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Патент USA US3063991

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Unite States
Patented Nov. 13, 1952
expense due to the di?iculty of recovery for reuse of these
Albert Bloom, Summit, and David E. Graham, West?eld,
N.J., assignors to General Aniline 8: Film Corporation,
New York, N.Y., a corporation of Delaware
No Drawing. Filed July 9, 1957, Ser. No. 670,647
6 Claims. ((11. 260-205)
promoters, and also due to the fact that they rapidly lose
the desired activity and function of carrying the reaction
beyond the hydrazo state. An additional de?ciency which
lies with the use of these promoters is the extremely slow
reaction time required to bring about a reduction from
a nitro to a hydrazo state.
It is therefore an object of this invention to provide a
process whereby the reductive power of metal alcoholates
This invention relates to improvements in the reduction 1O may be greatly increased when they are employed in
of aromatic nitrogen compounds containing nitrogen in
e?ecting the reduction of aromatic nitrogen compounds
reducible form as a nuclear substituent in an aromatic
containing nitrogen in reducible form and at a stage of.
ring. More particularly, this invention relates to im
oxidation higher than the hydrazo stage.
provements in the process of effecting reduction of such
It is a further object of this invention to provide a
nitrogen compounds under alkaline conditions, and spe 15 process whereby aromatic nitrogen compounds contain
ci?cally, under the reductive effect of metal alcoholates
ing nitrogen in a reducible form and at a stage of oxidation
whereby reduction products at a stage of oxidation lower
than the hydrazo stage may be reduced with
than azoxy are produced.
The alkaline reduction of aromatic nitrogen compounds
metal alcoholates in an economical manner.
,It is a still further object of this invention to provide
which contain nitrogen in a reducible state is Well known. 20 a process whereby aromatic nitrogen compounds con
For example, it is well known that aromatic nitro, nitroso,
taining nitrogen in a reducible state and at a stage of oxida
azo, azoxy and hydroxylamino compounds may be re
tion higher than the hydrazo stage may be reduced with
duced by alkaline reducing agents and that the ?nal stage
of reduction is a function of the reducing agent used,
metal alcoholates to give outstanding yields of products
having an oxidation level lower than azoxy.
the reaction conditions employed, and the absence or 25
Other objects will appear hereinafter as the descrip
presence of promoters and the like.
tion proceeds. According to this invention, the foregoing
During the alkaline reduction of an aromatic nitro
objects are accomplished by carrying out the reduction
compound, the following reduction products listed in order
of aromatic nitrogen compounds containing reducible
of, and by degree of reduction may be obtained:
nitrogen With metal alcoholates, and particularly alkali
ARNOz ——> ARNO ——> ARNHOH ——> ARN/—N—AR ——> AR—N=N—AR -——)
It is well known and has been established that under
the usual conditions the reduction of an aromatic nitro
alcoholates in the presence of a hydrogenation catalyst.
The catalysts which are contemplated for use herein in
compound by means of metal alcoholates, and especially
conjunction with the alkali alcoholates may be nickel or
an alkali metal alcoholate such as sodium methylate, gives
40 any of the noble metal catalysts such as palladium, plati
rise to the azoxy compound as the sole reduction com
pound. Such reductions are usually carried out by heat
num, and the like in a supported or unsupported state.
