Note: Descriptions are shown in the official language in which they were submitted.
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1,3-Diaryl triazenes are compounds o~ the formula
Ar-N=N-NH-Ar,
wherein Ar is optionally substituted aryl.
They are used as such, ~or example as foamers in
the manufacture of plastics, mainly, however, as inter-
mediates, in particular in the manufacture of aromatic
diamines and of arylhydrazines (in particular phenyl-
hydrazine), which latter are processed in known mannerto yield corresponding final products, mainly in the
field of polymers, dyestuffs and pharmaceuticals.
The 1,3-diaryl triazenes rearrange to form the
corresponding aminoazo compounds by heating and/or
by the action of acids. According to the process of
European Offenlegungsschrift 13 6l~3 this rearrangement
is conducted by using from about 0.4 to 2.0 weight %,
referred to the triazene-contain.ing solution, of
a strong acid, in particular nitric acid.
A number of processe3 for the rr.anufacture of
1,3-diaryl triazenes are known. One method is described,
by way of example, by G. Vernin et al. in Synthe~i~
1977, pages 691-693. This method consists in reaoting
i-amyl nitrite with primary aromatic monoamines at room
temperature in non-polar aprotic solvents (such as
hexane, petrol ether and the like). According to said
reference, triazene is said to be obtained in a high
yield in short reaction periods.
According to the sole example for the Lanufacture
of a triazene ~ 1,3-bis-(3,5-dichlorophenyl)-triazene
of said reference which comprise~ reacting i-amyl
nltrite with 3,5-dichloroaniline at room temperature
in petroi ether/benzene on a laboratory scale the
de~ired product is said to be obtained in a yield
of 90 ~ within 30 minutes i-Amylnltrite was used,
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however, in considerable excess (the 3-fold quantity).
The reaction batch was worked up by evaporation on
a rotary evaporator, suction-filtering of the residual
solid, washing out and drying.
This method is not advantageous for the industrial-
scale manufacture mainly because of the great excess
of i-amyl nitrite employed and because of the evaporation
of the reaction batch on the rotary evaporator. Said
reference does not specify whether evaporation has
been carried out in vacuum or under normal pressure. As
the water jet vacuum is the vacuum commonly employed for
such cases, it cannot be avoided, unless particular
possibly complicated measures have been taken, that part
of the relatively easily volatile solvent is entrained
with the current of water and passes into the waste
water, which should be avoided for reasons of environmen-
tal protection, in any case, with relatively great
batche~. Evaporation in vacuum could be conducted,
however, at least without an increase in temperature.
Evaporation under normal pressure, however, requires a
temperature increase, which ~urely is harmless for some
1,3-diaryl triazenes, which are rather stable owing to
very defined substituents. Other 1,3-diaryl-triazenes,
which constitute the great majority of the normal
1,3-diaryl triazenes, are easily subject to a rearrange-
ment, because of their relative instability at elevated
temperature, or are decomposed in other manner, which is
a considerable disadvantage.
According to G.Vernin et al.,the reaction of i-amyl
nitrite with primary aromatic monoamines at room tempe-
rature can be carried out as well at room temperature in
polar protic solvents (methanol~), if a mercury salt
such as Hg(OCOCH3)2 is added. However, thls reaction
does not result in the free l,3-triazene, but in the
corresponding Hg-complex. Nothing is disclosed in ~aid
reference above the ralease of the triazene from the
complex.
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If the mercury salt is o~itted, the reaction of
the alkyl nitrite and the primary aromatic monoamine
does take place at room temperature in methanol, only
after a considerable period o~ induction (of several
hours (as tests of the Applicant have shown).
Attempts to improve the process published by
G. Vernin et al. in a manner appropriate also for
large-scale conditions have shown that this object is
reached mainly by using gaseous alkyl nitrites and
by adding a small quantity of acid to the primary
aromatic monoamine, advantageously dissolved in a
polar protic solvent.
