The key difference between Woodward and Prevost reaction is that Woodward reaction proceeds in the presence of iodine and silver acetate whereas Prevost reaction proceeds in the presence of silver salt of benzoic acid.
Woodward and Prevost reactions are important in the formation of vicinal diols from alkenes. The term vicinal refers to the fact that functional groups of the diol (hydroxyl groups) are attached to neighbor carbon atoms or adjacent carbon atoms. When considering the geometry, they can be either cis or trans-isomers. However, Woodward reaction only forms the cis isomer.
CONTENTS
1. Overview and Key Difference
2. What is Woodward Reaction
3. What is Prevost Reaction
4. Side by Side Comparison – Woodward vs Prevost Reaction in Tabular Form
5. Summary
What is Woodward Reaction?
Woodward reaction is a type of chemical reaction where a cis diol forms from an alkene. The reaction is named after the scientist Robert Burns Woodward. This reaction proceeds in the presence of iodine and the silver acetate reagent. Also, this reaction requires a wet acetic acid medium. Furthermore, this is a type of addition reaction in organic chemistry.
Figure 01: A General Equation for the Woodward Reaction
Moreover, Woodward reaction has applications in the field of steroid synthesis. When considering the reaction mechanism of Woodward reaction, it first uses iodine, which reacts with the alkene. And, this reaction step is promoted by silver acetate. The product of this reaction step is iodonium ion. Thereafter, an SN2 reaction occurs; the iodonium ion opens due to the action of acetic acid or silver acetate and gives the first intermediate of the reaction, iodo-acetate. Then, another SN2 reaction occurs – it causes the iodine to be displaced, giving an oxonium ion. Subsequently, this product hydrolyzes to give a monoester.
What is Prevost Reaction?
Prevost reaction is a type of chemical reaction in which an alkene converts into a vicinal diol. This reaction was introduced by the French chemist Charles Prevost. The reaction proceeds in the presence of iodine and the silver salt of benzoic acid. Furthermore, the vicinal diol that forms through this reaction has anti-stereochemistry.
Figure 02: General Equation for a Prevost Reaction
When considering the reaction mechanism of Prevost reaction, it includes the reaction between silver benzoate and iodine (a very fast reaction), producing a very reactive iodonium benzoate intermediate. This intermediate then reacts with the alkene to give another short-lived iodonium salt. Thereafter, an SN2 reaction takes place, which gives the ester in the presence of the benzoate salt. Then another silver ion causes the benzoate ester to give an oxonium salt. A second SN2 reaction takes place, producing the desired diester. Finally, hydrolysis occurs to obtain the anti-diol from the ester groups in the final product.
What is the Difference Between Woodward and Prevost Reaction?
Woodward reaction and Prevost reaction are important in producing a diol from an alkene. The key difference between Woodward and Prevost reaction is that Woodward reaction proceeds in the presence of iodine and silver acetate whereas Prevost reaction proceeds in the presence of the silver salt of benzoic acid.
Below infographic shows more details of the difference between Woodward and Prevost reaction.
Summary – Woodward vs Prevost Reaction
Woodward reaction and Prevost reaction are important in producing a diol from an alkene. These two reaction types are different from each other, according to the reagents used during the reaction process. The key difference between Woodward and Prevost reaction is that Woodward reaction proceeds in the presence of iodine and silver acetate whereas Prevost reaction proceeds in the presence of the silver salt of benzoic acid.
Image Courtesy:
1. “Woodward Cis-Hydroxylation Scheme” By No machine-readable author provided. ~K assumed. Own work assumed (based on copyright claims) (Public Domain) via Commons Wikimedia
2. “Prevost Reaction Scheme” By ~K – Own work. High-resolution PNG; ChemDraw / The GIMP (Public Domain) via Commons Wikimedia