451. The kinetics of halogen addition to unsaturated compounds. Part XVIII. Iodine addition

Abstract

This is a general revision of the kinetics of iodine addition, w i t h a note on the equilibria in The rate of iodine addition over the concentration range that can be measured these reactions. is given by the expression the first term being chiefly operative in solvents such a s chlorobenzene, carbon tetrachloride, and carbon disulphide, and the second term in isobutyl ether, acetic acid, and nitrobenzene solutions. With certain aromatic compounds such as styrene and its derivatives iodine addition is accompanied by polymensation.AN earlier investigation on the kinetics of iodine addition (Bythell and Robertson, I., 1938, 173) established that these reactions, like the corresponding bromine and iodine chloride additions, showed third-order kinetics, with a small temperature coefficient in acetic acid and nitrobenzene solutions. Erroneous theoretical conclusions, however, were made from the measurements in carbon tetrachloride solution, chiefly as a result of confining the observations to a single compound, ally1 alcohol, the behaviour of which is now found to be anomalous. In the meantime several communications on the kinetics of iodine addition have appeared. Bhattacharyya and Rao ( J . Indian Chem. Soc., 1941, 18, 253), using 2-pentene and phenylacetylene as reactants, found third-order kinetics for iodine addition in acetic acid and ethyl alcohol solutions. Ghosh et al. (ibid., p. 245) state that iodine addition in carbon tetrachloride, carbon disulphide, and benzene solutions proceeds by a fourth-order mechanism. These observers, following Groh and Szelestey (2. anmg. Chem., 1927, 162, 333), who had previously investigated erucic acid in carbon tetrachloride and carbon disulphide and found f ourth-order kinetics, employed an elaborate formula, derived from the integration of the expression, -d[IJ/dt = k,[A][IJ3 -h,[AII][I2]2, and obtaining constant K, coefficients for p-amylene and pinene, concluded that the reaction proceeds, A + I,We, on the other hand, have followed the simpler procedure of adjusting the concentrations with one reactant A in excess, to reduce the effect of the reverse reaction, and have evaluated the reaction order by measurements a t different initial concentrations. To obtain the relative contributions of A and I, to the total reaction order, use was made of the formula : A11 +-21,. t,/t, = (c,/c,)"-* (G'"")":where t , and t, are the times of an equal fractional change of iodine addition, with concentrations cI and c2 for I,, and c' and c" for A, n being the order for I, and n' for A. The proposed formula holds only for the initial stages of the reaction, to -10% iodine addition, over which range, as is found experimentally, the yo addition-time curves are approximately straight lines.Employing this formula, we have established that in polar solvents, e.g., acetic acid, isobutyl ether, chloroform, chlorobenzene, and nitrobenzene, the reaction order for the organic compound (A) is unity ; in the non-polar solvents carbon tetrachloride and carbon disulphide, on the other hand, the v...

Mapping the Interactions of I2, I., I−, and I+ with Alkynes and Their Roles in Iodocyclizations

“…Following complex formation, Paths B–D differ in respect of which species attacks complex B . In Path B, B reacts with a second molecule of I 2 ( TSB ) to give ion pair [ A ]I 3 , which then gives diiodoalkene 14 b plus I 2 19. In Path C, complex B reacts with I − ( TSC ) to give diiodoalkene 14 b plus I − .…”

Reversible and Irreversible Chemisorption in Nonporous‐Crystalline Hybrids

“…The subtle structural change in the organic molecules resulted in a significantly longer half-life of 72 h for 3-2 I 2 -an increase of a factor of 22 from that of 2-2 I 2 and of a factor of 112 from the solution-state value. The solution-state half-lives of BEA-I 2 and PEA-I 2 are comparable; [12] therefore, solid-state packing effects, particularly iodine-iodine interactions, are likely to stabilize the molecules. Solid-state interactions in crystals have been used to isolate metastable molecules.…”

An Improved Synthesis of β-Iodo Ethers and Iodohydrins from Alkenes

“…According to the literature a metal salt would be necessary to perform this decomposition. 4a, 9 It should be also mentioned that in terms of kinetics, iodine addition to an alkene is not a simple process, 10 with the order of reaction varying tremendously with the nature of the solvent. On the other hand, the absence of diiodoalkane in this reaction could be explained by the low nucleophilicity of the triiodide ion.…”