About a new preparation of 1,2-dimethyl-3-phenyl-ethylenimine
by
R. HaberlMonatsheft 89, 814-816 (1958)
(
https://www.thevespiary.org/rhodium/Rhodium/pdf/aziridine2meth.pdf)
(-)-1,2-Dimethyl-3-phenyl-ethylenimin (
I) was identified as the by-product of the preparation of (+)-2-phenyl-3,4-dimethylmorpholine by dehydration with concentrated H
2SO
4 of (-)-N,ß-hydroxyethylephedrin. On hydrogenation as well on treatment with HCl
I undergoes ring opening to (+)-1-phenyl-2-methylamino-propan resp. (+)-psi-1-phenyl-1-chlor-2-methylamino-propan.
The prepration of (+)-2-phenyl-3,4-dimethyl-morpholin from (-)-N-ß-hydroxyethyl-ephedrin via ring closure with concentrated H
2O
4 according to
W. Otto1 can be shown with the following reaction scheme.
Molecule:
1 ("c1(ccccc1)C(C(C)N(C)CCO)O>>C1COC(C(N1C)C)c2ccccc2")
There is always as a by-product in varying, but always in little yields, a colourless liquid with a b.p.
12 85° and a specific rotation of [alpha]
18D = -131,7° (alcohol). From the values of the microanalysis and the volatility of the substance there follows the total formula: C
10H
13N.
The hydrogenation of the compound which already proceeds at room temperature very fast under consumption of an equimolar amount of hydrogen yields an optically active base which hydrochlorid was identified as (+)-1-phenyl-2-methylamino-propan · HCl [(+)-desoxyephedrin · HCl] because the mixed melting point of a (+)-desoxyephedrin · HCl prepared according to
H. Emde2 showed no depression and the specific optical rotation of both compounds matched.
On treatment of the by-product in absolute alcohol with absolute alcholic HCl at room temperature until weakly acidic pH a compound was created. The microanalysis gave the the total formula C
10H
15Cl
2N. The product is (+)-psi-1-phenyl-1-chloro-2-methylamino-propan · HCl which is identical with a compound prepared by
K. Tanaka3 by chlorination of l-ephedrin with PCl
3 which was shown by mixed meltingpoint and comparison of the specific optical rotation.
By the above experimental results it was shown that the by-product has the structure of 1,2-dimethyl-3-phenyl-ethylenimine (
I).
Molecule:
2 ("c1(ccccc1)C2C(C)N2C")
The isomeric phenylpropan with a double bond of
I which would behave similiar on hydrogenation and HCl-addition can be excluded as it would be optically inactive.
Compound
I was, according to my knowledge, described first by
K. Tanaka3 who got it by treatment of (+)-psi-1-phenyl-1-chloro-2-methylamino-propan with alkali as a colourless liquid with a b.p.
8 72° and specific rotation [alpha]
18D = -127° (alcohol). The structure assumed by
K. Tanaka has been confirmed by this work.
[personal blabla]
Experimental part1,2-dimethyl-3-phenyl-ethylenimine (I)When preparing (+)-2-phenyl-3,4-dimethylmorpholine according to
W. Otto1 I can be isolated as a lower boiling fraction when distilling the etheral extracts. B.p.
12 85°, [alpha]
18D = 131,7° (alcohol).
[details of the microanalysis]
Hydrogenation of I to (+)-1-phenyl-2-methylamino-propan20,0 g
I were dissolved in 75 ml alcohol and 0,3 10% Pd/animal charcoal and hydrogenated in a 250 ml Schüttelente [literally: shaker duck, probably a kind of shaken hydrogenation device]. The H
2-uptake is very fast at the beginning (2 l in 30 min) and is completed after about 4 hours. H
2-consumption: 3110 ml (0°, 760 torr). After filtration of the catalyst vacuum distillation gave 17,9 (+)-1-phenyl-2-methylamino-propan, 88,8% of theory, b.p.
12 84°.
(+)-psi-1-Phenyl-1-chloro-2-methylamino-propan · HCl from I10,0 g
I were dissolved in few absolute alcohol and treated with absolute alcoholic HCl until weakly acidic pH at room temperature. The reaction mixtures was cooled for a few hours with ice and then the formed crystalls were filtered. Yield: 9,5 g, 76% of theory, m.p. 202° (from alcohol), [alpha]
18D = 115,2 (water).
[details of the microanalysis]
1. W. G. Otto, Angew. Chem. 68, 181, (1956)
2. H. Emde, Helv. Chim. Acta 12, 365 (1929)
3. K. Tanaka, J. Pharm. Soc. Japan 79, 212 (1950)