摘要:

1972Substituent Effects on the Kinetics of Pyridine-catalysed Hydrolysis ofAromatic Sulphonyl Chlorides ; Br6nsted and Hammett CorrelationsBy 0. Rogne, Norwegian Defence Research Establishment, Division for Toxicology, N-2007 Kjeller, NorwayThe rates of hydrolysis of substituted benzenesulphonyl chlorides, catalysed by substituted pyridines, have beendetermined. Substituent effects in acid chloride and pyridine are correlated by Hammett and Brsnsted equations,respectively. The Hammett plots are curved because of an abnormal low reactivity of rn- and p-nitrobenzene-sulphonyl chloride. The sensitivity parameters, (3 and p (excluding the nitro-compounds), obtained from the free-energy relations, are dependent upon the reactivity of the system. Thus p, which varies from 0-406 forp-methoxy-to 0.557 for p-nitro-benzenesulphonyl chloride, are linearly related to the Q values for the sulphonyl chloride sub-stituents. Likewise the p values are linearly related to pK, of the pyridines.These results show that bond form-ation in the transition state increase with electron-attracting substituents in the acid chloride, whereas such sub-stituents in the nucleophile leads to increased bond stretching relative to bond formation.IN a previous paper the rates of reaction in methanol ofsubstituted benzenesulphonyl chlorides with various sub-stituted anilines were reported. It was shown that sub-stituent effects in the sulphonyl chloride and aniline couldbe correlated by Hammett and Brgnsted equations, re-spectively.It was further shown that the sensitivityparameters, p and p, obtained from the free-energy rela-tions, were themselves sensitive to the reactivity of thesystem. Thus, p and p varied linearly with the basicityof the anilines and the ts values for the sulphonyl chloridesubstituents, respectively. To confirm and extend theseresults, the rates of hydrolysis of some substitutedbenzenesulphonyl chlorides catalysed by various sub-stituted pyridines have been measured. This reaction,which has been investigated for benzenesulphonylchloride (R1 = Ph in Scheme), was shown to occur bya nucleophilic catalysis mechanism involving rate-determining formation of an unstable sulphonylpyridin-ium intermediate, as shown in the Scheme.R1S02C1 + R2C,H,N R1S0,&C,H4R2 + C1-k-iRISO,*OH + R2C,H4NHpOEXPERIN EKTALMuteriuZs.-All compounds were commercial samples.The sulphonyl chlorides were fractionally distilled or re-crystallised from light petroleum (b.p.60-80 "C). Thepyridines were dried (KOH) and fractionally distilled or re-crystallised (light petroleum). B.p.s or m.p.s agreed satis-factorily with literature value^.^'^ G.1.c. showed only asingle peak in each case.Rate Measurements.-The rate of hydrolysis of the sul-phony1 chlorides, in the presence of various pyridines, wasmeasured by continuous titration at constant pH of the acidproduced by means of the Radiometer Titrator. Theapparatus has been described.? The procedure was also asdescribed except for the initial concentration of sulphonylchlorides which was GU.8 x 1 0 - s ~ , and the concentrationof sodium hydroxide which was 0 . 0 2 5 ~ .All runs were done in water containing O.O5~-sodiumchloride at a pH at least 3 units greater than the pKa ofthe pyridine.2 The concentration ranges used for the0. Kogne, J . Chem. SOG. ( B ) , 1971, 1855.0. Rogne, J . Chem. SOG. ( B ) , 1970, 727.' Handbook of Chemistry and Physics,' The ChemicalRubber Co., Ohio, 45th edn., 1964.various pyridines varied from 1~@-10~0 x ~ O + M for thefastest reactions to 0.025-@-10~ for the slowest.Theobserved first-order rate constants were calculated from therecorded curve of amount of alkali added against time byGuggenheim's m e t h ~ d . ~ Reactions were also occasionallyrun to completion (10 half-lives) and tested for first-orderkinetics by means of conventional plots of log (u-x)against time.Second-order rate constants were calculatedfrom the slopes of plots of the observed first-order rateconstants against the pyridine concentration. Rate con-stants are estimated to be accurate f 5% or better. Activa-tion parameters were calculated from a least-squares treat-ment of ln(li/T) against T1. The estimated precision isca. k0.5 kcal mol-l in AH$ and ca. 1 2 cal moF K-l inAS$.Reactions were generally run to GU. 3 to 4 half-lives.RESULTSThe observed rates of reaction were, under conditions ofconstant pH, always of the first order. Plots of