title: Unusual behavior in the reactivity of 5-substituted-1H-tetrazoles in a resistively heated microreactor.
abstract: The decomposition of 5-benzhydryl-1H-tetrazole in an N-methyl-2-pyrrolidone/acetic acid/water mixture was investigated under a variety of high-temperature reaction conditions. Employing a sealed Pyrex glass vial and batch microwave conditions at 240 °C, the tetrazole is comparatively stable and complete decomposition to diphenylmethane requires more than 8 h. Similar kinetic data were obtained in conductively heated flow devices with either stainless steel or Hastelloy coils in the same temperature region. In contrast, in a flow instrument that utilizes direct electric resistance heating of the reactor coil, tetrazole decomposition was dramatically accelerated with rate constants increased by two orders of magnitude. When 5-benzhydryl-1H-tetrazole was exposed to 220 °C in this type of flow reactor, decomposition to diphenylmethane was complete within 10 min. The mechanism and kinetic parameters of tetrazole decomposition under a variety of reaction conditions were investigated. A number of possible explanations for these highly unusual rate accelerations are presented. In addition, general aspects of reactor degradation, corrosion and contamination effects of importance to continuous flow chemistry are discussed.
authors.affiliation: Christian Doppler Laboratory for Microwave Chemistry (CDLMC) and Institute of Chemistry, Karl-Franzens-University Graz, Heinrichstrasse 28, A-8010 Graz, Austria.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Gutmann
authors.forename: Toma N
authors.initials: TN
authors.lastname: Glasnov
authors.forename: Tahseen
authors.initials: T
authors.lastname: Razzaq
authors.forename: Walter
authors.initials: W
authors.lastname: Goessler
authors.forename: Dominique M
authors.initials: DM
authors.lastname: Roberge
authors.forename: C Oliver
authors.initials: CO
authors.lastname: Kappe