Hydrolyzable phosphorous

Mg ions activate some enzymes which hydrolyze phosphoric acid ester bonds (e. g. phosphatases cf. Table 2.4) or transfer phosphate residues from ATP to a suitable acceptor (e. g. kinases cf. Table 2.4). In both cases, Mg ions act as an electrophilic Lewis acid, polarize the P—O-linkage of the phosphate residue of the substrate or cosubstrate and, thus, facilitate a nucleophilic attack (water with hydrolases ROH in the case of kinases). An example is the hexokinase enzyme (cf. Table 2.16) which, in glycolysis, is involved in catalyzing the phosphorylation of glucose to glucose-6-phosphate with ATP as cosubstrate. The effect of a Mg ion within the enzyme-substrate complex is obvious from the following formulation ... 

Hexafluorophosphoric Acid. Hexafluorophosphoric acid (3) is present under ambient conditions only as an aqueous solution because the anhydrous acid dissociates rapidly to HF and PF at 25°C (56). The commercially available HPF is approximately 60% HPF based on PF analysis with HF, HPO2F2, HPO F, and H PO ia equiUbrium equivalent to about 11% additional HPF. The acid is a colorless Hquid which fumes considerably owiag to formation of an HF aerosol. Frequently, the commercially available acid has a dark honey color which is thought to be reduced phosphate species. This color can be removed by oxidation with a small amount of nitric acid. When the hexafluorophosphoric acid is diluted, it slowly hydrolyzes to the other fluorophosphoric acids and finally phosphoric acid. In concentrated solutions, the hexafluorophosphoric acid estabUshes equiUbrium with its hydrolysis products ia relatively low concentration. Hexafluorophosphoric acid hexahydrate [40209-76-5] 6 P 31.5°C, also forms (66). This... 

Phosphoric Acid and Phosphorothioic Acid Anhydrides. The aUphatic organophosphoms esters originally developed by Schrader (27) are extremely toxic to mammals and are largely of historic interest. Tetraethyl pyrophosphate [107-49-3] (40) (bp 104—110°C at 10.7 Pa, d 1.185, vp 6.1 mPa at 30°C) is miscible with water and hydrolyzes very rapidly with a half-life of 6.8 h at 25°C. The rat LD qS ate 1.1 (oral) and 2.4 (dermal) mg/kg. 

Hydrolysis. The first effect of either acid hydrolysis or alkaline hydrolysis (saponification) is the removal of the fatty acids. The saponification value of commercial lecithin is 196. Further decomposition into glycerol, phosphoric acid, and head groups (ie, choline, ethanolamine, etc) may foUow prolonged heating. Lecithin may also be hydrolyzed by enzymes. 

Synthesis. Hydroxyhydroquiaone is not produced on a large scale, but many uses for it are being developed. The most convenient preparation of hydroxyhydroquiaone is the reaction of -benzoquiaone with acetic anhydride ia the preseace of sulfuric acid or phosphoric acid. The resultant triacetate (29) can be hydrolyzed to hydroxyhydroquiaone (86). 

Esters of phosphorous acid derived from aUphatic alcohols and unhindered phenols, eg, tris(nonylphenyl)phosphate (24), hydrolyze readily and special care must be taken to minimize decomposition by exposure to water or high humidity. The phosphorous acid formed by hydrolysis is corrosive to processing equipment, particularly at high temperatures. 

A third screening smoke-type is white phosphoms [7723-14-0] (WP), P (see Phosphorus and THE phosphides), which reacts spontaneously with air and water vapor to produce a dense cloud of phosphoms pentoxide [1314-56-3]. An effective screen is obtained as the P2O5 hydrolyzes to form droplets of dilute phosphoric acid aerosol. WP produces smoke in great quantity, but it has certain disadvantages. Because WP has such a high heat of combustion, the smoke it produces from bulk-filled munitions has a tendency to rise in pillarlike mass. This behavior too often nullifies the screening effect, particularly in stiU air. Also, WP is very brittle, and the exploding munitions in which it is used break it into very small particles that bum rapidly. 

