Note: Descriptions are shown in the official language in which they were submitted.
s~
The present invention relates to a process for prepar-
ing an aminobenzylamine mixture. The aminobenzylamlne isomer
mixture obtained in the process of this invention is liquid at
the room temperature and gives excellent physical properties to
the cold cure epoxy resin.
Aminobenzylamine is an importan-t cornpound as a curing
agent for epoxy resin, a raw material for polyamides and poly-
imides, and a raw material for intermediates of agricultural
chemicals and medicines. Processes for preparing aminobenzyl-
amine by using nitrobenzaldehyde or nitrobenzonitrile as starting
material have so far been known. For example, as for the process
using the former as starting material-, there are known the fol-
lowing processes: (i) Nitrobenzylbromide is derived from
nitrobenzaldehyde, which is then reacted with potassium phthal-
imide to obtain N-nitrobenzylphthalimide, and m- and p-amino-
benzylamines is produced with an
~5~S~
yield of about 20% by reduced and hydrolyzed. (N. Kornblum et al7
J. Am. Chem. Soc , 71,2137 (1949)).
(ii) m-Nitrobenzaldehyde ls reacted with phenylhydrazlne and
A the resulting hydrazone compound ls catalytically reduced wherebym-aminobenzylamine is obtained in 60% yield (A. Siddiqui et al,
Synth. Commn., 7, 71-78 (1977))
(iii) m-Nitrobenzaldoxime is derived from m--nitrobenzaldehyde
and catalytically reduced on a Raney nickel catalyst under a high
pressure whereby p-aminobenzylamine is obtained in 52% yield. (J. R.
Griffith et al, N R L report 6439).
On the other hand, processes starting the latter are as
follows:
(iv) p-Aminobenzonitrile derlved from p-nitrobenzonitrile is
reduced by aluminum lithium hydride and thus, p-aminobenzylamine is
obtained in 37% yield (N. C. Brown et al, J. Medicinal Chem., 20,1189
(1977)).
(v) By catalytically reducing m-nitrobenzonitrile under a high
pressure on the Raney nickel catalyst, m-aminobenzylamine is obtained
in 49% yield. (J. R. Griffith et al, N R L Report 6439).
In other processes, aminobenzylamine is prepared by reducing
nitrobenzylamine as the starting materials. For e~ample,
(vi) m-Aminobenzylamine is prepared by reducing m-nitrobenzyl-
amine with tin and hydrochloric acid, (S. Gabriel et al, Ber., 20,
2869-2870 (1887)).
(vii) o-Aminobenzylamine is prepared by reducing o-nitro-
benzylamine with red phosphorus and large quantities of hydroiodic
acid (S. Gabriel et al, Ber., 37, 3643-3645 (1904)).
~s mentioned above,according to the known processes(i) and
(ii) which prepare aminobenzylamine by using nitrobenzaldehyde or
~s~
nitrobenzonitrile as the starting materlals, a more than equivalent
quantity of relatively expensive compound i5 used to prepare inter-
mediates which are reduced to obtaln intended products. llowever,
in these processes there are disadvantages that reduction steps are
complicated or expense and labor are required for recovering by-pro-
ducts and the like.
Also in the process(iv), there are the disadvan~ages that the
reducing agent is expensive and difficult in handling. In the
processes (iii) and (v), wherein the catalytic reduction on the
Raney nickel catalyst is carried out in an autoclave under a high
pressure, equipment apparatus is expensive and volume efficiency ls
low.
On the other hand, in the known process (vi), nitrobenzylamine
as the starting materials, is reduced by large quantities of tin and
hydrochloric acid to isolate a tin salt of the intended product
before its liberation by double decomposition. The process is
complicated because of separating procedure on resultant metallic
compounds and care is needed not to leave a trace of the metal. In
addition, considerable expense and labor are needed to prevent
environmental problems caused by large amount of heavy metals and
waste acids, as well as to recover these hazardous materials.
As a means of improving above mentioned processes, the product
is obtained in the process (vii) by reducing with red phosphorus and
hydroiodic acid. And yet expensive hydroiodic acid is requlred :Ln
large quantities and red phosphorus is in a great danger of ignition.
Therefore the known processes for preparing aminobenzylamine
have many steps, complicated after-treatments, or equipmental
problems.
