- Phosphite Radicals and Their Reactions. Examples of Redox, Substitution, and Addition Reactions
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Phosphite radicals HPO3(-) and PO3(2-), which exist in an acid-base equilibrium with pK = 5.75, are shown to take part in various types of reactions.In the absence of scavengers, they disappear mainly by second-order disproportionation and combination; a first-order contribution to the decay is also indicated.HPO3(-) and PO3(2-) are good reductants toward electron acceptors such as tetranitromethane.In this reactions phosphate and C(NO2)3(-) are formed.Phosphite radicals can, however, also act as good oxidants, e.g., toward thiols and thiolate ions.These reactions lead to the formation of RS. radicals which were identified either directly, as in the case of penicillamine, through the optical absorption of PenS. or more indirectly through equilibration of RS. with RS(-) to the optically absorbing RSSR.(-) disulfide radical anion.A homolytic substitution reaction (SH2) occurs in the reaction of the phosphite radicals with aliphatic disulfides, yielding RS. radicals and phosphate thioester RSPO3(2-).Lipoic acid, as an example of a cyclic disulfide, is reduced to the corresponding RSSR.(-) radical anion and also undergoes the SH2 reaction with about equal probability.An addition reaction is observed between phosphite radicals and molecular oxygen.The resulting peroxo phosphate radicals establish an acid-base equilibrium HPO5(-). PO5(2-). + H(+) with a pK = 3.4.Absolute rate constants were determined for all reactions discussed.
- Schaefer, K.,Asmus, K.-D.
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- Gas-phase reactions of weak br?nsted bases I-, PO3-, HSO4-,FSO3 -, and CF3so3- with strong br?nsted acids H2so4, FSO3H, and CF3so3H.
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Using a selected ion flow tube at 368 K, we have measured rate constants for ion-molecule reactions between I-, PO-, HSO4-, FSO3-, CF3SO3-, NO3-·HNO3, FSO3-·FSO3H, and H2SO4, FSO3H, CF3SO3H. Channels observed include proton transfer and clustering. These results allow free energies (enthalpies) of deprotonation (kJ/mol) to be estimated (within ±10 kJ/mol) as follows: HPO3, 1270 (1300); H2SO4, 1265 (1295); FSO3H, 1255 (1285); CF3SO3H, 1250 (1280). In two cases, electron affinities are estimated as follows: HSO4, 4.7 ± 0.2 eV. FSO3, 4.8 ± 0.2 eV. For the title acids, the gas-phase acidity order is discussed and is used to explain the differing acidity orders found for these acids in different solvents. The same data measure basicities for the conjugate bases, and these are related to nucleophilicity and leaving group ability. This study explores a region of the acidity scale where no acidities are established that would calibrate the scale. The scale is calibrated here using cluster ions whose free energy of protonation can be reliably estimated.
- Viggiano,Henchman,Dale,Deakyne,Paulson
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p. 4299 - 4306
(2007/10/02)
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- Polymerization catalyst and deodorizing agent and process of use
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Calcium silicate treated with an acid can be used as a polymerization catalyst or as a deodorizing agent. The acid is sulfuric acid, phosphoric acid or nitric acid.
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