Alkyl metaphosphate

The fact that the 3,P-NMR signal of 183a can only be observed in pyridine-containing solution provides food for thought124). Viewed in conjugation with the idea that alkyl metaphosphates could form adducts such as 173 and 174 U9,120) as discussed above, formulation as a zwitterionic pyridine/metaphosphate adduct (188) seems reasonable. Similar adducts have also been found in the reaction of TPS with dinucleotides and trinucleoside diphosphate 126). In any case, the reactions of 183 or 188 are in full accord with the expected properties of a monomeric metaphosphate and its reactivity towards alcohols is far greater than that of all other reactive phosphorylation intermediates which can arise on reaction of TPS with oligonucleotides 126). 

The value of the new approach to metaphosphoric acid chemistry is seen in the range of the species that can be generated, which includes so far alkyl metaphosphates... 

Mechanistic studies of the hydrolysis of phosphate diesters indicate similar possibilities, with alkyl metaphosphate (ROP02)-like transition states and 5 n2(P) pathways. The hydrolysis of m-nitrobenzyl uridine 3 -diphosphate, whose two potential leaving groups have equal pK s, is associated with isomerisation to the 2 -isomer in weakly acidic solution, which requires pseudorotation of a (probably neutral) phosphorane. ... 

Mass-speetrometric fragmentation patterns suggesting elimination of alkyl and aryl metaphosphates have also been observed with compounds 161-163 n3 115>. However, the peak expected for metaphosphate itself is actually observed only in the case of 162. 

Converging lines of evidence have led to a general acceptance of the monomeric metaphosphate mechanism for the hydrolysis of phosphate monoester monoanions. The pH rate profile for aryl and alkyl phosphate monoester hydrolyses commonly exhibits a rate maximum near pH 4. where the concentration of the monoanion is at a maximum. The proposed mechanism is based on these principal points of evidence (a) a general observation of P-O bond cleavage (b) the entropies of activation for a series of monoester monoanions are all close to zero, which is consistent with a unimolecular rather than a bi-molecular solvolysis where entropies of activation are usually more negative by 20 eu7 (c) the molar product composition (methyl phosphate inorganic phosphate) arising from the solvolysis of the monoester monoanion in a mixed methanol-water solvent usually approximates the molar ratio of methanol ... 

The generation of alkyl-substituted monomeric metaphosphoric acid esters (254) has been described using two different methods and the metaphosphate produced spontaneously self-condensed to give polymeric P—O—P bonds, hi the presence of styrene polymerization is avoided and happing occurs instead to give a diastereomeric mixture of 2-alkoxy-l,3,2-dioxophospholane-2-oxides with (254 R = Me).232 Pyridine A -oxidc-tricthylaminc mixtures individually or together catalyse the phosphorylation of... 

Figure 6.52 Mechanistic possibilities for transfer of a monophosphate, (a) 5 1 (P) involving a solvent-equilibrated metaphosphate intermediate. Protonation states are not shown, but different fonts for the phosphorus oxygens, representing different oxygen isotopes, indicate stereochemistry. (b) Canonical structures for metaphosphate and alkyl phosphate dianion, (c) 5n2(P) involving an intermediate which can pseudorotate, (d) Exploded 5Nl(P)-like >Sn2(P) transition states, and cartoon of calculated movements of phosphorus and non-bridge oxygens during phosphoryl transfer through such a transition state, where the leaving to nucleophile atom distance is constant.

The elimination-addition reaction for phosphate esters was first proposed to account for the shape of the pH-rate profile of alkyl monoesters (40), which are most reactive at the maximum concentration of the monoanion, that is, pH 4. The explanation for this observation was that the reaction proceeded via a metaphosphate intermediate by the expulsion of an alcohol group with the proton for the alcohol being transferred from the phosphate as the reaction proceeds. Further studies of the reactions of monoesters have implied that the above mechanism operates for all alkyl and aryl monoesters where the p fa of the leaving group exceeds about... 

Amides of nucleotides are, like carboxamides, more stable than the corresponding esters. Their hydrolysis rate depends on the pH of the medium and the nitrogen substituents. Aliphatic amine derivatives are unstable below pH 4, hydrolyze slowly at pH 4-6, and are virtually stable at or above pH 7. The conjugated acid is thus readily hydrolyzed the neutral forms and the anion are not. Aromatic amines react slower in acid media than the alkyl derivatives. In both cases, one frequently observes S l mechanisms corresponding to metaphosphate formation (Scheme 8.5.11). There is no selectivity toward the nucleophile. 

Linear 2. See Sodium metaphosphate Linear alcohol C13-15. See C13-15 alcohols Linear CIO alpha olefin. See Decene-1 Linear Cl6 alpha olefin. See Hexadecene-1 Linear CIS alpha olefin. See Octadecene-1 Linear C20 alpha olefin. See Eicosene-1 Linear (C12 and C14) alkyl alcohols, ethoxylated. SeeC12-14 pareth Linear polyethyleneimine. See Polyethylene imine... 

The detailed chemistry of these films is stiU controversial older works based on elemental analysis with SEM-EDX showed that the film contained Zn, S, P, C and O [14]. XPS [15] and AES [16,17] have also been used to provide chemical differentiation for the different elements P was claimed to be present as a phosphate and S as a sulfide, the corresponding cation being zinc or iron. XANES spectroscopy revealed that the chemical nature of P and S in the tribofikns was different from that of the pure ZnDTP substances and depends on the alkyl group used in ZnDTP [18]. With isopropyl ZnDTP, phosphorus is found to correspond closely to metaphosphate (polyphosphate with a cyclic structure) whereas with u-butyl ZnDTP pyrophosphates are found. This is important when discussing the results obtained from commercial ZnDTP, which often consist of a blend of ZnDTP molecules containing different alkyl groups [3]. 

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