Synthesis of carboxylic acids by oxidation of aldehydes
Highly efficient, mild, and simple protocols allow the oxidation of aldehydes to carboxylic acids and esters utilizing Oxone as the sole oxidant. These reactions may prove to be valuable alternatives to traditional metal-mediated oxidations.
B. R. Travis, M. Sivakumar, G. O. Hollist, B. Borhan, Org. Lett., 2003, 5, 1031-1034.
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.
An aerobic oxidation of a wide range of aldehydes to carboxylic acids in both organic solvent and water under mild conditions is catalyzed by 5 mol % N-hydroxyphthalimide (NHPI) as the organocatalyst in the presence of oxygen as the sole oxidant. No transition metals or hazardous oxidants or cocatalysts were involved.
P.-F. Dai, J.-P. Qu, Y.-B. Kang, Org. Lett., 2019, 21, 1393-1396.
VO(acac)2 catalyzes the oxidation of aromatic and aliphatic aldehydes to the corresponding acids efficiently and selectively in the presence of hydrogen peroxide as an oxidant. This method offers functional-group compatibility, easy workup procedure, and a short reaction time. The performance of titania-supported VO(acac)2 in the oxidation of aldehydes was also investigated.
D. Talukdar, K. Sharma, S. K. Bharadwaj, A. J. Thakur, Synlett, 2013, 24, 963-966.
An N-heterocyclic carbene (NHC) organocatalytic aerobic oxidation of aldehydes provides the corresponding carboxylic acids under mild reaction conditions. Remarkably, this method enables an efficient conversion of different classes of aldehydes including highly challenging electron-rich aryl aldehydes, ortho-substituted aryl aldehydes, various heteroaromatic aldehydes and α,β-unsaturated aldehydes.
A. K. Khatana, V. Singh, M. K. Gupta, B. Tiwari, Synthesis, 2018, 50, 4290-4294.
Sodium perborate in acetic acid is an effective reagent for the oxidation of aromatic aldehydes to carboxylic acids, iodoarenes to (diacetoxyiodo)arenes, azines to N-oxides, and various sulphur heterocycles to S,S-dioxides. Nitriles undergo smooth oxidative hydration to amides when aqueous methanol is employed as solvent.
A. McKillop, D. Kemp, Tetrahedron, 1989, 45, 3299-3306.
A convenient and efficient oxidation of hydroxylated and methoxylated benzaldehydes and acetophenones to the corresponding phenols uses hydrogen peroxide and methyltrioxorhenium as catalyst in ionic liquids [bmim]BF4 and [bmim]PF6.
R. Bernini, A. Coratti, G. Provenzano, G. Fabrizi, D. Tofani, Tetrahedron, 2005, 61, 1821-1825.
In an efficient and easily scalable continuous flow transformation of alcohols and aldehydes to carboxylic acids and nitroalkane derivatives to the corresponding carbonyls and carboxylic acids using permanganate as the oxidant, the generation and downstream processing of MnO2 slurries was not found to cause any blocking of the reactor when ultrasound pulses were applied to the flow system.
J. Sedelmeier, S. V. Ley, I. R. Baxendale, M. Baumann, Org. Lett., 2010, 12, 3618-3621.
Asymmetric hydration of α,α-dichloro aldehydes and α-halo enals via a NHC-catalyzed redox process gives enantioenriched α-chloro and α-fluoro carboxylic acids. The reaction allows the installation of an α-deuterium to give α-deutero α-halo acids using D2O as the deuteron source.
H. U. Vora, T. Rovis, J. Am. Chem. Soc., 2010, 132, 2860-2861.
A direct enantioselective α-hydroxymethylation of aldehydes employing an α,α-diarylprolinol trimethylsilyl ether organocatalyst enables efficient access to β-hydroxycarboxylic acids and δ-hydroxy-α,β-unsaturated esters via an intermediate lactol in good yields, excellent enantioselectivity, and compatibility with a broad range of functional groups in the aldehyde.
R. K. Boeckman, K. F. Biegasiewicz, D. J. Tusch, J. R. Miller, J. Org. Chem., 2015, 80, 4030-4045.