J. Chil. Chem. Soc., 48, N 3 (2003) ISSN 0717-9324

THERMAL AND X-RAY CRYSTALLOGRAPHIC STRUCTURAL
STUDIES ON (N,N-DIBENCYL)-4-NITROPHENYLSULFENAMIDE

¹Facultad de Ciencias Básicas, Universidad de Antofagasta, Antofagasta, Chile. E-mail: ibrito@uantof.cl
²Facultad de Ciencias de la Salud, Universidad de Antofagasta, Antofagasta, Chile.
³Centro de Productos Naturales Orgánicos "Antonio González", Instituto Universitario de Bio-Orgánica.
Universidad de La Laguna, La Laguna, Tenerife, Spain.

(Received: October 4, 2002 ­ Accepted: May 9, 2003)

SUMMARY

Crystal and molecular structure and the thermal properties of (N,N-dibencyl)-4-nitrophenylsulfenamide, (C₆H₅CH₂)₂ NSC₆H₄-4-NO₂, is herein presented. The structure is a divalent sulfur compound that crystallized in the monoclinic system, space group P2₁/c with a=9.274(2), b=6.013(1), c=32.147(9) Å, b=95.55(2) and Dx=1.305 g cm^-3 with Z=4. The plane C-S-N form a dihedral angle of 77.4(3) with the plane C19-N1-C20, and it represent a notable difference with other sulfenamides described in the literature. The thermogravimetric analysis reveal a decomposition of the product in two steps and another event, probably, associated to a endothermic phase transition.

Key Words: Sulfenamides, sulfenic acid derivatives, divalent sulfur compounds.

INTRODUCTION

Sulfenamides are important intermediates in organic synthesis and have proven useful in investigations of lone pair interactions (a effect), bond polarization effects and (p-d) p conjugation^1-3). Sulfenamides have also found important industrial applications⁴⁾. Bond polarization effects resulting from the difference in electronegatively between sulfur and nitrogen in sulfenamides derivatives activate the S-N bond for attack by both nucleophiles and electrophiles and appear to be the factor primarily responsible for the chemistry of these compounds. In accord with our continuous interest in the synthesis, characterization and crystal structure of sulfenamides^5-9), we here report the crystal and molecular structure and thermal properties of a novel sulfenamide.

EXPERIMENTAL

An important alternative to the synthesis of sulfenamides from amines and sulfenyl chlorides is the metal-assisted synthesis of sulfenamides from disulfides and amines¹⁰⁾ (Eq. 1). This method is more convenient and results in higher yields and a less reactive product than sulfenamides prepared from sulfenyl chlorides

In a 1000- ml three-necked flask equipped with overhead stirrer was placed 7.8 g (0.045 mol) of silver nitrate in 400 ml of methanol. After solution had taken place an equivalent amount of (NO₂-C₆H₄S)₂ was added and the reaction mixture cooled in an ice bath. An excess of N, N-dibencylamine (usually 5 equiv.) was added and the reaction mixture allowed to stir overnight. The silver mercaptide was filtred and the solvent removed at reduced pressure, at a temperature of 35-40C. The resulting residue was dissolved in ether, washed with water (4 x100 ml), and dried over MgSO₄. Removal of the ether solvent gave the sulfenamide. The compound was crystallized by slow evaporation from diethyl ether solution. Table I shows structure determination summary. All H atoms were located by a difference Fourier synthesis and refined with fixed individual displacement parameters [U(H)=1.2 Ueq(C)] using a riding model with C-H (aromatic)=0.93, C-H (secondary)=0.97 Å Geometrical calculations were made with PARST¹³⁾. The differential thermal analysis (DTA) and thermogravimetric analysis (TGA) were performed on Perkin Elmer Diffencial Thermal Analyzer DTA7 and Perkin Elmer Thermogravimetric Analyzer Pyris 1, respectively. The TG/DTA curves were registred in 313 - 873 K range, under argon atmosphere using a 5 K/min heating rate.

Table I. Structure determination summary for (C₆H₅CH₂)₂ NSC₆H₄-4-NO₂).