Other soluble iridium compounds, e.g. chloroiridic acid, can also be used, t Phosphorous acid can replace the ester the latter is probably largely or wholly hydrolyzed when it is used as a starting material. 

The complex thioamide lolrestat (8) is an inhibitor of aldose reductase. This enzyme catalyzes the reduction of glucose to sorbitol. The enzyme is not very active, but in diabetic individuals where blood glucose levels can. spike to quite high levels in tissues where insulin is not required for glucose uptake (nerve, kidney, retina and lens) sorbitol is formed by the action of aldose reductase and contributes to diabetic complications very prominent among which are eye problems (diabetic retinopathy). Tolrestat is intended for oral administration to prevent this. One of its syntheses proceeds by conversion of 6-methoxy-5-(trifluoroniethyl)naphthalene-l-carboxyl-ic acid (6) to its acid chloride followed by carboxamide formation (7) with methyl N-methyl sarcosinate. Reaction of amide 7 with phosphorous pentasulfide produces the methyl ester thioamide which, on treatment with KOH, hydrolyzes to tolrestat (8) 2[. 

However, a number of limitations are still evident when tetrafluorohorate and hexafluorophosphate ionic liquids are used in homogeneous catalysis. The major aspect is that these anions are still relatively sensitive to hydrolysis. The tendency to anion hydrolysis is of course much less pronounced than that of the chloroalu-minate melts, hut it still occurs and this has major consequences for their use in transition metal catalysis. For example, the [PF ] anion of l-hutyl-3-methylimida-2olium ([BMIM]) hexafluorophosphate was found (in the author s laboratories) to hydrolyze completely after addition of excess water when the sample was kept for 8 h at 100 °C. Gaseous HF and phosphoric acid were formed. Under the same conditions, only small amounts of the tetrafluorohorate ion of [BMlMjjBFJ was converted into HF and boric acid [10]. The hydrolytic formation of HF from the anion of the ionic liquid under the reaction conditions causes the following problems with... 

White P, either in bulk or in soln, is a good example of the burning type of smoke generator. The resulting colloidal suspension of P pentoxide is quickly hydrolyzed by moisture to become phosphoric acid droplets which are the actual visible constituent of the smoke. Various other burning type smoke generators exist such as those used for signaling purposes and which use red P, metallic phosphides, or P trichloride as the source of the particulate cloud... 

There are some means for synthesis of defined primary or secondary esters. Monoester salts of phosphoric acid, for instance, are prepared by addition of alcohol or ethoxylated alcohol, alkali fluoride, and pyrophosphoryl chloride (C12P0)20 in a molar ratio of 0.9-1.5 0.05-1 1.0 at -50 to +10°C and hydrolysis of the Cl-containing intermediates with base. Thus, 32.3 g (C12P0)20 was treated at -50°C with 23.9 g lauryl alcohol in the presence of 0.7 g KF and the mixture was slowly warmed to room temperature and hydrolyzed with H20 and 40% NaOH to give 83% sodium monolauryl phosphate. The monoester salts showed comparable or better washing and foaming efficiency than a commercial product [12]. 

Whereas nonionic ethylene oxide adducts discolor badly on contact with sodium hydroxide, phosphate derivatives of these nonionics exhibit good color stability even under these conditions. But in the presence of strong acids poly-oxyethylated phosphate esters undergo hydrolysis to the base nonionic and phosphoric acid. However, the free surface-active acids by themselves show little tendency to hydrolyze. They have a pH value of 2 in aqueous solution. 

An interesting reaction between iV-methyleneglycinonitrile 28 and phosphorous trichloride proceeded at low temperature under anhydrous conditions to form the glyphosate nitrile intermediate 40 as its hydrochloride salt (48). However, when the reaction was conducted in the presence of water, the glyphosate amide 41 was generated instead. Either intermediate 40 or 41 could be hydrolyzed di tly to glyphosate under acidic conditions (49). 

