The Ritter Reaction under Truly Catalytic Brønsted Acid Conditions

Abstract

Simple organic acids like 2,4‐dinitrobenzenesulfonic acid (DNBSA) catalyze the Ritter reaction of secondary benzylic alcohols giving rise to the corresponding N‐benzylacetamides in usually high yields. Reactions can be conducted without exclusion of oxygen and without the need of dry solvents. With tertiary α,α‐dimethylbenzylic alcohols a different pathway involving a formal dimerization reaction takes place under the acid‐catalytic conditions used. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Ritter Reaction: Recent Catalytic Developments

“…In 2007, Sanz et al reported a general method for Brønsted-acid-catalyzed Ritter reactions between secondary benzylic alcohols and acetonitrile. [4] After screening of various acids (10 mol-%), PPTS, 2,4-dinitrobenzenesulfonic acid (DNBSA), triflic acid (TfOH), and H 2 SO 4 were shown to catalyze the Ritter reaction between 1-phenylethanol and acetonitrile efficiently, with 82 % to 85 % yields of 2a being obtained after 12 h to 48 h (Table 1). When the catalytic loading of DNBSA was decreased to 5 mol-%, the reaction time was increased (24 h instead of 12 h) and the yield decreased to 75 %.…”

“…[3] tert-Butyl acetate was shown to be one of the best sources of tert-butyl carbocation when treated with concentrated sulfuric acid. However, 0.94 equivalents of H 2 SO 4 were still required to achieve fast conversion of the nitriles. Only p-methoxybenzonitrile, an electron-rich nitrile, allows the use of lower amounts of H 2 SO 4 (0.47 equiv.).…”

6.07 Ritter-Type Reactions

“…This suggestion is in accord with further observations where the smaller NO 2 group resulted in the predominantly anti-product. 171 As seen earlier, 170 Reaction of the phenyl alcohol was performed at 60°C using TfOH over the range of 1.2-0.12 equivalents. The maximum yield of 76% was obtained for 0.7 equivalent of acid.…”

“…47 Sanz et al demonstrated that 1-arylethanol 121 and benzhydrol 122 derivatives (equations 86 and 87) react efficiently with catalytic amounts (10 mol%) of 2,4-dinitrobenzenesulfonic (DNBSA), p-toluenesulfonic, sulfuric, or triflic acids in refluxing acetonitrile. 170 Interestingly, the former group of substrates were initially converted into their bis(1-arylethyl) ether before formation of the ultimate amide product. DNBSA was a particularly efficacious catalyst, giving both high yields and being easy to handle.…”

Catalysis of Zeolite in the Amidation of Alcohols with Nitriles for the Synthesis of N-Alkylacrylamides

“…The potential of environmental benign catalysts for the replacement of corrosive H 2 SO 4 catalysts in the Ritter reaction were explored. Other reported homogeneous systems such as metal (Cr, Sb) complexes, trifluoromethanesulfonic anhydride, boron trifluoride etherate, H 3 PW 12 O 40 , and 2,4-dinitrobenzenesulfonic acid [5][6][7][8][9] were all liquid acids. Solid catalysts are particularly of interests, for example, use of P 2 O 5 /SiO 2 for the Ritter reaction of tertiary alcohols [10]; Fe 3?…”