Ethylene glycol esters catalyst system

Other recent reports have also indicated that mixed-metal systems, particularly those containing combinations of ruthenium and rhodium complexes, can provide effective catalysts for the production of ethylene glycol or its carboxylic acid esters (5 9). However, the systems described in this paper are the first in which it has been demonstrated that composite ruthenium-rhodium catalysts, in which rhodium comprises only a minor proportion of the total metallic component, can match, in terms of both activity and selectivity, the previously documented behavior (J ) of mono-metallic rhodium catalysts containing significantly higher concentrations of rhodium. Some details of the chemistry of these bimetallic promoted catalysts are described here. 

C—C Bond-Forming Reactions. Heck coupling of iodobenzene and acrylate esters was studied in a biphasic system of ethylene glycol/toluene with various metal-TPPTS complexes as catalysts. Of the Pd-, Ni-, Rh-, Ru-, Pt-, and Cobased catalysts, Pd complexes afforded the highest activities and selectivities. The reactions were run at 140° C in the presence of potassium acetate for several hours and afforded the corresponding raras-vinylarene products in quantitative yields and with 100% selectivity (244). 

If the liberated alcohol is distilled from the system as it is formed, the reaction may be taken to completion. In the preparation of poly(ethylene terephthalate) two successive ester interchange reactions are performed. In the first step, dimethyl terephthalate is heated with an excess of ethylene glycol (the molar ratio is 1 2.1-2.2) at 150-210 C in the presence of a catalyst (see later). Ester interchange occurs, the principal product being bis(2-hydroxyethyl) terephthalate ... 

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