The present invention provides a process for prepariny
an aminobenzylamine isomer mixture by using rnineral acid salts of
a nitrobenzylamine isomer mixture obtained by nitratiny benzyl-
amine for use as nitrobenzylamine raw materials.
~ ccording to the present invention there is provided a
process for preparing an aminobenzylamine mixture which comprises
catalytically reducing, in the presence of a me-tal of platinum
group, mineral acid salts of a nitrobenzylamine isomer mixture,
obtained by nitrating benzylamine.
The aminobenzylamine isomer mixture obtained in the
process of this invention is li~uid at the room temperature and
gives excellent physical properties to the cold cure epoxy resin.
The starting materials used in this invention are the
mineral acid salts of a mixture of o-nitrobenzylamine, m-
nitrobenzylamine and p-nitrobenzylamine. These o-, m-, and p-
isomers are prepared with a high yield by reacting a correspond-
ing nitrobenzylchloride with ammonia or phthalimide (S. Gabrielet al, ser., 286g (1887); E.L. Holmes et al, J. Chem. Soc., 1800-
1821 (1925); H.L. Ing et at, J. Chem. Soc., 2348-2351 (1926)).
In particular mineral acid salts of nitrobenzylamine
which are used for the raw materials is nitrate and/or sulfate of
nitrobenzylamine mixture obtained by nitrating benzylamine. This
kind of nitrate and/or sulfate of nitrobenzylamine may be
obtained by nitrating benzylamine with a nitrating agent. The
nitrating agent which may be used in the process includes a mixed
acid, fuming nitric acid, a nitric acidtacetic acid mixture, and
the like. Normally, the mixed acid or fuming nitric acid is pre-
ferred. By using the nitrating agent, reaction is carried out as
follows. When nitrating with fuming
-- 4
nitric acid, nitric acid having a concentration of 80 to 98% is used
8 to 12 times the mol of benzylamine. When nitrating with the
mixed acid, it is composed of concentrated sulfuric acid and nitric
acid or nitrate such as sodium nitrate, potassium nitrate, and the
like. The mol ratio among benzylamine, nitric acid or nitrate, and
concentrated sulfuric acid is in a range of 1 : 1.2 - 5 : 1-5.
If necessary, nitration may be carried out in organic
solvents. Preferred organic solvents include halogenated
hydrocarbon solvents such as methylene chloride, 1,2-dichloroethane,
1,1,2-trichloroethane, chloroform, carbon tetrachloride, 1,1,2,2-tet-
rachloroethane, trichloroethylene, and the like.
The reaction can proceed either by dropping benzylamine into
the nitrating agent or by a reverse method. When applying the mixed
acid, the reaction can be carried out either by using the previously
prepared acid mixture, or by mixing benzylamine with one component of
the mixed acid before dropping the other component.
The reaction temperature is in the range of -10C to 80C,
preferably -5C to 30C. The reaction time is preferably in the
range of 2 to 10 hours.
After completion of reaction, the resultant mixture is poured
into a specified amount of ice water. Mineral acid salts of the
nitrobenæylamine mixture may be obtained by filtering the precipi-
tate. By pouring the reaction mixture into ice water, m-nitro-
benzylamine and p-nitrobenzylamine are mainly settled, and most of
o-nitrobenzylamine is removed to the filtrate. o-Nitrobenzylamine
content in the nitrobenzylamine mixture is lO to 15% by weight at the
end of nitrating reaction. Solubility of o-isomer in water is
large as compared with other isomers and thus, as stated above,
o-isomer content of the separated mixture reduces to 5% by weigllt and
less.
The mineral ac:Ld salts of nitrobenzylamlne mixture herein
mentioned are sulfate, nitrate or mixtures thereof of the o-, m-, or
p-substituted nitrobenzylamine mixture obtalned by nitrating benzyl-
amine as described above. The m-, p-, and o-isomer ratlo in thé
nitrobenzylamine mixture thus obtained is in the range of 30-70 :
30-70 : 0,2-10, and o-isomer content is normally not more than 5% by
weight. When the nitrating agent is composed of nitric acid alone
or the mixed acid containing not more than 2 mol ratio of sulfuric
acid and excess nitrlc acid, nitrobenzylamine is obtained as nitrate.
