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.
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).
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.
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