4-[(4-Amino­phen­yl)sulfan­yl]aniline

Uppu, R.M.; Agu, O.A.; Mensah, P.F.; Li, G.; Fronczek, F.R.

doi:10.1107/S2414314625007953

organic compounds

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ISSN: 2414-3146

Volume 10| Part 9| September 2025| x250795

https://doi.org/10.1107/S2414314625007953

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4-[(4-Aminophenyl)sulfanyl]aniline

Rao M. Uppu,^a ^* Ogad A. Agu,^b Patrick F. Mensah,^b Guoqiang Li ^c and Frank R. Fronczek ^d

^aDepartment of Environmental Toxicology, Southern University and A&M College, Baton Rouge, Louisiana 70813, USA, ^bDepartment of Mechanical Engineering, Southern University and A&M College, Baton Rouge, Louisiana 70813, USA, ^cDepartment of Mechanical and Industrial Engineering, Louisiana State University, Baton Rouge, Louisiana 70803, USA, and ^dDepartment of Chemistry, Louisiana State University, Baton Rouge, Louisiana, 70803, USA
^*Correspondence e-mail: [email protected]

Edited by W. T. A. Harrison, University of Aberdeen, United Kingdom (Received 28 August 2025; accepted 5 September 2025; online 16 September 2025)

The redetermined structure of the title compound, C₁₂H₁₂N₂S, was refined from low-temperature (100 K) single-crystal X-ray diffraction data. Although achiral, the compound crystallizes in Sohncke space group P2₁2₁2₁ in a chiral conformation distorted from idealized C₂ symmetry and the dihedral angle between the phenyl groups is 72.01 (7)°. In the extended structure, the NH₂ substituents participate in N—H⋯S, N—H⋯N, and N—H⋯π interactions, leading to a three-dimensional hydrogen-bonded array. These results highlight the role of sulfur bridges in tuning packing interactions relevant to polymer design.

Keywords: crystal structure; 4,4′-bridged dianilines; 4,4′-thiodianiline; shape-memory polymers and vitrimers.

CCDC reference: 2485505

Structure description

Bridged 4,4′-dianilines are important monomers for high-performance polymers. The nature of the bridging atom or functional group governs rigidity, polarity, and donor strength, which in turn affects curing kinetics, chain packing, and glass transition in dianiline-based polyimides, epoxides and related composites (Ghosh & Mittal, 1996 ; Sroog, 1991 ). Treated as para substituents on each aniline ring, classic Hammett/LFER considerations capture the quantitative electronic trend, namely –NH– > –O– > –S– > –CH₂– > –S(=O)– > –SO₂– (Hansch et al., 1991 ). The sulfur bridge in the title compound imparts electronic and steric effects that modulate hydrogen bonding and curing behavior (Mazumder et al., 2023 ). Such diamines are used in polyimides, epoxies, and dynamic polymer networks with shape-memory and vitrimer-like properties (Lendlein & Kelch, 2002 ; Xiao et al., 2015 ; Winne et al., 2019 ; Zi et al., 2021 ).

The crystal structure of the title compound, C₁₂H₁₂N₂S, Fig. 1, was previously reported at room temperature based on film data (Vijayalakshmi & Srinivasan, 1973 ; Cambridge Structural Database refcode DAPHSD). The present study refines the structure at 100 K with modern instrumentation, providing more precise molecular geometry and intermolecular interaction details.

Figure 1
Molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level.

The molecule crystallizes in the Sohncke space group P2₁2₁2₁, adopting a chiral conformation. The phenyl groups are rotated unequally with respect to the central C—S—C plane, giving C₁ symmetry in the solid state. The dihedral angle between the C1–C6 and C7–C12 phenyl groups is 72.01 (7)°, while the individual dihedral angles with the C1—S1—C7 plane are 34.96 (8) and 52.35 (10)°, respectively. These distortions highlight the conformational flexibility of the sulfanyl bridge. The bond-angle sums at atoms N1 and N2 are 338.3 and 350.2°, respectively, suggesting that the latter atom has more sp² electronic character, which may correlate with the fact that the C10—N2 bond [1.377 (3) Å] is shorter than C4—N1 [1.407 (3) Å].

