DE1085876B - Process for the preparation of n-trialkylboranes - Google Patents

Description

Process for the Preparation of n-Trialkylboranes The invention relates to a new and improved process for the preparation of n-trialkylboranes in which the alkyl groups contain 1 to 3 carbon atoms.

Those previously described for the preparation of trialkylboranes Processes were generally technically unsuitable or uneconomical or required the use of raw materials that are relatively expensive or not readily available are. Such methods include e.g. B. the implementation of boron trifluoride with Dimethyl zinc, the conversion of trimethyl borate or the diethyl ether addition product of boron trifluoride with Grignard reagents, the reaction of trimethyl borate with Methyl aluminum sesquiodide, the reaction of trialkyl borates with aluminum triethyl, the conversion of borohydrides or sodium borohydride in the presence of aluminum chloride with various olefins and the reaction of boron oxide with aluminum trimethyl or methyl aluminum sesquij odid.

According to the invention, n-trialkylboranes whose alkyl groups are 1 to Contain 3 carbon atoms, produced in such a way that one in an inert Atmosphere with exclusion of humidity boron oxide or anhydrous metal borates with n-alkyl aluminum chlorides or bromides, the alkyl groups of which have 1 to 3 carbon atoms have, heated, the reactions by means of ethyl or n-propylaluminum bromides takes place in the presence of metal chlorides, which with the bromides with the formation of Ethyl or n-propyl groups and chlorine atoms on aluminum-containing compounds react.

The alkyl aluminum halide is preferably a chloride. The bromides alone are not suitable if the alkyl groups are ethyl or n-propyl groups, however, they can be made available to the reaction if the reaction mixture Metal chlorides are added, which react with the alkyl aluminum bromide to form Compounds in which both alkyl groups and chlorine atoms are bonded to aluminum are able to implement. Suitable chlorides are e.g. B. aluminum chloride, organoaluminum chlorides, Alkali and alkaline earth chlorides.

The halide can be either a dialkyl aluminum monochloride or bromide or a monoalkylaluminum chloride or bromide or a mixture of such Be fabrics. However, those under the name alkylaluminum sesquihalides are preferred known substances applied by reacting aluminum with the appropriate Alkyl halide can be obtained.

According to a preferred embodiment of the invention, the alkyl aluminum halide is used applied in the form of a complex with an alkali or alkaline earth chloride or bromide. This complex can be before use or conveniently in the presence of Boron oxide or metal borate by implementing a Alkali halide with the appropriate Generate monoalkyl aluminum dihalide. These alkali metal alkyl aluminum trihalides give the advantage that the reaction takes place at a higher temperature and thus higher Speed can be performed as with the corresponding alkyl aluminum halide, since they are solids that are at temperatures that are considerably higher than that lowest temperature at which the corresponding alkylaluminum halides with React boron oxide or the metal borate to form the corresponding trialkylboranes, can be heated before forming the corresponding alkyl aluminum halide and alkali metal halide decompose.

According to a further embodiment of the invention, which in some In some cases, it is preferable to have the alkyl aluminum halide in situ in the presence of boron oxide or anhydrous metal borate from the corresponding alkyl halide or the alkyl halides and aluminum. In this case it should be boron oxide respectively.

Metal borate and the aluminum preferably by mixing with one inert diluents, e.g. B. a finely divided, solid inorganic material, such as crystallized silica. This allows the fumes of the alkyl halide more easily through the mixture of aluminum and boron oxide or metal borate pass through at the elevated temperature required for the reaction. at In the absence of such a diluent, the boron oxide or

Metal borate begin to sinter and thereby the passage of the steam make more difficult. If trimethylborane is to be produced, this embodiment will be however, not preferred, since the trimethylborane is difficult to remove from the excess Can separate methyl chloride. In this case, previously generated alkyl aluminum sesquichloride is preferred applied.

If boron oxide is used, it is preferably finely pulverized. When an anhydrous metal borate is to be used, the finely powdered one is preferred Used product obtained by dehydrating borax by using heat it, let it cool down and grind it.

The reaction leading to the formation of the trialkylborane is usually carried out at atmospheric pressure. If necessary, however, it can be reduced Printing. There is also no need to use a solvent, although such a solvent is used can be used if necessary. By using a solvent however, there are no advantages.

The trialkyl boranes and the alkyl aluminum halides can spontaneously ignite and the alkyl aluminum halides continue to react vigorously with water. It is therefore essential that the reaction take place in the absence of moisture and in an inert atmosphere, furthermore the condensation of the trialkylboranes in one inert atmosphere, e.g. B. a nitrogen atmosphere causes.

The reaction between the alkyl aluminum halides and the boron oxide or the metal borate proceeds more appropriately at temperatures above 100 "C. In this way, and preferably at temperatures in the range from 150 to 250.degree. C., the process is carried out.

