Question

Which of the following could reduce the percent yield of triphenylmethanol? Check all that apply. a) insufficient flame drying of glassware b) insufficient washing with glassware c)adding methyl benzoate too early d) refluxing too long e)overcooling the grignard reagent .

Why wouldn't Nacl solution reduce the yield since Nacl is added to remove water?

Also why does refluxing too long not reduce yield?

Thank you!

Answer 1

a) Triphenylmethanol [(C₆H₅)₃C-OH] is prepared by the reaction of methyl benzoate [C₆H₅-COOCH₃] with phenylmagnesium bromide [C₆H₅MgBr]. Phenylmagnesium bromide is a reactive compound and undergo hydrolysis to form phenol in presence of water. This means that if the glasswares are not completely dry it will affect the yield of triphenylmethanol because of the decomposition of the Grignard reagent.

b) As mentioned earlier phenylmagnesium bromide is very reactive. Insufficient washing will leave residues of other compounds on the glasswares which will interfere with this reaction thereby reducing the yield of the final product.

c) The formation of phenylmagnesium bromide takes time. If you add methyl benzoate too early formation of phenylmagnesium bromide will be incomplete and it will prevent or reduce the formation of the product

d) Refluxing for a long period does not necessarly decrease the yield of triphenyl methanol as it is sufficiently stable towards the action of heat and won't decompose.

e) Overcooling the phenylmagnesium bromide (Grignard reagent) might prevent its complete conversion to product thereby decreasing the yield.

Presence of NaCl does not decrease the yield of the reaction as it does not react with any of the reactants nor the product. So presence of NaCl will not reduce the yield.