Department of Chemistry, Indian Institute of Technology, Kanpur, India PLEASE SCROLL DOWN FOR ARTICLE

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1 This article was downloaded by: On: 17 January 2011 Access details: Access Details: Free Access Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK Synthetic Communications Publication details, including instructions for authors and subscription information: Facile Oxidation of Aldehydes to Carboxylic Acids with Chromium(V) Reagents T. K. Chakraborty a ; S. Chandrasekaran a a Department of Chemistry, Indian Institute of Technology, Kanpur, India To cite this Article Chakraborty, T. K. and Chandrasekaran, S.(1980) 'Facile Oxidation of Aldehydes to Carboxylic Acids with Chromium(V) Reagents', Synthetic Communications, 10: 12, To link to this Article: DOI: / URL: PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

2 SYNTHETIC COMMUNICATIONS, 10(12), (1980) FACILE OXIDATION OF ALDE3iYDES TO CARBOXYLIC ACIDS WITH CHROMIUM(V) REAGENTS T.K. Chakraborty and S. Chandrasekaran* Department of Chemistryr Indiar? Institute of Technology, Kanpur , India Recently we reported a convenient method of oxidation of alcohols to carbonyl compounds uring chromium(v) reagents. Although a variety of reagents are availa- ble for effecting this transformation, there are only a few reagents which have been successfully used for the oxidation of aldehydes to carboxylic s. Chromic, silver oxide and potassium permanganate are CORIRI.- only employed for this purpose and reactions are performed in protic media under conditions which are not that mild. The *non-aqueousn chroinlum(v1) reagent pytidinium dichromate, recently reported by Cony3 oxldises alcohols and aldehydes to carboxylic 8 in DMF at room temperature. Although Cr(V) species is postulated as an intermediate in all oxidations with Cr(VX), no systematic oxidation studies have been, reported with *To whom correspondence should be addressed. 951 Copyright by Marcel Dekker, Inc.

3 952 CHAKRABORTY AND CHANDRASEKARAN these reagents. This note reports the results of some fruitful investigations on aldehyde j carboxylic conversion involving some non-aqueous chromium (V) complexes A, 2, 2 and 5 under anhydrous conditions. As reported previously, oxidation of primary alco- hols with two equivalents of either 3 or 2 gave the aldehydes in good yield, with very little overoxida- tion, if any.l On the other hand when excess reagent was used and reaction mixture stirred for longerperiod, partial oxidation to carboxylic s took place. his prompted us to study the oxidation of aldehydes with these reagents. Although direct oxidation of primary alcohols to carboxylic s with excess CrW reagent 2 was not very clean, it has now been found that a variety of aldehydes can be oxidised conveniently to carboxylic s in very good yields with our non-aqueous* chrdum(v) complexes & and 2. Herein, we also report the bethavi- our of yet another set of closely related chromiun(v1 reagents 2 and $ which are similar in their reactivity to complexes 1. and 2 respectively, but are more economl- cal for large scale reactions. Complex 2. is prepared essentially in the same manner a8 reported for complex I. Dehydrochlorination of 2 around 80 under a current 4 of dry N2 yields complex f.

4 ALDEHYDES TO CAR63XYLIC ACIDS 953 (Phen)H2CrOC15-1 (Phen)CroC13 (phen = 1.10-phenonthrolin) - 2 The oxidation of aldehydes with any of these Cr(V) complexes takes place very reatilly at room temperature in CH2C12 under anhydrous conditions. Oxidation of ali- phatic aldehydes i n general are more facile than aroma- tic aldehydes. Aromatlc aldehyde like p-nitrobenxaldehyde containing electron withdrawing group reacts with ease to give p-nitrobenzoic in 96% yield. In a typical small scale experiment complex 1 or 3 (2 mmol) was rapidly added to a solution of the aldehyde (1 mmol) in 2-3 ml of CHZC12 with stirring at roam temperature under inert atmosphere. The reaction followed by thin layer chromatography was generally complete in 0.5 hr. The reaction mixture was then diluted with CH2Cl2 or CHC13 (10 ml) and filtered through a small pad of celite and silica gel and washed two or three times with 10 ml portions of CHC13. The canbined organic layer was then evaporated to isolate the product. The results of these oxidations are nurnmarized in the TABLE.

