Org. Synth. 1966, 46, 34
DOI: 10.15227/orgsyn.046.0034
3,4-DICHLORO-1,2,3,4-TETRAMETHYLCYCLOBUTENE
[Cyclobutene, 1,2,3,4-tetramethyl-3,4-dichloro-]
Checked by G. Brown and V. Boekelheide.
1. Procedure
A 400-ml. three-necked flask equipped with a mechanical stirrer, a gas dispersion tube, and a thermometer is charged with 216 g. (4 moles) of 2-butyne, 14 ml. of boron trifluoride etherate, and 1 ml. of water (Note 1). The mixture is stirred vigorously while the flask is partially immersed in a dry ice-acetone bath to maintain an internal temperature of −20°. Chlorine (195 g., 2.75 moles) is then added (Note 2) gradually over a period of 17–20 hours.
When all the chlorine has been added, the flask and contents (Note 3) are cooled to −78° and held at this temperature for 30 minutes. The white crystalline product which separates is collected on a sintered-glass funnel; 160–170 g. (45–48%) of crude crystals, m.p. 53–55°, is obtained. The crude product when stored at −20° takes on a reddish or blue color after a few days (Note 4).
Purification of the crude material is accomplished by dissolving it in petroleum ether (30–50°) or methylene chloride, shaking this solution three times with water, and passing the organic layer through a fluted filter paper. After the filtrate has been dried over anhydrous sodium sulfate, it is concentrated to a small volume and cooled to −78°. The perfectly white, crystalline product which separates is collected yielding 110–120 g. (30–33%) of crystals, m.p. 57–58° (Note 5).
2. Notes
1.
The submitter reports that he and his colleagues have found since the procedure was submitted and checked that the yield and purity of the product is the same whether the preparation is carried out in the presence or absence of
boron trifluoride etherate and water. Recommends that the
14 ml. of boron trifluoride etherate and 1 ml. of water
not be added.
2.
The
chlorine is most conveniently added by liquefying the required amount in a
gas trap. The gas trap is placed in an empty
Dewar flask and covered with glass wool. While the liquid
chlorine slowly warms up, the resulting gaseous
chlorine is passed through a
sulfuric acid wash bottle into the reaction mixture. The addition generally takes 17–20 hours.
3.
The final reaction mixture is slightly yellow, but at times it can be reddish. During the reaction some white crystalline product collects at the walls of the reaction vessel.
4.
It is important to purify the crude product as soon as possible since it decomposes readily in the impure state. Once decomposition has set in, purification is difficult.
5.
A still purer product is obtained if the dried
petroleum ether solution is evaporated to dryness with a
water aspirator and the residual crude product distilled through a
Vigreux column. After a small fore-run, pure
tetramethyl-3,4-dichlorocyclobutene distils at
59–60° at 12 mm. The product melts at
58° and is more stable at room temperature than the recrystallized but undistilled material.
3. Discussion
The method used is that of Criegee and Moschel.
2 Smirnow-Samkow
3 made the same substance by the reaction of
2-butyne with
sulfuryl chloride in
10–15% yield.
4. Merits of the Preparation
3,4-Dichloro-1,2,3,4-tetramethylcyclobutene is an unusually versatile intermediate.
4 The tertiary and allylic chlorine atoms undergo ready solvolysis. With
lithium aluminum hydride the chlorine atoms are replaced by hydrogen. The resulting
cis, trans-tetramethylcyclobutenes are starting materials for numerous transformations,
e.g., thermolysis leads to stereoiisomeric tetramethylbutadienes.
5 Lithium amalgam in
ether results in the formation of
octamethyltricyclooctadiene. With
nickel carbonyl the
nickel chloride complex of tetramethylcyclobutadiene is formed.
6 Ammonia transforms the dichloride into
tetramethylpyrrole.
7 Other reactions have been reported.
8
This method of preparation is simpler, more reproducible, and gives considerably better yields than the original one of Smirnow-Samkow.
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
petroleum ether
octamethyltricyclooctadiene
nickel chloride complex of tetramethylcyclobutadiene
ammonia (7664-41-7)
ether (60-29-7)
sodium sulfate (7757-82-6)
sulfuryl chloride (7791-25-5)
chlorine (7782-50-5)
methylene chloride (75-09-2)
lithium (7439-93-2)
nickel carbonyl
lithium aluminum hydride (16853-85-3)
boron trifluoride etherate (109-63-7)
2-butyne (503-17-3)
3,4-Dichloro-1,2,3,4-tetramethylcyclobutene,
Cyclobutene, 1,2,3,4-tetramethyl-3,4-dichloro-,
tetramethyl-3,4-dichlorocyclobutene (1194-30-5)
tetramethylpyrrole (1003-90-3)
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