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Vibrational and NMR spectroscopic studies of a thiolsulphonate produced from the non-catalytic hydrogenation of polybutadiene
Journal of Molecular Structure, 268 (1992) 363-372 Elsevier Science Publishers B.V., Amsterdam
363
Vibrational and NMR spectroscopic studies of a thiolsulphonate produced from the non-catalytic hydrogenation of polybutadiene H.G.M. Edwards”, A.F. Johnsona, I.R. Lewisa, D.J. Maitland” and N. Webb” “Interdisciplinary Research Centre in Polymer Science and Technology, Chemistry and Chemical Technology, University of Bradford, Bradford, West Yorkshire, BD7 1DP (UK) bCastrol Research Laboratories, Whitchurch Hill, Pangbourne, Reading, Berkshire, RG8 7QR (UK) ‘Schering Industrial Chemicals, Gorsey Lane, Widnes, Cheshire, WA8 OHE (UK) (Received 13 November 1991)
Abstract Mass spectrometry, ‘H NMR, 13CNMR, 2D NMR, FT-IR and Raman spectroscopy have been used to establish the structure of a thiolsulphonate by-product in the non-catalytic hydrogenation process for polybutadiene, which makes use of p-toluene sulphonylhydrazide as a reaction intermediate. The formation of this product has not been reported previously under such conditions. Spectroscopic evidence is presented for the molecular structure.
INTRODUCTION
p-Toluenesulphonylhydrazide is a convenient reagent for the hydrogenation [ 1,2] of unsaturated organic molecules, as it avoids the use of the high temperatures and pressure required by some other methods of hydrogenation [ 3 1. The mild hydrogenation conditions are attributed [ 2 ] to the in-situ generation of diimide from p-toluenesulphonylhydrazide: CH3-C6Hq-S02NH-NH2+CH3-C6Hq-SOnH+NH=NH
(1)
The by-products of the reduction reaction are believed to be nitrogen and ptoluene sulphinic acid [ 2 1. Reactions ofp-toluenesulphonylhydrazide in highly oxidising media such as peroxy acids [ 41 have produced other by-products. The pyrolysis ofp-toluenesulphonylhydrazide [ 51 in vacua at 140’ C has resulted in the formation of ptolyl p-toluenethiolsulphonate by disproportionation. This p-tolyl p-tolueneCorrespondence to: Dr. H.G.M. Edwards, Interdisciplinary Research Centre in Polymer Science and Technology, Chemistry and Chemical Technology, University of Bradford, Bradford, W. Yorkshire, BD7 lDP, UK.
0022-2860/92/$05.00
0 1992 Elsevier Science Publishers B.V. All rights reserved.
364
thiolsulphonate has also been prepared by the reaction of the acid chloride with powdered zinc metal [ 61. It has been postulated [ 41 that the p-tolyl p-toluenethiolsulphonate is only formed when there is no species present which allows the diimide to be reduced. Contrary to this suggestion, we now report the isolation of a solid by-product, which was formed during the hydrogenation with p-toluenesulphonylhydrazide, and which has been identified as p-tolyl p-toluenethiolsulphonate. The results of detailed NMR and vibrational spectroscopic studies of this by-product are reported. EXPERIMENTAL
Hydrogenation Polybutadiene (Aldrich 18, 128-2, 1.50 g) was dissolved in hot dry xylene (80 ml) with continuous stirring under a nitrogen atmosphere. p-Toluenesulphonylhydrazide (10.43 g) in dry xylene (70 ml) was added and the temperature raised to 115°C. After 2 h the mixture was allowed to cool and the solid residue filtered off. The filtrate was added to an excess of methanol (500 ml) and the polymer precipitated as a white solid. The methanol solution was concentrated by removing xylene and methanol under vacuum. The concentrated liquor yielded white crystals (0.5 g ) , m.p. 72-73.5 ‘C. Nuclear magnetic resonance spectroscopy ‘H and 13C!NMR spectra (‘H broad-band decoupled and DEPT135) were acquired (CF,COOD solution, relative to Me,Si as internal standard) using a JEOL GX270 FT NMR spectrometer fitted with a dual 5 mm C/H probe, operating at 270 and 67.8 MHz respectively, using standard JEOL software. Carbon atom assignments were verified using 2dimensional 13C-lH COSY and 13C-lH FLOCK [ 71 experiments to establish ‘Jc_n and 2’3Jc_Hcorrelations. Mass spectromtry Samples were analysed using an AEI-MS902 mass spectrometer with an electron voltage of 70 eV and a source temperature of 200°C. Infrared spectroscopy The infrared spectra of the crystals, isolated as described above, were recorded with a Perkin-Elmer Model 1720-X Fourier-transform infrared spectrometer fitted with a mercury cadmium telluride (MCT) detector operating at 77 K by preparing a KBr disc (9 : 1 of KBr: crystals ). The background spec-
