Under solvent free conditions, several aldehydes and ketones were efficiently and rapidly converted into the corresponding nitriles and amides respectively by treatment with hydroxylamine hydrochloride under microwave irradiation using silica chloride as catalyst. The yields of the products were very high and the time required for their preparation was very short compared to conventional heating experiments.
Silica chloride has been found to be an efficient catalyst for esterification of carboxylic acids (aliphatic, aromatic and conjugated) with alcohols (primary, secondary and tertiary) as well as for transesterification of esters (by both alcoholysis and acidolysis).Esterification of carboxylic acids with various alcohols is one of the most important and widely applicable transformations in organic synthesis. 2 A large number of methods for esterification catalyzed by various protic and Lewis acids including solid acids, ion exchange resins, zeolite and clay are now well-known. 2,3 However, some of the reported methods are associated with certain drawbacks such as harsh reaction conditions, tedious experimental procedures, long reaction times, poor yields, complex side reactions and narrow range of applicability. Moreover, the number of suitable methods for one-step esterification of carboxylic acids with tertiary alcohols are also limited. 3c The reagents (such as phosgene, isobutene etc.) which are generally utilized for this purpose are incompatable with harsh reaction conditions and tedious experimental procedures.Transesterification of an ester with an alcohol (alcoholysis) or with an acid (acidolysis) can also be applied for the preparation of another ester. 4a A variety of protic and Lewis acids, organic and inorganic bases, enzymes, and antibodies are known 3f,4 to catalyze this reaction. Recently some of the catalysts, like diphenylammonium triflate, iodine etc., have been employed for both esterification and transesterification. 5 However, the number of such catalysts are limited. Additionally, the transesterification of an ester applying both alcoholysis and acidolysis by utilizing the same catalyst is also not frequently observed. Here we report a simple and general method for esterification and transesterification using silica chloride as a heterogeneous catalyst.During our recent work on the development of novel synthetic methodologies we have observed that silica chloride is an efficient catalyst for esterification of carboxylic acids and transesterification of esters (Schemes 1 and 2) Scheme 1 Scheme 2
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