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1981 221 Nucleophilic Substitution at Sulphonyl Sulphur. Part 1. Reactivity of Thiophen-2-sulphonyl Halides in Water and Methanol-Acetonitrile By Antanino Arcaria," Francesco P. Ballistreri, Giuseppe Musumarra, and Gaetano A. Tomaselli, lstituto Bipartimentale di Chimica e Chimica Industriale, Universita di Catania, viale A. Doria 6,951 25 Catania, Italy The reaction kinetics of substituted thiophen-2-sulphonyl chlorides and fluorides (5-OMe, 5-Me, H, 5-CI, 4-NQ2, 5-NO2) with anionic and neutral nucleophiles were studied in water at 25 'C. For the reactions of chlorides with H20, AcO-, and N,- and for the hydrolysis of fluorides U shaped Hammett plots were observed. For the reaction of sulphonyl chlorides with aniline, pyridine, imidazole, and OH -an approximately linear Mammett correlation is found.Common chloride ion effects on the hydrolysis rate constants appear to be absent. Nucleophilic sub- stitution reactions of substituted thiophen-2-sulphonyl chlorides were also studied in MeOH-MeCN, where the Hammett equation is obeyed. The data appear consistent with an SN2-type mechanism which can shift toward an S,1 or an S,N process depending on the nucleophile, on the ring substituent. and on the leaving group ability. The application of the More O'Ferrall and Thornton approaches for the prediction of substituent effects on the transition state structure seems to support the above interpretation. SEVERALstudies on the hydrolysis of benzenesulphonyl chlorides have been made both in water and in mixed aqueous s~lvents.l-~ Substituent effects,8-10 the effect of co-solvents,ll the volume of activation, the heat capacity of activation,12 solvent isotope eff ects,13 and nucleophilic catalysis 14-16 have been examined.An interpretation of the reaction mechanism differing from those previously accepted has been given 495917918 and curvature of the Hammett plot claimed.a*B Recently, a study of this reaction for a large number of substituted benzenesulphonyl chlorides was reported.lg Despite this work in the benzene series, hydrolysis reactions of thiophensulphonyl chlorides have not been studied. In previous papers we have studied the reactions of heterocyclic sulphonyl halides extensively and postulated an SAN mechanism (a two-step addj tion-elimination leading to a metastable intermediate along the reaction co-ordinate) in which the rate-determining step involved attack of a nucleophile on the sulphonyl group or S-halogen bond-breaking depending on the substrate and on the The nucleophilic reactivity order, studied by means of the Bronsted, Ritchie, and Edwarcls equations, was found to depend mainly on basicity, although there may well be some dependence on polarizability and solvation.= To extend our investigation to pure water as solvent and compare the behaviour of thiophen with that of benzene, we report here a kinetic study of the hydrolysis of substituted thiophen-2-sulphonyl chlorides and the rate constants at various temperatures of the reactions with aniline and p-anisidine in MeOH-MeCN.Moreover, reactivity data for thiophensulphonyl fluorides are very scarce,2o owing to the lack of a con- venient method for the synthesis of these derivatives. A ready conversion of the more readily available sul-phony1 chlorides into the corresponding fluorides under phase-transfer catalysis conditions has recently been reported.