Phosphonate metaphosphate

All these fragmentation reactions are best interpreted by a metaphosphate mechanism starting from the phosphonic dianion 142, formulated as follows ... 

On the other hand, numerous examples are already known in which monomeric metaphosphoric esters are generated by thermolysis reactions. Most worthy of mention in this context is the gas phase pyrolysis of the cyclic phosphonate 150 which leads via a retro-Diels-Alder reaction to butadiene and monomeric methyl metaphosphate (151) 108,109, no). While most of the phosphorus appears as pyrophosphate and trimeric and polymeric metaphosphate, a low percentage (<5%) of products 152 and 153 is also found on condensation of the pyrolyzate in a cold trap containing diethylaniline or N,N,N, N,-tetraethyl-m-phenylene-diamine. The... 

Another instructive example is provided by a series of a-phenyl-a,P-dibromo-phosphonates 170, 171, 172. While the phosphonate dianion 170 fragments instantaneously at room temperature with formation of the POf ion (see also Sect. 4.1.3), the analogous reaction of the phosphonic monoester anion 171 leading to methyl metaphosphate 151 requires more drastic conditions and is at least 1000 times slower the diester 172 is essentially stable under the reaction conditions described for 171 addition of triethylamine leads to slow demethylation H0). The behavior of 171 contrasts with that of simple (3-haloalkylphosphonic monoesters which merely eliminate HHal on treatment with bases94. Thus it is the possibility of formation of a phenyl-conjugated double bond which supports the fragmentation of 171 to olefin + 151. 

The formation of 151 from the phosphonate 171 could be proved only by indirect means. Electron-rich aromatic compounds such as N,N-diethylaniline and N,N,N, N -tetraethyl-m-phenylenediamine U0 1I9> and N-methylaniline 120> are phosphorylated in the para- and in the ortho- plus para-positions by 151. Furthermore, 151 also adds to the nitrogen lone pair of aniline to form the corresponding phosphor-amidate. Considerable competition between nucleophiles of various strengths for the monomeric methyl metaphosphate 151 — e.g. aromatic substitution of N,N-diethylaniline and reaction with methanol or aromatic substitution and reaction with the nitrogen lone pair in N-methylaniline — again underline its extraordinary non-selectivity. 

The intermediate metaphosphate/phosphonate can then be made to react with ethylene oxide to effect the insertion of ethyleneoxy units into the P-O-P linkages. If a limited amount of water or an alcohol is added to the meta intermediate, the resultant oligomer can be produced with a controlled hydroxyl functionality (11, 12). An example of a functional oligomer made this way is the following ... 

There is some evidence that the reaction of ethylene oxide with the metaphosphonate/phosphate may actuary form some cyclic five-membered esters initially, as shown by P signals at 18.4, 17.4 (phosphates) and 49 (phosphonate) which then are converted to acyclic esters. In another example of this route to oligomeric phosphorus esters, P O q is reacted with tris(l,3-dichloroiso-propyl) phosphate to prepare a metaphosphate which is ethoxylated with ethylene oxide to produce a substantially hydroxy-free phosphate oligomer (12). 

SYNS C.I. 77620 DIBASIC LEAD METAPHOSPHATE DIBASIC LEAD PHOSPHITE LEAD OXIDE PHOSPHONATE, HEMIHYDRATE LEAD PHOSPHITE, dibasic (DOT)... 

Synthesis of Phosphoric Acids and their Derivatives. - Among various approaches to phosphate esters the phosphorylation of phenols with dialkyl cyanophosphonate and the synthesis of triaryl phosphates under phase-transfer conditions are worthy of mention. Mixed trialkyl phosphates are also reported to be formed by brief cathodic electrolysis of the reaction of dialkyl phosphonates with aromatic aldehydes and ketones, presumably by rearrangement of the initial a-hydroxy compounds. Further reports have appeared of the generation of metaphosphates by various methods. The synthesis of analogues 1 of famesyl pyrophosphate which incorporate photoactive esters has been reported both compounds are competitive inhibitors of farnesyl transferase. 

Metaphosphonic Acid Anhydrides. In a related process, the fragmentation of compounds 5 (77) and 7 (7) by thermal or photochemical means releases fragments (6 or 8) that are the metaanhydrides of phosphonic acids. The properties of these species are very similar to those of the metaphosphates. 

