This is very possible the original publication of the method which later was quoted by Vogel, which later was quoted by ReFlux which later was quoted in
Post 235579
(PrimoPyro: "Re: A new oxidation for MDP2-ol?", Methods Discourse). You gotta love third-hand information
Oxidation of secondary alcohols in diethyl ether with aqueous chromic acid.
Convenient procedure for the preparation of ketones in high epimeric purity.Herbert Charles Brown, Chandra P. Garg, Kwang-Ting LiuJ. Org. Chem. 36, 387-390 (1971)
(
https://www.thevespiary.org/rhodium/Rhodium/pdf/chromate.2-phase.alc-ox.pdf)
Convenient procedures have been developed to convert secondary alcohols into ketones in excellent yield and high epimeric purity utilizing oxidation of the alcohol in diethyl ether with aqueous chromic acid. In one procedure the stoichiometric amount of sodium dichromate and sulfuric acid in water is added to the diethyl ether solution of alcohol at 25-30°C and the reaction is continued for 2 hr.
To our surprise, the oxidation of secondary alcohols proceeded very simply and cleanly in a two-phase system involving diethyl ether and a water solution of sodium dichromate and sulfuric acid. There appeared to be significant advantages to such an oxidation procedure. Consequently, we decided to undertake a detailed study.
In one early experiment we observed that, when a solution of cyclohexanol was contacted at 25°C with an aqueous solution of the calculated quantity of sodium dichromate and sulfuric acid, the cyclohexanol disappeared almost immediately from the ether phase. Evidently, the cyclohexanol must be rapidly esterified and the chromic acid ester is extracted into the aqueous phase. Ketone then begins to appear at a moderate rate and is extracted into the ether phase as it forms.
The ether phase then protects the ketone from undesirable side reactions, such as further oxidation or epimerization. Indeed, it proved possible to develop procedures which give nearly quantitative yields of ketones from a wide variety of secondary alcohols, with remarkably low epimerization for derivatives subject to this side reaction.
Chromic Acid Solution
The chromic acid solution used for the oxidation was prepared from the appropriate amount of sodium dichromate and sulfuric acid as indicated by the following equation.
3 R2CHOH + Na2Cr2O7 + 4 H2SO4 -> 3 R2C=O + Na2SO4 + Cr2(SO4)3 + 7 H2O
The chromic acid solution is prepared by dissolving 100 g (0.33 mol) of sodium dichromate dihydrate in 300 ml of water. The sulfuric acid (97%), 136 g (1.34 mol), was then added. The solution was then diluted to 500-ml total volume. This solution will oxidize 1.00 mol of secondary alcohol by procedure A.
Oxidation of l-(-)-Menthol in Diethyl Ether with Stoichiometric Amount of Chromic Acid
A Representative Procedure A
Diethyl ether, 20 ml, and 7.80 g (50 mmol) of l-(-)-menthol were placed in a 100-ml three-necked flask fitted with a stirrer, a condenser, and an addition funnel. Chromic acid solution (25 ml) was added to the stirred solution over 15 min, maintaining the temperature at 25-30°C. After 2 hr at room temperature, the upper ether layer was separated and the aqueous phase was extracted with two 10-ml portions with ether. The combined ether extracts were washed with saturated sodium bicarbonate and then water. GC indicated 97% l-(-)-menthone, a trace of isomenthone, and 1.5% menthol. Vacuum distillation through a short Vigreux column gave 6.45g (84%) of l-(-)-menthone, bp 86-67°C/4mmHg.