Wittig Reaction

Wittig Reaction

  • Submitted By: sofiazira92
  • Date Submitted: 10/19/2013 7:23 PM
  • Category: Science
  • Words: 903
  • Page: 4
  • Views: 75

To synthesize 3-phenylpropenoic acid from Wittig reaction.

The Wittig reaction is a chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide (often called a Wittig reagent) to give an alkene and triphenylphosphine oxide. Wittig reaction is widely used in organic synthesis for the preparation of alkenes.
Scheme 1

Triphenylphosphine (1) reacts with an alkyl halide (2) to form a phosphonium halide (3). Subsequently, addition of a strong base eliminates the hydrogen halide to form an ylide, alkylidenephosphorane (4).

Scheme 2

The carbon of the ylide acts as a nucleophile and adds to the carbonyl group (5) to form a betaine intermediate which undergo an in situ 1,2-elimination to give the triphenylphosphine oxide (6) and an alkene (7) as the product.

Scheme 3

Triphenylphosphine react with methyl bromoethanoate to form phosphonium salt. Addition of NaOH eliminates the hydrogen halide to form ylide, methyltriphenylphosphoranyl-ethanoate. Ester formed from the reaction of the ylide, methyltriphenylphosphoranyl-ethanoate (9) and benzaldehyde. (E)-3-phenylpropenoate (10) which is formed then hydrolyzed with base and 3-phenylprepenoic acid (11) is then isolated as crystalline solids.

Results & Calculations
(I) Preparation of triphenylphosphoranyl ethanoate (4) from methoxycarbonyl – methylenyltriphenylphosphonium bromide.

Mass of triphenylphosphine = 5.00g
Number of mol of triphenylphosphine = 5.00 g262.3 g/mol = 0.019 mol

Mass of methyl bromoethanoate = 3.00g
Number of mol of methyl bromoethanoate = 3.00 g152.98 g/mol = 0.0196 mol

1 mol of triphenylphosphine = 1 mol of methyl bromoethanoate
0.019 mol of triphenylphosphine = 0.019 mol of methyl bromoethanoate
∴ triphenylphosphine is limiting reagent.

Mass of phosphorium salt (Theoretical) = 0.019 mol x 415.23 g/mol
= 7.92 g

Mass of plastic = 0.57 g
Mass of plastic + phosphorium salt = 4.65 g
Mass of...

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