365
of potassiumbromidewas also recorded.Spectrawererecorded (10 scans) at 2.0 cm-’ resolutionover the range 4000-400 cm-’ (Fig. 1). Data were collected by the spectrometerdata station and transferredonto an IRM compatible personal computer for subsequentdata analysis,e.g. spectral subtraction and band intensity measurements. trum
Raman spectroscopy
Raman spectra of the crystals were obtained using a Jobin-Yvon Raman microprobe‘MOLE’ inst~ment with argon-ion laserexcitation at 488 nm and typical laserpowers of 100 mW at source, representingapproximately20 mW at the sample. Using a microscope objective of 100x ma~ification and a coupled Hitachi colour television camera, a total magnification at the viewing screenof about 3 x 103timeswasobtained.This representsa displayof 125x 125 p2 of sampleareaon the 35 x 35 cm2screen.The couplingof the televisionwith a camera allowedthe production of pho~~aphs of the sample crystalsunder investigation.Spectrometercontrol and data acquisitionwere effected using a Thorn-~MI PET computer. This facility allowed spectralaccumulationto be made over predeterminedwavenumberrangesto improve the signal-to-noise ratio. The Raman spectraobtained are given in Figs. 2-4. A numberof model compounds (toluene andp-toluenesulphonicacid) were 100
I
I
I
I
I
I
I
1600
1200
I
80
4000
3600
3200 2800 2400 2000
Wavenumber
(cm-1
800
)
Fig. 1. Infrared spectrum of p-tolyl p-toluenethioleulphonate in the range 4000-400 cm-‘.
366
r
LL
J.di i
200
300
400
500 Roman
600 Shift
700 T-300
900
1
10
(cm-l)
Fig. 2. Raman spectrum ofp-tolyl p-toluenethiolsulphonate in the range .4v=200-1000 cm-‘.
1100
1200
1300 Roman
1400 Shift
1500
1600
1700
II
(cm-l)
Fig. 3. Raman spectrum of p-tolylp-toluenethiolsulphonate in the range Av= 1000-1800 cm-‘.
367
c-2600
2700
2800
2900 Roman
3000 Shift
3100
3200
3300
3 00
(cm-l)
Fig. 4.Raman spectrum of ~-~lylp-toiuenet~iolsulphona~
in the range Av=2600-3400cm-‘.
analysed using FT-IR and conventional Raman spectroscopy (described below), in order to facilitate the identification of the bands observed in the vibrational spectra of the crystals obtained from the reaction mixture. Excitation was effected using a Spe~ra-Physics Model 2020/5 argon-ion laser operating at 488 nm with a nominal output of 1.5 W. The scattered radiation was analysed using a SPEX Industries Model 1401 spectrometer with a reciprocal linear dispersion of 20 cm-’ mm-’ at 488.0 nm, andphoton-counting detection using an EM1 9789 QA photomultiplier. Acquisition of data and control of the spectrometer were accomplished using a Nicolet 1180 microcomputer which permitted the accurate multiscanning of predetermined spectral wavenumber ranges. The linearity of intensity response of the spectroscopic apparatus used in the study of the model compounds had previously been verified ]8 ] using systems of known internal-field effects, and a geometric-optical [9] effect of 1 was determined. Calibration was effected using a neon emission spectrum and wavenumbers are correct to within 1 cm-‘. RESULTS
The mass sp~tromet~ data were found to be very similar to those published previously [lo]. The NMR results are presented in Table 1 and the results of the vibrational
368 TABLE 1 ‘H NMR and 13CNMR spectroscopic data forp-tolylp-toluenethiolsulphonate
Atom No.
SH
2-H 3-H
7.55 7.35
d d
5-H 6-H 7-H,
7.35 7.55 2.48
d d s
2’-H 3’-H
7.26 7.21
d d
5’“H 6’-H 7’ -HQ
7.21 7.26 2.40
d d s
(1)in CF,COOD
Atom No.
