Ceric ammonium nitrate, or in lab jargon "CAN", is the chemical compound with the formula (NH4)2Ce(NO3)6. This orange-red, water-soluble salt is widely used as an oxidising agent in organic synthesis. This compound is used as a standard oxidant in quantitative analysis,
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 acetal with DMF or DMSO as solvent, or as para-methoxybenzyl trichloroacetimidate with ether and 0.3 mol% triflic acid. 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 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. 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. 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(NH4)2Ce(NO3)6 + H3CO-para-C6H4-CH2-O-R + H2O → 4NH4+ + 2Ce(III) + 12NO3- + 2H+ + H3CO-para-C6H4-CHO + H-O-R
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.