FR2505821A1 - Per:bromination of phenol or di:phenyl ether - using excess bromine as reaction medium - Google Patents

Abstract

Perbromination of phenol (I) or diphenyl ether (II) is carried out by adding (I) or (II) at 35-55 (pref. 45-55) deg.C to a 75-400% (pref. 100-200%) stoichiometric excess of Br2 contg. a small amt. of catalyst, and refluxing the mixt. while maintaining the excess of Br2. The catalyst is Fe or Al, a halide of Fe or Al, or a cpd. of Fe or Al which forms the bromide under the reaction conditions. The catalyst is pref. used in an amt. of 0.1-10 wt.% (calcd as metal) based on (I) or (II). The prods., i.e. pentabromophenol (III) and decabromodiphenyl ether (IV), are useful as flame retardants and intermediates for pesticides and drugs. The process gives high yields of high-purity product without the use of solvents, thus increasing reactor productivity.

Description

Process for perbromination of phenol and ether
high temperature diphenyl, using
bromine as reaction medium.

 The invention relates generally to a process for perbromination of phenol and diphenyl ether by bromination of the appropriate compounds at a temperature above 350C, in bromine as the only reaction medium, in the presence of selected catalysts.

 In the past, many methods have been employed to replace all of the nuclear hydrogen atoms in aromatic compounds such as diphenyl ether and the like. None of these processes has been found to be entirely satisfactory; it has been found that they all have disadvantages.

 The perbromination processes of the prior art generally call for the use of an excess of bromine of up to about 20%, in the presence of different kinds of reaction media and solvents such as ethylene dibroma, carbon tetrachloride, chloroform, methylene bromide, acetylene tetrachloride and the like depending on the particular aromatic compound to be brominated. Perbromination of aromatic compounds has also been carried out in reaction media such as oleum, concentrated sulfuric acid, fuming sulfuric acid, liquid sulfur hybrid year and the like.

 Each of these processes has serious disadvantages for perbromation, especially for industrial operations. The use of halogenated organic solvents has disadvantages such as low productivities, undesirably slow reaction rates, and the need to recover the solvents for recycling. In some cases, this technique results in the introduction of small quantities, but playing an important role of chlorine in the final product, thus limiting the quality of the product. In addition, a number of uncondensed aromatic compounds do not satisfactorily undergo perbromination under conditions which can easily be employed using halogenated organic solvents.

 Among the disadvantages presented by the use of oleum as reaction medium, we can cite, in addition to all the usual problems associated with its handling on a large scale, the need to use large volumes, thus reducing the productivity of the reactor, difficulties in isolating the product, removing large volumes of sulfuric acid, and the poor quality of products resulting from the presence of sulfur contaminants such as brominated benzene sulfonic acids. The latter contamination problem also arises when liquid sulfur dioxide is used as the reaction medium.

 The inherent difficulties that accompany perbromation on a large scale are illustrated by various "exotic" approaches to chemical synthesis proposed for hexabromobenzene. For example, the chemical literature describes the pyrolysis of octabromocyclohexenones and the reaction of hexabromocyclopentadiene with tribromoacetaldehyde at supra-atmospheric pressures and strongly elevated temperatures.

 Another approach to the preparation of hexabromobenzene and other perbrominated aromatics has been the use of bromine / chlorine mixtures as a brominating agent. This process suffers from the serious disadvantage of introducing small quantities but playing an important role of chlorine in the final products, thus limiting their final quality.

 Yet another process which has been described for the polybromination of aromatic compounds requires the use of powerful mechanical mixers to maintain the partially brominated solid intermediates in a sufficiently fine state of subdivision to allow access of the liquid bromine or the state of vapor in attempts to achieve high levels of bromination.

 It has also been proposed to prepare completely brominated derivatives of aromatic compounds containing one or more phenyl groups using a bromine-based solvent (100% excess or more) and a bromine transfer catalyst at relatively reaction temperatures. low about 100C to room temperature (i.e. about 20-250C).

A corresponding process included bromination in the aromatic ring using a minimum excess of 20% bromine in the presence of halogenation catalysts at room temperature (20-250C).

While these processes made it possible to obtain perbrominated products with good yields when they were brought to an end, such results were only obtained by accepting economic penalties. The inefficiencies resulting from the low bromination reaction temperatures make the use of such processes on an industrial scale even less desirable.

 Accordingly, one of the objects of the present invention is to prepare pentabromophenol and decabromodiphenyl ether in high yield and purity by means of a relatively simple reaction, using excess bromine as both reactive and as the only reaction medium.

 Another object of the invention is to prepare perbrominated compounds of the type described practically free from weakly brominated products.

 An object of the invention is also to use, for perbromation, an excess of bromine of at least 75% relative to the stoichiometric amount.

