Acid catalysed dimerisation of 2,3-dimethylbutadiene

Abstract

The acid catalysed dimerisation of 2,3-dimethylbutadiene has been carried out using sulphuric acid in acetic acid as solvent. Analysis by gas chromatography, mass spectroscopy revealed that the product, b.p.46 - 120° at 0.5 mm consisted of at least thirteencompounds. Of the eight major components (hydrocarbons), five have a molecular weight of 164 and three 162. No acetates appeared to be formed during the reaction and only one compound was found to be a solid (m.p. 87°). The major compounds were separated in a pure state using preparative G.l.c. and their molecular structure investigated using H and C n.m.r. and open-chain, mono-cyclic, bicyclic, tricyclic and aromatic structures have been found in these compounds.The following compounds were suggested: 3-methylene-2,6,7-trimethyl-1,6-octadiene or 4-methylene-2,3,7-'trimethyl-2,7-octadiene, 1,2,4-trimethyl 4-isopnopenyl cyclohex-1-ene, 2-methylene-1,3,3,4-tetramethyl-bicyclo[2,2,1]heptane, 2-methylene-1,4,7,7-tetramethylbicyclo [2,2,1]heptane (solid), 2,4-dimethyltricyclene or 1,2,4,7,7-pentamethyltricyclo(2,2,1,0,2-6) heptane, 2,4-2,5- and 3,4-dimethyl t-butylbenzene.The kinetic study of the reaction has shown that it is second order in 2,3-dimethyl-1,3-butadiene.