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Ammonium Cerium(IV) Nitrate

(NH4)2Ce(NO3)6 salt
Molar Mass
548.220 g/mol
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Properties

StateSolid
ColorBright orange-red
SolubilityVery soluble in water, acetone, acetonitrile, and other polar organic solvents
Melting Point107 °C (decomposes)

About Ammonium Cerium(IV) Nitrate

Ammonium cerium(IV) nitrate — every synthetic chemist who's used it just calls it CAN — is the bright orange-red salt that has become the standard one-electron oxidant for cleaving para-methoxybenzyl (PMB) and para-methoxyphenyl (PMP) protecting groups. The reduction potential of Ce(IV)/Ce(III) sits around 1.4 V in nitric acid, high enough to oxidize electron-rich aromatic ethers cleanly but low enough that the reagent doesn't touch alkenes, simple alcohols, or unsubstituted aromatics in the same molecule. That orthogonality is the entire selling point. The structural picture is unusual: each Ce(IV) sits in a 12-coordinate environment of six bidentate nitrate ligands forming the [Ce(NO3)6]²⁻ anion, with two ammonium counterions for charge balance. The intense orange color is the Ce(IV) → ligand charge-transfer band, and watching CAN go from orange to colorless during a reaction is the visual signal that the oxidation is complete. Beyond PMB deprotection, CAN oxidizes hydroquinones to quinones in nearly quantitative yields, dimerizes phenols to biaryls in some cases, oxidizes methylarenes to aldehydes (the Belluš–Klingbeil oxidation), and serves as the classical primary standard for cerimetric titrations in analytical chemistry where its sharp orange-to-colorless endpoint replaces less robust permanganate methods.

Where you'll encounter it

If you do natural-product total synthesis, CAN is the deprotection reagent you reach for when you've used PMB to protect an alcohol through several steps and now need to unmask it without disturbing the rest of the molecule. The standard procedure — CAN in acetonitrile/water, 0 °C, 15–30 minutes — is fast, reliable, and has been demonstrated on hundreds of complex intermediates in the literature. In an analytical lab, CAN is also the standard titrant for ferrous-iron determination (Ce(IV) + Fe(II) → Ce(III) + Fe(III)), where the orange-to-colorless endpoint is sharper and more reproducible than KMnO4's purple-to-clear transition. In a teaching lab, CAN-on-silica TLC stains are a classic visualization protocol: any spot that contains an oxidizable functional group turns from yellow to dark brown when the plate is heated.

Common Uses

  • PMB and PMP protecting-group removal in total synthesis
  • Quinone formation from hydroquinones and electron-rich phenols
  • Methylarene-to-aldehyde oxidation (Belluš–Klingbeil method)
  • Cerimetric titration standard in analytical chemistry
  • TLC visualization stain for oxidizable functional groups

Safety Information

Strong oxidizer — keeps reducing agents and organic solvents like ethers separated in storage, since accidental contact can ignite. Acute oral toxicity is moderate (Category 4). The nitrate component decomposes to NO2 if heated above 200 °C. GHS H272, H302, H315, H319. Standard handling involves a fume hood, nitrile gloves, and splash goggles; spills should be neutralized with sodium bisulfite before aqueous cleanup.

This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.

Constituent Elements

N — Nitrogen H — Hydrogen Ce — Cerium O — Oxygen

Frequently Asked Questions

What is the molar mass of ammonium cerium(IV) nitrate?
548.22 g/mol. Sum 2(NH4) at 18.04 each, cerium at 140.116, and 6(NO3) at 62.004 each, giving 548.22. The high molar mass means a 1 M solution is dense (~1.4 g/mL), so volumetric measurements need to account for the contribution of the dissolved salt to the total volume — relevant when preparing standardized titration solutions.
Why is CAN so useful for PMB deprotection?
Three properties together. First, the Ce(IV)/Ce(III) reduction potential is just high enough to oxidize the electron-rich PMB ether to a radical cation, which spontaneously fragments to release the free alcohol and produce p-anisaldehyde as a byproduct. Second, the kinetic selectivity: CAN doesn't oxidize simple alkenes, alcohols, or unactivated aromatics on the timescale of the deprotection (15–30 minutes at 0 °C), so the rest of a complex molecule stays intact. Third, the workup is trivial — extract into organic solvent, wash to remove the cerium salts, and the deprotected product is in the organic layer.
How does CAN compare to KMnO4 as an oxidant?
Different selectivity profile. KMnO4 is a strong four-electron oxidant that cleaves C=C bonds, oxidizes primary alcohols all the way to acids, and tends to over-oxidize anything it touches. CAN is a one-electron oxidant that's selective for electron-rich aromatic ethers, hydroquinones, and certain reduced metal centers — alkenes, simple alcohols, and unactivated aromatics survive untouched. CAN also works in acetonitrile/water, opening up substrate compatibility that pure aqueous KMnO4 doesn't have, and the orange-to-colorless color change makes endpoint detection cleaner.