2,994,586 United States Patent, 0 'ice . 7 _ ‘Patented Aug. 1, 1961 2 _ As an example of the practice of the invention, di _ 2,994,586 borane contaminated with ‘hydrogen halide is passed PURIFICATION OF DIBORANE George F. Huff, Pittsburgh, Pa., assignor to Gallery through a scrubbing tower containing a solution of so Chemical Company, Pittsburgh, Pa., a corporation of dium borohydride in a polyethylene glycol ether. If the Pennsylvania acid is hydrogen chloride it will be removed according to No Drawing. Filed Nov. 6, 1953, Ser. No. 390,719 the following reaction: S'Claims. (Cl. 23-204) Diborane (BZHG), which is useful for such purposes Thus in this case the impurity in the diborane is changed as a high energy fuel and as an intermediate in the 10 from HCl to hydrogen, with the gaseous mixture of BzHs preparation of a wide variety of other boron compounds, and H2 leaving the scrubbing tower in which the solid may be made by various methods. One involves passing sodium chloride remains. a mixture of hydrogen (H2) and a boron halide (BX3), In some applications in which diborane is used, further such as 'boron trichloride (BCl3) or boron tribromide puri?cation will be unnecessary since the hydrogen will (BBr3) through an electrical discharge. Diborane pre 15 be harmless. However, if pure diborane is desired, the pared by such a process is always contaminated with hydrogen can be easily removed by fractional condensa hydrogen halide. Other procedures for its preparation tion, by selective adsorption, or by diffusion which is involve the treatment of a hydride, such as lithium hy rendered more feasible than in the case of HCl by the dride (LiH), lithium aluminum hydride (LiAlH4), or large diiference in the molecular weights of hydrogen and an alkali metal borohydride, e.g., sodium borohydride 20 diborane. (NaBH4) with a boron halide, usually BF3. These The method of this invention is especially advantage procedures likewise result in diborane containing acid ous where the contaminant is a boron halide. In this contaminant such as hydrogen chloride (HCl) or a boron case the boron halide is removed in the scrubbing tower halide. in accordance with the following reactions: The removal of such acid contaminants from diborane 25 is exceeding di?icult by standard procedures. For in stance, both hydrogen chloride and, for example, boron tri?uoride form azeotropic mixtures with diborane so In these instances, as will be observed, the boron halide that separation of the two compounds can not be e?ected is converted to a sodium salt which is left behind as the by low temperature distillation. Likewise, those acid 30 puri?ed diborane leaves the scrubbing tower but there is materials have vapor pressures nearly equal to that of the special advantage that the boron halide can be com diborane so that removal of the acid from diborane by pletely removed with the formation of no other gaseous fractional condensation is not possible. Moreover, the material than pure diborane with an actual increase in molecular weight of hydrogen chloride is so close to that its amount of 1 mol for every 2 mols of boron halide of diborane that such separatory methods as thermal 35 present in the original mixture. diffusion or barrier di?usion would be extremely diffi Liquids other than the polyethylene glycol ethers that cult and expensive for the removal of HCl from di are inert to diborane may, of course, be used. Amines borane. are not suited to the purposes of the invention, however, It has been proposed (75 IACS 191) to separate hydro because they react with diborane. Although it is pre gen halides from diborane by adding pyridine (C5H5N) 40 ferred to use an inert liquid that is a solvent for the to the mixture with formation of CsH5NzBH3 which hydride, there may be used a suspension of the hydride then reacts with the hydrogen halide to form C5H5N:BX3 in the inert liquid with which the contaminated diborane and hydrogen. In addition to being unwieldy for prac is contacted. Similarly, although the invention has been tice on a commercial scale, this procedure is objectionable described in detail with reference to sodium borohydride in that it involves the loss of at least 1 mol of diborane 45 as the acid removing reagent, other hydrides are equally for each 6 mols of hydrogen halide, such as HCl. operative, examples being potassium borohydride (KBH4) , It is among the objects of this invention to separate the alkali metal hydrides, magnesium borohydride diborane from an acid impurity that is simple, easily and [Mg(BH4)2], lithium aluminum hydride (LiAlH4) and inexpensively practiced using standard apparatus and the like. readily available reagents, effectively removes the acid 50 The method is not dependent upon any speci?c pres impurity, and in certain embodiments actually increases sure and temperature conditions. The acid removing re the yield of diborane. action occurs with satisfactory rapidity and completion, Other objects will appear from the following speci?ca however, at normal room temperature and atmospheric tion. pressure. - I have discovered, and it is upon this that the inven— 65 According to the provisions of the patent statutes, I tion is largely predicated, that acid contaminant, for have explained the principle and mode of practicing my instance boron halide and hydrogen halide, of diborane invention and have described vwhat I now consider to can be removed readily by contacting the mixture of di represent its best embodiment. However, I desire to borane and acid with a hydride in an inert liquid where have it understood that, within the scope of the appended by the hydride reacts with the acidic constituent to form claims, the invention maybe practiced otherwise than as a metallic salt, and also in certain instances hydrogen speci?cally described. or diborane. I claim: The dialkyl ethers of poly 1,2 ethane diols: 1. That method of separating diborane from a mixture with a volatile acid impurity comprising contacting said 65 mixture with a metallic hydride in a lower alkyl ether where R is an alkyl radical and n is 2 or a greater whole of a polyalkyl glycol of the formula R(OCH2CH2),,OR number serve admirably as inert liquids for the practice where R is a lower alkyl radical and n is a whole number of this invention. Examples of such ethers are the di from 2 through 4, inclusive and thereby converting said . methyl ethers of diethylene glycol, of triethylene glycol acid impurity to a non-volatile inorganic salt, and re and of tetraethylene glycol. Similarly, the diethyl and 70 covering the acid-free diborane. . other lower dialkyl ethers of polyethylene glycol may 2. A method according to claim 1, said glycol bein be used. a polyethylene glycol. < ~ 2,994,586 ‘ _ g . \ l . 3 4 3. That method of separating diborane from a mix-' 5. A method according to claim 4, said borohydride ture with a volatile acid impurity comprising contacting being NaBH4. said mixture with a solution of a metallic borohydride in aolégiier alkyloether of a polyalkyl glycol of the formula References Cited in the ?le of this patent R( ZCHZ)1L1 R where R is a lower' alkyl radical and 5 ' n is a ‘whole number from 2 through 4, inclusive and UNITED STATES PATENTS thereby converting said acid impurity to an inorganic 2,550,985 Finholt __,. ______,May 1, 1951 salt, and recovering the acid-free diborane. 2,553,198 Lesesne _____, ______May 15, 1951 4. A method according to claim 3, said glycol being 2,555,512 Schlesinger'et a1. ______June 5, 1951 a polyethylene glycol. 10