In other nitrating conditions, the product is sulfate or the mixture
of sulfate and nitrate. The mixture of nitrobenzylamine isomers
thus obtained, particularly in the presence of nitrate, is not
desiccated from safety and operation view point. The wet mixture
may be applied as it is to the catalytic reduction from safety and
operation viewpoint.
The catalytic reduction in this invention may be carried out
in the absence of acid. In this invention, however, the catalytic
reduction may preferably be conducted in the presence of acids,
The acid which may be used in this invention is mineral acid,
organic acid or carbonic acid. As to mineral acid is at least one
member of selected from the group consisting of hydrochloric acidl
sulfuric acid, nitric acid, boric acid, phosphoric acld, boric acid
anhydride and phosphoric acid anhydride. The use of these mlneral
acids selectively proceeds the reaction to obtain desired products
The mineral acids are relatively low priced and accelerating
effect is found in the reducing reaction. Thus it is also a
characteristic of this process that the intended product may be
5~4~5Z
prepared efficiently and economically. In addition, mlneral acid
anhydrides absorb water existed in the reaction system and generated
from the reduction of nitro group. Thus reducing reactlon may be
carried out in anhydrous and ideal conditions, that is, undesired
actiori such as decomposition or side reaction by water ls prohibited
and the reducing reaction may be proceeded with excellent
selectivity.
Also, as to organic acid is aliphatic mono- or di-carboxylic
acids such as formic acid, acetic acid, propionic acid, oxalic acid,
malonic acid, succinic acid, maleic acid, aromatic carboxylic acids
such as benæoic acid, phthalic acid, sulfonic and sulfinic acids such
as p-toluenesulfonic acid and benzenesulfinic acid. A part of these
carboxylic acids may also be used as acid anhydrides. Acetic acid
is used preferably among the organic acids in commercial scale. Some
organic acids may also be used as solvents. When using the organic
acids, the reaction proceeds quickly under mild conditions due to the
good compatibility of organic acids with raw materials and other
solvents. Since a homogeneous solution is resulted from the
reaction, aftertreatment such as catalyst and solvent recovery etc.
may easily be carried out. The fact that almost no reduction is
found on the activity of recovered catalysts, is a great advantage of
this process, enables recycled use of the catalysts and makes the
process economical Further in some cases, it is possible to
recover organic acids by distillation or other means after amino-
benzylamine is isolated from its organic acid salts, which permits
better results on the commercial scale application.
As carbonic acid, satisfactory results may be obtained by use
of carbon dioxide. That is, carbon dioxide converts to carbonic
acid by reacting with water which exists in the reaction system or
~:25~
generates from the reductlon of nitro groups. Carbon dioxlde may
be used in gas, liquid and solid states. Relatively simple after-
treatment is a great merit of reactions using carbon dioxide.
Excess carbon dioxide is discharged after the reaction, the catalysts
are removed and distillation is carried out after adding base.
Thus solvents are recovered at a high rate and desired product of
aminobenzylamine may be obtained in high yield. The process has
also a characteristic of no reduction on the activity of recovered
catalysts, which enables their recycled use and makes the process
economical.
The amount of acid used is not less than 0,5 equivalent of
nitrobenzylamine, preferably in the range of 1 to 3 equivalent.
These acids may be used alone or in mixture of two or more
~ lso solvents are used for catalytic reduction in the process
of this invention. The solvent which may be used in this process
is water, alcohols, goycols and ethers, e.g. methanol, ethanol,
isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, methyl cel-
losolve, ethyl cellosolve~ ethylene glycol, propylene glycol,
diglyme, tetraglyme, dioxane, tetrahydrofuran, and the like. In
some cases, there are used aliphatic hydrocarbons, aromatic
hydrocarbons, esters and halogenated hydrocarbons e. g, hexane,
cyclohexane, benzene, toluene, ethyl acetate, butyl acetate,
dichloromethane, chloroform, 1,1,2-trichloroethane, and these like.
These solvents may be used alone or in mixture of two or more.
The amount of solvent used is not particularly limited, but
normally sufficient at 1 to 15 times by weight based on the amount of
raw materials.
