2,5-Bis(methylthio)-1,4-benzo­quinone and 2-methyl-3-(methylsulfonyl)benzo[b]thiophene

The structure of 2,5-bis­(methyl­thio)-1,4-benzo­quinone, C₈H₈O₂S₂, is composed of an essentially planar centrosymmetric benzo­quinone substituted with two methyl­thio groups. The important bond distances are S—Csp³ 1.788 (2) and S—Csp² 1.724 (2) Å, and the two Csp²—Csp² distances are 1.447 (3) and 1.504 (3) Å, which differ significantly. There are short S...S interactions of 3.430 (1) Å and Csp²—H...O-type contacts forming a dimeric motif with graph set R₂²(8). The structure of 2-methyl-3-(methyl­sulfonyl)­benzo­[b]­thio­phene, C₁₀H₁₀O₂S₂, is composed of an essentially planar benzo­thio­phene moiety substituted with methyl and methyl­sulfonyl groups. The mean values of the important bond distances are endocyclic S—Csp² 1.734 (3), S=O 1.434 (4) and C—C_aromatic 1.389 (10) Å. The exocyclic S—Csp² and S—Csp³ distances are 1.759 (4) and 1.763 (5) Å, respectively.

S1. Comment

Recently, 2,5-bis(methylthio)-1,4-benzoquinone, (I), has been used to prepare sulfur-quinone polyurethane coatings which are applied to protect iron surfaces. Surprisingly, the synthesis of (I) was not reported until 1998 and then was obtained in only 15% yield by reaction of 1,4-benzoquinone with sodium thiomethoxide (Hu & Nikles, 1998). Using a clay-catalyzed one-step thioalkylation procedure developed in our laboratories (Clark et al., 1996), we have been able to make compound (I) in good yield and on a large scale. Conveniently, one half of the quinone reagent re-oxidizes the intermediate product to yield the product, (I) (scheme). ¹H NMR analysis of (I), which is obtained from ethanol as brilliant red crystals, does not allow differentiation of (I) from its 2,3-bis(methylthio) isomer. X-ray analysis showed, however, that the clay-catalyzed synthesis reported herein yielded the 2,5-isomer as the sole product. \scheme

A one-step thioalkylation procedure developed in our laboratory allows addition of –SR groups to aromatics and heteroaromatics (Clark et al., 1996). However, it was clear that reaction of 2,3-methylbenzo[b]thiophene, (III), with dimethyl disulfide over a clay catalyst did not yield the expected 5,6-disubstituted product, but an oily compound in which one of either the 2- or 3-methyl groups had been replaced by an –SCH₃ substituent (scheme). Since an ipso-substitution of this type is quite rare and because other spectroscopic methods could not differentiate whether substitution had occurred at the 2- or 3- positions, the product was oxidized to its crystalline sulfonyl derivative using a literature procedure (Aitken et al., 1994) and was subjected to X-ray crystallographic analysis. This analysis showed that the 3-thiomethyl derivative, (IV), had been produced, suggesting that a sulfur-assisted ipso-substitution had taken place.

The structure of (I) is composed of centrosymmetric molecules which are essentially planar [maximum deviation 0.026 (2) Å for C3]. The bond distances agree well with the corresponding values reported for bis-, tris- and tetrakis(thiophenyl)benzoquinones (Cambridge Structural Database; Allen & Kennard, 1993). The S—C_sp3 and S—C_sp2 bond distances of 1.788 (2) and 1.724 (2) Å, respectively, differ significantly. The bonds C3=O1 [1.227 (3) Å] and C1=C2 [1.353 (3) Å] are double bonds. The C_sp2—C_sp2 bonds, C1—C3ⁱ [1.504 (3) Å; symmetry code: (i) -x, -y, 1 - z] and C2—C3 [1.447 (3) Å], are in excellent agreement with the values reported for the thiophenylbenzoquinone structures mentioned above. The S1—C1—C3ⁱ angle of 112.85 (15)° is smaller than the value of 120° expected for a C_sp2 C-atom, perhaps because of intermolecular methyl-methyl and methyl-carbonyl interactions.

