Beckmann rearrangement solvent-free reaction

Chandrasekhar, S., Gopaiaiah, K. Ketones to amides via a formal Beckmann rearrangement in one pot a solvent-free reaction promoted by anhydrous oxalic acid. Possible analogy with the Schmidt reaction. Tetrahedron Lett. 2003,44, 7437-7439. 

The solvent-free one step Beckmann rearrangement of ketones 1 and aldehydes in the presence of zinc oxide afforded the corresponding amides 3 (R = alkyl, aryl, cycloalkyl = H, cycloalky 1). Symmetrical ketones furnished the amides in good to excellent yields. In the case of unsymmetrical ketones the reaction was selective and one of the two possible amides was formed. Aromatic and aliphatic aldehydes were converted to the corresponding primary amides. 

Alumina sulfuric acid (ASA) was found to be an effective catalyst for the solvent-free one pot Beckmann rearrangement of several alkyl and aryl aldehydes and ketones 1. It has been reported that the electron rich aldehydes and ketones require shorter reaction times than the electron poor aldehydes. Cyclic ketones require longer reaction time than the aryl ketones ascribable to the steric factors. ... 

Phosphoric acid is an efficient and mild reagent for conversion of ketoximes to amide or lactam by Beckmann rearrangement (Baneijee and Mitra, 2005). The reactions are carried out in solvent-free condition under microwave irradiation. It gives good to excellent yields (73-82%). 

Bagheri and Karimkoshteh (2013) used nano silica-H SO as an efficient and mild catalyst for the Beckmann rearrangement of ketoximes to amides. The reactions were carried out in solvent-free conditions under microwave irradiation (600 W) within 50-120 sec in good yields. 

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