Pfitzner-Moffatt oxidation

Pfitzner-Moffatt oxidation

The Pfitzner-Moffatt oxidation is a chemical reaction that involves the oxidation of alcohols to aldehydes or ketones using a dimethyl sulfoxide (DMSO) and an electrophilic halogen compound, typically dicyclohexylcarbodiimide (DCC) or an acyl chloride, in the presence of a base. This reaction is named after the chemists who developed it, Hans Pfitzner and James Moffatt.

The Pfitzner-Moffatt oxidation is particularly useful for the synthesis of aldehydes and ketones from primary and secondary alcohols, respectively. It offers several advantages over traditional oxidation methods, including mild reaction conditions, high selectivity, and the ability to avoid over-oxidation of aldehydes to carboxylic acids.

Mechanism

The mechanism of the Pfitzner-Moffatt oxidation involves several key steps. Initially, the DMSO reacts with the electrophilic halogen compound to form an activated DMSO intermediate. This intermediate then reacts with the alcohol substrate to form an alkoxyalkylsulfonium salt. The presence of a base facilitates the elimination of this intermediate, leading to the formation of the desired aldehyde or ketone and dimethyl sulfide as a byproduct.

Applications

The Pfitzner-Moffatt oxidation has found widespread application in organic synthesis, particularly in the synthesis of complex molecules such as natural products and pharmaceuticals. Its ability to selectively oxidize sensitive alcohols without affecting other functional groups makes it a valuable tool in the chemist's arsenal.

Advantages and Limitations

One of the main advantages of the Pfitzner-Moffatt oxidation is its mild reaction conditions, which minimize the risk of over-oxidation and degradation of sensitive substrates. However, the reaction does have some limitations, including the generation of dimethyl sulfide, a malodorous byproduct, and the need for anhydrous conditions to prevent hydrolysis of the activated DMSO intermediate.

Comparison with Other Oxidation Methods

The Pfitzner-Moffatt oxidation is often compared with other oxidation methods such as the Swern oxidation, Dess-Martin periodinane oxidation, and Jones oxidation. Each of these methods has its own set of advantages and limitations, and the choice of oxidation method depends on the specific requirements of the reaction, including the sensitivity of the substrate and the desired yield and purity of the product.