PROCEDURE PRRfl Lfl PREPARATION OF CHEMICAL COMPOUNDS FLUORFlES
The processes for the preparation of fluorine-containing chemical compounds (fluorinated) are distinguished because, especially in acidic media, a very strong corrosion appears, caused by hydrogen fluoride. This reinforces the additional corrosion, which is caused by other influences. Furthermore, by the presence of ions of fluorides ß, it destroys the passive layer together with metals, in such a way that corrosion by other constituents of the mixture is also facilitated thereby. This avoids not only the use of stainless steel fittings, but also that of enamel fittings, since an enamel, due to the formation of hexafluorosilicic acid undergoes a strong wear, and the rate of wear, when an incipient corrosion occurs, increases greatly progressively.
As a general rule, at low temperatures, that is to say up to approximately 60 ° C, one changes to the use of installations of polyethylene (PE) apparatuses or of correspondingly coated apparatuses. Up to temperatures of 100 ° C to approximately 160 ° C it is also possible to use poly (tetrafluoroethylene) (PTFE), but it is already associated with considerable problems, especially at temperatures above 120 ° C special structures must be used, especially in the field of heat exchange and agitation mechanisms. n cold parts of appliances can also use parts and pieces of poly (vinylenide fluoride) (PVDF), which can certainly be made better than PTFE, but has a significantly lower softening temperature and therefore is greatly limited in its amplitude applications, especially for parts and pieces very mechanically loaded such as stirring arrangements. Especially, the high moments of rotation that appear when starting the agitation mechanisms, lead to deformations as a consequence of a lack of rigidity against torsional deformation. Other fluorinated synthetic materials (eg Fluoroshieldr) are also, in principle, stable against acidic media, which contain hydrogen fluoride. These synthetic materials (PTFE, PVDF, Fluoroshield) have, however, among others, the following disadvantages. On the one hand, the heat transfer coefficients of these synthetic materials are so small, in comparison with the usual materials such as co or p. ex. metals, that is forced to keep small the thicknesses of the walls forced to keep small the thicknesses of the walls. As a result of the mechanical properties of these synthetic materials (flow behavior in the case of approaching the softening point, resistance to compression, tensile and shearing, rigidity against torsional deformation), the devices can not be made from a solid material, but synthetic materials can be used only for the coating or must be applied by sintering. On the other hand, the materials, because of the lipophilic properties and their density, which as a rule are smaller, are not stable against the diffusion of organic compounds, and especially not against the diffusion of hydrogen fluoride. . However, this leads, especially in the case of reactions under pressure or at high temperature and facilitated by the small wall thicknesses due to the small heat transfer coefficients and the technical characteristics, to which, as a rule, after laying In operation of the equipment, corrosion caused by hydrogen fluoride or hydrofluoric acid appears to occur rapidly (especially phenomena, despite the wall thicknesses, which are generally small, devices covered with synthetic materials are only an unsatisfactory solution, since the heat transfer coefficients are so small that in spite of everything, no exothermic or endothermic reactions of any kind can be carried out, since heating or cooling is only difficult to achieve. Other disadvantages of technical materials based on fluorinated polymers are the poor processability and the limitation to procedures under normal pressure and low overpressure, since the application of a depression is hardly possible, given that the layers, because of their small adhesion, they detach from the outer containers and become irregularly deformed. Under the reaction conditions that frequently occur, especially in aqueous solutions, hydrofluoric acid is always in the vapor space or even a water vapor containing an acid must be condensed when the reaction gas is decompressed. However, corrosion caused by hydrofluoric acid diluted in condensation can hardly be controlled with the usual methods. There is therefore a need for a simple and universally applicable process which, together with the usual reactions, also allows the reactions in which hydrogen fluoride is contained in the reaction mixture, especially in aqueous solutions. According to Rbmpp, Chemie-Lexi on, 53 edition 1962 (volume 1, page 1.125), Diabonr is a technical