Selective dimerization of diisobutylene by oxo acids: Synthesis of isobutylene tetramer

Isobutylene tetramers (IB 4 ) were obtained in high yield by the cationic dimerization of commercial diisobutylene (DIB) (2,4,4‐trimethyl‐1‐pentene with isomeric impurities) with CF 3 SO 3 O 3 H or CH 3 COClO 4 as catalyst. The best IB 4 yields (80–90%) were achieved at 0–30°C in nonpolar solvents ( n ‐hexane and CCl 4 ). The major components in the IB 4 produced under these conditions were 2,2,6,6,8,8‐hexamethyl‐4‐methylenenonane (8) and 2,2,4,6,6,8,8‐heptamethyl‐4‐nonene (9) that arose via simple linear dimerization of DIB. The yield of IB 4 was almost independent of the monomer concentration ranging from 10 to 50 vol % at 0°C, but decreased at higher temperatures (>50°C) or in a polar solvent [(CH 2 Cl) 2 ] because of the formation of higher oligomers and side reactions such as cracking. A Lewis acid catalyst (AlEtCl 2 ) resulted in a very complex mixture of C 12 –C 20 hydrocarbons at 0°C in CCl 4 ; the yield of IB 4 was less than 40%. The catalytic difference between oxo acids and metal halides is discussed.