 Yet another object of the invention is to carry out perbromation reactions of the kind described at high temperatures in order to significantly increase the productivity of the equipment per unit of volume and time, without affecting the yield of product and its qualities.

 The objects, advantages and characteristics of the invention described above and others can be obtained by means of practically perbrominated phenol and diphenyl ether, produced by reacting phenol or diphenyl ether at a high initial reaction temperature. from about 350C to about 800C in the presence of an excess of bromine of at least about 75% and not more than about 400% relative to the stoichiometric amount and of a small but catalytically effective amount of a catalyst chosen in the group consisting of iron, iron halides, iron compounds which form iron bromide under reaction conditions, aluminum, aluminum halides and aluminum compounds which form bromide d aluminum under the reaction conditions and continuing the reaction at an elevated temperature of about 350C to about 800C when the addition of the reactants is complete, while maintaining the excess bromine in order to obtain p substantial erbromation of the aromatic compound.

In the accompanying drawings
FIG. 1 is a graphic representation showing that the minimum critical bromination temperature is 350C in the case of perbromination of diphenyl ether, and
- Figure 2 is a graphical representation showing that the minimum critical bromination temperature is 350C in the case of perbromination of phenol.

 According to the invention, one can obtain practically perbrominated phenol and diphenyl ether by reaction of such a compound in the presence of a significant excess of bromine, playing simultaneously with the rail of reagent and only reaction medium. It is desirable that the bromine be present in an excess of at least 75%, but not more than about 400%.

 The reaction takes place in the presence of a small but catalytic amount of a bromination catalyst which may include iron and aluminum, their halides, and the compounds which form iron or aluminum bromide under the conditions of the reaction.

 It is particularly important according to the invention that the reaction takes place at a high initial reaction temperature. The bromine-based reaction medium must be maintained at a temperature of at least about 350C and preferably at least about 45C up to about 800C before starting the addition of phenol or diphenyl ether. The reaction medium is maintained at such an elevated temperature throughout the addition of the aromatic compound and is then maintained at an elevated temperature, preferably at reflux, after the end of the addition of the phenol or diphenyl ether, while maintaining excess bromine.

 Bromination of diphenyl ether and phenol using an excess of bromine as reaction medium is carried out much faster than bromination using an excess of bromine at room temperature or at lower temperatures and however the yield of product and its quality is not adversely affected. The reaction time is even shorter, compared to that of reactions using molar equivalents or even the usual slight excess of bromine of up to 20% and an organic bromination solvent.

 The isolation and the purification of the perbrominated products obtained in the bromine-based reaction medium according to the invention can be carried out in different ways and the necessary steps are considerably easier and simpler than for the products prepared by the usual methods and in addition give higher yields of purer and more uniform products.

 By using bromine as reaction medium and high reaction temperatures, practically quantitative yields of perbrominated products are obtained, containing only very small quantities of "subbrominated" materials.

 The perbromination in a bromine-based reaction medium carried out according to the process of the invention takes place in practically identical manner with practically the same results which are used as starting reagents, a fresh supply of chosen starting organic reagent or mixtures of its "subbrominated" side products as they may have been obtained in previous reactions. For example, whether fresh diphenyl ether or partially brominated diphenyl ether is used as the starting reagents, practically the same results are obtained. It is preferable in certain cases that these secondary products are subjected to some form of distillation or other purification before reuse.

 Although the precise percentage of excess bromine relative to the necessary stoichiometric amount which is used as reaction medium is not decisive, it has been found that excess bromine of about 75% and up to 300% and at and up to 400% are required. It has been found that an excess of about 100 to 200 X is optimum and the preferred level for perbromination of phenol and diphenyl ether.

 Bromination in a large excess of bromine in the range of about 100 x to 200% in excess gives more homogeneous and more highly brominated reaction products, while the use of lower excess bromine (i.e. i.e. less than 75 X excess) gives lower reaction rates, longer reaction times, and leads to lumpy and more or less impure reaction products containing "subbrominated" material (ie - say incompletely brominated).

 Characteristic tests implementing the process according to the invention can be carried out using both "dry" bromine (that is to say common bromine containing up to about 15 ppm of water) and so-called "bromine" wet "(i.e. bromine containing more than about 15 ppm). The use of the above-mentioned "dry" bromine is preferred for carrying out the bromination reactions (that is to say as a brominating agent and only reaction medium). "Wet" bromine has been found to have several detrimental effects in the reaction.

 The reaction proceeds much more slowly when "wet" bromine is used, the degree of slowness being more or less directly related to the amount of water present. In addition, the reaction products obtained, even after prolonged reaction times, are more or less "sub-brominated" (that is to say that all the available nuclear hydrogen atoms are not replaced by bromine) , the degree of replacement depending more or less on the amount of water present.

