On the Solid-State Isomerization of Terpinolene Tetrabromide
Paul V. Bernhardt A B , Raymond M. Carman A and Tri T. Le AA School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, Qld 4072, Australia.
B Corresponding author. Email: p.bernhardt@uq.edu.au
Australian Journal of Chemistry 63(3) 458-462 https://doi.org/10.1071/CH09606
Submitted: 24 November 2009 Accepted: 16 January 2010 Published: 26 March 2010
Abstract
The isomerization of terpinolene tetrabromide from the cis-2,4- (diaxial) dibromo isomer (A) to the more stable trans-2,4- (equatorial–axial) compound (B) has been investigated in the solid state. The progress of the solid-state reaction as a function of time was followed by solution NMR analysis, and, more effectively, by micropowder X-ray diffraction of the bulk material in situ. Characterization of the solid-state reaction mixture is facilitated by the existence of X-ray crystal structures of both compounds A (monoclinic) and B (reported previously) in addition to a new triclinic polymorph of compound A reported herein, all three forms being observed by powder X-ray diffraction.
Acknowledgements
R.M.C. thanks Dr James De Voss for providing office and laboratory space and Dr Joanne Blanchfield and the De Voss research students for helpful practical assistance.
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# According to his MSc dissertation, Owen heated one of his preparations of terpinolene tetrabromide on a water bath to remove excess bromine, but then obtained compound B (‘β’). He also reports that an old comparison sample available in the Sutherland laboratory, although still crystalline, was ‘much decomposed’, and afforded compound B (‘β’) on recrystallization. It is not clear in his work how Owen distinguished his α compound, mp 116–117.5°C (now known to be compound A) from his β isomer (compound B), mp 117–118°C.