Subject of the present invention, consequently,
is a process for the manufacture of 1,3-diaryl triazenes
by reacting alkyl nitrites with primary aromatic mono-
amines at room temperature or at a temperature slightly
above room temperature, which comprises introducing
alkyl nitrites gaseous at the temperature applied into
primary aromatic monoamirJeq liquid at the temperature
applied or dissolved in a polar protic solvent, in the
presence of a small quantity of acid.
This prooes~ gives triazene in a high yield.
An alkyl nitrite excess is not required and possible
induction times (for example as in the oase of the
reaction proceeding without the addition of an acid)
are not observed. The reaction batch can be worked
up by precipitation of the triazenes with water because
of the hydrophilic character of the polar protic solvents,
in particular the low-molecular alcohols preferably
used in this case. Thus solvents do not pass into the
waste water (as in the method according to G.Vernin et
al. wherein the solvent is withdrawn by a water jet
vacuum) and the reaction products are not subjected
to a ternperature strain (as in the process of G.~/ernin,
if the solvent is withdrawn under normal pressure and,
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as a consequenoe thereof, at elevated temperature). The
proceQs is therefore excellently suitable for the
large-scale manufacture.
It was extremely surprising that the presence
or addition of a small quantity of acid has a catalytic
effect on the desired reaction without provoking
simultaneously to an undesired great extent the rearrange-
ment of the 1,3-diaryl triazenes giving the corresponding
p-aminoazobenzenes, which reaction, as is known, is
catalyzed by acids. This surpri~ing reaction course i~
probably caused at least partially by other conditions
of the process of the invention (use of gaseous alkyl
nitrites, preferably use of polar protic solvents).
Suitable alkyl nitrites that are gaseous at room
temperature or at a temperature slightly higher than
romm temperature are preferably methyl nitrite CH3NO2
and/or ethyl nitrite C2H5NO2. They may be ohtained~
~or example, according to the process described in
German patent 1,156,77~ from N2O3 or nitrose gclSeS
(= mixtures consisting mainly of NO and NO2) and
alcohols. The procedure i~ advantageously as follows: A
mlxture Or NO, NO2 and nitrogen in an alcohol, preferably
methanol or ethanol, is in~ected into a corresponding
reactor ~where effective mixing of the gas and liquid
takes place). The molar ratio of NO and ~2 in the
mixture of nitrose gases may be from about 100:1 to
about 40:60, preferably it is about 1:1, the portion of
inert gas may be from O to about 99 ~. This gaseou~
mixture may be readily obtained by oxidizing NO with air
or with pure oxygen. A technical mixture of nitrose
gases, as obtained in the nitric acid production, may
likewi~e be used.
The alkyl nitrite reactor is operated at a tempera-
t.ure which i8 chosen such that the alkyl nitrite formed
is withdrawn from the reaction mixture in ga~eous
.~tate. The methyl nitrite and ethyl nitrite (bo~ling
~ 171~50
- 6 - HOE ~1 /F 191
points -12C and 16C respectively3 may even be
discharged with the inert gas current without further
expenditure at normal temperature, the gas current
passing advantageous]y via a condenser in order to
avoid that an excessive quant ty of alcohol is entrained.
The quantity of alkyl nitrite is determined simply
by the quantity of nitrose gases injected. In a preferred
embodiment of the invention the alkyl nitrite thus
prepared is introduced into the primary aromatic mono-
amine in a further recipient connected i3nmediately withthe alkyl nitrite reactor said monoamine being present
as such in liquid form or, preferably, dissolved in a
polar protic solvent and containing a small quantity of
acid.
Suitable primary aromatic monoamines are on principle
any amines, the amines liquid at room temperature or at
a temperature slightly above room temperature being
used a.s sucn or in dissolved form and the solid amines
being used only in dissolved form. Preference .is given
to the primary aromatic monoamines corresponding to the
following formula
R3 ~ ~ 1
wherein R1, R2 and R3 independent from each other
denote H, halogen (F, Cl, Br, J), alkyl (preferably
C1-C4 alkyl) and N02, in particular only H.
