Kinetic studies of organochromium(III) cations and their hydrido analog

Technical Report · Thu Oct 01 04:00:00 EDT 1981

OSTI ID:5807761

Ryan, D A.P.

The kinetics of the reaction of the complex (CH/sub 3/)/sub 2/CHCr(H/sub 2/O)/sub 5//sup 2 +/ with molecular oxygen, in aqueous perchloric acid, were investigated primarily by spectrophotometry. A free-radical chain mechanism is proposed. The principal products of the autoxidation (acetone and Cr(H/sub 2/O)/sub 6//sup 3 +/) are accounted for by rapid protonolysis of the isopropylperoxochromium(III) intermediate. The complex HOCH/sub 2/CH/sub 2/Cr(H/sub 2/O)/sub 5//sup 2 +/ was prepared in dilute aqueous perchloric acid, by the photochemical generation of ..beta..-hydroxyethyl radicals in the presence of Cr/sub aq//sup 2 +/. The products of the reaction are ethylene and Cr(H/sub 2/O)/sub 6//sup 3 +/, consistent with a rate-limiting step of proton-assisted beta-elimination of a water molecule to form a highly unstable ..pi..-bonded C/sub 2/H/sub 4/Cr(H/sub 2/O)/sup 3 +/ intermediate. The complex HCr(H/sub 2/O)/sub 5//sup 2 +/ was made by the uv flash photolysis of aqueous chromium(II) perchlorate and its reaction with H/sub 3/O/sup +/ (to form H/sub 2/ and Cr(H/sub 2/O)/sub 6//sup 3 +/ investigated. The deuterated complex DCr(D/sub 2/O)/sub 5//sup 2 +/ shows a large kinetic isotope effect in its reaction with D/sub 3/O/sup +/(k/sub H//k/sub D/ = 4.8), which is similar in magnitude to the acidolysis of the CH/sub 3/Cr(D/sub 2/O)/sub 5//sup +2/ ion by D/sub 3/O/sup +/(k/sub H//k/sub D/ = 6.3), supportive of a mechanism where O-H bond breaking is rate-limiting for both complexes. Protonolysis of HCr(H/sub 2/O)/sub 5//sup 2 +/ is pictured as occurring via a nonlinear three-center transition state in which the H-Cr bond is still intact.

• Research Organization: Ames Lab., IA (USA)
• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 5807761
• Report Number(s): IS-T-956; ON: DE82005581
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
400202* -- Isotope Effects
Isotope Exchange
& Isotope Separation
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHROMIUM COMPLEXES
COMPLEXES
DECOMPOSITION
DEUTERIUM
ELEMENTS
HYDRATES
HYDROGEN ISOTOPES
ISOTOPE EFFECTS
ISOTOPES
KINETICS
LIGHT NUCLEI
NONMETALS
NUCLEI
ODD-ODD NUCLEI
OXIDATION
OXYGEN
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
RADICALS
REACTION KINETICS
SPECTROPHOTOMETRY
STABLE ISOTOPES
TRANSITION ELEMENT COMPLEXES