Formation of Hemiacetals under Acid and Basic Conditions

​
Acid catalyzed formation of a hemiacetal
Base catalyzed
Loss of proton
Nucleophilic attack
Proton transfer
Acid catalyzed
Proton transfer (alcohol)
Proton transfer (aldehyde)
Nucleophilic attack
Loss of proton
Reaction progress
Focus on functional groups
This Demonstration shows a typical nucleophilic addition with aldehydes or ketones. Both compounds have a carbonyl group (
>C=O
) and the oxygen atom is electronegative. Reaction can takes place in both acid and basic solutions by different mechanisms. Either can be selected by the
catalysistype
control. If an ion is formed and an excess of charge is present, a colored shadow helps to identify the charge and its center; a purple shadow indicates an excess of positive charge, while a green one indicates an excess of negative charge.
In
basecatalyzed
(
-
0
-R
, framed means acts only as catalyst not being consumed nor produced) it is possible to choose between one of the three stages of this reaction.
In
Acidcatalyzed
(
R-
+
OH
2
, framed means acts only as catalyst not being consumed nor produced) it's possible to choose between one of the four stages of this reaction.
You visualize functional groups with the last control.
The reaction summaries help to schematize the overall reaction and the animated arrows show how electrons move in the reaction.

Details

Snapshot 1: first step of the basic catalysis: a hydrogen is removed from the alcohol by the base, forming an anion (nucleophile).
Snapshot 2: second step of the basic catalysis: a nucleophile attack between the anion and the aldehyde.
Snapshot 3: final step of the basic catalysis: a proton is lost to obtain the hemiacetal.
References:
[1] Addizioni nucleofile ai chetoni https://www.youtube.com/watch?v=dKQLBPJ8Jew&list=PLswwssc6Q2ybl1IVEY56LVc16XsDKzFr-&index=48
[2] Hydrates, Hemiacetals, and Acetals https://www.masterorganicchemistry.com/2010/05/28/acetals-hemiacetals-hydrates/

External Links

Methyl Acetate Synthesis Using a Reactive Distillation Unit

Permanent Citation

D. Meliga, V. Giambrone, L. Lavagnino, S. Z. Lavagnino, F. Calcagno
​
​"Formation of Hemiacetals under Acid and Basic Conditions"​
​http://demonstrations.wolfram.com/FormationOfHemiacetalsUnderAcidAndBasicConditions/​
​Wolfram Demonstrations Project​
​Published: January 1, 1999