Nitrations alkenes, nitric acid

The authors of this work were concerned chiefly with additions to alkenes, and evidence about the mechanism of aromatic nitration arises by analogy. Certain aspects of their work have been repeated to investigate whether the nitration of aromatic compounds shows the same phenomena ( 5-3-6). It was shown that solutions of acetyl nitrate in acetic anhydride were more powerful nitrating media for anisole and biphenyl than the corresponding solutions of nitric acid in which acetyl nitrate had not been formed furthermore, it appeared that the formation of acetyl nitrate was faster when 95-98% nitric acid was used than when 70 % nitric acid was used. 

Bordwell and Garbisch71 contested this conclusion since they found that nitric acid in acetic anhydride prepared at —10 °C contained a much less effective nitrating species (the nitric acid could be recovered quantitatively) than when mixed at 25 °C and cooled to —10 °C (the nitric acid being then mostly unrecoverable). Further, these latter solutions reacted with alkenes to give predominantly cis addition products (nitro-acetates), whi h indicates association of the nitronium ion with some other species. It has been argued72 that this does not necessarily follow, since nitration of aromatics may involve a different... 

Alkenes can react with nitric acid, either neat or in a chlorinated solvent, to give a mixture of compounds, including v/c-dinitroalkane, jS-nitro-nitrate ester, v/c-dinitrate ester, /3-nitroalcohol, and nitroalkeneproducts. Cyclohexene reacts with 70 % nitric acid to yield a mixture of 1,2-dinitrocyclohexane and 2-nitrocyclohexanol nitrate. Frankel and Klager investigated the reactions of several alkenes with 70 % nitric acid, but only in the case of 2-nitro-2-butene (1) was a product identified, namely, 2,2,3-trinitrobutane (2). 

The reaction of fuming nitric acid with 2-methyl-2-butene (3) is reported to yield 2-methyl-3-nitro-2-butene (4). The reaction of alkenes with fuming nitric acid, either neat or in chlorinated solvents, is an important route to unsaturated nitrosteroids, which assumedly arise from the dehydration of /3-nitroalcohols or the elimination of nitric acid from /3-nitro-nitrate esters. Temperature control in these reactions is important if an excess of oxidation by-products is to be avoided. 

Solutions of acetyl nitrate, prepared from fuming nitric acid and acetic anhydride, can react with alkenes to yield a mixture of nitro and nitrate ester products, but the /3-nitroacetate is usually the major product. ° Treatment of cyclohexene with this reagent is reported to yield a mixture of 2-nitrocyclohexanol nitrate, 2-nitrocyclohexanol acetate, 2-nitrocyclohexene and 3-nitrocyclohexene. °/3-Nitroacetates readily undergo elimination to the a-nitroalkenes on heating with potassium bicarbonate. /3-Nitroacetates are also reduced to the nitroalkane on treatment with sodium borohydride in DMSO. ... 

NITRATION OF ALKENES AND ALKYNES WITH CONCENTRATED NITRIC ACID... 

Acetyl nitrate (or nitryl acetate, Ac0NO2), prepared from nitric acid and acetic anhydride, reacts with simple acyclic and cyclic alkenes to give complex mixtures of nitro acetates, nitro nitrates and nitroalkenes, which are often difficult to separate12 103, The reaction with unsubstituted cycloalkenes was recently reexamined and a complex mixture of products, including allylic and homoallylic nitroalkenes, 1,2-, 1,3- and 1,4-nitro acetates, and 1,4-nitro nitrates, was identified104. These experimental observations are best accommodated by the proposal, supported by theoretical calculations, that the initial reaction of acetyl nitrate with alkene substrates is a [2 + 2] addition of the nitryl cation to the C-C double bond to form a cyclic cationic intermediate. 

Nitration of alkenes and allcynes with concentrated nitric acid... 

Nitration of Alkenes. Alkenes may also be nitrated by nitric acid. This reaction has been exploited in tbe synthesis of a number of steroid derivatives. Fuming nitric acid converts cholesteryl acetate to 6-nitrocbolesteryl acetate in good yield (eq 5). The nitration of the more highly functionalized dienyl acetate (eq 6) provides the corresponding nitro steroid. Treatment of 1,1-dichloro-2-fluoroethylene with nitric acid in concentrated sulfuric acid provides fluoronitroacetyl chloride in 16% yield. 2-Sulfolenes have also been nitrated. ... 

Oxalic and malonic acids, as well as a-hydroxy acids, easily react with cerium(IV) salts (Sheldon and Kochi, 1968). Simple alkanoic acids are much more resistant to attack by cerium(IV) salts. However, silver(I) salts catalyze the thermal decarboxylation of alkanoic acids by ammonium hexanitratocerate(IV) (Nagori et al., 1981). Cerium(IV) carboxylates can be decomposed by either a thermal or a photochemical reaction (Sheldon and Kochi, 1968). Alkyl radicals are released by the decarboxylation reaction, which yields alkanes, alkenes, esters and carbon dioxide. The oxidation of substituted benzilic acids by cerium(IV) salts affords the corresponding benzilic acids in quantitative yield (scheme 19) (Hanna and Sarac, 1977). Trahanovsky and coworkers reported that phenylacetic acid is decarboxylated by reaction with ammonium hexanitratocerate(IV) in aqueous acetonitrile containing nitric acid (Trahanovsky et al., 1974). The reaction products are benzyl alcohol, benzaldehyde, benzyl nitrate and carbon dioxide. The reaction is also applicable to substituted phenylacetic acids. The decarboxylation is a one-electron process and radicals are formed as intermediates. The rate-determining step is the decomposition of the phenylacetic acid/cerium(IV) complex into a benzyl radical and carbon dioxide. 

Nitric acid acetic anhydride Nitrations with acetyl nitrate 2-Acetoxynitro compounds and 3-nitroalkenes from alkenes... 

Mixture of nitric and sulfuric acid (mixed acid) used extensively in nitration of aromatic hydrocarbons, is generally unsuitable for nitration of alkanes, since primary nitroalkanes are rapidly hydrolyzed by hot sulfuric acid and secondary and tertiary nitroalkanes form tars (in all probability via rapid alkene-forming elimination and subsequent polycondensation, polymerization, etc.). It is, however, significant to point out that it is not necessarily the lack of reactivity of paraffins with mixed acid that makes the nitration of saturated hydrocarbons unsuitable, but that fast secondary reactions of any nitro products formed (as well as oxidative side reactions) can take place. This difficulty can be, at least in part, overcome by using preformed nitronium salts as nitrating agents. 

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