Kinetics Studies of the Hydrolysis of Coordinated Nitriles

Robert J. Balahura, P. Cock, William L. Purcell

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The kinetics of the reaction (NH3)5CoN≡CR3+ + OH- → (NH3)5CoNHC(=O)R2+ (R = 4-CNC6H4, 3-CNC6H4, 4-COCH3C6H4, 4-CHOC6H4, 3-CHOC6H4) have been studied. For the 1,4-dicyanobenzene, 1,3-dicyanobenzene, and 4-acetylbenzonitrile complexes the hydrolysis follows the rate law - d ln [Co complex]/dt = kb[OH-]. The values of kh (M-1 sec-1), at 25°, μ = 1.0 M(NaClO4), Δ;H (kcal mol-1), and Δ;S (eu) are 369, 13.3, and -2 for the 1,4-dicyanobenzene complex, 322, 15.6, and +5 for the 1,3-dicyanobenzene complex, and 135, 12.3, and -7 for the 4-acetylbenzonitrile complex. The hydrolysis of the 3- and 4-formylbenzonitrile complexes is affected by hydration of the formyl substituent. The rate expression is -d ln [Co complex]/dt = {(k1 + k2K1· [OH-])/(1 + K1[OH-])}[OH] where K1 is the equilibrium constant for the reaction (NH3)5CoNCC6H4C(=O)H3+ + OH- ⇄ (NH3)5CoNCC6H4CH(-O)OH2+ and k1 and k2 are the second-order rate constants for hydrolysis of the carbonyl and hydrate forms of the nitrile complex. For the 3-formylbenzonitrile complex k1 = 117 M-1 sec-1 and K1 = 4.9 M-1 at 25°, μ = 1.0 M (NaClO4) with ΔH = 15.4 kcal mol-1, and ΔS = +2 eu. For the 4-formylbenzonitrile complex k1 = 142 M-1 sec-1 and K1 = 10.4 M-1 at 25°, μ = 1.0 M(NaClO4) with ΔH≠ = 16.0 kcal mol-1, and ΔS = +5 eu. The values of k2 could not be established unambiguously. The results are discussed with respect to other nitrile hydrolysis reactions catalyzed by metal ions.

Original languageEnglish (US)
Pages (from-to)2739-2742
Number of pages4
JournalJournal of the American Chemical Society
Issue number9
StatePublished - May 1 1974

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry


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