 The presence of water also supports the amount of bromination catalyst required up to a level much higher than normal optimum levels.

 As indicated, an essential parameter of the process according to the invention is that the bromination reaction of phenol or diphenyl ether using an excess of bromine as the reaction medium is started, at elevated temperatures considerably above ambient temperatures. (i.e. 20250C), which is to say that the reaction is started at temperatures above about 350C to about 800C, preferably at a temperature from about 450C to about 600C.

 When the addition of phenol or diphenyl ether is complete, the temperature can advantageously be further increased to the level of reflux during the subsequent stages of bromination. In the case of perbromation of phenol, characteristic reflux temperatures are observed of 60-640C, while in the case of the nerbromation of diphenyl ether, reflux takes place at about 59-600C.

 Significant advantages result from the use of high initial reaction temperatures as high as possible within the specified range. The solubilities of partially brominated products and / or intermediates are greatly increased by working at higher temperatures much higher than room temperature. This increased solubility effect gives higher titer products for any given reaction time, which results in higher equipment productivity. Thus, to achieve the completion of the perbromination reaction with the highest efficiency, it is desirable to use reaction mixture temperatures as high as the composition of the reaction mixture can allow, which temperatures, depending on the composition of the mixture, can significantly exceed the boiling point of the bromine contained therein and can in some cases reach 800C or more, when supra-atmospheric pressures are used.

 Significant advantages are obtained by operating at temperatures in the upper part of this range, including higher yields as well as higher contents of desired products. Surprisingly, the reaction can be carried out successfully at high initial reaction temperatures, without adversely affecting the desired quality objectives for the product.

 In adequately designed production facilities, operating at temperatures above 350C, preferably around 45-550C, the bromination cycle is reduced, the content of the product increases, the productivity of the reactor per unit of time increases by importantly, and you get significant industrial benefits. If desired, perbromination can also be carried out at temperatures well above the boiling point of the mixture, using supra-atmospheric pressures.

 It has been found that a total reaction time of 1 to 100 hours, depending mainly on the organic reagent, is adequate for obtaining a complete reaction under the conditions of the invention, for quantitatively converting the starting materials into perbrominated products in which practically all replaceable nuclear hydrogen atoms have been replaced with bromine, using bromine as the sole reaction medium (perbromation). This reaction time has been used fully satisfactorily both in laboratory tests and on a larger scale. In general, a total reaction time of up to about 20 hours has been found sufficient to produce high yields of high content products in the experiments studied. It has been found that in some cases the nerbromation is complete in three hours or less . Nothing is decisive as regards the duration of addition of the aromatic compound.

 It is desirable to add the aromatic compound at a rate slow enough to minimize loss of reagents from above and to allow the desired high reaction temperature to be maintained under control and safety conditions.

 The order of addition of the reagents (i.e. the aromatic compound to be brominated and the bromine) may change somewhat at will, and no method seems too critical. However, in order to obtain all the advantages of the invention for the preparation of perbrominated compounds, it is desirable that the necessary excess of bromine is present in the reactor during the last stages of bromination. For best results, the stoichiometric excess of 75% to 400% bromine should preferably be present during the second half of the reaction.

 The most normal and preferred procedure is the slow addition of phenol or diphenyl ether to the excess of bromine, acting both as a reaction medium and as a brominating agent, while maintaining the temperature under controlled conditions. desired level by heating cooling as appropriate. It is desirable, however, to add the feed of reactive aromatic compound at a rate slow enough to minimize losses of bromine, volatile reaction products and weakly brominated intermediates from above.

 A modification of the previous preferred method of adding the aromatic compound to the total bromine feed can also be advantageously used to increase the productivity of the reactor. The modification consists in the initial introduction of part of the total bromine into the reactor and in the subsequent addition of the aromatic compound described above. As bromination takes place, the volume of the reaction mass decreases and, as this decay takes place, the remaining portion of the total excess bromine is added.

 It is also possible to implement the process of the invention by adding bromine to phenol or diphenyl ether, preferably in liquid form. This method of addition has the advantage that bromine is introduced into the reaction mixture as it reacts, which also results in a reaction mixture of smaller volume and consequently increased productivity. A disadvantage of this procedure is that the relatively large amount of reagent is exposed to the bromine, and the bromination reaction is much more difficult to control. Thus, the risk of overheating the reaction mixture is considerably increased compared to other methods of contacting the reagent. This can, in the absence of control, result in loss of bromine, organic reagent and volatile brominated products. by the top. Another disadvantage is that the reaction mixture can go through a solid or semi-solid state with the presence of agitation difficulties.

 As noted, bromination in the bromine process of the present invention can advantageously be employed using phenol or diphenyl ether as starting reagents.

