“…When an extra 100 μL of H 2 O 2 was added to the partially dissolved sample solutions, they were all seen to readily convert to the same colorimetric state as the fully dissolved species without the need for any further heating. This colour change therefore suggests the presence of lower oxidation state complexes of iridium in the partially dissolved sample solutions, such as hexachloroiridate(III), which are then being rapidly oxidised to iridium(IV) [13, 14]. Fig.…”
To assist in nuclear forensic investigations, new techniques are required to evaluate radioactive materials that may be discovered outside of regulatory control. Using a recently developed pressure digestion method for iridium powder, assessments have been made of this techniques suitability for undertaking iridium target material evaluations. In addition to determining the reaction conditions necessary for total dissolution, these investigations have provided an insight into the elemental impurities that are present within unirradiated iridium targets that are used in QSA Global radiography sources, and established the speciation of the iridium solutions that are formed during this process.
“…When an extra 100 μL of H 2 O 2 was added to the partially dissolved sample solutions, they were all seen to readily convert to the same colorimetric state as the fully dissolved species without the need for any further heating. This colour change therefore suggests the presence of lower oxidation state complexes of iridium in the partially dissolved sample solutions, such as hexachloroiridate(III), which are then being rapidly oxidised to iridium(IV) [13, 14]. Fig.…”
To assist in nuclear forensic investigations, new techniques are required to evaluate radioactive materials that may be discovered outside of regulatory control. Using a recently developed pressure digestion method for iridium powder, assessments have been made of this techniques suitability for undertaking iridium target material evaluations. In addition to determining the reaction conditions necessary for total dissolution, these investigations have provided an insight into the elemental impurities that are present within unirradiated iridium targets that are used in QSA Global radiography sources, and established the speciation of the iridium solutions that are formed during this process.
“…While 2-3 equivalents of K 3 Fe(CN) 6 were sufficient to oxidize HoxC completely, 25 equivalents of K 2 Ir(Cl)6 were required to obtain the quantitatively oxidized [NiFe] cofactor. The higher demand for the iridium compound can be explained by its redox potential of +0.96 V, which is large enough to extract electrons from H 2 O 40. Nonetheless, since the treatments with K 2 Ir(Cl) 6 and K 3 Fe(CN) 6 resulted in exactly the same HoxCderived IR bands, we can exclude that further n(C^O) or n(C^N) stretching modes were covered by the r -B, but only in minuscule amounts (Fig.S12A ‡).…”
“…Reductions of IrCl 6 2− by substrates are too slow to be studied at higher acidities (pH < 3.0). Again, the rapid reduction of IrCl 6 2− with HO − takes place in alkaline solution . Hence, the present reactions have been studied in the pH range 3.42–4.63 and it is suggested that IrCl 6 2− reacts with α,β‐unsaturated compounds in the above‐mentioned pH range.…”
The hexachloroiridate(IV) oxidation of α,β‐unsaturated compounds such as acrylic acid, acrylamide, and acrylonitrile (CH2=CHX; X = –COOH, –CONH2, and –CN) was carried out in NaOAc‐AcOH buffer medium. The reaction follows complex kinetics, being first order in [IrIV] and complex order in [CH2=CHX]. H+ ion has no effect on the reaction rate in the pH range 3.42–4.63. The pseudo–first‐order rate constant decreases with a decrease in the dielectric constant and with a decrease of ionic strength of the medium. The oxidation rate follows the sequence: acrylonitrile > acrylamide > acrylic acid. A mechanism is proposed involving the formation of an unstable intermediate complex between the substrate and the oxidant which is transformed to the radical cation in a slow rate‐determining step with the concomitant reduction of Ir(IV) to Ir(III). The radical cation subsequently decomposes to the aldehyde that appears as the ultimate product of the carbon–carbon double bond cleavage. The major product of oxidation was identified as HCHO by 1H NMR. Activation parameters for the slow rate‐determining step and thermodynamic parameters associated with the equilibrium step of the proposed mechanism have been evaluated. The enthalpy of activation is linearly related to the entropy of activation, and this linear relationship confirms that the oxidation of all the α,β‐unsaturated compounds follows a common mechanism.
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