Low phosgene method for preparing aromatic bischloroformates

Organic compounds -- part of the class 532-570 series – Organic compounds – Carbonate esters

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528372, 558271, 558281, C07C 6802, C07C 6996

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active

050119664

ABSTRACT:
Aromatic bischloroformates are prepared by the reaction of a dihydroxyaromatic compound such as bisphenol A with phosgene in the presence of water, base and an organic liquid such as methylene chloride. Initially, a mixture of the bisphenol, organic liquid and about 5-15% of the total base is prepared, and phosgene is passed into said mixture. The remainder of the base is added initially at a constant rate, and then only when the measured pH of the aqueous mixture is below a targeted value in the range of about 8-11 and in about 5-10% excess with respect to the phosgene then being introduced. This method minimizes hydrolysis of phosgene and formation of such by-products as monochloroformates and hydroxy-terminated polycarbonate oligomers.

REFERENCES:
patent: 4737573 (1988-04-01), Silva et al.

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