A Mild and Efficient Oxidation of Alcohols in Water

Chinese Chemical Letters Vol. 15, No.10, pp 1149-1152, 20041149htp://ww.imm.ac.cnjournalccl.htmlA Mild and Efficient Oxidation of Alcohols in WaterChuan Zhi XU, Lin CHEN, Zhen LI, Wei SUN, Chun Gu XIA*State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of ChemicalPhysics, Chinese Academy of Sciences, Lanzhou 730000Abstract: A mild and efficient oxidation of alcohols to the corresponding carbonyI compoundsusing the PhI(OAc)2 (1.1 eq.) with n-Bu.NBr (8 mol %) in water at room temperature is described.This new procedure is very simple and affords the desired carbonyI compounds in high yields.Keyword: Oxidation , alcohols , n-Bu,NBr , PhI(OAc)2 , water.The oxidation of alcohols to corresponding carbonyl compounds is one of the mostimportant functional group transformations in organic synthesis, which has received muchattention over the years' .Despite the availability of many reagents for thistransformation', there still exists a need for mild and efficient methods. Hypervalentiodine(II) are now extensively used in organic synthesis'. In particular, phenyliodine(II)diacetate and phenyliodine(II) bis(urifluoroacetate) have received a great deal ofattention due to their reactivities similar to that of heavy metal reagents or anodicoxidation, low toxicity, ready availability and easy to handle. The use of water as thereactions habe been developed*. Recently, Kita et al, have briefly communicated theoxidation of alcohols using iodosobenzene (PhI=O) (1.5 eq,) with an inorganic bromidesalt, such as KBr <20~ 100 mol %), in water under neutral conditions'. On the other hand,(diacetoxyiodo) benzene [Ph(OAc)2], the previous substance of iodosobenzene (PhI=O),was found to be an effective oxidant in epoxidation of alkenes'.Herein, we report a mild and eficient oxidation of various alcohols such as benzylicalcohols, primary alcohols and secondary alcohols to carbonyl compounds with PhI(OAc)2catalyzed by bromide salt in water at room temperature (Scheme 1).Scheme 1PhI(OAC)2 (1.1 equiv)QH0中国煤化工RI'R2TYHCNMHGR2* E-mail:cgxia@ns.lzb.ac.cn1150Chuan Zhi XU et al. .Table 1 Oxidation of various alcohols with PhI(OAc)2 in H2O*EntrySubstrateProductTime(h)Yield(%)1c520.62d24.13698.54of2100qHi。R1=Me. Br. CF3R2=Me、C2H5OHoio)HpH1013.1的011moM如O°12O-oH< )=o11314iww15~ OH人n。16ppo341747.61849.6人oia， Unless otherwise noted, the reaction used n-Bu.NBr as the catalyst and the reaction conditionare: substrate : oxidant : catalyst= 1 : 1.11 m中国煤化工elds are average oftwo or more runs and base on the amount 0I1yst d. n-Bu,NCl ascatalyst. e. KBr as catalyst. f. [bmim]Br asfMYHC N M H Gyst=1:1.1 :0.25.h.Substrate : oxidant : catalyst= 1 :2.1 : 0.08.A Mild and Eficient Oxidation of Alcohols in Water1151As shown in Table 1, various types of alcohols have been successfully used. Theprocedure is very simple. The results of oxidation of sec-phenethyl alcohol catalyzedby various catalyst are summarized in entryl~5. One can see from the results that theaddition of bromide ions, such as n-Bu4NBr, [bmim]Br and KBr, was found to activatePhI(OAc)2 remarkably to give sec-phenethyl ketone in good yield. while n-Bu4NCI did notcatalyze the reaction effectively. Therefore n-Bu4NBr, the most active and relativeeconomic bromide, was chosen for further studies.The results for the oxidation of a variety of alcohols are summarized in Table1, it