Other interesting examples of proteases that exhibit promiscuous behavior are proline dipeptidase from Alteromonas sp. JD6.5, whose original activity is to cleave a dipeptide bond with a prolyl residue at the carboxy terminus [121, 122] and aminopeptidase P (AMPP) from E. coli, which is a prohne-specific peptidase that catalyzes the hydrolysis of N-terminal peptide bonds containing a proline residue [123, 124]. Both enzymes exhibit phosphotriesterase activity. This means that they are capable of catalyzing the reaction that does not exist in nature. It is of particular importance, since they can hydrolyze unnatural substrates - triesters of phosphoric acid and diesters of phosphonic acids - such as organophosphorus pesticides or organophosphoms warfare agents (Scheme 5.25) [125]. 

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 dialkyl(l-methylacetonyl)phosphates, which were easily hydrolyzed, are obtained in higher than 90% yields. Such reactions can also be carried out by making the phosphoric imidazolide in situ from the di(l,2-dimethylethylene)pyrophosphate and imidazole.[10]... 

Poly(methyl 3-(l-oxypyridinyl)siloxane) was synthesized and shown to have catalytic activity in transacylation reactions of carboxylic and phosphoric acid derivatives. 3-(Methyldichlorosilyl)pyridine (1) was made by metallation of 3-bromopyridine with n-BuLi followed by reaction with excess MeSiCl3. 1 was hydrolyzed in aqueous ammonia to give hydroxyl terminated poly(methyl 3-pyridinylsiloxane) (2) which was end-blocked to polymer 3 with (Me3Si)2NH and Me3SiCl. Polymer 3 was N-oxidized with m-ClC6H4C03H to give 4. Species 1-4 were characterized by IR and H NMR spectra. MS of 1 and thermal analysis (DSC and TGA) of 2-4 are discussed. 3-(Trimethylsilyl)-pyridine 1-oxide (6), l,3-dimethyl-l,3-bis-3-(l-oxypyridinyl) disiloxane (7) and 4 were effective catalysts for conversion of benzoyl chloride to benzoic anhydride in CH2Cl2/aqueous NaHCC>3 suspensions and for hydrolysis of diphenyl phosphorochloridate in aqueous NaHCC>3. The latter had a ti/2 of less than 10 min at 23°C. 

The pronounced proclivity of phosphoric monoester monoanions to eliminate POf is not always recognizable from the characteristic pH profile of Fig. 1. The hydrolysis rate maximum at pH w 4 may be masked by a faster reaction of the neutral phosphoric ester, as in the case of a-D-glucose 1-phosphate63) or on hydrolysis of monobenzyl phosphate 64). In the latter case, the known ability of benzyl esters to undergo SN1 and SN2 reactions permits fast hydrolysis of the neutral ester with C/O bond breakage. The fact that the monoanion 107 of the monobenzyl ester is hydrolyzed some 40 times faster than the monoanion 108 of the dibenzyl ester at the same pH again evidences the special hydrolysis pathway of 107, rationalized by means of the metaphosphate hypothesis. 

Retarded acids are primarily applicable to sandstone acidizing. Fluoroboric acid slowly hydrolyzes to form the more reactive hydrofluoric acid (109,110). The time required for this hydrolysis process may enable deeper penetration of the HF into the formation although one report contradicts these findings (111). Na TiF and similar salts also slowly generate HF in acid media (112). Phosphorous acid addition to hydrochloric acid has been used to reduce the HC1 reaction rate with limestone (113). 

When a phosphite is used as a catalyst modifier, it is susceptible to oxidation in the same manner as a phosphine. Unlike triphenylphosphine oxide, which is relatively innocuous except for precipitation when the solubility limit is reached, phosphite oxidation products may hydrolyze to give phosphoric acid. Since phosphites are esters, phosphoric acid can catalyst additional hydrolysis. Other than limiting formation of phosphite oxidation products, the best approach is to include some acidity control technology in the separation or reaction system. 

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