In the crystal, atom N1 donates a hydrogen bond (Table 1, Figs. 2, 3) to the sulfanyl sulfur atom of an adjacent molecule, while N2 accepts a hydrogen bond from a neighboring NH group. Additionally, one NH hydrogen atom is involved in an N—H⋯π interaction with a phenyl ring. These interactions generate a three-dimensional network of hydrogen bonds and π contacts, contributing to the stability of the packing arrangement. Graph sets for the conventional hydrogen bonds are a C₁¹(7) chain in the [100] direction, a C₂²(9) chain in the [010] direction, and a C₁¹(12) chain in the [001] direction.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H11N⋯S1ⁱ	0.92 (3)	2.88 (3)	3.675 (2)	145 (2)
N1—H12N⋯Cg2ⁱⁱ	0.86 (3)	2.80 (3)	3.553 (2)	147 (3)
N2—H22N⋯N1ⁱⁱⁱ	0.91 (3)	2.20 (3)	3.095 (3)	167 (3)
Symmetry codes: (i) $[x+{\script{1\over 2}}, -y+{\script{1\over 2}}, -z+1]$ ; (ii) $[-x+{\script{1\over 2}}, -y+1, z-{\script{1\over 2}}]$ ; (iii) $[-x+{\script{3\over 2}}, -y+1, z+{\script{1\over 2}}]$ .

Figure 2
Hydrogen-bonding network in the title compound; only N-bound H atoms are shown.

Figure 3
The unit cell of the title compound.

The molecular geometry of the title compound reflects the distinctive influence of the sulfanyl bridge. The C—S—C linkage is longer and more flexible than the C—C bond in 4,4′-methylenedianiline (Bel'skii et al., 1983 ; Gibson et al., 2010 ; Uppu et al., 2025a ) and less bent but electronically softer than the C—O—C bridge in N,N′-[oxybis(benzene-4,1-diyl)]diacetamide (Uppu et al., 2025b ) and 4,4′-oxydianiline (Sharma et al., 2019 ; Uppu et al., 2025c ). In contrast, the SO₂ bridge in 4,4′-sulfonyldianiline (dapsone) (Karle & Karle, 1964 ; Uppu & Fronczek, 2025 ) introduces polarity and strong hydrogen bonding, markedly altering the packing. Thus, a systematic variation in the bridging unit (NH, O, S, CH₂, SO, SO₂) governs bond distances, torsional distortions, and intermolecular interactions, providing a framework for understanding the structure–property relationships of these technologically important dianilines.

Synthesis and crystallization

4-[(4-Aminophenyl)sulfanyl]aniline (CAS 139–65-1) was purchased from AmBeed (Arlington Heights, IL, USA) with a reported purity of over 97% and used without further purification. Crystals suitable for X-ray analysis were grown by slow cooling hot aqueous solutions, yielding colorless needle-like crystals.

Refinement

Crystal data, data collection, and structure refinement details are summarized in Table 2.

Table 2
Experimental details

Crystal data
Chemical formula	C₁₂H₁₂N₂S
M_r	216.30
Crystal system, space group	Orthorhombic, P2₁2₁2₁
Temperature (K)	100
a, b, c (Å)	5.9287 (2), 9.8523 (3), 18.7766 (5)
V (Å³)	1096.77 (6)
Z	4
Radiation type	Cu Kα
μ (mm⁻¹)	2.34
Crystal size (mm)	0.34 × 0.06 × 0.04

Data collection
Diffractometer	Bruker D8 Venture DUO with Photon III C14
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.727, 0.912
No. of measured, independent and observed [I > 2σ(I)] reflections	13111, 2330, 2215
R_int	0.043
(sin θ/λ)_max (Å⁻¹)	0.637

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.028, 0.070, 1.07
No. of reflections	2330
No. of parameters	148
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.15, −0.23
Absolute structure	Flack x determined using 858 quotients [(I⁺)−(I⁻)]/[(I⁺)+(I⁻)] (Parsons et al., 2013 )
Absolute structure parameter	0.016 (9)
Computer programs: APEX5 and SAINT (Bruker, 2016 ), SHELXT2018/2 (Sheldrick, 2015a ), SHELXL2019/1 (Sheldrick, 2015b ), Mercury (Macrae et al., 2020 ) and publCIF (Westrip, 2010 ).

