Hypophosphoric acid

Phosphonic acid (commonly called phosphorous acid) may be crystallized from the solution obtained by adding ice-cold water to P4O6 (equation 14.118) or PCI3 (equation 14.72). Pure H3PO3 forms colourless, deliquescent crystals (mp 343 K) and in the solid state, molecules of the acid (Table 

7) are linked by hydrogen bonds to form a three-dimensional network. In aqueous solution, it is dibasic (equations 14.123 and 14.124). 

Salts containing the [HP03] ion are called phosphonates. Although the name phosphite remains in common use, it is a possible source of confusion since esters of type P(0R)3 are also called phosphites, e.g. P(OEt)3 is triethyl-phosphite. 

Phosphonic acid is a reducing agent, but disproportionates when heated (equation 14.125). 

The reaction between red phosphorus and NaOCl or NaC102 yields Na2H2P20g, which can be converted in aqueous solution into the dihydrate of the free acid which is best formulated 

A salt described as a diphosphite, Na3HP20s. 12 H2O, has been prepared by hydrolysing PBr3 with ice-cold aqueous NaHC03. Its n.m.r. spectrum is consistent with the structural formula shown. 

HsP30g and H6PgOi2. The ion P3OI has been studied in Na5P30g. 14 H2O. The P—P bond has the length of a normal single bond in this ion, in which P atoms are in the formal oxidation states iii, iv, and III. 

Salts of an acid H6PgOi2 have been prepared by treating red P suspended in alkali hydroxide solution with hypochlorite. An X-ray study of the Cs salt shows the ion to contain a chair-shaped ring of six directly bonded P atoms in which P—P is approximately 2-2 A. 

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Hypophosphorous acid, H3PO2, H2P(0)0H. A monobasic acid. Ba(H2P02)2 is formed when white phosphorus is dissolved in Ba(OH)2 solution. H3PO2 and its salts are strong reducing agents. 

Hypophosphoric acid, H4P2O6, HP(0)(0H)(/i-0)P(0)(0H)2 although can be letrabasic (Na salt from NaOCI on red phosphorus). 

Make a thin paste of 21 5 g. of finely-powdered o-tolidine (a commercial product) with 300 ml. of water in a 1-litre beaker, add 25 g. (21 ml.) of concentrated hydrochloric acid, and warm until dissolved. Cool the solution to 10° with ice, stir mechanically, and add a further 25 g. (21 ml.) of concentrated hydrochloric acid (1) partial separation of o tolidine dihydrochloride will occur. Add a solution of 15 g, of sodium nitrite in 30 ml. of water as rapidly as possible, but keep the temperature below 15° a slight excess of nitrous acid is not harmful in this preparation. Add the clear, orange tetrazonium solution to 175 ml. of 30 per cent, hypophosphorous acid (2), and allow the mixture to stand, loosely stoppered, at room temperature for 16-18 hours. Transfer to a separatory funnel, and remove the upper red oily layer. Extract the aqueous layer with 50 ml, of benzene. Dry the combined upper layer and benzene extract with anhydrous magnesium sulphate, and remove the benzene by distillation (compare Fig. II, 13, 4) from a Widmer or similar flask (Figs. II, 24, 3-5) heat in an oil bath to 150° to ensure the removal of the last traces of benzene. Distil the residue at ca. 3 mm. pressure and a temperature of 155°. Collect the 3 3 -dimethyldiphenyl as a pale yellow liquid at 114-115°/3 mm. raise the bath temperature to about 170° when the temperature of the thermometer in the flask commences to fall. The yield is 14 g. 

If the quantity of hypophosphorous acid is doubled, the yield is increased... 

The replacement of 2-amino group by a hydrogen can be achieved by diazotization, followed by reduction with hypophosphorous acid (1-8, 13). Another method starting from 2-aminothiazole is to prepare the 2-halo-thiazole by the Sandmeyer reaction (prepared also from the 2-hydroxy-thiazole), which is then dehalogenated chemically or catalytically (1, 9, 10). 