If one uses the alkyl aluminum halide as such, it is it is often expedient to work at the temperature at which the most volatile of the present Alkylaluminum halides boil, and furthermore it is expedient in such a case, carry out the reaction in a vessel equipped so that any unreacted alkylaluminum halide condensed in the vapor phase and to the Reaction vessel can be returned. Optionally, you can use a packed column to facilitate the separation of the desired product. As a rule however, this procedure is not required when the alkyl aluminum halide is used in the form of its complex with an alkali or alkaline earth halide, since the reaction can be carried out at such a temperature that the complex is melted.

In this case, the reaction is so rapid that practically the only vapor occurring is that of the trialkylborane.

When the process of the invention is carried out by the vapor of methyl chloride in a mixture, the aluminum and boron oxide or a metal borate and, as already stated, preferably contains an inert diluent, it is difficult to separate the vapors of methyl chloride from those of trimethylborane to separate, even if one works with a fractionation column. In this case One convenient method of isolation is to remove the vapors that the methyl chloride and the trimethylborane contained, cools to around -700 C to make them to condense, an excess of triethylamine is added and the resulting mixture at one above 0 ° C, but below the boiling point of triethylamine Distilled temperature. Under these conditions, the triethylmethylaluminum chloride formed is not decomposed, while the produced equimolar coordination compound of trimethylborane and triethylamine into their components disintegrates so that the trimethylborane can be condensed by cooling the steam to a temperature below -22 "C. This Operations are carried out in an inert atmosphere.

The invention is illustrated in the following examples in which parts and Unless otherwise stated, percentages are based on weight, in more detail explained.

Example 1 A suspension of 7 parts of boron oxide in 41 parts of methylaluminum sesquichloride was heated to boiling in a reaction vessel fitted with a calcium chloride moisture trap and a short fractionation column with a distillation head that leads to a led to -70 "C cooled condensation trap, provided and flushed with nitrogen before the methyl aluminum sesquichloride was introduced. The temperature in the reflux zone rose from 128 to 156 "C within 5.5 hours, and during this time a condensate of trimethylborane was formed from the passing through the cold trap Steam collected. The trimethylborane obtained was purified by pouring it into his Coordination compound was converted with trimethylamine and the latter sublimed, wherein the sublimate is then treated with hydrochloric acid in one Vessel from which the steam was directed to a trap cooled below -30 "C, decomposed in the presence of an inert atmosphere. The boiling point of the trimethylborane was about -22 "C, and after purification a yield of about 32 ° lo achieved in theory. Analysis of the sublimed coordination compound revealed a carbon content of 61,801, and a hydrogen content of 15.1 01o; on the other hand the calculated values are 62.7 01o C and 15.701 H.

Example 2 7 parts of boron oxide and 68 parts of methyl aluminum sesquibromide were 16 hours in a reaction vessel of the type described in Example 1, the had previously been purged with nitrogen, heated to boiling. The product that is in in a manner similar to that in Example 1 in a nitrogen atmosphere appropriately purified by using it in its coordination compound Trimethylamine was converted and recovered from the latter. The yield at Trimethylborane was 37010 of theory.

Example 3 35 parts of boron oxide and 248 parts of ethylaluminum sesquichloride were refluxed in a distillation apparatus equipped with a packed column and a still attached to a water cooled condenser and a template, the system before adding the ethylaluminum sesquichloride purged with nitrogen. After 8.5 hours of heating at a temperature which rose from about 190 to 230 "C, a fraction had collected that at 96 to 99 "C boiled and the almost completely from triethylborane in an amount consisted of 4601o which corresponded to the theory. The temperature of the distillation zone, which was originally 180 "C, dropped to 96 to 99" C and the triethylborane was formed and was distilled over.

Example 4 The same reaction vessel as in Example 1 was used used. After it was purged with nitrogen, it became 273 parts Methyl aluminum dichloride and a mixture of 141 parts sodium chloride and 28 Share boron oxide charged. As a result of the exothermic reaction started the temperature increased, and the reaction mixture was further heated until the Contents of the vessel had a temperature of about 220 to 2650 C.

The trimethyl boron apparently started to turn off shortly after with heating had started to condense in the condensation trap. After about 40 minutes the implementation was complete, and once it was so lively that the -70 "C cooled trap, the product was no longer able to condense completely.

The product was isolated by adding excess trimethylamine and the obtained product was purified by sublimation. The amount of sublimate corresponded to 60% of theory, based on the starting materials used.

Example 5 The same reaction vessel as in Example 3 was used used and initially purged with nitrogen. Were in the still 381 parts of ethylaluminum dichloride and a mixture of 176 parts of sodium chloride and 35 parts of boric oxide introduced. It started exothermic conversion, and after had been heated for a further 2.5 hours, 51 parts of a fraction had collected, which boiled at 92 to 98 "C and which practically consisted of triethylborane.

Example 6 The same reaction vessel as in Example 1 was used used and purged with nitrogen before use.

Into the jar was 340 parts of methylaluminum dichloride and a mixture introduced by 176 parts of sodium chloride and 53.2 parts of anhydrous sodium pyroborate, by melting borax in an open vessel as the temperature rises and subsequent cooling and pulverization had been prepared. After 5 hours had been heated, 23 parts of volatile colorless trimethylborane were collected, which corresponded to a yield of 41% of theory.

