Kinetics of the reactions of 2-bromo-3,5-dinitrothiophen withortho-substituted anilines in methanol. An application of the Fujitandash;Nishioka equation

摘要

1979 219 Kinetics of the Reactions of 2-Bromo-3,5-dinitrothiophen with ortho-Substituted Anilines in Methanol. An Application of the Fujita-Nishioka Equation By Giovanni Consiglio * and Renato Noto, Institute of Organic Chemistry, University of Palermo, Via Archirafi 20, Palermo 90123, Italy Domenico Spinelli and Caterina Arnone, Cattedra di Chimica Organica, Faculty of Pharmacy, University of Bologna, Via Zanolini 3, Bologna 401 26, Italy The rates of anilino-debromination of 2-bromo-3,5-dinitrothiophen (I) by some ortho-substituted anilines (I1; X = OMe, Me, Et, CI, Br, and F) have been measured in methanol. The kinetic results have been treated according to the multiparameter analysis of ortho-effects proposed by Fujita and Nishioka. This treatment of data has also been applied to acid-base equilibria of anilinium ions. The susceptibility constants obtained in the two series of reactions (respectively p -2.96 and -2.90, 6 1.31 and 0.56, f -1.83 and -1.70) have been explained by taking into account the structure of the transition states involved. RECENTLYwe examined the reaction of 2-bromo-All the reactions were first order both in (I) and (11).On 3,5-dinitrothiophen (I) with 14 meta-or paya-substituted changing from aniline to ortho-substituted anilines, irrespec- anilines in methanol and showed that the kinetic data tive of the nature Of the electron-withdrawing or -repelling TABLE1 Physical and analytical data for ortko-substituted N-(3,5-dinitrothienyl)anilines(111) Suhstituent Crystallizationsolvent M.p.("C) c-C Found (yo) 1-A H N Formula r C Required* () H bsol; N Lnsx./ nm log~~ Me0 Meb Ethanol-dioxan Ethanol 196 168 45.0 3.1 14.1 CllHgNsOaS 44.7 3.1 14.2 402 404 4.30 4.20 Et c1 Ligroin-benzeneEthanol-dioxan 92 184 49.5 40.3 3.7 2.0 14.2 13.8 C12HllNSO4S CloH~C1N,04S 49.1 40.1 3.8 2.0 14.3 14.0 405 394 4.22 4.25 Br F Ethanol-dioxan Ethanol-dioxan 174 178 35.1 42.6 1.7 2.0 12.0 14.6 Cl,H6BrN,04S CloH6FN,0,S 34.9 42.4 1.8 2.1 12.2 14.8 394 394 4.24 4.24 a In methanol, See ref. 3. obeyed the Ingold-Yukawa-Tsuno relationship 2 (1) effect of the substituent, a decrease in the rate of substitu-with p -3.00, r+ 0.38, and Y-0.99. tion was observed, which indicated the occurrence of log K/k= = p(d' + Y+ACR++ Y-AGR-) (1) important steric effects.TABLE2 As a natural extension of this work we now report Rate constants and activation parameters for the reactions rate constants and activation parameters for the reaction of 2-bromo-3,5-dinitrothiophen (I) with ortho-sub-stituted anilines (11)in methanol -AS c/ AHt b/ cal kcal mold' Substituent lo3k/l mol-l s-l (t/"C) mol-l K-I rn, rm, Meo 15.3 (10.03), 28.0 (20.10), 46.1 (30.00) 8.8 35.5+ Med 3.49 (19.95), 6.36 (30.02), 11.0 (39.98) 9.9 35.9 Et 3.39 (20.05), 6.08 (30.02), 10.5 RCsHLNHiBr (40.08) 9.7 36.7 C1 0.106 (20.10), 0.204 (29.98),of (I) with some ortho-substituted anilines (11; R = 0.364 (40.02) 10.6 40.2 MeO, Me, Et, C1, Br, and F) in methanol. We will show Br 0.0442 (20.10), 0.0872 (30.02),0.166 (40.06) 39.2that it is possible to embody ordinary and steric effects F 0.694 (20.10), 1.27 (29.98), 2.21 11.5 of substituents into a unique multiparameter free-energy (40.02) 10.0 38.8 Hd 13.2 (0.02), 23.0 (10.02), 41.9 relationship.(20.05) 9.2 33.4 a The rate constants are accurate to within f3. AtRESULTS 20"; the probable error is 0.5 kcal mol-l. At 20". See ref. Products.-2-Bromo-3,Ei-dinitro thiophen (I) gave the 3. expected anilino derivatives (111)on treatment with anilines DISCUSSION(11)in very high yields, as shown by t.1.c. and u.v.-visible spectral analysis. The relevant physical and analytical Among the numerous attempts to understand the data are shown in Table 1. nature and composition of the ' ortho-effect ', those of Farthing and Nam,6 and Chapman and Kinetic Data.