&
C-l c-2 c-3 c-4 c-5 C-6 c-7 C-l’ C-2’ C-3’ C-4’ C-5’ C-6’ C-7’
139.86 129.74 131.67 149.21 131.67 129.74 22.05 124.27 138.74 132.47 146.25 132.47 138.74 21.81
*In ‘H NMR ail J values 8.1 Hz.
analyses are given in Table 2. A full vibrational spectroscopic study of this type of compound has not been undertaken previously. The bands in the vibrational spectra have been assigned by reference to the IR [ 111 and Raman 112,131 spectroscopic studies of the selected model compounds, toluene andp-toluenesulphonic acid. DISCUSSION
A literature search revealed that, although ( 1) is a known compound [ 141, m.p. 76”C, for which some spectroscopic data have been reported [5,6,10], detailed interpretation of the infrared and NMR spectra has not been attempted. Raman spectra have not been reported previously for this compound. The mass spectroscopic data show inter alia a molecular ion at m/z 278 and a base peak at 139. This suggested that the molecule was symmetrical and possibly a simple dimer of C$H,SO. The ‘H NMR spectrum shows, in addition to two methyl singlets at 6 2.40 and 2.48, the presence of two pairs of doublets between S 7.21 and 7.55. The coupling constants for both doublet pairs are J= 8.1 Hz, suggesting the presence of two para-disubstituted benzene rings. A homonuclear spin-decoupling experiment revealed that the doublet resonances at 6 7.35 and 7.55 are spin coupled, as are the doublet resonances at S
369 TABLE 2 Vibrational assignment for p-tolyl p-toluenethiolsulphonate Band assignment
Wavenumbers (cm-‘) Infrared
v,(C-H) va(C-W v,(CH,) v,(CH,)
v(C-H) v(CH,) Aromatic ring stretch Aromatic ring stretch Aromatic ring stretch Aromatic ring stretch &CH,) k(CH,) &(C-CH,) &(C-CH,) v.((C)-w?-(S)) S(C-H) Aromatic ring stretch Aromatic ring stretch v,((C)-soz-(S)) &C-H) G(C-8) Aromatic ring stretch v(C-C) Aromatic ring deformation v(C-S) P(C-H)
2978 2952 2918 2864 1625 1593 1575 1487 1450 1401 1379 1321 1296 1220 1141 1073 1038 1015 812 703 653
ww
585
P@W
522 483 462
v(S-S) 6(CSO)
Raman
2900
1595 1495 1400 1390 1380 1320 1300 1220 1180 1140 1090 1080 1020 800
620 580 560 530 510 480 462 450
440
S(CSS) S(CSS) S(CS0)
r(CH,)
380 360 340 315 305 285 260 235
370
7.21 and 7.26. The presence of AX and AM pairs of doublets in the aromatic region, plus the fact that the methyl groups are magnetically non-equivalent, suggested the asymmetric molecule ( 1).
Whilst this proposed structure might appear at variance with the mass spectroscopic data, in particular the base peak at 139, it has been reported [lo] that sulphur-oxygen compounds are prone to fragmentary rearrangement during the mass spectroscopy experiment; therefore asymmetry in the compound is not excluded. A doublet resonance in the ‘H NMR spectrum at 6 7.55, the most downfield signal, obviously arises from H-2 and H-6, and the singlet resonance at 6 2.48 from 7-H3, as both sets of signals would be expected to be the most deshielded protons of their type due to ortho and para effects of the sulphonyl moiety. This information, together with the results of the homonuclear spin decoupling experiments, enabled unambiguous assignment of the ‘H NMR data (Table 2). A 13CNMR DEPT experiment confirmed that the signals at 6 149.21, 146.25, 139.86 and 124.27 were due to quate~ary carbons. The 13CNMR assignments of all methine and methyl signals were determined using a 13C-lH COSY [ lJC_H] experiment, which permitted correlation of the ‘H and 13CNMR data. The unambiguous assignments of the 13CNMR resonances of C-4 and C-4’ were established using the FLOCK pulse sequence of Reynolds et al. [ 71, which is useful for detecting long-range 13C-lH correlations ( nJc_Hwhere n is two or three), When the mixing times of d’ and 4’ were 84 and 44 ms respectively (equivalent to nJc_H of 10 Hz) the 7-H3 resonance at S 2.48 indicated correlations with 13CNMR resonances at 6 131.67 (C-3 and C-5) and 149.21 (C-4), and the 7’ -Hz resonance at 6 2.40 revealed correlations with the 13C NMR resonances at S 132.47 (C-3’ and C-5’ ) and 146.25 (C-4’ ). The FLOCK experiment also revealed Jc_c_n correlations between the signal in the ‘H NMR for 2’-H and 6’-H at S 7.26 and those in the 13CNMR at 6 132.47 (C-3’ and C-5’ ) and 6 124.27, which identi~ed the latter as C-l’. Thus the resonance at S 139.86 is due to C-l. Somewhat surprisingly these results indicate that it is the C-4 and C-4’, not the C-l and C-l’, carbon atoms that are most deshielded by the thiolsulphonate linkage. A similar effect has been noted recently in an NMR study of a series of 4-substituted and 4,4’-disubstituted diphenyl sulphoxides and sulphones [ 151. The infrared spectrum of thep-tolylp-toluenesulphonate shows absorptions at 3055, 3036 and 2918 cm-l which are ascribed to aromatic C-H stretching vibrations and bands at 2978,2952 and 2864 cm-’ which are assigned to the aliphatic CH3 vibrations. Prominent bands attributable to the aromatic ring stretching vibrations are also found at 1625, 1593,1575,1487,1220,1038 and