The molecules of (I) pack in layers which lie perpendiular to the (101) plane. Within the layers there are short S···S interactions of 3.430 (1) Å between the molecules related by inversion centers. There are also short Csp₂—H···O type contacts (H···O 2.56 Å and Csp₂—H···O 164°) forming a dimeric motif with graph set R₂²(8) (Fig. 2); similar interactions in the crystal structures of quinones have been discussed by Bernstein et al. (1994).

The structure of (IV) is composed of discrete molecules separated by normal van der Waals distances. The benzothiophene moiety is essentially planar [maximum deviation 0.021 (4) Å for C5], with S2 and C9 of the methylsulfonyl and methyl groups lying 0.045 (5) and 0.022 (6) Å, respectively, on the same side of the plane. The intramolecular repulsion between the two substituents is relieved by the widening of the C2—C1—C9 angle to 132.5 (4)°. The important bond distances are endocyclic S—C_sp2 (mean) 1.734 (3), exocyclic S—C_sp2 1.759 (4), S—C_sp3 1.763 (5), S=O (mean) 1.434 (4) and C—C_aromatic (mean) 1.389 (10) Å.

S2. Experimental

A mixture of 1,4-benzoquinone (54 g, 0.5 mol), dimethyl disulfide (28.2 g, 0.3 mol) and montmorillonite K-10 (ex-Fluka) impregnated with 2 mmol g^-1 ZnCl₂ (50 g; Clark et al., 1996) in dichloromethane (500 ml) was stirred for 16 h at 293 K. Filtration of the reaction mixture afforded a red solid comprised of the clay catalyst and the product, (I). The filtrate contained a small amount of (I), excess dimethyl disulfide and the quinol, (II), formed during re-oxidation of the reaction intermediate. Soxhlet extraction of the red solid with dichloromethane over 20 h gave (I) as a red solid (34 g, 63%). Recrystallization from ethanol afforded red plates. Compound (IV) was prepared using K-10 montmorillonite clay and the method described previously by Clark et al. (1996), and was oxidized to its sulfonyl derivative using a method employed by Aitken et al. (1994). Crystals of (IV) were obtained by slow crystallization from aqueous ethanol.

S3. Refinement

For both compounds, H atoms were treated as riding, with default C—H distances and U_iso values. The absolute structure of compound (IV) could not be established in this analysis because no Friedel pairs were collected.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1989) for (I); MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1988) for (IV). Cell refinement: CAD-4 Software for (I); MSC/AFC Diffractometer Control Software for (IV). For both compounds, data reduction: TEXSAN (Molecular Structure Corporation, 1994); program(s) used to solve structure: SAPI91 (Fan, 1991); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: TEXSAN; software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. ORTEPII (Johnson, 1976) drawing of (I) with the atomic numbering scheme. Displacement ellipsoids have been plotted at the 50% probability level and H atoms assigned arbitrary radii [symmetry code: (i) -x, -y, 1 - z].
	Fig. 2. The unit cell packing of (I) showing Csp2—H···O type contacts forming a dimeric motif.
	Fig. 3. ORTEPII (Johnson, 1976) drawing of (IV) with the atomic numbering scheme. Displacement ellipsoids have been plotted at the 50% probability level and H atoms assigned arbitrary radii.

(I) 2,5-Bis(methylthio)-1,4-benzoquinone

Crystal data

C8H8O2S2	Z = 1
Mr = 200.26	F(000) = 104
Triclinic, P1	Dx = 1.525 Mg m^−3
a = 4.032 (2) Å	Cu Kα radiation, λ = 1.54178 Å
b = 5.717 (1) Å	Cell parameters from 25 reflections
c = 9.626 (1) Å	θ = 10–20°
α = 86.04 (1)°	µ = 5.17 mm^−1
β = 80.60 (2)°	T = 293 K
γ = 86.09 (3)°	Plate, red
V = 218.0 (1) Å^3	0.36 × 0.28 × 0.08 mm