% The application of this crown ether catalysed fluorine-chlorine exchange reaction provided a suitable route for the preparation of thiophen-2-sulphonyl fluorides under very mild conditions. We also report here the synthesis of substituted thiophen-2- sulphonyl fluorides and the rate constants for their reactions with nucleophiles in water. RESULTS The reaction kinetics of thiophen-2-siilphonyl halides in water and MeOH-MeCN in the presence of excess of nucleo-phile were followed by potentiometric acid-base titrations (Scheme).Table 1 reports the rates of hydrolysis of sub-stituted thiophen-2-sulphonyl chlorides and fluorides in water, together with the chlorine-fluorine relative re-activities, and Table 2 the common ion effect on the hydro- lysis rate constants of substituted thiophen-2-sulphonyl chlorides by NaCl. I Hz0 SCHEMEX == 5-0hIe, &Me, H, fi-Cl, 5-NO,, 4-N0,; Y = C1; solvent = water; nu(1-I) == aniline, pyridine, iniiclazole, water, AcO-, NO,-, PI3-, OH--X = H; Y = F; solvent :water; Nu(FI) --aniline,, p-anisidine, imidazole, n-hutylamine, morpholine, piperitlinc X = 5-Me, H, 5-Cl, 5-N02, 4-E0,;Y = F; solvent water; Nu(I1) = water X = 5-OMe, &Me, H, 5-C1, &NO,; Y = C1; solvent =-MeOH-MeCN; Nu(H) = aniline, p-anisidine The Hammett plot (Figure 1) is a curve with an upward concavity, the minimum being the p-Cl derivative for chlorides and the unsubstituted compound for fluorides.Differently from the chlorides, for which a &NO2: 5-Me ratio of 0.25 is observed, sulphonyl fluorides show a 5-N02: 5-Me ratio of 17 and a larger dependence on sub-stituent effects. In water all the nucleophiles yield suliphonic acids by nucleophilic catalysis, except N3-, aniline, and imidazole for which the corresponding substitution products are obtained, in analogy to the observations for the benzene series.16 The reaction was first order in the sulphonyl halides and also TABZE1 Rate constants for the neutral hydrolysis of substituted thiophen-2-sulphonyl halides in water at 25 "C Chloride Fluoride Subs ti tuen t 1O3 kObS.*/s-l 107 kob..a/~-l kCI/kF 6-OMe 3.00 5-Me 1.27 6.169 2 054 H 0.478 1.754 2 723 5-C1 0.164 4.615 362 &NO, 0.301 104.6 29 4-NO, 0.270 30.45 89 hob& Values accurate to -&ti% (90% confidence limit); k,value can be obtained by dividing kobs, by 55.5.From ref. 24. first order in the nucleophile. The overall second-order rate constants were obtained from a plot of hoba. versus nucleophile concentration. The uncatalysed hydrolysis was in all cases negligible, as indicated by the zero intercept of this plot.k, Values are collected in Table 3. The reactions of sulphonyl chlorides with aniline, pyri- dine, imidazole, and NO,-show almost linear Hammett plots with positive p values (Figure Z), while for the re- actions with H,O, AcO-, and N,-U shaped Hammett plots I \ Y=O-31---I -5c \ / I 1 I 1 0 0.5 0-1FIGURE Hammett plots for the reactions of substituted thiophen-2-sulphonyl chlorides (I) and fluorides (11) with nucleophiles in water at 25 "C; N3-, AcO-(k = k2), H,O (k = bobs.) with a minimum value for 5-C1 derivative are observed (Figure 1). The logarithms of the rate constants of thiophen-2-sulphonyl fluoride are linearly correlated with the pK, of J.C.S. Perkin I1 0 hl -1 -L 0) 0 L + x -2 (Y-1.6) -3 (Y-1.3)U I I I I -0.5 0 0.50-2FIGURE Hammett plots for the reactions of substituted thiophen-2-sulphonyl chlorides with nucleophiles in water at 25 "C the nucleophiles in water (Figure 3) over a range of 8 log k units and 13 pK, units.Second-order rate constants for the reactions of thiophen-2-sulphonyl chlorides with aniline and p-anisidine in TABLE2 Conimon-ion effect on hydrolysis rate constants of sub- stituted thiophen-2-sulplzonyl chlorides by NaCl in water at 25 "C Substituent lo3koba./s-la lO[Nacl]/~ 1.27 0.0000 1.21 0.04081 1.27 0.3908 CH3 1.27 0.6036 1.23 1.7840 1.18 2.6791 1.07 3.6050 1.09 4.4165 0.478 0.0000 0.503 0.04226 H 0.507 0.2136 0.498 0.8876 0.501 4.3633 0.503 5.3303 0.605 9.0602 0.497 1.2074 0.164 0.0000 0.167 0.1991 c1 0.186 0.4374 0.177 0.5406 0.301 0.0000 0.292 0.01626 0.290 0.4473 NO, 0.295 0.6333 0.294 1.7392 0.280 1.9037 0.274 6 3486 * Values of kobs,are accurate to f6% (90% confidence limit).1981 223 MeOH-MeCN mixtures are reported in Tables 4 together with the activation parameters. and 5, can be ascribed to the possibility of the substituent changing the transition state structure considerably. -1 - Poor Hammett correlations seem to be feature of hydrolysis reactions of the sulphonyl group, because on changing the substituents or the solvents