371
1015 cm-‘. The symmetric and asymmetric v (SO) stretching vibrations of the C-S02-S unit are observed at 1321 and 1141 cm-‘. The C-S stretches are found at 1073 and 703 cm-’ and the S-S vibration is observed at 483 cm-‘. The symmetric and asymmetric CH3 deformation bands are observed at 1450 and 1401 cm-l respectively. The symmetric C-CH, deformation is seen at 1379 cm-‘. The CH deformation is assigned to a band at 1296 cm-’ and a C-H rock is observed at 653 cm-l. The band at 812 cm-l is assigned to a ring deformation that is characteristic of a para-disubstituted aromatic ring. The SO, deformation is found at 585 cm-‘. The CSO deformation is found at 462 cm-‘, whilst the SO, rock is observed at 522 cm-l. The detailed vibrational assignments proposed here were made by correlation with the vibrational spectra of toluene, p-toluenesulphonic acid and ethanesulphonic acid [ 161. The Raman spectrum shows the C-H vibrations, both symmetric and asymmetric, at 3075 and 3060 cm-‘. The aromatic ring stretching vibrations are observed at 1595,1495 and 1020 cm-l. The symmetric and asymmetric v (SO) stretching vibrations of the C-SO,-S unit are produced at 1320 and 1140 cm-l. The aromatic ring stretching vibrations are observed at 1220 and 1180 cm-l respectively. The other principal fundamental vibrations are the C-S stretch at 1080 cm-’ and the SS stretch at 480 cm-‘. The C-H deformations are observed at 1300 and 1090 cm-l, whilst the symmetric and asymmetric C-CH, deformations are seen at 1390 and 1380 cm-’ respectively. The band at 800 cm-’ is assigned to a ring deformation that is characteristic of a para-disubstituted aromatic ring. The SO, deformation is assigned to the band at 580 cm-‘. The CSO deformations are at 462 and 340 cm-‘, and the CSS deformation at 380 and 360 cm-‘. The SO, rocking band is found at 510 cm-l and the CHB torsion is assigned to 235 cm-l. There is generally very good agreement between the Raman and infrared spectral wavenumbers, and assignments favour the asymmetric C-SO,-S unit in the molecule. The symmetric C-SO-SO unit would provide an essentially different spectroscopic feature. Attempts were made to obtain polarization measurements in solution but, due to the limited solubility of the compound in a number of common solvents, these were not obtainable. Assignments are made on the basis of the model compounds (mentioned above) and the authors have no reason to believe that any untoward band shifts have occurred. CONCLUSIONS
This work provides evidence for the production of a hitherto unsuspected by-product found during the diimide hydrogenation process. This product has been identified unambiguously as p-tolyl p-toluenethiolsulphonate using vibrational and NMR spectra, and a vibrational analysis is presented. The product was prepared at lower temperatures than has been suggested in the litera-
ture and under novel reaction conditions, in the presence of polymer unsaturation and under diimide reduction. The isolation of the by-product establishes that the hydrogenation process is less efficient than previously thought. Conditions have not been established, of temperature, time, and ratio of hydrogenating agent to polydiene, where it is possible to carry out the hydrogenation of the polydiene without producingp-tolylp-toluenethiolsulphonate, i.e. the by-product is always present. ACKNOWLEDGEMENTS
The authors wish to express their thanks to the Science and Engineering Research Council and Castro1 Ltd. for financial support to IRL. We would like to thank Mr. D.W. Farwell for assistance with the recording of the Raman and NMR spectra and for the preparation of the diagrams for this publication. Also, thank you to Mr. R. Nettleton for recording the mass spectra.
REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
H.J. Harwood, D.B. Russel, J.J.A. Verthe and J. Zymonas, Makromol. Chem., 163 (1973) 1. L.A. Mango and R.W. Lenz, Makromol. Chem., 163 (1973) 13. H. Rachpudy, G.G. Smith, V.R. Raju and W.W. Graessley, J. Polym. Sci., Polym. Phys. Ed., 17 (1979) 1211. J.J. Jagodinski and R.R. Sicinski, Tetrahedron Lett., 23 (1982) 1837. H.S. Hertz, B. Coxon and A.R. Siedle, J. Org. Chem., 42 (1977) 2504. D. Barnard, J. Chem. Sot., (1957) 4073. W.F. Reynolds, S. McLean and M. Perpick-Dumont, Magn. Reson. Chem., 27 (1989) 162. H.G.M. Edwards, D.W. FarwelI and A. Jones, Spectrochim. Acta., 45A (1989) 1165. D.G. Rea, J. Opt. Sot. Am., 49 (1959) 90. S. Kosuka, H. Takahashi and S. Oae, Bull. Chem. Sot. Jpn., 43 (1970) 129. N.A. Colthup, Interpretation of Infrared Spectra, A.C.S. Audio Courses, ACS, Washington, D.C., 1972. D.A. Long, Raman Spectroscopy, McGraw-Hill, New York, 1977. G. Herzberg, Infrared and Raman Spectra of Polyatomic Molecules, Van Nostrand Co. Inc., London, 1945. R. Otto, J. Lowenthal and A. von Gruber, Justus Liebigs Ann. Chem., 27 (1869) 102. R. Chandraeekaran, S. Perumal and D.A. Wilson, Magn. Reson. Chem., 27 (1989) 360. H.G.M. Edwards and D.N. Smith, J. Mol. Strut., 238 (1990) 27.
363
Vibrational and NMR spectroscopic studies of a thiolsulphonate produced from the non-catalytic hydrogenation of polybutadiene H.G.M. Edwards”, A.F. Johnsona, I.R. Lewisa, D.J. Maitland” and N. Webb” “Interdisciplinary Research Centre in Polymer Science and Technology, Chemistry and Chemical Technology, University of Bradford, Bradford, West Yorkshire, BD7 1DP (UK) bCastrol Research Laboratories, Whitchurch Hill, Pangbourne, Reading, Berkshire, RG8 7QR (UK) ‘Schering Industrial Chemicals, Gorsey Lane, Widnes, Cheshire, WA8 OHE (UK) (Received 13 November 1991)
Abstract Mass spectrometry, ‘H NMR, 13CNMR, 2D NMR, FT-IR and Raman spectroscopy have been used to establish the structure of a thiolsulphonate by-product in the non-catalytic hydrogenation process for polybutadiene, which makes use of p-toluene sulphonylhydrazide as a reaction intermediate. The formation of this product has not been reported previously under such conditions. Spectroscopic evidence is presented for the molecular structure.
INTRODUCTION
p-Toluenesulphonylhydrazide is a convenient reagent for the hydrogenation [ 1,2] of unsaturated organic molecules, as it avoids the use of the high temperatures and pressure required by some other methods of hydrogenation [ 3 1. The mild hydrogenation conditions are attributed [ 2 ] to the in-situ generation of diimide from p-toluenesulphonylhydrazide: CH3-C6Hq-S02NH-NH2+CH3-C6Hq-SOnH+NH=NH
(1)
The by-products of the reduction reaction are believed to be nitrogen and ptoluene sulphinic acid [ 2 1. Reactions ofp-toluenesulphonylhydrazide in highly oxidising media such as peroxy acids [ 41 have produced other by-products. The pyrolysis ofp-toluenesulphonylhydrazide [ 51 in vacua at 140’ C has resulted in the formation of ptolyl p-toluenethiolsulphonate by disproportionation. This p-tolyl p-tolueneCorrespondence to: Dr. H.G.M. Edwards, Interdisciplinary Research Centre in Polymer Science and Technology, Chemistry and Chemical Technology, University of Bradford, Bradford, W. Yorkshire, BD7 lDP, UK.
0022-2860/92/$05.00
0 1992 Elsevier Science Publishers B.V. All rights reserved.
