Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PROCESS FOR THE CATALYTIC HYDROGENATION
OF DI (4-AMINOPHENYL) METHANE
BACKGROUND OF THE INVENTION
In the production of di(4-aminocyclohexyl)methane
5 by the catalytic hydrogenation of di(4-aminophenyl)
methane, essentially three stereoisomers are produced:
H ~ ~ H
H2N CH2 NH2
CIS CIS
H ~ H ~ y ~'~2
CIS TRANS
H CH~ ~ X
TRANS TRANS
It is known in the art that in order to produce a
corresponding isocyanate ~via the known phosgenation
process) which is liquid and storage stable at room tem-
perature (i.e. from 20C to 25C), the mixture of amine
20 stereoisomers used for phosgenation must contain the
trans, trans stereoisomer in relatively minor amounts
(typically from 15 to 40 percent by weight and prefer-
ably from 18.5 to 23.5% by weight). Numerous techniques
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are known in the art for the production of amine mixtures
containing the requisite amount of the trans, trans iso-
mer. Typical of these known techniques are those de-
sc~ibed in U.S. Patent Nos. 3,153,088; 3,155,724;
5 3,393,236; 3,644r522; 3,711,550; and 3,766,272. These
known processes generally require the separation of an
amine mixture containing the requisite amount of the
trans, trans isomer from an amine mixture formed after
hydrogenation and containing around 50~ by weight of the
10 trans, trans isomer Processes are known in the art for
the produ~tion of an amine mixture containing the
requisite amount of the trans, trans isomer directly from
di(4-aminophenyl)methane without the need for an inter-
mediate separation step (see, e.g., U.S. 2,606,928).
15 However, the rates of reaction are much too slow for
commercial applications.
The catalytic hydrogena~ion of di(4-aminophenyl)
methane to di(4-aminocyclohexyl)methane most commonly
used in the art involved the use of supported and un-
20 supported ruthenium catalysts. Typical of these proces-
ses are those disclosed in U.S. Patents 2,494,563,
2,606,924; 2,606,928; 2,606,925; 3,347,917; 3,676,495;
3,959,374; 3,743,677; 3,914,307; 3,825,586; 3,636,108;
and 4,161,492. While some of these processes yield an
25 amine mixture containing the trans, trans isomer in an
amount necessary to allow for the production of liquid,
storage stable isocyanates, the rates of reaction are
much too slow for commercial use.
The use of supported rhodium catalyst in the hy-
30 drogenation of di(~-aminophenyl)methane is also known
~see e.g. U.S. Patent 3,591,635 and 3,856,862). How-
ver, because these processes utilize relatively mild
reaction conditions, large amounts of catalyst and
long reaction times are necessary.
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DESCRIPTION OF THE INVENTION
The present invention is directed to the discovery
that a liquid di(4-aminocyclohexyl) methane containing
from 15 to 40% and pre~-rably from 18.5 to 23.5% by
5 weight of the trans, trans isomer can be produced direct-
ly from di~4-aminophenyl)methane by using a supported
rhodium catalyst and by using specific process conditions.
The specific conditions necessary are that the hydrogen
pressure be maintained at at least 500 psi, and prefer-
10 ably from 2000 to 8000 and more preferably at from 2000to 4000 psi and that the temperature be maintained at
from 196 to 235C, and preferably from 200 to 225C,
and more preferably from 205 to 219C during the hydro-
genation.
The catalyst employed in the process of the inven-
tion is one containing elemental rhodium supported on
any of the carriers converltionally employed for this
purpose in preparing hydrogenation catalysts. Examples
of such carriers are alumina, carbon, kieselguhr, bento-
20 nite, asbestos, silica gel, zirconium oxide and the
like. The preferred carrier employed in the process
of the invention is alumina. The amount of elemental
rhodium present in the catalyst employed in the process
of the invention can ~ary from about 0.5% to about 20%
25 by weight but is preferably within the range of about 1
to about 10% by weight. Most preferably, the amount
of elemental rhodium present in the catalyst is
within the range of about 1 percent to about 5 percent
by ~eight.
The supported rhodium catalyst employed in the
process of the invention can be prepared in accordance
with procedures well-known in the art. For example a
suspension of desired carrier in an aqueous solution
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of a soluble rhodium salt, such as rhodium chloride tri-
hydrate, is treated with base to deposit the rhodium
hydroxide on the support. When this is shaken in an
atmosphere of hydrogen, the rhodium salt is reduced to
S the elemental state o~ the carrier. The preparation
of the catalyst in this manner can be carried out as a
separate operation or can be incorporated as a prelim--
inary step in the process of the invention. For example,
the catalyst can be prepared in the above manner in the
10 hydrogenation vessel to be used in the process of the
invention and said catalyst then merely requires washing
with water prior to addition of the charge to be hydro-
genated.
