The Ritter reaction is a chemical reaction that transforms a nitrile into an N-alkyl amide using various electrophilic alkylating reagents. The original reaction formed the alkylating agent using an alkene in the presence of a strong acid:
Primary, secondary, tertiary, and benzylic alcohols, as well as tert-butyl acetate, also successfully react with nitriles in the presence of strong acids to form amides via the Ritter reaction.
The Ritter reaction is named after John J. Ritter, an American chemist who received his Ph.D. from Columbia University. In 1948, P. Paul Minieri, Ritter's student, submitted work on the reaction as his Ph.D. thesis. The reaction still has significance today due to its applicability and reproducibility of amides via stabilized carbocations.
The Ritter reaction proceeds by the electrophilic addition of either the carbenium ion 2 or covalent species to the nitrile. The resulting nitrilium ion 3 is hydrolyzed by water to the desired amide 5.
The Ritter reaction is most useful in the formation of amides in which the nitrogen has a tertiary alkyl group. It is also used in industrial processes as it can be effectively scaled up from laboratory experiments to large-scale applications while maintaining high yield. Real world applications include Merck’s industrial-scale synthesis of anti-HIV drug Crixivan (indinavir); the production of the falcipain-2 inhibitor PK 11195; the synthesis of the alkaloid aristotelone; and synthesis of Amantadine, an antiviral and antiparkinsonian drug. Other applications of the Ritter reaction include synthesis of dopamine receptor ligands and production of amphetamine from allylbenzene.[verification needed]
A problem with the Ritter reaction is the necessity of an extremely strong acid catalyst in order to produce the carbocation. This corrosive type of chemical poses an environmental hazard for chemical waste and safety risk for running the reaction itself. However, other methods have been proposed in order promote carbocation formation, including photosensitized electron transfer or direct photolysis.
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