364
thiolsulphonate has also been prepared by the reaction of the acid chloride with powdered zinc metal [ 61. It has been postulated [ 41 that the p-tolyl p-toluenethiolsulphonate is only formed when there is no species present which allows the diimide to be reduced. Contrary to this suggestion, we now report the isolation of a solid by-product, which was formed during the hydrogenation with p-toluenesulphonylhydrazide, and which has been identified as p-tolyl p-toluenethiolsulphonate. The results of detailed NMR and vibrational spectroscopic studies of this by-product are reported. EXPERIMENTAL
Hydrogenation Polybutadiene (Aldrich 18, 128-2, 1.50 g) was dissolved in hot dry xylene (80 ml) with continuous stirring under a nitrogen atmosphere. p-Toluenesulphonylhydrazide (10.43 g) in dry xylene (70 ml) was added and the temperature raised to 115°C. After 2 h the mixture was allowed to cool and the solid residue filtered off. The filtrate was added to an excess of methanol (500 ml) and the polymer precipitated as a white solid. The methanol solution was concentrated by removing xylene and methanol under vacuum. The concentrated liquor yielded white crystals (0.5 g ) , m.p. 72-73.5 ‘C. Nuclear magnetic resonance spectroscopy ‘H and 13C!NMR spectra (‘H broad-band decoupled and DEPT135) were acquired (CF,COOD solution, relative to Me,Si as internal standard) using a JEOL GX270 FT NMR spectrometer fitted with a dual 5 mm C/H probe, operating at 270 and 67.8 MHz respectively, using standard JEOL software. Carbon atom assignments were verified using 2dimensional 13C-lH COSY and 13C-lH FLOCK [ 71 experiments to establish ‘Jc_n and 2’3Jc_Hcorrelations. Mass spectromtry Samples were analysed using an AEI-MS902 mass spectrometer with an electron voltage of 70 eV and a source temperature of 200°C. Infrared spectroscopy The infrared spectra of the crystals, isolated as described above, were recorded with a Perkin-Elmer Model 1720-X Fourier-transform infrared spectrometer fitted with a mercury cadmium telluride (MCT) detector operating at 77 K by preparing a KBr disc (9 : 1 of KBr: crystals ). The background spec-
365
of potassiumbromidewas also recorded.Spectrawererecorded (10 scans) at 2.0 cm-’ resolutionover the range 4000-400 cm-’ (Fig. 1). Data were collected by the spectrometerdata station and transferredonto an IRM compatible personal computer for subsequentdata analysis,e.g. spectral subtraction and band intensity measurements. trum
Raman spectroscopy
Raman spectra of the crystals were obtained using a Jobin-Yvon Raman microprobe‘MOLE’ inst~ment with argon-ion laserexcitation at 488 nm and typical laserpowers of 100 mW at source, representingapproximately20 mW at the sample. Using a microscope objective of 100x ma~ification and a coupled Hitachi colour television camera, a total magnification at the viewing screenof about 3 x 103timeswasobtained.This representsa displayof 125x 125 p2 of sampleareaon the 35 x 35 cm2screen.The couplingof the televisionwith a camera allowedthe production of pho~~aphs of the sample crystalsunder investigation.Spectrometercontrol and data acquisitionwere effected using a Thorn-~MI PET computer. This facility allowed spectralaccumulationto be made over predeterminedwavenumberrangesto improve the signal-to-noise ratio. The Raman spectraobtained are given in Figs. 2-4. A numberof model compounds (toluene andp-toluenesulphonicacid) were 100
I
I
I
I
I
I
I
1600
1200
I
80
4000
3600
3200 2800 2400 2000
Wavenumber
(cm-1
800
)
Fig. 1. Infrared spectrum of p-tolyl p-toluenethioleulphonate in the range 4000-400 cm-‘.
366
r
LL
J.di i
200
300
400
500 Roman
600 Shift
700 T-300
900
1
10
(cm-l)
Fig. 2. Raman spectrum ofp-tolyl p-toluenethiolsulphonate in the range .4v=200-1000 cm-‘.
1100
1200
1300 Roman
1400 Shift
1500
1600
1700
II
(cm-l)
Fig. 3. Raman spectrum of p-tolylp-toluenethiolsulphonate in the range Av= 1000-1800 cm-‘.
367
c-2600
2700
2800
2900 Roman
3000 Shift
3100
3200
3300
3 00
(cm-l)
Fig. 4.Raman spectrum of ~-~lylp-toiuenet~iolsulphona~
in the range Av=2600-3400cm-‘.
analysed using FT-IR and conventional Raman spectroscopy (described below), in order to facilitate the identification of the bands observed in the vibrational spectra of the crystals obtained from the reaction mixture. Excitation was effected using a Spe~ra-Physics Model 2020/5 argon-ion laser operating at 488 nm with a nominal output of 1.5 W. The scattered radiation was analysed using a SPEX Industries Model 1401 spectrometer with a reciprocal linear dispersion of 20 cm-’ mm-’ at 488.0 nm, andphoton-counting detection using an EM1 9789 QA photomultiplier. Acquisition of data and control of the spectrometer were accomplished using a Nicolet 1180 microcomputer which permitted the accurate multiscanning of predetermined spectral wavenumber ranges. The linearity of intensity response of the spectroscopic apparatus used in the study of the model compounds had previously been verified ]8 ] using systems of known internal-field effects, and a geometric-optical [9] effect of 1 was determined. Calibration was effected using a neon emission spectrum and wavenumbers are correct to within 1 cm-‘. RESULTS
The mass sp~tromet~ data were found to be very similar to those published previously [lo]. The NMR results are presented in Table 1 and the results of the vibrational
368 TABLE 1 ‘H NMR and 13CNMR spectroscopic data forp-tolylp-toluenethiolsulphonate
Atom No.
SH
2-H 3-H
7.55 7.35
d d
5-H 6-H 7-H,
7.35 7.55 2.48
d d s
2’-H 3’-H
7.26 7.21
d d
5’“H 6’-H 7’ -HQ
7.21 7.26 2.40
d d s
(1)in CF,COOD
Atom No.
