CH619943A5 - Process for the synthesis of dibenzofuran - Google Patents

Abstract

Dibenzofuran is obtained by oxidative dehydrocyclization of 2-cyclohexenylcyclohexanone. The reaction is carried out in the presence of a catalyst selected from the oxides or mixtures of oxides of metals belonging to groups III, IV, V, VI and VIII of the Periodic Table of the elements. The dibenzofuran yield of the novel process is very high: > 60 %.

Description

The present invention relates to a new process for the synthesis of dibenzofuran.

Dibenzofuran is an important synthetic intermediate in the pharmaceutical industry; in fact some of its derivatives, obtainable from it with simple methods, known in organic chemistry, are claimed as drugs having anti-inflammatory, analgesic, hypotensive, muscle-relaxing, vasodilator, sedative or antiviral activity. Other derivatives are claimed as stabilizing agents for olefinic polymers, polyacrylates and PVC against UV radiation.

The methods known so far for the synthesis of dibenzofuran consist in the pyrolysis of phenol, or in the catalytic dehydrocyclization of diphenyl ether in the presence of H2 on a platinum-based catalyst supported on activated carbon. In the first case, the yields obtained are very low, while in the second case, a considerably expensive raw material and catalyst must be used and frequent regenerations of the catalyst itself are necessary, which make the process appear not economic.

In a patent of Farbenfabriken Bayer AG (DE Pat. 1 007 772), dibenzofuran is obtained with a yield lower than

10% per passage starting from 2-cyclohexenyl-cyclohexanone at 420-480 ° C, in the presence of water vapor, on a bed of activated carbon.

The process for the synthesis of dibenzofuran according to the invention is characterized in claim 1.

With the present invention, it is possible to obtain very high yields in dibenzofuran by conducting the dehydrocyclization of 2-cyclohexenyl-cyclohexanone at high temperature in the presence of air and a catalyst. The latter can consist of a common oxidative dehydrogenation catalyst, i.e. oxides or mixtures of metal oxides of the III, IV, V, VI and VIII group of the periodic system, for example oxides or mixtures of cerium, uranium, silicon oxides , titanium, tin, phosphorus, arsenic, antimony, bismuth, vanadium, niobium, tantalum, chromium, molybdenum, tellurium, tungsten, iron, cobalt or nickel.

The catalyst can be used alone or supported on common materials used as supports, such as silica, alumina, diatomite, silica-alumina. Particularly preferred is the use of silica as a support for its qualities as an oxidative dehydrocyclization catalyst, as shown in Italian patent No. 875 126.

The process of the present invention can be carried out with a fixed bed, a movable bed, or a fluidized bed.

According to a preferred embodiment of the present invention, the catalyst is constituted by a mixture of bismuth, molybdenum and vanadium oxides, the preparation of which is reported in Italian patents No. 690 486 and 769 588.

According to another preferred embodiment of the present invention, the catalyst consists of a mixture of antimony oxide or an oxide selected from the metals belonging to groups III, IV, V and VIII of the periodic system, for example a mixture of oxides of antimony and uranium, antimony and tin, antimony and tellurium, antimony and iron, and their more complex mixtures.

The temperature at which the oxidative dehydrocyclization reaction is carried out can be between 300 and 700 ° C, and preferably between 400 and 550 ° C. The reaction pressure can vary in a wide range, between a few mmHg and 10 atm .; preferably it is operated at atmospheric pressure or slightly higher.

Air is preferably used as oxidant, in a ratio that can vary from 4: 1 to 50: 1 by moles with respect to 2-cyclohexenylcyclohexanone; a ratio between 8: 1 and 30: 1 is preferred.

The use of an inert diluent which can be chosen from water vapor, nitrogen, argon, carbon dioxide, saturated hydrocarbons or any other substance that does not undergo changes in the reaction conditions is particularly advantageous.

The use of water vapor as a diluent in a molar ratio from 5: 1 to 100: 1 with respect to 2-cyclohexenylcyclohexanone is particularly preferred; a range of preferential ratios is between 10: 1 and 70: 1. In fixed bed operations the apparent contact time between reactants and catalyst can vary in the range from 0.1 to 10 sec, and preferably from 0.2 to 2 , 5 sec.

By apparent contact time between reactants and catalyst is meant the ratio between the volume of the catalytic bed and the flow rate of reactants in the gaseous state under the reaction conditions.

The following examples, as an illustration of the present invention, are intended to be non-limiting. An example of synthesis of 2-cyclohexenyl-cyclohexanone according to a method which can be deduced from the literature which therefore is not the subject of the present invention is also reported.

In the following examples the terms of conversion, selectivity and yield are used with the following meaning.

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619943

moles of 2-cyclohexenyl-cyclohexanone reacted

Conversion = X 100

moles of 2-cyclohexenyl-cyclohexanone fed moles of dibenzofuran obtained

Selectivity = X 100

moles of dibenzofuran reacted

Yield = Conversion X Selectivity

Example 1 Preparation of the 2-cyclohexenyl-cyclohexanone

In a 5-liter Pyrex glass flask, equipped with a stirrer and loading funnel, topped with a column filled with Raschig rings with head for reflux, coolant and collection cylinder for the mixing of the water-benzene azeotrope, 981.5 g (10 moles) of cyclohexanone, 1500 cc of benzene and 500 cc of an ion exchange resin in acid form of sulfonic type (Amberlyst 15 H, by Rohm & Haas) were loaded.

