2,6-Dicarboxypyridinium Fluorochromate: A Mild and Efficient Reagent for Oxidative Deprotection of Oximes, Phenylhydrazones, and Semicarbazones to Their Corresponding Carbonyl Compounds under Solvent-Free Conditions

Abstract

2,6-Dicarboxypyridinium fluorochromate as a new, rapid, and efficient reagent was prepared and used for the oxidative deprotection of oximes, phenylhydrazones, and semicarbazones to their carbonyl analogues under solvent-free conditions at room temperature.

An Improved Procedure for Oxidative Cleavage of Oximes to the Corresponding Carbonyl Compounds With Chromic Acid Supported on Kieselguhr Under Viscous Conditions

“…One of the most important procedures for the deoximation process is oxidation with hexavalent chromium derivatives, such as Jones reagent, [4] methylammonium chlorochromate-alumi na, [5] chromium trioxide-silica gel, [6] pyridinium fluorochromate, [7] quinolinium dichromate, [8] potassium dichromate, [9] pyridinium fluorochromate-hydrogen peroxide, [10] 2,6-dicarboxypyridinium chlorochromate, [11] γ -picolinium chlorochromate, [12] benzyltriphenylphosphonium chlorochromate, [13] quinolinium fluorochromate, [14] tetramethylammonium fluorochromate (VI), [15] benzyltrimethylammonium fluorochromate (VI), [16] imidazolium dichromate, [17] dicarboxypyridinium fluorochromate, [18] tetrabutylammonium chromate, [19] chromic acid, [20] chromium trioxide-NaHSO 4 ·H 2 O, [21] glycinium chlorochromate-silica gel, [22] and ammonium chlorochromatemontmorillonite K10. [23] Although some of the reported chromium(VI) or chromium(VI)-based reagents are carried out under mild conditions, most of them are often hazardous, expensive, or use not readily available reagents or use reagents that are needed to be freshly prepared.…”

“…Unfortunately, under solvent-free conditions, in general, it is not satisfied for the reaction between solid substrates and solid reagents, such as oximes and chromium(VI) oxidants, performed at the room temperature because both of molecules are in crystal forms that are of difficulty for collision to reach the reaction, so that such reactions are normally carried out at the temperature near or over the substrate melting point by either heating or other technologies in advance in order to dissolve the solid substrates into the liquid forms to increase the reaction rate. Of those chromium(VI) or chromium(VI)-based reagents for the oxidation of oximes described above only a few experiments were carried out under solvent-free conditions, [9,18] and basically the reaction procedure is that the solid mixture of substrate and oxidants in a mortar was ground with a pestle and OXIDATIVE CLEAVAGE OF OXIMES 1519 then the products were produced, which can be performed in the laboratory but might be not satisfied to carry out in a large scale.…”

A Facile Procedure for the Conversion of Oximes to Ketones and Aldehydes with Potassium Dichromate in Dimethylformamide under Homogeneous Conditions

“…Therefore, there has been considerable interest in the development of mild techniques for this transformation. The most important procedure for the regeneration of their corresponding carbonyl compounds from the oxime is oxidative cleavage reaction, which has been accomplished by a variety of chromium (VI) based reagents, such as Jones reagent [4], methylammonium chlorochromate-Alumina [5], chromium trioxide-silica gel [6], pyridinium fluorochromate [7], quinolinium dichromate [8], potassium dichromate [9], pyridinium fluorochromatehydrogen peroxide [10], 2,6-dicarboxypyridinium chlorochromate [11], γ-picolinium chlorochromate [12], benzyltriphenylphosphonium chlorochromate [13], quinolinium fluorochromate [14], tetramethylammonium fluorochromate (VI) [15], benzyltrimethylammonium fluorochromate (VI) [16], imidazolium dichromate [17], dicarboxypyridinium fluorochromate [18], tetrabutylammonium chromate [19], chromic acid [20], chromium trioxide-NaHSO 4 H 2 O [21], glycinium chlorochromate-silica gel [22], ammonium chlorochromate-montmorillonite K10 [23], etc. Most of them are carried out under either heterogeneous conditions or solvent-free/solid state conditions.…”