&
C-l c-2 c-3 c-4 c-5 C-6 c-7 C-l’ C-2’ C-3’ C-4’ C-5’ C-6’ C-7’
139.86 129.74 131.67 149.21 131.67 129.74 22.05 124.27 138.74 132.47 146.25 132.47 138.74 21.81
*In ‘H NMR ail J values 8.1 Hz.
analyses are given in Table 2. A full vibrational spectroscopic study of this type of compound has not been undertaken previously. The bands in the vibrational spectra have been assigned by reference to the IR [ 111 and Raman 112,131 spectroscopic studies of the selected model compounds, toluene andp-toluenesulphonic acid. DISCUSSION
A literature search revealed that, although ( 1) is a known compound [ 141, m.p. 76”C, for which some spectroscopic data have been reported [5,6,10], detailed interpretation of the infrared and NMR spectra has not been attempted. Raman spectra have not been reported previously for this compound. The mass spectroscopic data show inter alia a molecular ion at m/z 278 and a base peak at 139. This suggested that the molecule was symmetrical and possibly a simple dimer of C$H,SO. The ‘H NMR spectrum shows, in addition to two methyl singlets at 6 2.40 and 2.48, the presence of two pairs of doublets between S 7.21 and 7.55. The coupling constants for both doublet pairs are J= 8.1 Hz, suggesting the presence of two para-disubstituted benzene rings. A homonuclear spin-decoupling experiment revealed that the doublet resonances at 6 7.35 and 7.55 are spin coupled, as are the doublet resonances at S
369 TABLE 2 Vibrational assignment for p-tolyl p-toluenethiolsulphonate Band assignment
Wavenumbers (cm-‘) Infrared
v,(C-H) va(C-W v,(CH,) v,(CH,)
v(C-H) v(CH,) Aromatic ring stretch Aromatic ring stretch Aromatic ring stretch Aromatic ring stretch &CH,) k(CH,) &(C-CH,) &(C-CH,) v.((C)-w?-(S)) S(C-H) Aromatic ring stretch Aromatic ring stretch v,((C)-soz-(S)) &C-H) G(C-8) Aromatic ring stretch v(C-C) Aromatic ring deformation v(C-S) P(C-H)
2978 2952 2918 2864 1625 1593 1575 1487 1450 1401 1379 1321 1296 1220 1141 1073 1038 1015 812 703 653
ww
585
P@W
522 483 462
v(S-S) 6(CSO)
Raman
2900
1595 1495 1400 1390 1380 1320 1300 1220 1180 1140 1090 1080 1020 800
620 580 560 530 510 480 462 450
440
S(CSS) S(CSS) S(CS0)
r(CH,)
380 360 340 315 305 285 260 235
370
7.21 and 7.26. The presence of AX and AM pairs of doublets in the aromatic region, plus the fact that the methyl groups are magnetically non-equivalent, suggested the asymmetric molecule ( 1).
Whilst this proposed structure might appear at variance with the mass spectroscopic data, in particular the base peak at 139, it has been reported [lo] that sulphur-oxygen compounds are prone to fragmentary rearrangement during the mass spectroscopy experiment; therefore asymmetry in the compound is not excluded. A doublet resonance in the ‘H NMR spectrum at 6 7.55, the most downfield signal, obviously arises from H-2 and H-6, and the singlet resonance at 6 2.48 from 7-H3, as both sets of signals would be expected to be the most deshielded protons of their type due to ortho and para effects of the sulphonyl moiety. This information, together with the results of the homonuclear spin decoupling experiments, enabled unambiguous assignment of the ‘H NMR data (Table 2). A 13CNMR DEPT experiment confirmed that the signals at 6 149.21, 146.25, 139.86 and 124.27 were due to quate~ary carbons. The 13CNMR assignments of all methine and methyl signals were determined using a 13C-lH COSY [ lJC_H] experiment, which permitted correlation of the ‘H and 13CNMR data. The unambiguous assignments of the 13CNMR resonances of C-4 and C-4’ were established using the FLOCK pulse sequence of Reynolds et al. [ 71, which is useful for detecting long-range 13C-lH correlations ( nJc_Hwhere n is two or three), When the mixing times of d’ and 4’ were 84 and 44 ms respectively (equivalent to nJc_H of 10 Hz) the 7-H3 resonance at S 2.48 indicated correlations with 13CNMR resonances at 6 131.67 (C-3 and C-5) and 149.21 (C-4), and the 7’ -Hz resonance at 6 2.40 revealed correlations with the 13C NMR resonances at S 132.47 (C-3’ and C-5’ ) and 146.25 (C-4’ ). The FLOCK experiment also revealed Jc_c_n correlations between the signal in the ‘H NMR for 2’-H and 6’-H at S 7.26 and those in the 13CNMR at 6 132.47 (C-3’ and C-5’ ) and 6 124.27, which identi~ed the latter as C-l’. Thus the resonance at S 139.86 is due to C-l. Somewhat surprisingly these results indicate that it is the C-4 and C-4’, not the C-l and C-l’, carbon atoms that are most deshielded by the thiolsulphonate linkage. A similar effect has been noted recently in an NMR study of a series of 4-substituted and 4,4’-disubstituted diphenyl sulphoxides and sulphones [ 151. The infrared spectrum of thep-tolylp-toluenesulphonate shows absorptions at 3055, 3036 and 2918 cm-l which are ascribed to aromatic C-H stretching vibrations and bands at 2978,2952 and 2864 cm-’ which are assigned to the aliphatic CH3 vibrations. Prominent bands attributable to the aromatic ring stretching vibrations are also found at 1625, 1593,1575,1487,1220,1038 and