a change in the -2 - transition state can occur. In fact for the hydrolysis of benzenesulphonyl chlorides an inversion of effect of -3 -4 a--5--- substituents on the rate as the solvent became poorer in water has been observed.2 Wambly and his coworkers lo found a region of solvent composition in which all the substituents other than $-NO2 produce similar hydrolysis rates.Their interpretation, also based on the magni- tudes of ACp$arid AV$>is that in pure water the transition state has appreciable stretching of and production of a w 0- charge on the S-C1 bond, while in solvent mixtures of -6 - low dielectric constant bond-making will be dominant. This interpretation seems to be supported by our data, -7- as a very good Hammett correlation with a high positive p value is found for the reactions of aniline with thio- phensulphonyl chlorides in rnethanol,23y26 while in water the correlation is not so good and the slope is smaller. This could be ascribed to better solvation of the leaving chlorine group by water compared with methanol.I :The logarithms of the rate constants for the reaction of 0 5 10 PK, FIGURE Bronsted plot for the reaction of thiophen-2-sulphonyl 3 fluoride with nucleophiles in water. pK, from A. Albert and E. P. Serjeant, ' Ionization Constants of Acids and Bases ', Wiley, New York, 1962, p. 144. DISCUSSION Hammett CorreZatio.ns.-Hammett plots (Figures 1 and 2) give an indication that continuous modification of the nature of the transition state takes place as both the nucleophile and the substituents are changed. For the reaction of thiophen-2-sulphonyl chlorides thiophen-2-sulphonyl chlorides with nucleophiles like H20,AcQ-, and N,-and thiophen-2-sulphonyl fluorides with H,O show U shaped Hammett plots (Figure l), which could indicate a changeover of mechanism.The lack of a common-ion effect on the hydrolysis rate constants by NaCl (Table 2) seems to rule out the possi-bility of an Sxl mechanism and a more plausible hypo-thesis calls for an Ss2 mechanism leading to both ' loose ' and ' tight ' Sx2 type transition states depending on the substituent. For electron-donating groups a loose transition state woulcl be energetically favoured in water, which has both high ionizing power and provides TABLE3 Second-order rate constants k, for the reactions of substituted tliiophen-2-sulphonyl lialidcs with nncleophiles in water at 25 "C Substituent 5-OCH3 Halide c1 ZCO- NO,- Aniline Pyridine Iniidazolc lo3 k,"/l rno1-ls-l nucleophile ~-JCpp-----246 75.9 68.0 PIT,- 5-CH3 c1 3.00 16.2 340 98.9 73.6 2335 2 820 H 5-C1 c1 c1 2.5EiL 2.22 25.gb 13.3 709 b 220 b 126 b 613 133 99.6 163 b 110 5 280 12 400 5-NO2 C1 7.76 48.0 3 079 33 1 341 193 80 500 4-NOZ c1 6.76 34.7 306 332 162 H F" ~CII~F 0.0350 0.107 0.469 20 300 2 056 74 0 Values of k, are accurate to +60/;, (90% confidence limit).b Ref. 24. c Nucleophile, 103k,, kci/kp: p-anisidhe, 0.321, 7 220; n-butylamine, 17.9, -; morpholine, 20.3, -; piperidine, 40.8, -. with aniline, pyridine, imidazole, and NO2-the Hammett equation is not accurately obeyed (Figure 2).A treatment using o values gives the following results: Y (correlation coefficient) 0.97, p (slope) 0.98; Y 0.85, p 0'53; 0.97, p Oe6*; and p 0.43, for aniline, pyridine, imidazole, and NO.--. The positive p_" values are indicative of nucleophilic- substitution with more advanced than in the transition state. The failure to obtain good correlations strong electrophilic assistance to the leaving group by hydrogen-bonding.* On the other hand a tight transition state in which * In a previous study of solvent effects we advanccd the possi-bility of electrophilic solvation of the leaving group at the trans- ition state.23924 More recently, Kamlet and Taft 27 applied their _.solvatochromic comparison method to our data, claiming a ' push--pull ' mechanism where the lower the nucleophilicity of the attacking group, the greater the importance of electrophilic assistance to the leaving group by the protic solvent. bond-making is advanced with respect to bond-breaking would be expected for electron-attracting groups.This interpretation is supported by the selectivity order (which is expressed as kNu/KH,O and can be calculated from values in Tables 1 and 3) which increases from 5-OMe J.C.S. Perkin I1 niechanism, with appreciable participation of the empty d orbital of the sulphur atom in the bond-making pr0cess.