NL8000893A - METHOD FOR PREPARING DRILL TRICHLORIDE. - Google Patents

Description

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Process for the preparation of boron trichloride.

Boron trichloride is a compound with many technical applications. For example, it is well known that this compound can be used as an intermediate for the preparation of other boron-containing compounds, such as diboran and refractory metal borides, for example, titanium diboride.

The compound is also used as a coolant, as a catalyst and in Grignard reactions.

A number of methods have been described in the literature for the preparation of boron trichloride. According to one of these methods, chlorine gas is passed through a reactor, containing a mixture of boron oxide and carbon, at temperatures on the order of 700-1000 ° C. However, several difficulties arise when using this method. First, a significant portion of the chlorine reactant is wasted in the formation of phosgene, which is difficult to separate from boron trichloride. Second, a solid complex of boron trichloride and boron oxide (B2O3) is formed in the reactor effluent piping and subsequent solids collection facilities. Furthermore, special working conditions and construction materials are required and the use of chlorine at temperatures of 700 ° C and above. The process difficulties and corrosion problems of such a process contribute significantly to an increase in production costs.

The preparation of boron trichloride by chlorination of trimethyl borate or trimethoxy boroxine at room temperature and under autogenous pressures is described in U.S. Pat. No. 2,943,916. According to column 1, line 39 of this US patent, the reaction of trimethyl borate with chlorine proceeds according to the equation (1) B (OCH3) 3 + 9C12 → BC13 + 3C0C12 + 9HC1.

According to equation (1), 3 moles of phosgene are formed per mole of 5-boron trichloride product. The formation of a three times greater amount of phosgene than boron trichloride wastes the chlorine reactant. Also of importance is the difficulty of separating phosgene from boron trichloride.

The methods proposed in the literature for the separation of ibsenic from boron trichloride are (a) thermal cracking of the phosgene at high temperatures, for example about 1000 ° C, (b) contacting the boron trichloride phosgene stream with a carbon catalyst at, for example, 300-700 ° C and (c) fractional distillation. The separation of boron trichloride from phosgene by fractional distillation is difficult and expensive due to the closely spaced boiling points of these two materials, ie phosgene boils at about 8 ° C and boron trichloride boils at about 12.5 ° C. Thus, there is a need for a low temperature processable process for the preparation of boron trichloride, wherein the amount of phosgene formed is significantly reduced.

It has now been found that the amount of phosgene by-product formed in the chlorination of borate ester, for example trimethyl borate, can be significantly reduced by running the chlorination at about 20-100 ° C in the presence of a free radical initiator while maintaining the molar ratio from chlorine to borate ester reactant, fed to the reactor, between about 5.5: 1 and about 7.5: 1 and simultaneously removing gaseous products of the chlorination reaction from the reactor. The reaction may optionally be conducted in the presence of an inert organic liquid solvent. The absolute reactor pressures can vary, but are generally below 3 atmospheres. It has further been found that the yield of boron trichloride is substantially stoichiometric, that is, the yield is not reduced when less than 9 moles of chlorine are used per mole of trimethyl borate.

80 0 0 8 93 r t 3

The invention will be described in more detail below with reference to the accompanying drawing (Figure 1), which shows a schematic illustration of an embodiment of the invention, wherein the reaction is carried out in the presence of an inert liquid organic solvent and a free radical initiator.

According to the invention, chlorine is reacted with borate ester reactant in a molar ratio of considerably less than 9: 1. Surprisingly, it has been found that the major carbonaceous product produced in the process of the invention is carbon monoxide rather than phosgene. The reaction can be represented by equation (2) B (0CH3) 3 + 6C12 -► BC13 + 3C0 + 9HC1.

When comparing reaction equation (2) with reaction equation (1), it appears that in the second equation, 3 moles of carbon monoxide are formed instead of the 3 moles of phosgene, indicated in reaction equation (1), which is accompanied by a reduction in the used amount of chlorine reaction component. Furthermore, reaction equation (2) is less exothermic than reaction equation (1), making it easier to control the chlorination reaction represented by reaction equation (2).

The molar ratio of chlorine to borate ester reactant, for example trimethyl borate, fed to the reactor is less than the stoichiometric amount of 9: 1.25 prescribed in U.S. Patent 2,943,916.

Although reaction equation (2) requires a molar ratio of 6: 1, the molar ratio of chlorine to borate ester may vary slightly from the theoretical value of 6: 1. Generally, the molar ratio will be maintained during the reaction period between about 5.5: 1 and about 7.5: 1, and preferably between about 5.75: 1 and about 6.75: 1. When the borate ester reactant used is the chloromethyl ester of boric acid, the chlorine content of the ester is taken into account in the calculation of the molar ratio, that is, in the determination of the total amount of chlorine fed to the reactor.

The temperature at which the chlorination reaction is carried out can vary, for example between about 20 ° C and about 100 ° C. Generally, the reaction will be conducted between about 40 ° C and about 90 ° C. Preferably, the reaction temperatures will vary between about 60 ° C and about 80 ° C, for example, between about 65 ° G and about 75 ° C. Surprisingly, it has been found that temperatures above room temperature, e.g. 40 ° C and above, improve the selectivity of the reaction over carbon monoxide formation. At the more favorable temperatures, the amount of phosgene formed is thus considerably less than the amount formed at room temperature, for example 23 ° C. Substantial amounts of phosgene are formed at temperatures below 20 ° C.

The temperature at which the chlorination reaction is carried out will also depend on the special solvent (if used) used as reaction medium and on the reactor pressure. At atmospheric pressures, the maximum reaction temperature will be determined by the boiling point of the solvent or the temperature at which the reaction mixture boils when no solvent is used. Temperatures above the boiling point of the solvent or, for example, in the upper part of the above temperature, for example, 70-100 ° C, may be employed when the chlorination reaction is conducted at pressures slightly above atmospheric pressure. At super atmospheric pressures, temperatures above 100 ° C, for example 125 ° C, can be used. Analogously, if reaction pressures below 1 atmosphere are used, the reaction temperature will be correspondingly lowered.

