Organic Syntheses, CV 3, 141
[I. ACETIC ANHYDRIDE METHOD]
Submitted by Robert H. Baker and Frederick G. Bordwell.
Checked by R. L. Shriner and Fred W. Neumann.
1. Procedure
In a
1-l. flask equipped with a reflux condenser and drying tube are placed
200 ml. (2.1 moles) of tert-butyl alcohol (Note
1),
200 ml. (2.1 moles) of acetic anhydride, and
0.5 g. of anhydrous zinc chloride. After thorough shaking, the mixture is slowly heated to reflux temperature, maintained at gentle refluxing for 2 hours, and then cooled. The
reflux condenser is replaced by a
20-cm. Vigreux column through which the mixture is distilled up to a temperature of 110°. The crude distillate, weighing
200–250 g., is washed with two 50-ml. portions of water, then with
50-ml. portions of 10% potassium carbonate until the ester layer is neutral to litmus; the product is finally dried over anhydrous
potassium carbonate (about 20 g.).
After removal of the drying agent, the ester is fractionally distilled through an
efficient fractionating column (Note
2). A fore-run of
21–37 g. is collected up to a temperature of 95°. The pure ester distils between
95° and 96° and amounts to
129–148 g. (
53–60%) (Note
3).
2. Notes
1.
Eastman Kodak Company's best grade of tert-butyl alcohol and the practical grade of
acetic anhydride are satisfactory. If these are not available, the alcohol should be dried over quicklime and distilled, and the
acetic anhydride should be redistilled also.
2. The
fractionating column may be a 16-plate Stedman column or a 30-cm. Carborundum-packed column.
3. The corrected boiling point of the ester is given as
97.9°.
1
[II. ACETYL CHLORIDE METHOD]
Submitted by C. R. Hauser, B. E. Hudson, B. Abramovitch, and J. C. Shivers.
Checked by R. L. Shriner and Fred W. Neumann.
1. Procedure
In a
2-l. flask equipped with a reflux condenser, mercury-sealed stirrer, and a dropping funnel are placed
147 ml. (114 g., 1.5 moles) of tert-butyl alcohol (Note
1),
212 ml. (202 g., 1.67 moles) of dimethylaniline, and
200 ml. of dry ether. The solution is heated to refluxing, and
113 ml. (124 g., 1.58 moles) of acetyl chloride is run into the stirred solution at such a rate that moderate refluxing continues after the source of heat is removed. When approximately two-thirds of the
acetyl chloride has been added,
dimethylaniline hydrochloride begins to crystallize and the mixture refluxes very vigorously. An
ice bath is applied immediately, and, after refluxing ceases, the remainder of the
acetyl chloride is added. Finally, the mixture is heated for 1 hour on a
water bath. The mixture is cooled to room temperature, approximately 200 ml. of water is added, and stirring is continued until all the solid material dissolves. The
ether layer is separated and extracted with
50-ml. portions of cold 10% sulfuric acid until the extract does not become cloudy when made alkaline with
sodium hydroxide. After a final washing with
25 ml. of saturated sodium bicarbonate solution, the
ether solution is dried by shaking it with
10 g. of anhydrous sodium sulfate. The solution is decanted and allowed to stand over
10 g. of Drierite overnight. The solution is filtered, and the
ether is removed by distillation through a
good fractionating column (Note
2). The residue is fractionally distilled, and
110–119 g. (
63–68%) of
tert-butyl acetate boiling at
95–98° is obtained (Note
2). Most of the ester boils at
97.0–97.5° (Note
3).
2. Notes
2. Either a
30-cm. Carborundum-packed column or a
30-cm. Widmer column may be used. The pure ester was collected over a range of 94.5–95.5°.
3. The submitters report that the following
tert-butyl esters have been prepared in a similar manner. Eastman Kodak Company chemicals were used.
(
e)
tert-Butyl chloroacetate (submitted by Robert H. Baker).
Thirty-five and four-tenths milliliters (0.4 mole) of tert-butyl alcohol was added over a period of 10 minutes to a mixture of
30.6 ml. (0.4 mole) of chloroacetyl chloride and
50 ml. (0.4 mole) of dimethylaniline, care being taken to keep the temperature below 30°. After standing 45 minutes at room temperature, the mixture was poured into water and worked up in the usual way. The ester was fractionated in a
6-in. Widmer column. The yield was
38 g. (
63%) of ester which boiled at
48–49°/11 mm.;
nD20 1.4259–1.4260.
[III. ACETYL CHLORIDE-MAGNESIUM METHOD]
Submitted by A. Spassow
Checked by W. E. Bachmann and J. Korman.
1. Procedure
In a
1-l. round-bottomed flask are placed
12 g. (0.5 gram atom) of magnesium powder,
37 g. (0.5 mole) of tert-butyl alcohol, and
100 g. of anhydrous ether (Note
1). The flask is fitted with an
addition tube, one arm of which bears a reflux condenser and the other arm a dropping funnel. While the mixture is being shaken by hand, a solution of
55 g. (0.7 mole) of acetyl chloride (Note
2) in
50 g. of anhydrous ether is added dropwise (Note
3). A lively reaction gradually ensues with evolution of
hydrogen, mixed with
ether vapor and a little
hydrogen chloride (Note
4). After all the
acetyl chloride has been added, the reaction mixture is allowed to stand in a pan of cold water for 1 hour (Note
5). After another hour at room temperature the mixture is warmed in a water bath at 40–45° for 30 minutes in order to complete the reaction.
The solid reaction product is cooled in ice water and decomposed by addition of an ice-cold solution of
20 g. of potassium carbonate in 250 ml. of water, cooling being continued throughout (Note
6). The mixture is extracted three times with
35-ml. portions of ether; the
ether extract is dried over
calcium chloride and then distilled (Note
7). The ester is obtained from the fraction boiling at
85–98° by fractional distillation by means of a
good column (Note
8). The purified ester boils at
95–97°/740 mm. and weighs
37–45 g. (
45–55%).
2. Notes
3. The addition of the
acetyl chloride requires about 15 minutes. After the addition of about two-thirds of the acid chloride, the reaction mixture rapidly becomes semisolid.
4. The course of the esterification is best followed by the evolution of the
hydrogen, the
hydrogen being led by means of a tube from the top of the condenser through a
wash bottle containing a small amount of water. A moderate rate of reaction is obtained throughout by judicious immersion of the reaction flask in a pan of cold water.
5. After 30 minutes the reaction becomes more lively and the mixture more fluid.
7. Since the ester is quite volatile, the
ether is distilled through a
60-cm. Vigreux column. The distillation is interrupted at 40°, and a
40-cm. column is employed. A fraction boiling up to
85° and one boiling from
85° to 98° are collected. The first fraction, which contains considerable amounts of the ester, is redistilled, and the portion boiling above 85° is added to the second fraction. The fraction boiling from
85° to 98° weighs
43–48 g.
8. A
40-cm. Vigreux or Widmer column is used for this distillation. The fore-run is redistilled from the same flask.
3. Discussion
This preparation is referenced from:
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