material resistant to acids based on porous graphite, which had been made liquid-tight by impregnation with resins. This material is stable against hydrogen fluoride and other mineral acids. Mentions to which offers advantages the use of containers based on a material containing carbon since they combine mechanical strength, good heat transfer properties and high stability against corrosion, are also found in the following bibliography: J. Künzel , Chern. Tech. (Heidelberg), 17 (12), 16, IB, 20 (1988); 3 Künzel in VDI-Berichte 674, 87-103 (1988); H.Bóder, E. von Gellhorn, 3. Künzel, Chem. Ing. Tech. (1987) 59 (2), 122-126; 3. Künzel, fl. Swozil, H. Würrnseher, Swies Chem. (1983) 5 (10a), 17/22; G. L. Hart, G. Pritchard, in Carbon Fibers, 2s2 conf. int. Proc. London, Feb. 18-20, 1974, paper 34; 3. Künzel, E. von Gellhorn, H. Bbder, in Composite Polymers, 1 (6) (1988), K. S. Lally, U. C. Uebster, R. N. Salz an, Chem. Engng. Prog. 84 (11) (1988), Chem. Engng. 93 (10) (1986), 47. The invention relates to a process for the preparation of fluorinated compounds by reaction in a vessel provided with a stirrer, characterized in that a stirrer is used that is totally or partially made of a material of carbon. The stirring organs of the agitator used in the process according to the invention consist of a carbon-containing material. The shaker shaft of the agitator, on the other hand, may also consist of a metal, but it is also possible that this shaft also consists of a material containing carbon. This material can be filled, this is pressed, sintered or otherwise shaped to form a solid technical material, with phenolic, epoxy, polyimide or polyester resins, or also with fluorinated synthetic materials. Coating materials for the carbon material are generally used furanic or phenolic resins or fluorinated synthetic materials, for example CTFE / VDF (poly (chlorotrifluoroethylene-vinylidene fluoride)), PTFE (poly (tetrafluoroethylene)) , ECTFE
(poly (ethylene-co-chlorotrifluoroethylene)), ETFE (poly (etheno-co-tetrafluoroethylene)), FEP (poly (tetrafluoroethylene-co-hexa-fluoropropylene)), PCTFE (poly (chlorotri fluoroethylene)), PVDF
(poly (vinylidene fluoride)), PVF (poly (vinyl fluoride)), TFB (poly (tetrafluoroethylene-co-hexafluoro-propylene-co-vinylidene fluoride)) or CM-X (poly (hexaf luoroisobutylene-co-) vinylidene fluoride)). Other possible fluorinated synthetic materials are, for example, any copolymers of hexafluoroisobutylene, hexa luoropropylene, tetrafluoroethylene, vinyl fluoride and vinylidene fluoride or analogous compounds. In addition, these fluorinated polymers can be used wherever PTFE or PVDF is indicated. The shaker shaft of the agitator may preferably consist of a synthetic material reinforced with carbon fibers (CFK) or carbon fiber reinforced carbon (CFC). The carbon fibers in this material generally have a diameter of about 1 to about 100 μm, preferably about 3 to 30 μm, especially 5 to 15 μm, with the fiber content being, in the case of the materials CFK technicians, from approximately 30 to 90 Z, preferably from 50 to 70%
In the case of the fibers, it is preferably high modulus or very strong fibers, the fibers being able to adopt an angle between them of 0 to 45 °. Likewise, composite materials with fibers can be used. The carbon fibers may also be in the form of corresponding filaments. The materials of the types CFK and CFC have, as a rule, flexural strengths of approximately 50 to 2000 N / mm2, preferably of 80 to 1500 N / rnrn2. especially from 100 to 800 n / mm2. The values for the modulus of elasticity or modulus-E (under traction) are from about 10,000 to 400,000 N / mm 2, preferably from about 25,000 to 130,000 N / mm 2, and for the tensile strength are from about 0,05 to 8, preferably from about 0.3 to 1 n / mm2. The density of these materials is from about 1.2 to 2.0, preferably from 155, to 1.6 g / cm3. As examples of fibers or stretched (non-woven) fibrous webs for reinforcing synthetic materials, the Sigrafil C40, SFC 6 or 12 or sigratex (different types) or 320 products can be pointed out. The corresponding material and technical data can be obtained for example. ex. of the informative technical brochures of SGL Carbon. Structuring technical materials, likewise possible, are the SIGRABONDR types of the SGL Carbon entity, which are available both in the form of? CFC (carbon fiber reinforced carbon) and also in the form of a CFK (carbon reinforced synthetic material) ). These can also be coated with ceramic materials, such as p. e. Sic. Thus, types CC 1001 G and CC 1501 G (both of the CFC type) respectively uncoated and coated with silicon carbide infiltrated in silicon or with ae-SiC, as well as CFT CC 1506 G have been tested. The technical data can be obtained