2.4- Dinitrophenyl acetate

Ethyl bis-(2,4-dinitrophenyl) acetate (indicator) the stock solution is prepared by saturating a solution containing equal volumes of alcohol and acetone with the indicator pH range colorless 7.4-9.1 deep blue. This compound is available commercially. The preparation of this compound is described by Fehnel and Amstutz, Ind. Eng. Chem., Anal. Ed. 16 53 (1944), and by von Richter, Ber. 21 2470 (1888), who recommended it for the titration of orange- and red-colored solutions or dark oils in which the endpoint of phenol-phthalein is not easily visible. The indicator is an orange solid which after crystallization from benzene gives pale yellow crystals melting at 150-153.5°C, uncorrected. 

Ethyl bis-(2,4-dinitrophenyl)acetate [5833-18-1 ] M 358.3, m 150-153 . Crystd from toluene as pale yellow crystals. 

Pyridine groups show the nucleophilic catalytic activity. Letsinger and Saveride122 hydrolyzed 2,4-dinitrophenyl-acetate, 72 (DNPA) and 3-nitro-4-acetoxybenzene-sulfonate, 66 (NABS) with partially quaternized poly-4-vinylpyridine (QPVP). 

The effect of mixtures of surfactants and polyelectrolytes on spontaneous, water-catalysed hydrolysis (Fadnavis and Engberts, 1982) was mentioned in Section 4, but mixtures of functionalized polyelectrolytes and cationic surfacants are effective deacylating agents (Visser et al., 1983). Polymerized isocyanides were functionalized with an imidazole group and the deacylation of 2,4-dinitrophenyl acetate in the polyelectrolyte was speeded by addition of single or twin chain quaternary ammonium ion surfactants, up to a plateau value. Anionic surfactants had essentially no effect. It is probable that the cationic surfactants accelerate the reaction by increasing the deprotonation of the imidazole groups. 

The initial study of the La3 +-catalyzed methanolysis of carboxylate esters163 reported the apparent second-order rate constant for La2 + ( OCH3)2-catalyzed methanolysis of some representative examples of aryl esters (2, 5 and 2,4-dinitrophenyl acetate (14)), phenyl benzoate (15) and three aliphatic esters, ethyl acetate, isopropyl acetate (16) and tert-butyl acetate (17). Given in Table 6 are the rate constants for the La3+ and methoxide-catalyzed methanolysis of these esters along with... 

Reference reaction is attack on 2,4-dinitrophenyl acetate by RCOO- of pK, 2.4 (k2 = 3.3 x 10-3 s-1 based on a short extrapolation using P = 1.0 Jencks and Gilchrist, 1968). The reaction measured is the subsequent hydrolysis of the mixed anhydride the observed value thus sets only a lower limit for EM (Fersht and Kirby, 1967b, 1968a)... 

N 16.09% crysts (from glac acet acid or benz), mp 173—81°. It was prepd by nitrating diphenylmediane with nitric acid (d 1.53) 5 coned sulfuric acid (Ref 1) and by decarboxylation of ethyl bis(2,4-dinitrophenyl-acetic acid (Ref 2). No expl props are reported... 

Consider the hydrolysis of 2,4-dinitrophenyl acetate (DNPA), a compound for which the acid-catalyzed reaction is unimportant at pH > 2 (see Fig. 13.8). In a laboratory class, the time course of the change in concentration of DNPA in homoge-... 

Buckingham, D. A., and C. R. Clark, Metal-hydroxyde-promoted hydrolysis of activated esters. Hydrolysis of 2,4-dinitrophenyl acetate and 4-nitrophenyl acetate , Aust. J. Chem., 35,431-436 (1982). 

Fig. 13. Approximate pH-rate profiles for hydrolysis of A, ethyl acetate B, phenyl acetate and C, 2,4-dinitrophenyl acetate, all at 25°C. Data from Skrabal188, Kirsch and Jencks300 and Tommila...

This sensitivity to substitution of neutral hydrolysis means that the pH-independent reaction gradually becomes more important than the hydroxide reaction at the high pH end of the region, and becomes much more rapidly more important than acid-catalyzed hydrolysis at low pH. Thus from Fig. 13, the acid-catalyzed reaction can be seen to be significant for the hydrolysis of ethyl acetate between pH 4 and 5, and for phenyl acetate about pH 2 but for 2,4-dinitrophenyl acetate the acid-catalyzed reaction is not detectable at pH 1, and is presumably important only in relatively strong acid. It seems certain that this fast neutral hydrolysis is at any rate a partial explanation for the low efficiency of acid catalysis in the hydrolysis of very weakly basic esters, such as the trifluoroacetates and oxalates, in moderately concentrated acid (see p. 145). 

