Organic Syntheses, Coll. Vol. 4, p.746 (1963); Vol. 38, p.78 (1958).
[I. METHOD A]
The apparatus (Fig. 14
) is similar to that described on p. 795
and in a previous volume.2
It consists of a Pyrex glass reaction tube, 90 cm. long by 45 mm. in outside diameter, mounted vertically in an electric furnace about 50 cm. long
. Attached to the top of the tube are a graduated dropping funnel (Note 1)
, an inlet tube for nitrogen
, and a thermocouple
well extending to the bottom of the heated section and holding a movable thermocouple. The entire heated section, which begins 10 cm. from the top of the tube, is packed with Pyrex glass rings 10 mm. in outside diameter by about 10 mm. in length held in place by a plug of glass wool supported by indentations in the tube. The lower end of the tube is attached to a 1-l. round-bottomed flask
immersed in an ice bath
and having a side arm from which vapors pass successively through a trap immersed in an ice bath and a trap immersed in a bath of Dry Ice and acetone
. Each trap is capable of holding about 200 ml. of liquid. The temperature of the hottest part of the tube, which is located near the middle of the heated section, is raised to 575° ± 10° while nitrogen (Note 2)
is passed successively through a flowmeter
and the tube at a rate of 4–6 1./hr. Under these conditions (Note 3)
, 658 g. (645 ml., 3.5 moles) of 1,5-pentanediol diacetate (Note 4)
is added to the tube over a period of 3.5 hours. The contents of the three receivers are combined and distilled at atmospheric pressure through a 15-cm. indented Claisen-type still head
; the condenser is cooled with ice water, and the receiver
is immersed in an ice bath. The fraction boiling at 25–55°
, wt. 170–190 g.
, is redistilled through a 60-cm. column
packed with glass helices or a column of similar efficiency to give 150–170 g.
) of 1,4-pentadiene
, b.p. 26–27.5° /760 mm.
1.3861–1.3871 (Note 5)
A Hershberg dropping funnel3
modified by addition of a pressure-equalizing arm (Fig. 14
) makes it easy to add the diacetate at a constant rate.
A dry, oxygen-free grade of commercial nitrogen
is used. Nitrogen
can be omitted without diminishing the yield by more than a few per cent.
As the addition of the diacetate begins, the temperature of the hottest part of the tube (the location of which generally shifts lower at this time) decreases, necessitating an increase in current in the electric furnace.
[II. METHOD B]
A. α-Chloroethyl ethyl ether
. A mixture of 200 g. (201 ml.) of redistilled paraldehyde
, b.p. 121–122.5°
(equivalent to 4.54 moles of acetaldehyde
), and 200 g. (254 ml., 4.34 moles) of absolute ethanol
is placed in a 1-l. three-necked flask
fitted with a mechanical stirrer
and a gas inlet tube reaching to the bottom of the flask. The mixture is cooled to −5° in a mixture of Dry Ice and acetone, and dry hydrogen chloride (Note 1) is passed into the stirred reaction mixture maintained at about −5° until 200 g. (5.48 moles)
has been absorbed. During this operation, which requires about 2 hours, the reaction mixture separates into two layers. The upper layer of crude α-chloroethyl ethyl ether
is removed, and the dissolved hydrogen chloride
is swept out by bubbling dry nitrogen
gas through the mixture. The product is dried overnight with 25–50 g. of anhydrous calcium sulfate (Note 2)
. The yield of crude α-chloroethyl ethyl ether (Note 3)
is 411–432 g.
based on ethanol
). The product is not distilled, since it decomposes readily.
B. α,β-Dibromoethyl ethyl ether
. Four hundred and twenty-five grams (3.92 moles) of the crude α-chloroethyl ethyl ether
(part A) is placed in a dry 1-l. three-necked flask
, fitted with a dropping funnel, mechanical stirrer, and an outlet tube leading to a gas absorption trap8
to dispose of the hydrogen chloride
evolved. The flask is cooled in an ice bath, and 625 g. (200 ml., 3.92 moles) of bromine
is added in small portions from the dropping funnel with stirring. The reaction mixture is allowed to become almost colorless after each addition. When all of the bromine
has been added (5–6 hours), a slow current of dry nitrogen
is bubbled through the reaction mixture to sweep out the hydrogen chloride (Note 4)
. The product is dried overnight with 25–50 g. of anhydrous calcium sulfate
and then distilled at reduced pressure (Note 5)
. The yield of colorless α,β-dibromoethyl ethyl ether
is 599–663 g.
based on the α-chloroethyl ethyl ether
), b.p. 70–75° /27 mm.
