Organic Syntheses, CV 9, 72
2,2'-BI-5,6-DIHYDRO-1,3-DITHIOLO[4,5-b][1,4]DITHIINYLIDENE (BEDT-TTF)
Submitted by Jan Larsen
1 and Christine Lenoir
2.
Checked by Mathew Carson and David L. Coffen.
1. Procedure
Caution! This preparation should be conducted in an
efficient hood because of the obnoxious odor of
1,2-ethanedithiol.
A.
2-Oxo-1,4-dithiane. A
4-L, four-necked, round-bottomed flask equipped with a
mechanical stirrer,
500-mL pressure-equalizing dropping funnel,
thermometer, and
reflux condenser provided with a
calcium chloride drying tube, is charged with
1 L of dichloromethane,
1,2-ethanedithiol (102 mL, 1.2 mol) (Note
1), and
triethylamine (336 mL, 2.4 mol). The mixture is cooled while it is stirred in an
ice-acetone bath to 0–10°C while a solution of
chloroacetyl chloride (96 mL, 1.2 mol) (Note
2) in
400 mL of dichloromethane is added over a period of 1.5 hr, during which time a thick white precipitate of
triethylamine hydrochloride is formed. After the addition is complete, stirring is continued for another 2 hr at ambient temperature. To the stirred mixture is added 500 mL of ice water. During the addition all the precipitated
triethylamine hydrochloride is dissolved and a two-phase system is formed. The organic phase is washed with four 200-mL portions of water and dried over anhydrous
magnesium sulfate (MgSO4). The drying agent is removed by filtration, and the
dichloromethane is evaporated using a
rotary evaporator at ca. 13 mm. The residue is distilled at 0.7 mm using an
oil bath with the temperature set at 120–130°C (Note
3) and
2-oxo-1,4-dithiane is distilled at
92–93°C; yield,
96 g (
60%) (Note
4), (Note
5).
B. 3-Chloro-2-oxo-1,4-dithiane. A
250-mL, round-bottomed flask, equipped with a
magnetic stirring bar and a reflux condenser provided with a
nitrogen bubbler, is flushed with
nitrogen and charged with
150 mL of carbon tetrachloride (CCl4),
2-oxo-1,4-dithiane (10.0 g, 0.075 mol), and
N-chlorosuccinimide (11.0 g, 0.083 mol) (Note
6), (Note
7). The mixture is refluxed for 30 min. After cooling to 0°C the precipitated
succinimide is removed by filtration and washed with
20 mL of CCl4 (Note
8). The solution is filtered directly into a
1-L, conical flask equipped with a magnetic stirring bar, charged with a suspension of
potassium O-(2-propyl) dithiocarbonate (13.1 g, 0.075 mol) (Note
9) in
300 mL of dry acetone, and stirred at ambient temperature for 0.5 hr. The precipitate is removed by filtration and the solvent is evaporated at ambient temperature using a rotary evaporator at ca. 13 mm.
2-Oxo-3-(2-propoxythiocarbonylthio)-1,4-dithiane is obtained in quantitative yield as a slightly brown oil and used in the following step without further purification (Note
10).
2-Oxo-5,6-dihydro-1,3-dithiolo[4,5-b][1,4]dithiin. A 1-L conical flask, equipped with a magnetic stirring bar, is charged with
500 mL of concentrated sulfuric acid (H2SO4), and cooled to 0°C;
45 mL of ether is added dropwise.
2-Oxo-3-(2-propoxythiocarbonylthio)-1,4-dithiane is added in a thin stream during 10 min using an additional
5 mL of ether to complete the transfer. During the addition the
sulfuric acid becomes dark. After 1.5 hr the reaction mixture is poured onto 3 kg of ice, at which time a sticky mass appears. The mixture is filtered by suction through a
sintered glass funnel (D = 10 cm) charged with a layer of 2 cm of Celite. The Celite is washed with four 150-mL portions of water. A first crop is obtained by combining the water phase and leaving it for 5–7 days at room temperature. During this time the solution first becomes turbid and then clear, at which time
2-oxo-5,6-dihydro-1,3-dithiolo[4,5b][1,4]dithiin has separated as slightly yellow crystals. The water is removed by filtration, the product is washed with four 50-mL portions of water, and with two
20-mL portions of methanol, and dried under reduced pressure at ambient temperature.
