Organic Syntheses, CV 7, 372
Submitted by I. Thomsen, K. Clausen, S. Scheibye, and S.-O. Lawesson
1.
Checked by Clayton H. Heathcock, Mark Sanner, and Terry Rosen.
1. Procedure
A.
2,4-Bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide (1). A dry
1-L, three-necked, round-bottomed flask, fitted with a
reflux condenser,
mechanical stirrer, and
ground-glass stopper, is charged with
111.0 g (0.25 mol) of phosphorus sulfide, P4S10 (Note
1) and
270 g (2.5 mol) of anisole (Note
1). Stirring is commenced and the mixture is heated at reflux temperature by use of a heating mantle. After 1 hr, the solution is homogeneous and after a second hour
2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide (
1) begins to precipitate. The reaction mixture is allowed to cool to room temperature and the precipitate is filtered (Note
2) and washed with anhydrous
ether (2 × 50 mL) and
50 mL of anhydrous chloroform (free of alcohols) to yield
160–165 g (
79–82%) of pale-yellow crystals, mp
228°C (Note
3) and (Note
4).
B.
N-Methylthiopyrrolidone (2). A
200-mL, three-necked, round-bottomed flask is fitted with a
rubber septum,
thermometer,
magnetic stirring bar, and reflux condenser equipped with a
nitrogen bubbler. The flask is charged with
19.8 g (19.3 mL, 0.20 mol) of N-methylpyrrolidone (Note
5) and
40.4 g (0.10 mol) of 1, whereupon the temperature of the reaction mixture increases to 75–80°C. After 5 min,
35 mL of benzene (Note
6) is added by syringe and the mixture is stirred while being brought to reflux (Note
7). The mixture is heated at reflux for 2 hr (Note
8) and then cooled to room temperature, whereupon it again becomes heterogeneous. The
benzene is removed with the aid of a
rotary evaporator and the resulting yellow slurry is distilled under reduced pressure through a
5-cm Vigreux column to provide
23.0 g (
100%) of
N-methylthiopyrrolidone (
2) as a yellow liquid, bp
94–97°C/0.03 mm (Note
9).
2. Notes
1. Commercial
phosphorus sulfide, P
4S
10, is used without purification. Checkers used
P4S10 from Matheson, Coleman and Bell and from Alfa Products, Morton Thiokol, Inc. Best results (yield, melting point) were obtained with the Alfa sample, mp
291–295°C.
2. Excess
anisole (137 g) can be recovered by distillation of the filtrate.
3. The product is somewhat hygroscopic and should be stored in an
airtight container. It is also available as Lawesson's reagent from Aldrich, Fluka, and from Merck–Schuchard.
4. The checkers obtained
176 g (
87%) of
1, mp
228–231°C.
5. Commercial material from the Aldrich Chemical Company was stored over Linde 4A molecular sieves.
7. During this operation most of the yellow solid gradually dissolves, affording a clear yellow solution with small amounts of suspended solid. When reflux begins, the internal temperature of the reaction mixture is 95°C.
8. The reaction time can be decreased to 3 min by the use of
toluene as solvent.
9. The purified product freezes when stored in a
refrigerator. The spectral properties are as follows:
1H NMR (CDCl
3) δ: 2.07 (quintet, 2 H,
J = 7), 3.03 (t, 2 H,
J = 7), 3.29 (s, 3 H), 3.77 (t, 2 H,
J = 7). IR (neat): 1520 cm
−1.
3. Discussion
A variety of thiating reagents are known: H
2S,
2 H
2S/HCl,
3 H
2S
2/HCl,
4 (Et
2Al)
2S,
5 (EtAlS)
n,
6 SiS
2,
7 B
2S
3,
7 PCl
5/Al
2S
3/Na
2SO
4,
8 Na
2S/H
2SO
4,
9 P
2S
510 P
2S
5/Pyridine,
11 P
2S
5/NEt
3,
12 P
2S
5/NaHCO
3,
13 RPS (OR
1)
214 PSCl
x (NMe
2)
3–x (X = 0–3),
15 and SCNCOOEt.
16 The reagent described here,
2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide (
1),
17 offers a number of advantages as a thiating reagent. It is easily prepared in a simple one-step procedure employing commercially available starting materials. It has a satisfactory shelf life, provided it is protected from moisture. In contrast to commercial P
4S
10, compound
1 is a well-defined reagent that gives reproducible results, usually in high yield. Under defined conditions, certain selectivity has been observed.
18,19,20 Other methods for the preparation of analogs of
1 have been described.
21,22,23
The thiation procedure described here
24 is an example of a general synthetic method for the conversion of carbonyl to thiocarbonyl groups. Similar transformations have been carried out with ketones,
25 carboxamides,
26,27,28,29,30 esters,
31,32 thioesters,
31 lactones,
18,33 thiolactones,
18 imides,
24 enaminones,
34 and protected peptides.
35
Appendix
Compounds Referenced (Chemical Abstracts Registry Number)
Benzene (71-43-2)
ether (60-29-7)
chloroform (67-66-3)
hydrogen sulfide (7783-06-4)
Anisole (100-66-3)
toluene (108-88-3)
sodium wire (13966-32-0)
N-methylpyrrolidone (872-50-4)
2-Pyrrolidinethione, 1-methyl-,
N-Methylthiopyrrolidone (10441-57-3)
2,4-BIS(4-METHOXYPHENYL)-1,3,2,4- DITHIADIPHOSPHETANE 2,4-DISULFIDE,
2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide (19172-47-5)
phosphorus sulfide
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