Activated 2,4-dinitrophenyl

Viologens, V2+, Ve2+, 2V2+, and PV2+ are prepared by the Menschutkin reaction of the corresponding bipyridines with alkylhalide (or dihalide) as in Scheme 4.9 VArylviologens are prepared by sequential reactions ending with the replacement of an activated 2,4-dinitrophenyl substituent with arylamine (Scheme 5).10... 

If the fV-aryl group is strongly activated, then it can be removed in nucleophilic substitution reactions in which the azole anion acts as leaving group. Thus l-t2,4-dinitrophenyl)pyrazole reacts with N2H4 or NaOMe. 

Aryl halides with a halogen activated by electron-withdrawing groups react with pyrrolidine enamines of cyclic ketones (68) to give the a-arylated ketones after hydrolysis. The enamine (28) with 2,4-dinitrochlorobenzene gave an excellent yield of 2(2,4-dinitrophenyl)cyclohexanone (88). The... 

Ar-Cl), as compared to their reactivities with an anionic nucleophile. The reaction of 108 with trimethylamine at the pam-posi-tion contrasts with that of 2,4-dichloronitrobenzene which reacts with a large variety of nucleophiles at the oriA.o-position. Compared to the (2,6-dinitrophenyl)trimethylammonium ion, steric hindrance to activating resonance would be much less in 2-trimethyl-ammoniopyrimidine. 

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). 

GPT activity was determined by the colorimetric method with 2,4-dinitrophenyl-hydrazine (refs. 12,13). Results were calculated on the basis of the calibration prepared from pyruvate, made for each series of determinations. The amount of pyruvate (pmol/cm ) formed during 1 h incubation at 37 °C was assumed as the activity unit. 

We have also investigated other oxalate esters as a potential means to improve the efficiency. The most commonly used oxalates are the 2,4,6-trichlorophenyl (TCPO) and 2,4-dinitrophenyl (DNPO) oxalates. Both have severe drawbacks namely, their low solubility in aqueous and mixed aqueous solvents and quenching of the acceptor fluorescence. To achieve better solubility and avoid the quenching features of the esters and their phenolic products, we turned to difluorophenyl oxalate (DFPO) derivatives 5 and 6 (Figure 14). Both the 2,4- and the 2,6-difluoro esters were readily synthesized and were shown to be active precursors to DPA chemiluminescence. In fact, the overall efficiency of the 2,6-difluorophenyl oxalate 5 is higher than for TCPO in the chemical excitation of DPA under the conditions outlined earlier. Several other symmetrical and unsymmet-rical esters were also synthesized, but all were less efficient than either TCPO or 2,6-DFPO (Figure 14). 

Yet another situation is observed in the 2,4-dinitrophenyl phosphate dianion. A significant effect of amines on the rate of decomposition is admittedly observed however, typical 2nd order kinetics, lower enthalpy of activation compared with spontaneous hydrolysis, and strongly negative AS values (see Table 3) indicate an Sn2(P) reaction. Surprisingly, the reaction rate remains unaffected by the basicity of the amine, even when its pKa value changes by 8 units. 

Hydrolyses of p-nitrophenyl and 2,4-dinitrophenyl sulfate are accelerated fourfold and eightfold, respectively, by cycloheptaamylose at pH 9.98 and 50.3° (Congdon and Bender, 1972). These accelerations have been attributed to stabilization of the transition state by delocalization of charge in the activated complex and have been interpreted as evidence for the induction of strain into the substrates upon inclusion within the cycloheptaamylose cavity. Alternatively, accelerated rates of hydrolysis of aryl sulfates may be derived from a microsolvent effect. A comparison of the effect of cycloheptaamylose with the effect of mixed 2-propanol-water solvents may be of considerable value in distinguishing between these possibilities. 

As mentioned in Section II. C., the concerted bond cleavage of 1.2-dioxetane derivatives has been proposed to be of general importance in respect of the excitation step of a large number of chemiluminescence reactions. The first experimental results concerning simple dioxetanes were obtained by M. M. Rauhut and coworkers in their work on activated oxalic ester chemiluminescence 24>. From experimental data on the reaction of e.g. bis (2.4-dinitrophenyl)oxalate with hydrogen peroxide in the presence of rubrene, they concluded that 1.2-dioxetanedione... 