of the corresponding information brochures. The materials of the type CFK, which are in question, may contain the mastics described hereinafter or may be filled with epoxy, phenolic or furan resins, or with fluorinated synthetic materials such as for example poly (tetrafluoroethylene) (PTFE). The polymeric matrix in such CFK type materials may consist of unsaturated polyesters, phenolic resins, epoxy resins or polyimide resins, with thermosetting (thermosetting) materials being preferred. The shaft of the agitator structure (carbon material) generally consists of a solid material or of a hollow tubular structure, which may be optionally filled with a core based on a mechanically resistant material, e.g. ex. Metals such as technical materials 1.4571 and 2.4610 can be incorporated, in solid form or as a hollow tube as the core of the tree. Such hollow structures can be sealed, if desired, to avoid corrosion on the internal and external faces, with the pumaterials described below. Since these structures are generally attached to a structure which propels the agitator, which consists of a metal, as a rule the technical material with the number 1.4571, this transition site must be sealed especially by the described possibilities. The agitation geometry of the agitator used can be structured according to all the technically known variants (see, among others, the article by M. Zlokarnik, H. ZJudat in Ullrnann's Encyklopedia of Industrial Chernistry, volume B2 (1992), chapter 25). Thus, single-stage and multi-stage agitators are possible. Use is made of flat paddle agitators, crosshead stirrers, anchor agitators, impeller or propeller agitators, turbine and anchor agitators, or special forms of execution of these types, such as, for example, MIG »* or INTERMIGR, which guarantee a particularly intense mixing with simultaneous optimization of energy consumption (flat paddle, crosshead or anchor beam stirrers are preferred). For special problems, p. ex. for highly viscous reaction mixtures, the technical solutions indicated in the indicated literature are also possible. The size and shape of the stirring organs can be adapted to the respective requirements of the reaction apparatus and to the reaction itself. The length of the stirring shaft is dependent on the size of the reactor and generally amounts to 50 to 95 X, especially 70 to 90%, of the height of the reactor. The diameter of the stirring shaft is approximately 1 to 100 cm, the following values being particularly useful: from 4 cm in the case of pilot (experimental) installations, and from 40 to 100 cm in the case of production facilities ( on a technical scale). The respective material of the agitation shaft is dependent on whether the agitation shaft is hollow or solid structured. In the case of hollow trees, the thickness of the material is from 2 to 20%, preferably from 5 to 15%, based on the overall tree diameter. The same is true for the organs of agitation. The radial dimensions of the agitation organs are dependent on the container, in which the agitator must be used. Usually the stirring organs are structured such that they constitute from 10 to 90, preferably from 30 to 80 X of the diameter of the container. The height of agitator organs is greatly dependent on the type of agitator and amounts to approximately 3 to 20% of the height of the container. According to the invention, an agitated sealing arrangement with respect to the outside is preferred by means of a sliding ring seal, a magnetic coupling and a stuffing box gasket. These structural parts are used in the constructively usual way. An essential component of such sealing by means of slip rings is the use of corrosion-stable ceramic materials for slip rings, such as, for example, boron nitride, boron carbide, silicon nitride or silicon carbide, that these have the required hardness and therefore resistance to abrasion. These materials can be used in different variants, for example, by varying the manufacturing process (different sintering and different grain sizes) or by varying the constituents of the material (eg non-stechyium proportions of the components in the material). , such as silicon carbide infiltrated in silicon), which allows an adaptation of the real material properties to the chemical and mechanical requirements. Through the constructive mode, the agitator according to the invention has advantages in relation to the mechanical strength of the material, compared with that of other materials stable to corrosion, such as p. ex. fluorinated synthetic materials. In the process according to the invention, not only the stirrer alone, but additionally also the container for the reaction, can consist of the carbon material or can be coated with this material. This