Tetraethyl hydrolysis

The less branched, more associated tetraalkyl titanates are more slowly hydroly2ed because titanium is more fully coordinated. The hydrolysis of tetraethyl titanate has also been considered ia terms of its trimeric form ... 

Of the three organic phosphorus insecticides—hexaethyl tetraphosphate, tetraethyl pyrophosphate, and parathion—the first two have been shown to be mixtures (36) that contain tetraethyl pyrophosphate as the principal active ingredient. Several methods have been proposed for the determination of this compound in the commercial products (25, 35). All are based on the separation of the tetraethyl pyrophosphate from the related ethyl phosphates, followed by its hydrolysis to diethyl orthophosphoric acid and titration with standard alkali. Both hexaethyl tetraphosphate and tetraethyl pyrophosphate are soluble in water and are rapidly hydrolyzed to monoethyl and diethyl orthophosphoric acid. This rapid hydrolysis to nontoxic products greatly limits the duration of the in- secticidal effectiveness of tetraethyl pyrophosphate, but it also eliminates the danger of toxic residues on the crops treated. 

The purified tetraethyl pyrophosphate is a colorless, odorless, water-soluble, hygroscopic liquid (24, 4 )- It possesses a very high acute toxicity (28), exceeding that of parathion, and is rapidly absorbed through the skin. There is no spray-residue problem, however, for tetraethyl pyrophosphate hydrolyzes even in the absence of alkali to nontoxic diethyl phosphoric acid. Hall and Jacobson (24) and Toy (47) have measured its rate of hydrolysis, which is a first-order reaction. Its half-life at 25° C. is 6.8 hours and at 38° C. is 3.3 hours. Coates (10) determined the over-all velocity constant at 25° C. k = 160 [OH-] + 1.6 X 10 3 min.-1 Toy (47) has described an elegant method for preparing this ester as well as other tetraalkyl pyrophosphates, based upon the controlled hydrolysis of 2 moles of dialkyl chlorophosphate ... 

The hydrogen chloride is removed either by reduced pressure or by salt formation with pyridine or sodium bicarbonate the latter procedure gave high yields of the pure ester. Toy (47) also measured the hydrolysis rates and compared the toxicities of a series of tetraalkyl pyrophosphates. Of these tested, the tetraethyl ester was the most toxic to white mice. 

As a solvent for this reaction, anhydrous methyl ethyl ketone was found satisfactory. Coates (10) determined the rate of hydrolysis of the monothio analog as approximately one fifth that of tetraethyl pyrophosphate under similar conditions. The dithio analog has been prepared (22) in 90% yield from diethyl chlorothiophosphate, water, and pyridine in a modification of the reaction Toy (47) used to make tetraethyl pyrophosphate ... 

A mechanism proposed 87) for the alkaline hydrolysis of tetraethyl pyrophosphate, which is markedly accelerated by HPO e ions, has been substantiated by isotopic labeling 88). The nucleophilic attack by HPOJp on the symmetrical pyrophosphate 131 is considered to lead initially to the unsymmetrical P P1-diethyl pyrophosphate dianion 132 which decomposes spontaneously under the conditions of reaction to give the diethyl phosphate anion and POf 102. The latter reacts with water to form inorganic phosphate and with alcohols suclj as methanol and ethylene glycol to produce alkyl phosphates. 

Tetraethyl pyrophosphate (T.E.P.P.) was prepared by Toy1 in 73 per cent yield by the controlled hydrolysis of diethyl phosphorochloridate in the presence of a tertiary base ... 

Chemical/Physical. Tetraethyl pyrophosphate is quickly hydrolyzed by water forming pyrophosphoric acid (NIOSH, 1997). The reported hydrolysis half-life at 25 °C and pH 7 is 7.5 h (Ketelaar and Bloksma, 1948 Coates, 1949). 

Condensation of prednisone, 40 with tetraethyl orthocarbonate leads to the cyclic orthocarbonate 41 hydrolysis proceeds by protonation on the most accessible ether oxygen (that on carbon 21) to give the 17 mixed carbonate ester 42, Acylation with propionyl chloride proceeds on the remaining hydroxyl group to afford prednicarbate (43) [10],... 

