Acetalisation

Acetal ( acetalization) is a chemical reaction with the acetal formed. They can be done in different ways. Is known mainly the formation of aldehydes.

General presentation

This reaction is a true equilibrium reaction, that is, the equilibrium can be both far to the right, and far to the left. The equilibrium position can be changed by manipulation of the reaction conditions. The water formed can be continuously removed from the reaction mixture (e.g., by distillation) or alcohol is added in excess.

Addition reaction of aldehydes

In the analogous reaction with ketones arise ketals; with diols or polyols to form cyclic acetals, such as the isopropylidene ( Solketal ) from acetone and glycerol:

Reaction mechanism

Hemiacetal

First protonation of the carbonyl group of an aldehyde or alkanal:

2 Nucleophilic attack of the hydroxy group

3 loss of a proton ( recovery of the catalyst ):

Acetal

First protonation of the hydroxyl group of the hemiacetal:

2 elimination of water (H2O):

3 Nucleophilic attack

4 elimination of a proton:

Addition reaction of ketones

Also from ketones ( alkanones ) acetals can be formed, this reaction, however, is slower than with aldehydes or alkanals. The ketal formation is analogous to the acetal.

Acetals as protecting groups

In the conversion of an aldehyde or ketone to an acetal, the reactive carbonyl group is converted to a relatively inert etherähnliche unit. Since the acetal formation is reversible, makes you look in this synthesis being used to protect carbonyl groups before implementation.

• Chemical Reaction