Boron hydrides indicated hydrogen

Liq hydrogen represents the ultimate attainable in a fuel. However, its low density low bp make its use on a large scale difficult. Study of the periodic table of the elements indicated that a better HEF could be prepd only if hydrogen, beryllium or boron were used as "building blocks. Beryllium was eliminated,according to MartinfRef 35),because of its limited availability, extreme toxicity of its compds and because no liq complexes of Be are known. Consequently boron its hydrides were selected as the materials from which the synthesis of a better HEF would be attempted... 

The cyclization can be carried out with halogenated amines, and substitution products of the new ring systems can also be obtained in the conventional way, by nitration, etc. Similar compounds can be prepared directly by using arylboron dichlorides in place of boron trichloride in the procedure indicated above. The parent borazarene derivatives, with hydrogen attached to boron, can be made from the B-hydroxy compounds with lithium aluminum hydride in the presence of aluminum chloride. N-Alkyl derivatives can be made either by using N-alkyl derivatives of the aminobiphenyls as starting materials, or by N-alkylation of the unsubstituted compounds via their N-lithio derivatives. Apart from their inherent interest, compounds of this type can serve as intermediates in various syntheses. Thus benzocinnolines and 2,2 -dihydroxybiphenyls can be obtained from derivatives of 2-aminobiphenyl. ... 

The photochemistry of aluminum aryls bears certain features in common with boron aryls the low reactivity of the monomeric triaryl-metallic, the formation of biaryls in tetracoordinate systems having proximate aryl groups and the formation of subvalent metallic products (22-24). Thus, when irradiated at 254 nm in ethyl ether solution, triphenylaluminum ethyl etherate underwent no formation of biphenyl or aluminum metal. On the other hand, the irradiation of triphenylaluminum (99) in benzene or toluene solution, in which the aluminum aryl is largely dimeric, led to the production of biphenyl (45%) and aluminum metal. When such a reaction mixture was filtered to remove the aluminum and the filtrate treated with D2O, hydrogen gas was evolved that consisted of >98% H—D. The biphenyl now isolated was 20% undeuterated and 80% monodeuterated further spectral comparisons showed that the deuteron was at the 2-position. These findings indicated the formation of an aluminum-hydride and an o-biphenylyl aluminum bond [Eq. (47)]. The source of the hydrogen in H—D was not the... 

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