Organic Syntheses, CV 5, 474
Submitted by Norman Kharasch and Robert B. Langford
1.
Checked by D. C. Dittmer and B. C. McKusick.
1. Procedure
Caution! Both steps should be carried out in a good hood.
A.
2,4-Dinitrophenyl benzyl sulfide. The apparatus consists of a
1-l., three-necked, round-bottomed flask equipped with a
sealed mechanical stirrer and a
reflux condenser. In it are placed
202 g. (1.00 mole) of 2,4-dinitrochlorobenzene (m.p.
50–52°)
(Caution! A skin irritant), 400 ml. of methanol,
124 g. (1.00 mole) of benzyl mercaptan, and
87 g. (85 ml., 1.10 moles) of pyridine. The mixture is heated at the reflux temperature with stirring for 16 hours or more (Note
1) and cooled to 0°. The
2,4-dinitrophenyl benzyl sulfide that precipitates is separated by filtration, washed with two
250-ml. portions of ice-cold methanol, and dried at 60–80°. The sulfide, a yellow crystalline solid that melts at
128–129°, weighs
235–250 g. (
81–86%) (Note
2). It may be used in the next step without further purification.
B.
2,4-Dinitrobenzenesulfenyl chloride. Dry
2,4-dinitrophenyl benzyl sulfide (232 g., 0.80 mole) and
400 ml. of dry ethylene chloride are placed in a
2-l., one-necked, round-bottomed flask equipped with a stirrer (Note
3).
Sulfuryl chloride (119 g., 0.88 mole) (Note
4) is added to the resulting suspension at room temperature. A mildly exothermic reaction causes the solid to dissolve quickly, usually within 1 to 2 minutes, with a temperature rise of 10–15° (Note
5). The resulting clear yellow solution is concentrated to an oil by heating under aspirator vacuum on a
steam bath (Note
6).
(Caution! Do not heat with gas or electricity because the product, like many nitro compounds, can explode if overheated.) The residual oil is cooled to 50–60°, and
3–4 volumes of dry petroleum ether (b.p.
30–60°) are added with vigorous handswirling. The oil quickly crystallizes. The mixture is cooled to room temperature and filtered to separate
2,4-dinitrobenzenesulfenyl chloride as a yellow crystalline solid. The
sulfenyl chloride is washed well with dry
petroleum ether and dried at 60–80° (Note
7); weight
150–170 g. (
80–90%); m.p.
95–96° (Note
8), (Note
9).
2. Notes
1. After 2 or 3 hours, solid product usually appears in the reaction mixture.
2. When
practical grade 2,4-dinitrochlorobenzene (m.p.
46–47°) is substituted, a product of equally good quality (m.p.
128–129°) is obtained, but the yield is only
70–75%.
3. All materials and equipment used in Step B of this procedure must be completely dry to avoid loss of product by hydrolysis. The checkers found, however, that the reaction may be carried out open to the air without loss of yield.
4.
Practical grade sulfuryl chloride, obtained from Matheson, Coleman and Bell, gives satisfactory results.
5. The
2,4-dinitrophenyl benzyl sulfide normally undergoes cleavage at room temperature without the addition of a catalyst. If the reaction does not occur spontaneously, the mixture may be warmed gently and/or one drop of dry
pyridine may be added to initiate the reaction.
6. Rotary or other distillation equipment with metal parts should not be used in concentrating the reaction mixture because not only will the corrosive vapors damage the equipment, but also the resulting metal salts will discolor and partially decompose the product. The solution should not be heated any longer than is necessary to concentrate it; excessive heating gives a darkcolored product.
7. The product should not be dried longer than is necessary for it to reach constant weight, or there may be partial decomposition.
8. The product obtained by this procedure is pure enough for most purposes. Its melt, however, is faintly cloudy. A product of high purity, giving a clear melt, can be obtained by recrystallization from about
15 ml. of dry carbon tetrachloride per gram of
sulfenyl chloride. When stored in a sealed brown bottle with a plastic cap (no metal!), the
sulfenyl chloride is stable for years.
3. Discussion
4. Merits of the Preparation
2,4-Dinitrobenzenesulfenyl chloride is a versatile analytical reagent for the characterization of a wide variety of organic compounds, including alcohols, mercaptans, ketones, olefins, amines, aromatic compounds, olefin oxides, and hydroxysteroids. Review articles summarize these applications.
10,11
The chlorinolysis of
2,4-dinitrophenyl benzyl sulfide gives a good yield of product which is satisfactory for most purposes without recrystallization. Only simple equipment and inexpensive materials are needed, only 2 or 3 hours of the operator's time are required, and the entire procedure can be completed within 24 hours.
Appendix
Compounds Referenced (Chemical Abstracts Registry Number)
petroleum ether
sulfenyl chloride
sulfenyl bromide
methanol (67-56-1)
bromine (7726-95-6)
carbon tetrachloride (56-23-5)
ethylene chloride (107-06-2)
sulfuryl chloride (7791-25-5)
pyridine (110-86-1)
benzyl chloride (100-44-7)
2,4-dinitrochlorobenzene (97-00-7)
2,4-Dinitrobenzenesulfenyl chloride,
Benzenesulfenyl chloride, 2,4-dinitro- (528-76-7)
benzyl mercaptan (100-53-8)
2,4-Dinitrophenyl benzyl sulfide (7343-61-5)
2,4-Dinitrobenzenesulfenyl bromide
2,4-dinitrothiophenol
2,4-dinitrophenyl thiolbenzoate
bis-(2,4-dinitrophenyl) disulfide (2217-55-2)
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