2005
DOI: 10.1002/ejoc.200400434
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Protonation Sites of Indoles and Benzoylindoles

Abstract: Indomethacine (1) and acemethacine (2) contain the substituents -OCH 3 , -CH 2 COOH, -CH 2 COOCH 2 COOH, C-indole and O-benzoyl, which are susceptible to protonation in highly acidic media. To determine the protonation sites and the substituent effects reliably, the dissociation constants of the set of structurally related compounds 1-benzoyl-3-methylindole (3), 1-benzoyl-5-methoxyindole (4), 1-benzoylindole (5), 5-methoxy-2-methylindole (6), (2-methylindol-3-yl)acetic acid (7) and (5-methoxy-2-methylindol-3-y… Show more

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Cited by 16 publications
(21 citation statements)
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“…To the contrary, when H 2 L + has the positive charge buried in a small and not very polarizable molecule, solvation is greater than that of H 2 L m* Ͻ 1. [17] This data is consistent with the molecular volumes of the studied β-diketones.…”
Section: β-Diketones Studiessupporting
confidence: 87%
See 1 more Smart Citation
“…To the contrary, when H 2 L + has the positive charge buried in a small and not very polarizable molecule, solvation is greater than that of H 2 L m* Ͻ 1. [17] This data is consistent with the molecular volumes of the studied β-diketones.…”
Section: β-Diketones Studiessupporting
confidence: 87%
“…The m* (solvation coefficient) [17] values reported in this work are lower than 1.0 for L1 and L3 and are higher than or equal to 1.40 for other compounds. The m* values for indoles (1.3), amides (0.5-0.6), and tertiary aromatic amines (1.4) along with the difference in the m* values for C protonation (ca.…”
Section: β-Diketones Studiesmentioning
confidence: 53%
“…1). In the literature, there are no univocal p K IH values on the protonation equilibrium of indole, which varies from −3.5 to −2.2 (see Table I) 21–24. Such an inconsistency is due to the different activity coefficient functions employed in the calculation, suggesting that the nature of the process is not completely explained 16,23.…”
Section: Resultsmentioning
confidence: 98%
“…In the literature, there are no univocal p K IH values on the protonation equilibrium of indole, which varies from −3.5 to −2.2 (see Table I) 21–24. Such an inconsistency is due to the different activity coefficient functions employed in the calculation, suggesting that the nature of the process is not completely explained 16,23. In this paper, we use the more recent approach of the Mc activity coefficient function for sulfuric acid, which gives a p K IH value of −2.4 25, which is in good agreement with those reported in Andonowski and Garcia papers 23,24.…”
Section: Resultsmentioning
confidence: 99%
“…Figure 3 shows the Van't Hoff plot of dimerization and trimerization equilibrium constants in the range 288-318 K. It is interesting to observe that ΔH of reaction of dimer and trimer formation (À24 and À37 kJ mol -1 , respectively) is compatible with literature data. [52] On the contrary, the large difference of ΔS (28 and À65 J mol À1 K, respectively) between dimer and trimer is not easily explainable especially because dimerization shows a positive ΔS, although there is a reduction of mole numbers, which is, from thermodynamic point of view, not a common behaviour. As a matter of fact, this positive value in the variation of entropy observed for the dimerization equilibrium can be ascribed to the large variation of entropy observed in the protonation equilibrium of indole, which is responsible for the large decrease of the global entropy of the reaction.…”
Section: Dimerization and Trimerization Equilibria Of Indolementioning
confidence: 94%