Isomerization and Fragmentation of Cyclohexanone in a Heated Micro-Reactor

Area of Science:

• Chemical Kinetics
• Physical Chemistry
• Organic Chemistry

Background:

• Cyclohexanone (C6H10═O) is a cyclic ketone whose thermal decomposition is not fully understood.
• Investigating decomposition pathways provides insight into fundamental chemical reactions at high temperatures.

Purpose of the Study:

• To elucidate the thermal decomposition mechanisms of cyclohexanone.
• To identify and quantify the pyrolysis products of cyclohexanone.
• To determine the energetics of key reaction intermediates and products.

Main Methods:

• Flash pyrolysis in microreactors at 1200 K.
• Tunable vacuum ultraviolet (VUV) photoionization mass spectrometry for product detection and identification.
• Photoionization appearance thresholds and matrix infrared absorption spectroscopy for complementary identification.
• Coupled cluster electronic structure calculations for energetic analysis.

Main Results:

• Cyclohexanone decomposition proceeds via simultaneous competing pathways, including isomerization to cyclohexen-1-ol (C6H9OH).
• Retro-Diels-Alder cleavage yields ethylene and a reactive enol intermediate, which can isomerize to methyl vinyl ketone (MVK).
• Heats of formation for MVK and its enol were calculated, and reaction enthalpies for decomposition pathways were determined.

Conclusions:

• The thermal decomposition of cyclohexanone is a complex process involving multiple simultaneous reaction channels.
• Experimental and computational methods successfully identified key intermediates and products, providing thermodynamic data.
• The study contributes to a deeper understanding of high-temperature organic reaction mechanisms.