Ceric ammonium nitrate

Preparation, properties, and structure

The anion [Ce(NO
3)
6]2−
is generated by dissolving Ce
2O
3 in hot concentrated HNO₃.

The salt consists of the anion [Ce(NO
3)
6]2−
and a pair of NH₄⁺ counter ions. The ammonium ions are not involved in the oxidising reactions of this salt. In the anion each nitrate group is chelated to the cerium atom in a bidentate manner as shown below:

The anion [Ce(NO
3)
6]2−
has T_h (idealized O_h) molecular symmetry. The CeO₁₂ core defines an icosahedron.

Ce⁴⁺ is a strong one-electron oxidizing agent. In terms of its redox potential (E° ~ 1.61 V vs. N.H.E.) it is even stronger oxidizing agent than Cl₂ (E° ~ 1.36 V). Few shelf-stable reagents are stronger oxidants. In the redox process Ce(IV) is converted to Ce(III), a one-electron change, signaled by the fading of the solution color from orange to a pale yellow (providing that the substrate and product are not strongly colored).

Applications in organic chemistry

In organic synthesis, CAN is useful as an oxidant for many functional groups (alcohols, phenols, and ethers) as well as C–H bonds, especially those that are benzylic. Alkenes undergo dinitroxylation, although the outcome is solvent-dependent. Quinones are produced from catechols and hydroquinones and even nitroalkanes are oxidized.

CAN provides an alternative to the Nef reaction; for example, for ketomacrolide synthesis where complicating side reactions usually encountered using other reagents. Oxidative halogenation can be promoted by CAN as an in situ oxidant for benzylic bromination, and the iodination of ketones and uracil derivatives.

CAN is used in a modern synthesis of tametraline as well as an oxidizing agent in the synthesis of Sulbenox.

For the synthesis of heterocycles

Catalytic amounts of aqueous CAN allow the efficient synthesis of quinoxaline derivatives. Quinoxalines are known for their applications as dyes, organic semiconductors, and DNA cleaving agents. These derivatives are also components in antibiotics such as echinomycin and actinomycin. The CAN-catalyzed three-component reaction between anilines and alkyl vinyl ethers provides an efficient entry into 2-methyl-1,2,3,4-tetrahydroquinolines and the corresponding quinolines obtained by their aromatization.

As a deprotection reagent

CAN is traditionally used to release organic ligands from metal carbonyls. In the process, the metal is oxidised, CO is evolved, and the organic ligand is released for further manipulation. For example, with the Wulff–Dötz reaction an alkyne, carbon monoxide, and a chromium carbene are combined to form a chromium half-sandwich complex and the phenol ligand can be isolated by mild CAN oxidation.

CAN is used to convert para-methoxybenzyl and 3,4-dimethoxybenzyl ethers, which are protecting groups for alcohols. Two equivalents of CAN are required for each equivalent of para-methoxybenzyl ether. The alcohol is released, and the para-methoxybenzyl ether converts to para-methoxybenzaldehyde. The balanced equation is as follows:

Other applications

CAN is also a component of chrome etchant, a material that is used in the production of photomasks and liquid crystal displays.