3,111,372 United States Patent Office Patented Nov. 19, 1963

1. 2 earth metal borohydrides, which comprises reacting an 3,111,372 PROCESS FOR THE PRODUCTION OF ALKALI N-trialkyl borazane with an acetylide or METAL AND BORO alkaline earth metal acetylide in the presence of hydrogen HYDRIDES under pressure. For example, N-triethyl borazane can Roland Köster, Mulheim (Ruhr), Germany, assignor to 5 be split up at temperatures higher than 140 C., prefer Studiengesellschaft Kohle m.b.H., Mulheim (Ruhr), ably between 200 and 300° C. by calcium , the Germany acetylide fraction of the becoming free No Drawing. Filed Apr. 28, 1958, Ser. No. 731,125 mostly in the form of ethane. The temperatures used are Claims priority, application Germany Apr. 30, 1957 so low that the initial formation of calcium hydride from 7 Claims. (C. 23-14) O calcium carbide must be considered as not occurring in This invention relates to a process for the production of practice, since the temperatures at which calcium carbide alkali metal and alkaline earth metal borohydrides. reacts with hydrogen alone to form calcium hydride are Belgian patent specification No. 559,053 discloses a substantially higher. Moreover, calcium carbide only process for the production of alkali metal and alkaline reacts easily with hydrogen to form calcium hydride if earth metal borohydrides from borazanes having 3 hydro certain catalysts are present, and in addition the calcium radicals, especially N-trialkyl borazanes, by re hydride formation requires a substantially higher tem action with an alkali metal or alkaline earth metal hy perature than is necessary in the process of the inven dride, with a metal compound of the general formulae tion. The explanation of the surprising technical effect MX or MX, in which M is an alkali metal or alkaline obtained by using the process of the invention must be earth metal and X is a radical R or OR, in which R sought in the fact that the metal acetylides, in conjunction represents an aliphatic, aromatic or hydroaromatic hydro with the borine fraction of the borazanes, initially give carbon radical, or with a complex salt of one of these complex compounds such as the following for the simplest compounds with a boric acid ester. If metal alcoholates case of the complicx compound of monosodium acetylide or metal hydrocarbons, especially metal alkyls, are used and borine: for the reaction, then boric acid esters or boron trihydro 25 Na+ HBC=CH are obtained as secondary products. This compound probably dissolves in the borazane, and the triple bond is then Saturated with hydrogen, where after the saturated organic boron hydride which is formed is split up by reaction with hydrogen. 30 If the process of the invention is combined with other X represents H, R or OR; R represents a hydrocarbon known reactions, it is for example possible with the sole radical. use of boric acid anhydride, calcium carbide and hydro This process yields the metal borohydrides very smooth gen to produce at will either calcium borohydride or di ly and with a high degree of purity. The process has borane, the borazane starting material used in the process however certain disadvantages, since the starting materials of the invention merely representing one very convenient are almost always difficult to prepare. For example, the reaction promoter. alkali metal and alkaline earth metal hydrides are advan The process of the invention can also be carried out by tageously obtained from the corresponding metals them hydrogenating a boron alkyl in the presence of calcium selves by treatment with hydrogen, and therefore they 40 carbide and a tertiary amine. In this case, the N-trialkyl require the use of the pure metals, such as sodium or borazane is formed in situ, and this particular embodiment calcium metal, so that the production of the sensitive hy of the process of the invention leads to calcium hydride in drides is not in any case a reaction which is commercially one operation and in one and the same reaction vessel via very convenient, Although other processes have recently the N-trialkyl borazane. been proposed for the production of alkali metal and The following examples further illustrate the invention. alkaline earth metal hydrides which do not start from the Example I metals, these recently proposed processes operate at in conveniently high temperatures. The alkali metal and CaC-4- 2HB.NR -- 4H--> Ca(BHA) 2-C2H6 -- 2NR alkaline earth metal alcoholates are certainly more read A finely ground calcium carbide suspension consisting ily available than the hydrides, but, as already apparent of 12.8 g. (0.2 mol.) of calcium carbide in 50 cc. of from the equations set out above, it is not possible with perhydrocumene is introduced together with 30 cc. of te the aid thereof to convert all the boron of the borazane trahydrofurane and 4.6 g. (0.4 mol.) of N-triethyl bora into a complex metal borohydride. The same applies as Zane into a 300 cc. autoclave. Hydrogen is introduced regards the use of alkali metal and alkaline earth metal to give a pressure of 250 atm, and the autoclave is heated, alkyls, and in addition these metal alkyls are almost al 5 5 while shaking, to 230–240 C., the pressure falling over ways less readily available than the hydrides or alco a period of 6-8 hours to a constant final value. After holates. cooling, the