Carbonization under pressure

Coesite. Coesite, the second most dense (3.01 g/cm ) phase of silica, was first prepared ia the laboratory by heating a mixture of sodium metasibcate and diammonium hydrogen phosphate or another mineraliser at 500—800°C and 1.5—3.5 GPa (14,800—34,540 atm). Coesite has also been prepared by oxidation of silicon with silver carbonate under pressure (67). The stmcture is monoclinic = 717 pm, Cg = 1.238 pm, and 7 = 120°. 

Hydroxyl Group. The OH group of cyanohydrins is subject to displacement with other electronegative groups. Cyanohydrins react with ammonia to yield amino nitriles. This is a step in the Strecker synthesis of amino acids. A one-step synthesis of a-amino acids involves treatment of cyanohydrins with ammonia and ammonium carbonate under pressure. Thus acetone cyanohydrin, when heated at 160°C with ammonia and ammonium carbonate for 6 h, gives a-aminoisobutyric acid [62-57-7] in 86% yield (7). Primary and secondary amines can also be used to displace the hydroxyl group to obtain A/-substituted and Ai,A/-disubstituted a-amino nitriles. The Strecker synthesis can also be appHed to aromatic ketones. Similarly, hydrazine reacts with two molecules of cyanohydrin to give the disubstituted hydrazine. 

An intermediate position can be seen for pitches that are carbonized under pressure or by addition of elemental sulfur. Because of the high cost of precursor materials of the first group, the selection of precursor type and processing must be optimized carefully (20,32). 

Szepesy, L. Hies, V Adsorption of Gases and Gas Mixtures, II. Measurement of the Adsorption Isotherms of Gases on Active Carbon under pressures of 1 to 7 atm, Acta Chim. Hung. 35 (1963), p. 53/60... 

Lee CG, Yamada K, Hisamitsu Y, Ono Y, Uchida I (1999) Kinetics of oxygen reduction in molten carbonates under pressurized Air/C02 oxidant gas conditions. Electrochemistry... 

Rodriguez-Valero MA, Martinez-Escandell M, Molina-Sabio M, Rodrfguez-Reinoso F. CO2 activation of olive stones carbonized under pressure. Carbon 2001 39(2) 320-324. 

Inagaki M, Park KC, Endo M (2010) Carbonization under pressure. New Carbon Mater... 

Ayache J, Oberlin A (1990) Mechanism of carbonization under pressure, part II influence of impurities. Carbon 28(2-3) 353-362... 

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