Handling of diborane

Diborane is valued as a fuel for use in rocket propellants. Gallery Ghemical Co. developed equipment and procedures for the safe handling of diborane and by 1962 had produced about 5 million pounds of the material. It is offered for shipment in chrome-molybdenum steel cylinders at —80° (minimum order 100 g.), and technical bulletins present information on handling procedures and safety precautions. 

Although special care is demanded, no major difficulties are associated with the handling of diborane. The principal hazards arise from its toxicity and its reactivity and relative instability—reports of spontaneous ignition and detonation do not (322) refer to the pure compound, which has a flash point of 145°C in air, related to the wide flammability limits of 0.8... 

For additional information on the safe storage and handling of diborane, see the Callery Chemical Company publication entitled Diborane Handling Bulletin [1]. 

The process avoids the handling of diborane. The reaction is efficiently catalyzed by Ti derivatives such as Cp2TiCl2 [15] or TiCl3 [16]. 

Borazine has been known since the pioneering work of Alfred Stock early in this century. Stock s work was important in two regards He was the first to study compounds such as the boranes. silanes, and other similar nonmetal compounds, and he perfected vacuum line techniques for the handling of au- and moisture-sensitive compounds, invaluable to the modern inorganic chemist.67 Stock synthesized borazine by heating the adduct of diborane and ammonia 66... 

Caution. Diborane(6) is a highly toxic, extremely flammable gas (bp — 86.5°). Serious explosions have resulted from exposure of diborane(6) to atmospheric oxygen. All apparatus to be used for handling diborane(6) should be checked carefully for leaks. Suitable safety shields should be employed. 

Caution. This synthesis is not suitable for the preparation of diborane in a flow system at atmospheric pressure because flaming of the reaction mixture and for the formation of unwanted reduction products (i.e., phosphine) may occur. Inasmuch as diborane reacts violently with oxygen and is extremely poisonous, it must be handled either in a vacuum line or an oxygen-free reaction system at all times. 

Caution. Diborane(6) is a very toxic, flammable, and ill-smelling gas. It has an autoignition tempeature of 38 to 52°C. Some people cannot smell diborane(6) for those individuals, the handling of this compound may be especially dangerous. All work with diborane(6) must be carried out in a well-ventilated fume hood. 

Previous preparations of borazine in this series and elsewhere have suffered from low yields, difficult purification, and the handling of air-sensitive compounds such as 2,4,6-trichloroborazine and diborane. Described below is a convenient, one-step synthetic procedure for the laboratory production of multigram quantities of borazine, B3N3H6, in 55-65% yields. The method is based on the reaction of NaBH4 and (NH4)2S04 in tetraglyme solution at 120-140°C with continuous removal of the product in vacuo. Borazine is the only volatile product and is obtained in excellent purity by a single vacuum fractionation. 

Great care must be used in handling diborane and alkylboranes because they ignite spontaneously in air (with a green flame). The solution of THF BH3 is considerably less prone to spontaneous ignition but still must be used in an inert atmosphere and with care. 

A boron analog - sodium borohydride - was prepared by reaction of sodium hydride with trimethyl borate [84 or with sodium fluoroborate and hydrogen [55], and gives, on treatment with boron trifluoride or aluminum chloride, borane (diborane) [86. Borane is a strong Lewis acid and forms complexes with many Lewis bases. Some of them, such as complexes with dimethyl sulfide, trimethyl amine and others, are sufficiently stable to have been made commercially available. Some others should be handled with precautions. A spontaneous explosion of a molar solution of borane in tetrahydrofuran stored at less than 15° out of direct sunlight has been reported [87]. 

Diborane, B2Hg, is a gas and is difficult to handle. However, borane complexed with donors such as THE or dimethylsulfide are commercially available and have become valuable reagents for the reduction of various functional groups. BHg SMc2 is soluble in and unreactive toward a wide variety of aprotic solvents such as THE, Et20, CH2CI2, and hydrocarbons. 

Diborane is extremely toxic. It is an extremely reactive gas and hence should be handled in a special apparatus. Moreover, a serious drawback to using diborane is that the boron-containing product of combustion is a solid, B2O3. If an internal combustion engine is used, the solid will eventually coat the internal surfaces, increasing friction, and will clog the exhaust valves. 

Diborane should be handled using the "basie prudent practices" of Chapter 5.C, supplemented by the additional precautions for work with reactive and explosive compounds described in Chapter 5.G. In particular, diborane should be used only in a fume hood free of ignition sources and should be stored in a cold, dry, weU-ventUated area separated from incompatible substances and isolated from sources of sparks and open flames. 

Excess diborane and waste material containing this substance should be placed in an appropriate container, clearly labeled, and handled according to your institution s waste disposal guidelines. For more information on disposal procedures, see Chapter 7 of this volume. ... 

Because of their very much lower reactivity and, to a lesser extent, their relative insolubility in simple ethers, the tetrahydroborates of sodium and potassium will not participate in many of the above-mentioned reactions of the lithiiam salt. But because it is so much cheaper and is easier to handle, the sodixun salt in particular has received much study (163). Generally yields are lower, but in ether suspension NaBHij will give diborane with BF3-Et20 (280) or FeCl3 (276), whereas, in the vapor state, the latter substance is also effective in the absence of ether at 220 to 320°C... 

Diborane is available as the complex of THF (BH3 THF) by dissolving it in THF for easier handling. In the reaction with olefins (eq. (6.5)) or acetylenes, generally, trialkylborane is produced by the addition reaction of three hydrides. 

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