Toluene: acylation aroylation

Table 3.38 Acylation of toluene with aroyl chlorides to methylbenzophenones...

A series of 3-acyl and 3-aroyl-4-substituted 1,2,5-thiadiazoles 82 have been synthesised by reaction of 3,S-disubstituted isoxazoles 81 with tetrasulfur tetranitride antimony pentachloride (S4N4.SbCl5) in toluene at 90 C to reflux temperature. Compounds 82 are produced regioselectively and a plausible mechanism for their formation discussed. Under the same conditions, 3,4-dialkyl and 5-alkyl(aryl)-isoxazoles furnished chloroketones of type 83 <98JCS(P1)2175>. 

In a kinetic study of the acylation of toluene, with p-xylene and the corresponding perdeutero compounds with aroyl triflates, correlation was found between the primary kinetic isotope effect and the ortho para ratio.35 Different conformations of the bent cr complexes36 for the two isomers resulted in a much higher rate of deprotonation and rearomatization for the para isomer. By appropriately selecting reaction conditions and thereby affecting the ratio of the two conformations, unusually high amounts of ortho products may be obtained.37,38... 

Solid Catalysts. Nafion-H is an active catalyst for acylation with aroyl halides and anhydrides.60,61 The reaction is carried out at the boiling point of the aromatic hydrocarbons. Yields with benzoyl chloride using 10-30% Nafion-H for benzene, toluene, and p-xylene are 14%, 85% and 82%, respectively. Attempted acylation with acetyl chloride, however, led to HC1 evolution and ketene formation. Nation resin-silica nanocomposite materials containing a dispersed form of the resin within silica exhibits significantly enhanced activity in Friedel-Crafts acylations.62,63... 

The reaction occurs at room temperature or in refluxing benzene or toluene and yields are generally in the range 65-90%. The reagent also decarbonylates aroyl chlorides to aryl chlorides (ArCOCl — ArCI) at relatively low temperatures. Acyl halides of type (1) are converted into olefins 13... 

Coordination of palladium with the adjacent pyridine ring is likely to facilitate the acylation of 2-arylpyridines with ct-diketones. In the presence of t-butyl hydroperoxide (TBHP), cleavage of the diketones yields radicals that may allow the formation of intermediates such as (115), which yield the acylated products after reductive elimination. Interestingly the ortfto-aroylation of 2-aryl pyridines may also be achieved using the palladium-catalysed reaction with toluene in the presence of TBHP. Here the mechanism is likely to involve initial benzylation followed by oxidation at the benzylic position to give the acylated product. Acetanilides may also be acylated at the ort/jo-position using toluene and TBHP to yield products such as (116). Here a possible mechanism involves initial formation of a cyclopalladated intermediate followed by reaction with an acyl radical formed by oxidation of the toluene. ... 

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