The pressure at which the chlorination reaction is conducted is usually less than about 3 atmospheres absolute pressure. Such moderate pressures are significantly different from those used in the chlorination process described in U.S. Pat. No. 2,943,916, wherein the reaction of reaction equation (1) is conducted in a sealed tube, i.e., under autogenous pressures.

It has been determined that the reactor pressure developed in the reaction described in the above-mentioned US patent is higher 80 0 0 8 93 \

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5 than 10 atmospheres and probably in the vicinity of 15-20 atmospheres.

The chlorination reaction of the invention is more usually conducted between about 0 and about 1.4 kg / cm 2 and more particularly between about 0 and 1.05 kg / cm.

The chlorination reaction is conveniently carried out at atmospheric or ambient pressures; however, in its continuous operation, pressures above atmospheric pressure are used to overcome the pressure drop in the equipment and lines downstream of the reactor. As mentioned, reduced pressures, i.e. less than atmospheric pressure, can also be used, for example pressures as low as 200 mm Hg.

The chlorination reaction can, if desired, be carried out in a reaction medium, comprising an inert liquid organic solvent. The use of a solvent aids in controlling the reaction temperature. For example, a portion of the solvent can be vented from the reactor as vapor, passed to a reflux condenser in which the vapor is condensed, and then returned to the reactor. The solvent must be chemically inert to the reactants and the reaction products and is preferably a solvent in which the reaction products are soluble. Preferably, the reactants and the reaction product are soluble in the solvent.

As solvents, mention may be made of carbon tetrachloride and chlorofluorinated oils, such as halocarbon oil, Fluorolube heat exchange fluids (polymers of trifluorovinyl chloride) and polychlorinated aromatics, such as 1,2,4-trichlorobenzene. Use can also be made of the analogous liquid polyhalogenated, for example chlorinated, fluorinated and / or brominated, aliphatic hydrocarbons with 1-4 carbon atoms and aromatic hydrocarbons. Carbon tetrachloride is particularly useful as a solvent because it is chemically inert to the reactants and reaction products and is additionally a solvent therefor.

The special solvent or the amount of solvent used are not subject to strict limits.

Only the amount needed to solubilize the reactants and reaction products and to act as a heat absorbing material for the reaction heat need be used. Generally, the solvent to borate ester weight ratio will range from about 1: 1 to 10: 1. When the chlorination reaction is carried out in the absence of an additional solvent added, the borate ester and the intermediate compounds formed during the reaction serve as the reaction medium.

In the practical operation of the above-described process, the amount of phosgene coproduct formed is significantly reduced compared to that formed according to reaction equation (1), that is, the amount of phosgene formed is less than 0.6 moles per mole of borate ester, for example trimethyl borate, used as a reactant. In contrast, the amount of phosgene formed by the known process, for example, according to reaction equation (1), is about 3 moles of phosgene per mole of trimethyl borate reactant. The amount of phosgene formed according to the invention can be reduced to less than 0.2, for example, 0.1 mole of phosgene per mole of trimethyl borate and under the most preferred conditions, the amount of phosgene formed can be reduced to less than 0.03 mol, for example 0.01 mol, phosgene per mol of methyl methyl borate reactant,

Several advantages are obtained by reducing the amount of phos-25 formed in the reaction. First, the amount of chlorine wasted in the formation of such a co-product is correspondingly reduced. Unless such phosgene is recovered and treated, for example by cracking, to recover its chlorine content, the phosgene is destroyed, for example, by neutralization with strong alkali. Both of these alternatives result in an economic burden on the process. The latter treatment results in a loss of chlorine. Second, and perhaps more importantly, the smaller the amount of phosgene formed in the reaction, the less phosgene need be separated from the boron trichloride product.

As boron compound reactants, the borate esters, namely trimethyl borate, trimethoxy boroxine and chloromethyl esters of boric acid, can be used. Examples of chloromethyl esters are dimethoxyboron chloride, i.e. (CHgO ^ BCl, methoxyboric dichloride, ie, (CH30) BC12, and chloro-5 methyl esters of the general formulas B (0CH2C1) (OCH3) 2, b (och2cl) 2, b (och2ci ) 3 b (ochci2) (och3) 2, b (ochci2) 2 (och3), B (0CHC12) 3 (C1CH20) 2BC1, (C12CH0) 2BC1, (C1CH20) BC12 and (C12CH0) BG12.

Trimethoxyboroxine is understood to mean the product obtained in the reaction of boron oxide and trimethylborate in varying proportions. These products are conveniently represented by the formula B203 (0CH3) 3. It will be understood, however, that an excess of either boron oxide or trimethyl borate may be present, in which case the above formula 15 does not reflect the exact composition of the material.

Trimethyl borate is a commercially available material. It can be prepared by reacting boron oxide or boric anhydride with methanol. In this regard, reference may be made, for example, to Schlesinger et al., J. Am. Chem. Soc. 75, 20 213-215 (1953), while mention can also be made of the

U.S. Patents 2,217,354, 2,088,935, 2,808,424 and 2,818,115, all of which relate to the above process for the preparation of methyl borate.

The boron compound, for example trimethyl-borate, and the chlorine used as reactants must be substantially dry since boron trichloride is easily hydrolyzed by water. Therefore, in order to avoid an unnecessary loss of boron trichloride product, the reactants, solvent, reactor, and recovery equipment should be substantially anhydrous, that is, less than 10 ppm (parts per million) of water.

The chlorination reaction described above is initiated by free radicals, and therefore any free radial initiator that forms free radicals at the chlorination temperature, for example, Irht or organic peroxy compounds, can be used. The amount of initiator used is not limited to sharp limits as long as the free radical threshold is provided to initiate and maintain the chlorination reaction. Such an amount is generally referred to as an initiating amount.

