Charge-transfer complexes pyridine-halogen

Aloisi, G., Beggiato, G. and Mazzucato, U. (1970) Charge transfer complexes between halogens and pyridines. 4. Effect of the acid strength of the acceptors. Trans. Faraday Soc., 66, 3075-3080. 

The general trend is to increase the selectivity of the addition. Selectivity is often increased by substituting pyridine-halogen charge transfer complexes or tribromides of organic bases for the free halogens. Instead of pyridine an insoluble polymer can be applied. Although the rate of reaction is lower compared to the almost instantaneous reaction of free bromine, this technique facilitates isolation and purification of the product. ... 

McKinney, W.J. and Popov, A.I. (1969) Studies on the Chemistry of halogens and of poly-haUdes. XXX. Influence of solvent properties on the formation of pyridine-iodine charge-transfer complexes. J. Am. Chem. Soc., 91, 5215-5218. 

Energy parameters and charge-transfer spectra of complexes of Br2 with several substituted pyridines have now been compared with the force constants k(Br—Br) and k(N- Br2) and with the properties of the donors. The complexes with orr/to-substituted pyridines show systematic deviations from the relations found to be valid for the other donors. The n.m.r. spectrum of the pyridine-Br2 complex in a nematic phase has been obtained and analysed. The results indicate that the donor-acceptor interaction is similar to that found in the solid state for other halogen-pyridine complexes. The equilibrium constant for the formation of the 1 1 complex of Br2 with hexamethyl-phosphortriamide (HMPA) has been determined by n.m.r. spectroscopy. Solid adducts of Br2 with poly-HMPA could also be prepared. 

Beggiato, G., Aloisi, G.G. and Mazzucato, U. (1974) Charge transfer interactions of heteroaromatic compounds. 5. Complexes between pyridine 1-oxides and halogens. 7. Chem. Soc., Faraday Trans. 1, 70, 628-634. 

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