Phosphonate-phosphate

Cambella and Antia [385] determined phosphonates in seawater by fractionation of the total phosphorus. The seawater sample was divided into two aliquots. The first was analysed for total phosphorus by the nitrate oxidation method capable of breaking down phosphonates, phosphate esters, nucleotides, and polyphosphates. The second aliquot was added to a suspension of bacterial (Escherichia coli) alkaline phosphatase enzyme, incubated for 2h at 37 °C and subjected to hot acid hydrolysis for 1 h. The resultant hot acid-enzyme sample was assayed for molybdate reactive phosphate which was estimated as the sum of enzyme hydrolysable phosphate and acid hydrolysable... 

Further studies on 1,3-dipolar addition reactions of diazophosphonates have been recorded,122 and work on 2-diazo-l-hydroxyalkylphosphonates also continues.123 The ester (155 R = H) reacts with esters of acetylenedicarboxylic acid without liberation of nitrogen to give stereoisomeric C-phosphorylated pyrazolines, which can be decomposed with both phosphorus-carbon and carbon-carbon bond fission, affording mixtures containing dimethyl acetylphosphonate, dimethyl hydrogen phosphonate, and tri(alkoxycarbonyl)pyrazolines. In the reaction between the same diazophosphonate and diazomethane, the latter conceivably acts as a basic catalyst for proton transfer in a series of steps which includes phosphonate-phosphate isomerization. The importance of a labile proton is demonstrated by the fact that the ester (155 R = Me) does not react in the manner described above. 

Synthetic studies for the discovery of effective antidotes for cholinesterase inhibitors are continuing . Various reactivity studies of oximates with different functional organophosphorus compounds, such as phosphinates, phosphonates, phosphates and thiono analogues (shown in Scheme 5), have been reported . ... 

Acylphosphonates generate acyl anion equivalents with cyanide via phosphonate-phosphate rearrangement. These anions react with aldehydes to provide cross-benzoin... 

The formation of phosphates 90 can be explained by phosphonate-phosphate rearrangement catalyzed by bases [84], The authors of [82] were able to show that phosphonates 89 react with isatin (in the presence of sodium alkoxide), leading to compounds 90. 

Figure 11.2 Dominant groups of P found in DOP (phosphonates, phosphate monoesters, orthophosphate, phosphate diesters, pyrophosphates, and tri- and tetrapolyphosphates) in oceanic waters. (Modified from Kolowith et al. 2001.)...

The procedure of isotope effect studies will be illustrated on several examples. First one concerns studies of phosphonate-phosphate rearrangement (Scheme 1). Phosphite 3 reacts in the presence of triethylamine with o-nitrobenzaldehyde (Pudovik reaction) to form 1-hydroxyphosphonate 4 as mixture of two diastereo-isomers, 1 1. Amine also catalyses the reverse refro-phospho-aldol (retro-Abramov) reaction of 1-hydroxyphosphonate to phosphite and aldehyde and rearrangement to phosphate 5. In acetonitrile at 65°C Pudovik reaction is much faster than of retro-Abramov reaction and phosphonate-phosphate rearrangement, which rates are comparable. Important fact for the mechanism elucidation was experimental evidence that rearrangement occurs with retention of configuration at phosphorus atom.49... 

Because the phosphonate-phosphate rearrangement requires P-C bond breakage and formation of the P-O bond kinetic isotope studies by means of 13C NMR were chosen.50 13C KIEs were derived from NMR analysis of substrate-o-nitro-benzaldehyde or product-phosphate. Samples of aldehyde were prepared using the dead-end method. To the solution of phosphite 3 and triethylamine in acetonitrile an excess of aldehyde was added and solution was heated at 65°C to complete conversion of phosphonate 4 to phosphate 5 monitored by 31P NMR. The aldehyde conversions 0.2-0.8 were calculated from the balance of concentrations. The changes of 13C composition were determined for carbonyl carbon atom using signal of meta aryl carbon as an internal standard. KIE 1.0223(14) was calculated from the slope of linear relationship of isotopic ratio R and fraction of reaction,... 

