A New Process for the Production of Indigo.
Year: 1898

page_text: [Communicated from abroad by THE FARBENFABRIKEN,
BAYER & Co., of Elberfeld, Germany.]
vormals FRIEDRICH
A New Process for the Production of Indigo.
I, HENRY EDWARD NEWTON, of the Office for Patents, 6, Bream's Buildings,
Chancery Lane, in the County of London, Patent Agent, do hereby declare the
nature of this invention to be as follows:-
Manthner and Suida (see Wiener Monatshefte, volume 9, page 732) have
described that an acid ester is produced by the action of alcohol and hydro-
chloric acid on phenylglycine-orthocarbonic acid.
In contradistinction therewith, my foreign correspondents have now found that
the neutral esters of phenylglycine orthocarbonic acid can also be obtained by
a prolonged action of alcohols in the presence of dehydrating agents, such as
hydrochloric acid, concentrated sulphuric acid, or the like, on phenylglycine ortho-
carbonic acid. More profitably, the acetylphenylglycine orthocarbonic acid which
results from the oxidation of acetylorthotolylglycine is used as starting material
in this process.
The production of the said neutral esters is illustrated by the following example.
The parts are by weight.
1 part of phenylglycine orthocarbonic acid, or, more profitably, acetylphenylgly-
cine or orthocarbonic acid, is mixed with three parts of absolute alcohol, and the
resulting mixture, which is kept cool, is saturated with gaseous hydrochloric acid.
After standing for about 12 hours, the mass in heated by means of a water-bath,
The oily residue soon
and subsequently the alcohol in excess is distilled over.
solidifies, and becomes crystalline. If necessary, the mass is finally treated with a
sodium carbonate solution, diluted soda-lye or the like, in order to remove any
acid ester contained therein. The neutral diethyl ester which remains undissolved,
forms colorless crystals, which dissolve very readily in alcohol, ether, benzene,
and chloroform, whilst they are soluble with less readiness in ligroin. From an
ethereal solution, the neutral ester separates after some time in beautiful glass-
like crystals, if ligroin is added.
The process proceeds in a similar manner if, in place of ethyl alcohol prescribed
in the above example, other alcohols are used, the corresponding neutral esters
other de-
of phenylglycine orthocarbonic acid being thus produced. Of course,
hydrating agents, such as concentrated sulphuric acid, can be used, and in place
of phenylglycine orthocarbonic, or acetylphenylglycine orthocarbonic acid, deriva-
tives thereof may be employed with the same result.
According to the researches of my foreign correspondents, the neutral esters
hereinbefore defined are very valuable for the production of indigo, inasmuch as
they are transformed by the action of caustic alkalies, at comparatively low
temperatures, into indigo leuco compounds, which finally yield indigo in the usual
This transformation proceeds with such readiness that the production of
way.

