CATALYTIC DIMERIZATION OF ALKYL ACRYLATES

The review deals with the chemistry of dimerization of acrylic esters in the presence of various catalysts. The article covers literature fr om 1963 through early 1995. The dimerization reactions are divided int o three categories depending on the type of catalyst used, namely, pho sphine-catalyzed, metal-catalyzed, and miscellaneous catalysts. Phosph ine catalyzed dimerization leads to branched or head-tail dimers. Meta l catalyzed dimerization deals with the reactions that take place in t he coordination sphere of the transition metals (Ni, Pd, Ru, and Rh) c omplexes and are aimed at linear or tail-tail dimers. The tail-tail di mers, dialkyl hexenedioates, have a commercial potential as precursors of adipic acid, which is a raw material in the manufacture of nylon-6 ,6. Various strategies involved in designing the transition metal cata lysts for tail-tail dimerization are highlighted. A miscellaneous cata lyst section deals with systems that are not covered under the above t wo categories. It describes catalyst systems comprised of organic and/ or inorganic compounds leading to head-tail or tail-tail dimers. The h ydrodimerization reactions, which directly give dialkyl adipate from a crylic ester, are discussed separately. The mechanisms of the importan t dimerization reactions are outlined at appropriate places.