Improvements in the Manufacture of Hydrazo Compounds from Aromatic Nitro Hydrocarbons.
Year: 1894

page_text: Date of Application, 8th Sept., 1894
Complete Specification Left 6th Juge 1895 Accented 6th July 1895
PROVISIONAL SPECIFICATION..
Improvements in the Manufacture of Hydrazo Compounds from
Aromatic Nitro Hydrocarbons.
I, EUGEN STRAUB, of Blücherstrasse 30, Berlin S., in the Empire of Germany,
Chemist, do hereby declare the nature of this invention to be as follows:-
The production of hydrazo compounds by electrolytic reduction of aromatic nitro
hydrocarbons has not hitherto been sufficiently studied or described, nor has it been
practically applied. Häussermann (Chemiker Zeitung 1893, p. 129 and 209)
describes production of hydrazobenzol by electrolytic reduction of uitrobenzol in
alcoholic caustic soda lye. By filtering off the precipitated hydrazobenzol ani
acidifying the solution with sulphuric acid benzidinesulphate was obtained, but the
yield of the reduction products was only about 60% of the amount theoretically
calculated. In consequence of this unsatisfactory yield, Häussermann came to the
conclusion that the electrolytic reduction possesses no advantage over the ordinary
reduction methods, unless it were possible to utilize the oxygen evolved by the
electrolytic reduction.
Elbs, (Chemiker Zeitung 1893, p. 209) reduced a mixture consisting of a
saturated solution of nitrobenzol in alcohol, caustic alkali and undissolved nitro-
benzol, employing an agitator to move the undissolved nitro body to and fro over
the cathode. But in this manner he did not obtain hydrazobenzol but only
azobenzol, and for the greatest part azoxybenzol.
I have now discovered means of converting aromatic nitro-hydrocarbons into
hydrazo bodies, generally applicable, easily performed and giving results so good
that it can be practically applied with success.
This process is based upon the following considerations.
The azo and azoxy derivatives which are obtained as intermediate products are
less soluble than the corresponding nitro-bodies; consequently, in reducing a
concentrated solution of nitro hydrocarbons, the intermediate products separate
from the solution.
Experience has now shewn that these intermediate products, when precipitated,
can only be reduced with difficulty, if they are reduced at all. This fact explains
fully the negative results of Elbs' trials. It is absolutely necessary for the
successful reduction that the initial-products as well as the intermediate products
should remain in solution up to the end of the reaction. This condition is fulfilled
by employing certain composition and certain quantity of the conducting solution.
I have further found, that the nature of the alkali employed has the greatest.
influence. With caustic soda very bad results are obtained, whilst, on the contrary,
with caustic potash, very good results are obtained; moreover caustic potash is a
better conductor of electricity than caustic soda and requires therefore less energy
for the reduction. Besides, caustic potash is more soluble in the solvents employed
and allows, therefore, the use of more concentrated conducting solutions. Thus
employment of caustic potash in the electrolytic reduction effects great economy
of power and material, a result which is of the greatest value in the technical
application of the process. My invention may be carried out generally in the
following manner.
An electrolytic bath is divided by a diaphragm, such as a porous clay-cell, into
a compartment for the anode and another for the cathode.

page_text: The solution of the nitro-body is introduced into the cathode compartment whilst
the anode compartment is charged with a caustic potash lye of 10 to 20 per cent.
strength, or a corresponding quantity of carbonate or other suitable salt of
potassium. The employment of potassium carbonate has farther the advantage
that the diaphragms are less attacked. As cathodes, carbon or metal electrodes, as
anodes, metal electrodes, may be used. The current employed is from 17
to 18 ampères per square centimetre with a tension of four to five volts at a
temperature of 60° to 80° C.
When a volatile solvent is employed, a refrigerator above is required to prevent
escape of the vapours, and a second refrigerator allows the solvent to be distilled
off when the reduction is completed. The caustic potash lye and the solvent can
be used repeatedly. In order to prepare in this manner, hydrazobenzol, for
instance, from nitrobenzol, the following proportions may be used.
75 kilos. nitrobenzol are dissolved in 460 litres of alcohol of 96 per cent. and
80 litres of caustic potash lye 2 KOH to 1 H2O and subjected to the influence of the
electric current above specified at 60° to 80° C., until the reduction is completed,
which may be recognized by the light yellow colour of the liquor. The alcohol is
distilled off, and the residue is collected on a filter; 85 to 90 per cent. of the
theoretical yield may be obtained in this way. The hydrazobenzol may be
transformed, in the well known manner, into benzidine.
Instead of alcohol, other solvents, as, for instance, methylated alcohol may
be used.
When smaller quantities of alkali are employed, water may be substituted for
part of the alcohol; the composition of the conducting solution may be varied to a
considerable extent, provided that it is such as to prevent the intermediate products
from separating.
The quantities of the alkaline liquor required also vary according to the nature
of the nitro bodies employed, and of the azo or azoxy-bodies formed.
Dated this 8th day of September 1894.
ABEL & IMRAY,
Agents for the Applicant.
improvements in the Manufacture of Hydrazo Compounds from
Aromatic Nitro Hydrocarbons.
I, EUGEN STRAUB, of Blücherstrasse 30, Berlin S., in the Empire of Germany,
Chemist, 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 :-
The production of hydrazo compounds by electrolytic reduction of aromatic nitro
hydrocarbons has not hitherto been sufficiently studied or described, nor has it been
practically applied. Häussermann (Chemiker Zeitung 1893, p. 129 aud 209)
describes production of hydrazobenzol by electrolytic reduction of nitrobenzol in
alcoholic caustic soda lye. By filtering off the precipitated hydrazobenzol and
acidifying the solution with sulphuric acid benzidine sulphate was obtained, but the
yield of the reduction products was only about 60% of the amount theoretically
calculated. In consequence of this unsatisfactory yield, Häussermann came to the
conclusion that the electrolytic reduction possesses no advantage over the ordinary
reduction methods, unless it were possible to utilize the oxygen evolved by the
electrolytic reduction.
Elbs, (Chemiker Zeitung 1893, p. 209) reduced a mixture consisting of a
saturated solution of nitrobenzo! in alcohol, caustic alkali and undissolved nitro-

