These questions is regard to the accompany the stereoselective Wittig reaction.

Question

These questions is regard to the accompany the stereoselective Wittig reaction. A) The procedure calls for the addition of 7-8 drops of aqueous NaOH. What is the purpose of the base here? Be specific and show the reaction that occurs. B) Why the switch in drying agents? Anhydrous sodium sulfate is both efficient and inexpensive. Potassium carbonate is less efficient and somewhat more costly. *Hint: Sodium sulfate is actually a wee bit acidic whereas potassium carbonate is a bit basic! Your product is an alkene. C) The mass of your crude product (as well as the tlc) should clue you in that an impurity if present. Whatever it is must also be soluble in dichloromethane, right? What is the probable identity of this impurity? At what point is it being removed?

Explanation / Answer

A) From the phosphonium salts, these reagent are formed more readily, requiring only with NaOH, and they are usually more air-stablethey need strong base (like NaOH ) to give a basic environment and to capture the -/+ salt from the mix....................... b)Simple phosphoranes are very reactive and are unstable in the presence of moisture and oxygen in the air. They are therefore prepared in a super dry solvent (usually THF) under nitrogen or argon and the carbonyl compound is added as soon as the phosphorane has been formed............ C) DBU and Triphenylphosphine oxide are the impurity

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