The mechanism of the etard reaction

Etard reactions. I. Nature of complexes and their reactions with some oxygen and nitrogen donor molecules

“…Etard's proposal was based on analytical data and the nature of the hydrolysis products. A single magnetic susceptibility measurement by Wheeler (5) appeared to confirm Etard's assignment of oxidation state IV to chromium, but Necsoiu and co-workers (2) reported electron spin resonance (e.s.r.) data which were interpreted as showing only one of the two chromium atoms in this state, the other presumed to be still Cr(V1).…”

“…Various structures have been suggested for this product (1,2), but that due to Etard (3) has been most favored ( 4 7 ) . Etard's structure is CI C1 \ / /O-Cr-OH C6Hs--CH \ 0-Cr-OH / \ CI CI Very little direct work on the structure of 1 has been carried out.…”

Reaction of chromyl chloride with donor molecules

“…This complex, when hydrolyzed in water containing potassium iodide, liberated almost no iodine, so the chromium was apparently reduced very rapidly to chromium(1II). A possible sequence of reactions on hydrolysis might be If this is to be accomplished without oxidation of iodide by the very reactive chromium(1V) and (V) species, steps [I] to [3] must take place within such a closed environment as that afforded by a binuclear complex. We suggest, therefore, that the structure of the ether complex is something resembling 3, which is in accord with the facts noted above, and is analogous with the structure proposed earlier for the ternary complexes.…”

“…Chromyl chloride, CrO,Cl,, has been used as an oxidant for hydrocarbons from time to time for many years, and its reactions with saturated and unsaturated molecules have been extensively studied (1)(2)(3)(4)(5)(6)(7)(8). In the course of recent investigations of the structure of the main product of the Etard reaction of chromyl chloride with toluene (9), it was found that this product could react with two molecules of a Lewis base to form complexes containing the elements of the hydrocarbon, chromyl chloride, and the base, in the approximate molar proportions 1 :2:2.…”

Kinetics of Etard's Reaction: Part Iii. Effect of Ring Substitution

“…I t has usually been assumed (7) that the second molecule reacts with another hydrogen of the methyl group in a similar manner in a subsequent step. A recent paper from Nenitzescu's laboratory (11) reports that the two chromium atoms are not both reduced, one being still in oxidation state VI (a conclusion based on measurements of electron spin resonance absorption intensity), and suggests that the second step of the oxidation does not take place until the hydrolysis. The second molecule of chromyl chloride, it is suggested, is bound t o the first in an unknown manner, perhaps as in the dichromate ion (though this requires the unusual coordination number of five for Cr VI).…”