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THE

CHEMICAL NEWS

AND

JOURNAL OF PHYSICAL SCIENCE.

(WITH WHICH IS INCORPORATED THE "CHEMICAL GAZETTE.")

A Journal of Practical Chemistry

IN ALL ITS APPLICATIONS TO

PHARMACY, ARTS, AND MANUFACTURES.

EDITED BY

WILLIAM CROOKES, F.R.S., &c.

VOLUME XXVII.-1873.

LONDON:

HENRY GILLMAN, BOY COURT, LUDGATE HILL, E.C.
AND SOLD BY ALL BOOKSELLERS.

MDCCLXXIII.

HARVARD COLLEGE LIBRARY
FROM LIBRARY OF
GODERY M. HYAMS
NOVEMBER 9, 1928

LONDON:

PRINTED BY WILLIAM CROOKES, CHEMICAL NEWS OFFICE, BOY COURT, LUDGATE HILL, E.C.

97

THE CHEMICAL NEWS.

VOLUME XXVII.

EDITED BY WILLIAM CROOKES, F.R.S., &c.

No. 684.-FRIDAY, JANUARY 3, 1873.

SYNTHESIS OF AROMATIC MONAMINES BY INTRAMOLECULAR ATOMIC INTERCHANGE.*

By A. W. HOFMANN, M.D., LL.D., F.R.S.

In a paper submitted to the German Chemical Society about a year ago, we proved (Dr. Martius and myselft) that the action of methylic alcohol on aniline chlorhydrate at a high temperature and under pressure, far from yielding exclusively methyl- and dimethylaniline, as has been formerly believed, is capable of causing methylation of the phenyl group, and thus producing quite a series of higher homologues of dimethylaniline.

If we endeavour to gain an insight into the mechanism of this reaction, we are led to assume that in the first instance the chlorhydric acid of the aniline salt gives rise to the formation of methylic chloride, which in its turn induces substitution, first in the ammonia fragment, and ultimately in the phenyl group itself. If, on the other hand, we remember that a tertiary monamine, such as must be formed by the final methylation of the ammonia fragment in aniline when submitted to the action of an alcohol chloride, is invariably converted into ammonium compound, it must appear rather strange that in the process above alluded to only tertiary, and never any quartary bases are observed.

an

Under these circumstances the idea very naturally suggested itself of submitting the behaviour of quartary compounds at a high temperature under pressure to an experimental investigation.

The simplest compound that could be detected for such an inquiry appeared to be trimethylphenylammonium iodide, C6H5.CH3.CH3.CH3NI.

Reserving for a future communication the experimental details of this inquiry, I will limit myself for the present to a brief statement of the principal result obtained.

Leaving secondary reactions out of consideration, the transformation of the trimethylated phenylammonium iodide is represented by the following equations :

Transformation of quartary into tertiary compound. C6H5.CH3.CH3.CH3.NI (C6H4.CH3)CH3.CH3N.HI. Transformation of tertiary into secondary compound. (C6H4 CH3)CH3.CH3.N.HI= =C6H3(CH3(CH3)2] CH3.HN.HI.

Transformation of secondary into primary compound. [C6H3(CH3)2] CH3.HN.HI= [C6H2(CH3)3] HHN.HI. Accordingly trimethylated phenylammonium iodide, when submitted to the action of heat, is transformed in the first place into iodhydrate of dimethylated methylo

A paper read before the Royal Society. ↑ Hofmann and Martius, Bericht, 1871, p. 742.

phenylamine or dimethyl toluidine; this, in a second phase of the reaction, becomes iodhydrate of monomethylated dimethylophenylamine or xylidine, which in its turn is ultimately converted into iodhydrate of trimethylophenylamine, i.e., of cumidine. The essential character of the reaction is thus seen to be an intermolecular change in the position of the methyl groups. According to the duration of the process, there are incorporated in the benzol nucleus, first the methyl group of the alcohol iodide, and then successively the two methylic groups which are stationed in the ammonia fragments. The action of heat on the quartary ammonium compound thus places at our disposal a simple means of rising from the benzol series itself to the toluol-, xylol-, and cumol series, or, generally (for the reaction may probably be utilised in many other cases), of passing from a less carbonated to a more carbonated series of compounds.

In carrying out the researches, the general results of which are sketched in the preceding paragraphs, rather considerable quantities of trimethylated phenylammonium iodide were consumed. This I obtained partly by methylating pure aniline with methyl iodine, partly by starting from commercial dimethylaniline, which was most liberally supplied to me by my friends Dr. D. Martius and Mendelssohn Bartholdy, having been specially purified for this purpose by Mr. G. Krell, by fractional distillation in the laboratory of the factory. This purified material was found to boil between 192° and 200°; and only few rectifications were necessary in order to obtain from it dimethyaniline in a state of perfect purity, identical in every respect with the base prepared distillation. Pure dimethylaniline is a liquid of o'9553 by submitting trimethylated phenylammonium hydrate to V.W., solidifying to a crystalline mass at +0.5°, and boiling at 192°. The boiling-point was repeatedly determined, since it had been erroneously stated by M. Louth* to be 202°. The nature of the compound was ascertained by the analysis of the beautiful platinum-salt 2[C6H5(CH3)2N.HCI].PtC14, crystallising in well-formed tables of considerable solubility.

In the early experiments trimethylated phenylammonium iodide was employed in the pure state, such as is obtained by crystallisation; subsequently, however, it was found to be quite sufficient if I mol. of dimethylaniline was mixed with 1 mol. of methyl iodide, and the compound thus produced at once submitted to the action of heat.

The quartary iodides may be exposed to a temperature of 200 for a considerable time without undergoing any alteration; but when heated for a day to from 220° to 230°, the salt is changed, the whole crystalline compound

Louth, Bill. Soc. Chim. (2) vol. vii., page 448.

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