Any light source, which provides the required radiation, can be used. Such radiation is generally considered to be provided by light in the vicinity of the ultraviolet or barely visible light. Thus, an ordinary household tungsten filament lamp, solar lamp or mercury-10 arc lamp can be used. The amount of radiation required is difficult to define; however, one skilled in the art can easily determine whether the quantum of useful radiation is appropriate for the amount of reactants used by observing whether the chlorination reaction occurs. The photochlorination light source 15 may be an internal (inside the reactor) or an external (outside the reactor) light source). In the latter case, means must be provided for the radiation to enter the reactor, for example by using a glass reactor or a glass opening.

In addition to photoinitiation, the chlorination reaction can be initiated by an organic free radical initiator, ie an organic azo or peroxy compound. Examples of such compounds are diacyl peroxides, mono-peroxycarbonates, dialkyl peroxydicarbonates, peroxyesters and azo-compounds. The special free radical initiator used is not subject to sharp limits, provided that it is compatible with the reactants and the solvent (if used), that is, chemically non-reactive, and effectively forms free radicals at the chlorination temperature used. One skilled in the art can easily select a suitable initiator from the published half-value data, which is a means of expressing the decomposition rate of the initiator at a given temperature. The organic free radical initiators must be substantially anhydrous, ie substantially dry, and substantially free of materials, such as solvents, oils, etc., which can be chlorinated. In particular, the number of carbon atoms in any residue (alkyl, 80, 0, 0, 8, 93, 9, aryl or cycloalkyl) of the peroxide will range from 2 to 12.

Examples of suitable organic free-radical initiators are diacyl peroxides such as acetyl peroxide, benzoyl peroxide, caprylyl peroxide, p-chlorobenzoyl peroxide, decanoyl peroxide, 2,4-dichlorobenzoyl peroxide, lauroyl peroxide, butyl peroxyethylene butoxy esters, such as peroxy esters, such as t-butyl peroxyisobutyrate and t-butyl peroxy pivalate, dialkyl peroxydicarbonates, such as diethyl, diisopropyl, di-n-propyl, di-n-butyl, di-sec-butyl, diisobutyl, di-t-butyl dicapryl, di-2-ethylhexyl, dibenzyl, dicyclohexyl and di-4-t-butylcyclohexyl peroxydicarbonate, monoperoxycarbonates such as t-butylperoxyisopropyl carbonate and azo compounds, such as azo-bis-isobutyronitrile.

As in the case of light, only the amount of organic free radical initiator needed to initiate and maintain the chlorination reaction, ie, an initiating amount, needs to be used. This amount will vary depending on the free radial initiator used, the chlorination temperature and the amount of the reactants. Such an amount can easily be determined by a person skilled in the art. In the case of a peroxy dicarbonate, such as diisopropyl peroxydicarbonate, about 1% by weight based on the borate ester, for example trimethyl borate, will be used. The organic free radical initiator will be continuously fed to the reactor during a continuous chlorination, as opposed to a discontinuous chlorination, in order to maintain a continuous supply of free radicals in the reaction medium.

Reference is now made to the accompanying Figure 30, which gives a schematic illustration of an embodiment of the invention. A reactor 10 for carrying out the chlorination reaction is shown. The reaction components trimethyl borate and chlorine are fed to the reactor by feed lumps 5 and 3, respectively. The chlorine reactant is preferably fed below the level of the liquid in the reactor, for example by means of a sprayer, to provide 80 0 0 8 93 ï <10 in agitation of and contact between the reactants.

When fed in this manner, the chlorine is readily absorbed into the reaction medium, which reaction medium, as indicated, is carbon tetrachloride. Carbon tetrachloride solvent and initiator are fed to reactor 10 through feed lines 9 and 7, respectively. The organic free radical initiator can be replaced by a source of ultraviolet light, for example, an ultraviolet light source placed inside the reactor.

Generally, borate ester and solvent (if used) are fed to the reactor to form the reaction medium. Then, the reaction medium is exposed to the free radical initiator (light or organic peroxy or azo compound) and chlorine is introduced below the surface of the reaction medium. In a continuous reaction, the required reaction components are also supplied to the reactor via a dosage. After an initial induction period, for example less than about 5 minutes, the chlorination reaction proceeds rapidly under a significant consumption of the added chlorine reaction component. The products of the reaction, ie hydrogen chloride, carbon monoxide, phosgene and boron trichloride, are continuously removed from the reactor together with the solvent, for example carbon tetrachloride, as a gaseous effluent through flow line 12. This gaseous product effluent is passed to reflux condenser 15 in which the solvent and partially the chlorinated borate ester intermediates are condensed. The condensate is returned to the reactor to control the reactor temperature and to return the above borate ester intermediates for further chlorination. The gaseous effluent is passed through flow line 17 to absorber 20, in which it is contacted with a further amount of tetrachloro-carbon solvent, which is added thereto via flow line 32. Boron trichloride and phosgene are absorbed in the carbon tetrachloride solvent, fed to absorber 20, and removed through flow line 26 to stripper 30. The carbon monoxide and hydrogen chloride, which are not absorbed in the carbon tetrachloride solvent in absorber 20, 80 0 0 8 93 i -c 11, are removed therefrom by flow line 24. These gases can be separated and recovered for use in other chemical reactions or decomposed, for example, by combustion (CO) or neutralization with a base (HCl).

In stripper 30, boron trichloride and phosgene are separated from the carbon tetrachloride solvent and these products are passed via flow line 34 to distillation column 40, in which the phosgene is removed as overhead product via flow line 44 and boron trichloride product is removed as bottom product via flow line 42 Depending on the final application, the distillation column 40 may not be necessary. If, in the final use of boron trichloride, the amount of phosgene contained therein, such as less than 1.5 wt%, eg 0.5 wt%, can be tolerated, the phosgene can be left in the boron trichloride. The phosgene can be recovered and used as a reactant in other chemical reactions, e.g., phosgenation, or decomposed by reaction with a base, e.g., sodium hydroxide.

It will be understood that the product separations shown in Figure 20, i.e., in the absorber 20 and the stripper 30, are not complete and will contain small amounts of reaction products and solvent in these streams unless otherwise indicated. For example, the overhead product from absorber 20 will contain, in addition to carbon monoxide and hydrogen chloride, small amounts of boron trichloride, phosgene, and carbon tetrachloride. Similarly, the stripper 30 bottom product will contain small amounts of boron trichloride and phosgene in addition to carbon tetrachloride solvent.

