Esters hydrolyzed

Initial polymer hydrolysis products are the diol or mixture of diols used in the reaction with the diketene acetal, and pentaerythritol dipropionate, or diacetate if 3,9-bis(methylene-2,4,8,10-tetraoxaspiro-[5,5Jundecane) was used. These pentaerythritol esters hydrolyze at a slower rate to pentaerythritol and the corresponding aliphatic acid (13). 

Benzyl-type esters hydrolyze relatively easily. This is well-known for polymeric systems (22, 25, 26). 

Tetraisopropyl Pyrophosphate. This ester, a water-white liquid, has been prepared by Toy (47) in 94% yield from diisopropyl chlorophosphate and water in the presence of pyridine. The ester is insecticidal and is about one tenth as toxic to white mice as tetraethyl pyrophosphate. An insecticidal dust of much greater stability than tetraethyl pyrophosphate dust can be formulated from tetraisopropyl pyrophosphate, inasmuch as the tetraisopropyl ester hydrolyzes at approximately V50th the rate at which the tetraethyl ester breaks down in the presence of moisture. 

The substrate commonly employed is 0.5-1.0% of pectin in 50-200 mM sodium chloride (20-60 ml) at a suitable pH and 30°. The pectinesterase activity is mostly expressed in micro-equivalents of ester hydrolyzed per minute at the given pH and temperature. The use of a variety of units of activity, which was complicated and prevented ready comparison of the results of various authors, has now been discontinued. 

Phosphate esters hydrolyze easily, thus precluding their use in PET. 

On the basis of studies on the metabolism of the fish anesthetic, methane sulfonate of m-aminobenzoic acid ethyl ester (MS-222), by a shark (the spiny dogfish, Squalus aeanthias), Maren et al. (25) reported the formation of a metabolite, m-aminobenzoic acid, by cleavage of the ester bond (Figure 1). This ester-hydrolyzed product was not partitioned across the gill, but was slowly excreted by the kidney. 

Butanol is produced commercially by the indirect hydration of -butenes. However, current trends are towards the employment of inexpensive Raffinate II type feedstocks, ie, C-4 refinery streams containing predominandy -butenes and saturated C-4s after removal of butadiene and isobutylene. In the traditional indirect hydration process, -butenes are esterified with liquid sulfuric acid and the intermediate butyl sulfate esters hydrolyzed. DEA Mineraloel (formerly Deutsche Texaco) currendy operates a 2-butanol plant employing a direct hydration of -butenes route (18) with their own proprietary catalyst. 

The entropy of activation is generally positive or near zero for Aal1 reactions. Values for several different esters hydrolyzed by the Aal1 mechanism are summarized in Table 9. It must be remembered that the figures quoted in the first part of this table include the parameters for the protonation of the ester. Since the observed values of A5 are strongly positive it is unlikely... 

Recoverable oil (% by volume) of 10°B liquid reconstituted from concentrate is usually low (0.005 to 0.015%). Pulp-wash normally contains no floating pulp and should be reasonably free of hesperidin crystals and other defects. Pectinesterase activity should not exceed 5.0 P.E.U. (1 P.E.U. represents 1 meq. ester hydrolyzed per min per ml per °B) (43). 

Answer First, measure the total acid phosphatase activity in a blood sample in units of /nnol of phosphate ester hydrolyzed per mL of serum. Next, remeasure this activity in the presence of tartrate ion at a concentration sufficient to completely inhibit the enzyme from the prostate gland. The difference between the two activities represents the activity of acid phosphatase from the prostate gland. 

It is more difficult to remove an alcohol from the corresponding nitroalkane than it is to separate the nitrite ester and the nitroalkane. Minimal exposure to a moist atmosphere is, therefore, desirable since anhydrous ether is hygroscopic and nitrite esters hydrolyze readily, especially if a little acid is present. 