The reducing catalysts which may be used in the process of
this invention may be conventional one, e. g. nickel, palladium,
~2~
platinum, rhodium, ruthenium, cobalt, copper and the llke. Although
these catalysts may be used in the form of metal, they may be used in
form supported on a carrier such as carbon, bariurn sulEate, sillca
gel, alumlna,and the like. Nickel, coba]t, copper, and the llke may
also be used as Raney catalysts. The amount of catalysts used is in
the range of 0.01 to 30% by weight ln term of metal based on nltro-
e ~ered~
benzylamine. Usually, a range of 2 to 20~ by weight is ~4~r~
ln the case where Raney catalysts are used, while a range of 0,05 to
5% by welght in the case where noble metals supported on a carrler
are used.
The reaction temperature ls not particularly limlted, though
it is usually ln the range of 0 to 150C, preferably lO to 80C.
The reaction pressure may be usually ln the range of atmo-
spheric pressure to 50 Kg/cm G.
As for general embodiments of this invention, a catalyst may
be added to the raw materials in a state where it ls dissolved or
suspended ln a solvent, followed by lntroduclng hydrogen to carry out
at the specified temperature untll lts absorption stops. After the
completion of the reaction, the reaction mixture is filtered to
remove the catalysts and dlstilled to obtain the intended product.
When using mineral or organic acids, a catalyst may be added
to a solution or suspension of the raw materlals and the aclds in
the solvents, and reducing reaction ls carriecl out. When applying
carbon dioxide, a catalyst may be added to a solution or suspension
of the raw materials in a solvent and then reduclng reactlon is
carried out either by previously adding whole amount of carbon
dioxide or by continuously or lntermlttently addlng. In any case,
catalytic reduction is carried out untll absorption of hydrogen
stops. When catalytic reductlon is conducted in the absence of
6~5~
acids, the reaction product is dissolved after the reaction. Then
resultant mixture is filtered to remove the cata1ysts and distilled
to obtain the intended product, When a dissolved r~action mixture
is resulted from catalytic reduction in the presence of the acids, it
is filtered to remove the catalysts, When a preclpitated reaction
mixture is obtained, the same procedure is carried out after the
precipitate is dissolved by warming or by addition of water and the
like. In either case, the filtrate is neutralized with sodium
hydroxide, potassium hydroxide, ammonia, triethylamine, or the like
to liberate aminobenzylamine and distilled to obtain the end product.
Another method of treating the precip:Ltated reaction mlxture
is that the precipitate is filtered to isolate and purify the acid
salts which are neutralized to obtain the intended product.
Accordingly the process of this invention is basically the
catalytic reduction of nitrobenzylamine in solvents and by use of
catalysts, The reaction proceeds smoothly at low temperature to
obtain aminobenzylamine in high yields, When the reduction is
carried out in the presence of mineral acids, organic acids or
carbonic acid, the intermediates exist in a stable state of acid
salts of aminobenzylamine. That is, aminomethyl group of nitro-
benzylamlne is stabilized during the reduction in the form of mineral
acid salts, organic acid salts or carbonate, The stabilization
suppress decomposition and side reactions and results in a quick
reduction of nitro group to amino group, which enables selective
production of aminobenzylamine. Aminobenzylamine may easily be
isolated after the reducing reaction either by separation and
purification in the form of mineral acid salts, organic acid salts or
carbonate, or by distillation and refining after a simple
~ 10
` `` ~Z5~;~5:~
neutralization. Thus, the process of this invention is commer-
cially very advantageous.
Further, when nitrobenzylamine mixture resulted from
nitration of benzylamine is used as raw materials for reduction,
the mixture is obtained as mineral acid salts of o-, m-, and p-
isomers. On applying the mixture as it is to the reduction, it
stays in a stable form during the reaction to obtain aminobenzyl-
amine mixture with a high yield. The contents of o-, m-, and p-
aminobenæylamines in the mixture are in the range of 0-5, 30-70
and 30-70% by weight, respectively.
The process of this invention has a merit of no reduc-
tion in catalyst activity, enables recycled use of the catalysts
and is economically very favorable. The process is also commer-
cially advantageous, because solvent recovery and product isola-
tion may easily be carrled out by distillation after the reac-
tion.
This invention will now be desribed in detail by fol-
lowing Examples in which % represent percent by weight.
