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🥼organic chemistry review

Triphenylphosphine

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

Triphenylphosphine is an organophosphorus compound with the chemical formula PPh3, where Ph represents the phenyl group. It is a widely used reagent in organic synthesis, particularly in the Wittig reaction, which involves the nucleophilic addition of phosphorus ylides.

5 Must Know Facts For Your Next Test

  1. Triphenylphosphine is a colorless, crystalline solid that is widely used as a ligand in organometallic chemistry and as a reducing agent in organic synthesis.
  2. The Wittig reaction, which utilizes triphenylphosphine, is a powerful method for the synthesis of alkenes from aldehydes or ketones and phosphorus ylides.
  3. Triphenylphosphine can be easily converted to the corresponding phosphonium salt, which is a key intermediate in the Wittig reaction.
  4. The Wittig reaction is a stereoselective reaction, meaning that the geometry of the alkene product is controlled by the stereochemistry of the phosphorus ylide.
  5. Triphenylphosphine is also used as a ligand in transition metal catalysts, where it can stabilize the metal center and modulate the reactivity of the catalyst.

Review Questions

  • Explain the role of triphenylphosphine in the Wittig reaction and how it is used to generate phosphorus ylides.
    • Triphenylphosphine is a key component in the Wittig reaction, as it is used to generate the phosphorus ylide intermediate. In the first step of the Wittig reaction, triphenylphosphine reacts with an aldehyde or ketone to form a phosphonium salt. This phosphonium salt then undergoes deprotonation, typically with a strong base, to generate the phosphorus ylide. The phosphorus ylide then reacts with the carbonyl compound to form the desired alkene product in a stereoselective manner.
  • Describe the mechanism of the Wittig reaction and how the stereochemistry of the alkene product is controlled by the phosphorus ylide.
    • The Wittig reaction proceeds through a cyclic intermediate called an oxaphosphetane, which is formed by the nucleophilic addition of the phosphorus ylide to the carbonyl carbon. The stereochemistry of the oxaphosphetane, and hence the alkene product, is determined by the geometry of the phosphorus ylide. If the phosphorus ylide has an E (trans) configuration, the oxaphosphetane will have a trans geometry, leading to the formation of a trans alkene. Conversely, if the phosphorus ylide has a Z (cis) configuration, the oxaphosphetane will have a cis geometry, resulting in the formation of a cis alkene.
  • Evaluate the importance of triphenylphosphine in organic synthesis beyond its role in the Wittig reaction, and discuss how its properties and reactivity make it a versatile reagent.
    • Triphenylphosphine is not only a key component in the Wittig reaction, but it is also a widely used reagent in organic synthesis for a variety of other reactions. Its ability to act as a reducing agent, for example, in the Mitsunobu reaction, makes it useful for the conversion of alcohols to other functional groups. Additionally, the fact that triphenylphosphine can form stable complexes with transition metals allows it to be used as a ligand in catalytic reactions, where it can modulate the reactivity and selectivity of the catalyst. Furthermore, the ease with which triphenylphosphine can be converted to the corresponding phosphonium salt, and the stability of these salts, makes them valuable intermediates in various synthetic transformations. Overall, the versatility of triphenylphosphine as a reagent, its ease of handling, and its wide availability make it an indispensable tool in the organic chemist's toolbox.