Alcohols react with phosgene to yield carbonate esters according to the following reaction:
:2 ROH + COCl → ROC(O)OR + 2 HCl
Phenols react similarly.  Polycarbonate derived from bisphenol A is produced in this manner. This process is high yielding. However, toxic phosgene is used, and stoichiometric quantities of base (e.g. pyridine) are required to neutralize the hydrogen chloride that is cogenerated. Chloroformate esters are intermediates in this process. Rather than reacting with additional alcohol, they may disproportionate to give the desired carbonate diesters and one equivalent of phosgene:
: PhOH + COCl → PhOC(O)Cl + HCl
: 2 PhOC(O)Cl → PhOC(O)OPh + COCl
Overall reaction is:
: 2 PhOH + COCl → PhOC(O)OPh + 2 HCl