Hydrolysis of acetals, mercaptals, ketals, and orthoesters

Acetals, ketals, and mercaptals are excellently suited for masking of carbonyl groups. The carbonyl group that is masked as acetal is particularly readily regenerated after the compound has undergone the desired reaction. 

Hydrolysis of acetals is also important because unsaturated aldehydes are often prepared by way of their acetals and because aldehydes often arise as products of, e.g., Grignard syntheses. In general, acetals are smoothly hydro- 

Phenylpropiolaldehyde is obtained in 70-81 % yield from its diethyl acetal by heating the latter in approximately 12% sulfuric acid on a water-bath for 30 min with occasional shaking.80 

Glyceraldehyde diethyl acetal is cleaved to glyceraldehyde in 80% yield when shaken with O.In sulfuric acid for 7 days at 20°.81 

Most ketals are hydrolysed instantaneously by very dilute acid. Cyclic acetals and ketals are relatively stable, as are acetals of aldehydes containing basic groups. Hydrolysis of the last-mentioned class may lead to aldol condensation or formation of the Schiff base, so that concentrated acids are used in such cases. 

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