Addition of alcohols. Acetal formation

Aldehydes and ketones react with two equivalents of alcohol to form acetals. In an acetal, the carbonyl carbon from the aldehyde or ketone is now singly bonded to two OR (alkoxy) groups. 

This reaction differs from other additions we have seen thus far, because two equivalents of alcohol are added to the carbonyl group, and two new C-O o bonds are formed. Acetal formation is catalyzed by acids, commonly p-toluenesulfonic acid (TsOH). 

When a diol such as ethylene glycol is used in place of two equivalents of ROH, a cyclic acetal is formed. Both oxygen atoms in the cyclic acetal come from the diol. 

A Dean-Stark trap is an apparatus used for removing water from a reaction mixture. To 

The carbonyl compound, an alcohol, and an acid are dissolved in benzene. As the mixture is heated, the carbonyl compound is converted to the acetal with water as a by-product. Benzene and water co-distill from the reaction mixture. When the hot vapors reach the cold condenser, they condense, forming a liquid that then collects in the glass tube below. Water, the more dense liquid, forms the lower layer, so that as it collects, it can be drained through the stopcock into a flask. In this way, water can be removed from a reaction mixture, driving the equilibrium. 

Dean-Stark trap to convert a carbonyl compound to an acetal  

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I NtKl ophilic Addition of Alcohols Acetal formation... 

Addition of alcohols— Acetal formation Acetals as protecting groups... 

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