Examples of suitable monoam~nes of thi~ type are:
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.
~ 21~3C~I~H2 <~UH2
F ~-- N~lCl ~--NE72 ~ N~2
2 5
and the like.
1'he reaction temperature may range in general
from about tO to 50C, prcferably, it is from about 20
to 35C.
Suita~le polar protic 30lvents are on principle
all liquids covered by this designation, which do not
react themselves under the reaction conditions. Preferred
polar protic solvents are C1-C4 alcohols, in particu-
lar the aloohols on which the alkyl nitrite used is
based, in the first place, consequent].y, methanol and
ethanol.
The ratio of polar protic solvent to primary
aromatic monoamine may vary within wide limits. It
ranges generally from about 5:95 to about 90:10 (weight
ratio of polar protic solvent:amine).
Suitable acids added or to be added to the amines
are pratically any organic and inorganic weak and
strong acids. Mineral acids, in particular hydrochloric
acid, are used preferably.
t 17t850
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The quantity of acid may range in general from
about 0.01 to 5, preferably from about 0.05 to 1,
equivalent ~ per mol of primary aromatic monoamine.
This signifies that from about 0.01 to 5, pre~erably
from about 0.05 to 1, rnol % of a monobasic acid, half
of this quantity of a bibasic acid, a third of this
quantity of a tribasic acid and so on, each time per
mol of primary aromatic monoamine, is added. ~hen
relatively great quantities of acid are added, the
undesired rearrangement of the 1,3-triazenes formed
yielding mainly the corresponding p-aminoazobenzenes
takes place to an increasing degree.
The process of the invention yields the desired
triazene in most cases in the form of a crystal sus-
pension, which may be further used in very definedcases without isolation of the triazene, for example, if
a reduction yieldig phenylhydrazine or a rearrangement
yielding p-phenylene diamine is aimed at.
If an isolation of the triazenes is dssired,
this may be done advantageously by suction-filtration
or similar methods of the product solution from the
reactor and addition of water. In this case the triazenes
are obtained as yellow- to brownish-colored arystals,
which may be suction-filteed. The triazenes are not
sub~ect to a particular temperature strain in this
isolation method (this method being not applicable to
the proce~s of G. Vernin et al., loc. cit., where water
i9 used together with irnmisible non-polar aprotic
301vents). The mother liquor and the filtrate may be
worked up in a step independent from the triazene
production in little-polluting manner.
The yield~ obtained in the process of the invention
equal that obtained in the process of G. Vernin, loc.
cit.. The velocity of the formation of triazenes depends
naturally, partly to a considerable extent, on the
.. . .... . .
~ 171850
- 9 '- HOE 81/F 191
nature of the substituents at the aromatic nucleus of
the starting compounds. Electron-accepting substituents
decelerate the reaction, whereas electron-releasing
substituents accelerate the reaction.
The invention constitutes a considerable progress,
~ince the process can be carried out on an industrial
scale in simple,'little-polluting and product-preserving
manner.
The invention is illustrated by the following
examples. Part of the examples have not been caried out
until the complete conversion of the primary aromatlc
monoamine used a starting compound. The invention
examples are followed by a comparative example, which
demonstrates that a reaction does not take place practi-
cally, in any case within 2 and a half hours between the
gaseous alkyl nitrite (methyl nitrite) and primary
aromatic monoamine (aniline) in the presence of a polar
protic solvent (methanol), however, in the absence of an
acid.
E x z m p l e
A mixture of NO and N02 (1:1) produced from 2.7
l/h of NO and 3.6 l/h of air was passed through methanol
at room temperature and converted to methyl nitrite.