It has also been found that in the continuous free-radical chlorination of borate ester, as described above, dyes are formed in the reaction mixture. These colored substances are believed to be boron-containing compounds formed during the chlorination reaction.

As the reaction proceeds, the concentration of the dyes in the reaction mixture increases and thereby the effective activity of the free radical initiator is reduced. This 80 is particularly difficult when the free-radical initiator is light because the colored substances prevent the light energy from the light source from reaching the reactant activated by the light. The difficulties arising from the formation of colored substances in the reaction mixture are not so serious when using free-radical chemical initiators, for example organic peroxide compounds, but the colored substances are also expected to interfere with the effectiveness of the action of chemical initiators.

In another aspect of the invention, it was found that the dyes formed in the reaction mixture can be removed by distillation. According to the invention, a fraction of the reaction mixture is removed as a rinsing stream from the reactor and passed to a distillation zone, in which it is distilled. The distillate obtained in the above distillation is returned to the reactor. The colored substances present in the feed to the distillation zone are continuously or periodically removed from the distillation zone as bottom material. The invention allows the continuous free radical chlorination of borate esters to boron trichloride without the need to interrupt the reaction to remove colored impurities that are formed and accumulated in the reaction mixture.

This aspect of the invention will now be described in more detail with reference to the accompanying drawing (Figure 2), which gives a schematic illustration of an embodiment of the invention.

The accompanying drawing (Figure 2) shows a reactor 10 for carrying out the chlorination reaction. The reactants borate ester (trimethyl borate) and chlorine are supplied to the reactor via feed lines 5 and 3, respectively. The chlorine reactant is preferably supplied below the level of the liquid in the reactor, for example by means of a sprayer, to provide agitation of and contact between the reactants. When fed in this manner, the chlorine is easily and quickly absorbed into the reaction medium. Solvent (carbon tetrachloride) is fed to reactor 10 via feed line 9. A light source 7, for example ultraviolet light, within a transparent container 6, is shown within reactor 10. A chemical free radical initiator, the nature of which is described below, may replace the light source.

Generally, the borate ester and solvent (if used) are fed to the reactor to form the reaction medium. The free radical initiator (light or a chemical initiator) and chlorine are then fed to the reactor. In a continuous reaction, the reactants are fed to the reactor by continuous dosing. After an initial induction period, for example less than about 5 minutes, the chlorination reaction proceeds rapidly under a significant use of the chlorine reactant as soon as it is fed. The gaseous products of the reaction, for example hydrogen chloride, carbon monoxide, phosgene and boron trichloride, are continuously removed from the reactor together with the solvent, for example carbon tetrachloride, via flow line 12. This gaseous product effluent is fed to reflux condenser 15, in which solvent and partially chlorinated borate ester intermediates are condensed. Condensate from cooler 15 is returned to reactor 10, where it helps control the reactor temperature. Partially chlorinated borate ester intermediates in the condensate are thereby further chlorinated. The gaseous effluent from cooler 15 is passed through flow line 17 to absorber 35, where it is contacted with solvent, eg carbon tetrachloride, fed thereto via flow line 42. Boron trichloride and phosgene are adsorbed in the solvent and removed by flow 36 to stripper 40, Carbon monoxide and hydrogen chloride, which are not absorbed in the solvent, are removed from absorber 20 through flow line 38.

These gases (CO and HCl) can be separated and recovered or decomposed, for example by base combustion and neutralization, respectively.

on η η o 07 ï * 14

According to the invention, a rinse stream is removed from reactor 10 through flow line 18. The volume of the reaction mixture, which is removed as rinse stream, will vary depending on the rate at which the dyes 5 are formed in the reaction mixture. It can be expected that the rate of formation of the dyes will increase with temperature and therefore the volume of material removed as rinsing stream from the reactor will depend in part on the chlorination temperature used. The volume of the reactor coil flow must be sufficient to keep the reaction mixture substantially free of color-forming boron-containing compounds.

As mentioned, the rinse fraction of liquid reaction mixture removed from the reactor can vary within wide limits. Generally, the rinse fraction will vary between about 4 and about 20% by volume of the reaction mixture per hour, usually between about 6 and about 15% by volume, for example between 8 and 12% by volume, of the reaction mixture per hour. The above rinse fractions have been calculated to provide complete recirculation of the reaction mixture volume over a period of about 5-24 hours, for example every 8-12 hours. The one-time cycling of the reaction mixture within the above time periods prevents accumulation of dyes in the reaction mixture.

As indicated in the accompanying figure 2, the rinsing current is passed to receiver 20, from which it is led via flow runner 22 to distillation vessel 30. Receiver 20 makes it possible to operate the distillation vessel 30 batchwise or continuously. If distillation vessel 30 is operated continuously, receiver 20 can be eliminated or used as a storage vessel.

According to the method of the invention, the rinsing stream of the reaction mixture is subjected to a simple distillation, for example flash distillation, in vessel 30, although the pot temperature in vessel 30 will depend on the composition of the reaction mixture rinsing stream, the pot temperature in 35 generally lie between about 70 and about 100 ° C at a pressure of about 1 atmosphere.

80 0 0 8 93> / 15

Vapors, formed by the distillation in vessel 30, are removed through flow line 33 and fed to cooler 25, in which the vapors are condensed and recycled to reactor 10 through flow line 34. The high boiling materials, ie the bottoms, in distillation vessel 30 are periodically or continuously removed by flow line 32 for its discharge (rejection). The boron-containing compounds in the soil material can be decomposed by hydrolysis with 10-20% aqueous sodium hydroxide.

