3463-36-3Relevant academic research and scientific papers
HNO3/HFIP: A Nitrating System for Arenes with Direct Observation of π-Complex Intermediates
Lu, Le,Liu, Huixin,Hua, Ruimao
supporting information, p. 3197 - 3201 (2018/06/11)
This report describes an efficient nitrating system for the nitration of arenes at room temperature by using an equivalent of nitric acid in HFIP (1,1,1,3,3,3-hexafluoroisopropanol). The π-complex intermediate of an arene with a nitronium ion stabilized by HFIP can be directly observed by UV-vis spectra and is supported by theoretical calculations.
Aromatic nitration with bismuth nitrate in ionic liquids and in molecular solvents: A comparative study of Bi(NO3)3·5H 2O/[bmim][PF6] and Bi(NO3)3· 5H2O/1,2-DCE systems
Jacoway, Jonathan,Kumar, G. G. K. S. Narayana,Laali, Kenneth K.
, p. 6782 - 6785,4 (2012/12/12)
A suspension of bismuth nitrate pentahydrate (BN) in [bmim][PF6] or [bmim][BF4] imidazolium ionic liquid (IL) is an effective reagent for ring nitration of activated aromatics under mild conditions without the need for external promoters. Nitration can also be effected in 1,2-DCE, MeCN, or MeNO2 without additives. Nitration of activated arenes (anisole, toluene, ethylbenzene, cumene, p-xylene, mesitylene, durene, and 1,3-dimethoxybenzene) is considerably faster (time to completion) in BN/[bmim][PF6] relative to BN/1,2-DCE and there are also differences in isomer distributions (for anisole, toluene, and ethylbenzene). With introduction of strongly deactivating substituents (-CHO; -MeCO; -NO 2) the BN/IL system is no longer active but reactions still proceed with BN/1,2-DCE in reasonable yields. The ready availability and low cost of BN, simple operation, and absence of promoters, coupled to recycling and reuse of the IL, provide an attractive alternative to classical nitration methods for activated arenes. Switching from Bi(NO3)3·5H 2O/[bmim][PF6] to Bi(NO3)3· 5H2O/1,2-DCE increases the scope of the substrates that can be nitrated.
Photochemical nitration by tetranitromethane. Part XXXIII. Adduct formation in the photochemical reactions of 1,2,4,5- and 1,2,3,5-tetramethylbenzene
Butts, Craig P.,Eberson, Lennart,Fulton, Karen L.,Hartshorn, Michael P.,Robinson, Ward T.,Timmerman-Vaughan, David J.
, p. 991 - 1008 (2007/10/03)
The photolysis of the charge-transfer complex of tetranitromethane and 1,2,4,5-tetramethylbenzene in dichloromethane or acetonitrile gives the epimeric 1,3,4,6-tetramethyl-3-nitro-6-trinitromethylcyclohexa-1,4-dienes 8 and 9, in addition to products of nuclear nitration 12 and side-chain modification 10, 11, and 13-18. Similar reactions of 1,2,3,5-tetramethylbenzene gave trans-1,3,5,6-tetramethyl-6-nitro-3-trinitromethylcyclohexa-1,4-diene 30 and two isomeric 'double' adducts 31 and 32, in addition to products of nuclear nitration 27 and side-chain modification 26, 28 and 29. The eliminative rearrangements of adducts 8 and 30 to give re-aromatized products in acetonitrile or [2H3] acetonitrile and in [2H] chloroform are reported. The photolysis of the charge-transfer complexes of tetranitromethane with either 1,2,4,5-tetramethylbenzene or 1,2,3,5-tetramethylbenzene in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFP) gives a marked increase in the yields of ring-nitration products 12 or 27, respectively, reactions presumed to proceed via a nitrosation-oxidation sequence. Reaction of 1,2,4,5-tetramethylbenzene with excess nitrogen dioxide in HFP also results in extensive ring nitration to give 12 and 2,3,5,6-tetramethyl-1,4-dinitrobenzene (25); the latter compound is seen as arising via the 2,3,5,6-tetramethyl-1,4-dinitrosobenzene (34). Similar reaction of 1,2,3,5-tetramethylbenzene gives ring-nitration product 27 as the major product. X-Ray crystal structures are reported for 2,4,6-trimethyl-1-(2′,2′,2′-trinitroethyl)benzene (26) and trans-1,3,5,6-tetramethyl-6-nitro-3-trinitromethyl-cyclohexa-1,4-diene (30). Acta Chemica Scandinavica 1996.
Direct Nitrosation of Aromatic Hydrocarbons and Ethers with the Electrophilic Nitrosonium Cation
Bosch, Eric,Kochi, Jay K.
