Acetal protecting groups are commonly used in organic synthesis to protect carbonyl groups or alcohols from reacting with other reagents. In the case of selectively protecting primary alcohols in the presence of secondary alcohols, we can use a bulky acetal protecting group, such as di-tert-butylsilyl acetal, which will sterically hinder the secondary alcohol and favor the formation of acetal with the primary alcohol.Here is a step-by-step mechanism for the protection of a primary alcohol using di-tert-butylsilyl acetal:1. Protonation of the carbonyl oxygen of di-tert-butylsilyl acetal by a catalytic amount of an acid e.g., p-toluenesulfonic acid, TsOH to form an oxonium ion.2. Nucleophilic attack of the primary alcohol oxygen on the carbonyl carbon of the oxonium ion.3. Deprotonation of the alcohol oxygen by a base e.g., the conjugate base of the acid used in step 1 to form the hemiacetal intermediate.4. Protonation of the hydroxyl group of the hemiacetal intermediate by the acid.5. Intramolecular nucleophilic attack of the oxygen atom of the di-tert-butylsilyl group on the carbonyl carbon of the hemiacetal intermediate, forming a cyclic acetal and releasing water.6. Deprotonation of the oxygen atom of the cyclic acetal by the base to form the final protected primary alcohol.Example of a reaction that utilizes this strategy:Imagine we have a molecule with both primary and secondary alcohol groups, such as 1,2-propanediol. We want to selectively protect the primary alcohol at the 1-position and leave the secondary alcohol at the 2-position unprotected.1. Add di-tert-butylsilyl acetal and a catalytic amount of p-toluenesulfonic acid TsOH to a solution of 1,2-propanediol in an appropriate solvent e.g., dichloromethane .2. Stir the reaction mixture at room temperature for several hours.3. Monitor the reaction progress by thin-layer chromatography TLC or another analytical technique until the starting material is consumed.4. Quench the reaction by adding a base e.g., sodium bicarbonate to neutralize the acid.5. Purify the product by column chromatography or another purification technique to isolate the selectively protected primary alcohol.The product will be the 1-O-di-tert-butylsilyl acetal derivative of 1,2-propanediol, with the primary alcohol protected and the secondary alcohol still available for further reactions.