Process for producing 2,6-dimethyl-1,3,6-octatriene

A process for producing 2,6-dimethyl-1,3,6-octatriene which comprises contacting isoprene with a dimerization catalyst thereby to dimerize the isoprene, said dimerization catalyst comprising a combination of:

• I. a zirconium compound selected from the group consisting of:
• 1. compounds having the general formula
• ZrX.sub.4-n Y.sub.n ,
• 2. compounds having the general formula
• ZrOY'.sub.2, and
• 3. complexes of the compound (1) or (2) with a coordinating compound, wherein X represents a halogen atom;
• Y and Y' respectively represent a member selected from the group consisting of (i) alkoxy and chloroalkoxy groups each having from 1 to 20 carbon atoms, (ii) aryloxy and chloroaryloxy groups wherein each aryloxy group is a member selected from the group consisting of phenoxy and methyl-substituted phenoxy groups, and (iii) acyloxy groups each having the general formula RCOO-wherein R is a member selected from the group consisting of alkyl groups each having from 1 to 20 carbon atoms and aryl groups each having from 6 to 20 carbon atoms;
• and n is an integer of 1 to 4:
• Ii. an iodine compound which is a member selected from the group consisting of those having either of the general formulas
• R'I.sub.A and MeI.sub.B
• wherein R' represents a member selected from the group consisting of hydrogen, halogen atoms, straight and branched chain hydrocarbon groups each having from 1 to 20 carbon atoms and cyclic hydrocarbon groups each having from 3 to 10 carbon atoms;
• A is an integer of 1 to 3;
• Me represents a metal of Groups I through IV of the periodic table;
• and B represents the valence of the metal;
• and
• Iii. an organoaluminum compound having the general formula.
• AlR".sub.m Cl.sub.3-M
• wherein R" represents a member selected from the group consisting of alkyl groups each having from 1 to 10 carbon atoms, cyclic alkyl groups each having from 3 to 10 carbon atoms, and aryl groups each having 6 to 10 carbon atoms;
• and m is 1.5 or 2;
• in which dimerization catalyst, when iodine is present as a ligand in the zirconium compound I, the iodine compound II may be excluded.