The platinum and palladium class of catalysts includes,
in addition to these two elements, iridium, osmium, rho~
ing nitrobenzene with alcoholic caustic alkali at the boil
ing point of the mixture employing re?ux conditions at
dium, and ruthenium. In addition to the free metals,
atmospheric pressure. The major product, as indicated
45 one may employ the oxides and salts of these metals,
above, is azoxybenzene although minor amounts of ani
and as indicated above, one may use these elements or
line are produced. It has thus been recognized that these
compounds either unsupported as a ?nely divided powder,
alkali metal alcoholates are not sufficiently strong re
ducing agents to carry the reduction beyond the azoxy
stage under the above described conditions. It is also 50
known that the azoxy compounds so produced may be
reduced still further to azobenzene and to hydrazobenzene
by the use of stronger agents such as aluminum and
caustic, or zinc and alkali, or by operating at elevated
temperatures (140° to 180° C.) and elevated pressures
(above 10 atmospheres). The use of such elevated tem
peratures and pressures is of course contemplated in con—
or supported on any suitable base well known in the
catalyst art, such as charcoal, alumina, silica gel and the
like. By employing such auxiliary catalytic agents with
the metal alcoholates, it is possible to reduce aromatic
nitro, nitroso, hydroxylamino and azoxy compounds to
azo compounds and hydrazo compounds, and it further
becomes possible to effect reduction of azo compounds
to the hydrazo stage. The use of such catalytic agents
not only permits a smooth and rapid reduction to the
azo and hydrazo stages of reduction, but in addition, the
junction with the use of the aforementioned alcoholates.
processes are very economical due to the fact that the
These methods of carrying out the reduction of the azoxy
catalytic agents are separated in a simple manner from
compounds to further states of reduction suffer the ob
the reaction medium by ?ltration or centrifuging, and may
vious disadvantages of expense attendant with the use of
be reused time and again until the activity thereof has
‘additional raw materials and expensive equipment such
diminished sufficiently to warrant either reactivation or
as pressure apparatus and the like. It has been proposed,
regeneration by known means, or to discard them where
in order to overcome such disadvantages, to employ cer
economically feasible.
tain promoters in the reaction mixture, together with an 65
The amounts of~ the catalyst employed may be varied
alkali alcoholate in order to effect reduction beyond the
considerably. However, it is signi?cant that extremely
azoxy stage of compounds at a higher stage of oxidation
small amounts give effective conversion to stages of oxi
than the hydrazo stage. US. Patents 2,684,358 and
dation beyond the azoxy state. Such small amounts as
2,684,359 illustrate disclosures of such promoters. The
from about 3/1000 mol per mol of reducible aromatic hydro~
use of promoters in general, while permitting the reduc 70 gen compound are effective. Amounts up to about 1/10
tion to proceed beyond the azoxy state at atmospheric
mol per mol of nitrogen compound may be used, the
pressure introduces, however, an undesirable additional
speci?c quantities to be employed being dependent upon
the exact nitrogen compound being reduced and the
speci?c conditions employed. Amounts larger than the
aforementioned 1/10 mol per mol of nitrogen compound
are normally not necessaryor economically feasible.
The general process for carrying out the present inven
tion involves the subjection of the reducible aromatic
nitrogen compound to the reducing action of a metal a1
coholate in a reaction mixture which contains the afore
stage the mixture consists of two layers, a toluene layer
and an aqueous layer. The former layer is separated and
after distillation, 20.2 parts of unreacted azoxybenzene is
recovered for recycling without further distillation. To
the aqueous layer there is addedl part of nuchar, and
while hot (that is, at 65° C.) the mixture is ?ltered. To
the ?ltrate at this temperature there is added over a 1 hour
7 period, 88 parts of 100% sulfuric acid. The mixture is
then cooled to 50° C. and the resultant precipitate of
mentioned catalysts. The preferred form of the inven
tion involves the addition of the reducible aromatic nitro 10 benzidine sulfate is ?ltered off and washed acid free. The
roduct represents 63.5 parts of pure 'benzidine or 68.5%
gen compound to a suspension of the catalyst in the alco
of the theoretical amount based on the azoxybenzene con
holic medium while the latter is under re?ux conditions,
sumed, From the combined ?ltrate and washings of the
that is, at the boiling point of the resultant mixture. It is
benzidine sulfate cake there is obtained, after making the
further preferred to add the reducible nitrogen com
pounds slowly to the alcoholate catalyst combination to 15 solution alkaline and steam distilling, a yield of 10.4 parts
of aniline. This represents a yield of 11.2% based on the
obtain the highest yields. The isolation of the products
azoxybenzene consumed.
