PROCESS FOR THE PREPARATION OF 5H-DIBENZO-(B, F)-AZEPINE

Abstract: The invention refers to a new process for the preparation of a valuable intermediate, 5H-Dibenzo-(b, f)-azepine or iminostilbene by catalytic dehydrogenation of lO,ll-­ Dihydro-5H-dibenzo-(b, f)-azepine or iminodibenzyl in liquid phase in one step in the presence of hydrogen acceptor. Dimethylaniline or diphenylether may be used as a solvent and as catalyst, nobel metal catalysts, such as platinum or palladium on activated carbon or metaloxide catalysts, such as Fe₂O₃ may be used in the dehydrogena­ tion reaction. Nitrotoluenes, dimethylmaleate or tetra­ chlorobenzochinone may be used as hydrogen acceptors. The yield of iminostilbene is 77-82°C of the theoretical.

Description: The invention relates to a new process for the preparation of 5H-Dibenzo-(b, f)-azepine, or iminostilbene of the formula (I) above. Iminostilbene is used as an intermediate for the preparation of pharmacologically valuable substances such as opipramol or carbamazepine: The iminostilbene (I), prepared according to the invention in question, has earlier been produced in another way. Iminostilbene has thus been earlier prepared from iminodibenzyl, by using conventional chemical processes, by acylation, bromination, dehydrobromination and deacylation. This method of synthesis in four steps is, however, very laborious and puts a high demand on production capacity and is therefore uneconomical. According to US Pat.No. 3.O74.93l, the iminostilbene is produced from iminodibenzyl by catalytic dehydrogenation. By this process, iminodibenzyl in gaseous phase is forced through a glass column packed with a dehydrogenation catalyst at such a high temperature as 35O-62O°C. Sulfur, selenium or noble metals such as palladium, ruthenium, iridium, rhodium or osmium, together with a support such as carbon, barium sulfate or silica gel, could act as suitable catalysts. According to the abovementioned patent, the reaction could alternatively be performed in a vessel by heating iminodibenzyl, either plain iminodibenzyl as such or together with a diluent as diphenyl, diphenyloxide or dimethylaniline at a temperature of l75-3OO°C by using one of the abovementioned catalysts. The product is isolated by fractional crystallization or chromatographically. The disadvantage on a technical scale of the first method is, however, as described in the abovementioned patent, the need for a very expensive equipment because of the high reaction temperatures. The alternative process, according to the same patent, is only shortly presented and according to this method, hydrogen acceptors, which are necessary in order to achieve a more complete reaction, are not used at all. Moreover, this process does not at all appear in the claims or in the examples of this patent, because of difficulties with the isolation of the iminostilbene from the reaction mixture. In US Pat.No. 3.449.324 a process is disclosed, in which iminostilbene is prepared by forcing iminodibenzyl in gas phase over a catalyst comprising of 35-7O% Fe₂O₃, l,5-3,O% Cr₂O₃, lO-l5% CaO and K₂CO₃ combined with a carrier substance such as carbon. The reaction temperature is about4OO-5OO°C. Gases such as for instance nitrogen, ammonia, argon, steam etc., could be used as diluents. The iminostilbene thus produced by this process is recovered from the gas phase, which is later condensed by the aid of spraying water. The above described method has, according to the inventor, the advantage, that it is possible to use cheap catalysts, while on the other hand the yield of the desired substance is only about 6O% after the first reaction cycle. Moreover, the first reaction mixture contains about l2-2O% unreacted starting material. By recycling this reaction mixture over and over again, the yield could be raised, however. The total yield varies between 55% and 8O% as calculated from the amount of the starting material. According to the German patent, DBP l.545.736, iminostilbene is produced by dehydrogenating iminodibenzyl in gas phase at high temperatures, of about 38O-62O°C in the presence of catalysts such as cobalt, nickel, vanadium, chromium, copper, molybdenum or tungsten. The above-mentioned metals could act as catalysts as such or together with supports as silica gel, aluminium oxide, silicon or asbestos. The disadvantage of this method is a very high reaction temperature, which will be very expensive as to the heat economy of the process and the equipment. At the same time undesired decomposition products are produced. According to the method described above, hydrogen acceptors are not used. With this method, about 6O% of the iminodibenzyl is transformed into iminostilbene. Thus, object of the invention is to make available a process for the preparation of iminostilbene by catalytic dehydrogenation of iminodibenzyl avoiding these disadvantages. Subject matter of the invention is a process for the preparation of 5H-Dibenzo-(b, f)-azepine, or iminostilbene of formula (I), by catalytic dehydrogenation of 10,11-Dihydro-5H-dibenzo-(b, f)-azepine or iminodibenzyl of formula (II), the dehydrogenation being performed in one step in liquid phase in the presence of a catalyst and a hydrogen acceptor at elevated temperature, characterized in that nitrotoluene is used as hydrogen acceptor and that the dehydrogenation is carried out at a temperature of 180-280°C. As catalysts preferably noble metal catalysts, such as platinum or palladium on activated carbon or metaloxide catalysts, such as Fe₂0₃ or Cr₂0₃ are used. The reaction mixture may contain an excess of the hydrogen acceptor. The preferred temperature for the dehydrogenation reaction is 210-250°C. The product is recovered by filtration after filtering off the catalyst and the filtrate is cooled. According to an embodiment of the present invention, the iminostilbene is precipitated from the reaction mixture by the aid of methanol, ethanol, iso-propanol, hexane or heptane after the catalyst has been removed. An advantage of the present invention is that the reaction is performed by the aid of the hydrogen acceptor in one step and in a liquid phase at a considerably low temperature, whereafter the recovery of the product is made simply by first filtering off the catalyst from the hot solution and, after cooling of the filtrate, by filtering the mother liquid. Any special demands on the equipment are not needed because of the low reaction temperature, and the process is easy and cheap to perform even on a technical scale. The time for the reaction to occur is short, and as a consequence, the decomposition of the starting material and the product during the process is very low. Thus the end product does not contain any notable amounts of impurities. The yield of the reaction is high. The invention is explained by the following examples. Example l. To a mixture containing 3O g iminodibenzyl and 9O ml 2-nitrotoluene, l,8 g 5% palladium on activated carbon catalyst is added. The mixture is heated for 3-5 hours at l8O-23O°C under reflux. The catalyst is filtered off from the hot solution whereafter 9O ml of methanol is added to the filtrate. The filtrate is cooled and the crystallized iminostilbene is filtered from the mother liquid. The yield of the dried iminostilbene is 24,3 g (82% of theoretical), m.p. l96-l97°C. Example 2. To a mixture containing 3O g iminodibenzyl and 6O ml 3-nitrotoluene, l,8 g 5% palladium on activated carbon catalyst is added. The mixture is heated for 3-5 hours at 2lO-24O°C under reflux. The catalyst is filtered off from the hot solution whereafter 9O ml iso-propanol is added to the filtrate. The filtrate is cooled and the crystallized iminostilbene is filtered from the mother liquid. The yield of iminostilbene is 23,2 g (78% of theoretical), m.p. l95-l97°C. Example 3. To a mixture containing 30 g iminodibenzyl and 60 ml 2-nitrotoluene, 1,8 g 3% platinum on activated carbon catalyst is added. The mixture is heated for 3-5 hours at 210-240°C under reflux. The catalyst is filtered off from the hot solution. The filtrate is cooled and the crystallized iminostilbene is filtered from the mother liquid. The yield or iminostilbene is 22,2 g (77% of theoretical), m.p. 195-197°C.