the ob-served first-order rate constants against concentration ofpyridine were also in all cases linear, showing that the re-actions are of the first order in pyridine.The second-orderrate constants at 25OC obtained from the slope of theseplots are in Table 1. The reactions of the unsubstitutedpyridine were also studied at several temperatures. Theserate constants are in Table 2 together with the calculatedactivation parameters.TABLE 1Second-order rate constants for the reaction of substitutedbenzenesulphonyl chlorides with pyridines in water(0.05~-sodium chloride) at 25 "CK/1 mol-1 s-lPyridine3,4-Dimethyl-pyridine4-Methylp yridine3-MethylpyridinePyridine3-Acetylpyridine4-Cyanop yridine3-Cyanopyridinep-Me04.652.852.551-520.2380.06750.0395?-Me9-165.304.732.530.3560*09000.0510H11.56.545.653.080.4050.09490.0531WZ-NO,14.17.805-823-030.2540.04750.0240P-NO,31.415.911-75-840.5020,08450.0447The hydrolysis of the various sulphonyl chlorides pro-duced, at constant pH, 2 equivalents of acid per equivalentacid chloride consumed.This stoicheiometric amount of4 A. R. Katritzky and J. M. Lagowski, ' Heterocyclic Chemis-try,' Methuen, London, 1960.E. A. Guggenheim, Phil. Mag., 1926, 2, 538490 J.C.S. Perkin I1TABLE 2Rate constants and activation parameters for the reactionof pyridine with sulphonyl chlorides in water ( 0 . 0 6 ~ -NaC1)Sulphonyl kcal cal mol-1chloridek/l mol-1 s-1 AH1 A S 1K-l ' 15 "C 20 "C A 30 "C 35 'c' mol-lP-N08*C6H4*SO&l 2.87 4.02 8.60 11.6 11.9 -16m-NO,*C6H4*SO,C1 1.32 2-01 4.27 6.81 12.6 -14PhS0,Cl * 1.48 2.14 6.31 12.2 -15p-MeC,H,*SO,Cl 1.16 1.73 3.73 6-16 12.7 -14p-MeO*C,H4*S0,Cl 0.632 1-00 2.09 3.17 13.4 -13* Data from ref.2.TABLE 3Slopes (p) and correlation coefficients ( Y ) of the Brernstedplots (Figure 1) for the reaction of pyridines with sul-phony1 chloridesSulphonyl chloride u t B Yfi-NO,*C6H,*SO&I 0.78 0.657 f 0.006 * 0.999m-NO,*C6H4*SO,Cl 0.71 0.645 f 0.006 0.999PhS0,Cl 0-00 0.457 0.007 0.999p-MeC,H,*SO,Cl -0.17 0.441 f 0.007 0.999p-M&*C~H,*SO&I -0.46 0.406 f 0.007 0.999* Standard deviation.Me0 which is from ref. 7.Q Values, from ref. 6, except forp-TABLE 4Slopes (p), based on the p-methoxy, p-methyl, andunsubstituted compound, of the Hammett plots in Figure 3Pyridine3,4-Dimethylpyridine4-Methylpyridine3-MethylpyridinePyridine3-AcetylpyridineCC yanop yridine3-Cyanop yridinepKi3 *6-466.025-685-213-181.901.39P0.890.820.780.690.520.340.30* In aqueous solution a t 26", from D.D. Perrin, ' DissociationConstants of Organic Bases in Aqueous Solution,' Butter-worths, London, 1966. r 1.5 PI I I I I 11 3 5 7P 4FIGURE 1 Relationships of log k to pK, for the reaction of$-nitro- and p-methoxy-benzenesulphonyl chloride with sub-stituted pyridines in water. From left to right, the pointsrepresent pyridines with the substituents 3-CN, 4-CN,3-Ac, H, 3-Me, 4-Me, and 3,4-Me2, respectivelyacid produced remained unchanged in the presence of thevarious pyridines.The rate constants for the reaction of each sulphonylchloride with the various pyridines are related to the pK,(Table 4) in water of the corresponding pyridines as exempli-fied by the Brernsted plots in Figure 1.The slopes, standarddeviations, and correlation coefficients for these Branstedplots, calculated by a least-squares treatment of log k againstpK,, are in Table 3. The slope, p, of the Bransted plots isFIGURE 2 Dependence of the Bransted slopes, #I (Table 3),upon the (I values for the sulphonyl chloride substituents.The line has a slope of 0.122 f 0.002 (Y = 0.999)1.51.03,2 -Me, / H3 - COCH, 4I I 0- 0.4 0 0.5 0.n dFIGURE 3 Hammett plots for the reaction of substitutedbenzenesulphonyl chlorides with pyridines.The sulphonylchloride substituents are, with increasing Q: $-MeO, H,m-NO,, and $-NO,. The broken line represents the reactionof pyridine with the sulphonyl chlorides in methanol a t 26 OC;rate constants from ref. 7 except for the m-NO, compoundwhich was measured to 4.47 x lo-, 1 mol-l s-llinearly related to the Q values 6 (Table 3) for the sulphonylchloride substituents as shown in Figure 2. The Q valuesused in this correlation are the ordinary values except thatfor p-Me0 (= -0.45) which was determined as a ' best 'value in the reaction of para-substituted benzenesulphonyl6 P. R. Wells, Chem. Rev., 1963, 63, 1711972 491chlorides with pyridine in methanol.' This value was usedhere since it gave significantly better correlation than eitherts or G+.A similar G value for $-Me0 