Substitution reactions at octahedral centers. IV. Acid and base hydrolysis of chloropentakis(alkylamine)chromium(III) ions

1969 ◽  
Vol 47 (12) ◽  
pp. 2257-2262 ◽  
Author(s):  
M. Parris ◽  
W. J. Wallace
Keyword(s):  
Base Hydrolysis ◽  
Kcal Mole ◽  
Substitution Reactions ◽  
Hydroxide Ion ◽  
Rate Determining Step ◽  
Acid And Base ◽  
Ph Dependent ◽  
Pattern Of Variation ◽  
Hydrolysis Of ◽  
Independent Reaction

The compounds [Cr(RNH2)5Cl](ClO4)2, where R = H, CH3, C2H5, n-C3H7, and n-C4H9, have been prepared and the replacement of chloride by either water or hydroxide ion subjected to kinetic examination. Below about pH 7 the reaction was acid independent, and ΔHA* was 22.4 kcal mole−1 when ammonia was the inert ligand compared with about 26.4 kcal mole−1 when the inert ligand was a primary amine. The corresponding ΔSA* values increased continuously with R from H to n-C4H9. At higher pH the rate became inversely dependent upon the acidity of the solution, and ΔHB* decreased from 26.7 kcal mole−1 for ammonia as the inert ligand to 25.4 kcal mole−1 for an amine as the inert ligand. For the pH dependent reaction the values obtained for ΔSB* were much larger than for the pH independent reaction but the pattern of variation as the inert ligands were changed was quite similar in the two cases. The great similarity in the trends of ΔS* values for the acid and base hydrolysis reactions has been interpreted in terms of a rate-determining step that is primarily dissociative in both cases.

Base hydrolysis of trans-Halogenoamminebis(dimethylglyoximato) (III). Complexes

1969 ◽  
Vol 22 (12) ◽  
pp. 2569 ◽  
Author(s):  
SC Chan ◽  
PY Leung
Keyword(s):  
Equilibrium Constants ◽  
Base Hydrolysis ◽  
Hydroxide Ion ◽  
First Order ◽  
Rate Determining Step ◽  
Rapid Formation ◽  
Pseudo First Order ◽  
Conjugate Bases ◽  
Hydrolysis Of ◽  
Conjugate Base

The disappearance of trans-[Co(LH)2(NH3)X] (LH = dimethylglyoximate ion, X = chloride or bromide) has been studied in aqueous solutions over a range of alkali concentrations at various temperatures. The kinetics were done with excess of hydroxide ion at a constant ionic strength so that pseudo first-order rate constants were obtained in all the runs. The results were interpreted in terms of the rapid formation of a pre- equilibrium species which then reacts in a rate-determining step to give products. The relatively large equilibrium constants support a conjugate-base pre-equilibrium, in which the proton is lost from oxygen, while the relatively low reactivities of the conjugate-bases are consistent with the absence of electropositive electromeric effects. The similarity in the reactivities of the chloro and the bromo conjugate-bases suggests the possibility of an SN2CB mechanism.

Mechanism of Substitution Reactions of Complex Ions. IX. Contribution of Inductive Effects to the Rates of Acid and Base Hydrolysis of Cobalt(III) Complexes1,2

1956 ◽  
Vol 78 (12) ◽  
pp. 2676-2678 ◽  
Author(s):  
Fred Basolo ◽  
John G. Bergmann ◽  
Robert E. Meeker ◽  
Ralph G. Pearson
Keyword(s):  
Base Hydrolysis ◽  
Complex Ions ◽  
Substitution Reactions ◽  
Inductive Effects ◽  
Acid And Base ◽  
Hydrolysis Of

Phosphato complexes of cobalt(III). IV. Hydrolysis in basic solution

1968 ◽  
Vol 21 (7) ◽  
pp. 1733 ◽  
Author(s):  
SF Lincoln ◽  
DR Stranks
Keyword(s):  
Isotope Effects ◽  
Base Hydrolysis ◽  
Basic Solution ◽  
Tracer Technique ◽  
Hydroxide Ion ◽  
Solvent Water ◽  
Coordination Spheres ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

The rates of hydrolysis of phosphato complexes of cobalt(111) in sodium hydroxide concentrations ranging from 0.02M to 0.37M, and at several ionic strengths, have been measured with a tracer technique. Bidentate phosphato complexes exhibit the same rates of hydrolysis as the corresponding monodentate complexes, due to a rapid conversion of the bidentate into the monodentate form. The general rate law for base hydrolysis of all the phosphato complexes is: d[PO34]/dt = {kH2O + kOH[OH-]}[complex] At 60� and at unit ionic strength, the rate constants for the complexes cis-[Co(NH3)4OH.PO4]-, cis-[Co en2OH.PO4]-, and [Co(NH3)5PO4] respectively are: 103kH2O (min-l) 85.0, 2.0, <1; and 103kOH (1. mole-1 min-l) 42.7, 12.0, 69.5. Mechanistic conclusions have been based on the measured enthalpies and entropies of activation and deuterium solvent isotope effects. For all complexes, kH2O is identified with an aquation mechanism involving synchronous interchange of the phosphate and solvent water between the first and second coordination spheres of the complexes. In the case of the tetrammine and bis(ethylenediamine) complexes, kOH is identified with a process involving synchronous interchange of phosphate and hydroxide ion between the first and second coordination spheres of the complexes. In the case of the pentammine complex, an SN2CB mechanism is considered to be more probable. A comparison with the base hydrolysis of halogen complexes of cobalt(111) is presented.

Phosphato complexes of cobalt(III). I. General structural and hydrolytic properties

1968 ◽  
Vol 21 (1) ◽  
pp. 37 ◽  
Author(s):  
SF Lincoln ◽  
DR Stranks
Keyword(s):  
Infrared Spectra ◽  
Base Hydrolysis ◽  
Alkaline Media ◽  
Bond Rupture ◽  
Acidity Constant ◽  
Acidity Constants ◽  
Acid And Base ◽  
Ph Range ◽  
Hydrolysis Of ◽  
Tracer Experiments

Phosphorus-32 tracer experiments have demonstrated that the phosphato ligand in [Co en2PO4]0 [Co(NH3)4PO4]O, [CO(NH3)4OH2HPO4]+, and [Co en2OH2.HPO4]+ undergoes slow substitution in acid and alkaline media at 40-60� and that a reversible hydrolysis equilibrium is established from pH 3 to 11. Outside this pH range, acid and base hydrolysis of all these phosphato complexes to diaquo or dihydroxo complexes is complete. The infrared spectra of [Co en2PO4]0 and [Co(NH3)4PO4]0 are consistent with a bidentate phosphato structure and with a monodentate phosphato ligand in CO(NH3)5PO4 and probably [Co(NH3)4OH2HPO4]+I-. The bidentate and monodentate complexes may be rapidly and reversibly interconverted but significant concentrations of the bidentate complexes only persist in the range pH 5.5-7.5. P.m.r, studies have established the predominantly cis configuration of the aquophosphato complexes. These complexes exhibit four acidity constants, one due to the aquo ligand, and three due to the monodentate phosphato ligand. The bidentate [Co en2PO4]0 exhibits a single acidity constant above pH 2. The aquophosphato complexes undergo both acid and base hydrolysis entirely by Co-O bond rupture. Acid hydrolysis of [Co en2PO4]0 also proceeds entirely by Co-O bond rupture but at pH 6.8 and in 0.25M NaOH hydrolysis proceeds by 60-65% Co-O bond rupture and by 30-35% P-O bond rupture.

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