A dithietane of 2-methyl­propane­di­thio­ic acid

Under the action of BF₃·Me₂O, 2-methyl­propane­di­thio­ic acid does not give the expected adamantanoid product but the trans-2,4-diiso­propyl-2,4-bis­[(2-methyl-1-thio­xo)­propyl­sulf­an­yl]-1,3-dithietane. The X-ray structure of the centrosymmetric title compound confirms the trans conformation of the dithietane mol­ecule.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.038
• wR factor = 0.061
• Data-to-parameter ratio = 20.7

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

We recently described the action of BF₃·Me₂O on propanedithioic acid (Mahjoub & Zantour, 2000) and butanedithioic acid (Mahjoub & Zantour, 2001). Another linear aliphatic dithioacid (ethanedithioic acid) was also used in the same manner. In all cases we obtained a tetraalkyl hexathiaadamantanic compound.

The aim of the present work is to investigate the action of this Lewis acid, using the same conditions, on a ramified aliphatic dithioacid (2-methylpropanedithioic acid). This reaction occurs with a large evolution of H₂S and the formation of the dithiethane, (I), as shown in the reaction scheme. A similar compound was obtained by reaction of the same dithioacid with dicyclohexylcarbodiimide (Kato et al., 1982). The crystal structure determination was undertaken to establish the conformation of the reaction product, (I), and to understand the process of its formation.

The atomic arrangement of the title compound (Figure 2) is centrosymmetrical. The tetrahedral unit C5,S3,S2,C6 located close by the centre of symmetry shares an edge (S3—S3) with its centrosymmetrically related unit. This condensation creates at the centre of the molecule an almost regular square plane built by S3 and C5 and their centrosymmetrical counterparts. The angle S3—C5—S3 is 95.54 (6)°. The tetrahedral unit C5,S2,S3,C6 is mainly characterized by three very similar C—S distances ranging from 1.827 to 1.839 Å and one C5—C6 distance of 1.539 Å. In spite of this apparent distortion, the average angle C6—C5—S in this tetrahedron, 108.7° is close to the theoretical value for a regular tetrahedron. In the other organic moieties, the observed interatomic distances and bond angles are in accordance with expected values (Allen et al., 1987).

S2. Experimental

2-methylpropanedithioic acid (1.8 g, 0.0015 mol), prepared according to a method described by Beiner & Thuillier (1972), was dissolved in 10 ml of hexane. Boron trifluoride dimethyletherate (3.42 g, 0.03 mol) was then added. The mixture was cooled down to 253 K. After two weeks, crystals of crude dithiethane were collected by filtration. Good quality crystals for X-ray diffraction analysis were obtained by slow evaporation from an acetone solution.

S3. Refinement

The H atoms were located from the difference Fourier map and introduced in calculated positions. Owing to the large displacement ellipsoid components, the atom C2 was considered disordered and split into two positions, C2 and C2'. The refinement of the occupancy factors led to an almost equipartition, with occupancy rates of 0.55(?) and 0.45(?) for C2 and C2, respectively.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: TEXSAN (MSC, 1995); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: TEXSAN (Molecular Structure Corporation, 1995); software used to prepare material for publication: TEXSAN.

Figures

Fig. 1. ORTEP-III drawing (Burnett & Johnson, 1996), showing the molecular structure of the title compound and the numbering scheme (35% probability displacement ellipsoids).

(I)

Crystal data

C16H28S6	F(000) = 440.00
Mr = 412.76	Dx = 1.276 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.7107 Å
Hall symbol: -P 2ybc	Cell parameters from 25 reflections
a = 8.923 (2) Å	θ = 10.0–15.5°
b = 6.082 (2) Å	µ = 0.63 mm^−1
c = 19.828 (5) Å	T = 293 K
β = 93.29 (2)°	Square prism, yellow
V = 1074.3 (4) Å^3	0.22 × 0.20 × 0.20 mm
Z = 2

Data collection

Enraf-Nonius CAD4 diffractometer	Rint = 0.014
Radiation source: X-ray tube	θmax = 30.0°, θmin = 2.5°
Graphite monochromator	h = −12→12
ω scans	k = 0→8
3473 measured reflections	l = 0→27
3084 independent reflections	2 standard reflections every 120 reflections
2261 reflections with I > 2.50σ(I)	intensity decay: 0.1%

Refinement

Refinement on F	0 restraints
Least-squares matrix: full	0 constraints
R[F^2 > 2σ(F^2)] = 0.038	H-atom parameters not refined
wR(F^2) = 0.061	Weighting scheme based on measured s.u.'s w = 1/[σ^2(Fo) + 0.00036|Fo|^2]
S = 1.49	(Δ/σ)max = 0.006
2261 reflections	Δρmax = 0.39 e Å^−3
109 parameters	Δρmin = −0.27 e Å^−3

