The Preparation of Iodopentamminecobalt(III) Salts from Cobalt(II)

Yalman, Richard G.

doi:10.1021/ja01617a021

Cited by 19 publications

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“…As no suitable model compound was available for these bases, corrections for the medium effect at each base concentration were applied to the calculated value of Kadkd0H (in 1 M potassium chloride) before using this limiting rate constant to calculate the rate constants for the addition step. No corrections were applied for the strongly basic amines triethylenediamine, 3-quinuclidinol, or quinuclidine; the good agreement of the extrapolated k,_ values for 3-quinuclidinol (Fig- 6 In 0.05 M ethylenediamine buffer, 30% free base, pH 8.8. d In 0.02 M hexafluoroisopropyl alcohol buffer, 30% free base, pH 8.8-8.9 6 Free base concentration.…”

Section: Resultsmentioning

confidence: 91%

“…At high pH values a base-catalyzed dehydration mechanism becomes significant for the reac-Saver, Jencks j Mechanism and Catalysis of 2-Methyl-3-thiosemicarbazone Formation Determined by titration at 25°, ionic strength 1.0 (K.C1) unless otherwise noted. 6 Limits estimated by inspection of plots of k^an against buffer concentration. -Reference 18. d A. R. Fersht and W. P. Jencks, J. Amer.…”

Section: Discussionmentioning

confidence: 99%

“…Soc., 92, 5432(1970). 6 Corrected for self-association of the substituted pyridines. " Reference 18.…”

Section: Discussionmentioning

confidence: 99%

“…Caled for CjiHig'. C, 93.29; , 6.71. Found: C, 93.16; H, 6.84. Irradiation of 30 mg of 4 and 50 mg of 5 for 10 hr under the same conditions resulted in the recovery of unreacted starting materials in quantitative amounts.…”

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confidence: 99%

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Mechanism and catalysis of 2-methyl-3-thiosemicarbazone formation. Second change in rate-determining step and evidence for a stepwise mechanism for proton transfer in a simple carbonyl addition reaction

Sayer¹,

Jencks²

1973

J. Am. Chem. Soc.

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2-Methyl-3-thiosemicarbazone formation fromp-chlorobenzaldehyde undergoes a change in rate-determining step at high pH, similar to that at low pH, from rate-determining dehydration of the carbinolamine intermediate to partially rate-determining attack of the nucleophile on the carbonyl group. The attack step is subject to general base catalysis. Brpnsted plots for tertiary amines and oxygen anions exhibit breaks for bases of less than 6. This curvature is consistent with that expected for a simple rate-determining proton transfer reaction between the dipolar addition intermediate ± and the catalyzing base. However, the break occurs at a higher than expected from the estimated value for T= of 3.1. Better agreement is found for a preassociation mechanism with rapid, stepwise proton transfer within an encounter complex after the formation of T±. According to this mechanism, N-C bond formation within an encounter complex that contains the base catalyst is rate determining with strong bases and there is a change to rate-determining proton transfer with weaker bases. The magnitude of the observed catalytic constants is consistent with that expected for such a mechanism, but is significantly smaller than expected for a concerted mechanism. General acid catalysis of 2-methyl-3-thiosemicarbazide addition to p-chlorobenzaldehyde by carboxylic and cacodylic acids closely resembles that observed for the addition of other weakly basic amines (a -0.2). It is suggested that general acid, unlike general base, catalysis involves some stabilization of the transition state for carbon-nitrogen bond formation by the catalyst. Agrowing body of evidence concerning general gests that in some cases these proton transfers proacid-base catalysis of complex reactions involving ceed by discrete steps, rather than by a process that is proton transfers to or from electronegative atoms sug-4648) and the National Institute of Child Health and Human Develop-(1) Supported by grants from the National Science Foundation (GB ment of the National Institutes of Health (HD 01247).Sayer, Jencks / Mechanism and Catalysis of 2-Methyl-3-thiosemicarbazone Formation (11) J.

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Section: Resultsmentioning

confidence: 91%

Section: Discussionmentioning

confidence: 99%

“…Soc., 92, 5432(1970). 6 Corrected for self-association of the substituted pyridines. " Reference 18.…”

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Mechanism and catalysis of 2-methyl-3-thiosemicarbazone formation. Second change in rate-determining step and evidence for a stepwise mechanism for proton transfer in a simple carbonyl addition reaction

Sayer¹,

Jencks²

1973

J. Am. Chem. Soc.

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“…iodine is added to ammoniacal solutions of cobalt containing ammonium nitrate, chloride, bromide, or iodide, the formation of the corresponding salt of iodopentammmecobalt(III) occurs (9). The preparation of these compounds is direct and rapid, and does not require the exclusion of air.…”

Section: Whenmentioning

confidence: 99%

New Iodometric Determination of Cobalt Based on Formation of Iodopentamminecobalt(III) Nitrate

Yalman¹

1956

Anal. Chem.

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The reaction between cobalt and iodine in ammoniacal solutions of ammonium nitrate to form iodopentamminecobalt(III) nitrate can be used for the determination of cobalt(II). The reaction is rapid and oxygen does not need to be excluded. The end point can be determined either potentiometrically or by using the starch indicator.Copper, nickel, etc., do not interfere, nor do aluminum, iron, and chromium in the presence of tartrate.

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Photopolymerization of vinyl monomers initiated by pentaaminecobalt (III) complexes

Delzenne

1967

J. polym. sci., C Polym. symp.

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The polymerization of acrylamide in aqueous solution can be initiated by free radicals formed during the irradiation of pentaaminecobalt(III) complexes with light of wavelengths corresponding to the charge transfer band of the initiators. The kinetics were studied for two different cobalt(III) complexes: the chloropurpureosalt [CoCl(NH3)5]‐Cl2 and the roseosalt [Co(H2O)(NH3)5](NO3)3. In both cases the dependence of the rate of polymerization on the initiator concentration indicates a termination reaction due to an oxidation of the growing chains by the metal complexes. The effect of the chloro complex on the photopolymerization rate of acrylamide initiated by riboflavine showed the same termination activity. A termination constant, kt = 1.5 × 103 liter/mole‐sec., could be calculated. The first‐order dependence of the rate of polymerization on the monomer concentration for the initiation by the chloro complex agrees with an internal charge transfer during the photochemical activation of the initiator. The second‐order dependence of the rate of polymerization on the monomer concentration for the initiation by the aquo complex can be attributed to a substitution of the coordinative bonded water by a monomer molecule. An electron transfer within the intermediate complex agrees with the observed initiation.

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The Preparation of Iodopentamminecobalt(III) Salts from Cobalt(II)

Cited by 19 publications

References 0 publications

Mechanism and catalysis of 2-methyl-3-thiosemicarbazone formation. Second change in rate-determining step and evidence for a stepwise mechanism for proton transfer in a simple carbonyl addition reaction

Mechanism and catalysis of 2-methyl-3-thiosemicarbazone formation. Second change in rate-determining step and evidence for a stepwise mechanism for proton transfer in a simple carbonyl addition reaction

New Iodometric Determination of Cobalt Based on Formation of Iodopentamminecobalt(III) Nitrate

Photopolymerization of vinyl monomers initiated by pentaaminecobalt (III) complexes

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