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Zjawiska dysocjacji i asocjacji towarzyszące reakcjom przeniesienia protonu między C-kwasami i zasadami organicznymi w rozpuszczalnikach aprotonowych

Nowak I., Binkowska I., Stańczyk-Dunaj M., Jarczewski A.

Wiadomości Chemiczne

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2008

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[Z] 62, 1-2

67-95

EN

The proton transfer reactions in solutions have attracted the attention of a number of laboratories for many years. These processes seem to be quite simple as they proceed without perturbation of bounding electrons and have low steric demands what enables study of their mechanism. However, many factors influences the mechanisms of these reactions. Among them and not the trifling ones, are dissociation-association effects accompanying them. The definition, behavior and reactivity of carbon acids (C-acids) depending on the type of electron withdrawing group are given [1-57]. Also the values of dissociation constants of C-acids in protic and aprotic solvents are collated in Tables 4, 5 and 7 [11, 38, 49]. The nature of products, free ions and ion pairs, of proton transfer reactions of various C-acids and strong organic bases are carefully discussed. Also their spectral characteristics are given. The equilibria and the possible routes between the substrates and the products of these reactions are also shown [58-66]. The reasons of the homoconjugation effects as a result of an association of the ionic products of the proton transfer reactions in different solvents are discussed in the context of their solvation abilities [67-86]. The formation constants of the homoconjugation complexes of amidine and guanidine bases in relation to their pK? values are quoted in Table 6 [87-95]. The nature of heteroconjugation complexes formed as the result of hydrogen bonding of different entities in the system of proton transfer reactions is discussed [96-116]. The pK? values of a number of C-acids, derivatives of nitromethane, measured in acetonitrile by potentiometric method, are given in Table 7. The pK? values of these derivatives measured in DMSO/H2O systems are compared with those obtained in acetonitrile [18, 38]. The general view of these problems is discussed and carefully reviewed.

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Structure of Pyridine-2-azo-p-phenyltetramethylguanidine

Borowiak T., Dutkiewicz G., Binkowska I., Jarczewski A.

Polish Journal of Chemistry

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2003

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Vol. 77 / nr 11

1427-1435

EN

Replacement of dimethylamino group in pyridine-2-azo-p-dimethylaniline (PADA) by a stronger electron - releasing tetramethylguanidil (TMG) group forms a new complexing agent, pyridine-2-azo-p-phenyltetramethylguanidine (PAPT). The substitution does not enhance the expected complexing ability of PAPT in comparison with that of PADA. For steric reasons the tetramethylguanidil substituent CN3 and phenyl ring are not coplanar, which makes the resonance between them limited. This manifests in small contribution of quinoid form in the canonical structure distribution. The additivity of angular parameters in the phenyl ring is preserved.

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Proton Abstraction from 4-Nitrophenyl[bis(ethylsulphonyl)]methane with TMG, TBD and MTBD Bases in Acetonitrile

Jarczewski A., Binkowska I.

Polish Journal of Chemistry

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2001

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Vol. 75, nr 12

1895-1903

EN

4-Nitrophenyl[bis(ethylsulphonyl)]methane has been synthesized and used in kinetic studies of proton abstraction induced by 1,1,3,3-tetramethylguanidine (TMG), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and 7-methyI-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) bases in acetonitrile. The pK, values of this carbon acid in water and in acetonitrile solvents are 10.08 and 22.8 respectively. The electronic spectra of 4-nitrophenyl[bis(ethylsulphonyl)]methane and its anion ar well defined and temperaturę dependent. The rates of proton abstraction are large as the reaction occurs in the range of microseconds. The relaxation times were studied by spectrophotometric temperature-jump technique. The rate constants for proton transfer reaction promoted by TMG, TBD and MTBD bases in acetonitrile are: 1.39x10 5-2.1 Ix10 5; 8.8x10 6-19.2x10 6; 0.84x105-2.43x 10S [dm3 mol-1 s-1] respectively between 20-40°C. The enthalpies of activation are: deltaH# = 18.1, 28.7 and 40.0 [kJ mol-1] for TMG, TBD and MTBD respectively. The entropies of activation are all negative: deltaS# = -84.9, -13.6, -14.3 [J mol-1 deg-1] for the same sequence of bases reacting with 4-nitrophenyl[bis(ethylsulphonyl)]methane in acetonitrile solvent. The general discussion of the results obtained and their comparison with those for proton transfer reaction carried out with "normal" C-acids is given.