A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1955, 35, 85
DOI: 10.15227/orgsyn.035.0085
[Thiophene, 2-(methylthio)-]
Submitted by J. Cymerman-Craig and J. W. Loder1.
Checked by Charles C. Price and E. A. Dudley.
1. Procedure
In a 1-l. three-necked flask fitted with a liquid-sealed mechanical stirrer, a reflux condenser, and a dropping funnel are placed 8 g. (0.33 g. atom) of magnesium turnings and 600 ml. of absolute ether. There is placed in the dropping funnel 70 g. (0.33 mole) of 2-iodothiophene (p.545), the stirrer is started, and about 10 ml. of the iodothiophene is added. The reaction generally begins within a few minutes (Note 1), and the iodothiophene is then added dropwise at such a rate that moderate refluxing occurs. When the addition is complete, the mixture is refluxed gently until only a small residue of unreacted magnesium remains. The solution is then cooled in an ice bath, the dropping funnel is removed, and 10.7 g. (0.33 g. atom) of finely powdered sulfur (Note 2) is added (Note 3), the funnel is replaced, and the mixture is refluxed (Note 4) for 45 minutes. The solution is again cooled in an ice bath, and 22.6 ml. (0.36 mole) of methyl iodide is added dropwise from the funnel, and the stirring is then discontinued (Note 5). The reaction mixture is refluxed 10 hours. It is then cooled, and an aqueous solution of ammonium chloride is run in with vigorous stirring (Note 6). The liquid is transferred to a separatory funnel, the lower aqueous layer is run off, and the ethereal solution is washed three times with a 2% solution of potassium hydroxide, then with water, and finally is dried over anhydrous sodium sulfate. The ether is removed by distillation at ordinary pressure, and the residual dark liquid is distilled under reduced pressure. The yield of colorless methyl 2-thienyl sulfide is 23–26 g. (53–60%), b.p. 82–86°/22 mm., n25D 1.5978 (Note 7) and (Note 8).
2. Notes
1. If the reaction does not start, it may be assisted by the addition of a small amount of methylmagnesium iodide in ethereal solution.
2. The sulfur was distilled and then ground in a mortar before use.
3. The mechanical stirring is continued. The sulfur dissolves during the refluxing period to give a clear yellow solution. A sludge which adheres to the bottom of the flask may form, but the yield is unaltered.
4. On reheating, a vigorous reaction with the sulfur occurs. A means of cooling the reaction flask should be at hand to ensure control of the reaction.
5. The solution may be left overnight at this stage, sealed under nitrogen.
6. The decomposition of the unreacted Grignard reagent is best carried out in a hood to remove the strong odor of thiols.
7. Considerable decomposition occurs if distillation is attempted at atmospheric pressure. The product is sometimes pale yellow, and darkens slightly on standing.
8. A dark oil remains which decomposes at this pressure when strongly heated.
3. Discussion
Methyl 2-thienyl sulfide has been prepared by the action of phosphorus trisulfide on dimethyl succinate2 and by the action of methyl iodide on the sodium salt of 2-thiophenethiol,3 both of which methods are of little preparative value. The procedure described above is that of Cymerman-Craig and Loder.4 2-Bromothiophene has been used in the latter method in place of the iodine derivative.5

References and Notes
  1. University of Sydney, Sydney, Australia.
  2. Steinkopf and Leonhardt, Ann., 495, 166 (1932).
  3. Meyer and Neure, Ber., 20, 1756 (1887).
  4. Cymerman-Craig and Loder, J. Chem. Soc., 1954, 237.
  5. Gol'dfarb, Kalik, and Kirmalova, Zhur. Obshchei Khim., 29, 2034 (1959) [C. A., 54, 8775 (1960)].

Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

phosphorus trisulfide

ether (60-29-7)

ammonium chloride (12125-02-9)

magnesium turnings (7439-95-4)

sodium sulfate (7757-82-6)

nitrogen (7727-37-9)

sulfur (7704-34-9)

iodine (7553-56-2)

potassium hydroxide (1310-58-3)

Methyl iodide (74-88-4)

methylmagnesium iodide (917-64-6)

iodothiophene (3437-95-4)

Methyl 2-thienyl sulfide,
Thiophene, 2-(methylthio)- (5780-36-9)

dimethyl succinate (106-65-0)

2-Bromothiophene (1003-09-4)

sodium salt of 2-thiophenethiol