Example 1
At a temperature of not hlyher -than 0C, 107 grams (l
mol) of benzylamine were dropped into ~3 grams (1 mol) of 9~%
nitric acid over a period of 5 hours. After the end o~ dropping,
reaction was continued with stirring at 20-Z5C for 3 hours. The
resultant reaction mixture was poured into 750 grams of ice
water, followed by filtering separated crystals which were washed
with saturated sodium chloride solution to obtain nitrobPnzyl-
amine nitrate. The wet crystals thus obtained were 254 grams
having a solid content of 61% (72.1% yield).
The results of elemental analysis after recrystallizing
from water were as follows.
Elemental Analysis (C7 Hg N3 05)
___________________ ___________________________________________
C H N
_______________________________________________________________
Calculated (%) 39.07 4.19 19.53
Found (~) 38091 4~07 19~33
_______________________________________________________________
A sealed glass reaction vessel was then charged with
35.3 grams (0.1 mol) of the wet nitrobenzylamine nitrate
crystals, 0.2
-- 1~ --
~Z5~L5;i~
gram of 5% Pd/C catalyst and 50 grams of water. Hydrogen wasimmediately introduced with a vigorou~ stlrrlng. Reaction was
continued at 25-30C for 7 hrs. After the end of the reactlon, the
resultant mixture was warmed to 50-60C and flltered to remove the
catalyst. The filtrate was neutralized by adding 32 grams of
granular sodium hydroxide and allowed to stand for separating into
two layers. The lower layer was removed and the upper layer was
distiled in vacuum to obtain 11 grams of a colorless transparent oily
fraction having a boiling point of 130-140C /5-7 mmHg, (The total
yield calculated from benzylamine was 65%.) The product was a
mixture of aminobenzylamine. According to gas chromatography, it
contains 41.3% m-aminobenzylamine, 57 6% of p-aminobenzylamine and
1.1% of o-aminobenzylamlne.
Example ~
At a temperature of not higher than 0C, 107 grams (1 mol) of
benzylamine were dropped over a period of 5 hours into a mixed acid
containing 77 grams (1.2 mols) of 98% nitric acid and 300 grams
(3 mols) of 98% sulfuric acid After the end of dropping, reaction
was continued with stirring at 20-25C for 3 hours. The resultant
reaction mixture was then poured into 750 grams of ice water, fol-
lowed by filtering separated crystals which were washed wlth satu-
rated sodium chloride solution to obtain 218 grams of wet crystals
having a solid content of 60%. The results of elemental analysis
were as follows and the crystals obtained were nitrobenzylamine
sulfate (65% yield) .
f ~ 3
~5~a~5~
. ~
Elemental Analysls ( C14 lll8 ~4 8
C ll N 0
~. .
Calculated (%) 41.79 4.48 13 93 7.96
Found (%) 39 9 4.14 13.67 8.45
A sealed glass reaction vessel was then charged with 21.8
grams of the wet nitrobenzylamine sulfate crystals, 0.5 gram of 5%
Pd/C catalyst and 45 ml of water, and hydrogen was introduced with a
vigorous stirring, Reaction was continued at 25-30C for 7 hours.
After the end of the reaction, the resultant reactlon mixture was
warmed to 50-60C and filtered to remove the catalyst. The filtrate
was neutralized by addlng 22.5 grams of 45% sodium hydroxide solution
and 14 0 grams of sodium sulfate (ten hydrate), and allowed to stand
for separating into two layers, The lower layer was removed and
the upper layer was distilled in vacuum to obtain 7.1 grams of a
colorless transparent oily fraction having a boiling point 130-140C/
5-7 mmHg. (The total yield calculated from benzylamine was 58.0%.)
The product was a mixture of aminobenzylamine. According to gas
chromatography, it contains 48.5% of m-aminobenzylamine, 50.2% of
p-aminobenzylamine and 1.3% of o-aminobenzylamine.
Example ~
At a temperature of not higher than 0C, 107 grams (1 mol) of
benzylamine were dropped over a period of 5 hours into a mixed acid
containing 257 grams (4 mols) of 98% nitric acid and 200 grams (2
mols) of 98% sulfuric acid After the end of dropping, reaction
was continued with stirring at 20-25C for 3 hours. The resultant
reaction mixture was then poured into 750 grams of ice water,
!,
followed by filtering separated crygtals which were washed with satu-
rated sodium chloride solution to obtain 284 grarns of wet crystals
having a solid content oE 64.3%.