Special details

Refinement. The H atoms were located by difference-Fourier but introduced in calculated position. Owing to large thermal ellipsoid components, the atom C2 has been considered as disordered and splitted on two positions C2) and C'(2). The refinement of the occupancy factors led to an almost equirepartition with occupancy rates of 0.55 and 0.45 for C2) and C'(2) respectively.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
S1	0.23412 (8)	0.2107 (1)	0.63600 (3)	0.0659 (2)
S2	0.38200 (6)	−0.21056 (8)	0.60148 (3)	0.0508 (1)
S3	0.47558 (5)	0.19764 (7)	0.52801 (2)	0.0429 (1)
C1	0.2828 (3)	−0.1484 (6)	0.7235 (1)	0.0766 (8)
C2	0.378 (1)	−0.048 (2)	0.7773 (4)	0.106 (3)	0.550
C2'	0.303 (1)	0.054 (2)	0.7809 (4)	0.104 (3)	0.450
C3	0.1262 (5)	−0.2217 (7)	0.7314 (2)	0.110 (1)
C4	0.2943 (2)	−0.0359 (4)	0.6550 (1)	0.0538 (5)
C5	0.3791 (2)	−0.0669 (3)	0.52050 (8)	0.0391 (4)
C6	0.2207 (2)	−0.0726 (3)	0.4852 (1)	0.0484 (5)
C7	0.2086 (3)	0.0621 (4)	0.4206 (1)	0.0663 (6)
C8	0.1729 (3)	−0.3076 (4)	0.4703 (2)	0.0700 (7)
H1	0.3394	−0.3219	0.7194	0.074*
H2	0.0633	−0.0972	0.7354	0.131*
H3	0.0926	−0.3055	0.6929	0.131*
H4	0.1227	−0.3100	0.7708	0.131*
H5	0.1528	−0.0122	0.5154	0.058*
H6	0.1084	0.0562	0.4016	0.080*
H7	0.2748	0.0041	0.3893	0.080*
H8	0.2348	0.2106	0.4305	0.080*
H9	0.1713	−0.3877	0.5113	0.084*
H10	0.0756	−0.3083	0.4482	0.084*
H11	0.2421	−0.3742	0.4418	0.084*
H2A	0.3429	0.0984	0.7849	0.154*	0.55
H2B	0.4782	−0.0469	0.7645	0.154*	0.55
H2C	0.3689	−0.1341	0.8176	0.154*	0.55
H2D	0.2948	−0.0126	0.8247	0.165*	0.45
H2E	0.2201	0.1544	0.7728	0.165*	0.45
H2F	0.3947	0.1221	0.7770	0.165*	0.45

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.0732 (4)	0.0616 (4)	0.0641 (4)	0.0092 (3)	0.0157 (3)	−0.0091 (3)
S2	0.0576 (3)	0.0489 (3)	0.0465 (3)	0.0057 (2)	0.0091 (2)	0.0109 (2)
S3	0.0489 (3)	0.0337 (2)	0.0466 (3)	0.0003 (2)	0.0078 (2)	−0.0043 (2)
C1	0.073 (1)	0.110 (2)	0.049 (1)	0.002 (1)	0.016 (1)	0.015 (1)
C2	0.138 (7)	0.108 (6)	0.068 (4)	−0.019 (5)	−0.036 (4)	0.007 (4)
C2'	0.095 (6)	0.18 (1)	0.040 (3)	−0.042 (6)	−0.004 (3)	−0.003 (5)
C3	0.104 (3)	0.121 (3)	0.108 (3)	−0.021 (2)	0.030 (2)	0.039 (2)
C4	0.0482 (9)	0.069 (1)	0.0447 (9)	−0.0016 (9)	0.0080 (7)	0.0017 (9)
C5	0.0443 (8)	0.0337 (7)	0.0396 (7)	0.0011 (6)	0.0044 (6)	0.0003 (6)
C6	0.0453 (9)	0.048 (1)	0.052 (1)	0.0013 (8)	0.0007 (7)	−0.0034 (8)
C7	0.074 (1)	0.059 (1)	0.064 (1)	0.002 (1)	−0.019 (1)	0.004 (1)
C8	0.064 (1)	0.062 (1)	0.083 (2)	−0.019 (1)	−0.008 (1)	0.002 (1)

Geometric parameters (Å, º)

