Trioxide in Water or Aqueous Acetic Acid

A common way to change reaction conditions for the oxidation of alcohols is to modify the acid that is added to the medium. Indeed, chromium trioxide will have different oxidizing abilities in different acids. Since most organic compounds are insoluble in water, a cosolvent is usually required to dissolve not only the chromium reagent but also the alcohol substrate. This solvent must be resistant to oxidation, and acetic acid or acetone are commonly used. For the alcohol - carbonyl conversion several Cr(VI) reagents can be used, including chromium trioxide in water or aqueous acetic acid catalyzed by mineral acid, sodium dichromate in aqueous acetone catalyzed by mineral acid, sodium dichromate in acetic acid, the Cr03 pyridine complex, and err-butyl chromate.Both primary and secondary alcohols can be oxidized to the aldehyde or ketone, respectively. Aldehydes may be oxidized to the carboxylic acid under some conditions. 

Oxidation of primary alcohols leads to aldehydes in moderate to good yield. Aldehydes are relatively easy to oxidize to the corresponding carboxylic acid. In most cases, the oxidation stops at the aldehyde, but small amounts of the acid are a common byproduct. Heating and long reaction times lead to increased amounts of the acid, and in some cases, the aldehyde is the minor product. Where feasible, removal of the aldehyde as it forms will minimize side reactions. When the reaction is pushed to give the carboxylic acid, there are at least two reasonable mechanistic rationales for this conversion-44 These two approaches involve formation of a chromate ester such as 13. Removal of the a-hydrogen (analogous to the alcohol to aldehyde conversion) 

With some primary alcohols, it is possible to establish an equilibrium between the initially formed aldehyde and the precursor alcohol in which unreacted alcohol is converted to an hemiacetal (17), which can be further oxidized to an ester. This often accompanies the oxidation of lower molecular weight primary alcohols. Oxidation of 1-butanol to butyl butyrate with Cr(VI), for example, is an Organic Syntheses preparation.  

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