Formation of the N-Iodopyridinium Cation in an Alkane Environment. Mid-Infrared Linear Dichroism Investigation of the Pyridine-Iodine System in Stretched Polyethylene.
Dept. Life Sciences and Chemistry, Roskilde University (RUC), Universitetsvej 1, Roskilde DK-4000, Denmark
It is well known that pyridine (py) and iodine (I2) form a 1:1 molecular complex, py-I2. Within the framework of a student project at Roskilde University , we have recently investigated the formation and mid-infrared linear dichroism of the complex in a stretched polyethylene matrix. However, the observed spectra displayed not only the expected transitions due to py and py-I2, but also a third, prominent series of sharp transitions, evidently due to at least one additional product. On the basis of a comparison with literature spectra, these transitions can be assigned to the N-iodopyridinium cation, pyI+. This assignment is consistent with the observed polarization data.
Ionic side reactions such as py-I2 → pyI+ + I-, etc., are easily observed in binary pyridine-iodine mixtures and in polar solvents, but not so easily in non-polar media. We are thus surprised to see the apparent efficiency with which the pyI+ cation is formed in a non-polar medium like polyethylene. With excess iodine, the peaks assigned to pyI+ dominate the observed mid-infrared spectrum (see below). We suspect that a driving force for the ionic reaction is the formation of polyiodide anions in the channels of the polymer medium. Further investigation of the phenomenon is in progress.
 H. S. van Deurs, M. L. M. Espersen, R. Nissen, M. H. Rasmussen, C. J. S. Schönbeck, Student Project Report, Roskilde University, June 2006 (in Danish).
Presentation: oral at 18th Conference on Physical Organic Chemistry, Symposium 2, by Jens Spanget-Larsen
See On-line Journal of 18th Conference on Physical Organic Chemistry
Submitted: 2006-05-24 11:32 Revised: 2009-06-07 00:44
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