Aryl acyl chlorides, hydrolysis

The hydrolysis of acyl chlorides to a carboxylic acid and hydrogen chloride is rapid and violent in the lower aliphatic acyl chlorides. With increase in the complexity of the radical there is a corresponding increase in stability. Aryl acyl chlorides are only slowly hydrolyzed at low temperatures. In general, however, the halogen attached to the acyl group is very much more reactive than a halogen attached to other organic radicals. 

The nomenclature of this class of compounds is not at all clear. For example, the following names can be found in the literature hydroxamic acid chlorides, hydroxamic chlorides, hydroximic chlorides (Beilstein lists them as Hydroximsaure chloride ), and acyl and aroylchloride oximes. The latter names are used by Chemical Abstracts, Although the name benzoyl chloride oxime for benzhydroxamoyl chloride is formally correct, it does not reflect the close relationship between hydroxamoyl chlorides and hydroxamic acids, their hydrolysis products. In order to be consistent with the nomenclature used in the earlier chapters, I prefer the term hydroxamoyl to hydroxamic chloride. The interrelationship of the halides with the corresponding acids is shown below, and R is representative of the alkyl, aryl, acyl, aroyl, and carbalkoxy group. 

Some aryl- and aroyl-aminofuroxans and bis(dialkylamino)furoxans have been reported. 4-Amino-3-methylfuroxan has been prepared by hydrolysis of its O-benzylurethane. The 4-amino-3-aryl compounds can be acylated but the 3-amino-4-aryl isomers appear to be less reactive. On oxidation with hydrogen peroxide 3-aryl-4-nitrofuroxans are formed. The nitro group can be displaced by nucleophiles (see Section 4.22.3.2.4) or reduced back to the amino group using tin(II) chloride. 

Reactions of Pyrroles. 1,3-Di-t-butylpyrrole forms the first stable protonated pyrrole, the salt (104). Electrophilic substitution of pyrrole with MeaC or Me FC in the gas phase occurs mainly at the j3-position, as does nitration and Friedel-Crafts acylation of l-phenylsulphonylpyrrole2 Pyrrole-2,5-dialdehyde has been prepared by Vilsmeier-Haack formylation of the ester (105), followed by hydrolysis. A similar method has been used to convert the di-acetal (106) into pyrrole-2,3,5-tricarbaldehyde. AT-Benzoyl-pyrrole reacts with benzene in the presence of palladium(II) acetate to yield a mixture of l-benzoyl-2,5-diphenylpyrrole, the bipyrrolyl (107), and compound (108). Treating lithiated A-methylpyrrole with nickel(II) chloride results in the polypyrrolyls (109 = 0-4). 2-Aryl-1-methylpyrroles are obtained by cross-coupling of l-methylpyrrol-2-ylmagnesium bromide with aryl halides in the presence of palladium(0)-phosphine complexes. ... 

The industrial synthesis of ibuprofen is a well-known case study for green chemistry . [190] The original Boots route, starting from benzene, comprised seven steps, p-lsobutylacetophenone is accessible by alkylation of benzene with isobutene, followed by a Friedel-Crafts acylation with acetic chloride. Homologation to the corresponding aryl-propionaldehyde is achieved by a Darzens reaction. Transformations via the oxime and nitrile, and hydrolysis of the latter, finally give ibuprofen. 

Synthetic routes to acyl(methyldiphenyl)silanes have mainly been based on methodology developed by Brook and Corey. According to Brook s synthesis of aryl silyl ketones, benzyl-magnesium chloride or bromide, for example, were silylated with methyldiphenylchlorosilane to afford benzylmethyldiphenylsi-lane (28) that, on dibromination of the benzyl methylene group and subsequent hydrolysis, gave the benzoylsilane (29) (eq 17). ... 

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