resulting from the reduction of the starting reducible nitro
It will be observed that the total process for the con—
gen compound may be done in any suitable manner well
version to hydrazobenzene, that is, the reduction phase
known in the art. Thus, the reduction product or prod
ucts may be isolated by crystallization occurring upon 20 of the process, is carried out in 11 hrs. A similar process
employing prior art promoters requires from three to four
cooling of the reaction mixture, and further puri?ed by
washing with water and alcohol to remove any other end
times this length of time to eifect a similar conversion.
products, and in particular, the sodium salts present. One
Example 2
may also distill the methanol, and then isolate the end
A solution of 275 parts of sodium hydroxide ?akes in
products by crystallization. We have found it most ex 25 1300 parts of methanol is prepared. After the solution
pedient to carry out the isolation of the reaction products
has cooled down to room temperature, there is added 5
by forming two immiscible liquid phases, one an aqueous
parts of a 5% palladium on activated charcoal catalyst
phase and the other an organophilic phase immiscible with
similar to the one employed in Example '1. The mixture
the water phase, using a solvent such as toluene, benzene,
or the like. By adding large quantities of water and one 30 is then heated to re?ux in a ?ask and then there is added
over a period of 5 hrs., 184.5 parts of nitrobenzene. After
of these solvents to the reaction mixture and mixing thor
the addition of the latter has been completed, the mixture
oughly, the organophilic phase will extract the desired re
is re?uxed for an additional 2 hrs. Methanol is then
duction product such as azobenzene, hydrazobenzene and
distilled from the mixture until the ?ask temperature
the like, whereas the aqueous phase will contain the vari
reaches 100° C., at which time 400 parts of Water are
ous Water soluble components and particularly the sodium
added to the ?ask and then 300' parts of toluene. After
salts present.
vigorous stirring and ?ltration of the catalyst, the mixture
The amount of alkali and alcohol employed will vary
is permitted to separate into two layers, the one aqueous
and the other the toluene layer. The latter ‘is then sep
depending upon the compound undergoing reduction, and
also upon the desired end products. In all cases, an ex
arated from the aqueous layer and contains the desired
cess of these substances should be employed, that is, over 410
reduction products. This toluene solution is then treated
in the manner described in Example 1, employing the
and above the theoretical quantities necessary. 'Where it
is desired to go to the hydrazo state of reduction, usually
more alkali is necessary than Where the desired end prod
same quantities of materials as was cited therein to con
vert any hydrazobenzene formed during the reduction to
uct is the azo form. An excess of the alkali is also e?ec
benzidine. There is ?nally isolated, again following the
tive in promoting an increase in the rate of the reaction. 45 procedure of Example 1, 5.2 parts of benzidine which is
The following examples will serve to illustrate the pres
equivalent to a yield of 3.7%.’ .From the ?ltrates and
washes of the benzidine conversion there is obtained ‘by
making alkaline and steam distilling, a yield of 36.3 parts
ent invention without being deemed limitative thereof. In
these examples, parts are by weight unless designated
Example 1
89 parts of sodium’ hydroxide ?akes are dissolved in 85
parts methanol. The solution is accompanied by the evo-.
lution of heat, and after the solution has been cooled to
room temperature, a paste of 2 parts of a 5% palladium
on activated charcoal catalyst in 2 parts of water is added.
The mixture is then brought to re?ux and under this con
dition and with constant agitation, there is added over a
of aniline (26.1% of theory). The toluene layer present,
after the benzidine conversion, is treated to recover any
dissolved materials therein by distilling off the toluene.
