A solution of
21.4 g. (0.262 mole) of dimethylamine hydrochloride in 150 ml. of methanol is prepared in a
500-ml., round-bottomed flask.
Potassium hydroxide (4 g.) is added in one portion to the magnetically stirred solution (Note
1). When the pellets are completely dissolved,
19.6 g. (0.200 mole) of cyclohexanone is added in one portion. The resulting suspension is stirred at room temperature for 15 minutes before a solution of
4.75 g. (0.0754 mole) of sodium cyanoborohydride (Note
2) and (Note
3) in
50 ml. of methanol is added dropwise over 30 minutes to the stirred suspension. After the addition is complete, the suspension is stirred for 30 minutes.
Potassium hydroxide (15 g.) is then added, and stirring is continued until the pellets are completely dissolved. The reaction mixture is filtered with suction, and the volume of the filtrate is reduced to approximately 50 ml. with a
rotary evaporator while the bath temperature is kept below 45° (Note
4) and (Note
5). To this concentrate is added 10 ml. of water and
25 ml. of saturated aqueous sodium chloride, and the layers are separated. The aqueous layer is extracted with two
50-ml. portions of diethyl ether. The organic layer previously separated and the ethereal extracts are combined and extracted with three
20-ml. portions of 6 M hydrochloric acid (Note
6). The combined acid layers are saturated with
sodium chloride and extracted with four
30-ml. portions of ether (Note
7). The aqueous solution is cooled to 0° in an
ice bath and brought to pH > 12 by addition of
potassium hydroxide pellets to the stirred solution (Note
8) and (Note
9). The layers are separated, and the aqueous layer is extracted with two
40-ml. portions of ether. The combined organic layers are washed with
10 ml. of saturated aqueous sodium chloride, dried over anhydrous
potassium carbonate, and freed of
ether with a rotary evaporator (Note
4). This crude product is fractionated through a
15-cm. Vigreux column (Note
10). After
1–3 g. of a forerun, b.p.
144–155° (Note
11) is separated, the fraction boiling at
156–159° is collected, yielding
13.3–13.7 g. (
52–54%) of
N,N-dimethylcyclohexylamine,
n25D 1.4521 (Note
12).