MonoAmidophosphoric acid

Monoamidophosphoric acid is prepared by the Stokes method. Phenol and POCI3 are reacted to form the diphenyl ester of mono-chlorophosphoric acid. The latter is reacted with alcoholic ammonia to give the phenyl ester of monoamidophosphoric acid. Monoamidophosphoric acid is formed on saponification of the ester with KOH. It is isolated as the potassium salt, from which,according to Klement and Becht, free amidophosphoric acid can be obtained by reaction with HCIO 4 ... 

A quantity of freshly distilled POCI3 (154 g.) is refluxed for 2-3 hours with 188 g. of freshly distilled phenol. The product is kept overnight in vacuum over NaOH to remove additional HCl. The oily liquid is added by drops to a minimum of 300 ml. of absolute alcohol, presaturated with NH3 at 0°C. The reaction flask is ice-cooledand vigorously stirred. The mixture must be ammonia-cal at the end of the reaction. The alcoholic solution is poured into five times its volume of ice water. The precipitate of the diphenyl ester of monoamidophosphoric acid is filtered off by suction, freed of adhering oil by pressing on clay, and dried in vacuum. The crude ester (approximately 160 g.) is recrystallized from 200 ml. of alcohol. The yield is approximately 100 g. (m.p. 148°C). An additional 50 g. of impure ester can be obtained by precipitation of the alcoholic mother liquor with water. 

Disodlum monoamidophosphate is formed on saponification of the diphenyl ester of monoamidophosphoric acid (see p. 579) with the stoichiometric quantity of NaOH (Klement and Biberacher) ... 

A 25-g. quantity of the diphenyl ester of monoamidophosphoric acid is boiled in a solution of 16 g. of NaOH in 60 ml. of water for 10 minutes. Crystallization of the salt commences on cooling the clear solution to 0°C. This is aided by addition of ice-cold ethanol (200 ml. is needed for complete precipitation). The Na3P03NH3 6H3O obtained is already quite pure. To reprecipitate, or to obtain larger crystals, it is dissolved in a small quantity of water together with pellets of NaOH. Then ethanol is added to the filtered solution at room temperature. While the salt initially precipitates as an oily substance, larger crystals are formed after brief stirring. The crystals are washed with ethanol and ether and dried in vacuum. The yield is 20 g. 

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