Organic Chemistry 2

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Aldehyde Transformations XI


An alternative method to transform aldehydes/ketones into the corresponding acetals involves treatment with orthoformates ($HC(OR)_3$) and an acid catalyst at room temperature. An example of this reaction is depicted below.

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This reaction process is exothermic ($ΔH$ = -3.0 kcal/mol).

What is the most likely thermodynamic driving force for this reaction?


The byproduct, ethyl formate, is a gas at room temperature and leaves the system as it forms. The reaction is driven to completion by Le Châtelier's principle.


The carbonyl group of ethyl formate is an ester and thus highly stabilized by resonance interaction with the lone pairs of the OEt group. The starting aldehyde/ketone lacks this strong resonance stabilization.


Acetal formation is generally a thermodynamically favorable process, and triethyl orthoformate is merely another reagent for accomplishing this thermodynamically favorable process.


Acetal formation transforms the group on the benzene ring from an electron-withdrawing group into an electron-donating group.