Alcohols, primary chlorochromate

Conditions that do permit the easy isolation of aldehydes in good yield by oxida tion of primary alcohols employ various Cr(VI) species as the oxidant in anhydrous media Two such reagents are pyndmium chlorochromate (PCC), CsHsNH ClCr03 ... 

Perhaps the most important reaction of alcohols is their oxidation to carbonyl compounds. Primary alcohols yield either aldehydes or carboxylic acids, secondary alcohols yield ketones, but tertiary alcohols are not normally oxidized. Pyridinium chlorochromate (PCC) in dichloromethane is often used for oxidizing primary alcohols to aldehydes and secondary alcohols to ketones. A solution of Cr03 in aqueous acid is frequently used for oxidizing primary alcohols to carboxylic acids and secondary alcohols to ketones. 

Q Primary alcohols can be oxidized to give aldehydes (Section 17.7). The reaction is often carried out using pyridinium chlorochromate (PCC) in dichloro-methane solvent at room temperature. 

Quinolinium dichromate (QDC) oxidations of primary and secondary alcohols both proceed via a cyclic chromate ester. Acrylonitrile polymerization was observed in the oxidation of several para- and meffl-substituted benzaldehydes to the corresponding benzoic acids by quinolinium chlorochromate (QCC). QCC oxidations of diphenacyl sulfide and of aromatic anils have been studied. 

A better reagent for oxidation of primary alcohols to aldehydes in good yield is pyridinium chlorochromate (PCC), a complex of chromium trioxide with pyridine and HCl. 

A convenient reagent that selectively oxidizes primary alcohols to aldehyde is anhydrous pyridinium chlorochromate, abbreviated to PCC... 

Interestingly, the little studied inorganic chlorochromates, potassium397 and magnesium398 chlorochromates are very easy to prepare and are soluble in polar organic solvents, like acetone or acetonitrile. They are able to efficiently oxidize secondary alcohols to ketones, although they provide only low yields of aldehydes on the oxidation of primary alcohols. 

The oxidation of primary alcohols to aldehydes also suffers from the problem of overoxidation of the aldehyde to a carboxylic acid. Mild methods capable of stopping die oxidation at the aldehyde oxidation level are required if aldehydes are to be obtained. The most common and effective reagent for this purpose is pyridinium chlorochromate (PCC), produced by the reaction of pyridinium hydrochloride with chromium trioxide. This reagent is soluble in dichloromethane and smoothly oxidizes primary alcohols to aldehydes in high yields. Because of die mild, neutral reaction conditions and the use of stoichiomettic amounts of oxidant, the aldehyde product is not oxidized further. 

Oxidation of several primary aliphatic alcohols with potassium dichromate, pyri-dinium dichromate, quinolinium dichromate (QDC), imidazolium dichromate, nico-tinium dichromate, isonicotinium dichromate, pyridinium fluorochromate (PFC), quinolinium fluorochromate, imidazolium fluorochromate, pyridinium chlorochromate (PCC), quinolinium chlorochromate (QCC), and pyridinium bromochromate (PBC), in aqueous acetic acid and in the presence of perchloric acid, showed similar kinetics. The values of the reaction constants did not differ significantly, indicating operation of a common mechanism.1... 

Primary alcohols give aldehydes. The best oxidant is pyridinium chlorochromate (PCC). Secondary alcohols give ketones the reagent is usually Cr03, H+. 

Corey, E. J. and W. Suggs (1975) Pyridinium chlorochromate. An efficient reagent for oxidation of primary and secondary alcohols to carbonyl compounds. Tetrahedron Letters 16,2647-2650. 

A better reagent for the limited oxidation of primary alcohols to aldehydes is pyridinium chlorochromate (PCC), a complex of chromium trioxide with pyridine and HC1. PCC oxidizes most primary alcohols to aldehydes in excellent yields. Unlike most other oxidants, PCC is soluble in nonpolar solvents such as dichloromethane (CH2C12), which is an excellent solvent for most organic compounds. PCC can also serve as a mild reagent for oxidizing secondary alcohols to ketones. 

Pyridinium chlorochromate (PCC), C5H6NOO3CI Oxidizes primary alcohols to yield aldehydes and secondary alcohols to yield ketones (Section 17.7). 

In a brief communication, it was reported that quinolinium chlorochromate is a selective oxidant for primary alcohols for example, this reagent is reported to oxidize the diol (11) selectively to the aldehyde (12 equation 12). 

Poly(vinylpyridinium chlorochromate) (PVPCC) is a mild oxidant for primary, secondary, allylic and benzylic alcohols. Unfortunately, optimum conditions require the use of very nonpolar solvents (best is cyclohexane) at 80 C. More polar solvents (that would be more generally useful in synthesis) severely retard the rate of oxidation, thus necessitating an increase in the amount of oxidant used. Oxidations were found to have high inital rates, but were very slow to go to completion due to the inaccessibility of the chromium. This can be overcome by using a lower loading of oxidant or by an alternative preparation of the polymer, where the addition of 1-5% divinylbenzene gives a much more porous resin. 

Trimethylsilyl chlorochromate gives good yields for secondary alcohols and benzylic alcohols, but saturated primary alcohols give complex mixtures. It will also oxidise thiols to disulfides, and cleave... 

Pyridinium chlorochromate (PCC) Corey and Suggs prepared PCC by mixing CrOs with pyridine in HCl. PCC is used for the oxidation of primary and secondary alcohols in CH2CI2. This reagent is less efficient than Collins reagent for the oxidation of allyl alcohols. 

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