, p. 5573 - 5586 (2007/10/02)
Various polymethylbenzenes and anisoles are selectively nitrosated with the electrophilic nitrosonium salt NO(1+)BF4(1-) in good conversions and yields under mild conditions in which the conventional procedure (based on nitrile neutralization with strong acid) is ineffective.The reactivity patterns in acetonitrile deduced from the various time/conversions in Tables 2 and 3 indicate that aromatic nitrosation is distinctly different from those previously established for electrophilic aromatic nitration.The contrasting behavior of NO(1+) in aromatic nitrosation is ascribed to a rate-limiting deprotonation of the reversibly formed Wheland intermediate, which in the case of aromatic nitration with NO2(1+) occurs with no deuterium kinetic isotope effect.Aromatic nitroso derivatives (unlike the nitro counterpart) are excellent electron donors that are subject to a reversible one-electron oxidation at positive potentials significantly less than that of the parent polymethylbenzene or anisole.As a result, the series of nitrosobenzenes are also much better Broensted bases than the corresponding nitro derivatives, and this marked distinction, therefore, accounts for the large differentiation in the deprotonation rates of their respective conjugate acids (i.e.Wheland intermediates).
Thermal and Photochemical Nitration of Aromatic Hydrocarbons with Nitrogen Dioxide
Bosch, E.,Kochi, J. K.
, p. 3314 - 3325 (2007/10/02)
Aromatic hydrocarbons (ArH) are readily nitrated by nitrogen dioxide (NO2) in dichloromethane at room temperature and below (in the dark).The red colors, transiently observed, arise from the metastable precursor complex NO3(1-), which is formed in the prior disproportionation of nitrogen dioxide induced by the aromatic donor (eq 7).The deliberate irradiation of the diagnostic (red) charge-transfer absorption band (hνCT) of NO3(1-) at low temperatures results directly in aromatic nitration, even at -78 deg C, where the thermal nitration is too slow to complete.The mechanism of the photochemical (charge-transfer) nitration is established by time-resolved laser spectroscopy to proceed via the aromatic cation radical (ArH.+) formed spontaneously upon the charge-transfer excitation of NO3(1-) in Scheme 1.The related thermal activation of NO3(1-) derives from the adiabatic electron transfer that produces the same radical pair as the reactive intermediate in Scheme 3.The close relationship between the thermal/photochemical nitrations with nitrogen dioxide and those conventionally carried out with nitric acid (in the presence of nitrous acid) is delineated by Scheme 4.
Oxidative Aromatic Nitration with Charge-Transfer Complexes of Arenes and Nitrosonium Salts
Kim, E. K.,Kochi, J. K.
, p. 1692 - 1702 (2007/10/02)
Brightly colored solutions are obtained immediately upon the exposure of various arenes (ArH) to nitrosonium (NO+) salts.The colors arise from the charge-transfer transitions of 1:1 complexes +> that are reversibly formed as persistent intermediates.However the yellow-red charge-transfer (CT) colors are readily bleached by dioxygen, and the corresponding nitroarenes (ArNO2) can be isolated in excellent yields from acetonitrile solutions.Such an oxidative aromatic nitration of aromatic donors proceeds via the initial autooxidation of the charge-transfer complex.The collapse of the resulting radical ion pair .+,NO2> to the ?-adduct, followed by the loss of proton, affords ArNO2.Direct evidence for electron transfer in the initial step when anthracene is treated with NO+PF6- stems for the isolation of (a) the anthracene ion radical salt .+PF6-> along with nitric oxide in dichloromethane solution and (b) the formation of 9-nitroanthracene (admixed with anthraquinone) in the more polar acetonitrile.The aromatic products (and isomer distribution) from oxidative aromatic nitration are highly reminiscent of those from electrophilic aromatic nitration.The possibility of common reactive intermediates in these two distinctive pathways for aromatic nitration is discussed.
Direct Observation of the Kinetic Acidities of Transient Aromatic Cation Radicals. The Mechanism of Electrophilic Side-Chain Nitration of the Methylbenzenes
Masnovi, J. M.,Sankararaman, S.,Kochi, J. K.
, p. 2263 - 2276 (2007/10/02)
The transient cation radicals ArCH3(.+) are spontaneously generated by the 532-nm excitation of the charge-transfer complexes with a 10-ns laser pulse.The decay kinetics of the spectral transients in the presence of added base establish the kinetic acidities (kH) for various methylarene cation radicals with different pyridines and trinitromethide.Such a proton transfer from ArCH3(.+) proceeds with a deuterium kinetic isotope effect of kH/kD ca. 3.Side-chain nitration of hexamethylbenzene (HMB) is shown to proceed in high yields via the intimate triad of reactive fragments II, , that is produced upon the charge-transfer excitation.The subsequent annihilation of the reactive triad II occurs via a rapid succession of bimolecular steps involving either (i) the initial ion-pair collapse of by proton transfer, as shown in Scheme VI, or (ii) the alternative sequence with the initial ion-radical collapse of by homolytic coupling, as shown in Scheme VII.The marked variations of kH/kD with solvent polarity and added innocuous salt (Bu4N(+)ClO4(-)), as reflected in ion-pair separation and the "special" salt effect, serve to effectively distinguish these pathways.The direct bearing of Schemes VI and VII on the mechanism of the thermal (adiabatic) nitration of methylarene side chains with nitric acid is delineated.
