Boric Acid with Organic Nitrogen Compounds

Boric Acid with Organic Nitrogen Compounds 

The second important way to produce h-BN is the reaction of boric acid or alkali-borates with organic nitrogen compounds (melamin, urea, dicyanamide, guanidine) in nitrogen atmosphere [76-80]. These reactions are carried out at temperatures between 1000 °C and 2100 °C in N2 atmosphere. Before final thermal treatment, the product can be washed with methanol or diluted acids in order to remove all non-reacted products. For removing oxygen impurities a thermal treatment at 1500 °C in inert N2 or Ar atmosphere is used. BN with turbostratic structure (t-BN) is obtained which is characterized by partial or complete absence of three-dimensional order in the stacking of its atomic planes [81]. 

Annual world production of h-BN powder is approximately 400 tonnes at a price of 50-150 per kg. 

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Boric Acid with Organic Nitrogen Compounds... 

Reaction of boric oxide with organic nitrogen compounds. In this process, boric oxide or boric acid is made to react with nitrogen compounds such as melamine, urea, dicyanamide, or guanidine ... 

Kjeldahl nitrogen is the sum of nitrogenous organic compounds, free ammonia, and ammonium. In the presence of H2S04, K2S04, and selenium catalyzer organic nitrogen is converted to ammonium. Free ammonia is also converted to ammonium. After the addition of a base, the ammonia is distilled from an alkaline medium and absorbed in boric acid. The ammonia may be determined colorimetrically at 655 nm or by titration with a standard mineral acid... 

The comprehensive method determines the nitrogen content for all forms of nitrogen compounds (nitrite, nitrate, urea, organic nitrogen, and ammonia), which upon distillation can be collected in a known amount of sulfuric acid and titrated with sodium hydroxide. A great deal of time is consumed in performing this classical nitrogen method. Note Boric acid may be used for collection of ammonia in the distillation step rather than sulfuric acid. 

It was observed that organically bound phosphorus is completely decomposed to phosphate when oxidized with persulphate in an alkaline medium. Furthermore, more than 60 % of condensed phosphates are hydrolyzed. As concentrations of polyphosphates are negligible in most natural waters, a simultaneous oxidation procedure for organic phosphorus and nitrogen compounds has been developed by Korolejf (1977). Valderrama (1981) compared the procedure with former methods using separate determinations. In the simultaneous oxidation, the pH of the reaction starts at ca. 9.7 and ends at 4-5. These conditions are obtained by a boric acid-NaOH system. In seawater samples no precipitation is formed when the oxidation mixture is added. At elevated temperatures a precipitation is formed, which, however, dissolves as oxidation proceeds. 

Under the protection of nitrogen, the boric acid (10.6 g, 53.8 mmol) was dissolved in chloroform (100 mL), and then, lead tetraacetate (26.3 g, 59.1 mmol) and mercuric acetate (3.4 g, 10.8 mmol) were added at the temperature of 40 °C. The reaction was heated to 60 °C and stirred for 2 h. Compound 2.2.11 (8.4 g, 53.8 mmol) was dissolved in pyridine (15.2 mL) and added at 60 °C. After stirred for 1 h, the reaction was kept at room temperature overnight. TLC showed that the reaction was completed. The solid was removed by filtration and washed with chloroform (100 ml). Dilute sulfuric acid (3 N, 100 mL) was used to quench the reaction. After liquid separation, the aqueous phase was extracted with chloroform (3 X 100 mL). The organic phases were combined, washed with saturated brine (100 mL), dried over anhydrous sodium sulfate, and filtered. The filtrate was concentrated by rotary evaporator under reduced pressure. The resulting cmde product was isolated and purified by flash column chromatography (PE/EA = 10 1) to obtain 7.4 g white solid 2.2.20, yield 45 %, and 3.6 g white solid 2.2.21, yield 25 %. 

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