 Many different forms of metal-containing catalysts have been tried. The catalysts which have been found to be most effective are based on either iron or aluminum as the metallic component. Compounds found useful include, for example, metallic iron, iron bromide, iron chloride, metallic aluminum, aluminum chloride and aluminum bromide.

 It has been found that iron and the iron compounds which form iron bromide under the reaction conditions are the catalysts of choice for the preparation of pentabromephenol by bromination of phenol in a bromine reaction medium. Thus, the iron powder used as a catalyst gives the highest yield of perbrominated product having the best content. It has also been found that the iron powder remains active throughout the bromination period. It has also been found that iron bromide (ferric bromide) and iron chloride (ferric chloride) are quite satisfactory. It appears that ferric bromide gives an initial bromination slightly faster than iron powder. However, it has the disadvantage of giving a product which has a slightly lower titer in the desired product.

Iron chloride is slightly less effective as a catalyst than iron powder and iron bromide and can give perbrominated products slightly contaminated with chlorine. Aluminum chloride is slightly less effective than iron and produces somewhat lower content. It also tends to be inactivated faster than iron during bromination, which requires the introduction of additional portions of catalyst during the reaction period (bromination). Aluminum chloride, however, has the advantage of being colorless and therefore does not add color to the products.

For perbrominated end products for which it is not necessary to have chemical purity, the use of aluminum chloride allows the elimination of a purification step, or at least a simplified purification.

 It has been found that aluminum and aluminum compounds which form aluminum bromide under the conditions of the bromination reaction are the catalysts of choice for the preparation of deca bromodiphenyl ether by bromination in a reaction medium based on bromine. It has been found that the aluminum metal, for example in the form of a thin strip or powder, which is believed to be converted quickly, under the reaction conditions, to aluminum bromide, is an effective catalyst for the bromination process. .

Frequently, however, it is preferred to use, as catalyst, preformed, anhydrous aluminum bromide, or aluminum chloride. In some of these cases, aluminum bromide or aluminum chloride lead to somewhat faster bromination and / or more complete perbromination when used as catalysts for bromination. Another advantage of aluminum, aluminum halides and aluminum compounds which form aluminum bromide under the conditions of the bromination reaction is that these kinds of catalysts are colorless and do not add coloring to final products if left there, so that in final products that do not require chemical purity, the use of aluminum compounds allows the elimination or simplification of the purification step. metallic iron, iron halides and compounds which form iron halides under reaction conditions can also be used in the perbromination of diphenyl ether.

 It has been found that the amount of catalyst, i.e. iron, iron compound, aluminum or aluminum compound required, calculated on the basis of the metal, is a small amount but catalytically effective for the perbromination and can vary from about 0.1% to about 10% of metal relative to the weight of the organic substrate acting as a reactant. It is believed that amounts of catalyst of up to 15% by weight or more with reference to the metal are satisfactory but impracticable for economic reasons. It has however been demonstrated that within the above limits, relatively larger amounts of metal catalyst are required under certain specific conditions, for example if "bromine" bromine (ie containing Large amounts of catalyst can be used when adding aluminum and iron halides as the catalytic material.

 The reaction mixtures resulting from the implementation of the process of the invention using bromine as a perbromination reaction medium and a high initial reaction temperature can. be treated by a variety of treatment processes to isolate perbrominated products. The crude reaction mixture which may contain the brominated products, the excess bromine reaction medium, and the excess catalyst may, for example, be subjected to extraction either at atmospheric pressure or preferably under pressure reduced to about 800C up to constant weight of the residue. The crude product which is thus isolated can be further purified, for example by digestion with methanol, ethylene dibromide or dilute hydrochloric acid. This process of isolation by extraction is rapid, simple and gives reliable performance values. and relatively pure product. It has the disadvantage of being capable of leaving residual catalyst containing metal in the product.

 It is also possible to isolate the perbrominated product by replacing the excess bromine in the reaction medium with water, then by filtering the aqueous reaction mixture. The crude product obtained can then be purified by relatively simple digestion processes as described above. This isolation process can cause production and / or equipment problems in large-scale operations.

 It is also possible to replace the excess bromine in the reaction mixture with ethylene dibromide and then to filter. The crude product can then be further purified by digestion processes, as described above.

 According to a preferred embodiment of the isolation step, the whole reaction mixture is transferred into hot acidified water with simultaneous volatilization of the excess bromine followed by filtration of the aqueous mixture. Purification by digestion with suitable organic solvents can then be used as described above. When this process is carried out, the excess bromine gushes out almost immediately after contact with hot water, disintegrating the solid particles of perbrominated product and increasing their effective contact surface, while dissolving all residual catalyst.

When the bromine removal is complete, the crude reaction product is isolated by filtration.

