Nitration of 3,4-Dimethylacetophenone and 3,4-Dimethylbenzophenone. Formation and Rearomatization of Adducts

Fischer, Alfred; Greig, C. C.; Röderer, Rolf

doi:10.1139/v75-222

Cited by 10 publications

(4 citation statements)

References 7 publications

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“…Steady-state treatment of the dependence of the yields of cyclized products from each radical on initial stannane concentration enabled kc/kt to be calculated,2 9 where kc represents the rate constant for total cyclization. The rate constant for hydrogen atom transfer from stannane, k4, is expected6 to have a value of ~106 sec-1.…”

Section: Similar Resultsmentioning

confidence: 99%

Preferential cis cyclization of 6-hepten-2-yl and related radicals. Example of orbital symmetry control

Beckwith¹,

Blair²,

Phillipou³

1974

J. Am. Chem. Soc.

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Section: Similar Resultsmentioning

confidence: 99%

Preferential cis cyclization of 6-hepten-2-yl and related radicals. Example of orbital symmetry control

Beckwith¹,

Blair²,

Phillipou³

1974

J. Am. Chem. Soc.

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“…Striking examples arise from nitrations with solutions prepared from nitric acid and acetic anhydride, reagents for which there is still doubt about the identity of the electrophile.7 All involve intermediates of the type W;R, where R is methyl or some related hydrocarbon side chain. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] Examples are the stereoisomers la and lb from o-xylene.8,9 The position which captures acetate can also be substituted, as in the adducts from p-xylene9,20 and 3,4-dimethylanisole.15 li JJi Other nucleophiles such as the nitrate ion can capture Wi's. 13 Acidolysis of nitroacetates of the kind mentioned regenerates the W; which can attack reactive aromatics; loss of nitrous acid then gives biaryls.17,21…”

Section: Consequences Of Ipso Attackmentioning

confidence: 99%

Ipso attack in aromatic nitration

Moodie¹,

Schofield²

1976

Acc. Chem. Res.

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Aromatic Nitration 287ate), the necessary internal return results in insignificant oxygen ~c r a m b l i n g .~~ If ion pairs formed under solvolytic conditions undergo rearrangement, attack by an added nucleophile, although rate limiting, must always suppress rearrangement20~38kv3Q since no example of skeletal rearrangement accompanying second-order substitution has ever been reported, even for the potentially favorable neopentyl case.75 These ion pairs must be "more intimate than intiand must thus behave like polarized RX molecules. This is what we believe they are, but we see no reason to call them ion pairs, for in such terms a methyl iodide molecule could be regarded as an ion pair by virtue of the C-I bond polarity.43 This would be fine in the present context since mechanistic distinction would be lost, but chemical problems cannot be solved by such semantic extensions, although we agree with the view that genuine ion pairs may possess a degree of covalent character. In fact, the postulation of ion-pair intermediates (and their formation with solvent assistance) in simple primary and secondary substrate solvolysis in reasonably nucleophilic solvents may be incorrect, and sN2 solvent attack may be the favored mode. We know of no evidence that demands intermediates in such simple solvolyses, and specifically intermediates formed without solvent or neighboring group assistance. If so, (74) A. F. Diaz, I. Lazdins, and S. Winstein, J. Am. Chern. Soc., 90, 1904 (1968). If such scrambling were detected it would still be difficult to prove that it did not occur in a mechanistic blind alley (see also ref 5). (75) Reference 1, p 742. See also G. M. Fraser and H. M. R. Hoffmann, Chem Cornrnun, 561 (1967). (76) Reference 7, p 366.there is no reason why they should intervene in nonsolvolytic substitutions with stronger nucleophiles.In summary, the "extra-intimate ion pair" is in our opinion a polarized RX molecule. The polarization arises from approach of N-, and the energy buildup needed to cross the sN2 potential barrier arises largely from solvent re~rganization~~ attendant on the merging of the original Nand RX solvation shells. We deliberately choose these words to mimic Bordwell's description of an ion-sandwich intermediate,26 noting that Bordwell himself has not been definite in postulating actual intermediacy. His results could equally well be rationalized in terms of a loose sN2 transition state (4) for his tertiary substrate and a tighter transition state (3) for the model primary system.In conclusion, the verdict which must be passed on Sneen's proposed universal unification of s N 1 and SN2 mechanisms is one which is unique to the Scottish legal system, and so I turn to the words of my forbears in stating "not proven". A more positive conclusion is not presently available, but we note that strides in this direction are being made through heavy atom isotope effect studies.45 I warmly thank Professors P. B. D. de la Mare, J. M. Harris, P. v. R. Schleyer, J. Seyden-Penne, R. A . Sneen, and J. Warkentin for ex...

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“…The effect of the substituent in determining the reaction product of reactions camed out at a fixed acidity is nicely illustrated by reactions in trifluoroacetic acid. Whereas diene 1 am gives the (di)nitroxylenes by loss of acetic acid, dienes lcm, ldm, and l e m give the aryl acetate by loss of nitrous acid (4,20). Reaction of lam with hydrogen bromide in ether (which was not investigated in detail by glc) gave 4-nitro-o-xylene as the major product.…”

Section: Reactions Of Diene Lam With Acidsmentioning

confidence: 99%

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

Fischer¹,

Henderson²,

Iyer³

1985

Can. J. Chem.

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. 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 ...

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Nitration of 3,4-Dimethylacetophenone and 3,4-Dimethylbenzophenone. Formation and Rearomatization of Adducts

Cited by 10 publications

References 7 publications

Preferential cis cyclization of 6-hepten-2-yl and related radicals. Example of orbital symmetry control

Preferential cis cyclization of 6-hepten-2-yl and related radicals. Example of orbital symmetry control

Ipso attack in aromatic nitration

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

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