2.4- Dinitrophenylphosphate

Less is known about unequivocal reactions of the POf ion with amines. This is partly because the phosphate esters examined undergo direct SN2(P) reaction with amines via oxyphosphoranes or can at least react in the boundary area between SN1 (metaphosphate mechanism) and SN2(P)37) or because the reaction actually occurs at another part of the molecule (simple primary and secondary amines react with 2,4-dinitrophenylphosphate to give 2,4-dinitroanilines " ). 

Knowles and co-workers have studied the stereochemical consequences of the presumed S>jl(P) reaction. They have shown that the methanolysis of chiral 0 0 0-substituted phenol- and 2,4-dinitrophenylphosphate and phosphocreatine (13, 14), under conditions where they were expected to react by the metaphosphate pathway, all undergo complete inversion of configuration at phosphorus. This result implies that the putative metaphosphate is not a free intermediate that it is not even long-lived enough to equilibrate with the solvent cage in which it is formed. It was concluded that the reaction must be preassociative at least in aqueous-alcoholic media. A recent report (24) has shown that the Conant-Swan fragmentation described earlier also occurs with inversion about the phosphorus atom. 

The volume of activation for the hydrolysis of 2,4-dinitrophenylphosphate in aqueous solution is -4.8 cm -mol (116) and this has been interpreted as a reaction that involves some associative nature. In contrast, the activation volume for the hydrolysis of 2,4-dinitrophenyl-r/iio-phos-phate is +10 cm mol", which is indicative of a more dissociative pathway (19). 

The hydrolysis of 2,4-dinitrophenylphosphate to orthosphosphate and 2,4-dinitrophenolate has been shown to be accelerated in the presence of an excess of [Co(l,3-pn)2(OH2)2p or [Co(trpn)(OH2)2] (trpn = 3,3, 3"-triaminotripropyl amine) at pH values where the hydroxoaqua complex is the predominant species. In the hydroxoaqua form the coordinated water in these complexes is extremely... 

The hydrolysis of 2,4-dinitrophenylphosphate (DNPP) to orthophosphate and 2,4-dinitrophenolate is accelerated in the presence of excess [Co(pn)2(OH2)2] or [Co(trpn)(OH2)2] at rates which vary with pH in a manner suggesting that the hydroxoaquatetraamine cobalt(III) complex is the active catalyst (pn = trimethylenediamine trpn = 3,3, 3"-triaminotripropylamine). " Detailed mechanistic schemes are proposed. For the trpn complex at pH 6.0 and a 25 1 cobalt-to-DNPP ratio (5 x 10" M DNPP) the observed rate enhancement is - 3 x 10 -fold. The calculated specific rate constant for hydrolysis in the reactive 1 1 complex (k 0.2 s" ) represents a rate acceleration of some 3 x lO -fold. 

Phosphorus.—Oxoanions and Related Species. Ab initio and semi-empirical molecular orbital calculations on the metaphosphate anion [PO3]- attribute the electrophilic reactivity of this species to a low-lying acceptor orbital of a symmetry, nearly degenerate with a n molecular orbital. This species, metaphosphate, is suggested as intermediate in one of the two pathways involved in phosphorylation by phosphorocreatine. Kinetic isotope effect studies indicate that metaphosphate is also generated in the hydrolysis of 2,4-dinitrophenylphosphate ... 

Some exploratory experiments have also been carried out with some phosphate esters. Rate constants for one of these, dinitrophenyl-phosphate, are listed in Table VII. With this substrate, surprisingly, the intrinsic primary amines of the polymer seem to be acting in a turnover pathway, that is, are phosphorylated and then dephosphorylated, but this mechanism needs to be better substantiated. In any event it, it is clear that the rates in the presence of polymer are accelerated more than 103-fold with dinitrophenylphosphate. Even larger accelerations have been observed with other phosphate esters. 

In a continuation of their work on polyelectrolyte catalysis in ionic reactions, Ise and co-workers studied the effect of some cationic polyelectrolytes 20 in the hydrolysis of dinitrophenylphosphate dianion 21 (30). The dianion undergoes spontaneous decomposition [cf. Eq. (3—3)] (31, 32). The polycations employed are... 

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