Alternatively, since many of the supported rhodium
- 15 catalysts employed in the process of the invention are
readily available, in prepared form, from commercial
sources the actual preparation of the catalyst as a
preliminary step in the process can be avoided if
desired. In fact, the presently preferred catalyst is a
20 commercially available catalyst available from Engelhard
(5~ rhodium on an alumina carrier). Also, preferred
are the supported rhodium catalysts available from
Johnson-Matthey
In conducting th~ process of the invention, the
25 procedures commonly use~ in the art are employed, the
only requirements being the pressure and temperature
conditions noted above. The hydrogenation is pre-
ferably carried out in the presence of an inert
solvent, i.e. a solvent which does not substantially
30 interfere with the desired course of hydrogenation.
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Useful solvents include ethers such as butyl ether
or isopropyl ether; cyclohexane or other al~hatic
hydrocarbons; alcohols such as butyl alcohol, methanol,
ethanol, isopropanol, prop,lnol and the like; an~ cyclic
5 ethers such as tetrahydrofuran, dioxane, and the like.
The amount of solvent used can range from 0 to 95~ by
weight based on the amount of amine and solvent.
Preferably the amount of solven~ used is such that the
concentration of starting diamine in the reaction mixture
10 is from about 5% to a~out 50% by weight. The presently
preferred solvent is n-butyl ether.
The catalyst is suspended in a solution of the
starting diamine and the re~ultin~ suspension is sub-
jected to hydrogenation in an appropriate hydro~enation
15 vessel. The amount of catalyst employed is such that
the amount of rhodium present in the reaction mixture is
at least 0.005% by weight based on the starting diamine.
Preferably the amount used is such that the rhodium
content is within the range of about 0.01 to about 3% by
20 weight based on the amount of starting diamine present
in the reaction mixture. Most preferably the quantity
of catalyst employed is such that the amount of
rhodium present in the reaction mixture is within the
range of about 0.02 to about 2% by weight based on the
25 amount of starting diamine employed. As noted above,
the rhodium should be present in an amount of at least
0.005%. The upper limit is generally dictated by the
cost of the catalyst.
The hydrogenation is conducted at a temperdture
30 within the range of about 196C to about 235C, prefer-
ably from 200 to about 225C and most preferably within
the range of from about 205 to about 219C. The exact
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choice of temperature in any given instance ~s a
function of the reaction rate an~ trans, trans content
desired. In general, the higher the temperature, the
faster the reaction and the higher the trans, trans con-
5 tent of the final product. Thus the temperature will
, generally be selected to yield the optimum balance
';~ between the reaction time and trans, trans content.
The hydrogen pressure employed in the process of
the invention must be maintained at at least 500 psi and
10 generally will be within the range of 2000 to 4000 psi.
Of course, the pressures used are dependent on the
equipment used. Thus pressures of from 500 to 8000 psi
and higher can be used if suitable high pressure equipment
is availab~e. In general it has been found that the
' 15 yield will increase with increasing pressure~ However,
it has also been found that the trans, trans content
of the product decreases as the pressure increases.
The progress of the hydrogenation is followed
readily by observation of the amount of hydrogen ta~en
20 up by the reaction mixture'and the hydrogenation is
terminated at the point at which the theoretical quantity
of hydrogen has been absorbed. The catalyst is then
separated from the solution of reduced material and the
,latter is distilled to lsolate the di(4-aminocyclohexyl)
25 methane therefrom. In qeneral, the hydrogenation times
range from about 10 minutes to about 60 minutes.
Although no~ necessary to obtaining the results
of the present invention, if desired, ammonia can also be
used as described in U~S. Patents 3,591,635 and
30 3,856,862.
In general, the materials are mixed and added to
the reactor in a batch process, but of course, a
continuous process could also be used.
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In general, the improvements of the present
invention over prior art processes are a higher yield
process Eor providing a product having the desired
isomer content using commercially feasibly amounts of
5 rhodium catalyst at commercially feasible rates of hydro-
genation. The invention is further illustrated, but is
not intended to be limited by the following examples
in which all parts and percentages are by weight unless
otherwise specified.
EXAMPLES 1 through 13
In the examples which follow, the following general
procedure was followed:
~ n autoclave is loaded with an Engelhard rhodium-
on-alumina catalyst (containing 5~ rhodium)in the amount
15 noted, 200 parts of n-butyl ether and 200 parts of di(4-
aminophenyl) methane and sealed. The autoclave was
pressurized to about ~000 psi of hydrogen ~t room temper-
ature and the contents heated to the temperature noted in
Table I. Hydrogen consumption begins at 190-196C.
20 Cooling was used to prevent overshooting the desired
temperature. The reaction was maintained at the specified
temperature 30 to 40 minutes after hydrogen consumption
stops. The contents of the autoclave were removed at
room temperature and vacuum filtered. In contrast to
25 Examples 1 through 10 and 12 thru 15, in Example 11, the
pressure was maintained at 4000 psi throughout the re-
action time. The products were then analy~ed for trans,
trans content. Yields were determined for those
examples indicated. The results obtained were as
30 set forth in Table I.
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