--Kate constants and activation parameters Taft,4 Chart~n,~ for anilino-debromination of (I) are reported in Table 2.Shorter have met with varying degrees of success, but the approach proposed by Fujita and Nishiokaa seems to us the most promising. According to these authors, the total effect of ortho-substituents is expressed in terms J.C.S. Perkin 11 show similar p and f values indicating much the same susceptibility to ordinary and proximity polar effects. On the other hand, anilinodebromination has a 6 value TABLE3 Linear free energy relationships a for the reaction of 2-bromo-3,5-dinitrothiophcnwith ortho-, meta-, and para-substituted anilines in methanol, at 20 "C (A) and for the dissociation of anilinium ions in water, at 25 "C (B) EquationSystem used P fSP 6 fsa f fSf i fsi S R n Y'E~,F A (1) -3.00 f0.05 0.00 f0.03 0.08 0.9983 14 (2) -2.75 + 0.05 1.27 40.08 -1.91 amp; 0.21 -0.03 f0.09 0.09 0.9984 7 0.004 0.382 (3) -2.96 f0.05 1.31 f0.05 -1.83 f0.14 -0.01 f0.03 0.09 0.9980 20 0.229 euro;3 (1) -2.93 f0.03 0.01 amp; 0.02 0.05 0.9992 14 (2) -2.65 f0.18 0.53 f0.05 -1.83 f0.16 -0.01 f0.06 0.06 0.9988 7 0.004 0.502 (3) -2.90 amp; 0.04 0.56 amp; 0.04 -1.70 f0.10 -0.01 f0.02 0.06 0.9989 20 0.239 a sp, sa, s,, si represent standard errors, respectively, of p, 6, j, and i; i, intercept; s, standard error of estimate: R, correlation coefficient; n,number of data points; and are the coefficients of determination for simple correlation, respectively, between E, and F values and ucaloand F values.The values of tscalc, E,, F, log k/k~,and pKa used in correlations are shown in Table 4. of (i) the ' ordinary polar effect,' defined as being equal to that of para-substituents; (ii) the ' proximity polar effect,' represented by the Swain-Lupton and (iii) the ' primary steric effect,' represented by the Taft E, ~onstant.~~*~* The rate or equilibrium data of a series of ortho-substituted derivatives can be expressed by equation (2),where p, 6, and f are susceptibility constants, and c is a constant that corresponds to the log KH value of the unsubstituted compound. If the separation of proximity polar and steric effects from the ordinary polar effect is complete in equation (2),a set of rate or equilibrium data for a series including ortho-, meta-, and para-substituted derivatives can be expressed by equation (3).When applied to the anilinodebromination of (I) (system A), equations (2) and (3) give the results set forth in Table 3.t For the sake of comparison, parallel calculations have been carried out on acid dissociation of anilinium ions (system B) and are also included in Table 3.5 The levels of significance of all correlations with equations (1)-(3) are better than 99.95 as examined by F tests.14 One observes only a slight increase in the standard deviation, s, by including ortho-substituted derivatives; moreover all the terms in equations (2) and (3) are justified at better than 99.9by t tests.14 The strict correspondence between the regression parameters obtained with equations (2)and (3) indicates that in both systems A and B the separation of proximity polar and steric effects from the ordinary po1a.r effect is complete.We wish to emphasize that the set of com-bined ortho-, meta-, and para-substituted derivatives can be dealt with by means of a unique multiparameter free energy relationship, namely (4). Systems A and B * According to Fujita and Nishioka the reference substituent is changed to hydrogen. -f Taking for the ' ordinary polar effect ' of ortho-substituent that of the para-substituent we have used b,,tho = an + r+AuR++ Y-A~R-see notes b and d of Table 4 and equation (4)j.which is about two-fold higher than for the dissociation of anilinium ions. The different susceptibility to the log k/kH = p(on + Y'AOR' + Y-A~R-)+ 6Es +fF (4) ' volume-filling ' factor originates from a different crowding of transition state in the two