Amides Beckmann rearrangement, microwave

Activated Fly ash , an industrial waste pollutant, is found to be a good catalyst in Beckmann rearrangement promoted by microwaves under solvent-free conditions. The amides are obtained from the corresponding ketoximes in high yields (75-94%). 

Keywords oximes, zinc chloride, microwave irradiation, Beckmann rearrangement, amide, nitrile... 

Prolonged heating of Bi(OAc)3 wifh amines, N-substituted formamides, and alcohols affords moderate yields of amides, N-acetylformamides, and esters [203]. BiCU mediates the Beckmann rearrangement of ketoximes under microwave irradiation [204[, and Bi(NOj)3- il I,/) mediates fhe guanidylation of N-benzoylfhiour-eas (Scheme 14.100) [205]. 

The one pot synthesis of amide 18 was accomplished within 2 min. by P205/Si02 catalyzed Beckmann rearrangement of the ketone 17 under microwave irradiation." Other ketones such as cyclohexanone, benzophenone, acetophenone and benzil furnished the rearranged products in excellent yields. 

Moghaddam et reported that the Beckmann rearrangement of oximes 2 (R = alkyl or aryl and = aryl) in the presence of AlCls-ZnCb mixture supported on silica gel under microwave irradiation in solvent-free conditions furnished the corresponding amides 3 in excellent yields. 

A silica sulphate (Si02-OSOjH)-supported Beckmann rearrangement of oximes 2 (R = R = H, alkyl, aryl and heterocyclyl) under microwave irradiation in acetone was reported by Li et This recyclable catalyst upon simple workup procedure furnished amides 3 rapidly with high selectivity. 

Alternatively, the Beckmann rearrangement of aldoximes affords amides (see Beckmann reaction, under Section 9.3.2.2). Recent developments along these hnes have been focused on utihzing Si02 at high temperature under microwave irradiation [230]. Furthermore, a one-pot amide synthesis using hydroxylamine in the presence of AI2O3 and sulfonic add has been introduced [231]. 

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%). 

A new and efficient microwave induced bismuth trichloride catalyzed Beckmann rearrangement of oximes in the solid state has been achieved by Thakur et al. (2007). Beckmann rearrangement of aryl ketoximes catalyzed by In(OTf)3 gave amides in ionic liquid under microwave irradiation. These aryl ketoximes were converted to corresponding amides in good yields within very short times (10-270 sec). The catalyst and the ionic liquid were easily recovered and reused (Sugamoto et al, 2011). 

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. 

Eshghi, H., Gordi, Z. An Easy Method for the Generation of Amides from Ketones by a Beckmann Type Rearrangement Mediated by Microwave. Synth. Commun. 2003, 33, 2971-2978. 

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