Kinetic Study of the H2POOH-D2O Exchange by Nuclear Magnetic Resonance

Fratiello, Anthony; Anderson, E. W.

doi:10.1021/ja00888a007

Cited by 27 publications

(25 citation statements)

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“…At room temperature and neutral pH, the rate of isotope exchange between H2PO2 -1 (D2PO2 -1) or HPO3 -~ (DPO3 -2) and D20(H20) is negligible (8)(9)(10)(11)(12), but at room temperature and pH ~ 2 the rate of exchange for I'-I2PO2 -1 is comparable to the rate of decomposition cor~ducted at 100 ~ and neutral pH (13,14).…”

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confidence: 99%

The Nickel Metal Catalyzed Decomposition of Aqueous Hypophosphite Solutions

Marshall¹

1983

J. Electrochem. Soc.

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Hot aqueous hypophosphite (H2PO~ ') solutions are exhaustively decomposed to orthophosphite (HPO~2) in the presence of etched Ni wire according to the rate law d[H2PO~']/dt = -ko [H~PO~ ~] x (catalyst area). The activation energy is about 2.6 kcal/mol and the rate increases 4-fold with pH in the range 3 -< pH -< 7. Ni catalyzes the isotopic exchange between H~PO~ -~ and D20 as well as the decomposition. When [HPO~ -2] -> 0.15~/at the start of reaction, the catalyst is completely passivated with respect to the decomposition but not with respect to the isotopic exchange. The H2:HD:D2 volume ratio of the evolved gas is about 5:6:7. A mechanism for the decomposition is discussed and related to "electroless" plating.In spite of numerous investigations into the chemistry of "electroless" plating (1), experimental results relevant to the primal catalyzed hypophosphite decomposition Ni H2PO~ -1 + H20--> HPO3 -'2 ~ H2~ + H +1[1] A are few. Although H2PO~. -1 is distinguished by a standard redox potential of --0.SOV (2), reactions with most oxidizing agents are very slow, especially at 25 ~ and neural pH. This lack of reactivity is generally ascribed to very small concentrations of a "3-centered" intermediate (3-5) which H2PO2 -1 must rearrange prior to its oxidation.The electrochemical oxidation of H2PO2 -1 is also slow and occurs at appreciable rates only at elevated temperature on Ni and Pd surfaces (6). At room temperature only 02 is-evolved from an Ni anode, and H2PO2 -1 is not electrochemically oxidized on Pt even at elevated temperature.Similarities between the behavior of the standard hydrogen electrode 'and that of Ni electrodes immersed in hot H2PO2 -1 solutions suggested that Ni electrodes are saturated with hydrogen (7). At room temperature and neutral pH, the rate of isotope exchange between H2PO2 -1 (D2PO2 -1) or HPO3 -~ (DPO3 -2) and D20(H20) is negligible (8-12), but at room temperature and pH ~ 2 the rate of exchange for I'-I2PO2 -1 is comparable to the rate of decomposition cor~ducted at 100 ~ and neutral pH (13,14).Reaction [1] is negligible in the absence of catalyst at 100 ~ and does not take place without H20 (15). The .decomposition rate at 100 ~ is 1.2 mM/hr 9 cm 2 for [H2PO2-1] --0.25M (Fig. 2). In the presence of 3 mM Ni +2, but under otherwise comparable conditions, H2PO2 -1 is consumed at 3.2 mM/hr 9 cm 2 (16). During "electroless" plating ([Ni +2] -= 0.1M) H2PO2 -1 is consumed at 5 mM/hr 9 cm 2 (15).When H2PO2 -1 and D20 or D2PO2 -1 and H20 are decomposed at pH's between 3 and 5 over finely divided Ni, approximately equal amounts of the hydrogen isotopes are present in the evolved gas (17)(18)(19). During Ni plating the gas is heavily enriched in the hypophosphite isotope while this isotope is not detected in the water (17,20,21).Difficulties in preparing a reproducible Ni surface exhibiting a sustainable and useful level of activity have been a major hindrance to obtaining definitive mechanistic data. This problem was noted in Ref. (16 and 22). Catalyst sensitivity may be more noticeable under...

