Metaborates synthesis

Attempts to prepare uranyl borate from UO3 instead of U3O8 were only partially successful. The trioxide is more reactive than U3O8 and eliminates the necessity for an oxidation step in the metaborate synthesis reaction, but the low thermal stability of UO3 restricts the reaction temperature to <650°C. Infrared and x-ray analyses of products obtained after heating UO3 and B2O3 mixtures for several days at 650°C. indicated that only a minor conversion to the metaborate had been effected. 

Numerous methods for the synthesis of salicyl alcohol exist. These involve the reduction of salicylaldehyde or of salicylic acid and its derivatives. The alcohol can be prepared in almost theoretical yield by the reduction of salicylaldehyde with sodium amalgam, sodium borohydride, or lithium aluminum hydride by catalytic hydrogenation over platinum black or Raney nickel or by hydrogenation over platinum and ferrous chloride in alcohol. The electrolytic reduction of salicylaldehyde in sodium bicarbonate solution at a mercury cathode with carbon dioxide passed into the mixture also yields saligenin. It is formed by the electrolytic reduction at lead electrodes of salicylic acids in aqueous alcoholic solution or sodium salicylate in the presence of boric acid and sodium sulfate. Salicylamide in aqueous alcohol solution acidified with acetic acid is reduced to salicyl alcohol by sodium amalgam in 63% yield. Salicyl alcohol forms along with -hydroxybenzyl alcohol by the action of formaldehyde on phenol in the presence of sodium hydroxide or calcium oxide. High yields of salicyl alcohol from phenol and formaldehyde in the presence of a molar equivalent of ether additives have been reported (60). Phenyl metaborate prepared from phenol and boric acid yields salicyl alcohol after treatment with formaldehyde and hydrolysis (61). 

Other advanced methods for the manufacture of NaBH4 have been investigated by Toyota Motor Co and academic researchers in Japan. Most notable is the use of magnesium hydride for direct reduction of boron oxide feedstocks, including anhydrous borax, for initial synthesis of NaBlfj (Equation 16.15) and reduction of anhydrous sodium metaborate for regeneration of spent borohy-dride (Equation 16.16) [38], Aluminum metal has also been used instead of magnesium and catalysts employed to improve kinetics. 

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