Dinitrophenolate anions

To test the first hypothesis, solutions of 3,5-dinitroanisole and hydroxide ions were flashed and the absorption spectra at different time intervals after excitation were compared. The absorption ( max 400-410 nm) that remains after all time-dependent absorptions have decayed can be shown to be due to 3,5-dinitrophenolate anion, the photosubstitution product of 3,5-dinitroanisole with hydroxide ion. When the absorption band of the 550-570 nm species is subtracted from the spectrum of the solution immediately after the flash, there remains an absorption at 400-410 nm, which can also be ascribed to 3,5-dinitrophenolate anion. The quantity of this photoproduct does not increase during the decay of the 550-570 nm species. Therefore the 550-570 nm species cannot be intermediate in the aromatic photosubstitution reaction of 3,5-dinitroanisole with hydroxide ion to yield 3,5-dinitrophenolate. Repetition of the experiment with a variety of nucleophiles on this and other aromatic compounds yielded invariably the same result nucleophilic aromatic photosubstitution is, in all cases studied, completed within the flash duration (about 20jLts) of our classical flash apparatus. 

After 1-5 /xs there is no further decay of the 412 nm absorption. The optical density of the solution at that wavelength is higher than before the pulse, due to the formation of the photosubstitution product (3,5-dinitrophenolate anion X gx = 400-410 nm). Although the formation of the substitution product from the 412 nm species can thus not be observed directly, we propose this pathway as the most plausible. 

A reasonable mode of action for uncouplers can be proposed in light of the existence of a proton gradient. Dinitrophenol is an acid its conjugate base, dinitrophenolate anion, is the actual uncoupler because it can react with protons in the intermembrane space, reducing the difference in proton concentration between the two sides of the inner mitochondrial membrane. 

Orf/jo-nitroaryl-substituted acetonitriles are relatively strong C-H acids, and their C-aUcylation followed by hydrogenation leads to 3-substimted indoles [176]. It has been shown earlier that VNS in 2,4-dinitrophenol proceeds regiospe-cifically at the most hindered position 3 due to electronic configuration of the dinitrophenolate anion [14]. This orientation pattern has been employed for the synthesis of the precursor of damirone B from dinitroguaiacol, in which cyanomethylation proceeds exclusively at position 5 to form upon 0-methylation 3,4-dimethoxy-2,6-dinitrophenylacetonitrile. Further alkylation of the nitrile carb-anion with ethyl bromoacetate and hydrogenation provides the skeleton of damirone tricyclic system (Scheme 66) [183, 184]. 

Another example of the analogy between pyrazole and chlorine is provided by the alkaline cleavage of l-(2,4-dinitrophenyl)pyrazoles. As occurs with l-chloro-2,4-dinitrobenzene, the phenyl substituent bond is broken with concomitant formation of 2,4-dinitrophenol and chlorine or pyrazole anions, respectively (66AHC(6)347). Heterocyclization of iV-arylpyrazoles involving a nitrene has already been discussed (Section 4.04.2.1.8(i)). Another example, related to the Pschorr reaction, is the photochemical cyclization of (515) to (516) (80CJC1880). An unusual transfer of chlorine to the side-chain of a pyrazole derivative was observed when the amine (517 X = H, Y = NH2) was diazotized in hydrochloric acid and subsequently treated with copper powder (72TL3637). The product (517 X = Cl, Y = H) was isolated. 

Another factor that can influence the environmental distribution of a chemical is the presence of charged groups. Some pollutants, such as the sodium or potassium salts of phenoxyalkanoic herbicides, dinitrophenols, and tetra- or penta-chlo-rophenol, exist as anions in solution. Others, such as the bipyridyl herbicides diquat and paraquat, are present as cations. In either case, the ions may become bound to organic macromolecules or minerals of soils or sediments that bear the opposite... 

Doubts have recently been expressed regarding the validity of the metaphosphate pathway for hydrolysis of the monoanion of 2,4-dinitrophenyl phosphate (111) 70,71,72) since the basicity of the 2,4-dinitrophenolate group is insufficient to produce a zwitterion corresponding to 106 or even a proton transfer via intermediates of type 103 or 105 (pKa values in water 4.07 for 2,4-dinitrophenol, 1.0 and 4.6 for 2,4-dinitrophenyl phosphate). Instead, hydrolysis and phosphorylation reactions of the anion 111 are formulated via oxyphosphorane intermediates according to 114. 

Mitochondria do three things oxidize substrates, consume oxygen, and make ATP. Uncouplers prevent the synthesis of ATP but do not inhibit oxygen consumption or substrate oxidation. Uncouplers work by destroying the pH gradient. The classic uncoupler is dinitrophenol (DNP). This phenol is a relatively strong acid and exists as the phenol and the phenolate anion. 

The pH values of efficient extraction correspond to the pH range where the molecular form of the respective phenol dominates. The recovery of 4-nitro-phenol, 2,4-dinitrophenol, 2,6-dinitrophenol, 4-chlorophenol, 1-naphthol, and 2-naphthol is above 90% (the ratio of aqueous organic phase volume is 3 1). The extraction of naphthol and 4-chlorophenol is significant even at pH > pffa, more than 40 and 24% at pH > 10, respectively. Recovery of picric acid (2,4,6-trinitrophenol) is about 90% at pH 1.5-12.0, where the anionic form of picric acid dominates. Obviously, the high extraction is caused by high hydrophobicity of picrate anions. Recovery of the phenol itself and diatomic phenols, catechol and resorcinol is rather moderate (79,58, and 20%, respectively pH 1-7), which could be explained by relatively high hydrophi-licity of these compounds. 

Many compounds that uncouple electron transport from phosphorylation, like 2,4-dinitrophenol, are weak acids. Their anions are nucleophiles. According to the scheme of Fig. 18-12, they could degrade a high energy intermediate, such as Y B, by a nucleophilic attack on Y to give an inactive but rapidly hydrolyzed... 

At physiological pH, 2,4-dinitrophenol exists predominately as the anion, C6H4(N02)20. The membrane is permeable both to this anion and to the protonated form, Q,H4(NO)2OH. The latter form can carry protons across the membrane and return in the anionic form to be reloaded with a proton. Thus, 2,4-dinitrophenol can dissipate the H+ gradient. 

A further instructive study on the influence of protic and dipolar aprotic solvents on the rate of SnI heterolysis of tertiary R3C-X (with X = Cl, Br, I, 2,4-dinitrophenolate) shows that the rate-accelerating anion solvation due to H-bonding by protic solvents decreases dramatically on increasing the radius of the halide ions. Therefore, the differential solvation transferred from anion-solvating methanol to cation-solvating dimethyl sulfoxide as solvent is reversed on going from the chloro- to the iodoalkane at 60 °C /ji(DMSO)/ki(MeOH) = 0.05 (t-BuCl) < 0.57 (t-BuBr) < 6.9 (t-BuI) the 2,4-dinitrophenolate ion behaves like the iodide [830]. 

Uncoupling of oxidative phosphorylation by 2,4-dinitrophenol (2,4-DNP). The anionic form of 2,4-DNP is protonated in the intermembrane space, is lipid soluble, and crosses the inner membrane readily. In the matrix, the protonated form dissociates, abolishing the proton gradient established by substrate oxidation. The ionized form of 2,4-DNP is poorly soluble in the membrane lipids and therefore is not easily transported across the membrane (dashed arrow). It is lipophilic and capable of transporting protons from one side of the membrane to the other (a protonophore), thus abolishing the proton gradient. 

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