Direct Diphenyl Carbonate Process at GE

The history of direct DPC process development at GE can be considered as a case study. In the mid-1970s. Chalk discovered that /rara-substituted phenols can be oxidatively carbonylated using stoichiometric amounts of a Ru, Rh, Os, Ir, or Pd salt, from which the palladium salts were the most active (Eq. (12.3)) [5]. Yields of carbonylation products were high, but the reaction yielded 1 mol of Pd° for every mole of product, so it was stoichiometric [6]. In the late 1970s, Hallgren and Matthews assumed that DPC was formed by reductive elimination from the acyl Pd(ll) carbonyl complex [7]. 

However, DPC yield and Pd turnover number (Pd TON defined as mol DPC/mol Pd charged) obtained in early works remained low. Unlike aliphatic alcohols, the oxidative carbonylation of aromatic alcohols is difficult due to their increased acidity and oxidative instability. They, therefore, require expensive catalysts [7]. It was the high cost of the optimal Pd-based catalysts, which were superior compared with all others, and low reaction rates that prevented the direct DPC process from being commercially viable. 

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