Collins reagent is the complex of chromium(VI) oxide

Chromium trioxide

Chromium trioxide is the inorganic compound with the formula CrO3. It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name.This compound is a dark-red/orange brown solid, which dissolves in water concomitant with hydrolysis...

 with pyridine

Pyridine

Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one C-H group replaced by a nitrogen atom...

 in dichloromethane

Dichloromethane

Dichloromethane is an organic compound with the formula CH2Cl2. This colorless, volatile liquid with a moderately sweet aroma is widely used as a solvent. Although it is not miscible with water, it is miscible with many organic solvents...

. It is used to selectively oxidize primary alcohol

Alcohol oxidation

Alcohol oxidation is an important organic reaction. Primary alcohols can be oxidized either to aldehydes or to carboxylic acids , while the oxidation of secondary alcohols normally terminates at the ketone stage...

s to the aldehyde

Aldehyde

An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....

, and will tolerate many other functional group

Functional group

In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...

s within the molecule.
It can be used as an alternative to the Jones reagent and pyridinium chlorochromate

Pyridinium chlorochromate

Pyridinium chlorochromate is a reddish orange solid reagent used to oxidize primary alcohols to aldehydes and secondary alcohols to ketones. Pyridinium chlorochromate, or PCC, will not fully oxidize a primary alcohol to the carboxylic acid as does the Jones reagent. A disadvantage to using PCC is...

 (PCC) when oxidising secondary alcohols to ketone

Ketone

In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...

s. Moreover, the Collins reagent is especially useful for oxidations of acid sensitive compounds.

This complex is both difficult and dangerous to prepare, as it is very hygroscopic and can inflame during preparation. It is typically used in a sixfold excess in order to complete the reaction. Nowadays, PCC or PDC oxidation have largely supplanted Collins oxidation for these very reasons.

See also

• Jones oxidation
  Jones oxidation
  The Jones oxidation, is an organic reaction for the oxidation of primary and secondary alcohols to carboxylic acids and ketones, respectively. It is named after its discoverer, Sir Ewart Jones....
  
  
• Pyridinium chlorochromate
  Pyridinium chlorochromate
  Pyridinium chlorochromate is a reddish orange solid reagent used to oxidize primary alcohols to aldehydes and secondary alcohols to ketones. Pyridinium chlorochromate, or PCC, will not fully oxidize a primary alcohol to the carboxylic acid as does the Jones reagent. A disadvantage to using PCC is...
  
  
• Pyridinium dichromate
• Sarett oxidation
  Sarett oxidation
  The Sarett oxidation is the oxidation of an alcohol to a ketone or an aldehyde using chromium trioxide and pyridine. Primary alcohols will only be oxidised to the aldehyde and not on to carboxylic acids....