2706 Sharma
Asian J. Chem.
3. S. Kajigaeshi, T. Kakinami, M. Shimizu, M. Takahashi, S. Fujisaki
and T. Okamoto, Tech. Rep. Yamaguchi Univ., 4, 139 (1988).
4. S. Mitra and K. Sreekumar, Indian J. Chem., 36B, 133 (1997).
5. V.S. Chouhan and V. Sharma, Int. J. Chem. Sci., 1, 341 (2003).
6. V.S. Chouhan and V. Sharma, J. Indian Chem. Soc., 82, 302 (2005).
7. V.S. Chouhan, M. Sharma and V. Sharma, J. Indian Chem. Soc., 84,
582 (2007).
data, it is not possible to state definitely about the nature of
the complex. Heasley and co-workers22 have postulated the
formation of an intermediate π-complex in the reaction of
alkenes with pyridinium hydrobromide perbromide. The
formation of similar complexes has also been postulated in
the oxidation of aldehydes23 and diols24 with hexamethylene-
tetramine-bromine as well as in the oxidation of alcohols25
and organic acids26 by pyridinium hydrobromide perbromide.
The formation of moderately stable complexes is supported
by the values of thermodynamic parameters also. The complex
formation is favoured by the enthalpy term but there is a loss
of entropy indicating the formation of a rigid structure.
The large negative reaction constant and a substantial
deuterium kinetic isotope effect suggest a considerable carbo-
cation character in the transition state. Therefore, the following
mechanism (Scheme-I) involving transfer of a hydride ion
from the alcohol to the oxidant, in the rate-determining step, is
suggested.
8. V. Tiwari, A. Meena, A. Daiya, P.T.S.R.K. Prasadrao and V. Sharma,
Proc. React. Kinet. Mech., 37, 263 (2012).
9. M. Baghmar and P.K. Sharma, Int. J. Chem. Kinet., 33, 390 (2001).
10. J. Gosain and P.K. Sharma, J. Indian Chem. Soc., 79, 815 (2002); Proc.
Indian Acad. Sci. Chem. Sci., 115, 135 (2003).
11. P.K. Sharma, J. Indian Chem. Soc., 81, 291 (2004).
12. N.S. Srinivasan and N. Venkatasubramanian, Tetrahedron, 30, 419
(1974).
13. D.D. Perrin, W.L. Armarego and D.R. Perrin, Purification of Organic
Compounds, Pergamon; Oxford (1966).
14. L. Liu and Q.-X. Guo, Chem. Rev., 101, 673 (2001).
15. O. Exner, Collect. Czech. Chem. Commun., 29, 1094 (1964).
16. V.S.R. Raju, P.K. Sharma and K.K. Banerji, Indian J. Chem., 39A, 650
(2000).
17. P. Aukett and I.R.L. Barker, J. Chem. Soc., Perkin Trans. 2, 568 (1972).
18. A.H. Fainberg and S. Winstein, J. Am. Chem. Soc., 78, 2770 (1956).
19. K.B. Wiberg, Physical Organic Chemistry, Wiley, New York; p. 414
(1963).
The observed negative entropy of activation also supports
it.As the charge separation takes place, the charged ends become
highly solvated. This results in an immobilization of a large
number of solvent molecules, reflected in the loss of entropy27.
20. O. Exner, Prog. Phys. Org. Chem., 10, 411 (1973).
21. W.A. Pavelich and R.W. Taft Jr., J. Am. Chem. Soc., 79, 4935 (1957).
22. V.L. Heasley, T.J. Louie, D.K. Luttrul, M.D. Miller, H.B. Moore, D.F.
Nogales, A.M. Sauerbrey, A.B. Shevel, T.Y. Shibuya, M.S. Stanley,
D.F. Shellhamer and G.E. Heasely, J. Org. Chem., 53, 2199 (1988).
23. A. Pareek, S. Varshney and K.K. Banerji, React. Kinet. Catal. Lett.,
60, 127 (1997).
ACKNOWLEDGEMENTS
Thanks are due to UGC, New Delhi for financial support
in the form of BSR-One Time Grant No. F. 4 - 10/2010 (BSR)
dated 07.03.2012.
24. H. Gangwani, P.K. Sharma and K.K. Banerji, J. Chem. Res. (S), 180
(1999).
25. D. Mathur, P.K. Sharma and K.K. Banerji, J. Chem. Soc., Perkin Trans.
II, 205 (1993).
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