The Perkin reaction gives an α,β-unsaturated aromatic acid by the aldol condensation of an aromatic aldehyde and an acid anhydride, in the presence of an alkali salt of the acid. Here is an a diagram showing what the reaction does

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The anion of the salt acts as a base for abstracting the β-hydrogen in the acid anhydride. Later it attacks the carbonyl carbon of an intermediate but however leaves in the same step. Since the base is not ultimately involved in the product, is there any kinetic or thermodynamic reason as to why the salt of the acid of the acid anhydride is preferred over any other base?

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    $\begingroup$ To prevent side reactions. $\endgroup$ Aug 18 '18 at 15:17
  • $\begingroup$ Can you give an example? I think since the base is not involved in the product, different bases can only give different side product but the major product will be the same? Is this correct? $\endgroup$ Aug 18 '18 at 15:21
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    $\begingroup$ I was thinking about nucleophilic attack between the base and acid anhydride. Choosing the base to be the conjugate base corresponding to the acid anhydride negates this issue because then the acid anhydride reforms upon reaction. But this paper suggests other bases may be used, so I will defer to actual organic chemists. $\endgroup$ Aug 18 '18 at 15:41

The base, as you pointed out is nearly always the salt of the acid corresponding to the annhydride.

This is because the base which differs in structure will react with the given carbonyl compound and yield some other compound rather that abstracting a proton.

Eg. Let's say you have tertbutyl salt there instead of what we are having right now.The tert butyl could have directly attacked on the Carbon having the double bonded oxygen as it has a partial positive charge due to polarization.Which will result in to eliminating the other symmetric half of the annhydride and replacing it by tertbutyl.This changed your basic reacting molecule.And hence the product you obtained is definitely not the right one. Whereas using the salt of the acid that formed the annhydride will not change the annhydride even if it reacts with the annhydride the way I stated above.

Using the salt of the acid they produced the annhydride does nothing but abstracts the proton or simply regenerate the original carbonyl compound/annhydride if it reacts rather than abstracting a proton.


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