was also used inHammett correlations for the reactions of aromatic sul-phony1 chlorides with anilines in methano1.l The signifi-cance of this G value, which is about midway between 00 andcf was attributed to a certain amount of resonance stabilis-ation of the ground state of $-methoxybenzenesulphonylchloride.'The rate constants for the reactions of each pyridinewith the various sulphonyl chlorides are expected to corre-late with Q to give a family of Hammett plots similar tothat found in the reaction of sulphonyl chlorides withanilines in methano1.l Plots of log k against Q (Table 3) are,however, curved as shown in Figure 3. The plots for7P K,1 3 5 7FIGURE 4 Dependence of the Hammett p values (Table 4) uponThe line has a slope of 0.114 f the basicity of the aniline.0.004 (Y = 0.996)Pmethyl- and 3-methyl-pyridine are, for the sake of clarity,not shown.These follow the same pattern, falling betweenthe plots for 3,4-dimethylpyridine and pyridine. If thetwo nitro-compounds are excluded, a series of p values canbe obtained. These p values, which are given in Table 4,show a linear correlation with the basicity of the pyridines,as shown in Figure 4.DISCUSSIONThe pyridine-catalysed hydrolysis of benzenesulphon ylchloride has been shown to occur by a nucleophiliccatalysis mechanism.2 This involved rate-determiningformation of a sulphonylpyridinium intermediate whichrapidly hydrolyses to sulphonic acid, regenerating thepyridine, as shown in the Scheme.The kinetics, stoichei-ometry, activation parameters, and substituent effectsare in agreement with such a mechanism. Thus, thesecond-order rate constants reported here refer to a0. Rope, J . Chem. Soc. ( B ) , 1971, 1334.8 L. Senatore, E. Ciuffarin, and A. Fava, J . Amer. Chem. Soc.,9 W. A. Pryor and K. Smith, J . Amer, Chem. SOC., 1970, 92,lo E. Ciuffarin and A. Fava, Progr. Phys. Org. Chem., 1968,l1 E. T. Kaiser, Accounts Chem. Res., 1970, 3, 145.1970, 92, 3035.2731.6, 81.bimolecular nucleophilic substitution on sulphur. Anucleophilic substitution on tetraco-ordinate sulphurcould take place by a concerted one-step process, or byan addition-elimination mechanism involving a five-co-ordinate i~~terrnediate.~,~ Since no evidence for five-co-ordinate intermediates has been found in reactions ofsulphonateslOJ1 it seems less likely that they shouldoccur in reactions of sulphonyl chlorides, which have amuch better leaving group.Also since previous1 andpresent results can be consistently explained by a directS N ~ mechanism, a one-step process is preferred. Thetransition state for this reaction is most reasonablyformulated as a trigonal bipyramidd structure.lOg 1 2 9 1 3RThe effect of substituents in nucleophile and substrateis apparent from Table 1, the rate being increased byelectron-donating substituents in the pyridine and byelectron-attracting substituents in the sulphonyl chloride(except for some reactions of meta- and para-nitrobenz-enesulphonyl chloride discussed below).This is as ex-pected for nucleophilic attack of amines on the sulphuratom.The relationship of nucleophilicity to basicity is illu-strated in Figure 1 for the p-nitro- and #-methoxy-compound. The other sulphonyl chlorides gave similarplots. The slopes p (Table 3) of these plots decrease withincreasingly electron-donating ability of the substituentsin the sulphonyl chloride. Thus is correlated with Qas shown in Figure 2. Since p is a measure of the degreeof bond formation in the transition state,14 it can beinferred that N - - S bond formation decreases progres-sively from p-nitro- to p-methoxy-benzenesulphonylchloride, i.e. with increasing electron donation to thesulphur atom.This is in agreement with predictions ofsubstituent effects for a simple SNZ displacement re-action.l5 A similar conclusion was reached for thereaction of anilines with sulphonyl chlorides in methanol.1Kinetic solvent isotope effects (kn,o/kD,o) for para-substituted benzenesulphonyl chlorides are also in agree-ment with an increase in bond-making for electron-attracting substit uen ts .l6The Hammett plots for the reaction of each pyridinewith the various sulphonyl chlorides are curved, asshown in Figure 3. The curvature is due to an abnormallow reactivity of the nitro-compounds (see below), andthese were therefore excluded in the calculation of thep values (Table 4). Although the p values are based on12 R. E. Robertson and B.Rossall, Canad. J . Chem., 1971, 