Structural data

CCDC reference: 2485505

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2414314625007953/hb4534sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314625007953/hb4534Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2414314625007953/hb4534Isup3.cml

checkCIF report

Computing details top

4-[(4-Aminophenyl)sulfanyl]aniline top

Crystal data top

C₁₂H₁₂N₂S	D_x = 1.310 Mg m⁻³
M_r = 216.30	Cu Kα radiation, λ = 1.54184 Å
Orthorhombic, P2₁2₁2₁	Cell parameters from 6002 reflections
a = 5.9287 (2) Å	θ = 5.1–79.3°
b = 9.8523 (3) Å	µ = 2.34 mm⁻¹
c = 18.7766 (5) Å	T = 100 K
V = 1096.77 (6) Å³	Needle, colourless
Z = 4	0.34 × 0.06 × 0.04 mm
F(000) = 456

Data collection top

Bruker D8 Venture DUO with Photon III C14 diffractometer	2215 reflections with I > 2σ(I)
Radiation source: IµS 3.0 microfocus	R_int = 0.043
φ and ω scans	θ_max = 79.3°, θ_min = 4.7°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −7→7
T_min = 0.727, T_max = 0.912	k = −12→12
13111 measured reflections	l = −23→20
2330 independent reflections

Refinement top

Refinement on F²	Hydrogen site location: mixed
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F² > 2σ(F²)] = 0.028	w = 1/[σ²(F_o²) + (0.0356P)² + 0.160P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.070	(Δ/σ)_max = 0.001
S = 1.07	Δρ_max = 0.15 e Å⁻³
2330 reflections	Δρ_min = −0.23 e Å⁻³
148 parameters	Absolute structure: Flack x determined using 858 quotients [(I⁺)-(I^-)]/[(I⁺)+(I^-)] (Parsons et al., 2013)
0 restraints	Absolute structure parameter: 0.016 (9)
Primary atom site location: dual

