Improved Process or Method for Effecting the Separation of Isomeric Xylidines from Commercial Xylidine in a Pure State for the Production of Coloring Matters.
Year: 1888

page_text: Date of Application, 9th May, 1888
Complete Specification Left, 14th Jan., 1889
Complete Specification Accepted, 16th Feb., 1889
Improved Process or Method for Effecting the Separation of Isomeric
Xylidines from Commercial Xylidine in a Pure State for the
Production of Coloring Matters.
I LEONARD LIMPACH of 20 St. Mary Road Crumpsall, Manchester, in the County
of Lancaster, Doctor of Philosophy do hereby declare the nature of this invention to
be as follows:-
This invention relates to a certain discovery made by me, viz. that the substance
known to chemists as 1 : 3: 4 (NH,) metaxylidine forms with acetic acid a fine
crystalline salt whilst the other isomeric forms of xylidine without exception give
only non-crystalline salts with this acid.
For example in treating crude xylidine, the commercial product, with a definite
quantity of acetic acid, either in a dilute state or as glacial acetic acid all the
xylidine present in the form known as 1 : 3:4 (N.H,) metaxylidine can be
crystallized out as the ascetic acid salt of the said base and can then be easily
and perfectly separated from other salts of isomeric bases, or from isomeric bases,
present by pressing in any suitable form of press or better in a centrifugal machine
In this way
I obtain the isomeride 1: 3: 4 (N.H.) metaxylidine at once
perfectly pure so that it can be directly used in the production of coloring
matters.
in the usual manner.
I further find, by experiment, that the average content of pure 1: 3:4
(N.H.) metaxylidine in crude commercial xylidine amounts to as a rule between 40
and 50% of the weight of the crude substance and that it is therefore only
necessary for the application of this discovery aforesaid to use so much acetic acid as
is found necessary that is proportional to the quantity of 1: 3: 4 (N.H.) xylidine
present in the commercial product; which proportional quantity can be readily and
accurately experimentally determined on a very small quantity.
As an example of the manner in which my invention can be practically employed
(say) 121 parts commercial xylidine were treated with 30 parts of 100% acetic acid

page_text: (the corresponding quantity of dilute acid may also be used) the crystallisation of the
acetate of the metaxylidine commences shortly after mixing and is completed after 24
hours staying. On pressing away the mother liquors consisting of the uncrystallisable
bases, 85 parts of absolutely pure 1: 3 4 (N.H,) metaxylidine acetate were
obtained.
The mother liquors obtained in the above operation as described contain amongst
others, a valuable base, namely, paraxylidine. This base paraxylidine may now be
separated from the mother liquors as above obtained, by the addition of hydrochloric
acid, in the form of paraxylidine hydrochlorate. For this purpose one molecule of the
mother liquors from the separation of the 1: 3 4 (N.H,) metaxylidine which
consists of xylidines only, is mixed with an equivalent of aqueous hydrochloric acid :
after two or three days standing the salt of paraxylidine with hydrochloric acid
separates out in crystals and may be separated from still liquid substances by pressing
or in a centrifugal machine as a rule from 20 to 25% of the crude commercial
xylidine may be obtained in the form of paraxylidine.
The mother liquors from the separation of the hydrochloric acid salt of para-
xylidine consist for the most part of the isomeric ortho derivatives of xylidine and are
also of technical importance:
By these means I am enabled to effect successively and completely the separation of
the 1 3 4. (N.Hs) metaxylidine, the paraxylidine and leaving the orthoxylidines
in a pure or practically pure condition.
D
:
A
WM. BROOKES & SON,
55 & 56, Chancery Lane, London,
Agents for the Applicant..

page_text: from all the other isomerides in a state of chemical purity.
This invention is based upon my discovery that of all the isomeric varieties of
xylidine the one known as meta xylidine as above designated only forms with acetic.
acid a solid crystalline compound an acetate-which may be easily separated mechani-
cally from all the other varieties, which do not form crystalline compounds with
acetic acid.
My process consists in treating the commercial product, crude xylidine, as usually
obtainable, with a certain quantity of acetic acid. The acetic acid may be as glacial
acid or more or less diluted with water or other diluent. In the case of acetic acid in
a concentrated or dilute with water, state being, employed-a given amount of the
acid is added to the xylidine whereupon the crystalline compound aforenamed is
produced and separated from the other xylidines or if excess of acetic acid has been
employed, from the fluid acetates of the other xylidines, by pressing in any ordinary
filter press or by centrifugal action.
As I find that ordinary commercial xylidine coutains from 40 to 70 per cent. of this
variety meta xylidine 1-3-4 it is not necessary to add more acetic acid than the
calculated quantity and if even less be used the product is still pure meta xylidine
acetate.
The requisite quantity of acetic acid to be employed is ascertained by a preliminary
small experiment or test.
The advantage of using the theoretical quantity of acetic acid consists therein that
the isomeride known as para xylidine

page_text: The
As an example of the working of this my invention I give this small experiment:
121 grammes commercial xylidine treated with 30 grammes pure 100 per cent. acetic
acid, or a corresponding larger amount of a dilute acid will commence to crystallise
in a few minutes and after 24 hours the separation of the meta xylidine
acetate will be found complete. The crystals can be separated by a centri-
fuge from the mother liquors and will consist of absolutely pure meta xylidine
acetate. From this the base may be set free by any known method.
mother liquors separated by the action of the centrifuge consisting of para and
other varieties of xylidine may be treated with sufficient aqueous hydrochloric acid to
combine completely with the bases in the mother liquors and allowed to stand for 3
to 4 days at the end of this time nearly all the para xylidine will be separated
in the form of hydrochloride in crystals and can be in its turn separated from
the residual bases-ortho xylidines-by pressing or centrifugal action.
In this manner about 20 to 25 per cent. of the crude xylidine may be obtained
as para xylidine salt with hydrochloric acid.
The mother liquors again from this para xylidine compound, consisting mainly
of ortho derivatives of xylidine is also a valuable product and may be technically
made use of.
Having now particularly described and ascertained the nature of my said
Invention, and in what manner the same is to be performed, I declare that what
1 claim is:
The application of the described method of utilizing the crystallisation of the
acetate of meta xylidine for the easy and cheap technical separation and extraction
of pure meta xylidine and paraxylidine from the commercial product, that is to
say the application of acetic acid, as aforesaid, to crude xylidines for the formation
and separation of pure meta xylidine acetate and the soparation in consequence of
that action of pure para xylidine from the mother liquors by means of hydro-
chloric or other acid, this again leaving more or less pure ortho xylidines of
technical use and value.
Dated the 12th day of January 1980