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Wittig Reaction

About Wittig Reaction

Wittig reaction affords an important and useful method for the synthesis of alkenes by the treatment of aldehydes or ketones with alkyldinetripheylphosphorate (Ph3P =- CR2) or simply known as phosphorane.

Wittig Reaction

The Wittig reagent, alkylidenetriphenylphosphorane, is prepared by treating trialkyl or triarylphosphine usually the latter with an alkyl halide in ether solution. The resulting phosphonium salt is treated with a strong base (such as C65Li, BuLi, NaNH2, NaH, C2H5ONa, etc.

Reaction Mechanism of Wittig Reaction

The reaction probably proceeds by the nucleophilic attack of the ylide on the carbonyl carbon. The dipolar complex (betain) so formed decomposes to olefin and triphenyphosphine oxide via a four centred transition state.

mechanism of Wittig Reaction

The mechanism is supported by the fact that an optically active phosphonium salt reacts to produce a phosphine oxide with retention of configuration.

Phosphorous yields react in the same manner with the C = O groups of ketones and isocyanates as also with the N = O and C = N groups of nitroso and imine compounds respectively.

Note: The aldehydes and ketones are converted into alkenes by using a special class of compounds called phos- phorus ylides, also called Wittig reagents.The Triphenyl group of phosphorane has a strong tendency to pull oxygen atom of the aldehyde or ketone via a cyclic transition state forming an alkene.
 

Example of Wittig Reaction

example of wittig reaction

example of wittig reaction

List of Name Reaction of Organic Chemistry consist of detail Reaction Mechanism of all name reactions of Organic Chemistry.

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