Acylation catalyst

Friedel-Crafts acylation of aromatics is of considerable practical value owing to the importance of aryl ketones and aldehydes as chemical intermediates.346 Whereas alkylation of aromatics with alkyl halides requires only catalytic amounts of catalysts, acylation to ketones generally necessitates equimolar or even some excess of the Friedel-Crafts catalysts. Usually one molar equivalent of catalyst combines with an acyl halide, giving a 1 1 addition compound, which then acts as the active acylating agent [Eq. (5.137)]. 

Lewis acids used for acylation of allylsilanes with acid chlorides include titanium and tin tetrachlorides, aluminum, gallium and indium trichlorides and zinc dichloride, and boron trifluoride for reactions with acid anhydrides. Although gallium and indium chlorides have been used successfully in catalytic (ca. 2 mol %) amounts, most frequently aluminum chloride has been used as catalyst, with titanium tetrachloride also commonly employed, both in molar quantities. With these catalysts, acylations can often be carried out at low temperatures, and with short reaction times. 

Substrate Catalyst Acylating agent Conversion (%) Product/selectivity... 

Yadav, G. D. and Pujari, A. A. 1999. Friedel-Crafts acylation using sulfated zirconia as a catalyst. Acylation of benzene with 4-chlorobenzoyl chloride over sulfated zirconia as catalyst. Green Chem. 1 69-74. 

Friedel-Crafts acylation. With this catalyst acylation in fluorous biphasic system is achieved. Note that the triflamide Yb(NTf2)3 is also useful for the same purpose (not specified in fluorous solvent). ... 

For acylation and silylation reactions, the steric effect significantly influenced product yield in the DMAP-MSN system. To further investigate the recyclability and stability of DMAP-MSN catalysts, acylation of alcohols was chosen as the model reaction.2 Our results showed that the DMAP-MSN catalysts could be recycled for at least 10 times without losing any catalytic reactivity. The turnover number (TON) of DMAP-MSN catalysts was as high as 3340 for 24 days. 

This set of reactions is catalysed either by enzymes or acidobasic catalysts and is characterised by migration of acyls between the molecules of alcohols or in the glycerol molecule. When using acid-base catalysts, acyl migration is statistically random. There is a growing interest in using enzymes (lipases or phospholipases) in technological applications, where it is possible to perform selective interesterification reactions catalysed by specific enzymes. 

Bharathiraja, B., Chakravarthy, M., Rar TthKumar, R., Yuvaraj, D., Jayamuthunagai, J., PraveenKumar, R., Palani, S., 2014. Biodiesel production using chemical and biological methods - a review of process, catalyst, acyl acceptor, source and process variables. Renewable and Sustainable Energy Reviews 38,368-382. 

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