DiSodium dihydrogen hypophosphate

The methods commonly used for preparation of disodium dihydrogen hypophosphate depend upon the oxidation of yellow or red phosphorus. Yellow phosphorus may be oxidized by air1 or by copper(II) nitrate.2,3 Red phosphorus may be oxidized by chlorite,4 hypochlorite,5,6 alkaline permanganate,7 hydrogen peroxide,7 or iodine.8 The phosphorus (III) halides, upon hydrolysis and treatment with iodine, yield some hypophosphate.9-11 Electrolytic oxidation of a phosphide of copper, nickel, or silver3 has also been used. 

Of the various methods for preparing disodium dihydrogen hypophosphate, the one depending upon the oxidation of red phosphorus with sodium chlorite seems to be the best, considering both the yield and the simplicity of the procedure. In this reaction, phosphites and orthophosphates... 

Disodium dihydrogen hypophosphate hexahydrate is a stable, colorless, crystalline compound. It loses its water of crystallization completely at 110°. The solubility of the hydrate is 2.0 g./lOO ml. of water at 25°. Solutions of the compound are quite stable, but upon heating or the addition of acids, hypophosphate tends to disproportionate to phos-... 

P206Na2H2-6H20 Disodium dihydrogen hypophosphate, 4 68 P207H4 Pyrophosphoric acid, 3 96, 97... 

P20j[N(CH3)2]4 Octamethylpyro-phosphoramide, 7 73 P2O6 Phosphorus (V) oxide, 6 81 P20e(NH)Na4 Tetrasodium imido-diphosphate, 6 101 P206Na2H2-6H20 Disodium dihydrogen hypophosphate, 4 68 P2O7H4 Pyrophosphoric acid, 3 96, 97... 

According to Salzer, free crystalline hypophosphoric acid is obtained when lead hypophosphate, preparedfrom disodium dihydrogen hypophosphate (see below), is decomposed with H3S and the resulting acid solution evaporated (Baudler) ... 

Leininger and Chulski have demonstrated that disodium dihydrogen hypophosphate Is produced in the oxidation of red P with NaClOs in a yield of about 42%. In addition, 19% orthophosphate, 35% phosphite, and 2% hypophosphite are formed. The procedure, somewhat cumbersome because of the large cooling apparatus required, has been Improved and simplified by Baudler and, later, by Remy and Falius. According to the latter authors, special apparatus is unnecessary. Sufficient phosphorus must be available, however, and the heat of reaction must be rapidly removed. The yield Is better than that achieved by Leininger and Chulski. 

---