Answer
⚗️ Wittig Reaction Overview
The Wittig reaction converts a carbonyl compound (usually an aldehyde or ketone) into an alkene using a phosphorus ylide. The key steps include:
- Formation of a phosphonium salt from an alkyl halide and triphenylphosphine
- Deprotonation of the phosphonium salt using a strong base (often BuLi or NaH)
- Reaction of the resulting ylide with an aldehyde or ketone
🔍 Role of Each Reagent
- Triphenylphosphine: Required to form the phosphonium salt.
- Alkyl halide: Reacts with triphenylphosphine to form the phosphonium salt.
- Aldehyde: Acts as the electrophile that the ylide reacts with to form the alkene.
- Alkyl lithium (e.g., BuLi): Often used to deprotonate the phosphonium salt and generate the ylide.
⚠ Alkyl lithium is commonly used, but it is NOT absolutely required.
Other bases like NaH can also be used to form the ylide, depending on the reactivity of the substrate.
✅ Final Answer:
An alkyl lithium
It is not universally required in every Wittig reaction — it can be substituted by other strong bases.