C. Allylmagnesium bromide (Note 6)
. In a dry 5-l. three-necked flask
, equipped with a sealed stirrer, a reflux condenser
and drying tube, a pressure-equalized dropping funnel
, and a nitrogen inlet tube, are placed 195 g. (8.0 g. atoms) of dry magnesium turnings
and 2.4 l. of anhydrous ether
. The flask is cooled in an ice bath, a small crystal of iodine
is added, and a solution of 400 g. (287 ml., 3.31 moles) of allyl bromide
(redistilled, b.p. 69–71°
) in an equal volume of anhydrous ether is added dropwise over a period of 17 hours. During the reaction a slow stream of dry, oxygen-free nitrogen
is passed through the flask. After the addition is complete, the reaction mixture is stirred for 30 minutes. The Grignard reagent is decanted into a dry, graduated storage bottle; the residue in the flask is washed with 150–200 ml. of dry ether
; and the wash liquid is added to the storage bottle. Samples of the clear supernatant solution are analyzed by acidimetric titration.9
The yield of allylmagnesium bromide
is 2.62–2.95 moles
. A 2-l. three-necked flask
is equipped with a sealed stirrer and a 28-cm. reflux condenser
, at the top of which is a 2.5 × 35 cm. Vigreux fractionating column
attached to an efficient condenser arranged for distillation. Water at 35–40° is pumped through the reflux condenser, ice water is pumped through the downward condenser, and the receiver is ice-cooled and attached to a trap cooled by Dry Ice. The flask is charged with 380 g. (1.97 moles) of α-allyl-β-bromoethyl ethyl ether
(part D) in 550 ml. of n-butyl alcohol
; then 550 g. (8.4 g. atoms) of zinc dust
and 2 g. of anhydrous zinc chloride
are added. The mixture is stirred vigorously and heated gradually to the point where the pentadiene
distils at a rate of about one drop every 2 seconds. The reflux condenser and column return most of the butyl alcohol
to the flask. The reaction takes 5–6 hours for completion. The distillate is washed with five 100-ml. portions of ice water to remove most of the butyl alcohol
and is then dried overnight with 15 g. of calcium chloride
. The crude dry product is distilled through a 2.5 × 35 cm. Vigreux column to give 97–102 g.
) of colorless 1,4-pentadiene
, b.p. 26–27° /740 mm.
Commercial hydrogen chloride
from a cylinder is dried by passage through a train consisting of a wash bottle of concentrated sulfuric acid
, a 25-cm. calcium chloride tube
, and finally an empty safety trap.
This ether is a lachrymator, hydrolyzes rapidly in the presence of moisture, and resinifies readily at temperatures above 0°. It is advisable to store it in a Dry Ice chest during drying and until the next step is to be run. Hydrolysis at low temperatures appears to be negligible.
Analysis of the crude material for chlorine
gave 31.74% (calcd. 32.69%).
It is necessary to remove the hydrogen chloride
because it promotes decomposition of the dibromoether.
Distillation is required to remove aldehyde, alcohol, and water which would react with the Grignard reagent in the next step. α,β-Dibromoethyl ethyl ether
is also a lachrymator.
Either allylmagnesium bromide
or allylmagnesium chloride
may be used. The former is more conveniently prepared in higher yield and in a more concentrated solution, but allyl chloride
is considerably less expensive than allyl bromide
. The submitters state that the chloride is prepared just as the bromide with the following exceptions: the temperature is maintained between −10 and −15° with a Dry Ice-acetone cooling bath; 76.5 g. (82 ml., 1 mole) of allyl chloride
) dissolved in an equal volume of dry ether
is used (the amounts of all other reagents are unaltered); the addition is carried out over a 12-hour period, then the cooling bath is removed, and the mixture (containing considerable solid) is stirred until it reaches room temperature, during which time most of the solid material dissolves. The yield of allylmagnesium chloride
as determined by acidimetric titration9
is 0.67–0.69 mole
Method I is based on the work of Schniepp and Geller4
and of Paul and Tchelitcheff,5
while Method II is essentially that of Shoemaker and Boord12
with some modifications.13
This preparation is referenced from:
Copyright © 1921-, Organic Syntheses, Inc. All Rights Reserved