Data collection

Enraf-Nonius CAD-4 diffractometer	757 reflections with I<2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.030
Graphite monochromator	θmax = 68.0°, θmin = 5.0°
ω–2θ scans	h = −4→4
Absorption correction: empirical (using intensity measurements) ψ-scan (3 reflections) (North et al., 1968)	k = −6→6
Tmin = 0.22, Tmax = 0.66	l = −11→11
1535 measured reflections	3 standard reflections every 200 reflections
791 independent reflections	intensity decay: <0.5%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.043	H-atom parameters constrained
wR(F^2) = 0.111	w = 1/[σ^2(Fo^2) + (0.0671P)^2 + 0.0706P] where P = (Fo^2 + 2Fc^2)/3
S = 1.15	(Δ/σ)max < 0.001
791 reflections	Δρmax = 0.39 e Å^−3
56 parameters	Δρmin = −0.32 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.060 (10)

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
S1	0.08707 (14)	−0.02197 (9)	0.16908 (5)	0.0402 (3)
O1	0.2593 (5)	−0.3313 (3)	0.66402 (18)	0.0496 (5)
C1	0.0574 (5)	−0.0295 (4)	0.3500 (2)	0.0313 (5)
C2	0.1864 (5)	−0.1979 (4)	0.4351 (2)	0.0349 (5)
H2	0.3073	−0.3280	0.3955	0.042*
C3	0.1404 (5)	−0.1802 (4)	0.5863 (2)	0.0338 (5)
C4	0.2975 (7)	−0.2992 (4)	0.1260 (3)	0.0455 (6)
H4A	0.5134	−0.3105	0.1565	0.068*
H4B	0.3274	−0.3126	0.0258	0.068*
H4C	0.1646	−0.4234	0.1726	0.068*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.0562 (5)	0.0385 (4)	0.0247 (4)	0.0085 (3)	−0.0079 (3)	−0.0006 (2)
O1	0.0707 (12)	0.0401 (9)	0.0353 (9)	0.0213 (8)	−0.0131 (8)	0.0040 (7)
C1	0.0348 (10)	0.0304 (10)	0.0280 (10)	0.0005 (8)	−0.0054 (8)	0.0006 (8)
C2	0.0435 (11)	0.0300 (10)	0.0300 (11)	0.0070 (8)	−0.0064 (9)	−0.0017 (8)
C3	0.0405 (11)	0.0290 (11)	0.0314 (11)	0.0034 (8)	−0.0083 (8)	0.0017 (8)
C4	0.0562 (14)	0.0445 (13)	0.0338 (12)	0.0080 (10)	−0.0033 (10)	−0.0081 (10)

Geometric parameters (Å, º)

S1—C1	1.724 (2)	C1—C3^i	1.504 (3)
S1—C4	1.788 (2)	C2—C3	1.447 (3)
O1—C3	1.227 (3)	C3—C1^i	1.504 (3)
C1—C2	1.353 (3)
C1—S1—C4	102.83 (11)	C1—C2—C3	121.5 (2)
C2—C1—C3^i	119.5 (2)	O1—C3—C2	121.8 (2)
C2—C1—S1	127.68 (17)	O1—C3—C1^i	119.1 (2)
C3^i—C1—S1	112.84 (15)	C2—C3—C1^i	119.1 (2)
C4—S1—C1—C2	4.5 (2)	S1—C1—C2—C3	−179.95 (16)
C4—S1—C1—C3^i	−175.06 (15)	C1—C2—C3—O1	−179.4 (2)
C3^i—C1—C2—C3	−0.4 (3)	C1—C2—C3—C1^i	0.4 (3)

Symmetry code: (i) −x, −y, −z+1.

