Document Detail

Aromatic hydrocarbon nitration under tropospheric and combustion conditions. A theoretical mechanistic study.
MedLine Citation:
PMID:  17149846     Owner:  NLM     Status:  PubMed-not-MEDLINE    
The viability of some nitration pathways is explored for benzene (B), naphthalene (N), and in part pyrene (P). In principle, functionalization can either take place by direct nitration (NO2 or N2O5 attack) or be initiated by more reactive species, as the nitrate and hydroxyl radicals. The direct attack of the NO2 radical on B and N, followed by abstraction of the H geminal to the nitro group (most likely accomplished by 3O2) could yield the final nitro-derivatives. Nevertheless, the initial step (NO2 attack) involves significant free energy barriers. N2O5 proves to be an even worst nitrating agent. These results rule out direct nitration at room temperature. Instead, NO3 and, even more easily, HO can form pi-delocalized nitroxy- or hydroxycyclohexadienyl radicals. A subsequent NO2 attack can produce several regio- and diastereoisomers of nitroxy-nitro or hydroxy-nitro cyclohexadienes. In this respect, the competition between NO2 and O2 is considered: the rate ratios are such to indicate that the NO3 and HO initiated pathways are the major source of nitroarenes. Finally, if the two substituents are 1,2-trans, either a HNO3 or a H2O concerted elimination can give the nitro-derivatives. Whereas HNO3 elimination is feasible, H2O elimination presents, by contrast, a high barrier. Under combustion conditions the NO2 direct nitration pathway is more feasible, but remains a minor channel.
Giovanni Ghigo; Mauro Causà; Andrea Maranzana; Glauco Tonachini
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  The journal of physical chemistry. A     Volume:  110     ISSN:  1089-5639     ISO Abbreviation:  J Phys Chem A     Publication Date:  2006 Dec 
Date Detail:
Created Date:  2006-12-07     Completed Date:  2007-03-13     Revised Date:  2007-03-27    
Medline Journal Info:
Nlm Unique ID:  9890903     Medline TA:  J Phys Chem A     Country:  United States    
Other Details:
Languages:  eng     Pagination:  13270-82     Citation Subset:  -    
Dipartimento di Chimica Generale ed Organica Applicata, Università di Torino, Corso Massimo D'Azeglio 48-10125 Torino, Italy.
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