Mechanistic investigations on Pinnick oxidation: a density functional theory study

Area of Science:

• Organic Chemistry
• Computational Chemistry

Background:

• The Pinnick oxidation is a key method for converting aldehydes to carboxylic acids.
• Understanding the reaction mechanism is crucial for optimizing synthetic routes.

Purpose of the Study:

• To elucidate the detailed reaction mechanism of the Pinnick oxidation of aldehydes.
• To investigate the role of acid catalysis in the reaction using computational methods.

Main Methods:

• Density Functional Theory (DFT) calculations at the (SMD)-M06-2X/aug-pVDZ level.
• Analysis of transition states, intermediates, and reaction energetics.
• Supporting computational techniques including intrinsic reaction coordinate and molecular dynamics.

Main Results:

• The reaction proceeds via a six-membered ring transition state in the first step (FRS), forming a hydroxyallyl chlorite intermediate.
• The second reaction step (SRS) involves pericyclic fragmentation to yield the carboxylic acid.
• The FRS is rate-determining and thermoneutral, while SRS is highly exergonic with a low barrier.
• Hydrogen bonding between carbonyl and tert-butanol was found to be unlikely.

Conclusions:

• The computational study provides a detailed mechanistic understanding of the Pinnick oxidation, consistent with experimental data.
• The proposed mechanism highlights the critical role of acid in facilitating the aldehyde oxidation process.
• The findings offer insights into optimizing the Pinnick oxidation for efficient carboxylic acid synthesis.