Organic Syntheses, CV 4, 108
Submitted by F. L. Greenwood, M. D. Kellert, and J. Sedlak
1.
Checked by John D. Roberts and A. T. Bottini.
1. Procedure
The residue is transferred to a
125-ml. Claisen flask modified so that the distilling arm carries an 18 × 180 mm. section packed with glass helices.
Nitrogen is led into the capillary, and, after a forerun of
1–3 g., there is collected
28–31 g. (
58–64%) of
4-bromo-2-heptene, b.p.
70–71°/32 mm.,
n25D 1.4710–1.4715 (Note
5). A residue of
7–10 g. remains in the distilling flask (Note
6).
2. Notes
1. The
2-heptene was the pure grade material purchased from Phillips Petroleum Company, Bartlesville, Oklahoma. This olefin is comparable to material prepared by a Boord synthesis. The
N-bromosuccinimide was obtained from Arapahoe Chemicals, Inc., Boulder, Colorado. The
benzoyl peroxide was used as received from Distillation Products, Rochester, New York. The
carbon tetrachloride was reagent grade, from J. T. Baker Chemical Company, Phillipsburg, New Jersey.
2. The reaction is not rapid, and
benzoyl peroxide is necessary to effect reaction. Longer reflux times lead to darkening of the reaction mixture.
3. The
succinimide recovered corresponded to
97–98% of the theoretical amount and analyzed for 0.4% active
bromine.
4. Removal of the
carbon tetrachloride at a lower pressure results in loss of product. Distillation at a pressure much above 200 mm. causes considerable darkening of the liquid.
Carbon tetrachloride removed at the higher pressure gives no precipitate with aqueous
silver nitrate; this indicates the absence of product.
5. When first distilled, the product is nearly colorless. On standing under
nitrogen in the refrigerator for several days, the material acquires a pale yellow color. Evidence for the identity of the product as
4-bromo-2-heptene is outlined in Reference
2.
6. This includes the liquid wetting the helices as well as the small amount of dark residue in the flask.
3. Discussion
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