Boron compounds, vapor pressure

The reaction of adipic acid with ammonia in either Hquid or vapor phase produces adipamide as an intermediate which is subsequentiy dehydrated to adiponitrile. The most widely used catalysts are based on phosphoms-containing compounds, but boron compounds and siHca gel also have been patented for this use (52—56). Vapor-phase processes involve the use of fixed catalyst beds whereas, in Hquid—gas processes, the catalyst is added to the feed. The reaction temperature of the Hquid-phase processes is ca 300°C and most vapor-phase processes mn at 350—400°C. Both operate at atmospheric pressure. Yields of adipic acid to adiponitrile are as high as 95% (57). 

The vapor pressure of /i-[(CH3)2N]B2H5 obeys the relationship log P = 2158.56/T + 1.75 log T - 0.008061T + 7.518831 (101 torr at 0°). The gas-phase infrared spectrum has been reported in detail.5 The compound is a useful intermediate in the synthesis of other boron nitrogen compounds, including those containing NBNB6 and PBNB7 chains, and Na[(CH3)2-N(BH3)2].8 The compound can be stored at 25° for months in sealed, evacuated Pyrex tubes. It is soluble in ethers and aromatic hydrocarbons, but is attacked by protic solvents. 

A problem with this phosphor is that without precautions it usually contains a small amount of unreacted V2O5 which lowers the light output. For application in high-pressure mercury vapor lamps this pho.sphor is usually prepared with an excess of boric acid. The material has then a white body color and, in addition, the particle size can be controlled. The boron is not built into the lattice in some way or another the boron compound acts as a flux. 

Another reason for the poor sinterability is the extraordinarily high vapor pressure of boron oxides and suboxides. Since boron carbide powders are generally coated by a B2O3 layer [172] which quickly reacts to form boric acid, H3BO3, in humid atmosphere, vapor phase reactions are active at higher temperatures, in particular above 1500"C, providing a fast transport of boron compounds. Redox reactions such as... 

Exact determination of the thermal equilibrium mixture from (XVIII), and also, in general, for mixtures of compounds with more than one boron atom, is more difficult than for simple B-alkylboracyclanes, because direct gas chromatographic separation is almost impossible, due to the low vapor pressures and the high thermal instability of the compounds. 

Other reported binary boron sulfides include subvalent B12S, a black crystalline material prepared by a high-temperature reaction of amorphous boron with elemental sulfur, and BS, which has been studied spectroscopically in an electric discharge. A vapor-phase dimer, (BS)2, was identified, and a refractory condensed form of BS was reported from the reaction of elemental boron with sulfur at 1850°C and a pressure of 94 500 atmospheres. Boron disulfide, BS2, has been identified in the gas phase and appears to be the primary compound present in the vapor phase over diboron trisulfrde or elemental boron and sulfur. 

The compound PCU BCla is a white solid, easily hydrolyzed by water, and insoluble in nonpolar solvents such as carbon tetrachloride and chloroform. It sublimes completely in a sealed tube at about 340°, the temperature of sublimation varying somewhat with the pressure developed in the tube. The vapor at 340° is yellow-green, indicating dissociation into chlorine, boron chloride, and phosphorus-(III) chloride. Conductance in liquid phosphorus (V) oxychloride indicates an ionic structure, postulated to be [PCh]+[BCl4]-. 

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