means that either the structural parts for the containers in solid form can consist of this material or that only the surface is coated with these materials. It is essential in these cases that such parts of the container, which come in contact with the product, consist of the carbon materials or are coated with them. As known from the literature, graphite produced by special processes, such as for example carbonization, has extremely high compression and traction modules. In addition to this, the material is widely stable against diffusion, especially since, as explained above, the corresponding wall thicknesses do not represent any kind of problems. The container wall thicknesses, which are advantageous in the case of use according to the invention, can be between approximately 5 and approximately 200 nm, in particular between approximately 20 and approximately 80 nm. For the sealing and filling of joint joints as well as for the protection of non-inert structural parts in agitators and containers, customary materials for this purpose are filled with organic resins such as, for example, epoxy, elamine, furanic resins, alkyd, vinyl, polyester, urethane or phenolic. In particular, the "Asplif" types, especially the CV, CL, CN, ET, OC, 00 FN types and the acidic filler HB, HESHB or HFR, or the igneous mastic K12, K14, K16, are suitable in this case. Exact analogue types of eetae resins, which are considered under other names, can be used in exactly the same way Explanations about the exact composition of such masillae, especially of maeillas, with organic binders, are found in the Ullmann's Encyclopedia of Industrial Chemistry, to 5A 5o, (1986), pages 539 to 544. Preferred are the commercial maple nails Asplit CN, a putty of the type of a phenol and formaldehyde resin, and flsplit FN, a putty of the type of hard resin; however, a change to other types is appropriate, depending on the type of reaction medium. These can be explained perfectly in the example of these two types of Asplit, in fact the CN type has advantages in acidic zones, and the Asplit FN has them in an alkaline medium, and in relation to the stability against solvents, both types are almost equivalent. Together with this it is also possible to protect the sealing places or the structural parts, which are not inert in themselves, by means of layers based d? an inert material, especially by noble metals such as gold or platinum. It is also possible to mass-produce these parts based on noble metals, especially exposed. The metallic layers can be applied by plating, by melting, sintepzación or from vapor phase. In particular, the process according to the invention can be used for the preparation of organic fluorinated compounds. Among these are fluorinated compounds, aliphatic as well as aromatic, such as, for example, tri- or tetra-fluoropropane-carboxylic acids, 2,3,4,5-tetrafluoro-benzoic acid, 5-fluoro-2-nitro. -phenol or similar compounds. Especially preferred are the steps of synthesis or preparation of fluorinated compounds, in which these compounds are handled, especially at elevated temperatures, in acid solutions, especially in strongly acidic solutions. In these stages of the process, it is revealed that small amounts of fluorides are always separated from the organic material, which give rise to corrosion. In the process according to the invention it is also useful in the case of compounds, which, together with fluorine, also contain chlorine, and in which chloride ions or HCl, which also act corrosively, are similarly liberated. The halide concentration in total in the reaction batch can amount to 5 pprn up to 25%. Preferably, the process according to the invention is applied to fluorinated aromatic compounds as reactants or as products, especially to fluorinated aromatic carboxylic acids and / or phenols, alcohols or their functional derivatives such as esters, amides, halides, aldehydes, benzylic alcohols, ethers, benzyl halides, preferably benzyl fluorides, benzal halides, preferably benzal fluorides, benzo trihalides, preferably benzo-trifluoride, which additionally contain groups which react in an acidic or basic manner. In particular, the process according to the invention can be used, for example, for the preparation of the following compounds: tetrafluoro-benzetrafluoro-phthalic acid, 2,3,4,5-tetrafluoro-benzoic acid, 3-hydroxy-2,4 acid, 5-trifluoro-benzoic acid, 4-hydroxy-2,3,5-trifluoro-benzoic acid, 4-amino-3,5,6-tri luoro-phthalic acid, 2,3-dichloro-4,5-difluoro- benzoic acid, 3-amino-2,4,5-trifluorophthalic acid, 4-chloro-3,5,6-tnfluoro-phthalic acid, 3-chloro-2,4,5-tr? fluoro-benzoic acid , 4-hydrox -3,5,6-tpfluoro-phthalic acid, 3,5,6-tpfluoro-phthalic acid, 2,4,5-tr? -fluoro-benzoic acid, 2- acid