The gummy mass isolated on the Celite is dissolved by washing with four
100-mL portions of dichloromethane. The organic phase is washed with three 100-mL portions of water and dried over anhydrous
MgSO4. The drying agent is removed by filtration and the solvent is evaporated using a rotary evaporator at ca. 13 mm. The residue is purified by filtration on
silica gel (Note
11) with
toluene.
Toluene is evaporated using a rotary evaporator at ca. 13 mm. The residue is combined with the first crop and purified by recrystallization from absolute
ethanol to yield
2-oxo-5,6-dihydro-1,3-dithiolo[4,5b][1,4]dithiin as white crystals (yield
7.8–9.4 g,
50–60% based on
2-oxo-1,4-dithiane); mp
126–127°C (Note
12).
C.
2,2'-Bi-5,6-dihydro-1,3-dithiolo[4,5-b][1,4]dithiinylidene(BEDT-TTF). A 250-mL, round-bottomed flask equipped with a magnetic stirring bar and reflux condenser provided with a nitrogen bubbler is charged with
100 mL of freshly distilled trimethyl phosphite and
2-oxo-5,6-dihydro-1,3-dithiolo[4,5-b][1,4]dithiin (5.0 g, 0.024 mol). The solution is heated to reflux by immersing the flask in an oil bath preheated to 125°C (Note
13) for 2–3 hr. During this time bright orange-red crystals of product precipitate. The mixture is cooled to room temperature and the solid is filtered, and washed with four
20-mL portions of methanol and with four
20-mL portions of ether and dried under reduced pressure at ambient temperature to provide
BEDT-TTF. Recrystallization from
300 mL of chlorobenzene affords
4.3 g (
93%) of
BEDT-TTF as bright red needles; mp
245–247°C (dec).
2. Notes
1.
1,2-Ethanedithiol (99%) is available from Aldrich Chemical Company, Inc., and is used without further purification.
2.
Chloroacetyl chloride (98%) is available from Aldrich Chemical Company, Inc., and is used without further purification.
3. The use of an electric heating mantle results in local overheating of the initially formed poly- or oligomeric products giving red, foul-smelling products instead. The product distills rather slowly (2–4 hr).
4. The product was pure by NMR spectroscopy.
1H NMR (CDCl
3/TMS) δ: 3.2 (m);
13C NMR (CDCl
3/TMS) δ: 25.82 (CH
2), 31.02 (CH
2), 35.25 (CH
2), 197.11 (C=O).
5.
2-Oxo-1,4-dithiane can be stored for a long time at −20°C, at which temperature the product crystallizes.
6.
N-Chlorosuccinimide (98%) is available from Aldrich Chemical Company, Inc., and is used without further purification.
8.
3-Chloro-2-oxo-1,4-dithiane can be obtained by removing the solvent at ambient temperature using a rotary evaporator at ca. 13 mm. The product was pure by NMR spectroscopy.
1H NMR (CDCl
3/TMS) δ: 3.2 (m, 4 H, CH
2), 5.37 (s, 1 H, CH);
13C NMR (CDCl
3/TMS) δ: 24.52 (CH
2), 30.18 (CH
2), 61.91 (CH), 188.27 (C=O). The product becomes black in a few days, even when stored at −20°C.
10. The product was pure by NMR spectroscopy.
1H NMR (CDCl
3/TMS) δ: 1.40 (d, 6 H, CH
3), 3.41 (m, 4 H, CH
2), 5.62 (s, 1 H, CH), 5.70 (sept, 1 H, CH);
13C NMR (CDCl
3/TMS) δ: 21.00 (CH
3), 27.70 (CH
2), 31.74 (CH
2), 54.17 (CH), 79.53 (CH), 191.58 (C=O), 207.71 (C=S).
11.
Silicagel 60, 55 g, was used on a
5-cm column.
12. The product showed the following NMR data:
1H NMR (CDCl
3/TMS) δ: 3.43 (s, 4 H, CH
2);
13C NMR (CDCl
3/TMS) δ: 31.08 (CH
2), 113.41 (C=C), 188.72 (C=O).