~9 Lyate Ion E$ects.-The effect of added sodium hydr- oxide on the rates of hydrolysis of thiophensulphonyl TABLE4 Second-order rate constants for the reaction of thiophen-2-sulphonyl chloride with XC,H,NH, activation parameters 10%t/l mol-1 s-1 r A \ k,(p-OMe) MeOHQ X 15" 25" 35" 45" k, (H) AHS,,8d/kcal mol-' Ha 2.62 6.62 11.0 20.8 11.9 f0.40 1.0 5.8 p-OMee H 19.0 3.21 32.8 5.12 56.5 9.52 87.3 18.2 8.7 f0.34 10.0 f2.2 0.96 7.5 p-OMeH 21.3 3.41 38.3 f 5.70 75.2 10.1 121 17.6 10.1 f 1.1 9.4 f1.0 0.88 8.1 p-OMe 22.8 46.0 f 79.0 126 9.8 f1.4 H 2.94 5.41 8.95 14.7 9.1 f0.5 0.56 7.3 p-OMeH 22.8 1.40 39.6 f 2.45 67.2 3.88 106 5.59 8.8 & 0.3 7.8 f1.1 0.19 11.5 p-OMeHI 15.9 - 28.2 f 1.20 42.3 1.93 62.9 2.60 7.7 f1.1 6.9 f2.4 0.0 13.7 p-OMe 9.39 16.4 f 25.1 35.5 7.5 f1.3 in MeOH-MeCN and -ASt,,8d/cal mol-l K-l 28.7 1.3 36.0 f 1.1 35.4 f7.3 30.9 f3.7 37.2 f3.4 32.0 f4.7 38.3 1.7 35.5 f1.1 44.3 f3.7 39.9 f3.8 48.9 f7.9 41.7 & 4.4 a Molar fraction.trations, accurate to f6% 3.3 (see Table 1in ref. 24). 90% confidence limit. Ref. 21. and S. Gurrieri, J.Heterocyclic Chem., 1975, 12,333. to &NOz as expected for a more covalent structure in a tight transition state. The Hammett p value calculated for the H, 5-C1, and &NO, substituted sulphonyl fluoride (p 2.31, Y 0.998) * TABLE5 Second-order rate constants k, for the reaction of 5-sub-stituted thiophen-2-sulphonyl chlorides with aniline at 25 "C in MeOH-MeCN. 103k, mol-l s-l substituent MeOHb OCW, CH, H C1 NO2 p 1.0 4.80 5.05" 5.62" 10.98" 167.1" 1.06 0.96 5.46 6.13 5.12d 10.08 441.8 1.36 0.88 3.84 5.55 5.7Od 14.19 360.2 1.30 0.66 4.22 5.59 10.12 583.2 1.54 0.41 4.01 4.20 7.82 335.1 1.38 0.19 1.60 2.22 2.45d 4.31 186.1 1.36 0.0 0.758 O.89ga 1.206 1.81 14.8a 0.88 a Measured under pseudo-first-order conditions, accurate to -J=6% (90% confidence limit).6 Molar fraction. c From ref. 26. d From Table 4. c From ref. 23. is very large and comparable with that found for the alkaline hydrolysis of benzenesulphonyl fluorides (p 2.78).29 Such a large value in substitution at sul-phonyl sulphur was claimed to be indicative of an SAN f The analogous values for sulphonyl chlorides hydrolysis are p 0.46, r 0.998. McLennan 28 supported the use of p values as indicative of transition-state structure variations, if allowance is made for the different efficiency of charge transmission for differ- ent reaction series.The comparison between the p value of sulphonyl fluorides and that of sulphonyl chlorides is meaningful and would indicate a structure with more advanced bond-making in the former case. Measured under pseudo-first-order conditions from at least three kinetic runs at different nucleophile concen- (90% confidence limits). " Second-order rate constants ratio at 25 "C. The ratio in water is equal to 'Ref. 23. I A. Arcoria, E. Maccarone, G. A. Tomaselli, R. Cali, chlorides is to enhance the rates strongly (Table 3). Differently from the previous nucleophiles, OH- gives a good linear Hammett plot (Y 0.999 7, p 1.53)which indicates that in this case bond-making predominates.Our results are in agreement with those obtained pre- viously for the hydrolysis of benzer sulphonyl chlorides by R~gne,~ who found a balanced effect between bond- making and bond-breaking in the transition state for neutral hydrolysis, but dominant bond formation for alkaline hydrolysis. Bronsted Relationships.