Note: Descriptions are shown in the official language in which they were submitted.
Mo- 1 9 1 4
LeA 18,671
PROC~SS FOR THE PREPAR~ION OF POLYAMINES
OF TIIE DIP~ENYL METHANE S~RIES WHICH
AR~ RICH IN ORT~O ISOMERS
~ACKGROUMD OF THE INVF~NTION
This invention relates to an improved process for
the preparation of polyamines, of the diphenyl methane series
with a high yield of diaminodiphenyl methanes, i.e. di-
nuclear diamines with high yields of ortho isomers, in
particular, 2,2'- and 2,4'-diaminodiphenyl methane.
The problem of obtaining polyamine mixtures of the
diphenyl methane series which contain a high proportion of
dinuclear components having a high ortho isomer content has
not yet been satisfactorily solved by the known processes of
aniline/formaldehyde condensation. Although the process
disclosed in German Offenlegungsschrift 1,937,~85, for
example, enables polyamines which contain a high proportion
of ortho isomers to be obtained, the proportion of diamines
contained in the polyamine mixtures given in the examples of
the reference are below 80% in all cases. Also in the process
of the reference, the aminal formed from aniline and formal-
dehyde must be heated to at least 125C, which pre-supposes
careful removal of the last traces of molsture.
The process of the present invention provides a
means of preparing polyamine mixtures of the diphenyl methane
series having an exceptionally high proportion of diamines
and at the same time arl exceptionally high proportion of
ortho isomers, without the above-mentioned disadvantages of
the processes known in the art. The process of the present
invention also makes it possible to prepare polyamines with
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a high diamines content in which the proportions of isomers
can be adjusted within wide limits.
DESCRIPTION OE` THE INVENTION
Tll~ present invention relates to a process for
the preparation of polyamines of the diphenyl methane series
which are rich in ortho lsomers, comprising: reacting an
aromatic amine, preferably aniline, with formaldehyde to
produce N-substituted pre-condensates; removing the water
formed in the reaction and any water introduced in the form
of aqueous formaldehyde solution; rearranging the pre-con-
densates to the corresponding primary amines substituted on
the aromatic nucleus in the presence of aromatic amine salts,
preferably aniline salts of strong acids; neutralizing the
catalyst used; and working up the resulting reaction products
by known methods. The reactants and the aforesaid strong
acids are used in such quantities that the total quantity
of aromatic amine used corresponds to an aromatic amine~
formaldehyde molar ratio of from 4:1 to 20:1. Also, the
total quantity of strong acids used, based on the total
quantity of aromatic amine used, corresponds to an aromatic
amine/acid equivalent ratio of from 10:1 to 1,000:1. The
process is characterized in that at least half the total
quantity of aromatic amine used is combined with the acid
to form an aromatlc amine/aromatic amine salt mixture; the
mixture is heated to a temperature of from 100 to 200C; the
N-substituted pre-condensate, which is maintained at a
temperature of from 0 to 100C, is introduced into this
mixture; and rearrangement of the pre-condensate is then
completed at a temperature in the range of from 100 to 250C.
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The startinc3 materials used for the process according
to the present invention are aromatic amines and formaldehyde.
Aniline is the preferred aromatic amine. Examples
of other possible aromatic amines include o- and m-toluidine,
o- and m-anisidine, o- and m-phenetidine, N-methylaniline,
_
N-ethylaniline, 2,4-diaminotolue~e or any mixtures of such
amlnes,
The formaldehyde is preferably used in the form of
aqueous formaldehyde solution although any substance which
releases formaldehyde under the reaction conditions could,
of course, be used.
The catalysts which are preferably used in the
present invention are water-soluble acids having a pKa-value
below 2.5, preferably below 1.5. The following are examples:
hydrochloric acid, hydrobromic acid, sulfuric acid, tri-
fluoroacetic acid, methane sulfonic acid, trifluoromethane
sulfonic acid, benzene sulfonic acid and phosphoric acid.
The preferred catalyst is hydrochloric acid. The
acids mentioned above may be used as mixtures with acidic or
neutral salts of such acids, e.g. with the corresponding
ammonium salts or the corresponding alkali metal salts;
however, this is less advantageous.
Thebases used for neutralizing the acids are
preferably aqueous inorganic bases, such as sodium h~droxide.
To carry out the process of the present invention, a
N-substituted pre-condensate, i.e. an aminal, is first
prepared from an aromatic amine and formaldehyde in the
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absence of the above-mentioned catalysts. This reaction is
carried out by known methods at a temperature in the range
of from 0 to 100C, preferably from 30 to 80C. The water
of condensation formed in the reaction, as well as any water
introduced in the form of aqueous formaldehyde solution
(formalin), is removed by phase separation after aminal
formation. If required, this may be followed by a procedure
such as vacuum distillation to remove the last traces of
moisture, although such a complete removal of water is
generally not necessary after phase separation.
The reactants for this pre-condensation are used
in quantities corresponding to an aromatic amine/formaldehyde
molar ratio of at least 2:1. The ratio of the total quantity
of aromatic amine used in the process according to the
present invention, including the quantity used in the second
stage together with the acid catalyst, to the quantity of
formaldehyde corresponds to a molar ratio of aromatic amine
to formaldehyde of from 4:1 to 20:1, preferably from 8:1 to
20:1, and at the most half of the total quantity of aromatic
amine is used in the first stage, which leads to the formation
of aminal. ~his means that at least half the total quantity
of aromatic amine is used in the second reaction step.
The aminal obtained in the first stage of the
reaction, or its solution in any excess aromatic am ne
present, is at a temperature of from 0 to 100C, preferably
30 to 80C before the second stage of the reaction, i.e.
before it is combined with the aromatic amine salt catalysts.
