Collins reagent

Collins Reagent

Structural formula of Collins reagent

Collins reagent is a chemical reagent used primarily in organic chemistry for the oxidation of primary alcohols to aldehydes. It is a complex of chromium trioxide (CrO_) with pyridine, and it is known for its selectivity and mild reaction conditions.

Structure and Composition

Collins reagent is composed of chromium trioxide and pyridine in a 1:2 molar ratio. The complex is typically prepared by dissolving chromium trioxide in pyridine, resulting in a dark red solution. The reagent is sensitive to moisture and should be handled under anhydrous conditions.

Mechanism of Action

The oxidation of primary alcohols to aldehydes using Collins reagent involves the formation of a chromate ester intermediate. The chromate ester undergoes a redox reaction, where the alcohol is oxidized to an aldehyde, and the chromium is reduced from Cr(VI) to Cr(IV).

Applications

Collins reagent is particularly useful in organic synthesis due to its ability to selectively oxidize primary alcohols to aldehydes without further oxidation to carboxylic acids. This selectivity is advantageous in complex synthetic pathways where over-oxidation must be avoided.

Advantages and Limitations

One of the main advantages of Collins reagent is its mild reaction conditions, which help preserve sensitive functional groups in the substrate. However, the use of chromium-based reagents poses environmental and safety concerns due to the toxicity and carcinogenicity of chromium compounds. Proper disposal and handling procedures are essential when working with Collins reagent.

Related Reagents

Collins reagent is one of several chromium-based oxidizing agents used in organic chemistry. Other related reagents include:

• Jones reagent
• Pyridinium chlorochromate (PCC)
• Pyridinium dichromate (PDC)

Related Pages

• Oxidation (chemistry)
• Aldehyde
• Chromium trioxide
• Pyridine