371
1015 cm-‘. The symmetric and asymmetric v (SO) stretching vibrations of the C-S02-S unit are observed at 1321 and 1141 cm-‘. The C-S stretches are found at 1073 and 703 cm-’ and the S-S vibration is observed at 483 cm-‘. The symmetric and asymmetric CH3 deformation bands are observed at 1450 and 1401 cm-l respectively. The symmetric C-CH, deformation is seen at 1379 cm-‘. The CH deformation is assigned to a band at 1296 cm-’ and a C-H rock is observed at 653 cm-l. The band at 812 cm-l is assigned to a ring deformation that is characteristic of a para-disubstituted aromatic ring. The SO, deformation is found at 585 cm-‘. The CSO deformation is found at 462 cm-‘, whilst the SO, rock is observed at 522 cm-l. The detailed vibrational assignments proposed here were made by correlation with the vibrational spectra of toluene, p-toluenesulphonic acid and ethanesulphonic acid [ 161. The Raman spectrum shows the C-H vibrations, both symmetric and asymmetric, at 3075 and 3060 cm-‘. The aromatic ring stretching vibrations are observed at 1595,1495 and 1020 cm-l. The symmetric and asymmetric v (SO) stretching vibrations of the C-SO,-S unit are produced at 1320 and 1140 cm-l. The aromatic ring stretching vibrations are observed at 1220 and 1180 cm-l respectively. The other principal fundamental vibrations are the C-S stretch at 1080 cm-’ and the SS stretch at 480 cm-‘. The C-H deformations are observed at 1300 and 1090 cm-l, whilst the symmetric and asymmetric C-CH, deformations are seen at 1390 and 1380 cm-’ respectively. The band at 800 cm-’ is assigned to a ring deformation that is characteristic of a para-disubstituted aromatic ring. The SO, deformation is assigned to the band at 580 cm-‘. The CSO deformations are at 462 and 340 cm-‘, and the CSS deformation at 380 and 360 cm-‘. The SO, rocking band is found at 510 cm-l and the CHB torsion is assigned to 235 cm-l. There is generally very good agreement between the Raman and infrared spectral wavenumbers, and assignments favour the asymmetric C-SO,-S unit in the molecule. The symmetric C-SO-SO unit would provide an essentially different spectroscopic feature. Attempts were made to obtain polarization measurements in solution but, due to the limited solubility of the compound in a number of common solvents, these were not obtainable. Assignments are made on the basis of the model compounds (mentioned above) and the authors have no reason to believe that any untoward band shifts have occurred. CONCLUSIONS
This work provides evidence for the production of a hitherto unsuspected by-product found during the diimide hydrogenation process. This product has been identified unambiguously as p-tolyl p-toluenethiolsulphonate using vibrational and NMR spectra, and a vibrational analysis is presented. The product was prepared at lower temperatures than has been suggested in the litera-
ture and under novel reaction conditions, in the presence of polymer unsaturation and under diimide reduction. The isolation of the by-product establishes that the hydrogenation process is less efficient than previously thought. Conditions have not been established, of temperature, time, and ratio of hydrogenating agent to polydiene, where it is possible to carry out the hydrogenation of the polydiene without producingp-tolylp-toluenethiolsulphonate, i.e. the by-product is always present. ACKNOWLEDGEMENTS
The authors wish to express their thanks to the Science and Engineering Research Council and Castro1 Ltd. for financial support to IRL. We would like to thank Mr. D.W. Farwell for assistance with the recording of the Raman and NMR spectra and for the preparation of the diagrams for this publication. Also, thank you to Mr. R. Nettleton for recording the mass spectra.
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