fluoro-phthalic acid, 2,4,5-tr? fluoro-benzoic acid, 2-cyclo-4,5-difluoro-benzoic acid, 2-chloro-6-m-phenol, 2-chloro-3-fluoro- 6-nitro-phenol, 5-fluoro-2-n-tro-phenol and 2,3-d? Fluoro-6-n? Tro-phenol. The process according to the invention includes in particular the following types of reactions: exchange between halogen and alkoxide, exchange between halogen and hydroxide, exchange between halogen and amine (in each case, especially exchange of fluorine atoms), exchange between halogen and halogen, decarboxylation , dehydration, hydrolysis of nitriles, amides, anhydrides, esters, acid chlorides, amides, reaction of the Schiemann and Balz-Schiemann types, transposition of Bamberger, ethepication, acylation, especially in liquid hydrogen fluoride, which may eventually contain water. The processes according to the invention can be carried out in an aqueous solution and in solutions in the usual organic solvents, the aqueous solutions being preferred. The viscosity of the reaction mixture is from about 0.1 to 5,000 cP, preferably from 1 to 1,000 cP, especially from 25 to 250 cP. The speed of the agitator is generally between 1 and 2,000 revolutions per minute (rpm), in the case of laboratory procedures at 100 to 1,000 rpm, in the case of pilot installation (experimental) at 5 to 200 rpm and at the case of production facilities on a technical scale from 2 to 100 rprn. The process according to the invention can be carried out in containers with a capacity of from approximately 0.5 1 (laboratory scale) to approximately 20 m3, installations of intermediate dimensions, which contain reaction units with a capacity of from about 200 1 haeta about 5 m3. According to the invention, it is possible to work at temperatures between about -20 ° C and about 220 ° C, preferably between 50 and 1 ° C, especially at 100 ° to 180 ° C. The possible pressures amount to 0.05 to 4.0 MPa, preferably to 0.1 to 2.0 MPa. The use of the installations to be used according to the invention is particularly advantageous when impure reaction mixtures have to be processed and transformed, since they may contain greater amounts of free fluoride. In particular, this may be the case when, by nucleophilic exchange reactions, functionalisations are carried out on aliphatic or aromatic organic compounds, when these functionalizations release fluoride ions themselves and the mixtures must be acidified for further processing or processing, such as in the case of the synthesis of phenols or special carboxylic acids. As a result, a purification step can be saved in each case, thereby avoiding possible loss of performance and manufacturing cost can also be saved. It is understood only that the process according to the invention is limited to working with non-oxidizing media, since the carbon-containing material is attacked by the oxidation agents. This means that reactions with a sulfuric acid having a content greater than 70%, with halogens, such as chlorine or bromine, or with hydrogen peroxide are subject to limitations. In the case of very low temperatures, that is to say in general at temperatures below about 40 ° C, there are nevertheless perfectly exceptions. A great advantage of the process according to the invention is that the materials used, provided that they are not inherently inert under the reaction conditions in question, are constituted in such a way that their wear, loss of material or modification surface does not impact accelerating on additional corrosion. Therefore, these materials, in essential contrast with metallic materials and enamels, that when experiencing an incipient attack always have a progressive tendency to corrosion, even if only because of the increase in their surface area. The method according to the invention, using a special stirring arrangement, also has the advantage that the addition of fluoride-picking agents can be dispensed with (see R. Lorentz in "Uerkstoffe und Korrosion" 9/83, Inhibition of the attack by acid on a chemical enamel), which are also limited in their activity in acid and aqueous solutions. Consequently, the material costs for these unproductive additions as well as the problems of procedures, which as a rule can not be neglected, are eliminated, which are established especially when effecting the elimination of the resulting solid precipitates, such as those of dioxide. of silicon or calcium fluoride, which are filterable with much difficulty. The following Examples explain the procedure, but without limiting it. Example 1 Preparation of 2,3,4,5-tetrafluoro-benzoic acid
In 120 g of water and 6.0 g of 96% sulfuric acid, 3.4 g of calcium hydroxide and 27.0 g of crude octafluoro-bieftalimide (85.5%) were used. The mixture was introduced in a Hastelloyr C4 autoclave of 0.75 1 capacity, in which a stirrer had been incorporated. The agitator consisted of a hollow tube with a length of 22 cm (external diameter 2 cm), made of carbon reinforced with carbon fibers (SIGRABOND de SGL