page_text: benzol, employing an agitator to move the undissolved nitro body to and fro over
the cathode. But in this manner he did not obtain hydrazobenzol but only
azobenzol, and for the greatest part azoxybenzol.
I have now discovered means of converting aromatic nitro-hydrocarbons into
hydrazo bodies, generally applicable, easily performed and giving results so gool
that it can be practically applied with success.
This process is based upon the following considerations.
The azo and azoxy derivatives which are obtained as intermediate products are
less soluble than the corresponding nitro-bodies; consequently, in reducing a
concentrated solution of nitro hydrocarbons, the intermediate products separate
from the solution.
Experience has now shewn that these intermediate products, when precipitated,
can only be reduced with difficulty, if they are reduced at all. This fact explains
fully the negative results of Elbs' trials. It is absolutely necessary for the
successful reduction that the initial-products as well as the intermediate products
should remain in solution up to the end of the reaction. This condition is fulfilled
by employing certain composition and certain quantity of the conducting solution.
I have further found, that the nature of the alkali employed has the greatest
influence. With caustic soda very bad results are obtained, whilst, on the contrary,
with caustic potash, very good results are obtained; moreover caustic potash is a
better conductor of electricity than caustic soda and requires therefore less energy
for the reduction. Besides, caustic potash is more soluble in the solvents employed
and allows, therefore, the use of more concentrated conducting solutions. Thus
employment of caustic potash in the electrolytic reduction effects great economy
of power and material, a result which is of the greatest value in the technical
application of the process. My invention may be carried out generally in the
following manner.
An electrolytic bath is divided by a diaphragm, such as a porous clay cell, into
a compartment for the anode and another for the cathode.
The solution of the nitro-body is introduced into the cathode compartment whilst
the anode compartment is charged with a caustic potash lye of 10 to 20 per cent.
strength, or a corresponding quantity of carbonate or other suitable salt of
potassium. The employment of potassium carbonate has farther the advantage
that the diaphragms are less attacked. As cathodes, carbon or metal electrodes, as
anodes, metal electrodes, may be used. The current employed is from 17
to 18 ampères per square centimetre with a tension of four to five volts at a
temperature of 60° to 80° C.
When a volatile solvent is employed, a refrigerator above is required to prevent
escape of the vapours, and a second refrigerator allows the solvent to be distilled
off when the reduction is completed. The caustic potash lye and the solvent can
be used repeatedly. In order to prepare in this manner, hydrazobenzol, for
instance, from nitrobenzol, the following proportions may be used.
75 kilos. nitrobenzol are dissolved in 460 litres of alcohol of 96 per cent. and
80 litres of caustic potash lye 2 KOH to 1 H,O and subjected to the influence of the
electric current above specified at 60° to 80° C., until the reduction is completed,
which may be recognized by the light yellow colour of the liquor. The alcohol is
distilled off, and the residue is collected on a filter; 85 to 90 per cent. of the
theoretical yield may be obtained in this way. The hydrazobenzol may be
transformed in the well known manner, into benzidine.
Instead of alcohol, other solvents, as for instance, methylated alcohol may
be used.
When smaller quantities of alkali are employed, water may be substituted for
part of the alcohol, the composition of the conducting solution may be varied to a
considerable extent, provided that it is such as to prevent the intermediate products
from separating.
The quantities of the alkaline liquor required also vary according to the nature
of the nitro bodies employed, and of the azo or azoxy bodies formed.

page_text: Having now particularly formed and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
The process for producing hydrazo compounds from aromatic nitro-hydrocarbons
by electrolytical reduction which process consists in subjecting to electrolytical
reduction in presence of caustic potash or any other suitable salt of potassium the
aforesaid initial products, dissolved in any suitable conducting solution, care being
taken, that the quantity of the latter should be sufficient to keep the azo- and
azoxy-compounds formed by the reducing process in solution up to the end of the
reaction.
Dated this 6th day of June 1895
ABEL & IMRAY,
Agents for the Applicant.