-Previously for the reactions of thiophen-2-sulphonyl chloride with nucleophiles in water we found a good Bronsted relationship with a pE value of 0.68.24 In the present work we studied the reactions of thiophen-2-sulphonyl chlorides with fewer nucleophiles and the number of points does not allow suitable statistical correlations.However, even if the results are less accurate in this case, the PE values obtained (Table 6) give a rough indication that the sensitivity to the nucleophile change increases with the electron-attracting character of the substituent, accord- ing to the previous mechanistic interpretation. How-ever, if the log k values for the reactions of each sul- phonyl chloride with the nucleophiles are plotted, according to Hudson and Klopman,3O against the log k values for the corresponding reactions of the unsub- stituted thiophensulphonyl chloride with the same nucleophiles, a series with good correlation is obtained. The slopes of such correlations (pN, Table 6) give the sensitivity of the reaction rate to changes in charge distribution in the nucleophile (as do PB values).Also in this case, in which it is possible to consider all the nucleophiles, the pN pattern is analogous to the PE pattern. The Bronsted value for the reaction of thiophen-2- sulphonyl fluoride with nucleophiles in water (pN 0.54, see Figure 3) is comparable with that reported for the reactions of thiophen-2-sulphonyl chlorides with aniline in methanol.21 If the log k values for the reactions of substituted sulphonyl chlorides with water are plotted against the log k values for the corresponding reactions of thiophen- sulphonyl fluorides, we obtain PL values (Table 6) which indicate decreasing sensitivity to the leaving group effect upon decreasing the electron-donor character of the substituent. Leaving Group Mobilities.-Fluorides are hydrolysed more slowly than the corresponding chlorides and the relative reactivity ratios are strongly affected by the substituent in the aromatic framework.The kcl/klp ratios show a regular trend in decreasing with increasing electron-withdrawing character of the substituent. The data for the hydrolysis of sulphonyl chlorides and fluorides are consistent with an SN2 type mechanism leading to a range of transition states with different degrees of bond-making and bond-breaking depending on the substituent. For electron-releasing substituents bond-breaking would be more advanced than bond formation and a high kc~/k~ratio would be expected, owing to the larger energy required for the cleavage of the S-F bond with respect to S-C1.For electron-with-drawing subst ituents bond-making would be dominant and small kc,/kp values would be expected. Experi-mental results confirm this prediction (Table 1). How-ever, the possibility that an intermediate is formed along the reaction co-ordinate, according to an S-N mechan-ism, especially for powerful electron-attracting sub-stituents such as &NO,, cannot be completely ruled out in this case. The relative leaving-group mobilities in the neutral and alkaline hydrolysis of benzenesulphonyl chloride and fluoride, have been related by Swain and Scott 31 to the degree of bond-breaking, which is higher on increasing the ka/kp ratio. According to this interpretation, the decreasing kallk~ratios on increasing the basicity of the nucleophile in thiophen-2-sulphonyl fluoride reactions (Table 3) indicate a variable transition state structure with decreasing S-F bond cleavage along the series.Reactions of Substituted Thiophen-2-suLphony1 ChLorides in Mixed Solvents.-Second-order rate constants for the reactions of thiophen-2-sulphonyl chlorides with aniline and P-anisidine in CH,OH-CH,CN are reported in Tables 4 and 5 together with the activation parameters. An inversion of the substituent effect with respect to water is observed in CH,OH, CH,CN, and in mixed solvents. These findings suggest the possibility that bond-making is the predominant process in these solvents, owing to the lower electrophilic assistance to the leaving group by hydrogen bonding.The increasing ratio hp-anjsidinelkaniiinein the solvent series H20, CH30H, CH,OH-CH,CN, CH,CN (Table 4) seem to support the idea of an increasing predominance of bond-making leading to a tighter transition state along the series. More O'Ferrall Plot.-More O'Ferrall diagrams 32 have been recently used to examine the nucleophilic substitution reactions of benzyl The data for sulphonyl halides seem to have some affinity with these reactions. The predictions which can be made by applying this kind of approach are related to the placement of the TABLE6 pE and pN values for the reactions of substituted thiophen- sulphonyl chlorides with nucleophiles in H,O at 25 "C and pL values for the leaving group for the neutral hydrolysis of substituted thiophensulphonyl halides in H,O at 25 "C Substituent 5-OCH3 5-CH3 H 5-C1 4-NO, &NO; PE 0.50" 0.59 0.686 0.736 0.706 0.75 Yd 0.98 0.98 0.98 0.98 0.998 0.97 PN' 0.73 0.87 1.00 1.10 1.08 1.34 Yd 0.999 0.994 0.997 0.999 0.991 PL f -0.36 -0.38 -0.28 -0.21 -0.16 a Obtained with C,H,NH,, C,H,N, and H,O as nucleophiles.bObtained with C,H,N,H, C,H,N, NO,-, N3-, and H,O as nucleophiles. Obtained with C6H6N,NO,-, N3-, and H,O as nucleophiles. Correlation coefficient. e See text. For the nucleophiles we used the following pK, values: 2r C,H,NH,, 4.58; C,H,N, 5.23; NO,-, 3.37; N3-, 4.74; AcO-, 4.75; imid-azole, 7.10; OH-, 15.7; H,O, -1.74. /Obtained from the relationship log[k (XC4H2S-S0,CI) /k(XC,H,S-S0,F) J = PLA~K,where ApK, = pK,,, (-5.7) -pK,, (3.45).transition state along the reaction co-ordinate. Suppos-ing that in the sulphonyl chlorides hydrolysis the transi- tion state lies at the midway point A on the SN2 path when the ring substituent is 5-C1 (which represents a minimum in the Hammett plot), we can test the hypo- thesis by analysing substituent effects. Substituents with a larger electron-donor character than 6-C1 will have a stabilizing effect on the N 6 X structure (upper left corner, Figure 4). The corresponding transition state B will lie in a reaction co-ordinate lying between SN1 and SN2paths and will involve more S-X cleavage, less N-S form-ation, more positive charge development on s,and more negative charge development on X.Consequently for electron-donating ring substituents high ka/kp ratios are expected together with less selectivity, as observed from the k~l/k~ratios in Table 1 and from the ratios kAcO-/k,O or k~~,-/k~*o,taken as selectivity measure-ments, which can be calculated from the data in Table 3. On the other hand an electron-attracting substituent will stabilize the structure k-S-X (lower right corner, Figure 4). The new transition state C will be tighter with increased bond formation and reduced bond cleav- age with respect to A. This prediction is in agreement with the increasing sensitivity to the entering group basi- citv (increasing PE or PN values. Table 6) or with the de- 226 creasing sensitivity to the leaving group effect (decreasing pL values, Table 6) on increasing the electron-attracting character of the substituent.Both an early, D, and a late, F, transition state would not be consistent with the experimental results. In fact, in this case the upper left corner of Figure 4is essentially parallel to the reaction co-ordinate (Harnmond effect) and a more electron-releasing group than 5-C1 will affect 0 or cl > b u-. U U c 0 n X I u) *I -$-xN N-S bond formation N O* cf vo FIGURE A More O'Ferrall plot for nucleophilic substitution 4 reactions at sulphonyl sulphur, where N is the nucleophile and X the leaving group. Contour lines of potential energy are deleted, while single solid lines represent the paths of minimum potential energy.The x axis represents the reaction co-ordin- ate for an SN~or SAN process and the y axis that for an SN~ process. The structure in the lower right corner represents the penta-co-ordinate intermediate formed by the SANmechanism. Minima and maxima are represented by circles and crosses, respectively the position of the transition state little, because part of the motion is helped (allowing X to depart more easily) and part is hindered (making N less eager to bond). The