After the challenge of the dynamic thiolester system (CDS-1 A) with acetylcholinesterase, the optimal constituents were immediately identified and hydrolyzed to acid and thiol products. The thiol product formed was simultaneously incorporated in the dynamic system to regenerate the optimal thiolester. During the acetylcholinesterase resolution process, two acid products, acetic and propionic acid, respectively, were mainly detected, with the acetyl ester hydrolyzed more rapidly (tl/2 = 210 min) than the propionyl ester (t1/2 = 270 min) as shown in Fig. 2. Only after significant hydrolysis of these two acyl species did the enzyme start to hydrolyze slowly the butyrate thiolester (t1/2 = 1,100 min), a lag phase possibly caused by inhibitory activities of the present thiolesters [8]. All the other acyl groups remained untouched by enzyme, a result which is in accordance with the known specificity of acetylcholinesterase. 

Virantmycin is a tetrahydroquinoline alkaloid that has inhibitory activity against DNA and RNA viruses. A total synthesis of virantmycin making use of a key type II aziridine has elucidated the absolute stereochemistry at C-2 and C-3 <1996T10609>. An intramolecular photocyclization of an azide onto a Z-alkene produces type II aziridine 351 in excellent yield. A three-step reduction/selective reoxidation procees yields key aziridine alcohol 352 in 76% overall yield (Scheme 71). The alcohol is methylated and the ester hydrolyzed without harm to the azirdine. A TFA-induced ring opening of the aziridine by chloride provides the natural product virantmycin in good yield. This entire process was also carried out with the -alkene to produce /)(-virantmycin, thus proving the stereochemistry at C-2 and C-3. 

The solubility restrictions that apply to the manufacture of the mixed esters are the same as those for the cellulose acetate, in that no soluble products are obtained by partial esterification. Hydrolysis of the esters in acid solution, however, yields uniform products showing gradually changing physical properties with increasing free hydroxyl content. The exact ratio of hydrolysis of acetyl to hydrolysis of propionyl or butyryl groups depends upon the composition of the hydrolysis solution. Thus, a cellulose acetate propionate hydrolyzed in acetic acid solution will retain a higher proportion of acetyl groups than would the same cellulose ester hydrolyzed in propionic acid. 

Because they lack the phenolic hydrogen, esters are more stable than free vitamers, but they are not antioxidants in vitro. Tocopheryl esters hydrolyze slowly under, eg., acidic aqueous systems, thus providing antioxidant activity for emulsions, soft drinks and some dairy products (Schuler, 1990). 

Egger et al. (93) have reported that methylphenldate Is carbamylated by Hogs and rats (Figure 16). Carbamylated methylphenldate was excreted In urine and represented IZ of the applied dose In both rats and dogs. An additional IZ of the dose was Identified as the ester-hydrolyzed, carbamylated metabolite In rat urine. 

An ester hydrolyzed in the presence of an acid catalyst produces a carboxylic acid and an alcohol. This hydrolysis, the reverse of esterification, is an equilibrium reaction. 

Tab. 3 Effect of medium compositions on ester-hydrolyzing activity of Pseudomonas sp. DS-K-19.

The 2-hydroxypropyl 4-nitrophenyl phosphate (HPNP) transesterification reactivity (Fig. 40, bottom) of binuclear zinc complexes of the dianionic ICIMP and trianionic BCIMP ligands (Fig. 62) have been compared.245 Notably, both of these ligands contain imidazole and carboxylate donors akin to protein-derived residues that are found as ligands to the zinc centers in phosphate-ester-hydrolyzing enzymes such as phosphotriesterase. The initial rate for HPNP transesterification promoted by [(ICIMP)Zn2(Ph2Ac)]C104 in 50% acetonitrile-water solution (tris buffer) was determined to be five times faster than the reaction promoted by [(BCIMP)Zn2(Ph2Ac)]. 

We have seen that esters hydrolyze slowly because water is a poor nucleophile and esters have very basic leaving groups. The rate of hydrolysis can be increased by either acid or HO . When you examine the following mechanisms, notice a feature that holds for all organic reactions ... 

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