49,l3 R. M. Laird and M. J, Spence, J . Chem. Soc. ( B ) , 1971, 1434.l4 J. F. Bunnett. Ann. Rev. Phys. Chem., 1963, 14, 271.l6 J. C. Harris and J. L. Kurtz, J . Amer. Cham. Sac., 1970,1e. B. Rossall and R. E. Robertson, Canad. J . Chem., 1971,1441.92, 349.49, 1451J.C.S. Perkin I1three points only, the relative values are believed to besignificant. The p values, which decrease with de-creasing reactivity of the pyridine, are linearly relatedto pK, of the pyridine as shown in Figure 4, in agree-ment with that found in the reaction of anilines withsulphonyl ch1orides.l The slope of the plot of p againstpK, is, within experimental error, the same as that of theplot of p against B (Figure 2). This is as expected sincethe various p and values are inter-related throughequation (1) where C is a constant.17J8 As p is relatedto the extent of bond breaking relative to bond form-ation,lO the conclusion that stretching and charging ofthe S-C1 bond increases relative to the formation of theN-S bond, i.e.the transition state becomes more product-like, with in cr easing1 y electron- at t rac t ing subs t it uen t sin the nucleophile, is confirmed. This is also in agree-ment with predictions of substituent effects on transitionstate structure for a simple SN2 displacement reaction.15The ' normal ' behaviour of the p values derived fromthe $-methoxy-, $-methyl-, and unsubstituted com-pound agree with the assumption that the reactivity ofthe nitro-compounds is too low compared with the othercompounds. This is similar to the SNZ hydrolysisin aqueous dioxan of substituted benzenesulphonylchlorides.20 Here the hydrolysis of compounds withelectron-attracting substituents is progressively in-hibited] relative to the unsubstituted compound, as thesolvent approach pure water.The explanation 2o forthis behaviour is that stretching and charging in thetransition state of the S-C1 bond becomes more importantrelative to the bond-forming process with increasingdielectric constant of the solvent. Since electron-attracting substituents favour bond-making but opposebond stretching, their effectiveness in lowering the17 E. H. Cordes and W. P. Jencks, J . Amer. Chem. SOC., 1962,18 W. P. Jencks, Progr.Phys. Org. Chem., 1964, 2, 63.10 C . G. Swain and W. P. Langsdorf, J , Amer. Chem. SOC.,84, 4319.1961, 75, 2813.free energy of activation is reduced as the polarity of themedium is increased.The decreased reactivity of the nitro-compounds com-pared to the other compounds become more pronouncedas the reactivity of the pyridine decreases, and as thesolvent changes from methanol to water (Figure 3).This is consistent with the conclusion above that bondbreaking increases (and thus become a more importantfactor) as the reactivity of the nucleophile decreases, andas the solvent become more polar.2oThe decreased reactivity of the nitrobenzenesulphonylchlorides is also more pronounced for meta than for thepara compound, opposite to that expected from the Qvalues. A possible explanation may be that the highlyelectronegative reaction centre polarises the ring elec-trons away from the substituents so that the normalresonance of the $-nitro-group with the benzene ring isreduced. The electron-withdrawing effect of the nitro-substituents, which is then mainly inductive, is thus notadequately represented by the normal B value whichcontain a resonance contribution. A similar explanationhas been used in dissociation of pyridinium ionsI2lwhere 4-(M) substituents showed marked deviation fromthe Hammett line.Although the inhibitory effect of the nitro-substituentson the reactivity decreases as the solvent changes fromwater to methanol, the effect is still apparent for m-nitrobenzenesulphonyl chloride (Figure 3). This is incontrast to the reactions of aiiilines with sulphonylchlorides in methano1,l where no significant deviationof the m-nitro-compound occurred. This probablyreflects a more dominating influence of the bond-form-ing process in the reaction of anilines as compared topyridines, where a considerable charging and stretchingof the S-C1 bond is necessary to reach the transitionstate.I thank Mrs. I. Heggen for experimental assistance.[1/1744 Received, 23rd September, 197112o M. L. Tonnet and ,4. N. Hambly, Austral. J . Chem.. 1971,21 A. Fischer, W. J. Galloway, and J. Vaughan, J . Chem. SOC.,24, 703.1964, 3691

ISSN:1472-779X    

DOI:10.1039/P29720000489

出版商:RSC    

年代:1972

数据来源: RSC