larger positive p values observed in sulphonyl fluorides hydrolysis for electron-withdrawing substitu- ents with respect to that of sulphonyl chlorides in- dicates a transition state structure with more bond formation and less S-X cleavage (negative charge development on the sulphur atom) than that repre- sented by C, in which less negative charge development on the sulphur atom occurs.In this case the reaction co- ordinate would lie between SN2and SAN processes and closer to the latter one. The transition state could lie, say, at a midway point, such as E, or on the co-ordinate for the §AN reaction depending on the length of the motion (which depends on the symmetry of the energy surface at the saddle point). Moreover, every change making X a worse leaving group (change of C1 to I?, solvents with low electrophilic J.C.S. Perkin I1 assistance ability, etc.) will move the transition state, say, G, in order to give a new transition state with more N-S formation, essentially unchanged S-X cleavage, and more dispersal of positive charge from sulphur to the nucleophile. This prediction is in accord with the increasing p values in the reactions of substituted anilines with thiophen-2-sulphonyl chloride upon changing the solvent from water to alcohols and to aprotic solvents.* EXPERIMENTAL General.-Potentiometric titrations were carried out by a digital pH meter, Amel model 333, equipped with a motor-ized burette, Amel 233.Materials.-Aniline, p-anisidine, imidazole, n-butylamine, morpholine, pyridine, and piperidine were purified by distillation or crystallization. Reagent grade inorganic sodium salts were used. Commercial methanol and aceto- nitrile were used without further purification.Thiophen-2-sulphonyl chloride and 5-subs titu ted thiophen- 2-sulphonyl chlorides were obtained by literature procedures.26 Thio- phen-2-sulphonyl fluoride was prepared by a literature method,36 b.p. 75-76" at 1 mmHg. Substituted thiophen- 2-sulphonyl fluorides were synthesized by the procedure described by Bianchi and Cate.25 All new fluorides analysed correctly for C, H and N. 5-Methylthiophen-2-sulphonyl jlzcoride (600/,) had b.p. 44" at 0.1 mmHg, vmax, 1 325 (SO, asym. str.) and 1 15.5 cm-l (SO, sym. str.); m/e 180 (M+). 5-ChZorothiophen-2-sulphonyl fluoride formed yellow prisms (50yo), m.p. 11 1- 113'; vmax. 1 335 (SO, asym. str.) and 1 160 cm-l (SO, sym. str.); m/e 200 (M+). 5-Nitrothiop~~eiz-2-sulp~~onylfluoride afforded yellow prisms (520/,),m.p.35-37', v,,,,. 1 350 (SO, asym. str.) and 1 130 cm-l (SO, syni. str.); m/e 211 (Mt). 4-Nitrothiophen-2-sulphonylfluorzde yielded prisms (52%), m.p. 58-60', vmax. 1 330 (SO, asym. str.) and 1 180 cm-l (SO, sym. str.); m/e 211 (M+). Kinetic Procedures.-Second-order rate constants were measured potentiometrically, under pseudo-first-order con- ditions, following the procedure already described. 1, , Rates for thiophen-2-sulphonyl chlorides with azide were determined by titration. In a typical experiment, a solution of sodium azide (9.5 ml, lW3111) was added to each of 12 volumetric flasks (10 ml) and the volume was brought to the mark with a solution of thiophensulphonyl chloride in acetone (0.5 ml).Flasks were removed from a constant temperature bath at approximately equal percentage intervals of completed reaction and were quenched by swirling in a cold acetone bath. Two infinity flasks were removed and quenched after 10 half-lives. 'The solutions were titrated with standardized aqueous sodium hydroxide using Bromothymol Blue as indicator. Pseudo-first-order rate constants were calculated using a least-squares computer program by relationship ( 1) where V 1 17 -V,h --In ---t v --vt is the experimental infinity titre, V, the initial titre, and Vt the titre at time t. The second-order rate constant h, was obtained from at least three determinations of k, according to relationship (2). * p-Value, solvent: -1.85, H,O; -2.06, CII,OH; -1.98, C,H,OH; -2.02, butan-1-01; -3.28, acetone; -3.36, benzoni-trile; -3.22.nitroethane; -3.53. nitr~benzene.