The results of elemental ana:lysis were as follows and the
crystais obtained were nitrobenzylamine nitrate (85% yield).
E].emental Analysis ( C7 Hg N3 O5 )
C H N
. .
Calculated (%) 39.07 4.19 19.53
Eound (%) 38.35 4.21 19.86
The wet nitrobenzylamine nitrate crystals were then reduced
. ~ and aftertreated by the same procedure as described in Example ~r,
and a mixture of aminobenzylamine was obtained. (The total yield
calculated from benzylamine was 74.5%.) According to gas chromato-
graphy, the mixture contains 47.4% of m-aminobenzylamine, 51.1% of
p-aminobenzylamine and 1.5~ of o-aminobenzylamine.
Example ~r
One hundred and seven grams (1 mol) of benzylamine was nit-
rated with a mixed acid containing 128 grams (2 mols) of 98% nitric
acid and 200 grams (2 mols) of 98% sulEuric acid by the same proce-
dure as described in Example ~r and 272 grams of wet crystals were
obtained. The results of elemental analysis were as follows and the
product was a mixture of nitrate and sulfate of aminobenzylamine, the
ratio of which were assumed to be approximately 1/1.
~t,~ ~/S
~2~
Elemental Analysis
C ll N S
Caiculated (%) sulfate 41.79 4,48 13.93 7.96
nitrate 39.07 4,19 19.53 ---
Found (%) 40.52 4.25 16.82 3,81
The mineral acid salts of nitrobenzylamine thus obtained were
reduced and aftertreated by the same procedure as descrlbed in
Example ~ to obtain a mixture of aminobenzylamine. (The total yield
calculated from benzylamine was 68.7%.) According to gas chromato-
graphy, the mixture contains 47.2% of m-aminobenzylamine, 51.0% of
p-aminobenzylamine and 1.8% of o-aminobenzylamine.
Example ~
At a temperature of not higher than 0C, 107 grams (1 mol)of
benzylamine were dropped over a period of 5 hours into a solution of
mixed acid which contains 121 grams (1.2 mols) of potassium nitrate,
300 grams (3 mols) of 98% sulfuric acid and 400 ml of 1,2-dichloro-
ethane.
After the end of dropping, reaction was continued with
stirring at 20-25C for 3 hours. When allowed to stand, the
resultant mixture was separated into two layers. The lower layer
of the mixed acid solution was poured into 750 grams of ice water,
followed by filtering separated crystals which were washed with
saturated sodium chloride solution to obtain 230 grams of wet
crystals oE nitrobenzylamine mineral acid salts. A sealed glass
reaction vessel was then charged with 230 grams of the wet crystals
h~
56a~5æ
of nitrobenzylamine mlnera] acid saltg, 1.5 grams of 5% Pd/C catalyst
~_ and ~50 grams of water. The charge was reduced and aftertreated by
~3~-
~the same procedure as descrlbed ln Example ~ and a mixture of
aminobenzylamine was obtained. (The total yield calculated from
benzylamine was 58.9%.) According to gae chromatography, the
mixture contains 59.5% of m-aminobenzylamine, 35.0% of p-aminobenzyl-
amine and 5.5% of o-aminobenzylamine.
Example ~
A sealed glass reaction vessel was charged with 35.3 grams of
the wet crystals of nltrobenzylamine nitrate obtained in Example ~
0.1 grams of 5% Pd/C catalyst and 45 ml of methanol. Ilydrogen was
immediately introduced with a vigorous stirring. Reaction was
continued at 25-30C for 8 hours. After the end of the reaction,
the resulted reaction mixture was warmed to 60-65C to remove the
catalyst. The filtrate was concentrated in vacuum to distill off
most of methanol to obtain a yellow viscous liquid, wherein 130 grams
of 30% aqueous sodium hydroxide solution were added, mixed and
allowed to stand for separating into two layers. The lower layer
was removed and the upper layer was distilled in vacuum to obtain
11.1 grams of a fraction having a boiling point of 130~140C/ 5-7
mmHg, (The total yield calculated from benzylamine was 65.5%.)