The photochemical cleavage of the phosphorus-carbon bond in many benzylic phosphonic acids occurs through intramolecular electron transfer and gives monomeric metaphosphate together with substituted toluenes and, in many cases, 1,2-diarylethanes. The ultraviolet irradiation of (4-nitrobenzyl)phosphonic acid dianion in solution in aqueous ethanol yields l,2-bis(4-nitrophenyl)ethane, 4-nitrotoluene, H3PO4 and monoethyl phosphate (Scheme Irradiation of the same acid in the presence of dbu (other tertiary... 

A similar breakdown of (2-haloalk-l-enyl)phosphonate dianions into alkynes and inorganic phosphate, again probably via metaphosphate, has been known for many years, being observed both by Conant s group and by Bergmann and Bondi slightly later ... 

Oximes, which are valuable intermediates for the conversion of oxoalkyl phosphonic diesters into those of aminoalkylphosphonic acids (Chapter 4, Section IV.C. 1. d), are also readily available, although it is necessary to prepare them with some care. Nevertheless, the feature of interest here is their ready degradability, particularly under aqueous conditions, and which has been intensively investigated by Breuer and coworkers. The necessity for care in the preparation of oximes of acylphosphonic diesters, is illustrated by the synthesis of dimethyl [a-(hydroxyimino)benzyl]phosphonate this compound exists in the thermodynamically more stable ( ) form which, under the influence of acid is converted into the less stable (Z) form, and both forms have been separately characterized by X-ray crystallography. The geometric isomers of the oxime differ in their behaviour under basic conditions with NaOH-MeOH, the ( ) form undergoes monodealkylation, whereas the (Z) isomer decomposes to dimethyl phosphate and benzonitrile. In aqueous solution, ( )-[a-(hydroxyimino)benzyl]phosphonic acid also decomposes into benzonitrile together with phosphoric acid, in a manner which is pH dependent, and consistent with a dissociative mechanism that involves the early formation of monomeric metaphosphate. ... 

Monoalkyl esters of the same acid likewise decompose under acidic conditions to give benzonitrile and monoalkyl metaphosphates. The nature of the solvent in which degradation occurs can have a profound effect on the course of such degradation the predominantly ( )-oximes from the mono-2,2,2-trihaloethyl esters 121 and 122 of [a-(hydroxyimino)benzyl]phosphonic acid, as their anions, lose benzonitrile in boiling ethanol or propan-2-ol and yield mixed phosphodiesters 124 (R = Et or Pr ) ( )-(121) does... 

The well-known retro-Diels-Alder expulsion of SO2 and liberation of buta-1,3-diene when their adduct is heated has analogies in the phosphorus field. Flash thermolyses of the cyclic phosphonic ester 493 (R = OMe) and of the phosphinic ester 493 (R = 2,4,6-trimethylphenyl) afford buta-1,3-diene and the highly reactive metaphosphate 494 (R = OMe) or metaphosphonate 494 (R = 2,4,6-trimethylphenyl) species. The elimination of phenylmetaphosphonate or an analogous species was observed during the thermolysis of the 1,3,2-dioxaphospholanes 495 [Ar = (a) Ph or (b) (l,l -biphenyl)-2-yl or (c) 2,4,6-tri-tcrt-butylphenyl ] at 700-800 °C here the respective metaphosphonates were characterized through the formation of the indicated known products. The compound 496 (Ar = Ph)... 

Steroids possessing one or two isolated or conjugated double bonds are converted into their dihydrogen phosphates when brought into contact with (l-phenyl-l,2-dibromoethyl)phosphonic acid in the presence of ethyldiisopropyl-amine. The reactions presumably involve monomeric metaphosphate ion as the effective phosphorylating agent. ... 

Westheimer has reported on the results of a more deta d study of the formation of monomeric metaphosphate anion from (1,2-dibromo-l-phenyl-propyl)phosphonic acid, and its reaction with acetophenone. The yields of phenylethenyl phosphate can be raised to 40—80 % by careful choice of the nature and concentration of base. The effect of the pJ Ta of the added base appears to be complex some hindered bases, e.g., 2,2,4,4-tetramethylpiperidine and diisopropylamine, raise yields (to the maximum observed), but others, e.g. diisopropyl-methylamine, have the opposite effect. ... 

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