Method for preparing cycloaliphatic diamines from aromatic diamines

This invention relates to a method for preparing cycloaliphatic diamines by hydrogenating aromatic diamines in the presence of a supported ruthenium catalyst and a metal nitrite as a catalyst promoter to increase the rate of the hydrogenation reaction and decrease the amount of higher boiler by-products.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a preparation method of cycloaliphatic 
diamine by the hydrogenation of aromatic diamine in the presence of a 
ruthenium catalyst and a metal nitrite (MNO.sub.2) as a catalyst promoter. 
2. Description of the Related Art 
A polyurethane is a polymer having a carbamate group (--NHCOO--), and is 
prepared by reacting diisocyanate and polyol such as ethylene glycol. The 
properties of the polyurethane depend on its raw materials or its 
preparation method, and especially, the structure of a diamine which is a 
starting material of the diisocyanate. Urethane polymers derived from 
aromatic diisocyanates undergo slow oxidation in the presence of air and 
light, causing a discoloration which is unacceptable in some applications. 
However, urethane prepared from cycloaliphatic diamine is stable against 
light and air, as well as structurally flexible, which has better 
properties compared with urethane prepared from aromatic diamines. 
There are substantial literature in the art with respect to the 
hydrogenation of aromatic amines, especially, methylenedianiline to 
produce bis(4-aminocyclohexyl)methane, or 1,2-, 1,3-, 1,4-phenylenediamine 
to produce corresponding cyclohexane diamine. U.S. Pat. No. 2,511,028 and 
U.S. Pat. No. 2,606,924 disclose a method of preparing 
bis(4-aminocyclohexyl)methane from methylene dianiline under a pressure of 
200-1,000 psig and at a temperature of 80-270.degree. C. in the presence 
of a noble metal such as ruthenium, rhodium, iridium or mixture thereof or 
with platinum or palladium, either as a hydroxide, oxide, or the metal 
itself on an insert support. 
U.S. Pat. No. 3,636,108, U.S. Pat. No. 3,697,449 disclose a hydrogenation 
of an aromatic diamine using a ruthenium impregnated upon a support, 
wherein the activity and efficiency of the catalyst is increased by 
treating the catalyst and support with an alkali metal hydroxide or 
alkoxide. According to these disclosures, such alkali moderation of the 
catalyst could be effected prior to hydrogenation or in situ during the 
hydrogenation. They also describe that formation of tars, decomposition 
products and/or condensation products formed during the hydrogenation can 
be reduced and that catalyst can be used repeatedly without catalyst 
regeneration if the catalyst used is a supported ruthenium catalyst which 
has been alkali-moderated. 
U.S. Pat. No. 3,591,635 and U.S. Pat. No. 3,856,862 disclose a method for 
hydrogenating an aromatic diamine by pretreating rhodium with NH.sub.4 OH 
or in the presence of ammonia. It has been known that, in the early 
experiment of the hydrogenation of an aniline, ammonia suppressed the 
formation of by-products, but deactivated the catalyst. It has been 
reported that similar phenomenon also occurs in the presence of an alkali 
alkoxide or alkali hydroxide such as LiOH or NaOH. 
Further, U.S. Pat. No. 4,946,998 and U.S. Pat. No. 5,214,212 disclose a 
method for the hydrogenation of an aromatic diamine using a supported 
ruthenium catalyst modified by NaOH or FeSO.sub.4.7H.sub.2 O under a high 
pressure and high temperature. 
U.S. Pat. No. 4,448,995 discloses that the hydrogenation reaction should be 
carried out in an anhydrous state or at least maintained so that water 
concentration is less than 0.5% by weight to reduce the amount of 
N-alkylated and higher boiler by-products. In addition, the patent states 
that lithium salts reduce by-products. However, U.S. Pat. No. 4,946,998 
reported that the presence of LiOH increases the production of high 
molecular weight products. 
However, these conventional methods described above are not adequate for 
industrial processes due to low yields and the requirement of a corrosive 
base. 
