Understanding the Aldol Condensation: Heat & Base Identity

[SaintJude]

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2 Q:

1. How does heat actually drive the reaction forward to favor an aldol condensation reaction? Is the aldol condensation an endothermic process?

2. In addition to heat, we need a strong base for the condensation reaction to occur. Is this base relatively stronger or weaker than the first base used to deprotonate the original aldehyde?

 

[chiddler]

1. I think the heat is to dehydrate it and produce the alkene rather than the ketone-alcohol. Since entropy is decreasing (two molecules become one), the reaction should be exothermic.

2. ? you only need base to deprotonate the first proton. catalytic alcohol works too. whatever drives formation of an enol.

 

[SaintJude]

Is the acidity of the alpha hydrogen in the original aldehyde the same as acidity of alpha hydrogen in aldol?

 

[chiddler]

That becomes a question of inductive effect. Try to answer it yourself.

What happens to acidity of acetic acid as we fluorinate it, adding EWG? (ie, TFA)

What happens as we add more alkylation, adding EDG? (ie, propanoic acid)

Compared to the original aldehyde or ketone, what changes when it becomes an aldol? Should this change grant more or less acidity?

 

[SaintJude]

Less acidic, & then we'll need a stronger base! Thanks for making it instructive actually.

 

[chiddler]

To convert the aldol into an alkene, you just remove water from reaction since it is an equilibrium and water is on product side. A second base is unnecessary.