The first suggestion of a practical form of antidotal therapy came in 1949 from Hestrin, who found that acetylcholinesterase (AChE) catalyzed the formation of acetohydroxamlc acid when incubated with sodium acetate and hydroxylamine. Critical in vitro studies in the next decade led to the development of a practical approach to therapy. The crucial concept in these studies was the recognition that the compound formed when AChE reacted with a phosphorus ester was a covalent phosphoryl-enzyme Intermediate similar to that formed in the hydrolysis of acetylcholine. 3 Wilson and colleagues, beginning in 1951, demonstrated that AChE inhibited by alkyl phosphate esters (tetraethyl pyrophosphate, TEPP) could be reactivated by water, but that free enzyme formed much more rapidly in the presence of hydroxylamine. 0 21 Similar results... 

In this paper, we report the synthesis of mesoporous silica and alumina spheres with nanometer size (80 to 900 nm) in the present of organic solvent with aqueous ammonia as the morphological catalyst to control the hydrolysis of tetraethyl orthosilicate (TEOS) and aluminum tri-sec-butoxide.1181 Mesoporous silica spheres show hexagonal arranged pores with monodispersed pore sizes ( 2.4 nm) and high surface areas ( 1020 m2/g) similar to MCM-41. A large pore ( 10 nm) mesoporous alumina sphere templated by triblock copolymer is thermally stable. Calcined alumina sphere shows disordered mesoporous arrays with relatively uniformed pore size distribution and high surface areas ( 360 m2/g). 

In 1995, Tanev and Pinnavaia [1] have reported the synthesis of a new type of mesoporous molecular sieve designated as the hexagonal mesoporous silica (HMS). Instead of using the ionic inorganic precursor and surfactant as in the case of MCM-41 [2], HMS is manufactured by hydrolysis reaction between a neutral inorganic precursor, tetraethyl-orthosilicate (TEOS) and a neutral primary amine surfactant (8-18 carbons). HMS possesses numerous favourable characteristics, but, like MCM-41, its synthesis process can only be concluded by the removal of the surfactant. This was reportedly done either by calcination at 630°C or by warm ethanol extraction [1]. 

The resulting tetraethyl ester on hydrolysis and decarboxylation yields propane-1, 2,3-tricarboxylic acid.155 In this example the malonate anion is generated by using one molar proportion of sodium ethoxide this is Michael s original method. However, these conditions sometimes lead to competing side reactions and the formation of abnormal reaction products. Better yields of the required product are often obtained with small amounts of sodium ethoxide (the so-called catalytic method) or in the presence of a secondary amine (e.g. diethyl-amine, see below). 

In this representation of the course of the reaction with DFP it is assumed that the hydroxyl group of serine competes with water. Owing to the close spatial arrangement of all components of the active surface, the probability of phosphate transfer to the serine hydroxyl increases enormously. Nevertheless, reaction with water takes place simultaneously and in special cases may become preponderant. Thus, Aldridge and Davison (49) observed that during inhibition by tetraethyl pyrophosphate of ChE, bound to the surface of erythrocytes, a much larger proportion of the anhydride undergoes hydrolysis than is actually bound by the enzyme. 

Starting with the tetraethyl ester of DOTA the potassium salt of the triester 31 has been obtained by a partial saponification. To the solution of this compound in anhydrous tetrahydrofuran dicyclohexylcarbodiimide and 1-hydroxybenzo-triazole has been added followed by tris(2-aminoethyl)amine. Subsequent hydrolysis of the ester groups yielded the nonaacid 32. 

The P-O-P bond of tetraethyl dithiopyrophosphate is very labile to attack by hydroxide even at neutral pH. The resulting 0,0-diethylphosphorothioic acid is hydrolyzed to the final products, phosphoric acid and ethanol, by a neutral hydrolysis mechanism (Figure 13.7). The rate constants are ka = 0, kn = 84 Y 1 and kb = 9E6 M-1 Y 1. The neutral rate constant for 0,0- diethylphosphorothioic acid is = 0.2 Y 1. The rate constant for O-ethylphospho-rothioic acid is 1 = 1 Y-1. The rate constant for phosphorothioic acid is = 3 Y 1. 

Reaction pathway for the neutral and alkaline hydrolysis of tetraethyl dithiopyrophosphate. 

In a recent study the IT-catalyzed rearrangement of allyl (3,5-di-terr-butylphenyl) ether was used as selective probe for the outer surface activity.44 The best passivation results were obtained by treatment of the Beta crystals with tetraethyl orthosilicate (TEOS). Slow hydrolysis of TEOS by traces of water present in the pores of the zeolite provides a thin, porous layer of amorphous silica and leads to complete outer surface passivation on 1 p,m crystals. 

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