Nitrate-substituted catalysts

Scheme 8 Comparison of pivalate-substituted catalyst 52 and nitrate-substituted catalyst 62 in homodimerization reactions...

Of more preparative value are the reactions of nucleophilic radicals, such as HOCHa and RaNCO, which can be easily generated under mild conditions, for example HOCH2 from ethylene glycol by persulfate oxidation with silver nitrate as catalyst. These substitutions are carried out on the pyridine protonic salt, which provides both increased reactivity and selectivity for an a-position the process is known as the Minisci reaction (cf. 3.4.1). It is accelerated by electron-withdrawing substituents on the ring. 

Aromatic rings can undergo nitration, substitution of the nitro group —NO2, in a mixture of concentrated nitric and sulfuric acids at moderate temperatures. The H2SO is both a catalyst and a... 

There are very few homolytic reactions on triazolopyridines. A suggestion that the ring opening reactions of compound 1 involved free radical intermediates is not substantiated (98T9785). The involvement of radical intermediates in additions to ylides is discussed in Section IV.I. The reaction of radicals with compound 5 and its 1-substituted derivatives gives 4-substituted compounds such as 234 (96ZOK1085). A more detailed study of the reaction of the 1-methyl and 1-phenyl derivatives with r-butanol and ammonium persulfate produced 4-methyl substitution with a silver nitrate catalyst, and the side chain alcohol 235 without the catalyst (96ZOK1412). 

Certain groups attached to an aromatic ring can donate electrons into its delocalized molecular orbitals. Examples of these electron-donating substituents include —NH2 and —OH. Electrophilic substitution of benzene is much faster when an electron-donating substituent is present. For example, the nitration of phenol, C6H5OH, proceeds so quickly that it requires no catalyst. Moreover, when the products are analyzed, the only products are found to be 2-nitrophenol (ortho-nitrophenol, 37) and 4-nitrophenol (pnra-mtrophcnol, 38 . 

Montanari el al., for example, studied a Co—H-MFI sample through FT-IR spectroscopy of in situ adsorption and coadsorption of probe molecules [o-toluonitrile (oTN), CO and NO] and CH4-SCR process tests under IR operando conditions. The oTN adsorption and the oTN and NO coadsorption showed that both Co2+ and Co3+ species are present on the catalyst surface. Co3+ species are located inside the zeolitic channels while Co2+ ions are distributed both at the external and at the internal surfaces. The operando study showed the activity of Co3+ sites in the reaction. The existence of three parallel reactions, CH4-SCR, CH4 total oxidation and NO to NOz oxidation, was also confirmed. Isocyanate species and nitrate-like species appear to be intermediates of CH4-SCR and NO oxidation, respectively. A mechanism for CH4-SCR has been proposed. On the contrary, Co2+ substitutional sites, very evident and predominant in the catalyst, which are very hardly reducible, seemed not to play a key role in the SCR process [173],... 

There are certain formal analogies here to m- attack on nitrobenzene (cf. p. 152), but pyridine is very much more difficult to substitute than the former. Thus nitration, chlorination, bromination and Friedel-Crafts reactions cannot really be made to take place usefully, and sulphonation only occurs on heating with oleum for 24 hours at 230°, with an Hg2 catalyst. This difficulty of attack is due partly to the fact that pyridine has an available electron pair on nitrogen, and can thus protonate (66), or interact with an electrophile (67) ... 

The use of cerium(IV) ammonium nitrate (CAN) as a catalyst for an aza-Diels-Alder reaction was reported in two different publications. In one report Perumal and co-workers react a variety of anilines 86 and aldehydes 87 with enamine 88 in the presence of 5 mol% CAN to form a series of tetrahydroquinolines 89. The reactions were performed at room temperature with very short reaction times and in good yields. In addition, the resulting tetrahydroquinolines could be oxidized to the corresponding substituted quinolines using 2.5 eq of CAN in high yields <06TL3589>. 

Vanadium(V) oxytrinitrate [VO(N03)3] has been established as a powerful but moisture-sensitive reagent which nitrates a range of substituted aromatic compounds in good yield in dichloromethane at room temperature. The hydrated triflates Hf(OTf)4 and Zr(OTf)4 are excellent recyclable catalysts for the mononitration of o-nitrotoluene with 1 equiv. of concentrated nitric acid. ... 

Some reactions of 2,2 -bipyridine /V-oxides have been reported. The l,T-dioxide is nitrated readily to 4,4 -dinitro-2,2 -bipyridine 1,T-dioxide. ° ° °" 2,2 -Bipyridine 1-oxide is also nitrated in the 4 position. The nitro groups in 4,4 -dinitro-2,2 -bipyridine l,T-dioxide are reactive, being replaced by chlorine with concentrated hydrochloric acid," by bromine with acetyl bromide, by hydroxyl with dilute sulfuric acid, and by alkoxy groups with sodium alkoxides. Some of the dialkoxy derivatives are useful catalysts for the oxidation of aromatic compounds. The dinitro dioxide is deoxygenated to 4,4 -dinitro-2,2 -bipyridine with phosphorus trichloride in chloroform, and other substituted l,T-dioxides behave similarly, but with phosphorus trichloride alone, 4,4 -dichloro-2,2 -bipyridine results. The dinitro dioxide is reduced by iron powder in acetic acid to 4,4 -diamino-2,2 -bipyridine, whereas 4,4 -dichloro-2,2 -bipyridine l,T-dioxide is converted to its 4,4 -diamino analogs with amines. Related reactions have been described. ... 

Fe "-substituted heteropolyanions are not efficient in the electrocatalytic reduction of nitrate [160a]. Such observation complies with literature where Epstein etal. had shown that efficient oxidation of Fe" by nitrate necessitates a catalyst [160b]. In contrast, the electrocatalytic reduction of nitrate was observed here when the first W-reduction processes were reached. Furthermore, the potential domain where this electrocatalysis was obtained is comparable with those of the best... 

---