3. What byproduct is not formed during the synthesis of triphenylmethanol? a. be

ID: 547028 • Letter: 3

Question

3. What byproduct is not formed during the synthesis of triphenylmethanol? a. benzoic acid b. biphenyl c. benzene d. methanol 4. What is the expected yield of triphenylmethanol if 1.34 g of magnesium metal, 8.0 g of bromobenzene, 3.00 g of methyl benzoate and 25 mL of 3M sulfuric acid were used in its preparation? a. 13.2 g b. 14.3 g c. 5.72 g d. 6.6 g 5. What is the percent yield of triphenylmethanol if 1.34 g of magnesium metal, 8.0 g of bromobenzene, 3.00 g of methyl benzoate and 25 mL of 3M sulfuric acid were used to produce 3.00 g of triphenylmethanol? a. 22.7 b. 21.0 c. 52.4 d. 45.5

Explanation / Answer

3. While synthesizing triphenylmethanol from phenyl magnesium bromide (Grignard reagent) and methyl benzoate, via SN2 pathway, one should end up with methanol as a byproduct, for sure.

During this synthesis there are chances of phenyl magnesium bromide (Grignard reagent) getting decomposed due to moisture in to benzene and Mg(OH)Br. Similarly, it can also interact with atmospheric carbon dioxide which ends up with production of benzoic acid.

However, there is no chance for the production of biphenyl.

Hence,

Answer = b. biphenyl

4. In the present reaction initially, magnesium and bromobenzene reacts to form Grignard reagent (phenyl magnesium bromide). This Grignard reagent further reacts with methyl benzoate to produce benzophenone which in turn reacts with second mole of Grignard reagent to produce triphenylmethanol.

Hence, here one mole of methyl benzoate and two moles of bromobenzene/magnesium (generally magnesium taken in excess as compare to bromobenzene) reacts to give one mole of triphenylmethanol.

Therefore, as shown in table below 0.022035 moles of triphenylmethanol can be produced from 3 g of methyl benzoate (0.022035 moles) which gives 5.73 g of product.

Bromobenzene

Methyl Benzoate

triphenylmethanol

1.34

5.73637155

Mol wt

24.305

157.02

136.15

260.33

Moles

0.055133

0.050948924

0.022034521

0.022035

Answer = c. 5.72 g

5. As explained in the answer for Q 4, when reactants taken were 1.34 g, 8.0 g and 3.0 g of magnesium, bromobenzene and methyl benzoate, respectively, expected mass of triphenylmethanol could be 5.73 g.

However, if someone is getting 3.00 g of the product then the % yield is

% Yield = (3.0/5.73) x 100

= 52.35 %

Answer = c. 52.4 %