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Ammonium cerium(IV) nitrate

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Ammonium cerium(IV) nitrate
Image:Ceric ammonium nitrate.jpg
General
Systematic name Diammonium cerium(IV) nitrate
Other names Ceric ammonium nitrate (CAN)
Molecular formula (NH4)2Ce(NO3)6
Molar mass 548.26 g/mol
Appearance orange-red crystalline solid
CAS number [16774-21-3]
EINECS number 240-827-6
Properties
Solubility in water 141 g/100 ml (25°C)
227 g/100 ml (80°C)
Melting point 107-108 °C (? K)
Structure
Coordination
geometry 		Icosahedral
Crystal structure Monoclinic
Supplementary data page
Structure and
properties 		n, εr, etc.
Thermodynamic
data 		Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Other cations Ammonium cerium(III) nitrate
Related compounds Ammonium nitrate
Cerium(IV) nitrate
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Infobox disclaimer and references

Ammonium cerium(IV) nitrate, more commonly called ceric ammonium nitrate or in lab jargon "CAN", but also ammonium nitratocerate(IV) and ammonium hexanitratocerate(IV), is an oxidising agent widely used in organic synthesis. This orange-red, water-soluble salt has the formula (NH4)2Ce(NO3)6. This compound is used as a standard oxidant in quantitative analysis,

Contents

[edit] Properties and structure

Two components comprise this salt, the anion [Ce(NO3)6]2- and a pair of NH4+ counter ions, which are not involved in the reactions of CAN. In the anion each nitrato group is linked to the cerium atom in a bidentate manner as shown below:

Image:Metal nitrate bonding.gif

Although the N-O bonds (on the metal side of the nitrato group) are unsymmetrical. The anion [Ce(NO3)6]2- has idealized Th symmetry. The CeO12 core defines an icosahedron.

[edit] Preparation

The anion [Ce(NO3)6]2- is generated by dissolving Ce2O3 in hot concentrated HNO3.

[edit] Key reactions

(NH4)2Ce(NO3)6 is a stronger oxidizing agent (E° ~ 0.96 V vs. N.H.E.) than even Cl2. Few shelf-stable reagents are stronger oxidants. In the redox process Ce(IV) is converted to Ce(III), a one-electron change, signalled by the fading of the solution color from orange to a pale yellow (providing that the substrate and product is not strongly colored). CAN is useful as an oxidant for many functional groups, some of which are listed below.

  • Oxidation of C-H bonds:
    • Alkenes produces dinitroxylation, although the outcome is solvent-dependent.
    • Methylarenes undergo benzylic oxidation.
  • Oxidation of alcohols, phenols, and ethers
    • Benzylic alcohols are converted into carbonyl compounds.
    • Quinones are produced from catechols and hydroquinones.
  • Oxidation of nitroalkanes
    • An alternative to the Nef reaction, e.g. for ketomacrolide synthesis where complicating side reactions usually encountered using other reagents are avoided using CAN.

Oxidative halogenation can be promoted by CAN as an in situ oxidant, for benzylic bromination, the iodination of ketones and uracil derivatives.

In synthetic organic chemistry the use of protecting groups is basically ubiquitous. Two related protecting groups used to protect alcohols are the para-methoxybenzyl and 3,4-dimethoxybenzyl ethers. They are added to alcohols either as para-methoxybenzyl chloride in the presence of NaH, Ba(OH)2, Ag2O or a stannylene acetal1 with DMF or DMSO as solvent2, or as para-methoxybenzyl trichloroacetimidate with ether and 0.3 mol% triflic acid.1,2 3,4-Dimethoxybenzyl ethers are produced in the same ways. When no longer needed the para-methoxybenzyl ether can be cleaved either by aqueous mineral acids in methanol or camphor sulfonic acid (CSA) in methanol1,2 or they can be cleaved oxidatively with either 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in dichloromethane/water or with ceric ammonium nitrate (CAN) in acetonitrile/water.2 The reaction mechanism is probaly similar for DDQ and CAN. DDQ accepts two electrons from the para-methoxybenzyl ether, one at a time. The DDQ becomes 2,3-dichloro-5,6-dicyano-1,4-hydroquinone and the para-methoxybenzyl ether (minus two electrons) gains a water molecule on the benzylic carbon. The alcohol is remade and the para-methoxybenzyl ether becomes para-methoxybenzaldehyde.2 CAN probably works the same way. Since Ce(IV) gains one electron to become Ce(III), two Ce(IV) ions each accept one electron from the para-methoxybenzyl ether to become two Ce(III). Two electrons in total are taken from the para-methoxybenzyl ether. The para-methoxybenzyl ether (minus two electrons) gains a water molecule on the benzylic carbon. The alcohol is remade and the para-methoxybenzyl ether becomes para-methoxybenzaldehyde. The balenced equation is as follows:

2(NH4)2Ce(NO3)6 + H3CO-para-C6H4-CH2-O-R + H2O → 4NH4+ + 2Ce(III) + 12NO3- + 2H+ + H3CO-para-C6H4-CHO + H-O-R

[edit] Applications

It has been shown that catalytic amounts of aqueous CAN in tap water can be used to efficiently synthesize various quinoxaline derivates in excellent yields. Quinoxaline derivates are known for their applications in areas such as the following: dyes, organic semiconductors, and DNA cleaving agents. These derivatives are also important components in antibiotics such as Echinomycin and Actinomycin which are known to inhibit the growth of Gram-positive bacteria and can be used against transportable tumors. There are many methods for the synthesis of quinoxaline derivatives, however, most of these suffer from unsatisfactory product yields, expensive metal precursors, harsh reaction conditions for the use of those precursors, as well as other problems. CAN provides both an inexpensive and nontoxic solution to these problems.

CAN is also an important component of Chrome etchant, a material that is used in the production of LCDs.

[edit] References

1) Boons, Geert-Jan.; Hale, Karl J. (2000). Organic Synthesis with Carbohydrates (1st ed.) Sheffield, England: Sheffield Academic Press. pp.33

2) Kocienski, Philiip J. (1994). Protecting Groups Stuttgart, New York Georg Thieme Verlag. pp 8-9, 52-54

  • Budavari, Susan (Ed.). (1989). The Merck Index (11th ed.). Rahway, NJ: Merck.
  • Macintyre, J. E. (Ed.). (1992). Dictionary of Inorganic Compounds (Vol. 3). London: Chapman & Hall.
  • More, Shivaji V.; Sastry, N.V.; Yao, Ching-Fa. "Cerium (IV) Ammonium Nitrate (CAN) as a Catalyst in Tap Water: A Simple, Proficient and Green Approach for the Synthesis of Quinoxalines" Green Chemistry (2006) volume 8, pp.91-95.
  • Wells, A.F. (1984). Structural Inorganic Chemistry (5th ed.). Oxford, UK: Clarendon Press.
  • Connelly, N. G.; Geiger, W. E. "Chemical Redox Agents for Organometallic Chemistry" Chemical Reviews (1996), vol. 96, pp.877-910

[edit] External links

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