All pentavalent P=0 compounds catalyze this reaction and the order of catalytic activity is phosphine oxide > phosphinate > phosphonate > phosphate. For example, addition of a catalytic amount of hexamethylphosphoric acid triamide inaeases the rate of conversion of phenyl isocyanate to diphenylcarbodiimide. The catalytic conversion of phenyl isocyanate to diphenylcarbodiimide, using isopropylmethylphosphonofluoridate,... 

Nguyen, L.M., Niesor, E., and Bentzen, C.L., gezw-Diphosphonate and gezw-phosphonate-phosphate compounds with specific high density lipoprotein inducing activity, 7. Med. Chem., 30, 1426, 1987. Shi, X.-X., and Dai, L.X., Mild halogenation of stabilized ester enolates by cupric halides, 7. Org. Chem., 58, 4596, 1993. 

Several alternative self-assembly approaches for producing thermally stable, acentric chromophoric multilayers have been reported [142-144]. The most prominent example is that developed by Katz et al. [145,146], which takes advantage of the zirconium phosphonate/phosphate coordinative bonding to fix layers of a dye to one another producing films with a good structural regularity and stability to orientational randomization of up to 150°C. Another example utilizes the electric field-induced LbL assembly technique of ionic species, followed by UV irradiation to convert the ionic bonds between layers into covalent bonds [147],... 

Simultaneous electrical conductivity-DTA was used by Romanov et al. (67) to study the thermal behavior of a-oxyalkylphosphonates. It was found that the thermal transformations of these compounds and their analogs are preceded by the ionization of the hydroxy group near the a-carbon atom. On the phosphonate-phosphate rearrangement of a-oxyalkylphosphonates containing electron-donor substituents near the a-carbon atom, no prior decomposition to the initial components takes place, and rearrangement proceeds by an intramolecular tricenter mechanism. 

The relative reactivity in the alkyl exchange reaction is I > Br > Cl for alkyl halides (207,263), and phosphinate > phosphonate > phosphate for esters (207), in agreement with the suggested mechanism. 

An alkoxide-catalysed reaction between an unsaturated ketone and two equivalents of 188 (R = Me) gives 192 by way of the thermodynamically controlled (20-40 °C) initial formation of 191. Depending on R and R, further transformations of 192 lead to either 193, as a diastereoisomeric mixture, or 194, the latter an example of a product from a facile phosphonate-phosphate transformation ". ... 

In the absence of a solvent and excess of chloral, the reaction rate for this reaction may be expressed by a third-order equation-second order with respect to dimethyl H-phosphonate and first order with respect to the chloral [177]. In dioxane solution and excess dimethyl H-phosphonate, the dependence of the reaction rate on the chloral concentration is the same. In addition to the chloro-containing a-hydroxyalkyl phosphonate, which is the main product under the above conditions, a side product formed as a result of dehydrochlorination of the main product, followed by phosphonate-phosphate rearrangement, has been also isolated. The presence of a base such as triethylamine, alkali metal alkoxides and hydroxides, or sodium carbonate accelerates the dehydrochlorination process. An example of this side reaction is the transformation of dialkyl-2,2,2-trichloro-l-hydroxyethyl phosphonates into dialkyl-2,2-dichlQrovinyl phosphates in the presence of sodium hydroxide [181,182]. 

Chemical transformations of a-hydroxyphosphonates Phosphonate-phosphate rearrangement. Dialkyl alkylphosphonates are, in general, more reactive than the corresponding phosphate esters because the carbon has no unpaired electrons to contribute to allow a pn-dm contribution to the P-C bond. This makes the phosphorus atom of phosphonates more electrophilic than the phosphorus atom of the corresponding phosphate ester. The P-C bond is usually stable to hydrolitic procedures. However, a-hydroxyalkylphosphonates, in the presence of alkali, rearrange to give phosphate with cleavage of the P-C bond [220]. 

The phosphate carbanion I obtained as a result of phosphonate-phosphate rearrangement reacts further with a second molecule of aldehyde, forming 1,2-diphenyloxirane (stilbenic oxide) II. The latter undergoes the Homer-Emons reaction to furnish trani-stilbene III. 

Sodium diethyl phosphite reacts with fluorinated alkylketones at temperatures in the -10 °C to 0 °C range, yielding substituted fluoroalkenyl phosphates via phosphonate-phosphate rearrangement of the initially formed P-carbonyl phosphonates [381]. 

Phosphine oxide Phosphinate Phosphonate Phosphate DOPO... 

---