N-(2,6-Dinitro-4-trifluoromethylphenyl)aniline derivatives were prepared by anilino-dechlorination of 4-chloro-3, 5-dinitrobenzotrifluoride. IR, UV and 1H NMR studies suggested an intramolecular hydrogen bond between the amino hydrogen and one o-nitro group. An addition-elimination mechanism was suggested based on the second-order kinetics and the dependence of rates on the nature and the position of the substituent in the aniline ring, as well as the high negative values of ρ(-3.14, −3.16, −3.01). Such values indicate a positive charge on the aniline nitrogen in the transition state and that the rate is affected by the polar effect of the substituent. The β value (0.85 at 30°C) indicates an appreciable degree of bond formation in the transition state.

The kinetic of the nucleophilic substitution of methyl 2,4-dichloro-3,5-dinitrobenzoate with piperidine, piperazine, morpholine and thiomorpholine in methanol and benzene were determined spectrophotometrically at different amine concentrations and at temperatures ranging from 25 to 45 °C. The second order rate constants and the thermodynamic parameters show that the reactions are not amine catalysed and are greatly dependent of the nature of solvent and amine. UV, IR, 1 H NMR, and elemental analysis are used to prove the aminodechlorination at C-2.

Nucleophilic substitution in heteroaromatics is a subject of ongoing interest in our laboratory and especially the behaviour of substituted nitro pyridines towards different nucleophiles has attracted our attention. 1-6 It was reported that the alkaline hydrolysis of both 2-chloro-5-nitropyridine and 2-chloro-3,5-dinitropyridine often involves an S N (ANRORC) mechanism which starts by addition of the nucleophile (usually at the meta position to the leaving group) followed by ring opening and ring closure. 7 Recently the reactions of 2-chloro-5-nitropyridine, 2-chloro-3-nitropyridine, 2-chloro-3,5-dinitropyridine, with arene thiolates, 1,2 morpholine, 3,4 piperidine, 4 aniline derivatives 5 and aryloxide ions 6 were reported. The substitution product was found to be formed via the S N (AE) ipso mechanism. In continuation of these researches, we have examined the effect of the 2-substituent on the mechanism of the alkaline hydrolysis reaction of 2-thioaryl-3,5-dinitropyridines 2 since they do not appear to have been studied. 8,9 Experimental Material: Substituted 2-thioaryl-3,5-dinitropyridines 1a-h were prepared as reported earlier. 2 Carbonate free sodium hydroxide was prepared as reported. 10 General procedure: 2-thioaryl-3,5-dinitropyridines 1a-h (0.5 g) were treated with sodium hydroxide (10ml DMSO-H 2 O v/v) 1:100 respectively and refluxed at 40°C for 1 h. Upon cooling and acidification a mixture of diaryl disulfide, [11][12][13] (Table 1) and 3,5-dinitro-2-pyridone was obtained which was separated by fractional crystallisation.Kinetic measurements: The solvent used for kinetic runs was of reagent grade (Aldrich). The rate constants were measured in the thermostated cell compartment of a Shimadzu 160-A UV-VIS. spectrophotometer. Repetative scans of the reaction mixture showed the disappearance of activated complex which absorbed at λ 470 nm in 50% v/v DMSO-H 2 O. Good pseudo-first order kinetics were measured at different concentrations of NaOH (5×10 -4 -5×10 -3 M) and 2-thioaryl-3,5-dinitropyridine (5×10 -5 M). The first order rate constants k obs were calculated using equation (1), where A o , A t , and A are the values of absorbance at zero time, time t, and the end of the reaction respectively

The kinetics of solvolysis of trans — [Co(py)4Cl2]ClO4 have been investigated in aquo-organic solvent media such as water + ethanol (0-60% v/v) and water -+ urea (0-40% w/w) in the temperature range 40-60°C. The first-order rate constant varies nonlinearly with the reciprocal of the relative permittivity ∊r. The solvolysis of these types of complex involves a rate-determining dissociative step corresponding closely to 100% separation of Co3+ … Cl in the transition state. The Gibbs energy cycle relating the Gibbs energy of activation in water and in the mixtures to the Gibbs energies of transfer of individual ionic species between water and the mixtures ΔG°t(Cl) can be applied. Moreover, more than one extrema in the enthalpies and entropies of activation are found with both binary aqueous solvent mixtures. The solvolysis of trans — [Co(py)4Cl2]ClO4 has also been studied in the presence of Hg(II) and the ionic strength dependence of the reaction rate has been analysed.

The kinetics of the alkaline hydrolysis of 2-thiophenyl-3,5-dinitropyridine were studied spectrophotometrically in different aquo-organic solvents such as methanol, ethanol, npropyl alcohol, iso-propyl alcohol, t-butyl alcohol, acetonitrile, dimethyl sulfoxide, dioxane, and acetone at 30 • C with various solvent compositions up to 80% (v/v) of organic components. An increase in the organic solvent percentage (v/v) has different effects on the reaction rate constants presumably due to hydrogen bond donor HBD and acceptor HBA of the medium and other solvatochromic parameters. Linear and nonlinear plots of log k against the reciprocal of the dielectric constant of the solvent were obtained. The effects are too complex to be analyzed in terms of a single parameter, but an approach using the Kamlet-Taft solvatochromic parameters is applied successfully to six mixed aquo-organic solvent systems. C 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 159-165, 2006

The solvent effect on a nucleophilic substitution reaction of 2-and 4-chloro-3,5-dinitrobenzotrifluoride with substituted anilines was studied in methanol, acetonitrile, and toluene at 25 • C. This reaction is of second order, except 2-chloro-3,5-dinitrobenzotrifluoride in toluene shows third order. The k A values are found to be dependent on the substituent in aniline and give good Hammett correlations. The obtained ρ values are −4.07 and −4.62, for the reaction of anilines with 2-chloro-3,5-dinitrobenzotrifluoride in methanol and acetonitrile, respectively. The ρ values for the reaction of the anilines with 4-chloro-3,5-dinitrobenzotrifluoride are −3.38, −4.11, and −4.34 in methanol, acetonitrile, and toluene, respectively. The reaction of the former compound with anilines in toluene shows a second order in aniline. The dependence of the reaction on the external base such as DABCO suggests a proton transfer controlling step.

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Kinetics and solvent effects of the aquation of trans 4 Cl 2 ] + have been studied in ethanol + water ranging from 0 to 60% (v/v) and urea + water of various solvent compositions up to 40% (w/w) of organic solvent. Thermodynamic activation parameters were computed and discussed in terms of the solvation effect. Isokinetic temperature within the experimental range revealed that the existence of the compensation effect arising from the solute-solvent interaction. Nonlinear plots of log k with D −1 suggest that changes in the solvent structure are an important factor that influences these rates. The influence of the added cosolvent on reactivity was analyzed in light of various simple and multiple regression equations using Kirkwood, E T (30), and Kamlet-Taft parameters. The obtained results showed that the solvation phenomenon plays a dominant role in the aquation. C 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: [230][231][232][233][234][235][236][237] 2011