Lanthanide(III) and Group IV metal triflate catalysed electrophilic nitration: ‘nitrate capture’ and the rôle of the metal centre †

Combination of Transition Metals-(2,4-Pentanedionate) and P2O5 as a Regioselective Catalytic System for Nitric Acid Nitration of Ar-Himachalene

“…Many catalytic systems have been em-ployed, most of them heterogeneous; such as metal nitrates of iron(III ) or copper(II) supported on montmorillonite clay [12][13][14][15] have been shown to be efficient nitra-ting agents. Other examples involve the use of lanthanide (III), zirconium(IV) or hafnium(IV) triflate salts as catalysts of nitric acid nitration [16]. Iron (III)2,4pentanedionate [17,18] and zirconium(IV) 2,4-pentanedionate [19] have also been used as catalysts in the presence of dinitrogen pentoxide.…”

Lanthanide(III) Nitrobenzenesulfonates as New Nitration Catalysts: The Role of the Metal and of the Counterion in the Catalytic Efficiency

“…[10] It has been reasoned that the electrostatic interaction between the lanthanide ion and nitric acid, which is crucial for the formation of the nitronium ion (NO 2 ϩ ) as the de facto nitrating agent, increases as the polarising power (i.e. charge-to size-ratio) of lanthanide ion increases.…”

“…[3] A screening of the entire series of lanthanide() triflates for their catalytic activity in nitration also revealed a clear inverse correlation between the extent of nitration reaction and the ionic radius of the trivalent lanthanide ion. [10] The reaction we chose for the initial screening of the catalytic activity of Ln(p-NBSA) 3 , Ln(m-NBSA) 3 , and Ln(2,4-NBSA) 3 catalysts was the nitration of toluene. We first examined catalysts containing either ytterbium() or lanthanum() ions, as these two ions represent two extreme examples of the lanthanide() series in terms of ionic radius.…”

“…It has been shown that simple lanthanide salts such as lanthanide() chlorides or nitrates are poor nitration catalysts. [10] The counterion needs to be the conjugate base of a sufficiently strong acid so that nitric acid is preferentially protonated, producing a nitronium ion.…”

“…[8] On the other hand, Waller et al have shown that only catalytic amounts of scandium() or lanthanide() triflates were needed for the successful nitration of a range of simple aromatic compounds. [9,10] Unlike the commonly used industrial procedure, that requires use of potent mixtures of concentrated nitric and sulfuric acids, this procedure uses catalytic quantities of lanthanide() triflates as replacement for sulfuric acid and only one equivalent of nitric acid. In this way, excessive acid waste streams that are environmentally unfriendly and expensive to treat are avoided, and the only by-product of the nitration reaction is water.…”