Distillate from vessel 30, recycled to reactor 10, will contain less boron-containing compounds than the reaction mixture purge stream due to the removal of boron-containing dyes from the purge flow. In order to keep the boron concentration in the reaction mixture substantially constant, a further amount of borate ester can be added to the reactor by doping the distillate (before it is fed into the reactor) with borate ester or by the feed rate of borate ester reactant fed into the reactor via feed line 5, to be increased from the value present at the start of the chlorination reaction. This additional amount of borate ester (as boron) is substantially equal to the amount of boron, which is removed from the reaction mixture rinsing stream as a bottom material from distillation vessel.

Reference is again made to Figure 2 and in particular to stripper 40. Boron trichloride and phosgene are separated from the solvent and passed via flow line 44 to reactor 45, in which phosgene is separated from boron trichloride. Solvent is removed from the bottom of stripper 40 and returned to absorber 35 through flow line 42.

As one of the methods known in the art for effecting the separation of phosgene and boron trichloride, mention can be made of the catalytic preferential decomposition of phosgene, as described in U.S. Pat. No. 3,126,256. Thus, in the reactor 45, phosgene-containing boron trichloride is passed over an activated carbon catalyst at temperatures between about 300 ° C and about 700 ° C to decompose phosgene to 8 0 0 0 8 93 * 16 carbon monoxide and free chlorine without decomposition of the drilling trilo ride. The resulting gaseous products are removed from reactor 45 through flow line 48. The boron trichloride can be separated from the carbon monoxide and elemental chlorine using procedures known in the art, for example, by condensation.

Depending on the final application, reactor 45 may not be necessary. If, in the final use of boron trichloride, an amount of phosgene present therein, such as less than 1.5 wt%, for example 0.5 wt%, can be allowed, the phosgene can be left in the boron trichloride. Alternatively, the phosgene can be recovered, for example, by distillation, and used as a reaction component in other chemical reactions, for example, the phosgene ring.

It will be apparent to those skilled in the art that the product separations shown in the drawing, for example in absorber 35 and stripper 40, are incomplete and that small amounts of reaction products and solvent will be present in these streams unless otherwise indicated . For example, the overhead fraction from absorber 35 will contain, in addition to carbon monoxide and hydrogen chloride, small amounts of boron trichloride, phosgene, and carbon tetrachloride. Similarly, the stripper 40 bottom material will contain small amounts of boron trichloride 25 and phosgene in addition to carbon tetrachloride solvent.

The molar ratio of the chlorine and borate ester fed to the reactor can vary. Generally, only the amount of chlorine required to react with the borate ester reactant at the reaction temperatures is used because amounts which are an excess of this amount put an economic burden on the process, both as regards the loss of chlorine reactant as the equipment needed for the recovery or rejection of the excess chlorine. As noted above, the molar ratio of chlorine to borate ester, for example trimethyl borate, is maintained between 5.5: 1 and about 7.5: 1 and 80 0 0 8 93 * r 17 during the reaction period, preferably between about 5.75; 1 and about 6.75: 1. When the borate ester reactant used is the chloromethyl ester of boric acid, the chlorine content of the ester is taken into account when calculating the molar ratio, that is, when determining the total amount of chlorine fed to the reactor.

The temperatures, pressures, solvents, molar ratios of the reactants and the nature of the reactant components and initiators used according to this aspect of the invention are analogous to those mentioned above in the first aspect of the invention, namely the process for the reduction of the amount of phosgene in the preparation of boron trichloride by chlorination of borate ester using a free radical initiator and the simultaneous removal of gases from the reactor.

The invention is further illustrated but not limited by the following examples.

Example I

A 300 ml baffle containing four-necked glass flask 20 was equipped with a thermometer, magnetic stirrer, water-cooled condenser and glass tube for feeding chlorine below the surface of the reaction mixture. The reactor was irradiated with a 250 watt solar lamp. The reaction flask was cooled using a water bath. The gases exiting the reaction flask were passed through a water-cooled condenser and then into a 500 ml two-neck flask operating as an absorber.

This flask contained carbon tetrachloride and was immersed in ice water. The gases entering the absorber were fed through a glass tube below the surface of the carbon tetrachloride. The absorber was also equipped with a solid carbon dioxide cooler, through which the gases were passed which were not absorbed into the cooled carbon tetrachloride.

These unabsorbed gases were then passed through a caustic soda-containing scrubber, a moisture meter and finally through a gasmons withdrawal bubble.

After thorough purging of the above system with nitrogen, the reaction flask was charged with 100 ml of carbon tetrachloride and the absorber charged with 250 ml of carbon tetrachloride. Both amounts of the carbon tetrachloride were dried with molecular sieves. After a further nitrogen purge, the reaction vessel was heated to about 50 ° C using the water bath and the sun lamp. Trimethyl borate (0.088 mol, 9.15 g) was added to the reaction flask and after the nitrogen purge the nitrogen flow was stopped and chlorine was fed to the reaction flask at a rate of 0.27 g per minute.

The temperature of the reaction mixture rose to about 60 ° C after the addition of the chlorine reactant.

The chlorine flow was continued at a rate of 0.25-0.30 g per minute for 130 minutes during which time the reaction temperature was maintained at 60-62 ° C. Then the normally colorless reaction mixture turned yellow, indicating the presence of ni ± reacted chlorine. The chlorine flow was stopped and the nitrogen flow was restarted. The reaction mixture was then slowly heated to reflux to expel all products from the reaction vessel.

After cooling, the infrared spectrum of the reaction mixture showed that it contained only carbon tetrachloride. The material discharged from the absorber was found to be a solution of phosgene and boron trichloride.

The amount of phosgene collected was 2.0 g (0.020 mol) and was determined by an infrared calibration curve using the carbonyl absorbance at 1828 cm. The phosgene represented a yield of 7.5 mol%, based on trimethyl borate, whereby a stoichiometry according to equation (1) is assumed.

The amount of boron trichloride in the absorber was determined to be 9.1 g (0.078 mol). An infrared spectrum of the gas passed through the moisture meter during the addition of chlorine to the reaction flask showed that the gas was carbon monoxide with a small amount of carbon tetrachloride.

The amount of carbon monoxide generated during the chlorination was determined with the moisture meter and found to be about 0.25 mol.