Example 7 The same reaction vessel as in Example 3 was used and first flushed with nitrogen. Then 500 parts of n-propyl aluminum dichloride was put into the vessel and introduced a mixture of 210 parts of sodium chloride and 41 parts of boron oxide. An exothermic reaction set in and the alembic continued to heat. The reaction appeared to be complete within about 10 minutes after it started to be. That during this time at a distillation head temperature of 150 to 160 "C collected condensate was 88 parts, which was 530 / o of theory. This Product consisted of almost pure tri-n-propylborane. Such as trimethylborane and triethylborane if this product burns spontaneously in air with a green flame, it ignites not that fast. The analysis showed a carbon content of 76,5 ° / o a hydrogen content of 15.60 / ,. In contrast, the theoretical values are 77.3 01o C and 15.00 / 0H.

Example 8 The reaction vessel provided with a stirrer was with a steam inlet pipe leading to the bottom of the vessel and in the upper part with a steam outlet leading to an air cooled condensation chamber resulted in the fumes of aluminum chloride that evolved in the reaction vessel are condensed if the latter has been heated externally with the aid of a heating bath could be, this air cooler was provided with a side arm that to a cold trap in which the vapors of methyl chloride and tri- methylborane could be collected and condensed. The reaction vessel was initially with a mixture of 70 parts of boron oxide, 90 parts of ground aluminum grit (aluminum content 9101,) and 100 parts of finely divided quartz charged to a sieve of 0.076 mm mesh size happened. The vessel was then heated to 2700 ° C. Through the vessel were 0.5 hours sent dry nitrogen at a rate of 6.3 parts per hour, and then vaporous methyl chloride was passed in at the same rate.

At the start of the introduction of methyl chloride vapor, it became 0.5 parts anhydrous aluminum chloride introduced as a catalyst. In the condensation chamber collected about 15 hours after the catalytic amount of aluminum chloride was introduced significant amounts of a sublimate of aluminum chloride. Now the flow rate was of the methyl chloride through the reaction mixture with continued stirring of 14 Parts per hour increased to 42 parts per hour and methyl chloride was passed in for a further 10 hours. The product collected in the receiver cooled to -70 ° C. was a solution of trimethylborane in methyl chloride. This became purified trimethylborane by treatment with Triethylamine, distillation of the mixture and condensation of the trimethylborane vapor isolated at a temperature of -700C.

Example 9 The same reaction vessel as in Example 3 was used used. After flushing with nitrogen, 34.4 parts of ethyl aluminum sesquibromide, 12 parts of anhydrous aluminum trichloride and 3.14 parts of boron oxide were introduced. Thereafter the mixture was heated to 240 to 260 "C for 1.5 to 2 hours, and after this time 5.32 parts of a volatile colorless liquid had collected, which at Further distillation 3.8 parts of triethylborane, b.p. = 90 to 92 "C gave what a Yield of 430/0 corresponded to theory.

Example 10 The same reaction vessel as in Example 3 was used used. After purging with nitrogen, there was 325.8 parts of ethyl aluminum sesquibromide and 114 parts of anhydrous aluminum chloride and mixed for 5 minutes, to enable resolution and implementation.

29.8 parts of boron oxide were added and the mixture was left overnight ditched. The mixture was then heated to about 230-300 "C for 1.5 hours, after which 47.5 parts of triethylborane, b.p. 93 to 97 "C, were collected, resulting in a yield of 560in.

Example 11 The same reaction vessel as in Example 3 was used used and initially flushed with nitrogen. There were 38 parts in the reaction vessel Ethyl aluminum sesquibromide and then a mixture of 15.6 parts anhydrous aluminum bromide, 17.6 parts of sodium chloride and 3.5 parts of boron oxide were introduced. It continued exothermic Reaction on, and after an additional 1.5 hours of heating, 3.75 parts of a became at 90 to 94 "C distilling fraction collected, consisting essentially of triethylborane duration. The analysis gave the following values: 71.00 / 0C, 16.710 /, H, 10.950 / 0B; calculated: 73.50 / 0C, 15.40 /, H and 11.040 / oB.

Claims (4)

PATENT CLAIMS: 1. Process for the production of n-trialkylboranes, the alkyl groups of which contain 1 to 3 carbon atoms, characterized in that one in an inert atmosphere with exclusion of humidity Boron oxide or anhydrous metal borates with n-alkyl aluminum chlorides or bromides, whose alkyl groups have 1 to 3 carbon atoms, heated, the reactions takes place by means of ethyl or n-propyl aluminum bromides in the presence of metal chlorides, those with the bromides with the formation of ethyl or n-propyl groups and chlorine atoms react on compounds containing aluminum. 2. The method according to claim 1, characterized in that the alkyl aluminum halide in shape a complex with an alkali or alkaline earth chloride or bromide applied will. 3 The method according to claim 1 and 2, characterized in that the Alkyl aluminum halide in situ in the presence of the boron oxide or anhydrous metal borate of one or more alkyl halides and aluminum in the presence of an inert one Diluent is produced. 4. The method according to claim 1 to 3, characterized in that the Implementation at 150 to 250O C is carried out.