Carbon). -The tube was provided with 3 notches along the axis of agitation (in each case offset by 90 °), inside which had been inserted at right angles two flat stirring paddles based on the same material (dimensions, 3 c) height, 6 cm wide) and fixed with a PTFE tape (crosshead stirrer). The agitator shaft was placed with Hastelloy C4 pins to the propulsion arrangement (stainless steel 1.4571) and sealed with Asplit FN. The agitator was propelled with a rotation speed of 200 rpm. The mixture was heated at 160 ° C for 12 h in a PTFE autoclave with the preemption of a sample of technical material and enamel, which had been fixed to the agitator by a PTFE tape. After the reaction time period had ended, the enamel coating of the sample had completely worn away, so the sample was completely destroyed. The reaction, as controlled by gas chromatography (GC), was manifested as complete and the mixture was analyzed through calibrated GC. 17.7 g (91 mmol, 86.2%) of 2,3,4,5-tetrafluoro-benzoic acid was detected, which was transformed directly. Under analogous conditions, a steel V4A wheel (technical material number 1.4571) was used, the sample being approximately halved in the gaseous space and in the liquid space. After the end of the reaction, it was found that the lower part of the sample was almost completely missing, and the part used in the gaseous space showed intense wear, as well as corrosion due to cracking, stress and stress. If, under the same conditions, graphite blocks of SGL Carbon's Diabon materials, filled with a phenol and formaldehyde resin, NS 2, fine grained variants, NS 1 and NS 2, were used as potential material for the containers during 200 hours, no chemical attack could be verified nor any loss of mechanical resistance. The agitator did not show, like the tested pieces of carbon, any type of modifications under these conditions, and especially not the flat blades of the agitator of the cross-beam or cross-beam structure. EXAMPLE 2 Preparation of 5-fluoro-2-nitro-phenol In this example, the stirrer described in Example 1 was incorporated through a seal sealing ring in a PTFE reactor as is commercially available, the slip ring seal made of a-silicon carbide having been manufactured. Instead of Asplit FN, Aeplit CN was used as CFK material (synthetic material based on a phenolic resin, reinforced with carbon) for the tree. In the PTFE reactor, 119.4 g (0.75 mol) of 2,4-difluoro-nitrobenzene were initially introduced, at 104 ° C. in 4 h, 104.8 g (1.566 mol) of sodium hydroxide were added dropwise. potassium (85%) in 300 g of water, and after that the temperature was increased to 60 ° C. Samples (stainless steel V4A) of technical material number 1.4571 were placed in the liquid and in the vapor space. After the end of the reaction, 96 X sulfuric acid was added until pH 2.3 had been reached, and 40 g of highly disperse silicic acid (Aerosilr) and 38.0 g of fluoride were added as a fluoride scavenger. calcium hydroxide, adjusting to 4.2 the pH value. Water vapor was introduced, after which 5-fluoro-2-nitrophenol was distilled off with steam. The pH value was decreased to 1, By means of 96 X sulfuric acid during the steam distillation in the course of 1.5 h, and after that it was kept at this value. The distilled material was cooled to 10 ° C and then separated by filtration. 91.9 g (0.58 mol, 78 X) of 5-fluoro-2-nitrophenol were obtained as a yellow solid. The agitator was presented as unaltered after repeating the experiment variae vecee. The materials of the technical materials 1.4462 and 1.4539 already had a uniform attack (integral speed of between 1 and 6 mm / a) as well as partially stress corrosion cracking and tension cracking after an effective time of 50 hours. Example 3 Preparation of 2,6-difluoro-benzoic acid from 2,6-difluoro-benzonyl In a PTFE reactor, having the configuration described in Example 2, 139 g (20 g) were incorporated at 20 ° C. 1 mol) of 2,6-difluoro-benzonitrile in 235 g of 75% sulfuric acid and covered with nitrogen. The mixture was heated to 150 ° C in the transcureo for 1 h and after that it was maintained at 150 ° C for 6 h. After this period of time it was cooled, it was poured on 750 g of ice-water and the precipitated product was isolated by filtration and subsequent washing with water (3 times with 200 g each time) as well as subsequent drying. They were obtained
137 g (86.7 X, 0.867 mol) of colorless 2,6-difluoro-benzoic acid in the form of a powder. The material constitution of the agitator was checked after 10 charges and manifested as unchanged.