~~ Rates of reactions of thiophensulphonyl chlorides with the other nucleophiles were determined potentiometrically by continuous titration of the acid product with standard- ized aqueous NaOH, following the procedure described .21$ 24 The addition of the titrant was made using a suitable rate to keep the pH of the mixture almost constant. However preliminary measurements and Rogne’s data showed that the hydrolysis rates of sulphonyl chlorides are pH-inde-pendent in the pH range 3-9. In this case also the rate constants are the result of at least three determinations of hob& according to relationship (3).The reagent concen-(3) trations ranged from ca. 0.000 2 to GU. 0.003~for thiophen- sulphonyl chlorides and from ca. 0.01 to ca. 0.2111 for the nucleophiles, depending on the reaction rates. Although not identified, some of the presumed products are well known in the benzene series.36 Thus aromatic sulphonyl chlorides react readily in aqueous solution with NaN, and AcONa to yield sulphonyl azide and a mixed anhydride,,’ respectively. We thank C.N.R. (Rome) for financial support. [9/1913 Received, 3rd December, 19791 REFERENCES G. Berger and S. C. J. Olivier, Rec. Trav. chim., 1927, 46, 516. I. Hedlund, Arkiv. Kemi Min. Geol., 1940, 144, 1. H. K. Hall, J. Amer. Chem. SOL, 1956, 78, 1450. 4 F. E. Jenkins and A. N.Hambly, Austral. J. Chem., 1961,14, 190. R. V. Vizgert, Russ. Chem. Rev., 1963, 32, 1. 6 C. G. Swain and C. B. Scott, J. Amer. Chem. SOC., 1953, 75, 246. 7 A. F. Popov, V. I. Tokarev, L. M. Litvinenko, A. I. Torganik,Reakts. Sposobnost Org. Soedinenii, 1957, 4, 658 (Chem. Abs., 1969, 70, 28,26613). R. V. Vizgert and E. K. Savchuk, Zhur. obshchei Khim., 1964, 34, 3396. Q 0. Rogne, J. Chem. SOC.(B),1968, 1294. 10 M. L. Tonnet and A. N. Hambly, Austral. J. Chem., 1971,24, 703. 11 M. L. Tonnet and A. N. Hambly, Austral. J. Chem., 1970,23, 2435. 1% R. E. Robertson and B. Rossall, Canad. J. Chem., 1971, 49, 1441. 13 B. Rossall and R. E. Robertson, Canad. J. Chem., 1971, 49, 1451. 14 0. Rogne, J. Chem. SOC.(B),1970, 727. 0.Rogne, J. Chem. SOC.(B),1970, 1056. Is R. Foon and A. N. Hambly, Austral. J. Chem., 1962, 15, 684. 17 R. E. Robertson, Progr. Phys. Org. Chem., 1967, 4, 213. E. Ciuffarin, L. Senatore, and M. Isola, J.C.S. Perkin II, 1972, 468. A. R. Haughton, R. M. Laird, and &I. J. Spence, J.C.S. Perkin II, 1975, 637. zO E. Maccarone, G. Musumarra, and G. A. Tomaselli, J. Org.Chem., 1974, 89, 3286. 21 A. Arcoria, E. Maccarone, G. Musumarra, and G. A. Toma-selli, J. Org. Chem., 1973, 38, 2457; 1974, 39, 1689, 3595. E. Maccarone, G. Musumarra, and G. A. Tomaselli, J.C.S. Perkin 11, 1976, 906. 28 A. Arcoria, V. Librando, E. Maccarone, G. Musumarra, and G. A. Tomaselli, Tetrahedron, 1977, 33, 105. a4 A. Arcoria, F. P. Ballistreri, and G. A. Tomaselli, Tetra-hedron, 1978, 34, 2545. T. A. Bianchi and L. A. Cate, J. Org. Chem., 1977, 42, 2031. E. Maccarone, G. Musumarra, and G. A. Tomaselli, Ann. Chim. (Italy), 1973, 88, 861. 27 M. J. Kamlet and R. W.Taft, J.C.S. Perkin II, 1979, 349. D. J. McLennan, Tetrahedron, 1978, 2331. E. Ciuffarin and L. Senatore, Tetrahedron Letters, 1974, 17, 1635. 30 R. F. Hudson and G. Klopman, J. Chem. SOC., 1962, 1062. C. G. Swain and G. B. Scott, J. Amer. Chem. SOC., 1953, 75, 141. a* R. A. More O’Ferrall, J. Chem. SOC.(B),1970, 274. See also E. R. Thornton, J. Amer. Chem. SOC., 1976, 89, 2915; I). A. Winey and E. R. Thornton, ibid., 1975, 97, 3102; W. P. Jcncks,Chem. Rev., 1972, 72, 705. 33 P. R. Young and W. P. Jencks, J. Amer. Chem. Soc., 1979,101, 3288. 34 J. M. Harris, S. G. Shafer, J. R. Moffatt, and A. R. Becker, J. Amer. Chem. SOC., 1979, 101, 3295. 36 W. Steinkopf and T. Hopner, Annalen, 1933, 501, 174. 3u C. M. Suter, ‘ The Organic Chemistry of Sulphur,’ Wiley, New York, 1945, chs. 5 and 6. 37 R. M. Laird and M. J. Spence, J. Chem. SOC.(B),1971, 1434.

ISSN:1472-779X    

DOI:10.1039/P29810000221

出版商:RSC    

年代:1981

数据来源: RSC