OXIDATIVE CHLORINATION OF AROMATIC COMPOUNDS IN THE PRESENCE OF NITROGEN-CONTAINING OXIDIZING AGENTS
Makhon'kov, D. I.,Cheprakov, A. V.,Rodkin, M. A.,Beletskaya, I. P.
, p. 211 - 217 (2007/10/02)
Mixture of the chlorides and nitrates of alkali metals in aqueous trifluoroacetic acid can be used for the selective oxidative chlorination of benzene, halogenobenzenes, toluene, and p-toluic acid with preparative yields.By variation of the water content of the solvent and the nitrate-chloride ratio it is possible to suppress the nitration side reaction.In the presence of oxygen or air alkali-metal nitrites can also be used as oxidizing agents in this process.The chlorinating agent in these systems is molecular chlorine, as confirmed by a comparative study of the reactions of two groups of potential chlorinating agents (nitrosyl chloride and nitryl chloride) under these conditions.The reactions of naphthalene and polymethylbenzenes with nitrosyl chloride in trifluoroacetic acid, leading to the products from chlorination and dehydrooligomerization of the aromatic substrates, were also studied.
Electrophilic Aromatic Substitution. Part 27. Chemical Selectivities Disguised by Mass Diffusion. Part 6. The Kinetics of Nitration in Aqueous Sulphuric Acid of Durene (1,2,4,5-Tetramethylbenzene). Nitrodurene, and Nitroprehnitene (Nitro-1,2,3,4-tetramethylbenzene). A Comparison ...
Manglik, Ajay K.,Moodie, Roy B.,Schofield, Kenneth,Dedeoglu, Erol,Dutly, Andreas,Rys, Paul
, p. 1358 - 1366 (2007/10/02)
Durene (1,2,4,5-tetramethylbenzene) is nitrated in sulphuric acid at the encounter rate.Nitrations of nitrodurene and nitroprehnitene (nitro-1,2,3,4-tetramethylbenzene) are complicated by the formation of nitrous acid, presumably as a consequence of ipso-attack, and subsequent undefinied reactions of this.When an efficient nitrous acide trap is present the complications are removed and the kinetics become straightforward.Although nitrobenzene is 108 times less reactive than benzene in nitration, nitroprehnitene and nitrodurene are only 41 and 20 times less reactive than their respective parent hydrocarbons.These reduced relative reactiviities are a consequence of the fact that prehnitene and durene react at the encounter rate.The low relative reactivity of durene and 3-nitrodurene leads to the formation of some 3,6-dinitrodurene in the nitration of durene, even under the most favourable circumstances, and if mixing is inefficient the dinitro-compound may be the main product.By measuring the yield of 3-nitrodurene, as it varies with acidity, it is possible to determine the amount formed by direct attack at C-3 as distinct from that formed by ipso-attack followed by rearrangement.As a consequence the ratio of positional selectivity between C-3 and C-1 is shown to be 1 : 3.6.Thus, positional selestivity does not disappear.The intrinsic rate constants for nitronium ion nitrations in sulphuric acid of a number of methylnitrobenzenes show an excellent linear correlation with those for nitrations with nitronium hexafluorophosphate in nitromethane deduced by application of a theoretical mixing-reaction model.Differences between the two systems are not large, but appear to be in the direction showing the electrophile in sulphuric acid to be rather more reactive and more selective than in the organic solvent.
Aromatic Substitution. 48. Boron Trifluoride Catalyzed Nitration of Aromatics with Silver Nitrate in Acetonitrile Solution
Olah, George A.,Fung, Alexander P.,Narang, Subhash C.,Olah, Judith A.
, p. 3533 - 3537 (2007/10/02)
Benzene, alkylbenzenes, halobenzenes, and anisole were nitrated with silver nitrate/boron trifluoride in acetonitrile solution.Correlation of competitive rates with ?- and ?-complex stabilities indicated that the transition state of highest energy lies relatively early on the reaction coordinate.Data indicate that nitrations occur via a polarized complex of the nitrating agent, with the catalyst undergoing nucleophilic displacement by the aromatic substrate.