 This process has many advantages. Among these, mention may be made of the elimination of most of the residual catalyst and the easy recovery of excess bromine for reuse after drying.

 It is also possible to implement another variant of the previous isolation step according to which the isolation and purification steps are essentially combined. By operating in this way, the aqueous product is not filtered, but is brought into contact directly with an organic solvent immiscible with water. The product is concentrated in the organic phase from which the aqueous phase is then separated, thus separating the catalyst from the product. -The product can then be isolated from the organic phase and purified by known means.

 In general, organic solvents which can be used in the isolation, digestion and / or purification stages include low molecular weight alkanols such as methanol, ethanol, propanols and butanols, halogenated compounds of low molecular weight such as ethylene dibromide, chlorobenzene, chloroform, acetylene tetrachloride and carbon tetrachloride, and ketones such as acetone and other suitable solvents.

 The perbrominated products which result from the use of this bromination in bromine as a reaction medium are decabromodiphenyl ether and pentabromophenol.

 It is generally possible to predict the product (s) which will result (s) from the application of this perbromination process under optimum reaction conditions applied to any particular starting material. The general rule is that each atom of nuclear hydrogen will be replaced by one atom of bromine if the reaction is carried out, that is to say until the release of hydrogen bromide ceases. This level of bromination can be achieved by appropriate adjustment of the reaction temperature, the concentration of the catalyst and the reaction time. The perbromination process is continued until the sample shows that the desired degree of bromination has been reached. Or the bromination reaction can continue until the release of hydrogen bromide practically ceases. The continuation of the bromination and the extension of the reaction periods beyond the desired point of bromination are useless and can in certain cases lead to the degradation of the products, to the fragmentation of the organic matter and to the formation of secondary products. tarry or resinous.

 Among the advantages of the high temperature bromination process of the invention is the obtaining of practically quantitative yields of crude perbrominated products of relatively high purity. The very small amounts of impurities which may be present are metal-based catalysts, metal catalyst compounds and minor amounts of less brominated products of the organic reagent which can, if desired, be recycled as reactants for more complete perbromation.

 Surprisingly, the advantages due to starting the reaction at high temperatures as described here are quite specific to phenol and diphenyl ether and similar beneficial effects are not observed with other uncondensed aromatic compounds. such as toluene and xylenes.

 The process has high productivity (that is, there is a large amount of product per unit volume of reactor used). It has also been found that the process makes possible the easy production of perbrominated phenol and diphenyl ether which were previously impracticable on an industrial scale or which were only accessible by more difficult and / or complicated methods of synthesis. and with special equipment. The reaction conditions used when implementing the invention are relatively mild and require only simple equipment, important factors in terms of economics and safety in industrial operations. Bromination reactions are carried out much faster when bromine is the reaction medium with respect to the speed observed when using other solvents, both organic and inorganic, such as fuming sulfuric acid.

 Since both the thermal stability and the color of the perbrominated products are important factors for flame retardants, the production of these perbrominated derivatives in a relatively pure state offers great advantages for their final use in flame retardant compositions. The availability and purity of the products are also important for their use as chemical intermediates, for example for the production of possible pesticides and medicines.

 Any partially brominated secondary product possibly produced can be easily recovered and recycled for complete perbromation in the same process and the same equipment.

 The treatment, isolation and purification processes can be modified in different ways.

As described here, in combination with the indicated high initial reaction temperature, many steps can be changed with respect to contacting the reactants, the bromine-based reaction medium and catalysts, isolating the products, product purification, the proper combination of which produces good results.

 The following examples are given only for the purpose of illustrating the process of the invention and should in no way be taken as limiting the scope of the invention to the particular characteristics of the process described.

EXAMPLE 1.

Decabromodiphenyl ether.

 A liter flask with four necks and a round bottom is fitted with a mechanical stirrer, a double-walled reflux condenser, a sample extraction tube, a thermometer and a reagent addition tube. The flask is connected to a water trap for the recovery of the hydrogen bromide formed as a secondary product. 1164 g (7.26 moles, 150% excess) of dry bromine are placed in the reaction flask, then 250 mg (0.0093 mole) of aluminum of approximately 0.84 mm (20 mesh). This mixture is stirred for 15 minutes during which the aluminum is completely converted into aluminum bromide.

The temperature of the container is kept under control to within plus or minus 1 C by using a temperature regulator of the "THERM-O-WATCH" type (model
L7 / 800 which can be obtained from "Instruments for Research and Industry", Cheltenham, PA.19012) in combination with a device of type "JACK-O-MATIC" (model JOM-3 which can also be obtain from "Instruments for Research and Industry").

