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Novel synthesis of primary arylamides from aryl methyl ketone oxidations using iodine in aqueous ammonia. Norma A. Paseo Tollocan, Toluca, Mexico. Primary arylamides were obtained when several aryl methyl ketones were treated with iodine in aqueous ammonia at room temperature in goods yields. Keywords: amide, methyl ketone, iodine, ammonia, oxidation. The amide group has a special importance in chemistry and biochemistry, since this functional group is the frame of several biological and pharmaceutical products and it is a point of departure en route to many natural products.
Currently, one employed method to prepare aryl and heteroaryl amides involves the haloform cleavage reaction of trihalo acetyl derivatives. In connection with other synthetic studies, we were attracted by the reports of Fang and Talukdar 11 about the transformation of aldehydes to nitriles and amides, and we decided to apply these reactions in addition with other previous haloform reaction reports to the synthesis of primary amides from methyl ketones.
This report describes our successful endeavors in this area. In a model study, acetophenone was treated with an excess of iodine 3 molar equivalents in aqueous ammonia and THF as cosolvent. After 1 h, iodoform was separated and the product was extracted.
In order to explore the reaction scope, several aryl and heteroaryl methyl ketones were reacted under similar conditions see Table 1 , Scheme 2. In general, the results showed that amides were the preferred products.
It is noteworthy that ammonia concentration plays an important role, because the reaction is carried out only in a concentrated ammonium hydroxide solution, and at lower ammonia concentrations, the yields decreased or the amide is not formed, and only the starting material was isolated Table 2. The mechanism proposed for this reaction involves the triiodo methyl ketone formation, with the subsequent ammonia substitution Scheme 3. Alternatively, enamine formation and subsequent iodination can also explain amide formation.
At the moment, our group is investigating the mechanistic details of this reaction. On the other hand, this process represents a new variant of the Haller-Bauer reaction, which allows the direct conversion of nonenolizable ketones to primary amides, with the advantage that strong bases such as sodium amide are not required. In conclusion, the appropriately constituted methyl ketones are efficiently converted into primary amides through a simple and mild method.
In addition, the procedure is economic and environmentally benign. These elements suggest that this route will enjoy widespread application. The starting materials were purchased from Aldrich Chemical Co. Solvents were distilled before use. Silica plates of 0. Melting points were determined with a Fisher-Johns melting point apparatus and they are uncorrected. The dry powder explodes readily by mechanical shock, heat or irradiation.
Iodine 0. The mixture was stirred for 1 h at room temperature. The organic phase was washed, dried over Na 2 SO 4 , and the solvent was evaporated in vacuo. The final product was purified by crystallization. Reimann, J. E; Byerrum, R. Hassinger, H. Jiang, B. Kaiserman, J. Mamidyala, S. Banwell, M. Bando, T. Shie, J. Talukdar, S. Olivella S. Levin D. Zucco, C. Staunton, J.
V , ; p. Ishihara, K. Paquette, L. Walborsky, H. Roesky, H. McMaster, L. Feiring, A. Hartman, W. II , ; p. Joshi, K. Indian Chem. Prajapati, D. Chattopadhyaya, J. Peng, Y. Sakai, K. All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License. Services on Demand Journal.
Conclusions In conclusion, the appropriately constituted methyl ketones are efficiently converted into primary amides through a simple and mild method. Experimental The starting materials were purchased from Aldrich Chemical Co. References 1. How to cite this article.
The haloform reaction is a chemical reaction where a haloform CHX 3 , where X is a halogen is produced by the exhaustive halogenation of a methyl ketone RCOCH 3 , where R can be either a hydrogen atom, an alkyl or an aryl group , in the presence of a base. In the first step, the halogen disproportionates in the presence of hydroxide to give the halide and hypohalite example with bromine, but reaction is the same in case of chlorine and iodine; one should only substitute Br for Cl or I :. Under basic conditions, the ketone undergoes keto-enol tautomerization. At least in some cases chloral hydrate the reaction may stop and the intermediate product isolated if conditions are acidic and hypohalite is used. Substrates are broadly limited to methyl ketones and secondary alcohols oxidizable to methyl ketones, such as isopropanol. The only primary alcohol and aldehyde to undergo this reaction are ethanol and acetaldehyde , respectively.
Electrolytic preparation of iodoform