Isobutylbenzene acetylation

Isobutylbenzene is first acetylated to give isobutylacetophenone. 4-i-butylacetophenone (40 g), sulfur (11 g) and morpholine (30 ml) were refluxed for 16 hours, cooled, acetic acid (170 ml) and concentrated hydrochloric acid (280 ml) were added and the mixture was refluxed for a further 7 hours. The mixture was concentrated in vacuo to remove acetic acid and the concentrate was diluted with water. 

A very popular alternative to aspirin and acetaminophen is ibuprofen, which has tradenames such as Motrin and Advil . It can be synthesized from isobutylbenzene by a Friedel-Crafts acylation with acetyl chloride, followed by formation of a cyanohydrin. Treatment with H2/Pd reduces the benzylic hydroxyl to a hydrogen and hydrolysis of the nitrile gives the carboxylic acid. There are at least six published syntheses of ibuprofen. This illustrates the difficulty of knowing which technology a particular company is using. At the other extreme is the proprietary nature of some syntheses, where they have not yet been published. 

Ibuprofen can be synthesized from isobutylbenzene by a Friedel-Crafts acylation with acetyl chloride, followed by formation of a cyanohydrin. Treatment with hydrogen iodide and phosphorus reduces the benzylic hydroxyl to a hydrogen and hydrolyzes the nitrile to a carboxylic acid. 

These ketones are important intermediates in the synthesis of fragrances of the musk type, of UV absorbents and of pharmaceuticals such as paracetamol, ibuprofen, S-naproxen. Thus, in the processes of ibuprofen synthesis (9), the first classical step is the acetylation of isobutylbenzene with acetic anhydride in presence of HF (Hoechst process) or of A1C13 (Boots process) ... 

Acylation of isobutylbenzene with acetic anhydride leads with high yield and selectivity to para-acetylisobutylbenzene (Eq. 9) which is an intermediate in the synthesis of ibuprofen, an important antiinflammatory drug [18]. With H/1 zeolite at 140 °C after 1 h the yield is 80 % with 96 % para selectivity. Acylation of tetra-lin with acid chlorides and different zeolites has also been studied [19], For this reaction again acetyl chloride is much less reactive than higher acid chlorides such as butanoyl or octanoyl chloride. The selectivity is in favor of the 2-substituted isomer (85-90%) and limited quantities of the 1 isomer (10-15%) are formed (Eq. 10). 

The acetylation of isobutylbenzene with AAN catalyzed by boron trifluoride can be performed in anhydrous sulfur dioxide at -40°C and heating the autoclave container to 22°C for about 2 h2 The process can be applied to different aromatic compounds, including alkylarenes, naphthalenes, diphenyl ethers, and thioethers. 

The />-isobutyl acetophenone obtained by the acetylation of isobutylbenzene is subjected to Wilgerodt oxidation to yield ibufenac. 

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