 The bromine-catalyst mixture in the container is heated to 350C, and the addition of diphenyl ether, 49.5 g (0.29 mole), is started at a constant speed by means of an injector pump. in about 51 minutes. The reaction temperature is maintained at 350 ° C. more or less 10 ° C. throughout the addition of diphenyl ether. Additional heat is applied when the addition of diphenyl ether is complete and the temperature is increased to about 590C in about 20 minutes.

After about 120 minutes of heating after the addition, 300 ml of water is added to the reaction slurry and the reflux condenser, the sample collection tube and the reagent addition tubing are removed. A distillation head is fixed with a thermometer, a condenser and a receiving device to one of the connections of the flask and the excess bromine is removed by distillation until mulon reaches a temperature of 1000C.

 The decabromodiphenyl ether is separated from the aqueous slurry by filtration, washed with water and dried at 1100C in an oven with forced air circulation.

 The chromatographic analysis in vapor phase ("CPV") of the resulting product shows a surface percentage of 94.7% in decabromodiphenyl ether, isomers of nonabromodiphenyl ether totaling 4.5% and isomers of octabromodiphenyl ether totaling 0.5%.

EXAMPLE 2.

Ether decabromod iphenyl ipue.

 The procedure is as in Example 1, except that the bromine-catalyst mixture is heated to a temperature of 45 plus or minus 1 ° C. before starting the addition of dinhenyl ether and maintained at such a temperature for the whole the addition of diphenyl ether.

 The chromatographic analysis in vapor phase of the resulting product shows a percentage of area relative to the decabromodiphenyl ether of 96.4 X, to the nonabromodiphenyl ether of 3.2 X and to the octabromodiphenyl ether of 0.4%.

EXAMPLE 3.

Decabromod iphenyl ether.

 The procedure is as in Example 1 except that the initial temperature of the bromine-catalyst mixture is increased to 550C more or less 10C before the addition of phenyl oxide and maintained at this level until the end of addition of diphenyl ether.

About five minutes after the application of heat following the addition, a reflux temperature of 590C is obtained.

 The chromatographic analysis in vapor phase of the resulting product shows that it contains 96.3% of decabromodiphenyl ether, 3.3% of nonabromodiphenyl ether and 0.3 X of octabromodiphenyl ether.

EXAMPLE 4.

Pentabromophenol.

 The bromination of phenol is carried out in a reaction apparatus consisting of a reaction vessel fitted with a bromine bulb, an agitator, a thermometer and a water-cooled condenser connected to a tap. water. 1198.7 g (7.5 mol 150% excess) of bromine and 0.57 g of iron powder are introduced into the reaction flask. Phenol (56.7 g; 0.6 mole) is added dropwise from the dropping funnel with stirring over 100 minutes. Meanwhile, the temperature is maintained at approximately 46-470C.

 When the addition of the phenol is complete, the reaction mixture is heated to the reflux temperature (about 60-640C) and the reaction is allowed to continue until the evolution of HBr is stopped. The total reaction time is 3 hours.

 The reaction mixture is cooled to approximately 50 ° C. and transferred to 328 ml of aqueous hydrobromic acid. The excess bromine is removed by distillation at atmospheric pressure within 2.5 hours. The suspension is cooled to room temperature, filtered, and the solid reaction product is washed with water and dried. The crude product is obtained in the form of a cream-colored solid, melting at 229.90C (lit.: 229.50C) and having a content according to the CPV of 99.6%. The yield of crude product is practically quantitative.

EXPERIMENTAL EVALUATIONS.

 A study is carried out to determine the effect of the temperature of addition of the diphenyl ether on the productivity of the reaction and the yield and the quality of the decabromodiphenyl ether.

 The experimental results are obtained by checking the content of brominated product represented by the percentage of surface area in vapor phase chromatography (CPV) as a function of the addition temperature of the diphenyl ether and the reflux time after the addition. .

 In the preparations described in Examples 1 to 3, samples of the reaction mixture are taken at the end of the addition of diphenyl ether, at 15 minutes, 45 minutes, 75 minutes and 120 minutes after the addition of diphenyl ether.

 The samples taken are analyzed by vapor phase chromatography (CPV) by dissolving at least one gram of each in dibromomethane or dibromoethane in a proportion of I gram of sample per 40 milliliters of solvent and using an "HP 5754" instrument. with a flame ionization detector and a glass column of 2 mm inside diameter X 1.22 m (4 feet) provided with 3% of polysiloxanecarborane olive marketed under the brand DEXSIL 300 on SUPELCOPORT of 0.150 / 0.125 mm approximately (100/120 mesh) at a temperature of 200-3400C programmed at loOC per minute.

 For comparison purposes, similar tests are carried out at addiction temperatures of diphenyl ether of 150C plus or minus 10C and 250C plus or minus 1 C respectively, the samples being taken and analyzed at the same time intervals after 1 'addition.

