DE3935861A1 - METHOD FOR PRODUCING FLUORBENZENE AND FLUORTOLUENE - Google Patents

Abstract

Described is a method of preparation of fluorobenzenes and fluorotoluenes of the formula (I) in which X is H or a methyl group, R<1>, R<2> and R<3>, independently of each other, are at least one of the residues H, F, Cl and C1-C3 alkyl, at least one of these residues being fluorine, and S<1> and S<2>, independently of each other, are H and/or residues which decrease the electron density in the benzene nucleus, but preferably H, characterized in that benzaldehydes of the formula (II) in which R<1>, R<2>, R<3>, S<1> and S<2> are as defined above, are reacted at 150-600 DEG C on a catalyst, activated by treatment with hydrogen, comprising at least one transition metal of groups VII and VIII in the periodic table.

Description

The present invention relates to a method for Production of optionally substituted fluorobenzenes and / or optionally substituted fluorotoluenes the corresponding fluorobenzaldehydes. The possibly substituted fluorobenzenes and fluorotoluenes important intermediates, e.g. B. for the production of pharmaceutical products.

So far, fluorobenzenes are from the corresponding optionally substituted anilines by diazotization and subsequent replacement of the diazo group by fluorine been made. Such is the synthesis of fluorobenzene by diazotization of aniline hydrochloride, conversion of the obtained benzene diazonium chloride in the tetrafluoroborate and subsequent heating have long been known (G. Balz and G. Schiemann, Ber. 60 [1927] 1186, 1188; D. T. Flood, Org. Synth. Coll. Vol. II [1943] 295). 1,3-difluorobenzene could analogously by heating benzene-1,3-bis-diazonium tetrafluoroborate in a yield of 31%, based on m-phenylenediamine as a starting compound can be obtained (G. Schiemann and R. Pillarsky, Ber. 62 [1929] 3035-3043, specifically 3039). The diazotization of 3-fluoro-aniline in anhydrous hydrogen fluoride in the presence of either Ammonium fluoride or tertiary amines or dimethyl sulfoxide also led to 1,3-difluorobenzene. The yields were given as 46-73% (US-PS 40 75 252 and US-PS 40 96 196).

Similarly low yields (27-40%) were obtained by G. Balz and R. Pillarsky (loc. Cit.) In the production of 1,4-difluorobenzene from p-phenylenediamine.  

The thermal decomposition of the substituted benzene diazonium hexafluorophosphate instead of tetrafluoroborate resulted in higher cases in many cases, however economically still unsatisfactory yields corresponding fluorobenzenes (K.G. Rutherford et al., J. Org. Chem. 26 [1961] 5149-5152).

Fluorinated toluenes are obtained analogously from the respective C-methyl substituted anilines.

The decarbonylation of aromatic aldehydes Catalysts containing a platinum group metal, was developed by J. Smolik and M. Kraus (Collect. Czech. Chem. Commun. 37 [1972] 3042-3051).

It has also been proposed (DE No. 38 24 141.2) Fluorobenzenes by catalytic decarbonylation Zeolite catalysts from the corresponding To produce fluorobenzaldehydes. The production of Fluorotoluenes from fluorobenzaldehyden is after these Process only possible if one of fluoromethyl benzaldehydes going out.

The invention now makes it possible to use the fluorobenzaldehydes either fluorobenzenes or fluorotoluenes to manufacture.

The present invention now relates to a Process with which benzaldehydes of the general formula (II) (See claim 1), wherein R¹, R² and R³ are independent from each other hydrogen, fluorine, chlorine and / or C₁-C₃-alkyl represent, at least one of these radicals is fluorine, and S¹ and S² are independently hydrogen and / or Residues are the electron density on the aromatic nucleus lower, like chlorine, but preferably hydrogen are activated by treatment with hydrogen Catalyst of at least one transition metal from VII.  to VIII. Subgroup of the Periodic Table Meyer / Mendelejeff at 150 to 600 ° C to compounds of converts general formula (I) (see claim 1), wherein X is H or a methyl group and R¹, R², R³, S¹ and S² have the above meaning, implemented will. If the implementation without a carrier gas or with a under the reaction conditions compared to that at the Reaction involved compounds inert carrier gas carried out, a decarbonylation takes place in particular the corresponding fluorobenzenes while using hydrogen as a carrier gas, especially a hydrogenation to the corresponding fluorotoluenes takes place. For the Production of fluorotoluenes from fluorobenzaldehydes the presence of hydrogen is necessary.

