Synthesis of carboxylic acids by oxidation of alcohols
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.
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.
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.