Therefore, the present invention is directed to provide a method of 
preparing cyclodiamine compound by hydrogenating aromatic diamine in the 
presence of a ruthenium catalyst and metal nitrite. By this invention, the 
hydrogenation reaction time is significantly shortened and the formation 
of by-products are greatly suppressed. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention relates to a method of preparing a cycloaliphatic 
diamine by hydrogenating an aromatic diamine compound in the presence of a 
ruthenium catalyst and a metal nitrite (MNO.sub.2) as a catalyst promoter, 
and under a pressure of about 300 to 4,000 psig and at a temperature of 
about 50 to 250.degree. C. 
Aromatic diamines of the present invention are represented by the general 
formula (I) as follows: 
##STR1## 
wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are H or alkyl 
group having 1 to 6 carbon atoms, respectively. Examples of amines are 
1,2-, 1,3- or 1,4-phenylenediamine, 2,4- or 2,6-toluenediamine, 
1-methyl-3,5-diethyl-2,4 or 2,6-diaminobenzene, diisopropyl toluene 
diamine, tert-butyl-2,4 or 2,6-toluene diamine, xylene diamine, mesitylene 
diamine and alkyl derivatives thereof, etc. 
Alternatively, a compound having a general formula (II) as follows can be 
used: 
##STR2## 
wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 are H or 
alkyl group having 1 to 6 carbon atoms, respectively, and n=0 or 1. 
Examples of bridged amines are methylenedianiline, 
bis(4-amino-2-methylphenyl)methane, O-tolidine, and a secondary or 
tertiary amine derivatives thereof, etc. 
A ruthenium catalyst of the present invention is supported upon an inert 
carrier. The representative carriers include activated charcoal (C), 
calcium carbonate (CaCO.sub.3), ceria (CeO.sub.2), alumina (Al.sub.2 
O.sub.3), zirconia (ZrO.sub.2), titania (TiO.sub.2) and silica 
(SiO.sub.2). The activated charcoal is the most preferred carrier. The 
amount of the ruthenium catalyst used is in the range of about 0.05 to 20% 
by weight based on the starting diamine, and the ruthenium loading on the 
carrier is about 0.5 to 20% by weight. However, in the consideration of 
reactivity and economical aspect, the most preferred range of the catalyst 
amount and the ruthenium loading are 0.1 to 5% and 1 to 10% by weight, 
respectively. 
A metal nitrite which is used as a catalyst promoter in the present 
invention is selected from the group comprising of barium nitrite 
[Ba(NO.sub.2)], sodium nitrite (NaNO.sub.2), potassium nitrite (KNO.sub.2) 
and silver nitrite (AgNO.sub.2). The most preferred is NaNO.sub.2. The 
effective amount of the metal nitrite used is in the range from about 1 to 
50 times of ruthenium, and preferably about 5 to 20 times. 
The present invention may be carried out at any suitable pressure, 
preferably from about 300 to 4,000 psig. However, considering the 
equipment and operating cost, it is preferable to operate a reaction at a 
pressure of 500 to 2,000 psig. 
The reaction temperature used for the hydrogenation process range from 
about 50 to 250.degree. C., preferably from about 100 to 200.degree. C. 
The reaction of the present invention may be carried out in the presence of 
a solvent. Useful solvents include ethers such as diethylether and 
isopropylether; alcohols such as methanol, ethanol, isopropyl alcohol and 
butanol, etc.; and cycloethers such as tetrahydrofuran (THF) and dioxane. 
The most preffered solvent are isopropyl alcohol or n-butanol. The amount 
of solvent is about 50 to 10,000% by weight based on the amount of 
diamine, preferably from about 500 to 3,000% by weight. 
The hydrogenation of the present invention may be carried out either in a 
batch or in a continuous process followed by observing the amount of 
hydrogen taken up by the reaction mixture. The reaction is considered to 
be terminated when the theoretical amount of hydrogen has been consumed. 
In general, the hydrogenation time ranges from about 20 to 120 minutes. 
The longer reaction times at the higher temperatures generally cause an 
increase in the unwanted by-products.

The invention will be described further in the following examples. These 
examples are intended for illustrative purposes, and are not intended to 
limit the scope of the present invention. 