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. All H atoms were located in difference maps and those on C were thereafter treated as riding in geometrically idealized positions with C—H distances 0.95 Å. Coordinates of the NH hydrogen atoms were refined freely. U_iso(H) values were assigned as 1.2U_eq for the attached atom (1.5 for NH₂). The absolute structure (Parsons et al., 2013) was determined using 858 quotients, x = 0.016 (9).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
S1	0.02434 (8)	0.32288 (5)	0.70350 (3)	0.02444 (15)
N1	0.4024 (3)	0.46157 (19)	0.41708 (10)	0.0235 (4)
H11N	0.495 (5)	0.397 (3)	0.3971 (14)	0.035*
H21N	0.801 (5)	0.215 (3)	0.9358 (14)	0.035*
N2	0.7632 (3)	0.29720 (19)	0.91853 (11)	0.0264 (4)
H12N	0.296 (6)	0.484 (3)	0.3881 (16)	0.040*
H22N	0.878 (5)	0.359 (3)	0.9154 (15)	0.040*
C1	0.1541 (4)	0.3678 (2)	0.62144 (11)	0.0187 (4)
C2	0.3648 (3)	0.3204 (2)	0.59946 (11)	0.0190 (4)
H2	0.452849	0.265918	0.630629	0.023*
C3	0.4461 (3)	0.35248 (19)	0.53226 (11)	0.0185 (4)
H3	0.590611	0.320796	0.518102	0.022*
C4	0.3188 (4)	0.43047 (19)	0.48526 (11)	0.0182 (4)
C5	0.1109 (4)	0.4804 (2)	0.50778 (12)	0.0192 (4)
H5	0.023750	0.535640	0.476755	0.023*
C6	0.0302 (4)	0.44981 (19)	0.57538 (11)	0.0193 (4)
H6	−0.111145	0.485218	0.590355	0.023*
C7	0.2534 (4)	0.3146 (2)	0.76396 (11)	0.0208 (4)
C8	0.4022 (4)	0.4232 (2)	0.77322 (11)	0.0210 (5)
H8	0.385394	0.502546	0.744986	0.025*
C9	0.5729 (4)	0.41644 (19)	0.82279 (11)	0.0212 (5)
H9	0.673852	0.490715	0.827738	0.025*
C10	0.6002 (4)	0.3010 (2)	0.86635 (11)	0.0200 (4)
C11	0.4482 (4)	0.1934 (2)	0.85710 (11)	0.0236 (4)
H11	0.461301	0.114997	0.886228	0.028*
C12	0.2797 (4)	0.1995 (2)	0.80637 (11)	0.0234 (5)
H12	0.180799	0.124541	0.800321	0.028*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
S1	0.0210 (2)	0.0331 (3)	0.0192 (3)	−0.0047 (2)	0.0034 (2)	−0.0010 (2)
N1	0.0250 (10)	0.0259 (9)	0.0197 (10)	0.0004 (8)	0.0027 (8)	0.0011 (7)
N2	0.0280 (10)	0.0207 (9)	0.0303 (11)	0.0011 (8)	−0.0029 (9)	0.0037 (8)
C1	0.0200 (10)	0.0188 (9)	0.0172 (10)	−0.0034 (8)	0.0010 (8)	−0.0038 (8)
C2	0.0194 (9)	0.0168 (9)	0.0209 (11)	0.0007 (8)	−0.0022 (8)	−0.0014 (8)
C3	0.0162 (9)	0.0185 (9)	0.0207 (10)	−0.0008 (7)	0.0012 (8)	−0.0045 (7)
C4	0.0206 (10)	0.0150 (9)	0.0191 (11)	−0.0029 (7)	0.0008 (9)	−0.0040 (8)
C5	0.0198 (10)	0.0183 (9)	0.0195 (11)	0.0017 (7)	−0.0046 (9)	−0.0017 (8)
C6	0.0154 (9)	0.0198 (9)	0.0227 (11)	0.0020 (8)	−0.0012 (9)	−0.0057 (8)
C7	0.0241 (10)	0.0229 (9)	0.0154 (10)	−0.0020 (9)	0.0051 (8)	−0.0029 (8)
C8	0.0284 (11)	0.0184 (9)	0.0163 (11)	−0.0026 (8)	0.0037 (9)	0.0012 (8)
C9	0.0255 (11)	0.0170 (9)	0.0211 (11)	−0.0029 (8)	0.0024 (9)	−0.0012 (8)
C10	0.0219 (10)	0.0204 (9)	0.0176 (10)	0.0018 (8)	0.0048 (8)	−0.0024 (8)
C11	0.0305 (11)	0.0174 (9)	0.0230 (11)	−0.0002 (9)	0.0035 (9)	0.0021 (8)
C12	0.0285 (10)	0.0184 (9)	0.0233 (12)	−0.0045 (8)	0.0051 (9)	−0.0011 (8)

Geometric parameters (Å, º) top

S1—C7	1.772 (2)	C4—C5	1.393 (3)
S1—C1	1.778 (2)	C5—C6	1.390 (3)
N1—C4	1.407 (3)	C5—H5	0.9500
N1—H11N	0.92 (3)	C6—H6	0.9500
N1—H12N	0.86 (3)	C7—C12	1.394 (3)
N2—C10	1.377 (3)	C7—C8	1.398 (3)
N2—H21N	0.90 (3)	C8—C9	1.376 (3)
N2—H22N	0.91 (3)	C8—H8	0.9500
C1—C6	1.393 (3)	C9—C10	1.410 (3)
C1—C2	1.397 (3)	C9—H9	0.9500
C2—C3	1.387 (3)	C10—C11	1.402 (3)
C2—H2	0.9500	C11—C12	1.382 (3)
C3—C4	1.392 (3)	C11—H11	0.9500
C3—H3	0.9500	C12—H12	0.9500

