A mild and efficient way to prepare ε-caprolactam by using a novel salt related with ionic liquids

The Beckmann rearrangement of several ketoximes has been performed by treatment with tosyl chloride, using ionic liquids as both solvent and catalyst, without the need of any other promoter. High levels of conversion and selectivity were observed in the majority of experiments. Work-up is very simple and the product can be isolated in high yields. When the method was applied to cyclohexanone oxime, the novel salt [TMG][TsO] instead of the ionic liquid was used. This procedure afforded a conversion of 100% to obtain pure ε-caprolactam in a 98% yield. [TMG][TsO] is easy to prepare, cheap, and not corrosive. It can be recovered and reused.

The Beckmann rearrangement of cyclohexanone oxime is carried out by treatment with TsCl using a new salt, [TMG][TsO], as the promoter. This procedure requires mild reaction conditions and affords excellent levels of conversion and selectivity to obtain pure ε-caprolactam in a high yield. The new salt is cheap, easy to prepare, not corrosive, and can be recovered and reused.