The methyl nltrite formed was introduced continuously,
into a mixture of 100 g of aniline, 0.25 g (0.25 %)
of aniline hydrochloride and 5 ml of methanol. The
temperature of the reaction mixture rai~e to 33-34C
during the reaction and solid triazene precipi~ated
after 95 minutes. The introduction of ga~ was stopped
after 110 minutes and the reaction mixture was stirred
for 1.5 hours. During this period of time, 2.5 g of
methyl ni.trite had passed the qolutionn ln unreacted
state and were collected in a cooling trap at -78C.
The reaction mixture was introduced into 500 ml of
water, the crystals were suction-filtered and dried.
There were obtained 35.1 g OL slightly-yellow triazene
(99.3 %, referred to NO; 33.3 % referred to aniline).
.
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GC~an21ysis:
0.32 ~ of aniline,
98.47 % of 1,3-diphenyl triazene,
0.78 ~ of 4-aminoazoben7ene,
0.43 % of 5 unknown components.
E x a m p 1 e 2
The procedure was analogous to that of Example 1,
except that 1 % of aniline hydrochloride used as
the catalyst gave 34.3 e of 1,3-diphenyl triazene (97.0 ~,
referred to N0, 32.4 %, referred to aniline).
GC-analysis:
2.39 % of aniline,
0.16 ~ of 2-aminobiphenyl,
0.30 % of N,N-diphenylamine,
0.19 ~ of 4-amino-biphenyl,
2.70 % of 4-aminoazobenzene,
1.34 % of 8 unknown components.
E x a m p 1 e 3
Proceeding in the manner described in Example 1,
a methyl nitrite current was introduced into a mixture
of 80 g of aniline, 4 g of aniline hydrochloride (5 %
referred to aniline) and 20 ml of methanol. 33.8 g
of product (95.5 %, referred to N0; 31.8 % referred to
aniline), were obtained.
GC-analy~is:
0.18 % of 2-amino-biphenyl,
0.44 % of N,N-diphenylamine,
0.22 % of 4-amir.o-biphenyl,
79.62 % of 1,3-diphenyl triazene,
16.97 % of 4-aminoazobenzene,
2.57 ~ of 10 unknown components.
E x a m p 1 e 4
__
When proceeding analogously to Example 1, using,
however, in.stead of methanol, ethano', an ethyl nitrite
discharge was not observed and 42.0 g of 1,3-diphenyl
tria~ene were obtained (97 %s referred to N0; 39.5 %
referred to aniline).
- - - . ,.. ~ .... .. .... ..... . .. . . .
,
.
~ 1 71~0
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E x a m p l e 5
The procedure was analogou~ to that of Example 1,
using, however, instead of methanol, isopropanol and
heating the first reactor at 55C to separate the
nitrous acid ester by distillation. There were obtained
41.2 g of 1,3--diphenyl triazene (94.5 % referred to NO;
38.7 ~ referred to aniline~.
~C-analysis:
0.1 % of aniline,
98.0 % of 1,3-diphenyl triazene,
0.2 % of 4-aminoazobenzene,
1.7 % of 13 unknown components.
E x a m p l e 6
Methyl nitrite (from 8.1 l/h of NO; 10.8 l/h of
air and methanol) wa~ introduced into a mixture of 1,000 g
of aniline, 1 g of aniline hydroehloride (= 0.1 %
referred to aniline) and 50 ml of methanol placed in a
circulation reactor of 2 liters content, in the manner
descri.bed in Rxample 1, thus heating the reactor contents
to a temperature of 33-35C. Solid triazene precipitated
after 3 hours. Half of the reaction mixture was passed
to a corresponding reactor of the same s.ize and the
contents of both reactors were diluted each with
liter of methanol so as to form an ea~ily stirrable
mixture. Methyl nitrite (from 8.1 l/h of NO; 10.8
l/h of air and methanol) was introduced into each of both
reactors for a further 3.5 hours. The resultant yellow
~uspension was 3tirred for 2 hours and withdrawn in
vacuo from the apparatus. Triazene was precipitated in a
receptable with water. There were obtained 710 g (99.5 %
referred to NO; 67.2 % referred to aniline) Or slightly
yellow 1.4 diphenyl triazene.