The residue consists of 70.4 parts of azobenzene having
a freezing point of 65° C., indicating an extremely pure
product. This yield represents a conversion of 51.7% of
Example 3
A solution of 40 parts of sodium hydroxide ?akes in
period of 1 hour, 120 parts of azoxybenzene. After the
130 parts of methanol is prepared. After the solution has
addition, the resultant mixture is re?uxed for 10 hrs. and 60 cooled down to room temperature, there is added 1 part
then permitted to cool to room temperature. The catalyst
of 3% platinum catalyst supported on a silica base. This
mixture is brought to re?ux and over a period of 3 hrs.
is ?ltered oif, 200 parts of water and 70 parts of toluene
are'then added, and after vigorous shaking, the layers
there is added 19 parts of nitrobenzene. After the addi
are separated. The toluene layer contains the reduction
tion of the nitrobenzene, the mixture is re?uxed for an
product hydrazobenzene and a small amount of aniline,
additional 4 hrs. 30 parts of water and 20 parts of tolu
and also some 'unreacted azoxybenzene. This layer is
ene are then added to the mixture, and after vigorous
stirring and removal of the catalyst by ?ltration, the
washed several times with warm Water and then the hydra
toluene layer, after strati?cation, is separated from the
zobenzene content is rearranged to benzidine in the follow
aqueous layer. The toluene solution is then added to 100
ing manner. The toluene solution is added to 650 parts
of water and the mixture cooledrto 0° to 5° C. There 70 parts of water and cooled to 0° C. 30 parts of 20° Bé.
hydrochloric acid are added and the mixture, while under
is then added 175 parts of 20°eBé. hydrochloric acid and
this mixture vigorously stirred and allowed to warm up
to 10° to 15° C. The mass is maintained at the latter
temperature for 4 hrs. and then after adding 840 parts
of warm water, the mixture isheat-ed to 65° C. At this
constant agitation, is permitted to warm up to 15° C.
After 3 hrs. at this temperature, 150 parts of water at
40° C. are added and the temperature further raised to
65° C. Upon standing, the mixture strati?es into an upper
toluene layer and a lower aqueous layer. The latter is
treated with 1 part of activated carbon and ?ltered while
hot. To the ?ltrate, while at a temperature of 60° 0,
there is added slowly over a period of about 20 minutes,
15 parts of 100% sulfuric acid. The mixture is cooled
to 50° C. and the resultant precipitate of benzidine sulfate
is ?ltered oh" and Washed acid free. An exceptionally
pure benzidine sulfate is obtained. 13 parts of benzidine
and methanol, these being preferred because of their
are well known in the art and may be prepared in accord
tially in heating said aromatic nitrogen compound with
low cost, other alkalis and alcohols may be employed,
such use being well known in this art. \Instead of the
toluene employed in the examples to effect the isolation
of the desired end products, any other equivalent solvent
such as benzene, xylene and the like may be used.
Variations and modi?cations which will be obvious and
apparent to those skilled in the art may be made in the
are obtained which represents an overall theoretical yield
procedure above described without departing from the
of 87.5% of the nitrobenzene employed.
10 scope and spirit of our invention.
We claim:
Example 4
1. A method for reducing an aromatic nitrogen com
The procedure of Example 1 is repeated except that
pound containing nitrogen in a reducible form as a nuclear
the hydrogenation catalyst employed is a reduced and
substituent at a higher stage of oxidation than the hydrazo
stabilized nickel on kieselguhr ‘(10% nickel). Similarly, 15 stage,
said nuclear substituent selected ‘from the group
as in this example, 2 parts of this catalyst are used. The
of nitro, nitroso, hydroxylamino, azoxy and azo
yield of 'benzidine based on the amount of azoxybenzene
to a stage beyond the azoxy stage where the said nuclear
consumed in the reaction is 65% of the theoretical yield.
substituent is a member of the group consisting of nitro,
10% aniline is also formed in this reaction.
hydroxylamino and azoxy, and to hydrazo where
The various catalysts contemplated in this invention 20
the said nuclear substituent is azo, which consists essen
ance with the following references:
a reducing mixture of an alkali metal hydroxide and‘ a
lower alcohol in the presence of at least about 1/1000 of a.
Chemistry. D. Van Nostrand Co., New York, 1922
mole of a hydrogenation catalyst selected from the group
Platinum oxide-Adams, Voorhees and Shriner, Organic 25 consisting of nickel and noble metal catalysts per mole
Platinum black-Sabatier-Reid, Catalysts in Organic
of said aromatic nitrogen compound.
