Nitration solvent effects

NITRATIONS WITH NITRONIUM IONS THE GENERAL CASE 6.2.1 Evidence from solvent effects... 

Evidence in favour of the molecular nitrating species is the relative insensitivity of rate to solvent effects, rates differing in nitromethane by only a factor of 6... 

Distler, Blecher Lopex Explosives were patented safety expls consisting of nitro-xylenes as chief constituents. The nitro compds had varying amts of cumol, mesitylene xylene nitro constituents mixed with AN, other nitrates or KClOg or metal oxides. For example, if 12 parts nitrated solvent naphtha are intimately mixed with 88 parts of AN, a very insensitive expl is produced, which is unaffected by either shock or percussion which does not explode at 200° or in an open flame, but which has an extremely powerful shattering effect when suitably detonated Ref Colver (1918), p259... 

Extensive studies on hydrogen exchange in aqueous sulfuric acid on 1 -methylpyrazole,252 isoxazole,328 and isothiazole328 and their methylated derivatives252,328 have been reported, but calculated partial rate factors derived from treatment of the form of Eq. (12) do not tally with those observed. This emphasizes the contribution from interactions between donor and acceptor groups or solvent effects which also lead to breakdown in the interpretation of nitration results.83... 

Roberts and his associates (1954) re-examined the nitration of the halobenzenes using fuming nitric acid as the reagent in both acetic anhydride and nitromethane. These workers detected a significant solvent effect on the relative rate. Iodobenzene was nitrated by nitric acid in acetic anhydride at a rate 0.13 times that of benzene, in nitromethane this reagent provided a rate ratio of 0.22. 

Bonnesen, P. V., Sloop, F. V., Jr., and Engle, N. L. Stability of the Caustic-Side Solvent Extraction (CSSX) Process Solvent, Effect of High Nitrite on Solvent Nitration, ORNL Report ORNL/TM-2002/115, Oak Ridge National Laboratory, Oak Ridge, TN, July 2002. 

The anticatalytic effect of nitrous acid in nitration The effect of nitrous acid was first observed for zeroth-order nitrations in nitromethane ( 3.2).22 The effect was a true negative catalysis the kinetic order was not affected, and nitrous acid was neither consumed nor produced by the nitration. The same was true for nitration in acetic acid.23 In the zeroth-order nitrations the rate depended on the reciprocal of the square root of the concentration of nitrous acid Aobs = (a + b [HNOJatoioh)-1- First-order nitrations in the organic solvents follow a law of anticatalysis of the same form (but with different constants in the above equation). With both zeroth- and first-order nitrations a more powerful type of anticatalysis set in when higher (> o-i mol 1 1) concentrations of nitrous acid were present. 

Studies of Equilibria, Reactions, and Solvent Effects.—Lanthanide shift reagents have been found to be effective for phosphines and phosphoryl compounds, but not for thiophosphoryl compounds. - In a comparison of various shift reagents, europium nitrate hexadeuterium oxide (26) was found to give large shifts of 8 for phosphates and phosphonates. A contact contribution to the Sp shifts was established. When there are two possible sites for co-ordination, as in the aminophosphine (27), steric effects play an important role. Co-ordination occurs at nitrogen in (27 R = H) but at phosphorus in (27 R = Me). The n.m.r. parameters... 

Nitration and nitratation. Nitronium triflate is generated in situ from Bu NNOj and TfjO. Adamantane gives 1-nitro- or 1-nitratoadamantane on exposure to this reagent in nitromethane or dichloromethane, respectively. Thus, there is a marked solvent effect. 

Nitration in solvents other than water is to be preferred at times. In acetic acid for example, besides the advantages just spoken of, the solvent effect of the acetic acid may be of aid in increasing the concentration of the hydrocarbon. Such conditions as the hydrogen ion concentration of the mixture may also play a part and may be influenced favor-... 

There have been several experimental indications of the two-stage mechanism since it was first speculatively postulated by Lapworth (1901), e.g., the isolation of an intermediate in the electrophilic bromina-tion of l,l-di-(p-dimethylaminophenyl)ethylene by Pfeiffer and Wizinger (1928), and the interpretation of solvent effects in aromatic nitrations by Hughes et al. (1950). One might argue, however, that ethylene is not a good model for aromatic hydrocarbons and that solvent effects alone do not provide unequivocal evidence for a postulated mechanism. 

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