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Org. Synth. 1964, 44, 72
DOI: 10.15227/orgsyn.044.0072
N-METHYLBUTYLAMINE
[Butylamine, N-methyl-]
Submitted by John J. Lucier, Arlo D. Harris, and Philip S. Korosec1.
Checked by Max Tishler and M. Bennett.
1. Procedure
A 1-l. round-bottomed flask fitted with a reflux condenser bearing a soda-lime drying tube is successively charged with 100ml. of anhydrous benzene, 36.6 g. (0.50 mole) of n-butylamine, and 63.7 g. (61 ml., 0.60 mole) of benzaldehyde (Note 1). The mixture is heated under reflux for 30 minutes (Note 2). The condenser is replaced by a Claisen distillation head, and the mixture is distilled until the temperature reaches 100° (Note 3). The residue, which is mostly N-benzylidenebutylamine, is cooled, and the distillation head is replaced by the reflux condenser bearing a soda-lime drying tube.
A solution of 75.6 g. (57 ml., 0.60 mole) of dimethyl sulfate (Toxic! (Note 4)) in 200 ml. of anhydrous benzene is added through the condenser with intermittent swirling (Note 2). The mixture is then heated gently. After a short period (about 10 minutes) the reaction becomes mildly vigorous, and the heating is stopped (Note 5). The ebullition subsides after about 10 minutes. The mixture is heated under reflux for 30 minutes. It is then steam-distilled until the distillate becomes clear; about 500 ml. of distillate is collected (Note 6). The residue is cooled in an ice bath, and 60 g. (1.5 moles) of sodium hydroxide is added with continuous swirling. The layers are separated, and the amine layer is dried for several hours over 5 g. of sodium hydroxide. The amine layer is separated, dried over a second 5-g. portion of sodium hydroxide (Note 7), and distilled from a 50-ml. Claisen flask containing 2 g. of sodium hydroxide. N-Methylbutylamine is collected at 86–90° (745 mm.); weight 19.6–23.0 g. (45–53%); n20D 1.4010–1.4020. The product contains 3–5% of impurity according to vapor-phase chromatographic analysis.
2. Notes
1. The benzaldehyde and n-butylamine were obtained from the Eastman Kodak Company (white label grade). The benzaldehyde was used without further purification. The n-butylamine was redistilled before use.
The checkers dried benzene over sodium-lead alloy (dri-Na, Baker). Its water content was less than 0.1 mg. per ml. by Karl Fischer titration.
2. The checkers stirred the mixture with a magnetic stirrer.
3. This distillation is carried out to remove the water formed by the first reaction. No more water comes over after the temperature reaches 100°. Toward the end of distillation, slight bumping may occur.
4. The dimethyl sulfate was purchased from Matheson, Coleman and Bell and was used without further purification. Both the liquid and the vapors of dimethyl sulfate are toxic, and the compound must be handled with care.
5. An ice bath should be kept ready to restrain the reaction if necessary.
6. In a simpler alternative to steam distillation, 200 ml. of water is added to the benzene solution, and the mixture is vigorously stirred under gentle reflux for 20 minutes. The mixture is cooled to room temperature. The aqueous layer is separated, extracted with 100 ml. of ether to remove traces of benzaldehyde, and then treated with 60 g. of sodium hydroxide as in the present procedure.2
7. If a larger portion of sodium hydroxide is used, a semisolid mass is formed from which the product can be separated only with difficulty.
3. Discussion
Unsymmetrical secondary aliphatic amines have been prepared by reaction of alkyl halides with benzylidene amines and subsequent hydrolysis;3,4 by reaction of alkyl halides with alkyl amines;5 by reduction of amine-aldehyde adducts;6,7,8 and by dealkylation of tertiary amines with dibenzoyl peroxide.9
In the present procedure, the method of Decker and Becker3 has been modified by substitution of a dialkyl sulfate for the corresponding alkyl halide.
4. Merits of the Preparation
The procedure is a general one for the preparation of unsymmetrical aliphatic amines, for the submitters have used it to obtain good yields of N-methylpentylamine, N-methylhexylamine, N-methylheptylamine, N-ethylbutylamine, N-ethylpentylamine, and N-ethylheptylamine.
Compared to the procedure of Decker and Becker3 and that of Wawzonek, McKillip, and Peterson in this volume,4 the present procedure has the advantages of being simpler and using cheaper alkylating agents. It tends to give lower yields and less pure products than the procedure of Wawzonek, McKillip, and Peterson.
This preparation is referenced from:

References and Notes
  1. Department of Chemistry, University of Dayton, Dayton, Ohio. This work was supported by Wright Air Development Division of the United States Air Force, Air Research and Development Command, under Contract No. AF 35(616)-6607.
  2. C. L. Dickinson (E. I. du Pont de Nemours and Co.), private communication.
  3. H. Decker and P. Becker, Ann., 395, 362 (1913).
  4. S. Wawzonek, W. McKillip, and C. J. Peterson, this volume, p. 758.
  5. O. Westphal and D. Jerchel, Ber., 73B, 1002 (1940).
  6. H. Henze and D. Humphreys, J. Am. Chem. Soc., 64, 2878 (1942).
  7. K. Campbell, A. Sommers, and B. Campbell, J. Am. Chem. Soc., 66, 82 (1944).
  8. W. S. Emerson, Org. Reactions, 4, 174 (1948).
  9. L. Horner and W. Kirmse, Ann., 597, 48 (1955).

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

Benzene (71-43-2)

ether (60-29-7)

sodium hydroxide (1310-73-2)

dimethyl sulfate (77-78-1)

benzaldehyde (100-52-7)

n-butylamine (109-73-9)

dibenzoyl peroxide (94-36-0)

sodium-lead

N-Methylbutylamine,
Butylamine, N-methyl- (110-68-9)

N-benzylidenebutylamine

amine-aldehyde (14332-28-6)

N-methylpentylamine (25419-06-1)

N-methylhexylamine (35161-70-7)

N-methylheptylamine (36343-05-2)

N-ethylbutylamine (13360-63-9)

N-ethylpentylamine

N-ethylheptylamine