Ceric ammonium nitrate
985616
220138091
2008-06-18T13:28:43Z
134.82.134.37
/* Properties and structure */
{{Chembox new
| Name = Ammonium cerium(IV) nitrate
| ImageFile = Ceric ammonium nitrate.jpg
| ImageSize = 200px
| ImageName = Ammonium cerium(IV) nitrate
| IUPACName = Diammonium cerium(IV) nitrate
| OtherNames = Ceric ammonium nitrate (CAN)
| Section1 = {{Chembox Identifiers
| CASNo = 16774-21-3
| EINECS = 240-827-6
}}
| Section2 = {{Chembox Properties
| Formula = H<sub>8</sub>N<sub>8</sub>CeO<sub>18</sub>
| MolarMass = 548.26 g/mol
| Appearance = orange-red crystals
| Solubility = 141 g/100 mL (25 °C)<br />227 g/100 mL (80 °C)
| MeltingPt = 107-108 °C
}}
| Section3 = {{Chembox Structure
| Coordination = [[Icosahedral]]
| CrystalStruct = [[Monoclinic]]
}}
| Section8 = {{Chembox Related
| OtherCpds = [[Ammonium nitrate]]<br /> [[Cerium(IV) oxide]]
}}
}}
'''Ceric ammonium nitrate''', or in lab jargon "CAN", is the [[chemical compound]] with the formula ([[Ammonium|NH<sub>4</sub>]])<sub>2</sub>Ce(NO<sub>3</sub>)<sub>6</sub>. This orange-red, water-soluble salt is widely used as an [[Redox|oxidising agent]] in [[organic synthesis]]. This compound is used as a standard oxidant in quantitative analysis,
==Properties and structure==
Two components make up this salt, the anion [Ce(NO<sub>3</sub>)<sub>6</sub>]<sup>2-</sup> and a pair of [[ammonium|NH<sub>4</sub><sup>+</sup>]] counter ions, which are not involved in the reactions of CAN. In the anion each nitrato group is [[chelate]]d 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(NO<sub>3</sub>)<sub>6</sub>]<sup>2-</sup> has idealized T<sub>h</sub> [[molecular symmetry]]. The CeO<sub>12</sub> core defines an [[icosahedron]].
==Preparation==
The anion [Ce(NO<sub>3</sub>)<sub>6</sub>]<sup>2-</sup> is generated by dissolving Ce<sub>2</sub>O<sub>3</sub> in hot concentrated [[nitric acid|HNO<sub>3</sub>]].
==Key reactions==
(NH<sub>4</sub>)<sub>2</sub>Ce(NO<sub>3</sub>)<sub>6</sub> is a stronger oxidizing agent (E° ~ 0.96 V vs. N.H.E.) than even Cl<sub>2</sub>. 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). 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]], [[phenol]]s, and [[ether]]s
**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)<sub>2</sub>, Ag<sub>2</sub>O or a stannylene acetal<ref name="boons">Boons, Geert-Jan.; Hale, Karl J. (2000). ''Organic Synthesis with Carbohydrates'' (1st ed.) Sheffield, England: Sheffield Academic Press. pp.33</ref> with DMF or DMSO as solvent,<ref name="kocienski">Kocienski, Phillip J. (1994). ''Protecting Groups'' Stuttgart, New York Georg Thieme Verlag. pp 8-9, 52-54</ref> or as para-methoxybenzyl trichloroacetimidate with ether and 0.3 mol% triflic acid.<ref name="boons" /><ref name="kocienski" /> 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 methanol<ref name="boons" /><ref name="kocienski" /> 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.<ref name="kocienski" /> The reaction mechanism is probably 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.<ref name="kocienski" /> 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 balanced equation is as follows:
2(NH<sub>4</sub>)<sub>2</sub>Ce(NO<sub>3</sub>)<sub>6</sub> + H<sub>3</sub>CO-para-C<sub>6</sub>H<sub>4</sub>-CH<sub>2</sub>-O-R + H<sub>2</sub>O → 4NH<sub>4</sub><sup>+</sup> + 2Ce(III) + 12NO<sub>3</sub><sup>-</sup> + 2H<sup>+</sup> + H<sub>3</sub>CO-para-C<sub>6</sub>H<sub>4</sub>-CHO + H-O-R
==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.
<br />CAN has many other synthetic applications, and it sometimes allows to carry out reactions that are not possible using other catalysts. For instance, 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.
<br />CAN is also an important component of Chrome etchant,<ref name=CRCCr>{{cite book |title=CRC Handbook of Metal Etchants |last=Walker |first=Perrin |coauthors=William H. Tarn |year=1991 |pages=287-291 |isbn=0-8949-3623-6}}</ref> a material that is used in the production of
[[Photomasks]] and [[Liquid Crystal Display]]s.
==References==
<div class="references-small"><references /></div>
<!-- Dead note "3": Budavari, Susan (Ed.). (1989). ''The Merck Index'' (11th ed.). Rahway, NJ: Merck. -->
<!-- Dead note "4": Macintyre, J. E. (Ed.). (1992). ''Dictionary of Inorganic Compounds'' (Vol. 3). London: Chapman & Hall. -->
<!-- Dead note "5": 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 1, pp.91-95. -->
<!-- Dead note "6": Wells, A.F. (1984). ''Structural Inorganic Chemistry'' (5th ed.). Oxford, UK: Clarendon Press. -->
<!-- Dead note "7": Connelly, N. G.; Geiger, W. E. "Chemical Redox Agents for Organometallic Chemistry" [[Chemical Reviews]] (1996), vol. 96, pp.877-910 -->
<!-- Dead note "8": Sridharan, V.; Avendaño, C.; Menéndez, J. C. "CAN-catalyzed three-component reaction between anilines and alkyl vinyl ethers: stereoselective synthesis of 2-methyl-1,2,3,4-tetrahydroquinolines and studies on their aromatization " Tetrahedron (2007), volume 63, pp. 673-681. -->
==External links==
* [http://www.organic-chemistry.org/chemicals/oxidations/ceriumammoniumnitrate-can.shtm Oxidizing Agents: Cerium Ammonium Nitrate]
[[Category:Ammonium compounds]]
[[Category:Cerium compounds]]
[[Category:Nitrates]]
[[Category:Coordination compounds]]
[[Category:Oxidizing agents]]
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