Submitted by R. R. Read, L. S. Foster, Alfred Russell, and V. L. Simril.
Checked by C. F. H. Allen and James VanAllan.
1. Procedure
A
dry, 3-l., three-necked, round-bottomed flask (Note
1) and (Note
2) is fitted with an
efficient reflux condenser (Note
3) protected by a
drying tube, a
dropping funnel, and a
thermometer which extends well into the reaction mixture (Note
4); the flask is arranged so that it can be cooled externally (Note
5). In the flask is placed
161 g. (7 gram atoms) of sodium cut into shavings 1–2 mm. in thickness (Note
6) and (Note
7); the
sodium is just covered with dry
ether (about 300 ml.) (Note
8). A mixture of
411 g. (321 ml., 3 moles) of n-butyl bromide and
471 g. (315 ml., 3 moles) of bromobenzene (Note
9) is added slowly from the dropping funnel over a period of about 2.5 hours, the temperature being kept as near 20° as possible; the mass acquires a bluish color.
After the flask and contents have been allowed to stand at room temperature for 2 days with occasional shaking, the liquid is decanted (Note
10).
Three hundred milliliters of methanol> is then added carefully, and the mixture is refluxed on a
steam bath for 4 hours. Then 800 ml. of water is added to dissolve the salt, and the hydrocarbon layer is separated and added to the decanted liquid. The aqueous layer is extracted once with
250 ml. of ether (Note
11), and the combined hydrocarbon fraction, decanted solution, and
ether extract are dried over
40 g. of calcium chloride. Most of the
ether is removed on a
steam bath, and the residual liquid is distilled through an
electrically heated, jacketed column (Note
12). The fraction that boils at
180–182.5°/750 mm. is collected as
n-butylbenzene (Note
13) and (Note
14); the yield is
261–281 g. (
65–70%) (Note
15).
2. Notes
1. The size of the pieces of
sodium, the control of temperature, and the use of an electrically heated, jacketed fractionating column are important factors in the successful preparation of the compound.
2. A
copper flask and
copper condenser reduce the hazard from breakage but are not essential and are less convenient with the quantities indicated.
3. Unless the reaction gets out of hand, the only function of the condenser is to prevent loss of
ether. If the temperature gets above 30°, the reaction becomes violent and cannot be controlled by a single condenser.
4. A
thermometer on which the scale is well above the surface of the reaction mixture is advisable; one reading from −50° to 50° is convenient.
5. The temperature range is critical. Below 15° reaction is extremely slow, but in time a vigorous reaction suddenly sets in and blows a good part of the reactants out through the condenser. Above 30° the reaction gets out of hand (Note
3).
6. This is a very tedious task. It is best accomplished by flattening the usual bars of
sodium with a hammer and cutting the flattened strips with scissors. Alternatively the
sodium, in 1-lb. lots, can be rolled under a heavy lawn roller (Read and Foster).
7. If the
sodium is too thick, much of it fails to react, whereas
sodium "sand" reacts very vigorously but gives poor yields of the desired product.
10. Read and Foster recommend extracting the residue with
benzene, using an
automatic extractor.
11. Although this extract contains but 2–3 g. of hydrocarbon, its use facilitates drying later on and reduces loss through an occasional imperfect separation of layers.
12. A column such as the
Whitmore-Lux or Fenske column provided with an electrically heated jacket is essential.
13. Alternatively, a crude fraction boiling at
160–185° is collected; on redistillation, the product that boils at
181–184° is collected (Read and Foster).
14. The fore-run amounts to about
45 g. The residue is largely
biphenyl. Small additional amounts of product can be secured by combining these fractions from several runs and refractionating.
15. Without a heated column, the yield drops to
221 g. (
54%).
3. Discussion
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