Those suitable for the method according to the invention Catalysts contain one or more elements from VII. to VIII. subgroup, d. H. Manganese, rhenium, iron, cobalt, Nickel, ruthenium, rhodium, palladium, osmium, iridium or Platinum, preferably platinum and / or cobalt and / or platinum and rhenium. You can on conventional carriers such as Al₂O₃, Silica gel or activated carbon. As In principle, catalysts can also do all the usual zeolites serve by impregnation, ion exchange or other usual methods with an element of VII. to VIII. Subgroup have been endowed. The invention Catalysts used are advantageously in the form of Compacts or strands used. Also fluid bed Catalysts can be used.

The method according to the invention is preferably used in Temperatures of 180 to 440 ° C carried out. It can be both in the liquid phase, as well, which is preferred in the Gas phase are carried out. In the gas phase reaction can still be a carrier gas such as nitrogen or CO₂ or especially in the intended production of fluorotoluenes, Hydrogen can also be added.  

The total pressure is generally between 0.1 and 100 bar, preferably between 1 and 20 bar. Especially however, preference is given to working at atmospheric pressure or Back pressure resulting from the promotion of gaseous Starting materials through the z. B. fixed catalyst results.

The load on the catalyst (weight unit of the starting material per hour and per weight unit of the catalyst - dimension: h ^-1 - = WHSV = Weight Hourly Space Velocity - is preferably between 0.1 and 10 h ^-1 .

The gas mixture leaving the reaction zone can pass through usual methods of material separation are worked up, e.g. B. by cooling with fractional condensation. However, the desired reaction products are preferred obtained purely by distillation.

In the following examples means

U sales,
S _DFB the selectivity 1,3-difluorobenzene and
S _DFT the selectivity 2,4-difluorotoluene.

Examples

1-5) In a tubular reactor 30 mm in diameter and 600 mm The length became 34 g (50 ml) of a commercially available catalyst with about 0.5% by weight of platinum and about 0.3% by weight of rhenium Aluminum oxide installed as a carrier. Hydrogen (25 l / h) and 2,4-difluoro-benzaldehyde (14 ml / h) was added to the temperature-controlled catalyst bed passed. The reaction products were cooled and the condensed portions examined by gas chromatography. The following were obtained Results:  

6) In the apparatus described in Example 1, 50 ml of the catalyst mentioned there were treated with hydrogen for 3 hours at 350 ° C. and then the experiment from Example 1 was repeated at 440 ° C. using an equal amount of nitrogen instead of hydrogen. With a conversion of 50%, 1,3-difluorobenzene (S _DFB = 99%) was formed almost exclusively.

7-9) Instead of that in Examples 1 to 6 catalyst used a catalyst with approx. 0.5 wt .-% palladium on SiO₂ as a carrier and worked otherwise as in Examples 1 to 5, was obtained following results:

10) In a tubular reactor of 20 mm in diameter and 600 mm in length, a catalyst which had been produced by pressing 50% by weight of finely powdered cobalt and 50% by weight of γ-Al₂O₃ into strands of 2 mm in diameter was installed and 3 Treated with hydrogen at 300 ° C for hours. When using nitrogen (15 l / h) as the carrier gas, 1,3-difluorobenzene was then obtained at 400 ° C. and a WHSV of 0.5 h ^-1 with a conversion of 45% of the 2,4-difluorobenzaldehyde with a selectivity of 99% in addition to traces of 2,4-difluorotoluene.

