Question

What is the theoretical yield for the reaction of 4-bromobenaldehyde (0.095g) and benzyltriphenylphosphonium chloride: (0.200g) and of tribasic phosphate (0.425 g)

Answer 1

The reaction is called Wittig reaction: Convertion of aldehyde to alkene

The reaction can be written as The tribasic phosphate is used as catalyst in the reaction to maintain basic condition, so it is not involved inthe theoratical yield calculation.

The molecular weight of the two reactants and one product are given in figure as MW.

In order to calculate theoretical yield, first step is to convert the weight of reactants in to mole by dividing the weight with molecular weight

Number of mole involved in the reaction 4-bromobensaldehyde = Weight / molecular weight of 4-brombenzaldehyde

= 0.095 g /185 g mol^-1 = 0.0005135 mol =0.000514 mol

Number of mole involved in the reaction benzyltriphenylphosphonium chloride = 0.2 g /388.9 g mol^-1

= 0.0005142 mol = 0.00054 mol

The two reactants are taken in equimolar ratio, i.e., 0.00054 mol.

By seeing reaction one mol of 4-bromobensaldehyde reacts with one mol of benzyltriphenylphosphonium chloride to give one mol of product 1-bromo-4-[(E)-2-phenylethenyl]benzene.

So we can write 0.00054 mol of 4-bromobensaldehyde reacts with 0.00054 mol of benzyltriphenylphosphonium chloride to give 0.00054 mol of product 1-bromo-4-[(E)-2-phenylethenyl]benzene.

Theoretically 0.00054 mole of product is formed

To know the theoretical weight, multiply the number of mole of product with its molecular weight.

Theoretical weight of product = 0.00054 mol X 259 g mol^-1 = 0.13986 g = 0.14 g

Theoretical yield of the product is 0.14 g