gas (excess hydrogen and 6 g. of ethane) is However, this last premise must be qualified: a few wented, the contents are removed from the autoclave and organometallic compounds of the alkali metals and alka the solution (light yellow in colour) is filtered off and line earth metals exist which are very readily available, O concentrated by evaporation. After distillation under re namely the compounds of these metals with , duced pressure and drying, a completely colourless cal especially the compound calcium carbide but also sub cium borohydride is obtained (yield 13.5 g. -96.5% of stances such as for example NaCH or NaC. It there the thcoretical). fore seems obvious to split up the N-trialkyl borazanes Example 2 by reacting them with these acetylides. It has however in amino been found that such a splitting reaction is not readily CaC2 - 2B(C3I)3 -- 10H - Ca(BII) -- CII -- 60s possible. From 64 g. (1 mol.) of calcium carbide in a mixture It has now been found that N-trialkyl borazanes can be of 240 g. (2 nois.) of boron tri-n-propyl and 220 g. (2.18 split up by reacting them with alkali metal or alkaline mols.) of triethylamine (previously finely ground in a earth metal acetylides in the presence of hydrogen under 70 vibrating ball mill) in a 1 litre autoclave, calcium boro pressure, and accordingly the present invention provides a hydride is obtained in a substantially quantitative yield process for the production of alkali metal and alkaline over a period of 5 hours by introducing hydrogen to give 3, 11i,372 3. 4. a pressure of 350 atm. and heating to a maximum tem What I claim is: perature of 260 C. After the pressure has reached a 1. A process for the production of compounds selected constant final value, the autoclave is cooled and the gases from the group consisting of alkali metal and alkaline vented. The calcium borohydride does not generally earth metal borohydrides, which comprises reacting an N require purification, though recrystallisation from tetra 5 trialkyl borazane with a compound selected from the hydrofurane yields a completely colourless product. group consisting of alkali metal acetylides and alkaline earth metal acetylides in the presence of hydrogen under pressure in the absence of a catalyst and at a temperature not exceeding 300° C. A suspension of 48 g. (1 mol.) of sodium acetylide in O 2. A process according to claim 1, wherein calcium 115 g. of N-triethyl borazane and 100 cc. of perhydro carbide is used as alkaline earth metal acetylide. cumene is placed in a 500 cc, autoclave. Hydrogen is 3. A process according to claim 1, wherein sodium introduced to give a pressure of 200 atm. and the auto acetylide NaHC is used as alkali metai acetylide. cave is heated to 200-230 C., the pressure falling to a 4. A process according to claim 1, wherein tempera constant value over a period of 8-10 hours. The con tures between 140 and 200 C. are used. tents of the autoclave are cooled and the gases (excess 5. A process according to claim 1, wherein tempera hydrogen and ethane) vented, whereafter the suspension tures between 200 and 300° C. are used. obtained is removed from the autoclave. After the liquid 6. A process according to claim 1, wherein the N has been distilled off, sodium borohydride (38 g.) is ob trialkyl borazane is produced in situ from a boron alkyl tained as residue; the yield is quantitative. and a tertiary amine. 7. A process according to clairn 1, wherein said Example 4 acetylide is a compound having the formula M.H.C., 32 g. (0.5 mol.) of finely ground potassium acetylide wherein M represents a member selected from the group in 150 cc. of decahydronaphthalene are introduced to of alkali metals and alkaline earth metals, it is a whole gether with 37 g. of N-trimethyl borazane into a 500 cc. 2 5 number of from 1 to 2 (the valence of M) and y is a autoclave. After hydrogen has been introduced to give whole number of from 0 to 1, wherein, when x=2, y -0. a pressure of 150 atm., the autoclave is heated for 15 hours at 170-200 C., the pressure then falling. On References Cited in the file of this patent completion of the reaction, the excess hydrogen is vented UNITED STATES PATENTS together with the hydrocarbon gas. There remains a 30 suspension of potassium borohydride in decahydro 2,729,540 Fischer et al. ------Jan. 3, 1956 naphthalene and the amine which is formed. After the 2,852,335 Nigon ------Sept. 16, 1958 liquids have been distilled off, 25 g. of potassium boro FOREIGN PATENTS hydride are left; this can be recrystallised from water. 1,133,993 France ------Apr. 4, 1957 Example 5 792,017 Great Britain ------Mar. 19, 1956 By means of the procedure described in Example 1, a OTHER REFERENCES total of 30 g. of barium borohydride are obtained from Koster: "Angewandte Chemie,' vol. 69, page 94 32 g (0.2 mol) of extremely finely ground barium car (February 7, 1957). bide (BaC) and 40 g. of N-trimethyl borazane in 50 40 "Boron Compounds: More Spotlighted Than Ever.' cc. of dried xylene by heating for 12 hours in a shaker Chemical Engineering, vol. 64, May 1957, page 166. type autoclave with hydrogen under pressure (initial Thorpe et al.: "Thorpe's Dictionary of Applied Chem pressure with a 200 cc, autoclave-a-200 atm.) at 200 istry, 4th edition, 1937, vol. 1, page 73. 220 C. The resulting material is worked up as described in Example 1.