 In Table I are collected the contents of decabromodiphenyl ether (percentage of surface area in CPV) as a function of the temperature -'addition of diphenyl ether and of the reflux time after the addition.

TABLE I
Initial ether addition temperature 150C 250C 350C 450C 550C diphenyl
Time after addition Decabromodiphenyl ether of diphenyl ether - CPV assay (% of area) liquefied (min)
0 31.9 35.5 83.4 86.9 87.2
15 73.0 75.5 92.8 95.2 95.1
45 90.5 92.2 93.8 95.6 95.7
75 92.8 93.2 94.1 95.4 96.2
120 94.1 94.6 94.7 96.4 96.3
The study of the values appearing in Table I shows that at ambient temperatures of addition of the diphenyl ether of 15 and 250 ° C., an undesirably slow rate of product formation is observed, requiring two full hours of reflux after the addition for reach the desired minimum content of 94 in decabromodiphenyl ether. In very different ways, for reactions carried out at 450 ° C. and at 55 ° C., essentially identical results are obtained, with content levels of 95 × obtained - after only 15 minutes of reflux (i.e. after only 1/8 of the time previously required).

 At the level of addition of the 350C diphenyl ether (representing the minimum addition temperature which can be employed while obtaining the benefits of the invention), a somewhat prolonged period is required (about 75 minutes), but which is always shorter than the two hour period required when working at room temperature.

Figure 1 shows the results of the table
I and demonstrates in graphical form the rate of formation of decabromodiphenyl ether as a function of the temperature of addition of diphenyl ether ("DPO") and the duration of reflux after the addition.

The speed curves at 450C and 550C are identical and show the speed of product formation at these reaction temperatures. The velocity curve at 350C describes a slightly slower, but nevertheless significantly faster reaction than the unacceptably slow ones, which result from additions of diphenyl ether under ambient or lower conditions (i.e. 150C and 250C) .

 By using the high initial reaction temperatures according to the invention in the perbromination of diphenyl ether, it is possible to reduce the heating which follows the addition by 75% or more without adversely affecting the yield or the quality of the product, thereby increasing the usefulness and productivity of the reaction.

 Another study shows that the advantages of operating at high temperature are obtained very selectively. Tests carried out at 25, 35, 45 and 55 ° C for phenol, toluene and p-xylene show not only that it is highly desirable to perbrominate the phenol at high initial reaction temperatures, but also that it does not It is not desirable to do this in the case of toluene and in that of p-xylene.

For each test, the following general procedure is used. The substrate to be brominated (toluene, p-xylene and phenol) is added dropwise to an excess of bromine (300% relative to the theoretical amount necessary for the perbromation of the cycle) and of the iron-based catalyst (1 X in weight by weight of substrate) at a determined temperature (25, 35, 45 and 550C) within 1 hour. When the addition of the substrate is complete, the reaction mixture is stirred at the determined temperature for two more hours. A sample of the reaction mixture for analysis by
CPV is taken immediately after the addition of the substrate has finished (0 minutes) and 15, 45, 75 and 120 minutes from.

 The results of these tests are summarized as follows In the case of pentabromophenol, it is found that a high initial reaction temperature has a highly high beneficial effect. The best titer (99.4 X) of the desired perbrominated product is obtained at the highest reaction temperature: 550 C. The reaction is also the fastest at the highest temperature. The values observed in the phenol tests are collated in Table II and these values are also reported in FIG. 2 which shows the rate of formation of pentabromophenol.

TABLE II
Initial phenol addition temperature 250C 350C 450C 550C
Time after addi- Pentabromophenol tion of phenol (mn) CPV assay (% of surface)
0 60.6 82.6 88.0 88.3
15 79.5 93.4 95.5 98.2
45 93.2 98.6 99.0 99.3
75 97.5 98.9 99.2 99.3
120 98.5 99.2 99.2 99.4
As these values show, an undesirably slow rate of formation of pentabromophenol is observed at ambient starting temperatures (250C).

At such a starting temperature, a period of two (2) hours after the addition is necessary to obtain a product titer of 98.5%. A much shorter post-addition heating period (35-45 minutes) is required when the reaction begins at 35 and 450C, only about 30 to 40% of the time required at room temperature. When the starting temperature is 55oC, it takes only 15 minutes of heating after the addition, or 1/8 of the time required at room temperature, to obtain a product having a content of 98.2%.

 These observations are represented graphically in FIG. 2 which shows that the tests at high temperature (350, 450 and 550C) form a group which differs notably from the test carried out at room temperature (250C).

 Tables III and Iv contain the results obtained in the tests with toluene and p-xylene.

In each case, they demonstrate that, unlike diphenyl ether and phenol, the best contents are observed at ambient temperatures (i.e. at 250 ° C.) and that the high initial reaction temperatures have a deleterious effect. on the reaction.

