Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND A~D DE~AI'LED'D'E~'CRI'PTION OF THE IN~ENTION
The present inYentiOn relates to a process for
preparing 4-aminomethylbenzoic acid from 4-hydroxyiminomethyl-
benzoic acid. More particularly, the present invention relates
to a process in which 4-hydroxyiminomethylbenzoic acid is reduced
to 4-aminomethylbenzoic acid by using a catalyst containing at
least a palladium compound or a rhodium compound within an
aqueous medium of pH of not higher than 7.
Concerning the process for preparing 4-aminomethyl~
benzoic acid(hereinafter referred to as A~), the following
methods have been hitherto known:
(1) Amination of 4-chloromethylbenzoic acid by aqua ammoniae, 1,
(2) Reduction of 4-carboxybenzaldehyde in the presence of
Raney Nickel in methanol containing aqua ammoniae(refer to
Japanese Patent Publication No. 34-42L),
(3) Reduction of methyl 4-cyanobenzoate in the presence of ,'
Raney Nlckel in an aqueous alkali solution(refer to Japanese
Patent Application Laying Open No. 48-57951) and
(4) Reduction of 4-cyanobenzoic acid in the presence of a
ruthenium catalyst in an aqueous alkali solution(refer to
Japanese Patent Application Laying Open No. 51-32536).
However, although method (1) is carried out under an
ordinary pressure, a large amount of by-products such as secondary
amine and tertiary amine is formed and accordingly, the yield of
AM if not favorable; in order to improve the yield of method (2),
it is necessary to carry out the reaction under a high pressure;
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and the starting material of (3) and (4)~ 4-cyanobenzoic acid,
is not easily prepared in an industrial scale.
Accordingly, every one of the publicly known methods
cannot be said to be the sufficiently satisfactory method for
preparing 4-aminomethylbenzoic acid.
It is an object of the present invention to provide a
process for preparing 4~aminomethylbenzoic acid, comprising
catalytically hydrogenating 4-hydroxyiminomethylbenzoic acid
dispersed in an aqueous acidic- or neutral medium in the presence
of a catalyst containing at least one palladium compound or one
rhodium compound. Other objects will appear hereinafter.
The present invention will be explalned more in detail
as follows:
The starting substance of the present invention,i.e.,
4-hydroxyiminomethylbenzoic acid is an oxime compound which may
be obtained by the reaction of 4-carboxybenzaldehyde and
hydroxylamine hydrochloride. 4-Carboxybenzaldehyde is obtained
by oxidation of mono- or dichloromethylbenzoic acid as the object
compound. However, industrially, the 4-carboxybenzaldehyde
obtained as a by-product in the production of terephthalic acid
which is the raw material for synthetic fibers, is utili ed.
The catalyst used in the process of the present
invention (hereinafter referred to as the present process) is a
catalyst containing at least one member selected from the group
consisting of palladium compounds and rhodium compounds, and
preferably, a metallic catalyst comprising palladium and/or
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rhodium or a mixed catalyst comprising one or two members of
palladium and rhodium and one or more members of other meta]s of
platinum group, particularly, platinum and ruthenium. However,
mixed catalysts containing palladium, rhodium and platinum are
excluded in cases where the reduction is carried out in an
aqueous acidic medium. Specifically preferable is an unitary
catalyst comprising palladium or rhodium.
The form of the active metallic element contained in
the catalyst of the present process is metal, compound of the
metal, for instance, oxide, or alloy of the metals. These metals
and metal compounds are used while being carried on a carrier
such as activated carbon and diatomaceous earth, the preferable i1
¦ carrier being activated carbon. The -specifically preferable
catalyst is the catalyst comprising palladium metal carried on
activated carbon. In the ordinarily used c-atalyst, the content
of the metallic element carried on the carrier is about 2 to 10 %
by weight of the total weight of the catalyst. The amount of
catalyst used is so that the total sum of the weight of palladium
or rhodium becomes to about 0.25 to 10 % by weight, preferably,
about 0.5 to 5 % by weight of 4-hydroxyiminomethylbenzoic acia.
~The reaction medium used in the present process is the
medium of pII of lower than 7, that is, an acidic medium or a
neutral medium.
In the reduction of an oxime compound, an organic sol-
vent i5 generally used as the reaction medium, aqueous medium
not being used because of the extremely small solubility and
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the presumable hydrol~sis of the oxime compound in an aqueous
medium.
