Search results
Results From The WOW.Com Content Network
The hydrogen chromate ion may be protonated, with the formation of molecular chromic acid, H 2 CrO 4, but the pK a for the equilibrium H 2 CrO 4 ⇌ HCrO − 4 + H + is not well characterized. Reported values vary between about −0.8 and 1.6. [4] The dichromate ion is a somewhat weaker base than the chromate ion: [5]
It can be prepared by treating chromium metal with fluorine at 400 °C and 200 bar pressure. The peroxochromate(V) is another example of the +5 oxidation state. Potassium peroxochromate (K 3 [Cr(O 2) 4]) is made by reacting potassium chromate with hydrogen peroxide at low temperatures. This red brown compound is stable at room temperature but ...
It was popularized for selective oxidation of primary and secondary alcohols to carbonyl compounds. Collins reagent is a solution of the same CrO 3 (pyridine) 2 but in dichloromethane. The Ratcliffe variant of Collins reagent relates to details of the preparation of this solution, i.e., the addition of chromium trioxide to a solution of ...
A typical PCC oxidation involves addition of an alcohol to a suspension of PCC in dichloromethane. [6] [7] [8] The general reaction is: 2 [C 5 H 5 NH][CrO 3 Cl] + 3 R 2 CHOH → 2 [C 5 H 5 NH]Cl + Cr 2 O 3 + 3 R 2 C=O + 3 H 2 O. For example, the triterpene lupeol was oxidized to lupenone: [9]
As pH rises the chromate ion becomes ever more predominant, until it is the only species in solutions with pH > 6.75. At pH < pK 1 the hydrogen chromate ion, HCrO − 4 is predominant in dilute solution. The dichromate ion, Cr 2 O 2− 7, is predominant in more concentrated solutions, except at high pH.
At pH < 5.89 (pH < pK 1) the hydrogen chromate ion is predominant in dilute solution but the dichromate ion is predominant in more concentrated solutions. Predominance diagrams can become very complicated when many polymeric species can be formed as, for example, with vanadate, [4] molybdate [1] and tungstate. [1]
A chromate ester is a chemical structure that contains a chromium atom (symbol Cr) in a +6 oxidation state that is connected via an oxygen (O) linkage to a carbon (C) atom. The Cr itself is in its chromate form, with several oxygens attached, and the Cr–O–C attachment makes this chemical group structurally similar to other ester functional groups.
The structure of nickel chromate is the same as for chromium vanadate, CrVO 4. Crystals have an orthorhombic structure with unit cell sizes a = 5.482 Å, b = 8.237 Å, c = 6.147 Å. The cell volume is 277.6 Å 3 with four formula per unit cell. [5] [7] Nickel chromate is dark in colour, unlike most other chromates which are yellow. [3]