A Process for the Electrolytic Reduction of Nitro-benzol, Nitro- anisol, Nitro-aniline and their Homologues to Azo and Hydrazo- compounds.
Year: 1898

page_text: Date of Application, 4th June, 1898
Complete Specification Left, 4th Mar., 1899-Accepted, 29th Apr., 1899
A Process for the Electrolytic Reduction of Nitro-benzol, Nitro-
anisol, Nitro-aniline and their Homologues to Azo and Hydrazo-
compounds.
We, Professor Dr. KARL ELES, of 1, Bergstrasse, Giessen, and ABRAHAM Wulfing,
of 1, Kurzestrasse, Elberfeld, Merchant, both in the Empire of Germany, do hereby
declare the nature of this invention to be as follows:-
This invention relates to a process for the electrolytic reduction of nitro-benzol'
nitro-anisol, nitro-aniline and their homologues to azo-compounds and hydrazo
compounds.
Nitro-benzol and some of its homologues, as also o-nitro-anisol, have already been
reduced to azo-compounds and hydrazo-compounds electrolytically; to this end the
cathode liquid has always been made strongly alkaline from the commencement of
the process by caustic alkali or caustic soda. The strongly alkaline liquid has a
prejudicial effect upon the durability of the diaphragms, 18 favourable to the pro-
duction of resinous impurities and furthermore has the disadvantage that it consider-
ably reduces the power which alcohol and sumilar suitable solvents have of dissolving
nitro-compounds.
Now, according to this invention we obviate these disadvantages by dispensing with
the addition of alkali and by rendering the solution of the nitro-compound serving as
the cathode liquid electrically conducting by a neutral alkaline salt of an organic acid,
for instance, by means of sodium acetate.
For the anode liquid, in those cases in which it is necessary to separate the electro-
lyte into cathode and anode fluids, any alkaline salts can be employed, the anions of
which do not produce any disturbing products, for example, an aqueous solution of
sodium sulphate or sodium carbonate. The cathodes consist of plates or wire net-work
of iron or nickel. Under the described circumstances the reaction takes place very
smoothly under heat and in such a manner that the reduction of the nitro-compound
to the azo-compound is effected much more energetically than the further reduction
to the hydrazo-compound. This fact enables the manufacture of the azo-compounds
to be effected without difficulty as intermediate products and also enables the whole
reduction process to be carried out more quickly, as the quantity of electricity
necessary for the reduction to the azo-compound can be passed without any loss of
ourrent at a current density many times greater than can be employed for the trans-
formation into the hydrazo-compound. The conversion of a nitro-compound into
a corresponding azo-compound takes from 20 to 30 minutes and the succeeding
tranformation into the hydrazo-compound only another 20 to 30 minutes.
At the close of the process the products, if necessary after distilling off a portion of
the solvent, crystallise nearly completely out; the hydrazo-compounds are then
suitable for transformation into benzidines without any other preparation.
As the solvent for the nitro-compounds we can employ, besides ethylalcohol, other
fatty alcohols such, for example, as methylalcohol, and fatty ketones such as acetone,
as also mixtures of these substances,