(IV) 2-Methyl-3-(methylsulfonyl)benzo[b]thiophene

Crystal data

C10H10O2S2	F(000) = 236
Mr = 226.30	Dx = 1.454 Mg m^−3
Monoclinic, P21	Mo Kα radiation, λ = 0.71069 Å
a = 5.8228 (5) Å	Cell parameters from 25 reflections
b = 10.440 (1) Å	θ = 10–20°
c = 8.6217 (9) Å	µ = 0.48 mm^−1
β = 99.57 (1)°	T = 293 K
V = 516.8 (1) Å^3	Prismatic, colorless
Z = 2	0.55 × 0.38 × 0.35 mm

Data collection

Rigaku-AFC-6S diffractometer	1063 reflections with I<2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.027
Graphite monochromator	θmax = 27.6°, θmin = 2.4°
ω/2θ scans	h = 0→7
Absorption correction: empirical (using intensity measurements) via ψ-scan (3 reflections) (North et al., 1968)	k = 0→13
Tmin = 0.78, Tmax = 0.85	l = −11→11
1385 measured reflections	3 standard reflections every 200 reflections
1268 independent reflections	intensity decay: 1.3%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.029	H-atom parameters constrained
wR(F^2) = 0.109	w = 1/[σ^2(Fo^2) + (0.0656P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.19	(Δ/σ)max < 0.001
1268 reflections	Δρmax = 0.23 e Å^−3
128 parameters	Δρmin = −0.29 e Å^−3
1 restraint	Absolute structure: Flack (1983)
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: −0.07 (15)

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
S1	0.51440 (19)	0.30871 (11)	0.07085 (11)	0.0463 (3)
S2	0.65668 (15)	0.47553 (10)	0.52923 (10)	0.0388 (2)
O1	0.6269 (6)	0.6112 (4)	0.5389 (4)	0.0656 (10)
O2	0.8850 (5)	0.4247 (4)	0.5847 (4)	0.0607 (10)
C1	0.6643 (6)	0.3336 (4)	0.2593 (4)	0.0366 (8)
C2	0.5609 (6)	0.4265 (4)	0.3340 (4)	0.0333 (7)
C3	0.3523 (6)	0.4818 (4)	0.2406 (4)	0.0360 (7)
C4	0.1984 (7)	0.5750 (4)	0.2783 (5)	0.0471 (10)
H4	0.2240	0.6147	0.3762	0.057*
C5	0.0054 (8)	0.6072 (5)	0.1664 (6)	0.0563 (12)
H5	−0.0993	0.6681	0.1911	0.068*
C6	−0.0331 (8)	0.5507 (6)	0.0205 (6)	0.0590 (13)
H6	−0.1625	0.5745	−0.0522	0.071*
C7	0.1169 (7)	0.4595 (5)	−0.0196 (5)	0.0522 (11)
H7	0.0909	0.4218	−0.1187	0.063*
C8	0.3080 (7)	0.4249 (4)	0.0910 (4)	0.0399 (8)
C9	0.8775 (8)	0.2541 (5)	0.3081 (6)	0.0498 (10)
H9A	0.9323	0.2657	0.4186	0.075*
H9B	0.9965	0.2802	0.2499	0.075*
H9C	0.8408	0.1655	0.2873	0.075*
C10	0.4619 (8)	0.4013 (6)	0.6374 (5)	0.0538 (12)
H10A	0.5015	0.4248	0.7462	0.081*
H10B	0.4722	0.3100	0.6273	0.081*
H10C	0.3058	0.4287	0.5975	0.081*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.0513 (6)	0.0555 (6)	0.0322 (4)	−0.0040 (5)	0.0068 (4)	−0.0078 (5)
S2	0.0326 (4)	0.0503 (5)	0.0313 (4)	−0.0048 (4)	−0.0014 (3)	−0.0061 (4)
O1	0.080 (2)	0.050 (2)	0.060 (2)	−0.0099 (18)	−0.0084 (18)	−0.0157 (16)
O2	0.0322 (13)	0.100 (3)	0.0459 (16)	0.0022 (17)	−0.0047 (12)	−0.0082 (18)
C1	0.0355 (17)	0.043 (2)	0.0325 (16)	−0.0071 (16)	0.0085 (13)	0.0020 (15)
C2	0.0309 (16)	0.0404 (19)	0.0281 (15)	−0.0068 (15)	0.0031 (13)	0.0026 (14)
C3	0.0353 (15)	0.0391 (18)	0.0321 (16)	−0.0068 (18)	0.0013 (12)	0.0050 (17)
C4	0.046 (2)	0.042 (2)	0.050 (2)	0.0023 (18)	0.0010 (18)	−0.0007 (18)
C5	0.045 (2)	0.053 (3)	0.069 (3)	0.010 (2)	0.004 (2)	0.011 (2)
C6	0.046 (2)	0.070 (3)	0.055 (3)	0.000 (2)	−0.011 (2)	0.017 (2)
C7	0.051 (2)	0.066 (3)	0.0357 (18)	−0.010 (2)	−0.0065 (16)	0.008 (2)
C8	0.0403 (19)	0.047 (2)	0.0313 (17)	−0.0087 (18)	0.0031 (14)	0.0039 (16)
C9	0.047 (2)	0.051 (3)	0.053 (2)	0.006 (2)	0.0123 (19)	0.002 (2)
C10	0.045 (2)	0.084 (4)	0.034 (2)	−0.003 (2)	0.0115 (17)	−0.001 (2)