5 954 CHAKRABORTY AND CHANDRASEKARAN TABLE a I. Oxidations with the complex (bipy)h2croc15, 2 n-butyraldehyde 1:2 0.5 n-butytic 92 n-hept aldehyde l a n-heptanoic 85 Croton aldehyde l a Crotonic 90 2-Fur aldehyde 1s Furoic 85 p-tolualdehyde lr p-toluic d An thraldehyde la Anthracene-9- carboxy lic 95 p-ni trobenzalde- 1 a p-nitrobenzoic 96 hyde 11. Oxidations with the complex (phen)h2croc15, 1 n-butyraldehyde l r n-butyric 90 2-fur aldehyde 1s Furoic 85 p-tolualdehyde 1,2 3.0 p-toluic d Oxidation w ith the complex (bipy)croc15. 4 p-ni trobenzal- 1s p-ni trobenzoic 96 dehyde a. Oxidations were carried out at room tenperature 28-30' in CH2C12. b. Products were characterized by comparison wi'th authentic samples (spectra, TLC and m.p.). c. All yields refer to isolated products. d. Trace amount of starting material remains unreacted even after 4-5 hr.

6 ALDEHYDES TO CARBOXYLIC ACIDS 955 From the data presented in the table, it is evident that the chromium(v) complexes we have reported are important additions to the present methodology of aldehyde 3 carboxylic transformation under mild and anhydrous condl tlons. Preparation of complex (bipy)hzcroclg824 A SOh~On Of oc,o('-bipyridyl ( mol) In conc. HCl (25 m l) kept at 0' was added to a solution of CrOj (3.0 g, 30 mmol) in conc. HC1 (25 ml) and the mix- ture was stirred or 15 mln. at O*. The resulting brmn precipitate was filtered through a sintered glass funn- el 8nd washed twice with 10 rnl portions of cold (0') conc. HC1 and dried under vacuum. The dark brown free flowing powder (11.0 g, 92%) can be stored under vacuum for a few days. OxIdation of p-nitrobenzaldehvde to o-nitrobenzoic with COmD lex 5 In a 25 ml round bottomed flask was taken p-nitro- benzaldehyde (0.151 g, 1 mol) in CHZCIZ (5 ml) and to the magnetically stfrred solutlon at room temperature (28%) under N2 atmowhere was added to the canplex 2 (0.803 g0 2 mmol). After stirring for 0.5 hrr chloro- form (15 ml) was added to the reaction mixture and pas.- ed through a 8hort pad of cclite and silica gel and wa8hed 2-3 times with 10 ml portions of chloroform. Combfnad organic filtrate wa8 evaporated to got p-nitro-

7 956 CHAKRABORTY AND CHANDRASEKABAN benzofc add as a crystalline solid (0.160 g, 96%), mop. 240'. Acknowleduementg W e are thankful to Prof. M.V. George. Department of Chemistry, I.I.T., Kanpur for encouragement and Dr. S. Sarkar for useful discusl)ions. We also thank the Science and Engineerfng Research Council of the Department of Science and Technology, New Dalhl for financial assistance. References 1. T.K. Chakraborty and S. Chandrasekaran. Tetrahedron - Lett (1980). 2. H.O. HOU~~. "Modern synthetic Reaction." (second Ed.), p , W.A. Benjamin, Inc.. New York, E.J. Coray and 0, Schmidt, Tetrahedron Lett., 4499 (1979). 4. S. Sukat ivrd J.P. Sfngh. J. Sw.8 them. COllWll., 509 (1974).