Oxidative Carbonylation of Phenol

For the catalyst development, it is very important to elucidate the mechanism of Pd(0) reoxidation. Unfortunately, there is no literature data on redox potentials of potential cocatalysts in PhOH solution. Assuming that the difference in potentials in aqueous and phenolic solutions is similar, all metals used as cocatalyst can be divided into three groups (i) those with potentials less than the potential of Pd /Pd couple (+0.60 V vs. SHE in the presence of bromide anions), for example, Yb, Zn, and Pb (ii) those with potentials between the potentials of Pd /Pd and (Oj + H+l/HjO couples, for example, Fe andMn and (iii) those with potentials higher than that for the (O2 + H )/H20 couple, for example, Pb,  

and Co. In other words, only group 2 metals can oxidize Pd(0) and be reoxidized by oxygen, while metals from group 3 can oxidize Pd(0) but caimot be reoxidized by oxygen, and group 1 metals can be reoxidized by O2 but caimot oxidize Pd(0). 

In addition, bromide can serve as a redox mediator. The potential of Brj/Br couple allows the oxidation of Br by oxygen and oxidation of Pd(0) by generated bromine. This may explain the absolutely crucial role of a bromide salt, which is superior to other halides, in DPC synthesis. Nonadditive effect (positive or negative) of two or more cocatalysts confirms the hypothesis of formation of mixed-metal complexes in DPC catalytic system. 

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M-NHC catalysts in this area. Metal catalysed carbonylation also provides an alternative synthetic ronte to the prodnction of materials that traditionally reqnire highly toxic precnrsors, like phosgene. This section discnsses carbonylation of aryl hahdes, oxidative carbonylation of phenolic and amino componnds, carbonylation of aryl diazoninm ions, alcohol carbonylation, carbonylative amidation, and copolymerisation of ethylene and CO. 

Scheme 9.9 Oxidative carbonylation of phenol with CO/O with catalyst 39...

Solutions of Moiseev s giant Pd colloids [49,161-166] were shown to catalyze a number of reactions in the quasi homogeneous phase, namely oxidative ace-toxylation reactions [162], the oxidative carbonylation of phenol to diphenyl carbonate [166], the hydrogen-transfer reduction of multiple bonds by formic acid [387], the... 

In addition to the industrial apphcations, in Scheme 8.1, other reactions have been the focus of extensive research and development. For example. Chapter 12 surveys the research efforts directed toward Pd-catalyzed oxidative carbonylation of phenol affords the important monomer, diphenyl carbonate (Scheme 8.2a). Other reactions of potential industrial significance highlighted in this chapter include the oxidation of alcohols to aldehydes and ketones (Scheme 8.2b), oxidative coupling of arenes and carboxylic acids to afford aryl esters (Scheme 8.2c), benzylic acetoxylation (Scheme 8.2d), and oxidative Heck reactions (Scheme 8.2e). The chapter concludes by highlighting a number of newer research developments, including ligand-modulated catalytic oxidations, Pd/NO cocatalysis, and alkane oxidation. 

Cocatalysts for Oxidative Carbonylation of Phenol 12.2.3.1 Organic Cocatalysts... 

With heterogeneous Pd/C catalyst, CU2O showed superior performance in oxidative carbonylation of phenols [29]. However, copper ICCs promote side reactions such as phenol oxidation by oxygen to form 2,2-biphenol [16] or formation of o-phenylene carbonate [51]. 

A catalyst containing Pd(acac)2 and Bu NI produced 26.7% DPC in 4h under 100 bar with 99.1% selectivity [74]. Pd(acac)2 in combination with Ce(acac)3 or PbO catalyzed oxidative carbonylation of phenol in the presence of sodium iodide with Pd TON above 1000 [75]. In this case, bisphosphine ligands are necessary to maintain high regioselectivity of carbonylation reaction (96% vs. 

As already mentioned, water removal in the oxidative carbonylation of phenols to make diaryl carbonates is a necessary process since it greatly enhances the productivity of the reaction and thus reduces reactor cost per unit mass of product. The use of 3 or 4 A molecular sieves, effectively removing water in laboratory-scale runs [8d], is impractical at an industrial scale. 

Dimethyl carbonate (467) is produced under low pressure CO. Dimethyl carbonate is now produced commercially by Ube industries based on the oxidative carbonylation of MeOH in the gas phase using methyl nitrite (466) as an oxidant as shown below. Another promising reaction is the preparation of commercially important diphenyl carbonate (468) by the oxidative carbonylation of phenol. So far the technology developed in many industrial laboratories is far from commercialization [191]. 

Another route to DPhC, besides transesterification of DMC or EC with phenol as in Section 4.3.3.7, is the oxidative carbonylation of phenol with carbon monoxide (CO) and aerial oxygen, as catalyzed by a Pd dinudear complex and a redox catalyst [702, 703]. 

Oxidative Carbonylation of Alcohols. The oxidative carbonylation of phenol provides diphenyl carbonate in the presence of PdBr2, a cocatalyst ([Mn], [Cu], or [Ce]), and an ammonium salt or amine under a CO-O2 or air atmosphere (eq 5). ... 

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