摘要:
CHEMICAL COMMUNICATIONS, 1968 199 Competitive Alkali-metal Flame Reactions: Potassium Atoms with Ethyl Iodide, Cyclopentyl, and Cyclohexyl Chlorides By E. U. Elwovo~ and J. F. OJO (Department of Chemistry, University of Ibadalz, Nigeria) THE reactions of potassium atoms with mixtures of ethyl and cyclopentyl chloride and of ethyl iodide and cyclohexyl chloride pairs have been studied by the competitive method developed by Trotman- Dickenson, et aZ.1 A stream of the mixed organic halide vapours was carried into the Pyrex glass reaction chamber by pure nitrogen, as also were the potassium atoms. The reaction chamber was heated by mercury vapour and its temperature was maintained to within f0-2". The mixture of potassium iodide and potassium chloride formed was analysed conductometrically. The ethyl iodide-cyclopentyl chloride system was studied over the temperature range 199.0- 305-2" with reactant ratios, EtI : cyclo-C,H,Cl, between 0.68 and 2-88.The relative rate con- stants (k,/k,) for the system (1) K + EtI = KI + Et K + cyclo-C,H,Cl = KI + cyclo-C,H, (2) where cyclo-C,H, represents cyclopentyl radical, have been calculated for the 36 runs distributed over 25 groups of temperatures using the sameCHEMICAL COMMUNICATIONS, 1968 method as Trotman-Dickenson et aZ.1 The following relative Arrhenius parameters were obtained by the least-squares calculation using the IBM 1620 computer. E, - E, = 4652.6 & 186.3 cal./mole log A1/A, = 2.29 f 0.01 The ethyl iodide-cyclohexyl chloride pair repre- sented by K + EtI = KI + E t (1) K + CyC10-C6H11C1 = KC1 + CyClO-C6H11 (3) where cyclo-C6Hll refers to cyclohexyl radical, was studied between 216-0 and 298-8" with reactant ratios, EtI : cyc10-C6H,,C1, between 2-00 and 3.57.The following Arrhenius parameters calculated by the method of least squares were obtained from the relative rate constants (K1/k3) for 21 runs fairly evenly distributed over 18 temperature groups : El - E , = 4984.2 f 168.5 cal./mole log (A,/A,) = 2.74 f 0.01 From the results, the relative Arrhenius para- meters for the cyclopentykyclohexyl chlorides pair (2) and (3) can be calculated. Hence E, - E , = 331.6 &- 32=2cal./mole and log ( A , / A , ) = 0.45 & 0-00 The relative rate constant for this reaction (k2/k3) a t 246-8" is 2.05 which is in good agree- ment with the value of 2.16 obtained by Gowenlock et aLB for the reaction of sodium atoms with cyclopentyl and cyclohexyl bromides. The higher reactivity of the cyclopentanoid system can be explained in terms of the entropy factol-3p4 which is a consequence of the relief of internal strain in the transition state. The entropy effect more than compensates for the small but significantly greater activation energy for the cyclopentyl chloride than the cyclohexyl chloride reacti0ns.l 9536 (Received, Decenzber 13th, 1967; Cow. 1337.) J. A. Kerr, E. A. Lissi, and A. F. Trotman-Dickenson, J . Chem. SOC., 1964, 1673. B. G. Gowenlock and K. E. Thomas, J . Chem. SOC., 1962, 5068. R. P. Smith and H. Eyring, J . Amer. Chem. SOL, 1952,74, 229. C. K. Ingold, "Structure and Mechanism in Organic Chemistry", G. Bell, London, 1957, 3rd edn., pp. 410-412. E. U. Emovon and E. A. Lissi, J . Chem. Soc., 1964, 3609. A. F. Trotman-Dickenson and E. W. R. Steacie, J . Chem. Phys., 1951, 19, 329.
ISSN:0009-241X
DOI:10.1039/C19680000199
出版商:RSC
年代:1968
数据来源: RSC