80 0 0 8 93 19

Example II

The photochlorination described in Example 1 was repeated with the exception that the reaction mixture was maintained at a temperature of 23-25 ° C throughout the chlorination by periodic addition of ice to the water bath surrounding the reaction vessel. The amount of boron trichloride, phosgene and carbon monoxide obtained were determined and are indicated below: Boron trichloride 9.2 grams (0.078 mol)

Phosgene 5.0 grams (0.050 mol)

Carbon monoxide 0.22 mol. 10 The above amount of phosgene represented a yield of about 19 mol%, based on trimethyl borate, assuming a stoichiometry according to equation (1).

Examples I and II show that boron trichloride is formed according to equation (2). No reduction in the yield of boron trichloride compared to that obtained at a molar ratio of chlorine to trimethyl borate of 9: 1 was observed. The data also shows that the main carbonaceous product of the reaction is carbon monoxide and that the amount of the phosgene coproduct is significantly reduced compared to that obtained when the molar ratio of chlorine to trimethyl borate is 9: 1 and the reaction is conducted under autogenous pressures and without the simultaneous removal of the gaseous products from the reaction. The data further shows that the amount of phosgene formed according to the reaction represented by equation (2) is significantly reduced when performed at 60 ° C compared to the case where the reaction is carried out at 23 ° C (room temperature) .

Example III

A 500 ml five-necked flask was used as a reaction vessel and was equipped with a thermometer, magnetic stirrer and water-cooled cooler. A glass tube was placed in the flask for the supply of chlorine below the surface of the reaction mixture. A fluorocarbon resin tube was inserted into the reaction flask for the addition of trimethyl borate using a syringe pump. The reaction vessel was cooled by a water bath as in Example 1. A glass source was placed in the center portion of the neck of the reaction flask and a 6 watt light bulb was placed in the glass source to serve as a radiation source for the photochlorination reaction.

The gases exiting the reactor were passed through a water-cooled condenser and passed to a 500 ml three-necked flask containing carbon tetrachloride. The aforementioned flask, which acts as an absorber, was equipped with a bottom valve for sample removal and a plastic pipe for the supply of carbon tetrachloride from a reservoir. The gases from the reaction flask were introduced into the absorber below the surface of the carbon tetrachloride through a sintered glass member. Cooled refrigerant at about -5 to -4 ° C was circulated through a cooler on the absorber and through a bath around the absorber. Gases that were not collected in the absorber were passed through a caustic soda scrubber, a moisture meter, and finally through a gas sampling bubble.

After thorough flushing of the system with nitrogen, the absorber was charged with 250 ml of pre-dried carbon tetrachloride. The water bath around the reactor was heated to 60 ° C and 200 ml of pre-dried carbon tetrachloride were fed to the reaction flask. Trimethyl borate was fed to the reactor at a rate of 0.060 g per minute (0.035 mol / hour). After the addition of approximately 1 g of trimethyl borate, a flow of 0.26 g per minute (0.22 mol / hour) of chlorine was started and the nitrogen flow was stopped. The system was run for about 5 hours, during which time the absorber was periodically emptied and the solution was analyzed for boron trichloride and phosgene. The amount of carbon monoxide (identified via an infrared spectrum of the gaseous effluent) was determined with the moisture meter. After the first two hours of operation, the average forming rate of each of the main products was found to be as indicated below: 80 0 0 8 93 T f 21

Boron trichloride 3.8 grams / hour (0.032 mol / hour)

Phosgene 0.20 grams / hour (0.002 mol / hour)

Carbon monoxide 0.10 mol / hour

The actual rate of formation of boron trichloride and phosgene in the above example is believed to be slightly higher than that found due to the incomplete absorption of these products in the carbon tetrachloride under the operating conditions.

From the data of Example III, it appears that boron trichloride is formed in substantially stoichiometric amounts based on the trimethyl borate reactant and phosgene is formed in an amount of only about 1.9 mole percent based on the trimethyl borate, the stoichiometric metric according to equation (1) is assumed.

Example IV

A 1000 ml stirred glass autoclave was used as the reaction vessel and was fitted with a thermocouple and stainless steel tubes for the supply of chlorine and trimethyl borate below the surface of the reaction mixture.

The reaction vessel had a water jacket through which water of 64 ° C was circulated. The reaction mixture was irradiated with a 275 watt solar lamp.

The gases exiting the reactor were passed through a water-cooled cooler and through a solenoid valve controlled by a pressure transducer. The pressure within the reactor was kept at 0.49-0.56 kg / cm throughout the test. After the solenoxd valve, the effluent gases flowed into the bottom of a packed tower (absorber), filled with carbon tetrachloride. The tower was cooled by circulating a cooled glycol-water solution (-3 ° C) through a jacket surrounding the tower.

Carbon tetrachloride was continuously fed to the top of the tower at a rate equal to that of removing the carbon tetrachloride solution from the bottom. The solution exiting the absorber was periodically analyzed by infrared spectroscopy for boron trichloride and phosgene. The gases not absorbed in carbon tetrachloride flowed through a cooling cooler, caustic soda scrubber, moisture meter and gas sampling bubble.

After thoroughly flushing the system with nitrogen, the reaction vessel was charged with 400 ml carbon tetrachloride and 2.5 g (0.024 mol) trimethyl borate. Chlorine was then added to the reaction vessel at a rate of 0.77-0.89 mol / hour and the addition of trimethyl borate at a rate of 0.134 mol / hour was started and this feeding was continued for 6 hours. During this time, the temperature of the reaction mixture was kept at 67-68 ° C by maintaining the jacket temperature at 64 ° C.

After an operating time of 2 hours, the average rate of formation of each of the main products as indicated below, namely boron trichloride 0.13 mol / hour 15 phosgene 0.017 mol / hour carbon monoxide, 0.38 mol / hour

The data of example IV shows that at a reactor pressure 2 o

of 0.49-0.56 kg / cm, a reactor temperature of about 67-68 ° C

and a molar ratio of chlorine to trimethyl borate between about 5.7: 1 and 6.6: 1 forms only about 0.13 moles of phosgene per mole of tri methyl borate.