GC-analy~is:
0.11 % of aniline,
0.04 % of 4 aminobiphenyl,
~ ~7~8~0
- 12 - HOE 81_E` 191
99.54 ~ of 1,4-diphenyl triazene,
0.02 % of 4-aminoazobenzene,
0.25 ~ of 1 unknown component.
E x a m p l e 7
In a manner analogous to Example 6, mQthyl nitrite
(from 8.1 l/h of NO; 10.8 l/h of air and methanol)
was introduced into a mixture of 800 g of aniline, 1 g
of aniline nydrocbloride and 50 ml of methanol. After
halving and diluting the contents, methyl nitrite was
injected into both reactors for 4 hours each and the
batches were allowed to stand overnight to complete
their reaction. There were obtained 820 g (100 % referred
to NO; 96.6 p referred to aniline) of yellow triazene.
GC-analy~is.
0.71 % of aniline,
o.38 ~ of N,N-diphenyl amine,
0.09 % of 4-aminobiphenyl,
93.56 % of 1,3-diphenyl triazene,
4.27 % of 4-aminoazobenzene,
0.98 % of 6 unknown components.
E x a rn p l e 8
In a manner analogous to Example 6, methyl nitrite
waA introduced into a mixture Or 500 g of aniline, 0.5 g
of aniline hydrochloride and 20 rnl of rnethanol. Methyl
nitrite had been produced by passing a technical
nitrose mixture (11 % of nitrose, degree of oxidation 33 ~,
38 l/h) through methanol. The gas current wa~ switched
off after 6 hours, the mixture was stirred for one hour,
triazene was preciitated with water, suction-filtered
and dried. 148 g of slightly yellow crystals (99 %
referred t,o N203; 28 % referred to aniline) were
obtained.
GC-analysis:
0.04 ~ of 4-aminobiphenyl,
98.83 % of 1,3-diphenyl triazene,
0.7a ~ of 4-aminoazobenzerJe,
0.33 % of 3 unknown components.
! 171850
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E x a m p l e 9
Substituted 1,3-diaryl triazenes were prepared in
the manner described in Example 6 (cf. Table). To this
end there was prepared in each case a solution of the
aniline derivative in methanol as concentrated as
possible, which contained ~.1 % of the corresponding
hydrochloride. The semi-molar portion of methyl nitrite
(referred to the aniline component) was injected to the
resultant solution and stirred overnight~the solid
product,s were precipitated with water, suction-filtered
and dried.
! l 718~0
- 14 - HOE 81/F 191
Aniline 'rriazene derivatives Yield,¦ Mp
derivatives referred
to aro-
matic
amine
~ _ ___ _.
Cl ~ -NH2 Cl-. ~ -N=-NH- ~ -Cl 94 % 132C
~10 ~ 2 ~ Cl Cl ~ B7 ~ ~ 66C
F- ~ -NH2 F- ~ -N=N-NI1- ~ -F 67 '~ 116C
2 ~ -N-N-NH ~ 60 '~ 166C
. . (deconlp.)
CII - ~ -N~T CiI3- ~ -N=~-N11- ~ -c~l3 67 g 119C
C~ 2 Cl ~r~ -N--N~ Cl 65 % 1;~C
~ -I~H ~ ~ -N=1~-NH ~ 54 % 1~0C
! 171850
.- 15 - HOE 81/.F 191
Comparative Example
Analogously to Example 1 methyl nitrite (from
2.7 l/h of NO and 3.6 l/h of air and methanol) was
. introduced into 100 g of aniline and 5 ml of methanol.
The temperature of the reaction mixtue was kept at
22C. 17 g of methyl nitrite were collected in the
course of 2 and a half hours in a subsequent trap.
According to gas chromatographic analysis of this
reaction mixture upon this period of time, less than 0.2
of 1,3-diphenyl triazene had been formed.