A second approach demonstrating the existence of the intermediate anhydride is exemplified by the aniline trapping technique of Gold el al.2si. Low concentrations of added amines, particularly aniline, react much more rapidly with the anhydride than does the solvent. Thus, if the hydrolysis of, for example, 2,4-dinitrophenyl acetate catalyzed by acetate ion, is carried out in the presence of low concentrations of aniline, acetanilide is formed281, viz. 

The demonstration that the mechanism of catalysis may change to general base catalysis for weakly basic nucleophiles further complicates the interpretation of such plots. The most useful generalizations that can be extracted from the data for aryl acetates are illustrated in Fig. 18. This is a plot of data for the reactions of oxyanions with three esters, phenyl, 4-nitrophenyl, and 2,4-dinitrophenyl acetates under the same conditions. Only nucleophiles showing normal reactivity are included points for hydro, de ion and a-effect nucleophiles have been excluded. The data are those of Jencks and Gilchrist283, who published a slightly different version of this plot. 

Data for the reactions of several cyclic tertiary amines with phenyl, 4-nitro-phenyl and 2,4-dinitrophenyl acetates, at 25°C and ionic strength 1.0, appear in Table 40, and as a Bronsted plot in Fig. 20. The usual irregularities of such plots for nucleophilic attack are evident. Linear relationships between log k and pKa are generally found for groups of compounds of closely similar structure, as for the substituted pyridines in Fig. 20. The data for the two tricyclic amines fall on separate curves, and the points for imidazole clearly fall on neither of the first two sets of lines. The separate lines for the reactions of particular classes of nucleophile are approximately parallel, as is usually found. 

Artificial catalysts have also been incorporated into amphiphilic structures (Guler and Stupp, 2007). These catalysts were imidazolyl-functiona-lized peptides, which demonstrate a greater rate of 2,4-dinitrophenyl acetate hydrolysis when immobilized on the peptide amphiphile than the rate observed when the same enzyme is present in solution. Although the density of the enzymes on the fiber surface has not been established, the authors attribute the increase in enzymatic activity to the likely concentration of enzyme along the fiber surface, and this study illustrates one of the advantages of enzyme immobilization. 

PY-PY cooperation. In the study of the hydrolysis of the neutral substrate, 2,4-dinitrophenyl acetate, by poly(4-vinylpyridine), the hydrolysis rate profile shows an upward curvature as the fraction of the neutral pyridine residue increases (41). 

Second-Order Rate Coefficients" for Hydrolysis of 2,4-Dinitrophenyl Acetate in Water1 "... 

A more recent study [265] is concerned with the action of a large number of nucleophiles of different types on the hydrolyses of phenyl acetate, p-nitrophenyl acetate, 2,4-dinitrophenyl acetate, and 1-acetoxy-4-methoxypyridinium ion. 

The [Co(NH3)50H] -promoted hydrolysis (and that promoted by other exchange-labile anc non-labile metal hydroxide species) of 2,4-dinitrophenyl acetate and 4-nitrophenyl acetate haf been studied in some detail." Kinetic studies (25 °C, / = 1.0 M) show that these reactions follov shallow Bronsted slopes (/3 = 0.33 and 0.40) for the two substrates which extend over a range o lO " in nucleophile basicity. A correlation is reported which allows the prediction of reactioi... 

Oximes of type 4, prepared by nitrosation of 2,6- and 2,4-dinitrophenyl-acetic acid derivatives, cyclize in strong base, e.g., sodium hydride in 1,2-dimethoxyethane, to indoxazene-3-carboxylic acid derivatives, e.g., 5 (R = OMe or NHAr).8-10... 

Three papers in the same line of work have been published from Kopple s school. Kopple and Nitecki (161) found that in the hydrolyses of PNPA and 2,4-dinitrophenyl acetate by Cyclo-(Gly-His-Gly-Tyr-Gly-Gly), the acylation by the sub-arate occurs fira at the histidyl imidazole group, and then the acyl group migrates intramoleculaily to the phenolic oxygen of the tryosyl teadue. This reaction route is different from that of a-chymotrypsin, but it is quite interesting to show that the functional groups of the cyclic hexapeptide interact mwe or less. 

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