TABLE III
Initial toluene addition temperature 250C 350C 450C 550C
Time after addi- pentabromotoluene tion of toluene (min) CPV assay (% of area)
O 94.0 88.2 84.6 84.3
15 91.0 90.2 85.7 84.5
45 92.5 91.0 84.8 86.7
75 93.0 90.9 87.3 87.7
120 93.0 91.7 85.1 88.0
TABLE IV
Initial temperature of addition of 250C 350C 450C 550C p-xylene
Time after addi- Tetrabromo-p-xylene p-xylene tion (min) CPV assay (% of area)
O 91.1 93.0 91.5 90.1
15 94.8 92.9 91.1 90.9
45 95.6 93.3 91.9 91.1
75 95.4 93.6 93.0 92.0
120 95.7 93.9 93.9 92.1
As the above values show, with diphenyl ether and phenol only among the non-condensed aromatics evaluated, it is highly advantageous in terms of product yield and equipment productivity to employ high initial reaction temperatures ( ie 350C or more) which clearly exceed the ambient conditions (ie about 250C or less).

Claims (12)

 1. Process for the practically complete perbromination of an aromatic compound chosen from the group consisting of phenol and diphenyl ether, characterized in that it comprises the steps consisting in: adding the aromatic compound at a high initial temperature of about 350C to about 550C, to a mixture of at least 75% excess and not more than about 400% excess, relative to the amount stoechio ;; metric, bromine and a small but catalytically effective amount of a catalyst selected from the group consisting of iron, iron halides, iron compounds which form iron bromides under reaction conditions, aluminum, aluminum halides, and aluminum compounds which form aluminum bromide under the reaction conditions, and continue the reaction at an elevated temperature at which reflux can take place when the addition of the compound aromatic is complete, while maintaining the excess bromine in order to obtain an almost total perbromation of the aromatic compound.  2. Method according to claim 1, characterized in that the reaction is initially carried out at a temperature of about 45 C to about 55 C.  3. Method according to claim 1 or 2, characterized in that the excess of bromine is from approximately 100 X to approximately 200% relative to the stoichiometric quantity necessary for the perbromation of the aromatic compound.  4. Method according to one of claims 1 to 3, characterized in that the catalyst is present in an amount of about 0.1% to about 10% by weight, based on the weight of metal equivalent, relative to the amount of aromatic compound.  5. A method for the practically complete nerbromation of diphenyl ether, characterized in that it comprises the steps of adding diphenyl ether at an initial high temperature of about 350C up to about 550C to a mixture of "an excess of at least 75 and not more than about 400%, relative to the stoichiometric amount of bromine and of a small but catalytically effective amount of a catalyst chosen from the group consisting of iron, iron halides , the iron compounds which form iron bromides under the reaction conditions, aluminum, the aluminum halides, and the aluminum compounds which form aluminum bromide under the reaction conditions, and continuing the reaction at an elevated temperature at which reflux can take place after the addition of the diphenyl ether is complete, while maintaining the excess bromine to obtain substantially complete perbromination of the diphenyl ether.  6. Method according to claim 5, characterized in that the reaction is initially carried out at a temperature of about 45 C to about 550C.  7. Method according to claim 5 or 6, characterized in that the excess of bromine is from approximately 100 to approximately 200% relative to the stoichiometric quantity necessary for the perbromination of diphenyl ether.  8. Method according to one of claims 5 to 7, characterized in that the catalyst is present in an amount of about 0.1% to about 10% by weight based on the weight of the metal equivalent, relative to the amount of diphenyl ether.  9. A process for the practically complete perbromination of phenol, characterized in that it comprises the stages consisting in adding phenol at a high initial temperature of approximately 350C up to approximately 550C to a mixture of an excess of at least 75% and not more than about 400 X of bromine, relative to the stoichiometric amount and a small but catalytically effective amount of a catalyst chosen from the group consisting of iron, iron halides, iron compounds which form iron bromides under reaction conditions, aluminum, aluminum halides, and aluminum compounds which form aluminum bromide under reaction conditions, and continue the reaction at a temperature high at which reflux can take place, after the addition of the phenol is complete, while maintaining the excess bromine in order to obtain an almost complete perbromination of the phenol.  10. Method according to claim 9, characterized in that the reaction is initially carried out at a temperature of about 45 C to about 55 C.  11. The method of claim 9 or 10, characterized in that the excess of bromine is from approximately 100 X to approximately 200 X of the stoichiometric quantity necessary for the perbromination of the phenol.  12. Method according to one of claims 9 to 11, characterized in that the catalyst is present in an amount of about 0.1% to about 10% by weight, based on the weight in metal equivalent, by relative to the amount of phenol.