Abstract
In order to evaluate the influence of substituents in position 5 of indole and in the para position of phenyl on the stability of 2-ethoxycarbonylindole-3-indolyphenylmethyl cations (IPMCs) we have experimentally determined by a spectrophotometric method the values of the acidity constants (pKR+) of the IPMCs in H2SO4 solutions. The IPMCs were generated from 3-(α-chlorobenzyl)-2-ethoxycarbonylindoles by dissolving them in sulfuric acid with a concentration of 55–93%. Two reaction series were studied. In the first, the correlation equation pKR+ = −5.18σ −10.5 was obtained for substituents in the para position of the phenyl ring. In the second series we evaluated the influence of substituents in position 5 of the indole ring: pKR+ = −2.6σ −11.3. The lower influence of substituents on the stability of the IMPCs from position 5 as compared with the para position of the phenyl ring is due to the delocalization of the charge in the heterocycle of the indole system. It was established that in sulfuric acid solutions di(2-ethoxycarbonylindol-3-yl)phenylmethanes dissociate with the formation of IMPCs and 2-ethoxycarbonylindoles.
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