page_text: A Process for the Electrolytic Reduction of Nitro-benzol, Nitro-
anisol, Nitro-aniline and their Homologues to Azo and Hydrazo-
compounds.
We, PROFESSOR Dr. KARL EL.BS, of 1, Bergstrasse. Giessen, and ABRAHAM WULFING,
of 1, Korzentrasse, Elberfeld, Merchant, both in the Empire of Germany, do hereby
declare the nature of this invention and in what manner the saine is to be performed,
to be particularly described and ascertained in and by the following statement :-
This invention relates to a process for the electrolytic reduction of nitro-benzol,
nitro-anisol, nitro-aniline and their homologues to azo-compounds and hydrazo-
compounds.
Nitro-benzol and some of its homologues, as also o-nitro-anisol, have already been
reduced to azo-compounds and hydrazo-compounds electrolytically; to this end the
cathode liquid has always been made strongly alkaline from the commencement of
the process by caustic alkalı or caustic soda The strongly alkaline liquid has a
prejudicial effect upon the durability of the diaphragms, is favourable to the production
of resinous impurities and furthermore has the disadvantage that it considerably
reduces the power which alcohol and similar suitable solvents have of dissolving
nitro-compounds.
Now, according to this invention we obviate these disadvantages by dispensing
with the addition of alkali and by rendering the solution of the nitro-compound
serving as the cathode liquid electrically conducting by a neutral alkalme salt of an
organic acid, for instance, by means of sodium acetate.
For the anode liquid, in these cases in which it is necessary to separate the
electrolyte into cathode and anode fluids, any alkaline salts can be employed, the
anions of which do not produce any disturbing products, for example, an aqueous
solution of sodium sulphate or sodium carbonate The cathodes consist of plates or
wire net-work of iron or nickel. Under the descubed circumstances the reaction
takes place very smoothly under heat and in such a manner that the reduction of the
uitro-compound to the azo-compound is effected much more energetically than the
further reduction to the hydrazo-compound This fact enables the manufacture of
the azo-compounds to be effected without difficulty as intermediate products and also
enables the whole reduction process to be carried out more quickly, as the quantity of
electricity necessary for the reduction to the azo-compound can be passed without any
loss of current at a current density many times greater than can be employed for the
transformation into the hydrazo-compound. The conversion of a nitro-compound into
a corresponding azo-compound takes from 20 to 30 minutes and the succeeding
transformation into the hydrazo-compound only another 20 to 30 minutes.
At the close of the process the products, if necessary after distilling off a portion of
the solvent, crystallise nearly completely out; the hydrazo-compounds are then
suitable for transforination into benzidines without any other preparation.
As the solvent for the nitro-compounds we can employ, besides ethylalcohol, other
fatty alcohols, such, for example as methylalcohol, and fatty ketones such as acetone,
as also mixtures of these substances.

page_text: cathode chamber and at boiling temperature first subjected to 780 ampère-hours with
a current-density of from 1000-1600 A per square metre (reduction to o-azotoluol),
and then to 200-210 ampère-hours with a current density decreasing from 200 to
100 A per square metre. A portion of the alcohol is then distilled off and the cathode
liquid allowed to cool, whereby nearly pure o-hydrazotoluol crystallizes out in quantity 5
about 85% of the theoretical yield. If the reduction be interrupted after the
780 ampère-hours 90% of the calculated quantity of o-azotoluol is obtamed.
1 kilogramme of m-nitroaniline and kilogramme of sodium acetate are dissolved
in 8 kilogrammes of 50-60% alcohol and this solution is then treated in the cathode
chamber first with 770 ampère-hours with a current density of from 1000-2000 A per
square metre (transformation into m-di-amidoazobenzol) then to a further 200-220
ampère hours at a current density of 200 A-100 A per square metre (transformation
into m-di-amidohydrazobenzol). If it is desired to obtain m-di-amidoazobenzol the
cathode liquid is allowed to cool after the 770 ampère-hours, whereby about 90% of
the calculated quantity of the azo-compound crystallizes out in the form of orange
coloured needles. In the preparation of m-di-amidohydrazobenzul, on passing further
current the hydrazo-compound, which is only very slightly soluble, is nearly all
separated out as a sandy crystal powder
The hitherto unknown hydrazoaniline (m-di-amidohydrazobenzol) is a white powder
consisting of microscopic and highly light-refracting pyramids; it fuses at 150° C.
and is with difficulty soluble in alcohol and practically not at all in water and ether.
With hydrochloric acid it is easily converted into m-di-amidobenzidine, which 18
identical with the product described by Tauber (Berichte dei deutschen chem. Ges.
23,797) and obtained from di-nitrobenzidine.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim 18:-
The described process for the electrolytic reduction of aromatic nitro-hydrocarbons,
nitrophenolethers and nitroamines, wholly or partially dissolved in aqueous alcohols or
ketones, to azo-compounds and hydraso-compounds, wherein the cathode liquid is
rendered electrically conducting by suitable alkaline salts of organic acids and-wherei

page_text: the current density during the reduction to aso-compounds is many times greater
than during the further reduction to hydrazo-compounds, substantially as herein-
before described.
G. F REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicants.