Willgerodt reaction thioamide synthesis

DMF is recommended as diluent in the Ullmann synthesis of diaryls from aryl halides and as solvent for the Beckmann rearrangement of steroidal enone oximes. The Willgerodt-Kindler reaction (a carbonyl compound with a secondary amine and sulfur to give a thioamide) can be carried out in good yield at 50-60 if DMF is... 

Reichardt (2003, p. 504) presents a table of solvents recommended as replacements for more hazardous ones. Total avoidance of solvent is sometimes a possibility. An example was mentioned in Chapter 1. Scott (2003) discusses the scope of solvent-free methods and considerations of mutual solubility of reactants and of control, including exothermic reactions. A recent application is the solvent-free synthesis by Valdez-Rojas et al. (2012) of thioamides and alpha-ketothioamides through the Willgerodt-Kindler reaction. Scheme B. 

The Kindler variation, - which promises to be more useful than the original Willgerodt procedure, consists in heating the ketone with approximately equimolecular amounts of sulfur and a dry amine instead of aqueous ammonium polysulfide. A thioamide is formed as the principal product and on hydrolysis with acid or alkali affords the carboxylic acid, usually in good yield. Generally a secondary aliphatic amine but sometimes a primary amine or even anhydrous ammonia is used the development of a method for the electrolytic reduction of the thioamides to amines extended the usefulness of the reaction as a new route to the synthesis of many important nitrogen bases. Early descriptions of this... 

Several papers have reported on the application of the Willgerodt-Kindler reaction in the synthesis of thioamides. In an investigation of a modified form of this reaction, Ried and his co-workers treated some 2,4,6-trimethylphenyl alkyl ketones with dimorpholinodisul-phide (215). Only the methyl ketone afforded a normal Willgerodt-Kindler product (216), but otherwise a clear relationship between the nature of the product and the nature of the ketone alkyl group, Le. the number of... 

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