However, in the present process, it is characteristic
that the hydrogena-tion of the oxime compound dispersed in an
aqueous medium is possibly carried out at a relatively low
temperature and under a relatively low pressure. Namely, the
starting substance, the oxime compound, is reduced in an
emulsified state in an acidic medium containing a mineral acid,
and the thus formed AM by reduction of the oxime becomes to the
salt of the mineral acid. The reason why the mineral acid salt
of AM is easily obtained in a high yield is considered to be the
protection of tne aminomethyl group by the mineral acid
resulting in the prevention of side reactions such as deamination
and formation of secondary amine.
~ On the other hand, in the case where the reaction
medium is an aqueous neutral medium, the reduction of the oxime
compound proceeds in a nearly emulsified state of the oxime, and
after the reaction is over, AM is obtained as crystallites.
Under the neutral condition, it is characteristic that the
reaction proceeds in a heterogeneous state.
In the case where the reaction is carried out in an
aqueous basic medium, although the reaction proceeds in a
homogeneous system, it has been found that by-production of
secondary amine is inevitable resulting in a poor yield of AM.
As an aqueous acidic medium, an aqueous solution of
a mineral acid such as hydrochloric acid, sulfuric acid and
llflO~3
¦ nitric acid which forms a water-soluble salt with AM, is used
at an ordinary concentration of 3 to 5 %. The amount of the
mineral acid used in the reaction is at least more than the
equivalent amount of 4 hydroxyiminomethylbenzoic acid, preferably,
about 1 to 3 times of the equivalent amount. The amount of
the reaction medium is 10 to 50 times by weight of 4-hydroxy-
¦~iminomethylbenzoic acid, preferably, 10 to 20 times in bothcases of acidic- and neutral conditions.
I The reaction of the present process is ordinarily
llcarried out at a temperature of about 10 to about 80C,
and in the case of using a palladium catalyst, the reaction
proceeds smoothly enough at about 10 to about 50C, however,
in the case of using rhodium catalyst, a little higher temperature ,
l¦is necessary.
The reaction of the present process can be carried
¦out under a pressure of hydrogen of higher than 1 atm, and
the reaction easily proceeds under a pressure of hydrogen of
I 1 to 10 atm in usual cases.
~ The time period of the reaction of the present process
depends on the reaction conditions such as the kind of the
catalyst and the amount thereof, the temperature, the pressure
of hydrogen, etc., however, the absorption of hydrogen completes
usually within about 2 to 7 hours.
After the reaction is over, in the case of using
an aqueous acidic medium, the catalyst is removed by filtering
the real ion mixt~re and the crystals of ~ is sedimented by
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neutralizing the filtrate, and after collecting the crystals by
filtration, the filtrate is condensed to further obtain the
crystals of AM. On the other hand, in the case of using
~an aqueous neutral medium, concentrated aqua ammoniae or
l concentrated hydrochloric acid is added to the reaction
! mixture to dissolve the product, and after removing the
I catalyst by filtration, the filtrate is neutralized to obtain
¦Ithe crystals of AM.
Il The present invention will be further explained
l~more in detail while referring to the non-limitative examples
Illas follow5:
EXAMPLE 1
! i
In an autoclave of a capacity of 500 ml made of
llpressure-resistant glass, 16.5 g (0.1 mol) of 4-hydroxyimino-
I ~ methylbenzoic acid was dispersed into 200 ml of aqueous 3.5 %
hydrochloric acid solution, and 1.6 g of 5 ~ palladium on
activated carbon (hereinafter abbreviated to as 5 ~ Pd-C~
was added to the dispersion. The catalytlc hydrogenation
. of 4-hydroxyiminomethylbenzoic acid was carried out under the
initial pressure of hydrogen of 5 kg/cm at a temperature of from
ordinary temperature to 45C. The absorption of hydrogen came
to an end after 3 hours. After removing the catalyst by filter-
ing the reaction mixture, the filtrate was condensed and the
thus sedimented crystals were collected by filtration, washed
with a~ tone and dried to obtain 16.0 g of white powdery
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crystals melting at 2~4 - 288C. The crystalline product thus
obtained was identified as 4-aminomethylbenzoic acid
hydrochloride by comparing its infrared absorption spectrum with
that of the authentic specimen of 4-aminomethylbenzoic acid
hydrochloride, the yield being 85.0 %.
A saturated aqueous solution of the product, 4-amino-
methylbenzoic acid hydrochloride(hereinafter abbreviated to as
AM-~CL) was neutralized with aqueous 20 % sodium hydroxide
Il solution, and after collecting the thus sedimented crystals by
¦ filtration, the filtrate was condensed to obtain a further amount
of the crystals. After drying the thus obtained crystalsj the
combined crystals amounted to 12.5 g.
