation on supported metal catalysts 19.20. There­ fore in this study, to determine as how olefin structure influences rate of_hydrogenation, the catalyst was tested with a series of olefins of varying double bond substitu­ tion like 2-methy l -2~propen-l-ol (I), 4-pent en-3-01 (II), trans-2-buten-l-ol (III), trans-3-penten-2-01 (IV) and 4-methyl-3-penten-2-ol (V)(Scheme.l )