Synthesis of carboxylic acids by oxidation of alcohols
A simple and readily accessible cobalt pincer catalyst (NNNHtBuCoBr2) catalyzes a facile oxidation of alcohols to carboxylate salts. This acceptorless dehydrogenation displays good functional group tolerance.
D. R. Pradhan, S. Pattanaik, J. Kishore, C. Gunanathan, Org. Lett., 2020, 22, 1852-1857.
Oxidation from alcohols to carboxylic acids are often conducted using at least a stoichiometric amount of an expensive and toxic oxidant. An efficient and practical sustainable oxidation technology of alcohols using pure O2 or even air as the oxidant in the presence of a catalytic amount each of Fe(NO3)3·9H2O/TEMPO/MCl provides a series of carboxylic acids in high yields at room temperature.
X. Jiang, J. Zhang, S. Ma, J. Am. Chem. Soc., 2016, 138, 8344-8347.
A CrO3-catalyzed oxidation of primary alcohols to carboxylic acids proceeds smoothly with only 1-2 mol % of CrO3 and 2.5 equivalents of H5IO6 in wet MeCN to give the carboxylic acids in excellent yield. No significant racemization is observed for alcohols with adjacent chiral centers. Secondary alcohols are cleanly oxidized to ketones.
M. Zhao, J. Li, Z. Song, R. Desmond, D. M. Tschaen, E. J. J. Grabowski, P. J. Reider, Tetrahedron Lett., 1998, 39, 5323-5326.
Various aromatic, aliphatic and conjugated alcohols were transformed into the corresponding carboxylic acids and ketones in good yields with aq 70% t-BuOOH in the presence of catalytic amounts of bismuth(III) oxide. This method possesses does not involve cumbersome work-up, exhibits chemoselectivity and proceeds under ambient conditions. The overall method is green.
P. Malik, D. Chakraborty, Synthesis, 2010, 3736-3740.
Pd/C along with NaBH4 in aqueous ethanol or methanol and either K2CO3 or KOH as base at room temperature under molecular oxygen or air is capable of oxidizing alcohols to its desired carbonyl or carboxyl counterpart. Room temperature reaction in aqueous system and recyclability of the catalyst make the process safe and cheaper.
G. An, H. Ahn, K. A. De Castro, H. Rhee, Synthesis, 2010, 477-485.
A dehydrogenative reaction of primary alcohols in the presence of hydroxide and the ruthenium complex [RuCl2(IPr)(p-cymene)] as catalyst provides carboxylic acids. The use of toluene enables a simple product isolation by precipitation and extraction. A range of benzylic and saturated aliphatic alcohols containing halide and (thio)ether substituents can be converted, while olefins and ester groups are not compatible.
C. Santilli, I. S. Makarov, P. Fristrup, R. Madsen, J. Org. Chem., 2016, 81, 9931-9938.
Catalytic use of o-iodoxybenzoic acid (IBX) in the presence of Oxone as a co-oxidant is demonstrated for the oxidation of primary and secondary alcohols. In addition, the in situ oxidation of 2-iodosobenzoic acid (IBA) and even commercially available 2-iodobenzoic acid (2IBAcid) by Oxone to IBX allows the use of these less hazardous reagents, in place of potentially explosive IBX, as catalytic oxidants.
A. P. Thottumkara, M. S. Bowsher, T. K. Vinod, Org. Lett., 2005, 7, 2933-2936.
A facile and quantitative preparation of carboxylic acids by a pyridinium chlorochromate (PCC) catalyzed (2 mol%) oxidation of primary alcohols and aldehydes using 2.2 equivalents and 1.1 equivalents of H5IO6, respectively, in acetonitrile is described here.
M. Hunsen, Synthesis, 2005, 2487-2490.
The use of low loadings of a silver NHC catalysts enables a mild, selective oxidation of alcohols to aldehydes or carboxylic acids in the presence of BnMe3NOH or KOH under dry air in excellent yield. The catalytic system can also be used for a one-pot synthesis of imines in excellent yield.
L. Han, P. Xing, B. Jiang, Org. Lett., 2014, 16, 3428-3431.
A facile and mild photooxidation of alcohols gives carboxylic acids and ketones using easily handled 2-chloroanthraquinone as an organocatalyst under visible light irradiation in an air atmosphere.
Y. Shimada, K. Hattori, N. Tada, T. Miura, A. Itoh, Synthesis, 2013, 45, 2684-2688.
Optimized selective aerobic oxidations in ionic liquids convert various activated primary alcohols into their corresponding acids or aldehydes in good to excellent yields. The newly developed catalytic systems could also be recycled and reused for three runs without any significant loss of catalytic activity.
N. Jiang, A. J. Ragauskas, J. Org. Chem., 2007, 72, 7030-7033.
Catalytic amounts of TEMPO and NaOCl enable a chemoselective oxidation of 1,2-diols to in the presence of NaClO2 as terminal oxidant. The use of a two-phase condition suppresses the concomitant oxidative cleavage. The observed selectivity seems to be derived from the precise solubility control of diols and hydroxy acids as well as the charge transfer complex TEMPO-ClO2, which dissolves into the organic layer.
K. Furukawa, M. Shibuya, Y. Yamamoto, Org. Lett., 2015, 17, 2282-2285.
The use of a NaOtBu-O2 resulted in an efficient oxidative cleavage of vic-1,2-diols to form carboxylic acids in high yields. The present protocol is a green alternative to conventional transition metal based methods. Large-scale production with nonchromatographic purification is also possible.
S. M. Kim, D. W. Kim, J. W. Yang, Org. Lett., 2014, 16, 2876-2879.
A smooth, organocatalytic one-pot oxidative cleavage of terminal 1,2-diols to one-carbon-unit-shorter carboxylic acids is catalyzed by 1-Me-AZADO in the presence of a catalytica amount of NaOCl and NaClO2 under mild conditions. A broad range of substrates including carbohydrates and N-protected amino diols were converted without epimerization.
M. Shibuya, R. Doi, T. Shibuta, S.-i. Uesugi, Y. Iwabuchi, Org. Lett., 2012, 14, 5006-5009.
An aerobic photooxidative cleavage of vicinal diols yields carboxylic acids using 2-chloroanthraquinone in the presence of photoirradiation with a high-pressure mercury lamp. This is a metal-free reaction in which molecular oxygen is used as the terminal oxidant.
Y. Matsusaki, T. Yamaguchi, N. Tada, T. Miura, A. Itoh, Synlett, 2012, 23, 2059-2062.
An atom-economical and environmentally friendly dehydrogenation of amino alcohols to amino acid salts using just basic water, without the need of pre-protection or added oxidant is catalyzed by a ruthenium pincer complex. Water is the solvent, the source of the oxygen atom of the carboxylic acid group, and the actual oxidant. Many important and useful natural and unnatural amino acid salts can be produced in excellent yields.
P. Hu, Y. Ben-David, D. Milstein, J. Am. Chem. Soc., 2016, 138, 6143-6146.