Phosgene as a reagent in organic syntheses

It is not the intention here to review the organic chemistry of phosgene (that is exhaustively covered in Chapter 10), but the scope for its use as an industrial synthetic reagent is apparent. 

Phosgene has many uses and potential uses as a synthetic intermediate. It reacts with aromatic compounds in the presence of aluminium(III) chloride to give mostly acid chlorides, although the passage of phosgene into benzene at 50 C, in the presence of aluminium(III) chloride, produces benzophenone as the final product [1415a]. 4,4 -Diphenoxybenzophenone, (4.20), is prepared from diphenyl ether and phosgene under similar conditions it is used 

4 -difluorobenzophenone (BDF see Section 10.1.5), a precursor for the high-performance thermoplastic, Victrex PEEK [509a]. 

Phosgene can also be used to convert acetic acid to its anhydride [92], and the addition of phosgene to propene, followed by treatment with methanol and dehydrochlorination of the ester (see Section 10.1.2) results in the production of methyl methacrylate [1699]. 

Despite their simplicity, neither of these routes have been developed commercially. However, the use of phosgene with carboxylic acids to form acid chlorides has many advantages over the use of PCI 5 or SOClj, in that the by-products (COj and HCI) are readily removed, leaving a high purity product this is especially important in the synthesis of acid chlorides of fatty acids, which resist distiliation [1841a]. Isophthaloyl dichloride and terephthaloyl dichloride are both produced commercially by the action of phosgene on their respective acids [1804a]. 

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