A chromate ester is a chemical structure that contains a chromium

Chromium

Chromium is a chemical element which has the symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable...

 atom in a +6 oxidation state

Oxidation state

In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...

 that is connected via an oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 linkage to a carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 atom. The Cr itself is in its chromate

Chromate

Chromate salts contain the chromate anion, CrO42−. Dichromate salts contain the dichromate anion, Cr2O72−. They are oxyanions of chromium in the oxidation state +6. They are moderately strong oxidizing agents.- Chemical properties :...

 form, with several oxygens attached, and the Cr–O–C attachment makes this chemical group structurally similar to other ester

Ester

Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...

 functional groups. They can be synthesized from various chromium(VI) metal compounds, such as CrO₃, chromium chloride complexes, and aqueous chromate ions, and tend to react via redox reactions to liberate chromium(IV).

Chromate esters are the key reactive intermediate

Reactive intermediate

In chemistry a reactive intermediate is a short-lived, high energy, highly reactive molecule. When generated in a chemical reaction it will quickly convert into a more stable molecule. Only in exceptional cases can these compounds be isolated and stored, e.g. low temperatures, matrix isolation...

s in the Jones oxidation

Jones oxidation

The Jones oxidation, is an organic reaction for the oxidation of primary and secondary alcohols to carboxylic acids and ketones, respectively. It is named after its discoverer, Sir Ewart Jones....

 the mechanistically related oxidations using pyridinium dichromate or pyridinium chlorochromate

Pyridinium chlorochromate

Pyridinium chlorochromate is a reddish orange solid reagent used to oxidize primary alcohols to aldehydes and secondary alcohols to ketones. Pyridinium chlorochromate, or PCC, will not fully oxidize a primary alcohol to the carboxylic acid as does the Jones reagent. A disadvantage to using PCC is...

. Chromate esters of allyl alcohol

Allyl alcohol

Allyl alcohol is an organic compound with the structural formula CH2=CHCH2OH. Like many alcohols,it is a water soluble, colourless liquid, but it is more toxic than typical small alcohols. Allyl alcohol is used as a raw material for the production of glycerol, but is used as a precursor to many...

s may isomerize via formal [3,3]-sigmatropic shift

Sigmatropic reaction

A sigmatropic reaction in organic chemistry is a pericyclic reaction wherein the net result is one σ-bond is changed to another σ-bond in an uncatalyzed intramolecular process. The name sigmatropic is the result of a compounding of the long-established sigma designation from single carbon-carbon...

to give rearranged enone products.

An example of an isolable chromate ester is ((CH₃)₃CO)₂CrO₂.