Hypophosphite ions, reactions

The interesting complex chemistry of rhodium has been rather neglected this is probably because most of the synthetic methods for obtaining complexes have been tedious. In general, substitutions of chlorine atoms bonded to rhodium by other ligands are slow, and products have usually been mixtures. The situation is now changing, since novel catalytic approaches to rhodium complexes have been developed.1 The catalysis in the present synthesis involves the rapid further reaction of the hydrido complex formed from l,2,6-trichIorotri(pyridine)rho-dium(III) in the presence of hypophosphite ion. 

The BafHjPOj) formed is a major source of the hypophosphite ion and the source of HjPOj which is obtained upon H SO acidification of the salt. Moderate yields of PHj are reported from reaction with Oj in HjO at 19°C ... 

As a typical example, we can mention nickel electroless plating. The process generally utilizes hypophosphorous acid solution. When iron is immersed into the solution, the metal surface works as a catalyst and promotes the dehydrogenatimi reaction of hypophosphite ion as follows. 

The reaction between perruthenate and hypophosphite ion, HaPOa", has been studied in basic media. The rate law is of the form... 

In electroless deposition, the substrate, prepared in the same manner as in electroplating (qv), is immersed in a solution containing the desired film components (see Electroless plating). The solutions generally used contain soluble nickel salts, hypophosphite, and organic compounds, and plating occurs by a spontaneous reduction of the metal ions by the hypophosphite at the substrate surface, which is presumed to catalyze the oxidation—reduction reaction. 

Mital et al. [40] studied the electroless deposition of Ni from DMAB and hypophosphite electrolytes, employing a variety of electrochemical techniques. They concluded that an electrochemical mechanism predominated in the case of the DMAB reductant, whereas reduction by hypophosphite was chemically controlled. The conclusion was based on mixed-potential theory the electrochemical oxidation rate of hypophosphite was found, in the absence of Ni2 + ions, to be significantly less than its oxidation rate at an equivalent potential during the electroless process. These authors do not take into account the possible implication of Ni2+ (or Co2+) ions to the mechanism of electrochemical reactions of hypophosphite. 

The incorporation of a third element, e.g. Cu, in electroless Ni-P coatings has been shown to improve thermal stability and other properties of these coatings [99]. Chassaing et al. [100] carried out an electrochemical study of electroless deposition of Ni-Cu-P alloys (55-65 wt% Ni, 25-35 wt% Cu, 7-10 wt% P). As mentioned earlier, pure Cu surfaces do not catalyze the oxidation of hypophosphite. They observed interactions between the anodic and cathodic processes both reactions exhibited faster kinetics in the full electroless solutions than their respective half cell environments (mixed potential theory model is apparently inapplicable). The mechanism responsible for this enhancement has not been established, however. It is possible that an adsorbed species related to hypophosphite mediates electron transfer between the surface and Ni2+ and Cu2+, rather in the manner that halide ions facilitate electron transfer in other systems, e.g., as has been recently demonstrated in the case of In electrodeposition from solutions containing Cl [101]. 

Electroless Ni-Ge-P was studied as a model system for ternary alloy deposition [112], A chloride-free solution with GeC>2 as a source of Ge, hypophosphite as reducing agent, aspartic acid as a selective complexant for Ni2+ ions, which was operated at 80 °C in the pH range of 5-5.8, was developed for depositing Ni-Ge-P films with a tunable Ge content from 0 to 25+ at%. The use of a complexant such as citric acid, which complexed Ge(IY) ions as well as Ni2+ ions, resulted in a much lower Ge content in the electroless deposit, and a more complicated solution to study for the reasons discussed above. The aspartate-containing electroless solution, with its non-complexing pH buffer (succinic acid), approximated a modular system, and, with the exception of the aspartic acid - Ni2+ complexation reaction, exhibited a minimum level of interactions in solution. 

By treating sodium hypophosphite, NaH2P02 with an ion-exchange resin. The sodium salt may be produced by boding white phosphorus with a solution of sodium hydroxide, a reaction similar to (1) above. 

A systematic study of the diazonium salt ypophosphorous acid redox initiation is available. (40) Whilst this involves an aque ous solution - precipitation sysTem, it would be interesting to apply the results to emulsions. Under the acid conditions used there is evidence that the hypophosphite radical(HPO ) is that which actually initiates polymerisation. Electrophilic substituO, ents in the diazonium salt, e.g., p-nitro, accelerate the polymer isation rate. Several schemes have been suggested to account for the reaction. (4I) One involves the formation of an ion radical ... 

The kinetics of this reaction have been studied for 1-6 M NaOH from 60-90°C and it is reported to be first order in hypophosphite but second order in hydroxide ion, viz. 

Write balanced equations to describe the oxidation of the following substances with strongly alkaline permanganate in the presence of barium ion (Stamm reaction) iodide, phosphite (HP03 ), hypophosphite (H2PO2 ), cyanide, thiocyanate, formate. 

Therefore, the analysis of the product distribution in the H2, HD, and D2 mixtures obtained during electrocatalytic hypophosphite oxidation on nickel electrode suggests that the hydride mechanism, assuming the release of hydride ion and instantaneous reaction with water, is unlikely due to HD content lower than the equilibrium values (hydride mechanism should lead to HD as a prevailing component [77]). Furthermore, this also puts to a question the electrochemical mechanism, according to which equilibrium H2, HD, and D2 mixtures must be formed due to the statistical recombination of H and D atoms for equally accessible electrode surface. To clarify this issue, computer simulations for the H2, HD, and D2 formed by the recombination of H and D atoms were performed. 

There is now abundant evidence for the homolytic decomposition of covalent azo- and diazo-compounds of many types, but evidence for one-electron transfer reactions of diazonium salts is very scanty. Cooper (4) and Marvel ( ) have shown that reduction of diazonium salts by ferrous ions can initiate.vinyl polymerization, while Kornblum s work ( ) has shown that the reduction of diazonium salts by hypophosphite is promoted by oxidizing agents in a manner indicative of the chain reaction ... 

Characteristically, too, the addition of cupric ions inhibits completely this polymerization induced by hypophosphite and an oxidizer. Consequently, the reactions... 

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