Organic Syntheses, CV 5, 35
Submitted by Peter Kovacic and Sohan S. Chaudhary
1.
Checked by R. A. Haggard and William D. Emmons.
1. Procedure
Caution! The reactions should be carried out in a
hood behind a protective screen since
trichloramine is noxious and potentially explosive; however, no difficulties from decomposition have been encountered under the conditions described.
A.
Trichloramine. A mixture of 600 ml. of water (Note
2),
900 ml. of methylene chloride (Note
3), and
270 g. (1.32 moles) of calcium hypochlorite (Note
4) is cooled to 0–10° in a
3-l., three-necked, vented flask equipped with a stirrer, a
thermometer, and a
dropping funnel. A solution of
66.0 g. (1.23 moles) of ammonium chloride in 150 ml. of concentrated hydrochloric acid and 450 ml. of water is added dropwise with stirring over a 1-hour period at 0–10°. After an additional 20 minutes of stirring, the organic layer is separated, washed with three 200-ml. portions of cold water, and dried over anhydrous
sodium sulfate. The yellow solution is filtered, and the
trichloramine concentration is determined by iodometric titration (Note
5).
B.
1-Amino-1-methylcyclohexane. A 3-l. three-necked flask is fitted with a
paddle stirrer, a
condenser, a thermometer, and a dropping funnel with an extension for below-surface addition. Provision is made for introduction of
nitrogen by use of a
side-arm adapter. The vessel is charged with
196 g. (2.0 moles) of methylcyclohexane (Note
6) and
106 g. (0.80 mole) of anhydrous aluminum chloride. A solution
(ca. 600 ml.) of trichloramine (0.40 mole) in methylene chloride is added with efficient stirring over a period of 2 hours at −5° to 5° (Note
7). Throughout the reaction a stream of
nitrogen is passed through the flask (Note
8). The brown mixture is stirred for an additional 20–30 minutes at the same temperature.
The reaction mixture is then added with good stirring to a slurry of 800–900 g. of ice and
50 ml. of concentrated hydrochloric acid (Note
9). The layers are separated, and the dark organic layer is washed with three
100-ml. portions of 5% hydrochloric acid and discarded. Traces of non-basic organic material are removed from the combined aqueous layer and washings by extraction with pure
ether (Note
10) until the extract is colorless. The aqueous solution is treated with
600 ml. of 50% aqueous sodium hydroxide (Note
11) with cooling, and the basic organic product is extracted with three
125-ml. portions of pure ether (Note
10). The ethereal solution is dried over
sodium sulfate, and the solvent is distilled on the
steam bath to give
42–46 g. of a clear, amber product (Note
12). To this crude product is added
10 g. of triethylenetetramine (Note
13). Distillation through a
small Vigreux column yields
21.5–30 g. (
48–67%, based on
trichloramine) of
1-amino-1-methylcyclohexane, b.p.
44–49° (20–25 mm.),
n22D 1.4516 (Note
14).
2. Notes
1. The stoichiometry of the reaction is not known.
2. Deionized water is used throughout.
5. Iodometric determination of positive
chlorine is carried out as follows:
2.0 g. of potassium iodide or sodium iodide is dissolved in 10 ml. of water, and
40 ml. of glacial acetic acid is added. Into this solution is pipetted
1.0 ml. of the methylene chloride solution of
trichloramine. The liberated
iodine is titrated with
0.100N sodium thiosulfate. The solution is found to be 0.6–0.7
M in
trichloramine. Storage for several days at 0–5° results in negligible decomposition, although it is not recommended unless adequate safety precautions are observed. Excess
methylene chloride-trichloramine solution can be conveniently disposed of by its slow addition to a cold, stirred, dilute aqueous solution of
sodium metabisulfite.
6. A
pure grade of methylcyclohexane (Eastman Organic Chemicals) is used. Subsequent to the checking of this preparation, the submitters reported
69–72% yields with
78.4 g. (0.80 mole) of methylcyclohexane.
2 In this case a
1-l. three-necked flask is employed for the reaction; the remainder of the procedure is unchanged.
7. Cooling is accomplished with either an
ice-salt bath or preferably a
dry ice-acetone bath. The time of addition can be reduced to 1 hour by use of the latter. However, if the temperature is much below that designated, unchanged
trichloramine accumulates, resulting eventually in an uncontrollable reaction.
8. Purging with
nitrogen results in some increase in yield. If the flow is too vigorous,
trichloramine is lost by volatilization.
9. The mixture can be stored overnight at this stage.
10. High-purity
ether (
e.g., Baker Analyzed Reagent) is used since a grade of lower quality gives a product that is more difficult to purify because of contamination with alcohol.
11. Excess
sodium hydroxide is needed to dissolve the aluminum-containing precipitate.
12. The last portion of solvent is carefully removed at the
water aspirator.
13.
Triethylenetetramine (redistilled, Eastman Organic Chemicals) prevents bumping and foaming and acts as a chaser for the distillation.
14. The product contains less than 10% of lower-boiling impurities determined (by the checkers) by vapor-phase chromatography with a column packed with 15% XF-1150 on Chromosorb W. Further purification can be effected readily with good recovery by drying over
sodium hydroxide pellets and fractionating at atmospheric pressure through an
efficient spinning band column, with collection of the fraction, b.p.
142–146°,
n22D 1.4522.
3. Discussion
4. Merits of the Preparation
This procedure constitutes the first example of one-step conversion of a
t-alkane to the corresponding
t-alkylamine. Other hydrocarbons in this class, such as
isobutane, have also been aminated with good results.
7 Only a very limited number of convenient routes,
e.g., the Ritter reaction, are available for the preparation of
t-carbinamines. The present preparation illustrates a simple method that utilizes a novel substrate.
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