isclear that, in spite of chromanol (entry 10) failing to be oxidated, the reaction of benzylalcohols to the corresponding carbonyl compounds is fast and efficient. Oxidation ofmost benzyl alcohols was completed within two hours and gave the corresponding ketonesin good yield. Aliphatic alcohols are also viable substrates. As expected, secondaryaliphatic alcohols (entry 12 ~ 14) were oxidized more quickly than primary alcohols (entry16~ 19). Oxidation of primary allylic alcohols give the corresponding aldehyde cleanly.Not surprisingly, the oxidation of alylic alcohols is challenging problem (entry 15~17).The 3-methy1-2- buten- 1 ol was oxidized (entry 15) successfully under the same condition.In addition, in the case of gerianol (entry16~ 17), the yield cannot be enhanced greatly byincreasing the catalyst and reaction time. Oxidation of primary aliphatic alcohols (entry18~ 19) only gave carboxylic acid and none of the corresponding aldehyde was obtained,when 4.1 eq. PhI(OAc)2 was used, but when using 2.1 eq. oxidant the substrate can beconsumed completely within the same time (entry 19).Typical procedure: PhI(OAc) (70.8 mg, 0.22 mmol) and n-Bu4NBr (5.2 mg, 0.016mmol) were added to water (3 mL) and stired at room temperature.2-Octanol (260.5 mg,0.2 mmol) was then added and stiring was continued at room temperature for 1 hour.The reaction mixture was extracted with ethyI acetate, washed with brine. The organiclayers were dried over anhydrous MgSO4. The yields were determined by gaschromatography (HP 5890I1). The products were characterized by GC-MS (Agilent6890N GC/5793 MS).In summary, we have achieved a mild and efficient oxidation of alcohols tocorresponding carbonyl compounds with the catalysts, the PhI(OAc) and n-Bu4NBr, inwater at room temperature.AcknowledgmentsThis work was supported by the National Natural Science Foundation of China (29933050).References1. (a)1. E. Marko, M. Tsukazaki, P. R. Giles, et al, Angew. Chem. Int. Ed. Engl, 1997, 36,中国煤化工(b) M. Zhao, J. Li, E. Mano, Z. Song, e: (c) R. A. Sheldon,I w. C. E.Arends, G. J. T. Brink, Acc.YHCNMH G_2. R. C. Larock, Comprehensive Organic ........ u, 1 ork: John Wiley &Sons, 1999.3. (&) R. M. Moriarty, R. K. Vaid, Synthesis, 1990, 431. (b) P. J. Stang, Angew. Chem. Int Ed.1152Chuan Zhi XU et al.Engl, 1992, 31, 274. (c) P. J. Stang, V. V. Zhdankin, Chem. Rev, 1996, 96, 1123. (d) H.Tohma, S. Takizawa, T. Maegawa, Y. Kita, Angew. Chem. Int. Ed, 2000, 39, 1306. (e) H.Tohma, T. Maegawa, S. Takizawa, Y. Kita, Adv. Synth. Catal, 2002, 344.4. (a) Organic Symthesis in Water (Ed: P. A. Grieco), Blackie Academic, London, 1998. (b)Organic Reactions in Aqueous Media (Eds. , C.J. Li, T-H. Chan), Wiley, New York, 1997.(c)Aqueous Phase Organmatallic Catalysis (Eds, B. Comils, W. A. Hemmann), Wiley-VCH,Weinheim. 1998.5. (a) H. Tohma, T. Maegawa, S. Takizawa, Y. Kita, Adv. Synth. Catal, 2002, 344. (b) H.Tohma, S. Takizawa, T. Macegawa, Y. Kita, Angew. Chem. Int. Ed, 2000, 39, 1306. (c) H.Tohma, S. Takizawa, H. Watanabe, Y. Kita, Tetrahedron Lelt, 1998, 39, 4547. (d) H. Tohma,S. Takizawa, Y. Fukuoka, T. Maegawa, Y. Kita, J. Org. Chem, 1999, 64, 3519.6(a)乙. Li, C. G. Xia, Tetrahedron Lelt, 2003, 44, 2069. (b) N. Hisao, S. Tomoo, I. Hirofumi, S.Hirofumi, M. Yukihiro, Chem. Commun, 1997, 1863. (c)J H. In, S.E. Park, R. Song, WNam, Inorg. Chim. Acta, 2003, 343, 373.Received 1 September, 2003中国煤化工MHCNMHG