11-14) the repetition of that described in Example 10 Experiment with hydrogen (15 l / h) as a carrier gas instead of Nitrogen gave the following values:

15-17) In the tubular reactor described in Example 10 20 ml of a strand-shaped rhodium zeolite Catalyst with 1 wt .-% rhodium installed. This Catalyst was made from H-ZSM 5 zeolite (SiO₂ / Al₂O₃ = 90) by ion exchange with RhCl₃ · xH₂O (38% Rh), then drying at 110 ° C, calcining at 350 ° C and subsequent treatment with for three hours Hydrogen at 350 ° C. Then 10 ml 2,4-difluorobenzaldehyde in a hydrogen stream of 15 l passed through the reactor. The following were obtained Results:

18-20) Instead of that in Examples 15 to 17 used catalyst a catalyst with 2.5 wt .-% Rhodium on γ-Al₂O₃ and otherwise worked as in the Examples 15-17 gave the following results:  

21) Instead of that in Examples 15 to 17 used catalyst a catalyst with 1 wt .-% Platinum on charcoal as a carrier and otherwise worked like in Examples 15 to 17, one obtained in the Implementation of 2,4-difluoro-benzaldehyde in one Nitrogen stream at 370 ° C selectively 1,3-difluorobenzene.

22-25) In the tubular reactor described in Example 10 20 ml of a platinum-zeolite catalyst were installed. This catalyst was made from 100 g of zeolite H-ZSM 5 (SiO₂ / Al₂O₃ = 90) by impregnation with a Solution of 1.65 g of platinum (II) tetrammine chloride in 300 ml Water, then drying at 110 ° C, four hours Calcine at 350 ° C and then three hours later Treat with hydrogen at 350 ° C. Then every hour 10 ml of 2,4-difluorobenzaldehyde in a hydrogen stream from 15 l passed through the reactor. The following were obtained Results:

26) In a tubular reactor 50 mm in diameter and 600 mm Length became 20 ml of a granulated catalyst with 5 % By weight of rhodium installed on activated carbon as a carrier. Per 15 ml of 2,4-difluoro-benzaldehyde were mixed in one hour 15 l nitrogen flow at 165 ° C. through the reactor  headed. It was 1,3-difluoro-benzene in one Selectivity of 99% obtained with a conversion of 40%.

27-29) In the tubular reactor described in Example 1 were 20 ml of the platinum-rhenium catalyst mentioned there arranged. Then 10 ml 2-chloro-6-fluoro-benzaldehyde in a hydrogen stream of 15 l passed through the reactor. The following were obtained Results:

30) If a catalyst with about 5% by weight of nickel on aluminum oxide was used as the support in a test arrangement as described in Example 1, a WHSV of 0.78 h ^-1 and a temperature of 470 ° C. were obtained Hydrogen carrier gas flow of 15 l / h with almost complete conversion, but significantly lower selectivity, 1,3-difluorobenzene and 2,4-difluorotoluene in a weight ratio of about 13: 1.

Claims (7)

1. Process for the preparation of fluorobenzenes and fluorotoluenes of the formula (I) in which X represents H or a methyl group, R¹, R² and R³ independently of one another represent at least one of the radicals H, F, Cl and C₁-C₃-alkyl, at least one of these radicals being fluorine, and S¹ and S² independently of one another H and / or radicals which reduce the electron density on the benzene nucleus, but are preferably H, characterized in that benzaldehydes of the formula (II) wherein R¹, R², R³, S¹ and S² have the abovementioned meaning, on a catalyst activated by treatment with hydrogen of at least one transition metal of sub-groups VII to VIII of the periodic system at 150 to 600 ° C. 2. The method according to claim 1, characterized in that the catalyst cobalt, platinum and / or platinum-rhenium contains. 3. The method according to claim 1 or 2, characterized in that the reaction takes place in the gas phase.   4. The method according to one or more of claims 1 to 3, characterized in that at a temperature of 180-440 ° C works. 5. The method according to claim 3 or 4, characterized in that at a total pressure of 0.1 to 100 bar, advantageously 1-20 bar, preferably at atmospheric pressure or with the dynamic pressure, which is promoted by the gaseous starting materials through the catalyst system hires, works. 6. The method according to one or more of claims 1 to 5, characterized in that the manufacture of the Fluorotoluenes of formula I (see claim 1), wherein X = methyl is the implementation of the fluorobenzaldehydes of the formula II (see claim 1) in the presence of hydrogen executes. 7. The method according to one or more of claims 1 to 5, characterized in that the manufacture of the Fluorobenzenes of formula I (see claim 1), wherein X = H is the implementation of the fluorobenzaldehydes of the formula II (see claim 1) in the presence of at least one of the Reaction conditions compared to those of the reaction involved compounds of inert gas such as nitrogen and preferably also in the absence of hydrogen.