In the examples below, a 1000 ml stirred glass autoclave was used as the reaction vessel. This reactor was equipped with a thermocouple, stainless steel tubes for the supply of chlorine and trimethyl borate below the surface of the reaction mixture, a dip tube through which part of the reactor contents could be removed and a supply tube for the supply of make-up liquid. The reactor had a jacket through which water of 70 ° C was circulated. The reaction mixture was irradiated with a 275 watt solar lamp.

The gases exiting the reactor were sequentially fed to a water-cooled cooler and a solenoid valve controlled by a pressure transducer. Pressure 2 within the reactor was kept at 0.63-0.77 kg / cm. After the solenoid valve, the effluent gases were passed to the bottom of a packed tower (absorber), filled with carbon tetrachloride. The 80 0 0 8 93 23 tower had a jacket through which a cooled glycol-water solution (-3 ° C) was circulated. Carbon tetrachloride was continuously fed to the top of the tower at a rate equal to that of removing the carbon tetrachloride solution from the bottom. The solution exiting the absorber was periodically analyzed by infrared spectroscopy for the boron trichloride and phosgene content. The gases not absorbed in carbon tetrachloride were passed through a cooled condenser, a caustic soda scrubber, a moisture meter and a gas-drawing sample bubble led.

Example V

The reaction system described above was thoroughly purged with nitrogen and the reactor was charged with 400 ml of carbon tetrachloride and 6 g of trimethyl borate. Chlorine was fed to the reaction at an average rate of 0.83 mol / hour and trimethyl borate was fed at a rate of 0.135 mol / hour for 2 hours. At the end of this, 50 ml of the reaction mixture (rinse material) was removed from the reactor and replaced with 50 ml of carbon tetrachloride. This procedure was repeated once every 20 hours for the next 5 hours. During this time, the trimethyl borate feed rate was maintained at 0.135 mol / hour, but the average chlorine feed rate was lowered to 0.72 mol / hour to compensate for the amount of borate esters removed with the rinse material. During this period of 25 hours, the average rate of formation of each of the following products was determined to give the results obtained below, namely boron trichloride 0.125 mol / hour phosgene 0.008 mol / hour, carbon monoxide 0.38 mol / hour

The reaction was stopped and the slightly colored reaction mixture collected.

A portion of the reaction mixture (300 ml) was combined with 200 ml of the rinse material, which was also slightly colored. This solution was distilled at atmospheric pressure and 495 ml of colorless distillate (boiling range 74-90 ° C) θ η η n o s <1 24 were collected. The distillate was found to contain a mixture of borate compounds at a total concentration of 0.23 mol / liter.

Example VI

The reaction system of Example V was thoroughly purged with nitrogen and the reactor was charged with 400 ml of carbon tetrachloride and 6.3 g of trimethyl borate. Chlorine was fed to the reactor at an average rate of 0.84 mol / hour and trimethyl borate was added at an average rate of 0.14 mol / hour for 10 hours. The temperature in the reactor was maintained at 72 ° C during the test by maintaining the temperature of the reactor jacket at 70 ° C.

During the last 8 hours of the run, 50 ml of rinse material was removed from the reactor once per hour and replaced with 50 ml of the colorless distillate described in Example V. During this 8 hour period, the average formation rate of each of determined the following products to give the results indicated below, namely boron trichloride 0.14 mol / hour 20 phosgene 0.04 mol / hour carbon monoxide 0.40 mol / hour

The results of Examples V and VI show that the distillation of a rinse fraction of a trimethyl borate chlorination reaction mixture containing color-forming compounds gives a colorless distillate. Furthermore, it appears that the recirculation of this distillate to the reaction mixture does not interfere with the chlorination reaction because almost identical results are obtained with or without addition of the distillate to the reactor.

30 80 0 0 8 93

Claims (48)

