DE1112071B - Process for the production of tetraalkyldiboranes in addition to boron trialkyls - Google Patents

Description

Process for the preparation of tetraalkyldiboranes in addition to boron trialkyls Alkylborines and alkyl-substituted diboranes are much sought-after compounds that are suitable as high-energy fuels. Earlier methods of preparing alkyl-substituted Diboranes had the use of diborane itself as a chemical intermediate to the basis. Diborane has become a strategic raw material and is quite expensive, although much effort has been put into improving manufacturing processes. It is therefore desirable to make the production of alkyl-substituted diboranes more economical and store more accessible raw materials.

The invention relates to a process for the preparation of tetraalkyldiboranes in addition to boron trialkyls, characterized in that under essentially anhydrous Conditions an aluminum compound of the general formula Al R3 X Hn, wherein R denotes an alkyl radical and n is 1 or 2, with a boron halide or a boric acid ester, is preferably reacted in an inert solvent or diluent and the reaction products are separated, e.g. B. by distillation.

In the aluminum compound, the alkyl groups can be branched or unbranched, identical or different, e.g. B. ethyl, propyl and octyl.

The main reactions that take place can be represented as follows: In the formulas, X denotes halogen or an ester radical. The compound type R2A1H is preferred because it is more accessible and provides a valuable mixture of reaction products. It should be noted that the use of an aluminum compound of consistent purity is important if consistent results are expected.

Suitable solvents are hydrocarbons such as n-hexane and benzene and xylene, as well as ethers, for example dibutyl, diethyl and dihexyl ethers, as well as Diether of glycol and diethylene glycol. The procedure is at temperatures above -30 "C feasible and can be with good yields at temperatures up to 150" C or also perform higher.

Instead of the boron halides, these coordination complexes can advantageously be used can be used with an aliphatic ether.

In the following examples, the yields relate to consumed BX3, unless otherwise specified.

Example 1 A l-l three-necked flask with dropping funnel, stirrer and dry ice-acetone condenser was charged with 500 cc of n-hexane and 78 g (0.92 mol) of diethylaluminum hydride. 120 g (0.84 mol) of boron trifluoride etherate were added to this mixture in the course of 2 hours slowly admitted. Due to the exothermic nature of the reaction, the n-hexane began to reflux to boil. After the addition, heating was continued for a further 2 hours at reflux temperature. The aluminum fluoride was filtered off and the filtrate at low temperature distilled off under reduced pressure. The liquid residue was distilled.

There was a yield of 400 / o of tetraethyldiborane, boiling point 112 "C, obtain.

The tetraethyldiborane has been identified in a number of ways. During hydrolysis in acidic solution, 95% of the theoretical amount developed of hydrogen gas. The cryoscopic determination of the molecular weight was 133 (theor. 140). Mass spectral analysis indicated a molecular weight of 140.

Example 2 A l-l two-necked flask with cold finger condenser, stirrer and the dropping funnel was filled with 500 cc of dry n-hexane and 86.0 g (1.0 mol) of (C2Hs) 2AlH loaded.

To this mixture were 98.3 g (0.95 mol) in the course of 2 hours B (OCH3) 3 added so that the temperature is at the reflux temperature of n-hexane was held. The reaction was initially very violent, but became more severe towards the end of the Addition a little sluggish. A precipitate of mainly Al (O CH3) 3 was only found when when approximately 20 cc of the B (OCH3) 3 was added.

The reaction mixture was left at the reflux temperature for an additional 2 hours of hexane hold, cooled, filtered and the n-hexane under reduced pressure evaporated. Fractional distillation of the residue gave 27.4 g of B2H2 (C2Hs) 4 (440/0 yield) and 13.6 gB (C2H5) 2 (21% yield).

The results obtained under various reaction conditions and with various boron compounds as starting material are summarized below. (C2H5) 2AIH was used as the aluminum compound. All yields are based on BX3 consumed. BX3 solvent temperature 32 H2 (C2 H2) 4 B (C2 Hs) 3 c010 Olo B F3 O (C2H5) 2 n-hexane 64 40 not certainly B (OCH3) 3 n-hexane 68 44 21 BF3 - O (C2Hs) 2 n-hexane 45 23 10 BF3 - O (C2Hs) 2 n-hexane -20 to -30 10 26 B (OCH3) 3 xylene 100 to 110 29 11 B (OCH3) 2 n-dodecane 150 63 18 B (OCH3) 3 xylene 140 50 8 B (iso-OC3H7) 3 xylene 100 6 89 B (iso-O CoHI0) 3 xylene 140 23 72 B (iso-O C4H, 0) 3 decalin 105 29 57 B (iso-O C4H, 0) 2 decalin 105-57 The process according to the invention has some obvious advantages which derive from the fact of the simple direct route to the tetraalkyldiboranes. However, by-products are also formed in this process, mainly diborane and trialkylborines; however, the reaction products can be separated off with ease by distillation, and all the products are valuable, so that the by-products are not a burden and, for example, increase operating costs.

Claims (3)

PATENT CLAIMS: 1. Process for the preparation of tetraalkyldiboranes in addition to boron trialkyls, thus characterized records that under essentially anhydrous Conditions an aluminum compound of the general formula A1R3.nHn, wherein R is a Alkyl radical and n = 1 or 2, with a boron halide or a boric acid ester, is preferably reacted in an inert solvent or diluent, and the reaction products are separated. 2. The method according to claim 1, characterized in that a boron halide is used in the form of a coordination complex with an aliphatic ether. 3. The method according to claim 1 and 2, characterized in that a dialkyl aluminum hydride is used as the aluminum compound.