ipso Nitration. XXVI. Nitration of 1,2-dimethyl-4-nitrobenzene. Formation and reactions of adducts

Abstract

. Nitration of 1,2-dimethyl-4-nitrobenzene in a mixture of acetic anhydride and trifluoroacetic anhydride gives the diastereoisomers of 4,5-dimethyl-2,4-dinitrocyclohexa-2,5-die acetate (50%), in addition to the 1,2-dimethyldinitrobenzenes. In moderate and more strongly acid conditions the adduct gives 4-nitro-, 3,4-dinitro-, and 3,5-dinitro-o-xylene. In neutral and weakly acid solutions 4-nitro-and 3,5-dinitro-o-xylene are formed by a radical and a sigmatropic pathway. ' The adduct reacts facilely with nucleophiles by allylic substitution to give a 5,6-dimethyl-6-nitrocyclohexa-2,4-dienyl derivative which, in many instances, undergoes a second allylic substitution to a new 4,5-dimethyl-2,4-dinitrocyclohexa-2,5-die derivative. Depending on the nature of the introduced substituent, these 2,4-and 2,5-dienyl products may eliminate nitrous acid, under the reaction conditions, to give the corresponding aromatic compound. The dienyl acetates undergo acid-catalysed transesterification to the corresponding dienols. ALFRED FISCHER, GEORGE N. HENDERSON et LOKANATHAN M. IYER. Can. J. Chem. 63, 2390Chem. 63, (1985. La nitration du dimtthyl-1,2 nitro-4 benzkne dans un mtlange d'anhydride acCtique et d'anhydride trifluoroacCtique conduit, en plus des dimtthyl-1,2 dinitrobenzknes, a la formation des diasttrtoisomkres de I'acktate du dirnkthyl-4,5 dinitro-2,4 cyclohexadikne-2,5 yle (50%). Dans des milieux modtrtment et plus forternent acides, I'adduit conduit aux nitro-4, dinitro-3,4 et dinitro-3,5 o-xylknes. Dans des milieux neutre ou Itgkrement acide, les nitro-4 et dinitro-3,5 o-xylknes se foment par un mtcanisme radicalaire suivi d'une transposition sigmatropique. Par substitution allylique, I'adduit rtagit facilement avec les nucltophiles et il conduit un dtrivt dimtthyl-5,6 nitro-o cyclohexadikne-2,4 yle qui, dans plusieurs cas, subit une deuxikme substitution allylique pour conduire i un nouveau dtrivt dirntthyl-4,5 dinitro-2,4 cyclohexadikne-2,5 yle. Dtpendant de la nature des substituants introduits, ces produits dikne-2,4 (ou -2,5) yles peuvent Climiner de I'acide nitreux dans les conditions de la rkaction &in de conduire i la formation du compost aromatique correspondant. Les acttates de dienyles subissent des transesttrifications acido-catalystes conduisant aux ditnols correspondants.[Traduit par le journal]Nitration at a substituted position, ipso nitration (3), is competitive with nitration at an unsubstituted position in many aromatic compounds. The resulting ipso-nitrocyclohexadienyl cation is captured as a relatively stable acetate ester in acetic anhydride and can be isolated. In previous work the adduct from 3,4-dimethybenzonitrile has been obtained (4). The nitro group has directing and deactivating effects similar to those of the cyano group and it was anticipated that nitration of 1,2-dimethyl-4-nitrobenzene (4-nitro-o-xylene) would occur at the 2 position, ipso to methyl, to form an adduct. Results and discussion4-Nitro-o-xylene did not react at all when it was treated with nitric acid (5 mol ratio) in ...

ipso Nitration. XXVIII. Nitration of 4-substituted toluenes: 1,2 adducts

“…For preparative nitrations the reaction temperature was -40°C and trifluoroacetic anhydride was added to increase the activity of the nitrating mixture (4) in the cases of the less reactive substrates (X = F, C1, I, NHAc). Reaction mixtures were neutralized by the addition of aqueous ammonia at low temperature or by addition to cold aqueous sodium bicarbonate followed by stirring for 1.5 h. Generally the composition of the reaction product isolated after work-up was the same as that present in the reaction mixture prior to 'For part XXVI1.…”

“…All fractions were collected in flasks cooled to -78"C, and evaporated below -40°C. Elution, first with 60% ether -petroleum ether and then with 80% ether -petroleum ether, gave 4 …”

“…Nitration in acetic anhydride of aromatic compounds in which a substituted position is activated often leads to the formation of nitronium acetate adducts in which the nitro group is attached to the activated substituted site (3,4). There are many examples in the polymethylbenzenes and p-alkyltoluenes (5)(6)(7)(8)(9)(10)(11).…”

A Fast, High-Yield Preparation of Vicinal Dinitro Compounds Using HOF·CH3CN

“…We reacted 4,5-dimethyl-1,2-phenylenediamine ( 13 ) with HOF·CH 3 CN for 4 min at −15 °C and obtained 4,5-dimethyl-1,2-dinitrobenzene ( 14 ) in 87% yield. This compound was previously described as a low-yield byproduct during the nitration of 1,2-dimethyl-4-nitrobenzene .…”

“…This compound was previously described as a low-yield byproduct during the nitration of 1,2-dimethyl-4-nitrobenzene. 23 The presence of an electron-withdrawing group on the aromatic ring reduces the nucleophilicity of the amino nitrogen atoms, and the reaction of 3,4-diaminobenzophenone (15) proceeded with 55% yield only to give 3,4dinitrobenzophenone (16). 24 An additional factor contributing to the reduced yield of this particular reaction is the slower, but still noticeable, competitive Baeyer-Villiger reaction with the HOF‚CH 3 CN.…”