13. It is essential that the mixture be heated rapidly, otherwise the yield decreases dramatically.
Waste Disposal Information
All toxic materials were disposed of in accordance with "Prudent Practices in the Laboratory"; National Academy Press; Washington, DC, 1995.
3. Discussion
BEDT-TTF [Bis(ethylenedithio)tetrathiafulvalene] has been synthesized by a variety of methods, mostly by reduction of
carbon disulfide with alkali metals,
3,4,5 or electrochemically,
6 followed by alkylation of the formed
disodium 4,5-dimercapto-1,3-dithiole-2-thione with
1,2-dibromoethane,
3,4,5 The thione is converted to
2-oxo-5,6-dihydro-1,3-dithiolo[4,5-b][1,4]dithiin by oxidation with
mercuric acetate.
4 Finally coupling with
triethyl phosphite,
4,7,8 or direct coupling of the thione with
triethyl phosphite5,9,10 or with
triethyl phosphite under photochemical conditions
11 or with
triethyl phosphite under high pressure
12 yields
BEDT-TTF. Coupling has also been effected by alkylating the thione followed by electrochemical reduction of the formed 2-alkylthio-1,3-dithiolium salt.
13 Pyrolysis then yields the final product.
The present procedure, which is based on those of Schumaker
8 and Larsen and Lenoir,
14 is simple and avoids the use of the troublesome and sometimes hazardous reduction of
carbon disulfide with alkali metals. On several occasions a violent explosion has occurred in our laboratories during this reaction.
The present method gives high yields of
BEDT-TTF in excellent purity. Actual investigation of super-conducting salts of
BEDT-TTF show that
BEDT-TTF made by the present route gives material of superior purity.
15 Also by the present method
BEDT-TTF is obtained from readily available starting materials.
Appendix
Compounds Referenced (Chemical Abstracts Registry Number)
silica gel
2-Oxo-3-(2-propoxythiocarbonylthio)-1,4-dithiane
2,2'-BI-5,6-DIHYDRO-1,3-DITHIOLO[4,5-b][1,4]DITHIINYLIDENE (BEDT-TTF)
2-oxo-5,6-dihydro-1,3-dithiolo[4,5b][1,4]dithiin
2,2'-Bi-5,6-dihydro-1,3-dithiolo[4,5-b][1,4]dithiinylidene(BEDT-TTF)
BEDT-TTF
Silicagel
BEDT-TTF [Bis(ethylenedithio)tetrathiafulvalene]
disodium 4,5-dimercapto-1,3-dithiole-2-thione
ethanol (64-17-5)
sulfuric acid (7664-93-9)
methanol (67-56-1)
ether (60-29-7)
carbon tetrachloride,
CCl4 (56-23-5)
nitrogen (7727-37-9)
mercuric acetate (1600-27-7)
acetone (67-64-1)
chlorobenzene (108-90-7)
potassium hydroxide (1310-58-3)
toluene (108-88-3)
2-propanol (67-63-0)
carbon disulfide (75-15-0)
1,2-dibromoethane (106-93-4)
chloroacetyl chloride (79-04-9)
dichloromethane (75-09-2)
Succinimide (123-56-8)
magnesium sulfate,
MgSO4 (7487-88-9)
N-bromosuccinimide (128-08-5)
potassium xanthate
triethylamine (121-44-8)
N-chlorosuccinimide (128-09-6)
Triethylamine hydrochloride (554-68-7)
Triethyl phosphite (122-52-1)
1,2-ethanedithiol (540-63-6)
trimethyl phosphite (121-45-9)
2-Oxo-1,4-dithiane (74637-14-2)
3-Chloro-2-oxo-1,4-dithiane (88682-21-7)
potassium O-(2-propyl) dithiocarbonate (140-92-1)
1,3-Dithiolo[4,5-b][1,4]dithiin, 2-(5,6-dihydro-1,3-dithiolo- [4,5-b][1,4]dithiin-2-ylidene)-5,6-dihydro- (66946-48-3)
1,3,4,6-tetrathiapentalen-2,6-dione
2-Oxo-5,6-dihydro-1,3-dithiolo[4,5-b][1,4]dithiin (74962-29-1)
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