1. Process for preparing boron trichloride by chlorination of borate ester, whereby phosgene is formed as a by-product, characterized in that the amount of phosgene formed is reduced by contacting the borate ester with chlorine in a reactor in the presence of a free radical initiator at temperatures from about 20 ° C to about 100 ° C and simultaneously removing gaseous products of the chlorination reaction from the reactor, the molar ratio of 10 chlorine to borate ester fed to the reactor being between about 5.5: 1 and about 7.5: 1. 2. Process according to claim 1, characterized in that the borate ester is trimethyl borate, trimethoxy boroxine, a chloromethyl ester of boric acid or a mixture of such borate esters. Process according to claims 1 or 2, characterized in that the reaction is carried out at moderate reactor pressures. 4. Process according to claim 3, characterized in that the reactor pressure is about 0-1.4 kg / cm. 5. Process according to claim 1 or 2, characterized in that the reaction is carried out in an inert liquid organic solvent. 6. Process according to claim 5, characterized in that the organic solvent is carbon tetrachloride. Process according to claims 1 or 2, characterized in that the reaction temperature is about 40-90 ° C. Process according to claims 1 or 2, characterized in that the reaction temperature is about 60-80 ° C. Process according to claims 1 or 2, characterized in that the molar ratio of chlorine to borate ester is between about 5.75: 1 and about 6.75: 1. 10. Process according to claims 1 or 2, characterized in that the free radical initiator is light, an organic peroxy compound or azobisisobutyronitrile. 11. Process according to claim 10, characterized in that the organic peroxygen compound is a dialkyl peroxy dicarbonate, diacyl peroxide or peroxyester. 12. Process according to claim 4, characterized in that the reaction is carried out in an inert liquid organic solvent. Process according to claim 12, characterized in that the solvent is carbon tetrachloride. 14. A method according to claim 12, characterized in that the free radical initiator is light, an organic peroxy compound or azobisisobutyronitrile. 15. Process for preparing boron trichloride by chlorination of borate ester, whereby phosgene is formed as a by-product, characterized in that the amount of phosgene formed is reduced by adding a borate ester selected from trimethyl borate, trimethoxy boroxine, chloromethyl esters of boric acid and mixtures of such borate esters, in contact with chlorine in the presence of a free radical initiator in a reactor, containing an inert liquid organic solvent at temperatures from about 40 ° C to about 90 ° C and at reactor pressures of about 0-1.05 kg / and at the same time gaseous products of the chlorination reaction are removed from the reactor, the molar ratio of chlorine to borate ester fed to the reactor being between about 5.5: 1 and about 7.5: 1. The method according to claim 15, characterized in that the temperature is about 60-80 ° C and the molar ratio of chlorine to borate ester is between about 5.75: 1 and about 6.75: 1. Process according to claims 15 or 16, 30, characterized in that the inert organic solvent is carbon tetrachloride. A method according to claim 17, characterized in that the free radical initiator is light, an organic peroxygen compound, or azobisisobutyronitrile. Process according to claim 15, characterized in that the borate ester is trimethyl borate, the free radical initiator light and the inert liquid organic solvent is carbon tetrachloride. A method according to claim 19, characterized in that the temperature is about 60-80 ° C and the molar ratio is between about 5.75: 1 and about 6.75: 1. 21. Continuous process for preparing boron trichloride, wherein liquid borate ester is contacted with chlorine in the presence of a free radical initiator in a reactor at temperatures from about 20 ° C to about 100 ° C and vaporous boron trichloride is withdrawn from the reactor characterized in that a rinse fraction of the liquid reaction mixture is removed from the reactor, the liquid reaction mixture removed from the reactor is distilled and the distillate obtained from the distillation is recycled to the reactor. Process according to claim 21, characterized in that the rinse fraction is about 4 to about 20% by volume of the reaction mixture per hour. 23. A process according to claim 21, characterized in that the rinse fraction is about 6 to about 15% by volume of the reaction mixture per hour. 24. Process according to claims 21 or 22, characterized in that borate ester is added to the distillate in sufficient amounts to enrich the boron content of the distillate to the boron content of the rinsing fraction removed from the reactor. Process according to claims 21-23, characterized in that the borate ester is selected from trimethyl borate, trimethoxy boroxine, a chloromethyl ester of boric acid and mixtures of these borate esters. A method according to claim 25, characterized in that the chlorination temperature is about 40-90 ° C. 27. Process according to claims 21-23, characterized in that the chlorination reaction is carried out in an inert liquid organic solvent. A method according to claim 27, characterized in that the free radical initiator is light. 80 0 0 8 93 Λ J 29. Continuous process for the preparation of boron trichloride, wherein liquid borate ester selected from trimethyl borate, trimethoxy boroxine, chloromethyl esters of boric acid and mixtures of such borate esters is contacted with chlorine in the presence of a free radical initiator and an inert liquid organic solvent in a reactor at temperatures from about 20 ° C to about 100 ° C and vaporous boron trichloride is removed from the reactor, characterized in that a rinse fraction of the liquid reaction mixture is continuously removed from the reactor, the liquid reaction mixture removed from the reactor is distilled and recirculates the distillate obtained in this distillation to the reactor, thereby preventing the build-up of colored substances in the reaction mixture. 30. Process according to claim 29, characterized in that the rinse fraction is about 6 to about 15% by volume of the reaction mixture per hour. 31. Process according to claim 30, characterized in that the borate ester is added to the distillate to about the boron content of the rinse fraction removed from the reactor. A method according to claims 29 or 30, characterized in that the free radical initiator is selected from light, organic peroxygen compounds or azobisisobutyronitrile. 33. Process according to claim 32, characterized in that the chlorination reaction is carried out in an inert liquid organic solvent. 34. Continuous process for preparing boron trichloride, wherein liquid trimethyl borate is contacted with chlorine in a reactor in the presence of a free radical initiating amount of light and an inert liquid organic solvent at temperatures from about 40 ° C to about 90 ° C and vaporous boron trichloride. is removed from the reactor, characterized in that a rinsing fraction of the liquid reaction mixture is continuously removed from the reactor, the liquid reaction mixture removed from the reactor is continuously distilled and the distillate obtained during the distillation is recycled to the 80 0 0 8 93 reactor. preventing the build-up of colored substances in the reaction mixture. 35. Process according to claim 34, characterized in that the rinse fraction is about 8 to about 12% by volume of the reaction mixture per hour. A method according to claim 35, characterized in that the organic solvent is carbon tetrachloride. 37. Process according to claim 36, characterized in that the reaction temperature is about 60-80 ° C and the reactor pressure is about 0-1.4 kg / cm. A method according to claim 36, characterized in that additional trimethyl borate is added to the distillate. 39. Process for preparing boron trichloride by chlorination of borate ester in a reactor, characterized in that the reaction is carried out in the presence of a solvating amount of an inert liquid organic solvent and in the presence of a catalytic amount of a free radical initiator. 40. Process according to claim 39, characterized in that the inert solvent is selected from chlorofluorinated oils, polyhalogenated aliphatic hydrocarbons with 1-4 carbon atoms and polychlorinated benzenes. 41. Process according to claim 39, characterized in that the inert solvent is carbon tetrachloride. A method according to claims 40 or 41, characterized in that the weight ratio of solvent to borate ester is about 1: 1 to 10: 1. 43. Process according to claims 40 or 41, 30, characterized in that gaseous inert solvent is removed from the reactor with the chlorination products, inert solvent is condensed and returned to the reactor, 44. Process for preparing boron trichloride by chlorination of borate ester selected from trimethyl borate, trimethoxy boroxine, chloromethyl esters of boric acid and mixtures of these borate esters in a reactor, characterized in that 80 0 0 8 93 reaction in the presence of a solvating amount of carbon tetrachloride and in the presence of a catalytic amount of a free radical initiator. 45. Process according to claim 44, characterized in that the weight ratio of solvent to borate ester is about 1: 1 to about 10: 1. 46. Process according to claim 45, characterized in that the reaction is carried out at temperatures of about 0-100 ° C. The process according to claim 46, characterized in that gaseous carbon tetrachloride is removed from the reactor with the gaseous chlorination products, condensed and returned to the reactor. 48. Methods as described in the description and / or examples. 80 0 0 8 93