page_text: indigo takes place on heating the above neutral esters with soda lye of 40 degrees
Baumé. More profitably, caustic alkalies free from water are used, as is described
in the following example:
Equal parts, by weight, of the neutral diethylester and dry powdered caustic
potassa are mixed. If this mixture is heated by means of a water-bath, it assumes,
às soon as the ester has melted, a yellow color, and after a few minutes, an
energetic reaction sets in, which is at an end after a short time, alcohol being
evolved. The resulting mass, when cool, is diluted with water. Thus, a yellowish
liquid is obtained, from which a good yield of pure indigo is obtained, if atmos-
pheric air is allowed to pass through the same."
The process proceeds in the same manner, if, in place of the diethyl-ester used
in the last example, other neutral esters of phenylglycine orthocarbonic acid,
or derivatives thereof, are employed.
I, HENRY EDWARD NEWTON, of the Office for Patents, 6, Bream's Buildings,
Chancery Lane, in the County of London, Patent Agent, do hereby declare the
nature of this invention and in what manner the same is to be performed, to be
particularly described and ascertained in and by the following statement:-
Manthner and Suida (see Wiener Monatshefte, volume 9, page 732) have
described how an acid ester is produced by the action of alcohol and hydro-
chloric acid on phenylglycine orthocarbonic acid.
My foreign correspondents have now found that neutral esters of phenylglycine
orthocarbonic acid can be obtained by a prolonged action of alcohol in the
presence of dehydrating agents, such as hydrochloric acid, concentrated sulphurie
acid, or the like, on phenylglycine orthocarbonic acid. The acetylphenylglycine-
orthocarbonic acid which results from the oxidation of acetylorthotolylglycine can
likewise be used as a base or starting point in this process.
The production of the said neutral esters is illustrated by the following example,
The parts are by weight.
1 part of phenylglycineorthocarbonic acid, or acetylphenylglycine orthocar-
bonic acid, is mixed with 3 parts of absolute alcohol, and the resulting mixture,
which is kept cool, is saturated with gaseous hydrochloric acid. After standing
for about 12 hours, the mass is heated by means of a water-bath, and subsequently
the alcohol in excess is distilled over. The oily residue soon solidifies, and
becomes crystalline. If necessary, the mass is finally treated with a sodium car-
bonate solution, or the like, in order to remove any acid ester contained therein.
The neutral diethylester which remains undissolved forms colorless crystals which
dissolve very readily in alcohol, ether, benzene, and chloroform, "whilst they
are soluble with less readiness in ligroin. From an etheric solution, the neutral
ester separates, after some time, in beautiful glass-like crystals, if ligroin is
added.
The process proceeds in a similar manner if, in place of ethyl alcohol prescribed
in the above example, other alcohols are used, the corresponding neutral esters
of phenylglycine orthocarbonic acid being thus produced. Of course, other de-
hydrating agents, such as concentrated sulphuric acid, can be used, and, in place

page_text: of phenylglycine orthocarbonic, or acetylphenylglycine orthocarbonic acid, deriva-
tives thereof can be employed with analogous results.
According to the researches of my foreign correspondents, the neutral esters
hereinbefore defined are very valuable for the production of indigo, inasmuch as
they are transformed by the action of caustic alkalies, at comparatively low
temperatures, into indigo leuco compounds, which finally yield indigo in the usual
way. This transformation proceeds with such readiness that the production of
indigo takes place on heating the above neutral esters with soda-lye of 40 degrees
Baumé.
It is however desirable to use caustic alkalies free from water, as described in
the following example.
Equal parts, by weight, of the neutral diethylester and dry powdered caustic
potash are mixed. If this mixture is heated by means of a water bath, it assumes,
as soon as the ester has melted, a yellow color, and an energetic reaction sets
in, which is at an end after a short time, alcohol being evolved. The resulting
mass, when cool, is diluted with water. Thus, a yellowish liquid is obtained,
from which a good yield of pure indigo is obtained on passing atmospheric air
through the same.
The process proceeds in the same manner if, in place of the diethyl-ester used
in the last example, other neutral esters of phenylglycine orthocarbonic acid,
or derivatives thereof, are employed.
Having now particularly described and ascertained the nature of the said
invention, and in what manner the same is to be performed, as communicated to
me from abroad, I declare that what I claim is:
1. The process for producing neutral esters of phenylglycineorthocarbonic
acid, or derivatives thereof, which process consists in treating the said acids with
alcohols in the presence of dehydrating agents, and isolating the neutral esters
in any suitable manner, substantially as hereinbefore described.
2. The process for producing leuco compounds of indigo or its derivatives,
which process consists in treating the neutral esters obtainable according to the
process claimed in the foregoing Claim 1 with caustic alkalies, substantially as
hereinbefore described.
3. The transformation of the indigo leuco compounds obtainable according to
the process claimed in the preceding Claim 2, into indigo or its derivatives, by
subjecting the said leuco compounds to the action of oxidizing agents, substantially
as hereinbefore described.
4. The process for producing indigo or its derivatives, which process consists in
first treating the neutral esters obtainable according to the process claimed in
the above Claim 1 with caustic alkalies, and, secondly treating the leuco com-
pounds thus obtained with oxidizing agents, substantially as bereinbefore
described.