, '.
~XAMPLE 2
In the same manner as in Example 1 except for using
distilled water as the reaction medium and at a temperature of
from room temperature to 40C, the catalytic hydrogenation of
4-hydroxyiminomethylbenzoic acid was carried out. The absorption
of hydrogen came to an end after 3 hours. After adding 20 g of
concentrated hydrochloric acid into the reaction mixture to
! dissolve the product, the mixture was filtered to remove the
catalyst and the filtrate was condensed under a reduced pressure.
The thus sedimented crystals were collected by filtration, washed
with acetone and dried to obtain 14.5 g of white powdery crystals
which were identified as 4-aminomethylbenzoic acid by comparing
its in:~ared absorption with that of the authentic sFecimen of
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4-aminomethylbenzoic acid hydrochloride. The yield was 77.3 %.
By treating the thus obtained product with alkali in
the same manner as in Example 1, to obtain 8.2 g of crystals in
the first step and 2.6 g of crystals in the second step. These
crystals were identified as ~M by comparing their infrared
absorption spectrum with that of the authentic specimen of 4-
aminomethylbenzoic acid.
EXAMPLE 3
In the same manner as in E~ample 1, except for using
as the catalyst 5 % rhodium carried on activated carbon(herein-
after abbreviated to as 5 % Rh-C), catalytic hydrogenation of
4-hydroxyiminomethylbenzoic acid was carried out at a temperature
from room temperature to 60C. Absorption of hydrogen came to
an end after 5 hours. By treating the reaction mixture as in
Example 2, 14.0 g of white powdery product melting at 282 to
285C was obtai~red, and identified as AM~HCl by comparing its
infrared absorption spectrum with that of the authentic specimen
of AMHCl, the yield being 74.6 %.
By treating the thus obtained product with neutraliza-
tion with alkali, 10.2 g of white powdery substance was prepared,
which was identified as AM by infrared spectral analysis.
EXAMPLES 4 to 6
A series of catalytic hydrogenation experiments were
carried out in the same manner as in Example 1, however, using
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each one of the mixed catalysts shown in Table at a temperature
of from room temperature to 50C. In these experiments, the
reactions of hydrogenation of the oxime moiety and of the
benzene ring could be traced by observing the consumed amount
of hydrogen corresponding to the reduced pr~ssure of hydrogen
~ in the autoclave.
i After the reaction was over, the catalyst was removed
by filtering the reaction mixture, and after confirming that the
1~ filtrate contained solely AM-HC1 by the presenc-e of ultraviolet
l~ absorption at 228 nm, the filtrate was condensed. The thus
sedimented crystals were collected by filtration and dried.
,~ The product was identified by infrared analy-sis to be ~M HCl.
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I Table '`
!l ,
EXAMPLE Composition of Period for Product --
catalyst H absorption --
No 2 (hours) wRight(g) Identification
., .
5 % Pd-C 1 6 2.5 13.7 AM-HCl
5 % Pt-C 1.6 5 0 13 1 the same
5 % Rh-C 1.6 as above
5 % Pd-C 1~6 the same
6 5 % Ru-C**1.6 2.5 13.5 as above
Note: *5 % Pt-C means a catalyst containing 5 % by weight of
platinum on activated carbon.
**5 % Ru C means a catalyst containing 5 % by weight of
uthenium on activated car~on.
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EXAMPLE 7
In the same manner as in Example 1, except for using
distilled water as the reaction medium and using a mLxed catalyst
consisting of 1.6 g of 5 % Pd-C, 1.6 g of 5 % Pt-C and 1.6 g of
5 % Rh-C, catalytic hydrogenation of 4-hydro~yiminomethylbenzoic
acid was carried out at a temperature of from room temperature
to 50C. The absorption of hydrogen came to an end after about
Il 4 hours.
1~ Since some crystals appeared in *he reaction mixture,
1l 20 ml of concentrated hydrochloric acid was added to the mixture
to dissolve the crystals, and the solution was filtered to remove ,
the catalyst by filtration. After condensing the filtrate and
I adding acetone to the condensate to sediment the crystals, they
were collected by filtration and dried to obtain white powdery
1~ crystals melting at 284 to 286C in amount of 14.5 g, which were
ideneified as ~~ C1 by in rared analysis, the yield being 77 %.
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