Syntheses, Coll. vol. 1, p. 452. John Wiley & Sons,
New York, 1932
Palladium on charcoal—Mannich and Thiele, Ber.
2. A method for reducing an aromatic nitrogen com
pound containing nitrogen in a reducible form as a nuclear
Deutches pharm. Ges. '26 36-48 (1916)
substituent at a higher stage of oxidation than the hydrazo
30 stage, said nuclear substituent selected from the group con
Platinum on charcoal-Ellis, US. Patent 1,174,245
Nickel on kieselguhr—Covert and Conner, J. Am. Chem.
sisting of nitro, nitroso, hydroxylamino, azoxy and azo to a
Soc. 54 165 (1932)
stage beyond the azoxy stage where the said nuclear sub
stituent is a member of the group consisting of nitro, ni
Patent 1,111,502.
troso, hydroxylamino and azoxy, and to hydrazo where
As pointed out above, the foregoing examples merely 35 the nuclear substituent is azo, which consists essentially in
heating said aromatic nitrogen compound with an alkali
illustrate the present invention, and it is of course ob
metal alcoholate in the presence of at least about 1/1000 of a
vious that many changes and equivalent materials may be
mole of a hydrogenation catalyst selected from the group
used in the process Without departing from the scope of
of nickel and noble metal catalysts per mole
the invention. Thus, the present invention may be ap 40 consisting
nitrogen compound.
plied to the reduction of other aromatic nitrogen com
Platinum or palladium on
alumina-—Schwarcman, U.S.
3. A method as de?ned in claim 1 wherein the hydro
genation catalyst is pr-esent in the amount of from about
pounds containing nitrogen in a reducible form as a
nuclear substituent. Examples of such compounds in
clude the following: the nitrotoluenes, 0-, m-, and p-nitro
toluene, 0-, m-, and p-nitrochlorobenzenes, nitrophenoli-c
1/1000 of a mole to about 1,40 of a mole per mole of said
aromatic nitrogen compound.
4. A method as de?nedin claim '1 wherein nitroben
Zene is reduced to azo‘benzene.
5. A method as de?ned in claim 1 wherein nitrobenzene
others such as o-nitrophenetole, 0-, m-, and p-nitroanisole,
nitro aromatic carboxylic acids such as o-nitrobenzoic
acid, p- and m-nitro‘benzoic acid, nitrobenzene sulfonic
is reduced to hydrazobenzene.
acids, 0-, m-, and p-nitroaniline and the like. As pointed
6. A method as de?ned in claim 1 wherein azoxyben
out ‘above, the end product or products obtained in carry 50 zene
is reduced to hydrazobenzene.
ing out the present invention depend on numerous fac
tors such as starting material, that is, the state of oxida
References Cited in the ?le of this patent
tion of the nitrogen compound, and the amounts of alkali
and alcohol employed. It is also possible to carry out the
described processes at various temperatures and pres
Andrews _____________ __ Sept. 2, 1919
sures. Thus, by employing an inert and miscible diluent
Weiland ____________ __ Aug. 20, 1935
in addition to the alcohol as the solvent, it is possible to
Henke et a1. __________ __ Feb. 25, 1941
exceed the temperatures normally obtained during re?ux
operations with metal alcoholates alone. By the use of ‘2,608,582
pressures above atmospheric pressure, it is also possible 60 ‘2,688,040
to increase the re?ux temperature. Usually, however,
such elevated temperatures are neither necessary nor de
sirable because while the rate of reaction may be there
by increased, secondary and side reactions may reduce
the yields of the desired reduction product. Further,
while the examples illustrate the use of sodium hydroxide
6 UK
Sargent et al. __________ __ Oct. 9, ‘1951
Huey et al. __________ __ Aug. 26, 1952
Adams et a1 ___________ __ Aug. 31, 1954
France _______________ -_ Oct. 13, 1913
Switzerland __________ __ Mar. 16, 1915
Great Britain ________ __ Mar. 24, 1943
Germany _____________ __ July 2, 1953
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