RESULTS AND DISCUSSION

The crystal structure can be described in term of discrete molecules with one independent molecule in the asymmetric unit. Table II gives the atomic coordinates and equivalent isotropic displacement parameters for all non-H atoms. The molecular structure including the atom labelling scheme is illustrated in Fig. (1).The packing in the unit cell viewed down the b axis, showing the hydrogen-bonding interactions as broken lines is illustrated in Fig. (2). Table III shows selected geometric parameters. The compound crystallizes in the monoclinic space group P2₁/C. The fragment nitrophenyl is planar. As expected, p-nitro group is slightly rotated out of their respective aromatic plane (8.0(3) ). The average N-O bond lengths are in usual range (Table III) for aromatic NO₂ groups in accord with similar structures reported in Cambridge Structural Database¹⁴⁾ (version 5.23, update September 2002). The C-N distance is 1.481(6) Å slightly upper than the upper quartile value of 1.476 Å (for primary amine). The pyramidal nature of the N1 atom is demonstrated by the sum of interbond angles (334(3)). The C_sp3-C_aryl distances are essentially identical in the range 1.491(6)-1.500(6), mean 1.496(6). All phenyl rings are planar [maximum deviation 0.01 Å]. The average of the 18 phenyl C-C distances is 1.380(7). The C-S bond distance 1.750(5) Å is in agreement with the 1.738(10) Å value reported for N,N-dibenzyl-phenylsulfenamida⁸⁾ but, significantly shorter than: 1.760(4) Å reported for 5-nitro-piridine-piperidinesulfenamide¹⁵⁾ ; 1.765(3) Å for (N, N-dicyclohexyl)bencene-sulfenamide⁶⁾; 1.873(2) Å for triphenylmethanesulfenamide¹⁶⁾; 1.901(4) for triphenyl-methane-piperidinesulfenamide⁹⁾ ; 1.766 Å for N-(1,2-dihydro-2-oxoquinolin-1-yl)-N-(1-methylallyl)-p-chlorobenzenesulfenamide ¹⁷⁾ and for 1.835 Å for N-(1-a-naphthylethyl)-N-(benzenesulfonyl)trichloro-methanesulfenamide ¹⁸⁾. The S-N distance of 1.713(4) Å is in agreement with the values of 1.699(4); 1.698(2); 1.695(4); 1.715 Å reported for 5-nitro-piridine-piperidinesulfenamide¹⁵⁾ ; triphenylmethane sulfenamide¹⁶⁾; triphenylmethane-piperidinesulfenamide⁹⁾ and N-(1,2-dihydro-2-oxoquinolin-1-yl)-N-(1-methylallyl)-p -chlorobenzenesulfenamide¹⁷⁾ respectively and it is consistent with S-N single bond exhibing p character. The C-S-N plane form a dihedral angle of 77.4(3) with the C-N-C plane (90 for the torsional fundamental state). This geometric situation increases the repulsion among the couples of electrons on the sulfur and nitrogen, what is reflected in a bigger distance S-N. The Fig. (3) shows a inverse lineal relationship (slope=-0.004; R² =0.9956) that exist among the S-N distance and the deviation of the torsional fundamental state for some sulfenamides described in the literature. The molecule contains four potential hydrogen-bond acceptors. Hunter¹⁹⁾, has formulated that an excess of acceptors, can sometimes be accommodated by formation of C-H···X hydrogen bonds involving weakly acidic C-H bonds on benzenoid rings as the hydrogen-bond donors. The short intramolecular SH contact involving H2 at distance of 2.81 Å. The short intramolecular N1H contacts involving H6 at distance of 2.51 Å and N2H involving H3, H5 at distances of 2.68 Å and 2.67 Å respectively. The short intramolecular O1H contact involving H5 at distance of 2.42 Å and O2H3 at distance of 2.50 Å are all within the sum of the Van der Waals radii, but probably depend in part on the concerted twist of the three phenyl rings (see Table III).

Fig.1. A. Molecular view of (C6H5CH2)2 NSC6H4-4-NO2 with the atom labelling scheme.

Table II. Atomic coordinates (Åx10⁴) and equivalent isotropic displacement parameters founded for (C₆H₅CH₂)₂ NSC₆H₄-4-NO₂

Table III. Selected distances (Å) and angles () founded for (C₆H₅CH₂)₂ NSC₆H₄-4-NO₂

Fig.2. Hydrogen-Bonding interactions in solid state for (C6H5CH2)2 NSC6H4-4-N02 are shown as dashed lines.

References: · = 20; %= This work; != 18; "= 17 000000000Slope = -0.0040 00R2 = 0,9956

Fig.3. Torsion angles () v/s S-N Distances (A) for some sulfenamides.

In the crystal structure each molecule is linked to two others by C-HO hydrogen bonds [H3O2ⁱ 2.38 Å, C3O2ⁱ 2.408(6) Å and C3H3O2ⁱ 158, and H20AO2ⁱⁱ 2.53 Å, C20O2ⁱⁱ 3.353(7) Å and C20-H20AO2ⁱⁱ 132] to form sheets built from alternating R²₂ (10) and R²₂ 20)²¹⁾ ring both of which are centrosymmetric [symmetry code: ⁱ⁾ -x, -y, -z+1; ⁱⁱ⁾ -+1, x-y, -z+1].