C7—S1—C1	103.60 (10)	C5—C6—C1	120.75 (19)
C4—N1—H11N	115.4 (16)	C5—C6—H6	119.6
C4—N1—H12N	112 (2)	C1—C6—H6	119.6
H11N—N1—H12N	111 (3)	C12—C7—C8	118.7 (2)
C10—N2—H21N	117.1 (18)	C12—C7—S1	119.29 (16)
C10—N2—H22N	117.3 (19)	C8—C7—S1	121.90 (16)
H21N—N2—H22N	116 (3)	C9—C8—C7	120.76 (18)
C6—C1—C2	118.9 (2)	C9—C8—H8	119.6
C6—C1—S1	117.02 (16)	C7—C8—H8	119.6
C2—C1—S1	124.03 (17)	C8—C9—C10	121.04 (19)
C3—C2—C1	120.20 (19)	C8—C9—H9	119.5
C3—C2—H2	119.9	C10—C9—H9	119.5
C1—C2—H2	119.9	N2—C10—C11	121.24 (19)
C2—C3—C4	120.95 (19)	N2—C10—C9	121.04 (19)
C2—C3—H3	119.5	C11—C10—C9	117.6 (2)
C4—C3—H3	119.5	C12—C11—C10	121.15 (19)
C3—C4—C5	118.8 (2)	C12—C11—H11	119.4
C3—C4—N1	120.41 (19)	C10—C11—H11	119.4
C5—C4—N1	120.7 (2)	C11—C12—C7	120.7 (2)
C6—C5—C4	120.4 (2)	C11—C12—H12	119.7
C6—C5—H5	119.8	C7—C12—H12	119.7
C4—C5—H5	119.8

C7—S1—C1—C6	−146.49 (16)	C1—S1—C7—C12	−129.04 (17)
C7—S1—C1—C2	36.99 (19)	C1—S1—C7—C8	54.41 (19)
C6—C1—C2—C3	−1.3 (3)	C12—C7—C8—C9	0.6 (3)
S1—C1—C2—C3	175.15 (15)	S1—C7—C8—C9	177.12 (16)
C1—C2—C3—C4	−0.9 (3)	C7—C8—C9—C10	−1.0 (3)
C2—C3—C4—C5	2.4 (3)	C8—C9—C10—N2	−176.5 (2)
C2—C3—C4—N1	−179.57 (18)	C8—C9—C10—C11	0.3 (3)
C3—C4—C5—C6	−1.6 (3)	N2—C10—C11—C12	177.7 (2)
N1—C4—C5—C6	−179.62 (18)	C9—C10—C11—C12	0.9 (3)
C4—C5—C6—C1	−0.7 (3)	C10—C11—C12—C7	−1.4 (3)
C2—C1—C6—C5	2.1 (3)	C8—C7—C12—C11	0.7 (3)
S1—C1—C6—C5	−174.60 (15)	S1—C7—C12—C11	−175.99 (16)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H11N···S1ⁱ	0.92 (3)	2.88 (3)	3.675 (2)	145 (2)
N1—H12N···Cg2ⁱⁱ	0.86 (3)	2.80 (3)	3.553 (2)	147 (3)
N2—H22N···N1ⁱⁱⁱ	0.91 (3)	2.20 (3)	3.095 (3)	167 (3)

Symmetry codes: (i) x+1/2, −y+1/2, −z+1; (ii) −x+1/2, −y+1, z−1/2; (iii) −x+3/2, −y+1, z+1/2.

Funding information

Research was supported by the National Institutes of Health (NIGMS IDeA Program, Grant P20 GM103424–21), the US Department of Education (Title III), and the National Science Foundation (Grant No. 2418415 RII FEC). The diffractometer was purchased with NSF MRI award CHE–2215262.

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