S1—C4	1.630 (2)	C3—H4	0.95
S2—C4	1.721 (2)	C5—C6	1.541 (2)
S2—C5	1.827 (2)	C6—C7	1.518 (3)
S3—C5	1.827 (2)	C6—C8	1.516 (3)
S3—C5^i	1.839 (2)	C6—H5	0.95
C1—C2	1.460 (8)	C7—H6	0.95
C1—C2'	1.68 (1)	C7—H7	0.95
C1—C3	1.483 (5)	C7—H8	0.95
C1—C4	1.529 (3)	C8—H5	2.02
C1—H1	1.17	C8—H9	0.95
C2—C2'	0.92 (1)	C8—H10	0.95
C3—H2	0.95	C8—H11	0.95
C3—H3	0.95
C4—S2—C5	105.24 (9)	C5—C6—H7	99.1
C5—S3—C5^i	85.40 (8)	C5—C6—H8	98.0
C2—C1—C2'	33.2 (4)	C5—C6—H9	96.4
C2—C1—C3	124.2 (4)	C5—C6—H10	136.5
C2—C1—C4	113.4 (4)	C5—C6—H11	96.1
C2—C1—H1	100.9	C7—C6—C8	109.8 (2)
C2—C1—H2	112.4	C7—C6—H5	107.8
C2—C1—H3	150.0	C7—C6—H6	26.0
C2—C1—H4	105.3	C7—C6—H7	26.0
C2'—C1—C3	102.4 (4)	C7—C6—H8	26.0
C2'—C1—C4	105.3 (4)	C7—C6—H9	135.7
C2'—C1—H1	132.5	C7—C6—H10	93.6
C2'—C1—H2	82.8	C7—C6—H11	97.7
C2'—C1—H3	127.6	C8—C6—H5	107.8
C2'—C1—H4	95.4	C8—C6—H6	94.8
C3—C1—C4	109.9 (3)	C8—C6—H7	96.5
C3—C1—H1	98.6	C8—C6—H8	135.8
C3—C1—H2	26.4	C8—C6—H9	26.0
C3—C1—H3	26.5	C8—C6—H10	26.0
C3—C1—H4	26.5	C8—C6—H11	26.1
C4—C1—H1	106.8	H5—C6—H6	93.6
C4—C1—H2	98.7	H5—C6—H7	133.8
C4—C1—H3	92.5	H5—C6—H8	94.0
C4—C1—H4	136.0	H5—C6—H9	92.8
H1—C1—H2	125.0	H5—C6—H10	94.8
H1—C1—H3	84.9	H5—C6—H11	133.8
H1—C1—H4	85.0	H6—C6—H7	44.6
H2—C1—H3	45.4	H6—C6—H8	44.6
H2—C1—H4	45.4	H6—C6—H9	117.6
H3—C1—H4	45.4	H6—C6—H10	72.9
C1—C2—C2'	86.6 (9)	H6—C6—H11	93.2
C1—C2—H1	34.4	H7—C6—H8	44.6
C2'—C2—H1	119.5	H7—C6—H9	121.1
C1—C2'—C2	60.3 (9)	H7—C6—H10	90.3
C1—C3—H1	35.0	H7—C6—H11	77.3
C1—C3—H2	109.6	H8—C6—H9	161.4
C1—C3—H3	109.4	H8—C6—H10	117.3
C1—C3—H4	109.4	H8—C6—H11	121.6
H1—C3—H2	144.6	H9—C6—H10	44.7
H1—C3—H3	90.0	H9—C6—H11	44.7
H1—C3—H4	90.1	H10—C6—H11	44.7
H2—C3—H3	109.5	C6—C7—H5	26.6
H2—C3—H4	109.6	C6—C7—H6	109.5
H3—C3—H4	109.4	C6—C7—H7	109.5
S1—C4—S2	125.5 (1)	C6—C7—H8	109.5
S1—C4—C1	125.4 (2)	H5—C7—H6	94.8
S2—C4—C1	109.1 (2)	H5—C7—H7	136.1
S2—C5—S3	111.51 (9)	H5—C7—H8	95.3
S2—C5—S3^i	106.14 (8)	H6—C7—H7	109.4
S2—C5—C6	110.8 (1)	H6—C7—H8	109.4
S2—C5—H5	94.9	H7—C7—H8	109.4
S3—C5—S3^i	94.60 (8)	C6—C8—H5	26.6
S3—C5—C6	118.2 (1)	C6—C8—H9	109.5
S3—C5—H5	108.7	C6—C8—H10	109.5
S3^i—C5—C6	114.1 (1)	C6—C8—H11	109.4
S3^i—C5—H5	140.3	H5—C8—H9	94.0
C6—C5—H5	26.3	H5—C8—H10	96.1
C5—C6—C7	113.0 (2)	H5—C8—H11	136.0
C5—C6—C8	110.5 (2)	H9—C8—H10	109.6
C5—C6—H5	107.8	H9—C8—H11	109.4
C5—C6—H6	139.0	H10—C8—H11	109.4

Symmetry code: (i) −x+1, −y, −z+1.