Figure (4) shows TGA and DTA curves. From the TGA curve it can be see that the title compound decompose in two steps. In the first one the sulfenamide loss half mol of O₂NC₆H₄S per mol of sulfenamide about 423 K (O₂NC₆H₄S % Cal. 21.99, Dm%=23). In the second step the compound loss another half mol O₂NC₆H₄S about 470 K. The mass of the final residue was consistent with the N(CH₂C₆H₅)₂ fragment, probably yielding a polymeric species, not determined in this work. DTA curve show that both steps correspond to exothermic events. DTA curve also show a endothermic event at 363 K which is probably related with a phase transformation. Thermal behavior of this compound is similar to other sulfenamides²²⁾, Table IV. The decomposition of these products generally begins around the 313 K. In the studied compound the decomposition begins to a higher temperature probably due to the influence of the group NO₂ and to its crystalline structure governed by hydrogen-bonding interactions.

Fig.4. TGA and DTA curves for (C6H5CH2)2 NSC6H4-4-NO2

Table IV. Thermal stabilities of Sulfenamides of the type R¹SNR²

ACKNOWLEDGMENTS

IB thanks DGI (Universidad de Antofagasta, grant PRO-1345-02).

REFERENCES

1. L. Craine & M. Raban. Chem. Rev. 89, 689 (1989).

2. M. Makosza & M. Bialecki. J. Org. Chem. 63:15, 4878 (1988).

3. M. B-D. Blanca, E. Maimon & D. Kost. Angew. Chem. Int. Ed.Engl. 6:20, 2216 (1997).

4. C. Brown & B. T. Grayson, Mech. React. Sulfur Compd., 5, 93 (1970).

5. M. L. Rodríguez, C. Ruiz-Pérez, I. Brito, C. Díaz, J. Cuevas, G. González & V. Manríquez. J. Organomet. Chem. 377, 235 (1989).

6. M. L. Rodríguez, I. Brito, C. Díaz, J. Cuevas, G. González & V. Manríquez. J. Organomet. Chem. 425, 49 (1992).

7. C. Díaz, V. Manríquez, G. González, I. Brito & M. L. Rodríguez. Bol. Soc. Chil. Quím . 38, 83 (1993).

8. I. Brito, C. Díaz, G. González, M.L. Rodríguez & V. Manriquez. Bol. Soc. Chil. Quím., 44, 459 (1999).

9. I. Brito, Y. León, C. Gacitua, M. Arias, J. Ponce, O. Wittke, M.L. Rodríguez. Bol. Soc. Chil. Quim. 45, 509 (2000).

10. F. A. Davis, A. J. Friedman, E.W. Kluger, E. B. Skibo, E. R. Fretz, A. P.Milicia, W. C. LeMasters. J. Org. Chem. 42, 967 (1977).

11. G. M. Sheldrick. SHELXS86. Program for crystal structure deter mination. University of Göttingen, Germany (1986).

12. G. M. Sheldrick. SHELXL93. Program for refinement of crystal structures. University of Göttingen, Germany (1993).

13. M. Nardelli. Comp. Chem., 7, 95 (1983).

14. F. H. Allen & O. Kennard. Chem. Des. Autom. News, 8, 1, 31 (1993).

15. I. Brito, Y. León, M. Arias, D.Vargas, F. Carmona, E. Ramirez, A. Restovic, A. Cardenas. Bol. Soc. Chil. Quim. 47, 159-162 (2002).

16. C. Glidewell, G. Ferguson. Acta Crystallogr. Sect C (Cr. Str. Comm.) 50, 1302 (1994).

17. R. S. Atkinson, S. B. Awad, J. H. Barlow, D. R. Russell. J. Chem. Res. 331, 4138 (1978).

18. J. Kay, M. D. Glick, M. Raban. J. Am. Chem. Soc. 93:20, 5224( 1971).

19. C. A. Hunter. J. Chem. Soc. Chem. Commun. 749, (1991).

20. P. Ruostesno, A. M. Hakkinen, R. Kivekos, M. R. Sundberg. J. Chem. Soc. Perkins Trans. 2, 1397 (1989).

21. J.Bernstein, R.E.Davis, L.Shimoni, and N. Chang. Angew. Chem. Int. Ed. Engl. 34, 1555 (1995).

22. V. Manriquez, C. Díaz , G. González and I. Brito. Journal of Ther mal Analysis, 46, 1875 (1996).

23. N. Heimer and L. Field, J. Org. Chem., 35, 3012 (1970).