New process for isophoronediamine synthesis

M. Guisnet et al. (Editors),Heterogeneous Catalysis and Fine Chemicals III 0 1993 Elsevier Science Publishers B.V. All rights reserved.

321

New process for isophoronediamine synthesis

J.Ph.Gillet ; J.Kervennal ; M.Pralus

Elf Atochem - centre de recherche Rhbne-Alpes, rue Henri Moissan - B.P. 63, 69493 Pierre-Bbnite Cedex. France. ABSTRACT A new process for synthesis of 3-aminomethyl-3,5,5-trimethylcyclohexylamine (IPDA) has been investigated. The reaction was performed in two steps. In the first step bis (3-cyano-3,5,5 trimethylcyclohexylidene) azine (IPNA) was synthesized from 3-cyano-3,5,5 trimethyl- 1 0x0 cyclohexane (IPN) and hydrazine hydrate in solvent. The reaction yield was nearly quantitative. In the second step the azine (IPNA) was hydrogenated under mild conditions on a Raney nickel or cobalt catalyst in the presence of a small amount of ammonia. lsophorone diamine (IPDA) was obtained at high yields (90-95 %). But the main interest of a such process is to minimize the production of byproducts (aminoalcohol, azabicyclic compound, secondary amine) and to use less severe pressure conditions than those generally employed.

1. INTRODUCTION At the present time isophorone diamine (IPDA) is experiencing a good expansion in its traditional markets such as polyurethanes, paints and varnishes. For this reason a real interest has been shown in the synthesis of IPDA. Until now, this compound was synthesized by aminoreduction of isophoronenitrile (IPN).

Until the beginning of the eighties, the hydrogenation was carried out under severe temperatures (120"-150°C) and pressures (150-270bar) (ref.1,2). Over the last ten years, these conditions have been constantly improved. In 1987, Daicel patented a process operating at 120°C and 70bar to loobar, but the yield was only 89 % (ref.3). More recently, Union Carbide described a process using Raney cobalt, doped or not with chromium. The best yields (about 90 %) were obtained under a pressure of 80bar and at a temperature of 100"-120°C. But this process still generated several byproducts. (ref.4,5).

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More recently, BASF patented a new two step process which minimized the byproduction of aminoalcohol (ref.6). The first step consisted in synthesizing the intermediate imine with acid catalyst and the second one in hydrogenating the latter, without intermediate isolation. The announced yields were 95 to 97 % and impurities decreased but the condiiions remained very severe (12O0C-250bar).To conclude, it did not seem possible to minimize the rate of impurities by operating under mild conditions and with yields better than 90 %. The main cause of byproduct generation is the hydrogenation of the ketone, giving aminoalcohol, separable with difficulty from isophoronediamine.

\

CN

L

'CN

1

cn2Nn2

So we looked for a reaction blocking the carbonyl group to avoid the side reactions and it was the reason why we investigated a new process passing through the azine formation. 2. RESULTS AND DISCUSSION

This new process involves two consecutive reactions. k i n e synthesis :

IPDA synthesis :

We tried a one pot reaction but it failed. The main reason being the unstability of hydrazine in the presence of catalysts such as cobalt or nickel. We noticed a large decomposition which prevents azine formation and subsequently the IPDA yield was very low (10-30 %). So, only a two step process was available.

323

2.1. k i n e synthesis The reaction between a carbonyl group and hydrazine is a classical reaction but in this case we obtained a bis(3-cyano-3,5,5-trimethylcyclohexylidene)azine which was a new product. The preferred hydrazine source was hydrazine hydrate since it is an industrial product easy to use. In order to obtain an industrially viable process different parameters of the reaction have been optimized. - catalyst influence : It is well known that the addition of acid greatly enhances the rate and yield in azine synthesis. In our case, we chose formic acid as catalyst due to its acidity and miscibility in the organic medium. Formic acid was used at a 2 % molar ratio vs. IPN. - solvent influence : The reaction can be conducted in miscellaneous solvents like xylene or alcohols. Nevertheless, polar solvents like alcohols are preferred. There were no great differences in selectivity between C1 to C4 alcohols but we preferred methanol for several reasons. The main one was the homogeneous medium and the good solubility of IPN at the reaction temperature. In addition, at room temperature, isophoronenitrile azine (IPNA) precipitated and the white crystals produced were easily recovered by filtration (isolated yield 96 YO vs.97,9 % for the reaction yield). By comparison, in xylene medium, aqueous hydrazine was not completely miscible and isophoronenitrile azine was partially soluble. Thereby the yield of the isolated product was only 76 % vs. 92,6 % for the reaction yield. - Reaction time : Good conversions and selectivities were obtained after two hours, with methanol as solvent and formic acid as catalyst. Below this time we observed traces of unconverted isophoronenitrile and especially hydrazone which precipitated with the isophoronenitrile azine. 2.2. IPDA synthesis : In the second step the intermediate was submitted to hydrogenation and isophoronediamine (IPDA) was obtained according to the global reaction below.

