Sodium hypophosphite, oxidation

Commercial processes Commercial electroless nickel plating stems from an accidental discovery by Brenner and Riddell made in 1944 during the electroplating of a tube, with sodium hypophosphite added to the solution to reduce anodic oxidation of other bath constituents. This led to a process available under licence from the National Bureau of Standards in the USA. Their solutions contain a nickel salt, sodium hypophosphite, a buffer and sometimes accelerators, inhibitors to limit random deposition and brighteners. The solutions are used as acid baths (pH 4-6) or, less commonly, as alkaline baths (pH 8-10). Some compositions and operating conditions are given in Table 13.17 . 

The principal evidence in favor of the electrochemical mechanism is the observation that metal deposition can occur, albeit at a much reduced rate, in a two-compartment cell. When one of the compartments contains only the metal ions and the other only the sodium hypophosphite, metal deposition occurs on the electrode in the first compartment, being driven by hypophosphite oxidation at the electrode in the other half-cell [36, 37],... 

L. P. de St. Gilles, and I. M. Kolthoff, found that potassium permanganate oxidizes hypophosphorous acid completely to phosphoric acid. L. Amat found that the oxidation proceeds more quickly the more cone, the soln., the more acidic the soln., and the higher the temp. at ordinary temp., and in dil. soln., the oxidation is incomplete. If the soln. be too hot, some permanganate may be decomposed without interaction with the hypophosphorous acid. The reaction was studied by I. M. Kolthoff. M. Major, and A. Sieverts found that reduced iron readily dissolves in a hot soln. of sodium hypophosphite ferric salts are reduced to the ferrous state and ferric alum reacts at the temp, of the water-bath, while phosphorous acid is not attacked after several hours. 

The oxidation process of sodium hypophosphite with iron has been studied. To establish conditions of quantitative oxidation of NaH2P02 with iron and the possible reaction surface, an experiment has been defined for obtaining a mathematical model of the process. The experimental objective deals with the conditions for obtaining 100% oxidation of NaH2P02. 

Deoxygenation of pyridine A-oxides has been achieved using dimethyldioxiran <95CC1831> and palladium with sodium hypophosphite <95GCI(124)385>. Pyridine A-oxides, with ruthenium porphyrin catalysts, have been used as an oxidant of aromatic compounds <95JA(117)8879> or olefins, alcohols, sulfides and alkanes <95FI(40)867>. 

Palladised copper oxide has also been used 6 for a similar purpose, and for other catalytic reactions palladised metals have been tried. For example, the oxidation of sodium hypophosphite solution takes place according to the equation... 

Caution Take care in mixing Sodium Hypophosphite with nitrates, chlorates, or other oxidizing agents because an explosion may occur if the mixtures are triturated or heated. 

Violent reacdon with Al, BP, cyanide, esters, PN2H, P, NaCN, SnCb, sodium hypophosphite, thiocyanates. Dangerous disaster hazard due to fire and explosion hazard. When heated to decomposidon it emits toxic fumes of NOx. They are powerful oxidizing agents that may cause violent reacdon with reducing materials. Nitrates should be protected carefully in storage. 

Cacodylic acid is reduced to cacodyl when treated -with an excess of sodium hypophosphite in hydrochloric acid solution, Cacodyl may be obtained from dimethylarsine by the action of oxides of nitrogen, aqueous chromic acid, le peroxide, cacodyl chloride, auric chloride, or potassium ferricyanide. It also results w hen cv/cZopentamethyl-penta-arsine is distilled under atmospheric pressure in a carbon dioxide atmosphere, the decomposition commencing at 270° C. ... 

A nickel hydroxide dispersed in water was reduced with a sodium hypophosphite solution and then heated up to 90-100°. After a certain induction period, a black precipitate was suddenly formed, evolving hydrogen simultaneously. This powdery precipitate was washed with water at first, then with alcohol, and finally with ether, and can be dried in the air without oxidation at room temperature. 

Raney nickel hydrogenation of nitriles is aqueous acetic acid or in aqueous acetic acid-pyridine in the presence of sodium hypophosphite (NaH PO-i), which becomes oxidized to the phosphate, converts the nitriles into the corresponding aldehydes. The reaction takes place at room temperature and pressure. Yields are in the range 50-90%. Thus a solution of 1 g. of benzonitrile and 2 g. of hydrated sodium hypo-phosphite in 29 ml. of a 1 1 2 water-acetic acid-pyridine mixture was stirred with 0.3-0.4 g. of Raney nickel at 40-45° for 1 hr. benzaldehyde was isolated as the 2,4-dinitrophenylhydrazone. 

Aldehydes N,N -Carbonylimidazole. Ethoxymethyleneaniline. Ethyleneimine. For-maldoxime. Imidazole. N-Methyl-N-phenylcarbamyl chloride. p-Nitro-N.N-dimethylaniline. Phosgene. Silver tosylate. Sodium ethoxide. Sodium hypophosphite. Sodium 2-nitropro-panenitronate. Trimethylamine oxide. 

The major reactions in this section are those involving an V-oxide oxygen. Deoxygenation of 2,3-disubstituted quinoxaline 1,4-dioxides is achieved under mild conditions by treating with hexa-chlorodisilane, TMS-1, TFAA-sodium iodide, or titanium tetrachloride-zinc dust <81H(i6)4ii>. Quinoxaline and phenazine V,A( -dioxides are also deoxygenated under mild conditions by sodium hypophosphite catalyzed by Pd/C or by treatment with sodium iodide in the presence of pyri-dine/sulfur trioxide complex <83JHC1735>. Deoxygenation of 6-chloro-2(l//)-quinoxalinone 4-oxide is effected particularly by sodium borohydride or sodium hydrosulfite <85H(23)143>. 

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