In the next stage of the process according to the
present invention, the aminal or its solution in excess
aromatic amine is combined with an aromatic amine acid
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mixture whic~- has bee~ ob-tained by partial neutralization of
a second quantity of aromatic amine with one of the acid
catalysts exemplified above.
For this partial neutrali2ation, the acid may be
used in quantities corresponding to a deyree of protonation
of from 0.1 to 10~, preferably from 0.1 to 5%, based o~ all
the amino nitrogen atoms present in the reaction mixture.
These figures should include all the amino nitrogen atoms
present, including those of the aromatic amine used in excess
for aminal formation, and those of the aromatic amine used
together with the acid. 13y "degree of protonation" is
meant the percentage of amino nitrogen atoms present in the
form of ammonium groups, i.e. of "protonated" amino nitrogen
atoms, based on the total quantity of amino nitrogen atoms.
When the partially neutralized aromatic amine is
combined with the aminal component, the former is maintained
at a temperature in the range of from 100 to 200C, preferably
from 100 to 150C.
When the two compounds have been combined, the
aminal is rearranged to the polyamine substituted in the
nucleus by heating of the reaction mixture to from 100 to
250C, preferably from 120 to 200C, for a period of from
ca. S to 300 minutes.
The choice of temperature employed for the
rearrangement reaction depends mainly on the molar ratio
of aromatic amine/catalyst employed and on the adjusted
dwell time for the rearrangement. If the molar ratio is low
and the dwell time is long, the rearrangement temperature may
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LeA 18,671
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be maintained at the lower limit of the given range of from
100 to 250C, whereas under converse conditions, high
rearrangement temperatures are to be recornmended, especially
if the aromatic amine/catalyst molar ratio is high. The temper-
S ature employed in the process according to the presentinvention is generally from 120 to 200C at atmospheric or
excess pressure.
The process according to the present invention may,
of course, be carried out either continuously or intermittently,
and known apparatus may be used in both cases. The continuous
process may, for example, be carried out as follows:
Measured and regulated streams of aromatic amine
and aqueous formaldehyde solution (formalin) are converted
into the ~-substituted aminal in a continuously operated
reactor within the above-mentioned temperature range. The
heat liberated in the reaction may either be left in the
reaction mixture or removed by a heat exchange process.
The resulting two phase reaction mixture is separated in
a continuously operated phase separator. The upper, aqueous
phase is transferred to an apparatus for working up the
effluent. The lower, organic phase is combined with a
measured and regulated stream of an aromatic amine/hydro-
chloric acid mixture in another continuously operated
reactor, said aromatic amine/hydrochloric acid rnixture
conforming to the particulars given above in its cornposition
and temperature. The rearrangement reaction is subsequently
carried out in several reactors arranged in series maintained
at a temperature within the range mentioned above for the
rearrangement reaction. Any water or azeotropic mixture of
water/aromatic amine evaporating at a temperature above 100('
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is transferred to the reactor for aminal formation or to the
separator following this reactor. The usual working up of
the reaction mixture then takes place. This consists mainly
of neutralization of the catalyst and isolation of the
products of the process by distillation.
The products obtained by the process according to
the present invention may be reacted with phosgene to produce
isocyanates by known methods. The products obtained by the
present process are also suitable for use as cross-linking
agents for epoxides or for modified i~socyanates.
The following examples illustrate the present
invention. Both the hydrochloric acid and the formalin
are used as 30% aqueous solutions.
EXAMPLES
EXAMPLE 1 (comparison)
558 g (6 mol) of aniline and 200 g (2 mol) of
formalin are mixed together with stirring at room temperature.
The temperature rises to 65C. Stirring is continued for
30 minutes at 65C, and the phases are separated at 65C.
The organic phase is introduced into a mixture of 1302 g
(14 mol) of aniline and 40.6 g (0.33 mol) of hydrochloric
acid which has been pre-heated to 40C. The mixture is
heated to boiling and kept under reflux at 128C for 4 hours.
It is then neutralized with 350 ml of 6% sodium hydroxide
solution. The separated organic phase is heated in a water
jet vacuum to a head temperature of 220C. The distillation
residue constitutes the product of the process. It contains
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89.1~ of diamines. The distribution of isomers determined
using gas chromatography is shown in the table.
EX~MPLE 2 (comparison)
The procedure is the same as in Example 1, except
that the aniline/hydrochloric acid mixture is not pre-heated
to 40C but to 80C. The analysis is shown in the table.
EXAMPLE 3
The procedure is the same as in Example 1, except
that the aniline/hydroc~loric acid mixture is not pre-heated
to 40C but to 120C. The analysis is shown in the table.
EXAMPLES 4 - 9
The procedure is analogous to that described in
Example 1. The analyses are shown in the table. As is
evidenced by Examples 7 and 8, pre-heating the aniline/
hydrochloric acid mixture in accordance with the instant
invention to at least 100C increases the yield of ortho
isomers.
XAMPLE 10
The procedure is analogous to that described in
Example 1, and is carried out in accordance with the
particulars given in the table, except that the reflux
temperature of the acid reaction mixture is raised to 180C
by distilling off water. After 60 minutes at 180C, the
subse~uent procedure is the same as that described in
Example 1. The analyses are shown in the table.
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113751~
EXAMPLES 11 - 12
__
The procedure is similar to that described in
Example 10, but the boiling point of the acid reaction
mixture is raised to 185C by removal of water by distilla-
tion. This temperature is then maintained for 90 minutesand 180 minutes, respectively. The analyses are shown in
the table.
LeA 18,671
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LeA 18,671
