Dimerization of Isoprene by Means of Titanium Tetrabutoxide-Diethylaluminum Chloride Catalyst System

Abstract

The oligomerization of isoprene and its simultaneous cis-1, 4-polymerization occur by the use of titanium tetrabutoxide [Ti(OBu)₄]-diethylaluminum chloride [AlEt₂Cl] catalyst system. On the basis of gaschromatography and infrared spectrum the dimers of isoprene obtained were found to be the same as those obtained by the use of TiCl₄-Al (i-Bu)₃, catalyst system. Thus, 2, 6-dimethyl-1, 3, 6-octatriene[1] is a chain dimer and 2, 4-dimethyl-4-vinyl-1-cyclo hexene[2] is a cyclic dimer and these are the main products.
The rate equation of the dimerization of isoprene is shown below:
Despite the variation of Al/Ti mole ratio in the catalyst system, the[1]/[2] ratio is constant. The dimerization of isoprene is inhibited by the addition of 2, 2'-bipyridyl, which acts as a bidentate ligand. On the basis of the above mentioned facts, it was assumed that the dime rization of isoprene proceeded in terms of the bimolecular reaction between the isoprene monomers coordinated unidentately and/or bidentately on the same Ti active species.