Dialkyl phosphates, hydrolysis

Problem 13.60 Explain why trialkyl phosphates are readily hydrolyzed with OH to dialkyl phosphate salts, whereas dialkyl hydrogen phosphates and alkyl dihydrogen phosphates resist alkaline hydrolysis. 

The same change, from classical general base to nucleophilic catalysis by selected nucleophilic bases, has been observed and studied recently for the hydrolysis of activated amides (an example is l-benzoyl-3-phenyl-l,2,4-triazole 2.2, Scheme 2.11) [21], and is observed also for esters of various oxyacids of phosphorus. The changeover to general base catalysis of the hydrolysis of aryl dialkyl phosphates... 

Dialkyl phosphates can be obtained by hydrolysis of the appropriate pyrophosphate ester. 

Several grafted calcium ISEs have been reported (73,76,77). In one instance membranes were synthesized by cross-linking the styrene-b-butadiene-b-styrene (SBS) triblock elastomer with triallylphosphate, followed by alkaline hydrolysis of the resultant covalently bound trialkyl phosphate to give a pendant dialkyl phosphate. Good calcium electrodes with lifetimes greater than 6 months were obtained, but the limited selectivity for magnesium and sodium could relate to the absence of a solvent mediator (76). 

The thymidine oxyphosphorane 135 has been prepared by ester exchange, and underwent hydrolysis to give primarily the 5 -dialkyl phosphate. The cyclic analogue 136 of UMP has been synthesized for incorporation into antisense sequences to impart nuclease resistance. Its conformation was found to be similar to that of a nucleotide unit in A-type DNA duplexes. ... 

Plapp FW, Casida JE. 1958. Hydrolysis of the alkyl-phosphate bond in certain dialkyl aryl phosphorothioate insecticides by rats, cockroaches, and alkali. J Econ Entomol 51 800-803. 

It is commonly assumed that the base-catalyzed hydrolysis of substituted dialkyl (i.e., dimethyl or diethyl) phenyl phosphates occurs by nucleophilic attack of OH" at the phosphorus with the phenolate being the leaving group (see also Section 13.4) ... 

Phosphate esters are prepared by the partial esterification of fatty alcohol with phosphorous oxychloride followed by hydrolysis (20). This method yields a product that is a mixture of monoalkyl, dialkyl, and trialkyl phosphates. 

The preparation of dialkyl 1-alkynylphosphonates by an appropriate P-elimination procedure was first recorded in 1957, when it was reported that the action of EtONa on diethyl 2-[3-(diethoxyphosphinyl)propenyl] phosphate in refluxing EtOH leads to diethyl 1-propynylphosphonate in 69% yield (Scheme 1.13). The experimental conditions are crucial, and it has been shown that successful elimination of phosphate takes place to the exclusion of the ethanolysis reaction only at elevated temperature. At room temperature, diethyl 2-[3-(diethoxyphosphinyl)propenyl] phosphate is reported to undergo competing ethanolysis to triethyl phosphate and diethyl 2-oxo-propylphosphonate. Because of the drastic reaction conditions required for the subsequent conversion to 1-alkynylphosphonates, this method was rarely used and remained underdeveloped for a sigiuficant period of time. Fortunately, many efforts have been made to discover bases that might cause elimination of the phosphate from the enol without also bringing about isomerization or hydrolysis. The development of a variety of milder alternative methods has led to the much more widespread adoption of this elimination sequence. ... 

Hammett (and related sigma) relationships have been applied to aquatic reactions of several classes of aromatic contaminants. For example, alkaline hydrolysis of triaryl phosphate esters fits a Hammett relationship (Table 3) is t he sum of the substituent constants for the aromatic groups and k0 is the hydrolysis rate constant for triphenyl phosphate (0.27 M 1 s-1 t1/2 = 30 days at pH 8). Triaryl esters thus hydrolyze much more rapidly than trialkyl or dialkyl-monoaryl esters under alkaline conditions. Rates of photooxidation of deprotonated substituted phenols by singlet oxygen have been found to be correlated with Hammett a constants (Scully and Hoigne, 1987). The electronic cllects of substituents on pKa values of substituted 2-nitrophenols also fit a I lammett relationship this, of course, is not a kinetic LFER. Two compounds (4-phenyl-2-NP and 3-methyl-2-NP) did not fit the relationship and were not included in the regression. Steric effects may account for the discrepancy for the latter compound. Nitrophenols are used as intermediates in synthesis of dyes and pesticides and also used directly as herbicides and insecticides. 

Contact of one cm of a 0.025 molar solution of dialkyl phosphite in tetradecane at 403 K (130 C) with one gram of iron powder which had been ball milled under pentane resulted in depletion of the phosphorus in solution, as shown in Fig. 11-9. Reaction as well as adsorption took place, for soluble iron was found in the solutions of di(2-ethyIhexy1), dilauryl and distearyl phosphites. Chromatography of the solutions after contact revealed large quantities of alcohol dibutyl phosphite and di(2-ethylhexyl) phosphite yielded 92-97% of the theoretical amount of alcohol after 24 hours. Hydrolysis of the phosphite esters was ascribed to water adsorbed on the walls of the reaction tube and on the iron powder. Forbes and Battersby [46] postulated that hydrolysis is an important aspect of the mechanism of the additive action of phosphite esters. Oxidation to phosphate by the oxygen of the ambient air is deemed minor maximum augmentation of the oxygen uptake by a 6.5% solution of dibutyl phosphite over that of the tetradecane carrier fluid in the presence of iron was 20%. The easy hydrolysis of phosphites is well known. Partial... 

A calorimetric study of the hydrolysis of the esters (117 R = Me or Et) and of dimethyl 2-hydroxyethyl phosphate (and also of the phostonic esters (118 R = Me or Et) and comparison of their hydrolytic behaviour with that of dialkyl (2-hydroxyethyl)phosphonates) has been carried out so allowing a full analysis of thermodynamic aspects of the hydrolysis processes7 ... 

Dialkyl H-phosphonates are hydrolytically unstable compounds. The hydrolysis of H-phos-phonate diesters and phosphate esters is believed to proceed via pentacoordinated intermediates and transition structures that are formed by nucleophilic attack of the tetracoordinated phosphorus atom [14-16]. These intermediates undergo further pseudorotation [17] and elimination of alcohol to form the final products of the nucleophilic substitution. 

During Purex process thermal degradation and hydrolysis of TBP also takes place. The thermal degradation yields a large number of products including butane, butene, N2, NO2, CO2, NO, and butanol. The specific concern is the dealkylation of the phosphate ester since the dialkyl phosphoric acid ester, formed in the reaction, is capable of nonspecific interactions with metal ions (Katsumura 2004 Shkrob et al. 2007). 

Seven new enantiopure acidic crown ethers containing a dialkylhydrogen phosphate moiety (9) were prepared starting from optically active dialkyl-substituted oligoethylene glucols and phosphorus oxychloride followed by mild hydrolysis of the resulting macrocyclic chlorophosphates. ... 

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