Polarographic Characteristics of Chloro Complexes of +5 Antimony

Abstract

Vol. 60 methylammonium salt is 3.26 X low5. The weakest of the substituted salts is choline (hydroxyethyltrimethylammonium) picrate, whose constant is 0.66 X while the strongest salt is methoxymet hyltrimethylammonium picrate (K = 2.54 X an isomer of the choline salt. The two isomeric ions have the same conductance but one contains the weakly polar methoxy group, the other, the strongly polar hydroxyl group.Bromomethyltrimethylammonium picrate is a markedly weaker electrolyte than the corresponding bromoethyl salt (K = 0.78 X and 1.32 X Evidently, the effect is the greater, the nearer the substituent lies to the central charge on the nitrogen atom. Larger dissociation constants result with substitution of larger atoma, as, for example, the bromomethyl derivative is weaker than the corresponding iodomethyl compound. The arsenocholine salt is stronger than the choline salt but the corresponding salt of acetylcholine is stronger than that of acetylarsenocholine.In what rnanner the electronegative atoms or groups in the onium ions act in order to reduce the values of the dissociation constant of the ion-pair equilibrium is somewhat uncertain as yet. In the case of choline, hydrogen bonding with the negative ion might be suspected through the intermediation of the hydrogen of the hydroxyl group. That such hydrogen bonding occurs in the case of unsubstituted and partially substituted ammonium ions in nitrobenzene is well established.6 However, the halogens, when introduced into the onium ions, have much the same effect as has the hydroxyl group It seems unlikely that the observed effect may be accounted for on the basis of hydrogen bonding. respectively). (6) Witschonki!, Thesis, Brown University, 1941.The introduction of a negative element or group serves to introduce an electrical dipole into the ion. It is conceivable that interaction occurs between the ions and the dipoles. Perhaps the greatest objection to the dipole interpretation is the fact that the nearer the substituent atom lies to the charge on the nitrogen atom, the greater is its effect. Thus, the constant of the bromoethyl derivative is 1.32 X lov5, while that of the bromomethyl derivative is 0.78 X loF6. If dipole interaction is a controlling factor, we should expect the effect to be the greater the more exposed the position of the dipole.On the basis of the available experimental results, it seems more reasonable to ascribe the effect of electronegative elements to a displacement of the center of charge in the ion. This accords with the fact that the effect is the greater, the nearer the negative atom, or group, lies to the nitrogen atom.V. Summary 1. The conductance of the following picrates has been measured in ethylene chloride a t 25': ethyltrimethylammonium, choline, acetylcholine, arsenocholine, acetylarsenocholine, bromoethyltrimethylammonium, bromomethyltrimethylarnmonium, iodomethyltrimethylammonium, and methoxymethyltrimethylammonium.2. Values of A. and of K (dissociation constant) were obtained for all salts by the method of Fuoss.3. The dis...

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“…Received by editor June23,1967 Submitted for publication July31, 1967 Downloaded by [McMaster University] at 11:20 18 February 2015…”

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