2.4- Dinitrofluorobenzene reactions

The dinitrophenyl group has been used to protect the imidazole — NH group in histidines (45% yield)" by reaction with 2,4-dinitrofluorobenzene and potassium carbonate. Imidazole —NH groups, but not a-amino acid groups, are quantitatively regenerated by reaction with 2-mercaptoethanol (22°, pH 8, 1 h)." The 2,4-... 

Treatment of 228 with 2,4-dinitrofluorobenzene (227) provided 230. The assumed intermediate A -benzoyl-A -(2,4-dinitrophenyl)-A -phenylhydrazine (229) underwent the denitrocyclization reaction in its enol form (80JOC3677). Similar reaction is probably involved also in the thermal cyclization of antraquinone 231 leading to 232 (Scheme 35), which took place even during attempts to crystallize the compound (60T107). 

Nucleophilic aromatic substitution is much less common than electrophilic substitution but nevertheless does have certain uses. One such use is the reaction of proteins with 2,4-dinitrofluorobenzene, known as Sanger s reagent, to attach a "label" to the terminal NH2 group of the amino acid at one end of the protein chain. 

This characteristic dependence of rate on catalyst concentration was first observed by Bunnett and Randall28 for the reaction of 2,4-dinitrofluorobenzene... 

Bifunctional catalysis has also been observed by Pietra and Vitali35 for a more typical nucleophilic aromatic substitution reaction, that of 2,4-dinitrofluorobenzene and piperidine in benzene. For this reaction triethylamine does not have an... 

It has also been argued10,40 that the second mechanism (rapid, reversible interconversion of II and IV) cannot be general. The basis for this contention is the fact that electrophilic catalysis is rare in nucleophilic aromatic substitution of non-heterocyclic substrates, an exception being the 2000-fold acceleration by thorium ion of the rate of reaction of 2,4-dinitrofluorobenzene with thiocyanate... 

Fluorobenzene-type compounds have been used as functional groups in homobifunctional crosslinking agents (Chapter 4, Section 4). Their reaction with amines involves nucleophilic displacement of the fluorine atom with the amine derivative, creating a substituted aryl amine bond (Reaction 9). Detection reagents incorporating reactive aryl chemistry include 2,4-dinitrofluorobenzene and trinitrobenzenesulfonate (Eisen et al., 1953). These compounds form... 

The enhanced nucleophilicity in the cationic micelle is similarly expressed in the reaction with 2,4-dinitrofluorobenzene and vitamin B12 (Chaimovich et al., 1975 Nome and Fendler, 1977). In general, the extent of the rate increase observed in the thiolate reaction is somewhat smaller than that in oxyanionic reactions. This may be an important clue for elucidating the activation mechanism of the thiolate reaction. 

FIGURE 1. Diagram to show the effect of the increase in the initial concentration value of amine on the rate of substitution expressed as a second-order rate coefficient. Indicative [RNFLlo values and kjbs values are from reactions between 2,4-dinitrofluorobenzene and n-butylamine in toluene259... 

Values of N+ for morpholine and piperidine in methanol solution were obtained by taking the average value of N+ determined by fitting the rate constants for the reactions of these nucleophiles with 2,4-dinitrofluorobenzene, 2,4-dinitrochlorobenzene, 2,4-dinitrobromobenzene and 2,4-dinitroiodobenzene, to plots of log k against N+ (using the data reported in Reference 80c). Data for the reactions of these substrates with azide ion were excluded from the correlation lines for the purpose of calculating these N+ values. 

FIGURE 12. Reaction rates, kA(f), of DNF (2,4-dinitrofluorobenzene) with aniline in A acetonitrile (xlO4) ethyl acetate (xlO4) A chloroform (xlO7) and toluene (xlO7) as a function of [aniline] O in toluene (5 x 104) as a function of [pyridine]190... 

In contrast, the 0-aryl derivative of Af-methyl-6-(hydroxyamino)-l,3-dimethylpyrimi-dine-2,4(1/7,3i7)-dione 44, prepared by reaction with 2,4-dinitrofluorobenzene (DNFB), yields the corresponding barbiturate 45 by a spontaneous [3,3]-sigmatropic rearrangement (equation 14). 

Amine 212 was also coupled with peptides [233], acetic anhydride [215, 234], dinitrobenzoyl chloride [235] or a ferrocene carboxylic add chloride [215, 236] in good yields. Reaction with dinitrochlorobenzene [237] or dinitrofluorobenzene... 

Dienes, 11 addition to, 194-198 cisoid conformation, 197, 350 conjugated, 11 Cope rearrangement, 354 cycUsation, 346 cycloaddition to, 348 Diels-Alder reaction, 197, 349 excited state, 13 heat of hydrogenation, 16,194 isolated, 11 m.o.s of, 12 polymerisation, 323 Dienone intermediates, 356 Dienone/phenol rearrangement, 115 Dienophiles, 198, 350 Digonal hybridisation, 5 Dimedone, 202 Dimroth s Et parameter, 391 solvatochromic shifts, 391 solvent polarity, 391 Y and,392 Dinitrofluorobenzene proteins and, 172... 

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