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confidence: 99%

The Nickel Metal Catalyzed Decomposition of Aqueous Hypophosphite Solutions

Marshall¹

1983

J. Electrochem. Soc.

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“…conversion of I to 2 is proposed to occur through the mechanism depicted in Figure 5, and the geometries of all the species involved are included in Figure 3. Tautomerization starts with a proton transfer from one of the P-H bonds to an external tet-H 3 [7][8][9] Proton abstraction from a P-H bond has been also found to be relevant in the mechanism of the Atherton-Todd reaction of oxidation of dialkyl phosphonates with chlorocarbons. 22 The calculations show that conversion of I to I 2 has a moderate energy cost (22.4 kcal/mol) and it takes place without any additional activation barrier, as revealed by scan calculations (see Figure 6).…”

Section: First Step: Substitution At the Pd Centrementioning

confidence: 99%

“…3,4 Hypophosphorous acid (systematic name phosphinic acid) can adopt two different tautomeric structures: the tetrahedral form (tet) [H 2 PO(OH)] is the most stable one and contains two hydrogen atoms directly bound to the phosphorus, whereas the pyramidal form (pyr) [HP(OH) 2 ] only has one P-H bond and there is a lone pair of electrons over the phosphorus atom (see Scheme 1). 5,6 For a long time it was impossible to isolate or observe directly this pyr form of the acid, though its presence in equilibrium with the tet tautomer was repeatedly postulated from kinetics studies, [7][8][9] and it was estimated that the pyr/tet ratio in aqueous solutions does not exceed 10 -12 . 10 Nowadays it is known that the unstable pyr-H 3 PO 2 tautomer can be stabilized via coordination to a soft metal center and, as a matter of fact, there are several well-characterized metal complexes containing the pyr forms of H 3 PO 2 and related acids in low oxidation states.…”

Section: Introductionmentioning

confidence: 99%

Combined kinetic and DFT studies on the stabilization of the pyramidal form of H3PO2 at the heterometal site of [Mo3M′S4(H2O)10]4+ clusters (M′ = Pd, Ni)

et al. 2009

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4+ complexes, in which the rare pyramidal form of H 3 PO 2 is stabilized by coordination to the M' site of the clusters. The reaction proceeds with biphasic kinetics, both steps showing a first order dependence with respect to H 3 PO 2 . These results are interpreted in terms of a mechanism that involves an initial substitution step in which one tetrahedral H 3 PO 2 molecule coordinates to M' through the oxygen atom of the P=O bond, followed by a second step that consists in tautomerization of coordinated H 3 PO 2 assisted by a second H 3 PO 2 molecule. DFT studies have been carried out to obtain information on the details of both kinetic steps, the major finding being that the role of the additional H 3 PO 2 molecule in the second step consists in catalysing a hydrogen shift from phosphorus to oxygen in O-coordinated H 3 PO 2 , which is made possible by its capability of accepting a proton from P-H to form H 4 PO 2 + and then transfer it to the oxygen. DFT studies have been also carried out on the reaction at the Mo centres to understand the reasons that make these metal centres ineffective for promoting tautomerization.

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“…The phosphorus oxyacids are weak acids [28], and in the presence of a strong acid like perchloric acid, they would exist almost wholly in the undis- The 'active' form is thought to be produced as an intermediate in the exchange of phosphorus bonded hydrogen with tritium and deuterium [3,4].…”

Section: Effect Of Temperaturementioning

confidence: 99%

“…In addition, organo-phosphorus compounds are used as anti-oxidants and in general organic synthesis, e.g., Wittig Reaction [ 13. Phosphinites are used as reductants in industry and both phosphinic and phosphorous acids find use as anti-oxidants and stabilizers for polymers [2]. The study of the reactions of lower oxyacids of phosphorus is also of interest because of the existence of the two tautomers, RP(OH)2 and RPH(0)OH [3,4]. Kinetics of oxidation of lower oxyacids of phosphorus by various transition metal ions has been reported [5-161.…”

Section: Introductionmentioning

confidence: 99%

Kinetics of the oxidation of phosphinic, phenylphosphinic, and phosphorous acids by N‐bromoacetamide

Moondra

Mathur

Banerji

1991

Int J of Chemical Kinetics

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The oxidation of phosphinic, phenylphosphinic, and phosphorous acids by N-bromoacetamide (NBA) in acid solution, results in the formation of corresponding higher oxyacids of phosphorus. The reaction is first order with respect to NBA, second order in the oxyacid and inverse first in hydrogen ions. The oxidation of deuteriated phosphorus oxyacids showed the presence of a substantial primary kinetic isotope effect. The reaction failed to induce polymerization of acrylonitrile. Added acetamide has no effect on the reaction rate. It has been shown that the 'inactive' tautomer of the phosphorus oxyacids, RHP(O)OH, participates in the oxidation process. A rate-determining step involving transfer of a hydride ion from the P-H bond to the oxidant has been proposed.

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Kinetic Study of the H₂POOH-D₂O Exchange by Nuclear Magnetic Resonance

Cited by 27 publications

References 1 publication

The Nickel Metal Catalyzed Decomposition of Aqueous Hypophosphite Solutions

The Nickel Metal Catalyzed Decomposition of Aqueous Hypophosphite Solutions

Combined kinetic and DFT studies on the stabilization of the pyramidal form of H3PO2 at the heterometal site of [Mo3M′S4(H2O)10]4+ clusters (M′ = Pd, Ni)

Kinetics of the oxidation of phosphinic, phenylphosphinic, and phosphorous acids by N‐bromoacetamide

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