The main arameters of the reaction were optimized at the laboratc I with Raney nickel as catalyst (10 wt %). Firstly, we chose methanol as solvent because it is the most convenient solvent in azine synthesis while being efficient for hydrogen solubility. In addition there were no great differences in selectivity and yield compared with other solvents like upper alcohols and xylene. Moreover it can be easily recovered at the end of the reaction. Temperature and pressure were optimized and the best results were obtained with a temperature of 150°C and a pressure of 60bar. This temperature is a good compromise allowing a normal hydrogenation rate without loss of selectivity. Higher temperatures affect the selectivity. We observed formation of methylated IPDA (mono and di) and some other unknown products. If we operated below 100°C the reaction did not occur. The pressure was also chosen as low as possible to obtain a good selectivity in IPDA. Another point is the use of ammonia during this step. As it

324

is well known, ammonia is required to promote primary amine formation during nitrile or imine hydrogenation. We found that the lowest suitable NHdazine molar ratio was about 8. Below this value, selectivity in IPDA decreased and with lower ratio or without ammonia we observed secondary amine formation. This phenomenon was also noticed with Raney or supported cobalt catalysts. The main parameter was the choice of the catalyst. Generally catalysts such as Raney nickel or cobalt are convenient for hydrogenation of nitrite groups and are able to cleave the N-N bond of hydrazine by hydrogenolysis. We tested different catalysts under various forms.The main results are indexed in table I . Table 1 : influence of catalyst solvent : MeOH ; H, pressure : 60bar Catalyst

Temperature

"C

Raney Ni Raney Co PdlC RulC

Azine conversion

Selectivity

%

150

% 95 96 494 45

100 100 96,6 87

I,

115 130

IPDA yield %

95 96 42 39

The best selectivity in IPDA was obtained with Raney cobalt or nickel but the supported forms were also suitable. Noble metals like palladium or ruthenium failed in this case. H, consumption is lower with Pd and we found unconverted azine (IPNA).

0

CO raney Pd/C

*- . I

0

50

100

150

200

250

300

350

TlME (MN)

Figure 1. H, consumption in fonction of time and catalyst exp. conditions : azine : 123 mmol ; MeOH : 400 cm3 ; NH, : 984 mmol a) Ni or Co : 8 g (wet) ; 8 : 150°C ; P: 60 bar b) PdlC (5 %) : 2 g ; 8 : 115°C ; P:GObar

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Finally, Raney nickel was preferred to cobalt due to its industrial availability and relatively low cost. But for a better optimisation of this process we studied the hydrogenation in detail.

2.3. Hydrogenation mechanism The results were obtained by continuous analysis of the hydrogenation medium. The reaction was performed in a 1 I autoclave equipped with a magnetically driven stirrer at a speed of about 1000 r/m. Samples were periodically withdrawn through a decanter tube from the bottom of the reactor. The main products were analysed by gas chromatography coupled with mass spectroscopy, NMR and infrared spectroscopy. At the beginning of the hydrogenation, isophoronenitrile azine (IPNA) is quickly converted to the azine with hydrogenation of the nitrile groups. This diamine exists in two isomeric forms (X3, X4) (ciso’ide or transoide). These two isomers are further hydrogenated and give IPDA. The intermediate hydrazine is not observed. The hydrogenation rates of X, and X, are different. Four or five hours were necessary to obtain the complete conversion of this intermediate diamine. All these obervations led to the following mechanism :

/D=N-N4 \C N

CN CN

CN

,

CH2NH2

r

i

J pp ZH2

NH-NH

CH2NH2

Figure 2 : hydrogenation mechanism

C

‘

H 2N H 2

CHzNH2

]

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We can also compare the effect of Raney nickel and cobalt in this hydrogenation (fig. 3,4)

0

Figure 3.

