Study On The Activation Mechanism Of Dimethyl Carbonate And The Reaction Mechanism Based On Bisphenol

Polycarbonate (called PC for short) is a kind of colorless, transparent and amorphous thermoplastic material, belonging to one of the five major engineering plastics. PC has excellent electrical insulating properties, heat resistance, impact resistance and resistance to chemical corrosion. DMC has attracted much attention as an important intermediate for polycarbonate resins and environmentally benign substitute for highly toxic phosgene and dimethyl sulfate in carbonylation and methylation reactions. This paper systematically studies the catalyst structure and the catalytic mechanism in the green synthesis of the intermediate (MmC(1) and DmC(1)) of PC from BPA and DMC.Firstly, the catalytic mechanism of TiO2(B) and anatase TiO2 was studied by TG-MS and In situ DRIFTs. The main factor to determine carboxymethylation and methylation reactions is the activation morphology of DMC on the surface of catalyst.Secondly, a series of homogeneous organic tin oxide catalysts were synthesized, including phenyl organic tin oxide such as Ph2SnO, (PhCF3)2SnO and (PhCH3)2SnO, and heterocyclic organic tin oxide for example (C5H4N)2SnO, (C4H3S)2SnO and (C4H3O)2SnO. The catalysts were characterized systematically. The selectivity of synthesized PC intermediates were characterized by using GC. Base on the conversion of BPA, the catalyst active sequence was listed as following: (PhCF3)2SnO> Ph2SnO> (PhCH3)2SnO. In terms of the selectivity of MmC(1), the catalystic selectivity was listed as following:Ph2SnO> (PhCH3)2SnO> (PhCF3)2Sn0, and the maxium selectivity of MmC(1) can reach 93.33%. Among heterocyclic organic tin oxide, (C4H3O)2SnO exhibits the best catalytic performance, and the conversion of BPA can reach 75.40% and the selectivity of MmC(1) achieves 49.08%.Thirdly, the catalytic mechanism of homogeneous catalyst was studied. Sn=O was activity sites for reaction, and the interaction mode between Sn=O and DMC was main factor to influence carboxymethylation and methylation selectivity. DMC was attacked by Sn=O on two oxygen atoms of the CH3-O moiety, inducing a shortening of C=O bond, and then the oxygen of BPA attacked the carbonyl carbon to form carboxymethylated products. If the interaction occurs through the oxygen of the C=O moiety, inducing an elongation of C=O bond and then the oxygen of BPA attacked the methyl carbon to form methylated products.Finally, the effect of CO2 on the transesterification of DMC with BPA was studied. CO2 can inhibit methylation reactions, but it also restrains transesterification reaction. Temperature plays a more significant role on transesterification reaction, and higher temperature is benign to methylated products formation.