Claims: A process for the preparation of 5H-Dibenzo-(b, f)-azepine, or iminostilbene of formula (I), by catalytic dehydrogenation of 10,11-Dihydro-5H-dibenzo-(b, f)-azepine or iminodibenzyl of formula (II), the dehydrogenation being performed in one step in liquid phase in the presence of a catalyst and a hydrogen acceptor at elevated temperature, characterized in that nitrotoluene is used as hydrogen acceptor and that the dehydrogenation is carried out at a temperature of 180-280°C. A process according to the claim 1, characterized in that the dehydrogenation is performed at a temperature of 210-250°C. A process according to one or more of the claims 1-2, characterized in that as catalysts, noble metal catalysts on activated carbon or metaloxide catalysts, are used. A process according to claim 3, characterized in that the noble metal catalysts are platinum or palladium on activated carbon. A process according to claim 3, characterized in that the metaloxide catalysts are Fe₂O₃ or Cr₂O₃. A process according to one or more of the claims 1-5, characterized in that after the catalyst has been removed, the iminostilbene is precipitated from the reaction mixture by the aid of methanol, ethanol, iso-propanol, hexane or heptane.

Inventors: HILDEN, LEIF, MANNONEN, MATTI TAPANI
Applicants: ORION-YHTYMAE OY FERMION
Application year: 1987
Main classification: C07D223
IPC codes: C07D223