RANEY Ni

l4

50

100

150

200

T

0

250

300

TIME (mn)

I

50

100

150

200

300

TIME (mn)

Figure 4.

RANEY Co

lsophoronenitrile azine is quickly converted to partially hydrogenated azines (X, and X,) during the first hour. The hydrogenation rate is faster with cobalt, that is confirmed by H, consumption. Moreover we observed only one isomeric form of the intermediate diamine with Raney cobalt. As we previously described, we can see a different behaviour between these 2 intermediates. For one of them (at the present time we are unable to distinguish between cisoi'de and transoi'de) hydrogenation rate is low. Another characteristic of this process relates to IPDA isomeric composition. Usually by reductive amination of isophoronenitrile, the isomeric ratio cisltrans is about 80120 but in our case the proportion of trans isomer increased considerably to reach a ratio of 50/50 to 44/56, depending on the nature of the catalyst (table 2).

327

cis

80 493 44

1

1

trans 20

50,5 56

1

I

process

1 commercial IPDA

azine way (cobalt) azine way (nickel)

Another interesting point is the low coproduction of impurities. Nevertheless we observed the formation of small amounts of low boiling points products (X,,X2) compared with IPDA. After analytical characterisation we assigned to the most important of them the azabicyclic (1,3,3-trimethyl-6-azabicyclo[3,2,1]octane) structure. In anhydrous conditions as in our case, byproduction of aminoalcohol is minimized. On the other hand, when water is present the proportion of aminoalcohol increases. These observations can be explained by the following mechanism.

+

C H ~ N .-.* HZ

CH2NH2

i CH2NH2

& OH

Figure 5

Conclusion :

CH2NH2

This reaction through formation of an azine opens a new route to primary amines from ketones and presents several real interests. In case of IPDA, the global yield is about 93 % and for the first time byproduction of impurities is lowered while using mild conditions. The most convenient catalyst for the hydrogenation step is a simple Raney nickel contrary to the classical process which often uses more sophisticated catalysts.

328 3. EXPERIMENTAL

Before use, isophoronenitrile (IPN) was recrystallized from diisopropylether MP:7O0C. a) typical procedure for bis(3-cyano-3,5,5-trimethyl cyclohexylidene) azine synthesis : The reaction was performed in a 500 cm3 glass reactor fitted with stirrer and condenser. 150 g of methanol and 82,5 g (0,5M) of isophorone nitrile (IPN) were placed into the reactor. While stirring the mixture, the catalyst was added : 0,53 g (1,15-10-2M) of formic acid dissolved in 8 g of water. Then 12,5 g (0,25M) of hydrazine hydrate were fed through the dropping funnel at room temperature under stirring, over a 1Omn period. The homogeneous mixture was heated at reflux for 2 hours. After cooling the suspension was filtered to remove azine. The crude product was washed with cold methanol and dried. The yield was 98 % (purity 99 %). IR :

MP : 191"-193'C 6 :(C=N) : 1641 cm-1 6 : (C=N) : 2234cm-1 13C and 1H NMR were in accordance with the structure. b) Hydrogenationof bis (3-cyano-3,5,5-trimethylcyclohexylidene) azine : The reaction was performed in a 1 I autoclave. 40 g (0,123M) isophorone nitrile azine were placed into the reactor with 400 cm3 methanol and 8 g Raney nickel (solvent wet weigh!). The apparatus was purged of air by nitrogen. Liquid ammonia was introduced 16,7 g (0,98M) at room temperature. The reactor was then heated to 150°C under gentle stirring. When the reaction temperature was reached, stirring was stopped and hydrogen was introduced until a total pressure of 60bar. Stirring was restarted and the reaction began immediatly. Hydrogen uptake under the above mentioned conditions ended after 4 or 5 hours. The mixture was filtered and solvent removed. The yield in IPDA was about 95 % (GC with internal standart).

REFERENCES 1 A.Sommer, R.Bruecker, Ger.Patent No.3 011 656 (1981) 2 J.Disteldorf, W.Huebel, L.Broschinski, Ger-PatentN0.3 021 955 (1981) 3 Y.Hirako, J.P.Patent No 62 123 154 (1987) 4 B.D. Dombeck, T.T.Wenze1, Eur.Patent No 394 968 (1990) 5 B.D.Dombeck, T.T.Wenzel, Eur.Patent No 394 967 (1990) 6 F.Merger, C.U.Priester, T.Witzel, G.Koppenhoeffer, W.Harder, Eur.Patent No 449 089 (1991)