QUESTION: Calculate the theoretical yield of triphenylmethanol for the overall c
ID: 963735 • Letter: Q
Question
QUESTION:
Calculate the theoretical yield of triphenylmethanol for the overall conversion of bromobenzene to triphenylmethanol. Since we will
not isolate the Grignard reagent, use the assumption that all of the original alkyl halide was converted to Grignard reagent.
Note molar amounts used in the experiment and the stoichiometry of the reactions to determine the limiting reagent.
(1) How much triphenylmethanol will the reaction produce? (Show your theoretical yield calculation.)
Background for experiement if needed:
-Phenylmagnesium bromide will be prepared by the reaction of Mg with bromobenzene in diethyl ether.
• Methyl benzoate will be added to the solution containing the Grignard reagent to form the magnesium alkoxide salt of triphenylmethanol. The salt will be neutralized via acid work-up to yield the final product alcohol.
• Triphenylmethanol will be purified by a modified mixed solvent recrystallization. This will be achieved by adding a nonpolar hydrocarbon solvent (ligroin) to an ether solution of the final product, then concentrating the solution.
Preparation of phenylmagnesium bromide
Contains: 1 g of magnesium, 10 mL of anhydrous diethyl, 4.5 mL of bromobenzene,
Reaction of phenylmagnesium bromide with methyl benzoate
Contains:10 mL of diethyl ether to reaction mixture, 2.5 mL of methyl benzoate. Slowly pour the reaction mixture into a 250 mL Erlenmeyer flask containing 25 mL of 10% H2SO4 and about 12-15 g of ice,Add about 12-13 mL of ligroin . Collect crystals
Explanation / Answer
from the reaction no of moles of product formed is equal to the no of moles of methyl benzoate
because in this case excess amount of grignard reagent was used
so first find out the no o fmoles of methyl benzoate
use the formula density = mass / volume to convert ml to grams
density of methyl benzoate is 1.08 g/ml
volume of methyl benzoate given is 2.5 mL
mass = density x volume
mass = 2.5 mL x 1.08 g / ml = 2.7 gr
no of moles of methyl benzoate = weight / molar mass = 2.7 g / 136.15 g/mol
= 0.0198 mol
no of product formed theritically should equal to no of moles of methyl benzoate = 0.0198
mass of the product = moles of the product x molar mass of the product
= 0.0198 mol x 260.34 g/mol (molar mass of the product = 260.34 g/mol)
= 5.16 grams