reactions and TABLE4 Parameters used in statistical correlations 1 aSubstituent k/k~ acaic ' pKac acaicd Es FB p-OMe p-Mem-Me 1.086f --0.36 0.534f -0.18 0.188J -0.069 5.36 5.08 4.71 H 0.000f 0.000 4.60 p-Brm-c1 p-Cl -0.647 f -0.724f -1.109f 0.22 0.24 0.373 3.98 3.89 3.52 m-F -1.125f 0.337 3.59 m-Br -1.130' 0.391 3.53 -0.26 -0.15 -0.069 0.000 0.24 0.26 0.373 0.337 0.391 p-C0,Me -2.063 f 0.74 2.38h 0.74 WZ-NO~ -2.174f 0.710 2.46 0.710 p-COMe -2.290f 0.82 2.19 0.82 p-CN -2.986 f 0.99 1.74h 0.99 P-N -3.785f 1.22 1.02 1.23 o-OMe -0.183 -0.36 4.53 -0.26 -0.55 0.26 o-Me -1.075 -0.18 4.45 -0.15 -1.24 -0.04 0-Et -1.090 -0.19 4.37 -0.17 -1.31 -0.05 0-c1 -2.593 0.22 2.66 0.24 -0.97 0.41 o-Br -2.978 g 0.24 2.53 0.26 -1.16 0.44 0-F -1.779 g 0.08 3.20h 0.12 -0.46 0.43 a From k values calculated at 20 "C by the activation para- meters.acagc for anilino-debromination, ucelc= an + 0.38 AaR+ + 0.994aR-, see ref. 1. Values from ref. 10 unless noted otherwise. acalcfor the acid dissociation of anilinium ions, rrCalc = an + 0.84 AOR++ ADamp;-, see ref. 1. Values from ref. 8. f Values from ref. 1 g This work. Values from ref. 11. lValues from ref. 12. j Value from ref.13. confirms indications from an examination of molecular models. The activation parameters for anilino-debromination are consistent with this picture in that on going from aniline to ortho-substituted anilines AH: increases and AS: decreases, indicating some steric strain in the transition st ate. The regression parameters obtained by us compare well with those obtained by Fujita and Nishioka * using a larger number of substituted anilinium ions. 1979 EXPERIMENTAL Synthesis and Purifzcation of Compounds .-Methanol, (I),and (11)were prepared and/or purified as previously.lsquo; The anilino derivatives (111) were prepared according to the general method reported in ref. 15: physical and analytical data are shown in Table 1.Kinetic Measurements.-The kinetics were followed spectrophotometrically as previously described .16 The concentrations employed were CZ~O-~Mfor (I) and 6 x 10-3-3 x 10-l~for (11) as a function of the nucleophilicity. U7e thank the C.N.R.for support. 8/330 Received, 24th February, 19781 REFERENCES D. Spinelli, G. Consiglio, R. Noto, and V. Frenna, J. Org. Chem., 1976, 41, 968. 2 C. K. Ingold, lsquo; Structure and Mechanism in Organic Chemis- try?rsquo;, Cornell University Press, Ithaca, 1969, 2nd. edn., p. 1217; Y. rsuno, T. Ibata, and Y.Yukawa, Bull. Chem. Soc., Japan, 1959,32, 960; Y. Yukawa and Y. Tsuno, ibid., pp. 965, 971; Y. Yuk- awa, Y. Tsuno, and M.Sawada, ibid., 1966, 39, 2274; 1972, 45, 1198; A. J. Hoefnagel and B. M.Wepster, J. Amer. Chem. Soc., 1973, 95, 5357. D. Spinelli and G. Consiglio, J.C.S. PevRin 11,1975, 1388. R. W. Taft, jun., lsquo; Steric Effects in Organic Chemistry rsquo;, ed. M. S. Newman, Wiley, New York, 1956, p. 556. M. Charton, Progr. Phys. Org. $hem., 1971, 8, 235. A. C. Farthing and B. Nam, Steric Effects in Conjugate Systems I, Academic Press, New York, 1956, pp. 587, 648. N. B. Chapman, J. Shorte,r, and J. H. P. Utley, J. Crsquo;hem. Soc. (B),1962, 1824; J. Shorter, Advances in Linear Free Energy Relationships rsquo;, eds. N. B. Chapman and J. Shorter, Plenum Press, London, 1972, p. 71. T. Fujita and T. Nishioka, Progr. Phys. Org. Chem., 1976,12, 49. C. G. Swain and E. C. Lupton, J. Amer. Chem. Soc., 1968, 90, 4328. lo P. D. Bolton and F. M. Hall, J. Chem. Soc. (B),1969, 1047 and references therein. l1 A. Albert and E. P. Serjeant, lsquo; Ionization Constants of Acids and Bases rsquo;, Methuen, London, 1962. 12 K. B. Whetsel, Spectrochim. Ada, 1961, 17, 614. 13 B. M. Wepster, Rec. Trav. cham., 1957, 76, 357. l4 E. L. Crow, F. A. Davis, and M. W. Maxfield, lsquo; Statistical Manual rsquo;, Dover, New York, 1960. 15 C. D. Hurd and K. L. Kreuz, J. Amer. Chem. Soc., 1962, 74, 2965. 16 D. Spinelli, C. Dellrsquo;Erba, and A. Salvemini, Ann. Chim. (Italy),1962, 52, 1156.