Russian Journal of General Chemistry, Vol. 71, No. 10, 2001, pp. 158131583. Translated from Zhurnal Obshchei Khimii, Vol. 71, No. 10, 2001, pp. 166931671. Original Russian Text Copyright C 2001 by Morozova, Kazakova, Mustafina, Konovalov.
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Dialkylaminomethylated Calix[4]resorcinarenes. Reaction with Carboxylic Acids Yu. E. Morozova, E. Kh. Kazakova, A. R. Mustafina, and A. I. Konovalov Arbuzov Institute of Organic and Physical Chemistry, Kazan Research Center, Russian Academy of Sciences, Kazan, Tatarstan, Russia Received June 26, 2000
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Abstract 5,11,17,23-Tetrakis(N,N-dimethylaminomethyl)-2,8,14,20-tetranonylcalix[4]resorcinolarene was found to form in solutions host3guest complexes with tartaric, phthalic, and succinic acids; the stability of the complexes depends on the degree of protonation of the host in the complex and the structure of the guest. Host3guest complexes are known to be formed by noncovalent interactions, such as ion3ion interactions, hydrogen bonds, p-stacking, and solvatophobic effects. Thus, Tanaka et al. [1] used NMR spectroscopy to show that the complex formation between nonfunctionalized calix[4]resorcinarene and dicarboxylic acids involves H bonding between two donor centers of the host and carboxyl protons of the guest 3O3H...O(H)3. In the present work we studied the complex-forming ability of 5,11,17,23-tetrakis(N,N-dimethylaminomethyl)-2,8,14,20-tetranonylcalix[4]resorcinarene (I) prepared by the procedure in [2] with respect to a series of carboxylic acids.
compound I is protonated to a lesser degree. As a result, its solubility in aqueous 2-propanol solutions of acetic, malonic, adipic, glutaric, and malic acids (cacid 0.02 M) proved rather low (cI < 0.001 M). However, the solubility of H8X in similar solutions of succinic (II), tartaric (III), and o-phthalic (IV) acids was found to be sufficient for pH-metry (cI ~0.003 M). For quantitative assessment of the interaction of organic acids with host I we applied pH-potentiometric titration, as the complex formation of protonated calixarene I with acid monoanion should affect the protonation constants of amino groups of the former [4]. Titration was performed at pH 632. In the course of titration, along with protonation of calixarene I [equlibria (1)3(4)], equilibrium (5) took place, whose constant was determined by the same method and comprised, in log. units, 4.5 (tartaric acid), 3.6 (phthalic acid), and 5.8 (succinic acid). 76 H X+, H8X + H+ 47 9 + + 76 H X + H 47 H X2+, 9
Earlier [2, 3] we studied the acid3base properties of compound I and found that in aqueous-organic media at pH < 7 hydrochloric acid protonates its amino nitrogen atoms, giving rise to cationic forms of the macrocycle. We proposed that polybasic organic acids, too, would protonate dimethylamino groups of compound I, and the resulting anion would play the role of the anionic guest with respect to the cationic form of the host. Naturally, carboxylic acids are less dissociated compared with hydrochloric acid, and, therefore,
10
76 H 47 11
(3)
76 H X4+, H11X3+ + H+ 47 12
(4)
76 HOOC(R)COOH. HOOC(R)COO3 + H+ 47
(5)
+
H+
(2)
X3+,
H10
X2+
(1)
3
As follows from our data, in the presence of the anions of acids II IV the experimental Bjerrum function nexp [Eq. (6)] (V0 is the initial volume of the solution with titrated compound, V is the titrant volume, c0 is the concentration of compound I, and c is the titrant concentration, and [H+] is the equilibrium concentration of protons) deviates from the
1070-3632/01/7110-1581 $25.00 C2001 MAIK
Nauka/Interperiodica]
[
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n
MOROZOVA et al.
Here n is the number of protons added as the result of complex formation (or the degree of protonation of the host).
2.5 2.0
1
1.5 1.0
2
0.5 0 2.4
3.4
4.4
5.4 pH
3
Fig. 1. Dependence of the Bjerrum function (n) on the pH of the medium in the system compound I3succinic acid II3HCl. (1) ncalc and (2) nexp.
theoretical value ncalc, calculated with allowance for all possible forms of the components of the system (ai) in the absence of their interaction [Eq. (7)]. The magnitude of this deviation depends on the nature of the acid and pH (Fig. 1), which reflects the degree of protonation of compound I and the stability of the complex formed. [Vc/(V0 + V) 3 [H+] nexp = 77777777 , c0V0/(V0 + V)
(6)
N
ncalc = S niai.
(7)
i =1
For adequately treating the pH-metric titration data we had to include equilibrium (8): 76 47 a, %
H8X + 3OOC(R)COOH + nH+
{(H8+nX)n+[3OOC(R)COOH]}31+n.
