Microwave Flash Pyrolysis

• Published in: Journal of organic chemistry 2009-06, Vol.74 (11), p.4137-4142
• Main Authors: Cho, Hee Yeon, Ajaz, Aida, Himali, Dibya, Waske, Prashant A, Johnson, Richard P
• Format: Article
• Language: English
• Subjects: Chemistry; Condensed benzenic and aromatic compounds; Exact sciences and technology; Free radicals chemistry; Graphite; Heating - methods; Hot Temperature; Methods; Microwaves; Nanotubes, Carbon; Organic Chemicals - chemistry; Organic chemistry; Organic Chemistry Phenomena; Preparations and properties; Reactivity and mechanisms; Vacuum
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo900245v

In a microwave reactor, graphite heats rapidly to high surface temperatures; applications of graphite thermal “sensitization” have been described previously. We report here that microwave thermal sensitization with graphite, carbon nanotubes, or silicon carbide can be used to carry out reactions more typically accomplished by flash vacuum pyrolysis (FVP) and which usually require temperatures much higher than the nominal limit of a microwave reactor. The graphite-sensitized microwave reaction of azulene in the solid phase at temperatures of 100 to 300 °C affords rapid rearrangement to naphthalene, a reaction typically observed by FVP at 700−900 °C. Multiwall carbon nanotubes give similar results when used as a thermal sensitizer. Other graphite-sensitized reactions that we have observed include the following: conversion of 2-ethynylbiphenyl to phenanthrene, fragmentation of phthalic anhydride to benzyne, cleavage of iodobenzene to phenyl radical, aryl−aryl bond cleavage, and a variety of cycloaromatizations. An advantage is seen for less volatile substrates. Rearrangement of azulene and generation of benzyne from phthalic anhydride have also been observed on powdered silicon carbide. Because of the high temperature, rapid heating, and frequent ejection of material from the irradiation zone, we refer to this general method as microwave flash pyrolysis (MFP).