It was heated for 3 hours to reflux of benzene, separating the water by azeotropic distillation, then the reaction mixture after filtration of the resin was distilled to remove the solvent and subsequently the cyclohexanone was recovered (179.6 g, conversion 81 , 7%) (p. Eb. 90 ° C at 100 mmHg). The distillation residue contained 1301.2 g (73.1% yield) of 2-cyclohexenylcyclohexanone together with small quantities of heavier condensation by-products.

The purity of this residue (approximately 2% titre in 2-cyclohexenylcyclohexanone) allowed its direct use as feed to the oxidative dehydrocyclization reactor.

Example 2

Oxidative dehydrocyclization on Bi-Mo-V oxides

337 g of a catalyst consisting of a mixture of bismuth, molybdenum and vanadium oxides, prepared according to example 7 of the Italian patent, was loaded into a 7.8 "internal diameter stainless steel reactor, heated with electrical resistances. No. 769 558. The composition of the catalyst was 1 Bi203: 1 MoOs 0.6 V20B; the catalyst was 50% supported on Ludox AS silica

85 cc / hour of 2-cyclohexenylcyclohexanone (about 90% purity), 22 NI / hour of air and 400 cc / hour of water vapor were fed for a molar ratio 1: 20: 50. The average temperature in the reactor was 45.0-500 ° C. The contact time was 0.8 sec.

The average pressure in the reactor was 1.1 ata. The reactor effluent was collected by countercurrent washing with toluene.

At the end of the test, for 3.5 hours, the reaction mixture was distilled at room pressure to remove the toluene, then a fraction p was collected at 10 mmHg. b. 130-135 ° C which contained 54 g of unreacted 2-cyclohexenylcyclohexanone (conversion 79.8%).

The distillation residue was crystallized from ethyl alcohol 15. 159.2 grams of dibenzofuran, crystalline yellow m.p. 85 ° C.

• The recovery corresponds to a yield of 63%.

The selectivity in dibenzofuran was 79.1% in this test. The cyclization products 20 of the 2-cyclohexenylcyclohexanone not fully flavored, i.e. tetrahydro - and octahydro dibenzofuran were absent in the product.

Example 3

Oxidative dehydrocyclization on Fe-Sb oxides

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The catalyst for this test was prepared by melting Fe (N03) 3. 6HaO, so it was added to small portions Sb2Os. At the end of the addition of Sb2Os, it was heated until the nitrous vapors disappeared. 30 The catalyst was activated by heating up to 850 ° C; the final composition was as follows: 21.5% by weight of Fe203 - 78.5% by weight of Sb203, corresponding to an atomic ratio Sb / Fe = 2: 1.

No support material was used. 35 700 grams of the catalyst thus prepared were loaded into the reactor of Example 2, then, at an average reactor temperature of 450-500 ° C, 85 cc / hour of 90% 2-cyclohexenylcyclohexanone were fed, 22 Nl / hour of air and 400 cc / hour of water vapor, feeds corresponding to 40 molar ratios 2-cyclohexenylcyclohexanone / air / H20 = 1: 20: 50 and at a contact time of about 0.8 sec.

The effluent from the reactor was treated according to the same process of Example 3.

In this test there was a conversion of 77.5% 45 of 2-cyclohexenylcyclohexanone with selectivity of 80.0% to dibenzofuran. The yield in dibenzofuran was therefore 62.0%.

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Claims (9)

619943 1. A process for the synthesis of dibenzofuran consisting in subjecting 2-cyclohexenylcyclohexanone to oxidative dehydrocyclization, characterized in that the reaction is carried out in the presence of a catalyst selected from the oxides or mixtures of metal oxides belonging to III, IV , V, VI and VIII group of the periodic system of elements. 2. Process according to claim 1, characterized in that the reaction is carried out in the presence of the catalyst as it is or in the presence of a supported catalyst. 2 3. Process according to claim 1, characterized in that the reaction is carried out in the presence of air. 4. Process according to claim 3, characterized in that the air is used at a molar ratio with respect to the 2-cyclohexenylcyclohexanone variable from 4: 1 to 50: 1 preferably from 8: 1 to 30: 1. 5. Process according to claim 1, characterized in that the reaction is carried out at a temperature of between 300 and 700 ° C, preferably between 400 and 550 ° C and that the reaction is carried out at a pressure varying from a few mmHg to 10 atmospheres . 6. Process according to claim 1, characterized in that the reaction is carried out in the presence of an inert diluent selected from water vapor, nitrogen, argon, carbon dioxide, saturated hydrocarbons. 7. Process according to claim 6, characterized in that the reaction is preferably carried out in the presence of water vapor in a molar ratio with respect to the 2-cyclohexenyl-cyclohexanone variable from 5: 1 to 100: 1, preferably from 10: 1 to 70: 1. 8. Process according to claim 1, characterized in that the reaction is carried out on a fixed bed, at an apparent contact time between reactants and catalyst varying from 0.1 to 10 seconds, preferably from 0.2 to 2.5 seconds. 9. Process according to claim 1, characterized in that the catalyst consists of a mixture of bismuth, molybdenum and vanadium oxides or a mixture of antimony oxide or an oxide selected from the metals belonging to groups III, VI, V and VIII of the periodic system, for example a mixture of antimony and uranium oxides, antimony and tin, antimony and tellurium, antimony and iron.