Checked by Melvin S. Newman and S. Ramachandran.
1. Procedure
In a
2-l. three-necked flask, equipped with a
Dry Ice-acetone reflux condenser, a
mechanical stirrer, and a
250-ml. dropping funnel, is placed
29.2 g. (1.2 g. atoms) of magnesium turnings. Enough
tetrahydrofuran (THF) (Note
1) to cover the
magnesium is added, stirring is begun, and about
5 ml. of vinyl bromide (Note
2) is added. After the reaction has started (Note
3), an additional
350 ml. of the THF is added. The rest of the
vinyl bromide (140 g., 1.3 moles, total), dissolved in
120 ml. of THF, is added at such a rate that a moderate reflux is maintained. After the addition has been completed, the solution is refluxed for 30 minutes (Note
4). The Grignard solution is then cooled to room temperature, and the Dry Ice-acetone condenser is replaced with a water condenser which is fitted with a
Drierite-filled drying tube. A solution of
135 g. (0.44 mole) of di-n-butyltin dichloride (Note
5) in
250 ml. of THF (Note
6) is then added, with stirring, at such a rate that a moderate reflux is maintained. After the addition has been completed, the reaction mixture is refluxed for 20 hours. The mixture is cooled to room temperature and is hydrolyzed by the slow addition of
150 ml. of a saturated ammonium chloride solution (Note
7). The organic layer is then decanted and the residual salts are washed thoroughly with 3 portions of
ether, the washings being added to the organic layer. The
ether and the
THF are stripped off at atmospheric pressure; a
Claisen distillation head is used. The residue is distilled at reduced pressure using a
vacuum-jacketed Vigreux column equipped with a
total-reflux partial take-off head to give
95–116 g. (
74–91%) of
di-n-butyldivinyltin, b.p.
60° /0.4 mm.,
nD25 1.4797 (Note
8) and (Note
9).
2. Notes
1.
Tetrahydrofuran, obtained from the Electrochemicals Department of E. I. du Pont de Nemours & Co., was distilled from
lithium aluminum hydride prior to use. It is not advisable to leave
THF purified in this manner standing around for longer periods, since, in the absence of the inhibitor present in the commercial material, peroxides form fairly rapidly. (See also
p. 793, Note 2).
2.
Vinyl bromide, obtained from the Matheson Company, was redistilled prior to use. The distillate was collected in a
receiver cooled with a Dry Ice-acetone mixture and protected from day-light.
3. In most cases the formation of the Grignard reagent began in the absence of any initiator. In cases where the reaction did not begin within a few minutes,
0.5 ml. of methyl iodide served to initiate attack on the
magnesium.
4. In small-scale preparations of
vinylmagnesium bromide it is advisable to carry out the reaction in an atmosphere of dry
nitrogen in order to prevent hydrolysis and oxidation of the Grignard reagent. In larger-scale preparations such as the one described here, where a considerable excess of Grignard reagent is used, such precautions are not necessary.
6. The checkers found that
250 ml. of dry ether was equally effective.
7. Enough saturated
ammonium chloride solution is added to cause coagulation of the inorganic salts to a particle size of about 2–5 mm. in diameter; the volume of solution required varies but averages about 100–120 ml. per mole of Grignard reagent. If the hydrolysis is stopped at this point, a clear, essentially dry organic layer results, and in most instances no further drying is required before distillation.
8. This general procedure has been used to prepare
2,3 a large number of vinyltin compounds, including:
CH2=CHSnR3 (R = CH3, C2H5, n-C3H7, n-C4H9, C6H5)
(CH2=CH)2SnR2 (R = CH3, n-C4H9, (CH3)3SiCH2, C6H5)
(CH2=CH)3SnR (R = n-CH4H9, CH6H5)
(CH2=CH)4Sn
9. Grignard reagents other than
vinylmagnesium bromide may be used in this general procedure. The initial use of a Dry Ice-acetone condenser, is then not required. Use of the
THF solvent provides a distinct advantage over the method recently described in detail
(p. 881), in which
ether is used as a solvent, since fewer steps are required.
3. Discussion
Copyright © 1921-2002, Organic Syntheses, Inc. All Rights Reserved