Thermal denitrogenation

Photoisomerization of c/.y-stilbene 191 Ionic fragmentation reaction 191 Cyclopropyl radical ring-opening 192 Ionic molecular rearrangement 193 Ene reaction 196 Thermal denitrogenation 198 Unimolecular dissociation 199 Sn2 reaction 200... 

Concerted versus stepwise issue was studied for another radical reaction. The thermal denitrogenation of 4-spirocyclopropane-l-pyrazolines (27) gives alky-lidenecyclobutanone (28) and spiropentane (29) in three possible pathways (Scheme 5), via (a) diazenyl diradical intermediate (30), (b) 1,3-diradical intermediate (31), or (c) concerted cycloreversion TS. 

Synthetic fuels derived from shale or coal will have to supplement domestic suppHes from petroleum someday, and aircraft gas turbine fuels producible from these sources have been assessed. Shale-derived fuels can meet current specifications if steps are taken to reduce the nitrogen levels. However, extracting kerogen from shale rock and denitrogenating the jet fuel are energy-intensive steps compared with petroleum refining it has been estimated that shale jet fuel could be produced at about 70% thermal efficiency compared with 95% efficiency for petroleum (25). Such a difference represents much higher cost for a shale product. 

Some desulfurization occurs thermally but essentially no denitrogenation occurs without the aid of catalysts. ... 

The thermal decomposition of 8 in tetrachloroethene at 134 C gave a chromatographically separable mixture of cyclobutane 9 and 1,8-divinylnaphthalene 10 in 7 1 ratio. Although several experiments have been carried out to identify the spin multiplicity of the intermediate diradical, the results were inconclusive.17 A recent report stated that while triplet-sensitized photolysis resulted in predominant denitrogenation, laser/liquid jet photochemical reaction also gave cyclopentenes by 1,2-hydrogen shift.18 Indications are that the amounts of cyclopentenes increase with increasing lifetime of the intermediary 1,3-cyclopentadiyl triplet diradical.18... 

Thermal Baseline Study. PDU Run 2LCF-21 (Thermal Baseline) processed a 70/30 volume percent SRC-I/500°F IBP KC-Oil feed blend over an inert 1/32 inch Shell catalyst support. The inert support was the extrudate base for the modified Shell 324 catalyst and had been calcined at 1100-1150°C. The purpose of this run was to determine the extent of conversion and denitrogenation in the absence of an active catalyst ingredient - nickel and molybdenum (Ni/Mo). 

In a similar way, the 1,3-diradicals postulated in the di-ir-methane rearrangement of several benzonor-bomadienes and related species have been produced via denitrogenation of the appropriate azoalkanes (27)-(30). The products obtained in the thermal and photochemical denitrogenation of (27), for example, are the norbomadiene and the tricyclic di- ir-methane product (occasionally other products not derived from denitrogenation have been observed). The latter hydrocarbon, which derives from direct collapse of the 1,3-diradical, is formed almost exclusively (equation 37). 

Nitrenes (R—N) are hypovalent species that are commonly formed by thermal or photochemical denitrogenation of azides (R—N3), which are readily synthesized and isolated, especially acyl and aryl azides. Simple alkyl azides do not in general produce alkyl nitrenes as detectable or trappable reactive intermediates upon direct irradiation (254 nm) due to rapid 1,2-migration to form the corresponding imines. Trifluoromethylnitrene is, however, formed by irradiation of CF3N3.408... 

Unlike deazatation (denitrogenation) of azoalkanes, loss of N2O from aliphatic azoxy compounds is rarely observed. Thus they are neither free radical initiators nor thermally labile, contrary to published comments. For example, the common free radical initiator azoisobutyronitrile (AIBN) decomposes readily at 80 C but the azoxy analog 1 is stable up to 180 Thermolysis of azoxycumene 2 is very slow and does not yield N2O, leading instead... 

The first investigation on the stereoselectivity of the stepwise thermal denitrogena-tion of the diethoxy-substituted azoalkane has been reported. The double inversion product was the major isomer of the ring closure product. In photochemical denitro-genation, the inverted azoalkane was also the major isomer at 70 °C, although the stereoselectivity of the reaction was temperature dependent. An inversion process was proposed as the mechanism that determines the stereochemistry of the denitrogenation reaction products. The inversion product may alternatively be formed as a result of dynamic effects. 

Passing to organic chemistry, an interesting case is that of thermal or photochemical solid phase denitrogenation of a triazoline bearing bully ... 

The double inversion of the molecular skeleton upon thermal and photochemical denitrogenation, first observed for the parent 2,3-diazabicyclo[2.2.1]hept-2-ene, DBH (1), constitutes a unique stereoselective process, much under mechanistic dispute for almost four decades. The mechanistic alternatives for the denitrogenation process pertain to whether the diazenyl ( DZ) or the nitrogen-free cyclopentane-1,3-diyl ( DR) biradical intervenes in the product-branching point to afford the diastereomeric housane... 

---