[10102-05-3] · N2O6Pd · Palladium(II) Nitrate · (MW 230.44)
(catalyst for alkene nitration to glycol dinitrates1)
Physical Data: no mp (dec).
Solubility: sol nitric acid; sol w/dec. water.
Form Supplied in: brown, deliquescent crystals; probably exists as the dihydrate;2 commercially available.
Handling, Storage, and Precautions: store under anhydrous conditions, protected from light.
Palladium(II) nitrate is a useful stoichiometric reagent for the nitration of alkenes to glycol dinitrates.3 The reaction can be made catalytic in the presence of nitric acid and nitrite ion, the latter being necessary to reoxidize the metallic Pd that is formed (eq 1).1 Alternatively, oxygen can be used to reoxidize the NO2 coproduct back to nitric acid and water (eq 2). This reaction is most useful for the production of ethylene glycol dinitrate, which is formed in up to 88% selectivity in a 1:1 mixture of dioxane and Nitric Acid. With higher a-alkenes the NO2 coproduct adds to the alkene at rates that are competitive with oxidation, even in the presence of oxygen, so that the selectivity for dinitrate is reduced to the 40-60% range.
Palladium nitrate can often be substituted for other palladium salts in catalyst mixtures, but the catalyst performance varies with the particular salt chosen. For instance, although Pd(NO3)2 can be used in Wacker-like oxidation reactions,4 Palladium(II) Chloride or related salts often give better results.5 However, Pd(NO3)2 is often preferred in industrial oxidation processes, such as the oxidative coupling of Carbon Monoxide to give oxalic acid esters (eq 3).6
Another example where Pd(NO3)2 appears to work better than other Pd salts is in the stoichiometric carboxylation of aromatic compounds to give aryl carboxylic acids (eq 4).7
Palladium(II) nitrate can also be used in place of other palladium salts as a precursor to palladium catalysts formed in situ, such as PdII or Pd0 phosphine complexes. One example where only Pd(NO3)2 works well is in the Triphenylphosphine-promoted dimerization of 1,3-Butadiene with Schiff bases to give divinylpiperidines (eq 5).8
Palladium(II) nitrate is also commonly used as a precursor to supported Pd catalysts.9
Timothy T. Wenzel
Union Carbide Corporation, South Charleston, WV, USA