Geometric parameters (Å, º)

S1—C1	1.731 (4)	C2—C3	1.460 (5)
S1—C8	1.736 (4)	C3—C4	1.397 (6)
S2—O1	1.431 (4)	C3—C8	1.405 (5)
S2—O2	1.437 (3)	C4—C5	1.395 (6)
S2—C2	1.759 (4)	C5—C6	1.374 (8)
S2—C10	1.763 (5)	C6—C7	1.375 (7)
C1—C2	1.359 (6)	C7—C8	1.387 (5)
C1—C9	1.494 (6)
C1—S1—C8	92.9 (2)	C3—C2—S2	121.0 (3)
O1—S2—O2	117.4 (2)	C4—C3—C8	118.8 (3)
O1—S2—C2	108.7 (2)	C4—C3—C2	130.8 (4)
O2—S2—C2	109.8 (2)	C8—C3—C2	110.4 (4)
O1—S2—C10	108.0 (3)	C5—C4—C3	118.7 (4)
O2—S2—C10	107.6 (2)	C6—C5—C4	121.4 (5)
C2—S2—C10	104.4 (2)	C5—C6—C7	120.9 (4)
C2—C1—C9	132.5 (4)	C6—C7—C8	118.6 (4)
C2—C1—S1	111.0 (3)	C7—C8—C3	121.6 (4)
C9—C1—S1	116.5 (3)	C7—C8—S1	127.1 (4)
C1—C2—C3	114.5 (3)	C3—C8—S1	111.3 (3)
C1—C2—S2	124.5 (3)
C8—S1—C1—C2	0.0 (3)	S2—C2—C3—C8	−178.3 (3)
C8—S1—C1—C9	−179.0 (3)	C8—C3—C4—C5	0.5 (6)
C9—C1—C2—C3	179.1 (4)	C2—C3—C4—C5	−177.7 (4)
S1—C1—C2—C3	0.3 (4)	C3—C4—C5—C6	−1.0 (7)
C9—C1—C2—S2	−3.2 (6)	C4—C5—C6—C7	0.6 (8)
S1—C1—C2—S2	178.0 (2)	C5—C6—C7—C8	0.4 (7)
O1—S2—C2—C1	142.6 (3)	C6—C7—C8—C3	−0.9 (7)
O2—S2—C2—C1	12.8 (4)	C6—C7—C8—S1	177.4 (3)
C10—S2—C2—C1	−102.3 (4)	C4—C3—C8—C7	0.4 (6)
O1—S2—C2—C3	−39.9 (4)	C2—C3—C8—C7	179.0 (4)
O2—S2—C2—C3	−169.6 (3)	C4—C3—C8—S1	−178.1 (3)
C10—S2—C2—C3	75.2 (3)	C2—C3—C8—S1	0.5 (4)
C1—C2—C3—C4	177.8 (4)	C1—S1—C8—C7	−178.7 (4)
S2—C2—C3—C4	0.1 (6)	C1—S1—C8—C3	−0.3 (3)
C1—C2—C3—C8	−0.5 (4)