****PHOSPHONIUM SALT recovered is (carbethoxymethylene)triphenylphosphonium brom

Question

****PHOSPHONIUM SALT recovered is (carbethoxymethylene)triphenylphosphonium bromide.***

Introduction The most effective method of making an alkene selectively is the Wittig reaction, named after Georg Wittig, who won the Nobel Prize in 1979 for this and related reactions. The reaction combines an alkyl halide and an aldehyde or ketone, and forms an alkene. The magic ingredient here is triphenylphosphine, which allows the formation of an "ylide" - a nucleophilic carbon species that can attack the aldehyde electrophile. In this experiment, you will perform a Wittig reaction and analyze the stereochemistry of the reaction by 'H NMR spectroscopy PPh3 PPh3 O2N OEt EtO Toluene KOC(CH3)3, Toluene O2N 3/3» Figure 1. Reaction Scheme

Explanation / Answer

Moles of (carbethoxymethylene)triphenylphosphonium bromide = (300 mg ) *1 mol/ 429.29 g

= 0.699  mmol

Moles of p-nitrobenzaldehyde = (130 mg) *1 mol/ 151.12 g = 0.860 mmol

Mole ratio of (carbethoxymethylene)triphenylphosphonium bromide : p-nitrobenzaldehyde = 1:1 from the reaction

We have,

0.699  mmol (carbethoxymethylene)triphenylphosphonium bromide:0.860 mmol p-nitrobenzaldehyde

So the limiting reactant is (carbethoxymethylene)triphenylphosphonium bromide

Moles of product

=0.699  mmol (carbethoxymethylene)triphenylphosphonium bromide*1 mol product/1 mol (carbethoxymethylene)triphenylphosphonium bromide = 0.699 mmol product

Mass of product formed = 0.699 mmol x 222.21 g/ 1 mol = 155.32 mg product

Theoretical yield of the product 155.32 mg

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