A single centre aluminium(III) catalyst and TBAB as an ionic organo-catalyst for the homogeneous catalytic synthesis of styrene carbonate

A non-symmetrical aluminium complex containing a single metal centre has been synthesised and used as a catalyst in the cycloaddition reaction of carbon dioxide to styrene oxide to yield a cyclic carbonate. The reaction proceeds to around 70% conversion using the catalyst alone; however, it can be increased to 90% conversion with the addition of tetrabutylammonium bromide (TBAB) as a co-catalyst. Interestingly, the reaction proceeds as well with the organo-catalyst TBAB alone as it does with the aluminium catalyst alone. This offers the potential for reduced cost processing and scale-up of the reaction through elimination of the aluminium catalyst due to reduced catalyst costs and ease of separation of TBAB as a salt from the reaction mixture. The rate constants for the aluminium catalysed reactions were determined as a function of process temperature in the range 80-150 degrees C, as well as the activation energies for the reactions determined from the Arrhenius plots. The activation energy for the aluminium catalyst alone was determined to be 34 kJ mol(-1), while adding TBAB as a co-catalyst reduced the activation energy by 11 kJ mol(-1).