J Steffans et al., 1973, 1975. The reference reaction is the attack of the anion of a carboxylic acid of pK, 3.91 on methyl 2,4-dinitrophenyl phosphate at 39° (Kirby and Younas, 1970). The intramolecular reaction is corrected for the better leaving group using y LO=1.26 (Khan et al., 1970), and to 39° using the activation energy measured for the intermolecular reaction with acetate (Kirby and Younas, 1970). 

For dinitro-substituted substrates, it has been recently shown that activation in 2,4-dinitrophenyl substrates is mainly due to the mesomeric effect of the 4-nitro group, thus reducing the electron density at the reaction site83. However, another important feature of highly polarizable groups, such as a nitro group in the ortho position, has been considered to be the field effect101. 

K. Yoshida, Y. Kurono, Y. Mori, K. Ikeda, Esterase-Like Activity of Human Serum Albumin. V. Reaction with 2,4-Dinitrophenyl Diethyl Phosphate , Chem. Pharm. Bull. 1985, 33, 4995-5001. 

A dissociative elimination-addition pathway has also been proposed to account for the kinetics of alkaline hydrolysis of 2,4-dinitrophenyl 4 -hydroxyphenylpropionitrile in 40% (v/v) dioxane-water, although participation of the associative Bac2 mechanism cannot be ruled out since it may be facilitated by the electronic effect of the triple bond. Formation of intermediate (15), having a conjugated and cumulated double-bond system, should favour the ElcB mechanism and thereby account for the contrasting entropies of activation found for hydrolysis of (14) and the corresponding 4 -methoxyphenylpropionate. 

Example 7 the bis(2,4-dinitrophenyl)phosphoroamidite which can be prepared by a standard procedure reacts with alcohols in a non-selective way which leads to a mixture of products [28]. From a mechanistic point of view this result is consistent with spontaneous displacement of a 2,4-dinitro-phenoxy group in the reaction with alcohol which liberates free DNP. The latter activates the amino group allowing further ligand exchange. However if phosphitylation by the bis(2,4-dinitrophenyl)phosphoroamidite is performed in the presence of one equivalent of triethylamine, high chemoselec-tivity is observed, and the nucleoside (2,4-dinitrophenyl)phosphoramidite is formed in over 92% yield. 

Pentachlorothiophenol was formed Iji vitro from S-(PCP)Cys by a C-S lyase enzyme from onion root. This enzyme was active with S-(PCP)Cys, S-(2,M-dinitrophenyl)cysteine, and the cysteine conjugate of propachlor. A C-S lyase from Alblzzla lophanta was previously shown to utilize a broad range of cysteine derivatives (2U). 

Alkenes can be aminated172 in the allylic position by treatment with solutions of imido selenium compounds R—N=Se=N—R.173 The reaction, which is similar to the allylic oxidation of alkenes with Se02 (see 4-4), has been performed with R = f-Bu and R = Ts. The imido sulfur compound TsN=S=NTs has also been used.174 In another reaction, compounds containing an active hydrogen can be converted to primary amines in moderate yields by treatment with 0-(2,4-dinitrophenyl)hydroxylamine.175... 

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). 

Only highly activated aryl halides react with pyridines. Thus, 2,4-dinitrochlorobenzene with pyridine forms l-(2,4-dinitrophenyl)pyridinium chloride active heteroaryl halides such as 2-chloropyrimidine react similarly. To phenylate pyridine, diphenyliodonium ions are needed Ph2I+BF4 + pyridine —>> 1-phenylpyridinium BF4" + Phi. This reaction may involve initial electron transfer. 

Analogous methyl azidoformate forms with norbornene a thermal unstable triazoline.251 The decomposition products are 40% aziridine and 55% imide. Furthermore it has been observed that the rate of nitrogen evolution of the triazoline from methyl azidoformate increases threefold when triglyme and 20-fold when dimethyl sulfoxide are substituted for 1,1-diphenylethane as solvents. This fact supports a betaine intermediate in the thermal decomposition reaction. The triazoline from 2,4-dinitrophenyl azide and norbornene could just be isolated, but from picryl azide only the aziridine was obtained.252-254 Nevertheless, the high negative value of the activation entropy (—33.4 eu) indicates a similar cyclic transition state for both reactions. 

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