Collins reagent: Difference between revisions

Latest revision as of 11:53, 15 February 2025

Collins Reagent[edit]

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[edit]

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[edit]

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[edit]

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[edit]

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[edit]

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

Related Pages[edit]

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-'''Collins reagent''' is a powerful [[oxidizing agent]] used in [[organic chemistry]] for the oxidation of primary and secondary [[alcohol]]s to [[aldehyde]]s and [[ketone]]s, respectively. It is composed of chromium(VI) oxide in pyridine and dichloromethane. The reagent is named after its inventor, organic chemist E.J. Collins, who introduced it in the 1960s. Due to its high reactivity and selectivity, Collins reagent has become a staple in synthetic organic chemistry laboratories.
+== Collins Reagent ==
-==Composition and Preparation==
+[[File:Collins-Reagenz.svg|thumb|right|Structural formula of Collins reagent]]
-Collins reagent consists of a complex of chromium(VI) oxide with pyridine (PyH) in dichloromethane (DCM). The preparation involves dissolving chromium(VI) oxide in pyridine, followed by the addition of dichloromethane. The resulting mixture is a potent oxidizing agent, capable of converting alcohols to their corresponding carbonyl compounds under mild conditions.
-==Mechanism of Action==
+'''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.
-The mechanism of action of Collins reagent involves the formation of a chromate ester intermediate from the alcohol, which then undergoes a two-electron oxidation process, leading to the formation of the carbonyl compound. The high selectivity of Collins reagent for alcohols, along with its ability to perform oxidations under relatively mild conditions, makes it particularly useful for complex molecule synthesis where other functional groups need to be preserved.
-==Applications==
+== Structure and Composition ==
-Collins reagent is widely used in the synthesis of fine chemicals, pharmaceuticals, and other complex organic molecules. Its ability to selectively oxidize primary and secondary alcohols to aldehydes and ketones, respectively, without overoxidation to carboxylic acids, makes it an invaluable tool in the chemist's toolkit.
-==Safety and Environmental Considerations==
+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.
-While Collins reagent is highly effective, it is also associated with several safety and environmental concerns. The reagent contains chromium(VI), a known carcinogen, which requires careful handling and disposal. Additionally, the use of dichloromethane, a volatile organic compound (VOC), raises concerns regarding air quality and health. As a result, alternative oxidizing agents that are safer and more environmentally friendly are often sought.
-==Alternatives==
+== Mechanism of Action ==
-Several alternatives to Collins reagent have been developed, including the [[PDC (Pyridinium dichromate)|Pyridinium dichromate (PDC)]] and [[Dess-Martin periodinane]], which offer similar oxidizing power but with reduced health and environmental risks. These alternatives are increasingly preferred in modern organic synthesis.
-==Conclusion==
+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).
-Collins reagent remains a powerful tool in organic synthesis, particularly for the oxidation of alcohols to aldehydes and ketones. However, due to safety and environmental concerns, its use is often reserved for specific applications where its high selectivity and reactivity offer clear advantages over safer alternatives.
-[[Category:Reagents]]
+== Applications ==
-[[Category:Organic chemistry]]
-[[Category:Chromium compounds]]
-{{Chemistry-stub}}
+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]]
+[[Category:Reagents for organic chemistry]]