100 80
It should be noted that pH-titration data give no conclusive evidence indicating protonation site: amino group of the host or carboxy group of the guest, but the number of protons involved in complex formation can determined with certainty. Mathematical treatment of the experimental data showed that the succinate anion (HSuc3) is bound with the di- and trication of compound I [equilibrium (8), n = 2 and 3, respectively], while the phthalate (HPhtal3) and tartrate anions (H3Tart3) are bound with the tri- and tetracation of compound I [equilibrium (8), n = 3 and 4, respectively]. The stability constants of the complexes (b) of the monoanions of acids II IV with cations of calixarene I are as follows: log b1 7.0 (n = 2; acid II); log b2 5.3, 3.2, and 3.9 (n = 3; acids II IV, respectively); and log b3 5.6 and 4.9 (n = 4; acids III and IV, respectively). Figure 2 depicts the plots of distribution of the components of the equilibrium systems studied.
(8)
(a)
The highest stability constant is characteristic of the complex of the dication of compound I with the succinate anion (log b1 7.0), and further protonation of the host to trication reduces the log b value to 5.3. The decrease in the stability constants of the complexes with increasing degree of protonation suggests a considerable contribution into the complex formation of specific interactions, such as H bonding between nonprotonated nitrogen-containing groups of the calixarene and undissociated carboxy group of the acid. At the same time, the fact that the stability constants of the complexes with H3Tart3 and HPhtal3 are much increased by the protonation of the host (b)
(c)
3
1
1
1
3
60 40
2
20 0 2.5
3
2
2 3.5
4.5 pH
5.5
6.5
3
4
5
6
2.5
pH
3.5
4.5
5.5
pH
Fig. 2. Component distributions for the system H8X I3acid II3IV3HCl. (a): (1) [(H12X)4+(H3Tart)3]3+, (2) (H11X)3+ . (H3Tart)3]2+, and (3) H3Tart3; (b): (1) [(H12X)4+(HPhtal)3]3+, (2) [(H11X)3+(HPhtal)3]2+, and (3) HPhtal3; and (c): (1) [(H11X)3+(HSuc)3]2+ and (2) [(H10X)2+(HSuk)3]+ [the fractions of undissociated acids II3IV and cations of the host are not shown]. RUSSIAN JOURNAL OF GENERAL CHEMISTRY
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DIALKYLAMINOMETHYLATED CALIX[4]RESORCINARENES
from tri- to tetracation may imply a greater contribution into the complex formation of nonspecific (ion3ion) interactions compared with specific.
EXPERIMENTAL
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ACKNOWLEDGMENTS The work was financially supported by the Russian Foundation for Basic Research (project nos. 96-1597 374, 98-03-33 051a, and 98-03-32 760a).
REFERENCES 5,11,17,23-Tetrakis(N,N-dimethylaminomethyl)2,8,14,20-tetranonylcalix[4]resorcinarene (I) was synthesized by the procedure in [2]. 2-Propanol was purified by a standard procedure [5]. pH-Metric titration was performed in a temperaturecontrolled cell at 20oC on an I-130 ionometer. Calibration was performed using standard buffer solutions with subsequent estimation of the liquid-junction potential in going from aqueous to aqueous 2-propanol solutions according to [6]. The pKw values for aqueous 2-propanol solutions were taken from [7]. The protonation constants for compound I were taken from [2]. The dissociation constants of acids II IV and the stability constants of the complexes were found by the mathematical treatment by the CPESSP program [8] of the results of pH-metric titration of aqueous 2-propanol solutions (79 vol % of propanol) of the acid salt of compound I and of the complexes of compound I with acids II IV (cI 3.35 0 1033 M and cII3IV 3.35 0 1033 M) with an aqueous 2-propanol solution of hydrochloric acid (cHCl 1032 M) by variousvolume titration.
3
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1. Tanaka, Y., Kato, Y., and Aoyama, Y., J. Am. Chem. Soc., 1990, vol. 112, no. 7, pp. 280732808. 2. Ryzhkina, I.S., Kudryavtseva, L.A., Mustafina, A.R., Morozova, Yu.E., Kazakova, E.Kh., Enikeev, K.M., and Konovalov, A.I., Izv. Ross. Akad. Nauk, Ser. Khim., 1999, no. 3, pp. 4563460. 3. Morozova, Y.E., Kuznetzova, L.S., Mustafina, A.R., Kazakova, E.Kh., Morozov, V.I., Ziganshina, A.Yu., and Konovalov, A.I., J. Incl. Phenom. Macrocycl. Chem., 1999, vol. 35, nos. 132, pp. 3973407. 4. Bazzicalupi, C., Beoneini, A., Fuso, V., Giorgi, C., Massoti, A., and Valtancoli, B., J. Chem. Soc., Perkin Trans. 2, 1999, no. 8, pp. 167531682. 5. Gordon, A.F. and Ford, R., The Chemist’s Companion, New York: Wiley, 1972. 6. Jordan, F., J. Phys. Chem., 1973, vol. 77, no. 22, pp. 268132683. 7. Wooley, E.M., Hurkot, D.J., and Hepler, L.G., J. Phys. Chem., 1970, vol. 74, no. 22, pp. 390833913. 8. Sal’nikov, Yu.I., Glebov, A.I., and Devyatov, F.V., Poliyadernye kompleksy v rastvorakh (Polynuclear Complexes in Solutions), Kazan: Kazan. Gos. Univ., 1989.
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