Why would it be difficult to monitor the hydrolysis of the dimethyl ketal of ace
ID: 496823 • Letter: W
Question
Why would it be difficult to monitor the hydrolysis of the dimethyl ketal of acetone by TLC? There are two answers. The reaction to hydrolyze the dimethyl acetal of benzaldehyde, methanol is one of the products. However, it is not seen in the NMR. Suggest one reason to explain this. PhCH(OCH_3)_2 + A-15 + water + acetone rightarrow PHCHO + CH_3 OH Synthesizing the diphenyl acetal from benzaldehyde and phenol is a slow reaction compared to the formation of many acetals. Suggest a reason for this.Explanation / Answer
15. In the reaction acetone is used as a solvent, thus the reaction becomes completely reversible. Any hydrolysis results into methanol formation which combines with acetone present to give back the dimethylacetal.
thus making it difficult to follow by tlc.
16. Methanol formed as one of the products immediately reacts with acetone and forms dimethylketal as one of the products. Thus released methanol is not free to be seen in the NMR.
17. The nucleophilicity of phenol oxygen is lower than the nucelophilicity of methanol oxygen. In phenol the benzene ring pulls the electron towards itself which makes the oxygen less electron-rich in nature.
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