It IS possible to replace ammo substituents on an aromatic nucleus by hydrogen by reducing a diazonium salt with hypophosphorous acid (H3PO2) or with ethanol These... 

Reductive deamination of primary arylamines The ammo substituent of an arylamine can be replaced by hydrogen by treatment of its de rived diazonium salt with ethanol or with hypophosphorous acid... 

Mercury(II) nitrate Acetylene, aromatics, ethanol, hypophosphoric acid, phosphine, unsaturated organic compounds... 

Mercury(II) oxide Chlorine, hydrazine hydrate, hydrogen peroxide, hypophosphorous acid, magnesium, phosphorus, sulfur, butadiene, hydrocarbons, methanethiol... 

Gravimetric methods more suitable for general use involve the precipitation of metallic gold from tetrachloraurate solutions by reduction with oxaUc acid, SO2, or hydroquinone. Formaldehyde, hydrazine, ferrous sulfate, and hypophosphorous acid also have been used but are considered less efficient (40). 

Complexes of Ir(III) are kineticaHy inert and undergo octahedral substitution reactions slowly. The rate constant for aquation of prBr(NH3)3] " [35884-02-7] at 298 K has been measured at 2 x 10 ° (168). In many cases, addition of a catalytic reducing agent such as hypophosphorous acid... 

Nylon-11. Nylon-11 [25035-04-5] made by the polycondensation of 11-aminoundecanoic acid [2432-99-7] was first prepared by Carothers in 1935 but was first produced commercially in 1955 in France under the trade name Kilsan (167) Kilsan is a registered trademark of Elf Atochem Company. The polymer is prepared in a continuous process using phosphoric or hypophosphoric acid as a catalyst under inert atmosphere at ambient pressure. The total extractable content is low (0.5%) compared to nylon-6 (168). The polymer is hydrophobic, with a low melt point (T = 190° C), and has excellent electrical insulating properties. The effect of formic acid on the swelling behavior of nylon-11 has been studied (169), and such a treatment is claimed to produce a hard elastic fiber (170). 

A widely used procedure for determining trace amounts of selenium involves separating selenium from solution by reduction to elemental selenium using tellurium (as a carrier) and hypophosphorous acid as reductant. The precipitated selenium, together with the carrier, are collected by filtration and the filtered soflds examined directly in the wavelength-dispersive x-ray fluorescence spectrometer (70). Numerous spectrophotometric and other methods have been pubHshed for the deterruination of trace amounts of selenium (71—88). 

Diarsines and Diarsenes. Under certain conditions, the reduction of compounds with two organic groups attached to arsenic may give rise to tetraalkyl-or tetraaryldiarsines. Thus a number of diarsines have been obtained by the reduction of arsinic acids with phosphorous or hypophosphorous acid (100). Diarsines can also be prepared by the treatment of a metal dialkyl- or diarylarsenide with iodine (101) or a 1,2-dihaloethane (102). 

A large number of polymeric substances, (RAs) or (ArAs), are also known (113). They are usually prepared by the reduction of arsonic acids with hypophosphorous acid (100,114) or sodium dithionite (115). Most of these polymers have not been well characterized. An insoluble, purple material, poly(methylarsinidene) [26403-94-1], (CH As), prepared by the interaction of methylarsine and a dihalomethylarsine, however, has been shown by an x-ray investigation to have a ladderlike polymeric stmcture in which the inter-mng distances correspond to one-electron bonds (116) ... 

The hydriodic acid employed was a 56% aqueous solution preserved with 0.8% hypophosphorous acid obtained from Fisher Scientific Co. Once a bottle is opened, the contents tend to deteriorate, becoming dark-colored in less than 2 days. However, shelf life can be extended indefinitely if the container is purged with dry nitrogen before resealing. 

Note that the value of pKa for hypophosphorous acid H3PO3 is consistent with its (correct) formulation as HPO(OH)2 rather than as P(OH)3, which would be expected to have pKa > 8. Similarly for H3PO2, which is H2PO(OH) rather than HP(OH)2. 

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