DE1071703B - - Google Patents

Description

Boron alkyls and boron hydrocarbons are of technical importance not only as high-performance fuels, but also also as reducing agents and intermediates for fuels, fuel additives and reducing agents.

A synthesis between the two types of compounds, the reducing boron hydrocarbons and the boron hydrocarbons with their unsaturated character, are the boron hydrocarbon compounds, for example the alkyiborohydrides B ₂ H _n R _e - _n , in which R AUcyl radical and η is an integer from 2 to 5 is. The literature names four basic methods for obtaining them:

1. The reaction of diborane with boron alkylene, 12 hours at room temperature.

2. The hydrogenation of boron alkylene with hydrogen.

3. The reaction of sodium boronate with vinyl bromide or alkyl bromide in tetraethylene glycol dimethyl ether.

4. The reaction of boron hydrogen with sodium alkyl.

These methods suffer from a number of shortcomings. Method 1 requires working with diborane, which is extremely poisonous, volatile and explosive; in addition, the response times for a technical application too long. Method 2 offers the possibility. a technical implementation, but here a boron alkyl must first be obtained by alkylation, in which alkyl groups then pass through again Hydrogen can be substituted. The yield, based on alkyl, is therefore considerably reduced. After 3 must Inaccessible alkylene bromides and inaccessible tetraethylene glycol dimethyl ether are used. Method 4 uses difficult-to-handle hydroboron and sodium alkyls alike.

The invention relates to a process for the preparation of alkyl or aryl borohydrides, which consists in reacting trialkyl or triaryl boranes with boranates and boron halides or their addition compounds. For example, boron alkyls sit with sodium boronate and boron trifluoride, preferably in a solvent, e.g. B. tetrahydrofuran, to alkyl borohydrides according to the following equation: 3/4 "NaBH ₄ + η BF ₃ + (6-") BR ₃ = 3 B ₂ H _ft R ₆ -. " 4- 3/4 «NaBF ₄ (η = integer 2 to 5; R = alkyl or aryl radical). Furthermore, not only the free boron halides, but also their addition compounds, e.g. B. (especially when using ethers as solvents) use boron halide ether compounds.

There are no difficulties in carrying out the reaction; it only has to be carried out because of the sensitivity to oxygen the reactants can be made under nitrogen or argon. The implementation between the tri

Process for the preparation of alkyl or aryl borohydrides

Applicant: '

Paint factories Bayer Aktiengesellschaft, Leverkusen-Bayerwerk

Dr. Konrad Lang and Dr. Friedrich Schubert, Leverkusen, have been named as the inventor

alkyl or triarylboranes and the nasal borane, BH ₃ , proceed very quickly under the conditions chosen, so that, despite the very low solubility of the diborane in the ethers preferably used as solvents, practically no diborane escapes from the reaction mixture. This is surprising because it is known that on the one hand, for example, alkahboranates react practically quantitatively and very quickly with boron halides in ethers to form diborane B ₂ H ₆ and, on the other hand, boron alkyls react only hesitantly with diborane. It would therefore have been expected that the major part of the boranate-boron halide-boroalkyl reaction leads to the formation of diborane and not, as is actually the case, to the virtually quantitative formation of alkyl borohydrides. The reaction temperature chosen is preferably slightly elevated temperatures; to complete the reaction, the reaction mixture can still be refluxed. After filtration and removal of the solvent, the crude alkyl or aryl borohydride mixture remains, which is separated off by fractional distillation from the by-products, the borohydrides containing more or less alkyl or aryl groups resulting from disproportionation.

A technical advance is given by the process insofar as it is technically easily accessible and inexpensive starting materials such. As sodium borohydride, boron trialkyls or -triaryle and boron halides used, wherein both the employed in the form of borohydride on Hydrogen W ^r as well as the boron alkyl and aryl are consumed in a process step to form the desired alkyl or Arylborhydrids. Another advantage of the process is that the starting materials are relatively easy to handle bodies of low toxicity, so that the reactions can be carried out in an inert atmosphere without further precautionary measures

909 690/581

Claims (1)

Can be carried out. In contrast, the use of which requires the toxic and explosive diborane which .ußerdem responds relatively slowly, extensive protective measures for a possible technical implementation of these procedures difficult vill. The alkyl and aryl> orhydrides produced according to the invention are used as chemical intermediates, High-performance fuels and reducing agents soluble in organic liquids. example 1 In a round bottom flask with reflux condenser, dropping funnel, mechanical stirrer and immersion thermometer, a suspension of 64 g of sodium borohydride,> 60 g Bortripropyl in 0.751 of tetrahydrofuran under nitrogen in the course ron 1.5 hours under vigorous stirring with 280 g of boron: rifluorid-diethyl ether was added. The internal temperature is not allowed to rise above 50 ° C. during this process. The mixture is then refluxed for 2 hours in a water bath, the mixture obtained is filtered and the solvent is driven off. The residue is distilled at 16 to 50 ° C / 2Torr and receives in ^o O ⁰ Z ₀ yield Tetrapropylborhydrid, a colorless, with water, acids rnd liquors highly reactive with evolution of hydrogen liquid whose composition by volunetrische determining the entstanlenen in the hydrolysis of hydrogen and acidimetric determination of the boron content after digestion with sodium peroxide. In addition to tetrapropyl borohydride, which propylborohydrides could be obtained from the distilled solvent by reaction with triethylamine in the form of the N-triethylborazane. Mainly N-triethyl-B-propylborazane, (C ₂ H ₅ ) ₃ N-BH ₂ (C ₃ H ₇ ), was formed. Example 2
8 (C ₆ H ₅ ) ₃ B +3 NaBH ₄ +4 BF ₃ • C ₄ H ₈ O
* 12 (C _e H ₆ ) ₂ BH + 3 NaBF ₄ + 4 C ₄ H ₈ O In a round bottom flask equipped with a reflux condenser, dropping funnel, stirrer and immersion thermometer, it is added dropwise with vigorous stirring to a suspension of 20 g of sodium boranate and 195 g of triphenylborane in 21% of tetrahydrofuran slowly add 65 g of boron trifluoride-tetrahydrofuran so that the internal temperature does not exceed 40.degree. The mixture is then refluxed for 3 hours, allowed to cool, filtered and the filtrate is distilled From tetrahydrofuran. Cleans the distillation residue so one by vacuum distillation or sublimation and receives the diphenylborohydride as a solid body from Mp. 180 ° C in a yield of 90% of theory. Claim: Process for the preparation of alkyl or aryl borohydrides, characterized in that trialkyl or triarylboranes reacted with boranates and boron halides or their addition products will.