EXAMPLE 1 
5% Ru/C 1 g (0.5 mmol atom of Ru) and NaNO.sub.2 0.34 g (5 mmol), isopropyl 
alcohol 25 mL and 1,4-phenylene diamine 5.4 g (50 mmol) were added to a 
high pressure reactor. The reactor was then sealed and pressurized to 800 
psig and heated to 140.degree. C. After reacting for 20 minutes at 
140.degree. C., it was cooled to room temperature and then the product was 
isolated. Analysis of the product, i.e. 1,4-cyclohexane diamine, using a 
GC and HPLC revealed that the conversion of 1,4-phenylene diamine was 
98.3% and the selectivity was 97.5%. 
EXAMPLES 2-7 
Using various catalyst promoters and changing the amount thereof, 
experiments were carried out in the same manner as described in Example 1. 
The results are shown in Table 1. 
TABLE 1 
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amount of promoter 
conversion 
selectivity 
example promoter (mmol) (%) (%) 
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2 -- -- 75.3 84.3 
3 Ba(NO.sub.2).sub.2 5 85.7 93.1 
4 NaNO.sub.2 3 81.5 91.4 
5 NaNO.sub.2 10 97.2 98.6 
6 KNO.sub.2 5 89.3 95.1 
7 AgNO.sub.2 5 80.8 93 
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EXAMPLES 8-13 
Using various reactants, experiments were carried out in the same manner as 
desribed in Example 1. The results are shown in Table 2. 
TABLE 2 
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time conversion 
selectivity 
example reactant product (min) (%) (%) 
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8 1,3-phenylene 
1,3-cyclo- 20 96.5 96.5 
diamine hexane diamine 
9 2,4-toluene 1,3-diamino-4- 40 95.3 98.7 
diamine methyl 
cyclohexane 
10 4,5-diamino-O- 1,2-diamino-4, 40 92.1 98.4 
xylene 5-dimethyl 
cyclohexane 
11 bis(4-amino- bis(4-amino- 20 99.8 95.3 
phenyl) cyclohexyl) 
methane methane 
12 bis(4-amino-2- bis(4-amino-2- 30 97.2 92.1 
methyl phenyl) methyl cyclo- 
methane hexyl) methane 
13 N,N'-dimethyl- N,N'-dimethyl- 30 92.5 96.5 
1,4-phenylene 1,4-diamino 
diamine cyclohexane 
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EXAMPLES 14-20 
Using various support and changing the amount thereof, experiments were 
carried out in the same manner as described in Example 1. The results are 
shown in Table 3. 
TABLE 3 
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Ru impregnated 
conversion 
example support amount (wt %) (%) 
______________________________________ 
14 activated charcoal 
1 42.5 
15 activated charcoal 10 100 
16 alumina 3 61.7 
17 alumina 5 89.4 
18 titania 5 51.2 
19 silica 5 73.7 
20 ceria 5 53.8 
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EXAMPLES 21-26 
Using various solvents, experiments were carried out in the same manner as 
described in Example 1. The results are shown in Table 4. 
TABLE 4 
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conversion 
selectivity 
example solvent (%) (%) 
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21 methanol 93.1 68.5 
22 ethanol 95.3 73.4 
23 diethylether 47.2 85.7 
24 THF 58.1 83.4 
25 dioxane 37.9 81.6 
26 n-butanol 90.3 96.5 
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EXAMPLES 27-31 
Under various pressures and temperatures, experiments were carried out in 
the same manner as described in Example 1. The results are shown in Table 
5. 
TABLE 5 
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temperature 
pressure conversion 
selectivity 
example (.degree. C.) (psig) (%) (%) 
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27 100 1000 23.7 72.1 
28 120 1000 67.1 83.7 
29 140 500 90.4 96.7 
30 140 2000 99.5 92.8 
31 200 800 100 81.6 
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Although the preferred embodiments of the present invention have been 
disclosed for illustrative purposes, those skilled in the art will 
appreciate that various modifications, additions and substitutions are 
possible, without departing from the scope and spirit of the invention as 
recited in the accompanying claims.