Ester concentrator

Fig. 1. Methyl ester concentration versus reaction time for solid bases and acids catalysts. Temperature 230 C, catalyst 2wt%, CH30H/oil= 12 1.

Fig. 4. Methyl ester concentration at different temperatures for catalysts Mg0-Al203 and Ti02-S04 . Catalyst 2wt%, CHjOH/oil = 12 1.

The reaction takes place in aqueous solution. Equimolal concentrations of the ester and the phenolate are used. These concentrations are equal to 30 moles/m3. By the time the samples are brought to thermal equilibrium in the reactor and efforts made to obtain data on ester concentrations as a function of time, some saponification has occurred. At this time the concentration of ester remaining is 26.29 moles/m3, and the concentration of phenol present in the reactant mixture is 7.42 moles/m3. The rate expression for the reaction is believed to be of the form... 

Methylcoumarin is prepared by the condensation of phenol and acetoacetic ester. Concentrated sulfuric acid1,2 and 73% sulfuric acid have been used.3 4 The method given here was mentioned by Sethna, Shah, and Shah,6 and the procedure is adapted from that of the same authors 6 for another coumarin derivative. 

From scheme I, together with the experimentally observed first-order dependence on the total ester concentration, the rate relationship illustrated in Eq. (1) may be derived. In applying this equation, the cycloamylose concentration must be at least tenfold greater than the initial substrate concentration to ensure first-order conditions. Equation (1) may be rearranged in two ways to yield linear forms which permit graphical evaluation of fa, the maximal rate constant for release of phenol from the fully com-plexed ester and Kd, the cycloamylose-substrate dissociation constant (defined in Scheme I as A i/fa). These two methods are illustrated in Eqs. (2) and (3) and may be attributed to Lineweaver and Burk (1934) and to Eadie (1942), respectively. Although in theory both methods should give... 

This work was extended to include the lead tetraacetate oxidation of methyl esters of meta- and para-substituted mandelic acids183,184 shown in equation 121. A kinetic study by Banerjee and collaborators showed the kinetic dependence on the ester concentration changed from second order in 1% (v/v) acetic acid in benzene to first order when the solvent contained more than 10% (v/v) acetic acid. These workers observed a significant decrease in AH (from 82.9 to 53.6 kcalmol-1) and in AS (from —5.84 to —35.6 e.u.) when the solvent composition was changed from 1% acetic acid to greater than or equal to 10% acetic acid in benzene. 

Peterson JC, Freeman DH. 1984. Variations of phthalate ester concentrations in sediments from the Chester River, Maryland. Inter J Environ Anal Chem 18 237-252. 

Metal-ion catalysis has been extensively reviewed (Martell, 1968 Bender, 1971). It appears that metal ions will not affect ester hydrolysis reactions unless there is a second co-ordination site in the molecule in addition to the carbonyl group. Hence, hydrolysis of the usual types of esters is not catadysed by metal ions, but hydrolysis of amino-acid esters is subject to catalysis, presumably by polarization of the carbonyl group (KroU, 1952). Cobalt (II), copper (II), and manganese (II) ions promote hydrolysis of glycine ethyl ester at pH 7-3-7-9 and 25°, conditions under which it is otherwise quite stable (Kroll, 1952). The rate constants have maximum values when the ratio of metal ion to ester concentration is unity. Consequently, the most active species is a 1 1 complex. The rate constant increases with the ability of the metal ion to complex with 2unines. The scheme of equation (30) was postulated. The rate of hydrolysis of glycine ethyl... 

If the monomer is the trne reacting species and the reaction of the monomer with an electrophile is fast enough compared to the monomer-aggregate eqnilibrinm, then the rate should be independent of the electrophile concentration. This was indeed fonnd for the reaction of BuLi with methyl trifluoroacetate in diethyl ether the reaction was extremely fast (18.5 s at — 28 °C) and was 0th order with respect to the ester concentration. Reaction of benzonitrile with BuLi in diethyl ether was slower, bnt the rate increased with increasing the benzonitrile concentration and reached a maximnm valne similar to that (7 X 10 s at —82°C) with methyl trifinoroacetate and the reaction order approached 0. Thus, the rate-determining step for the reaction of benzonitrile changed with its concentration. 

Gugala etal. [167] have studied adsorption of butyl acetate at mercury electrode in 1, 0.5, and 0.1 M NaCl04. The zero charge potential values at the streaming mercury electrode were found to shift to positive values with the increasing ester concentration, which indicated the hydrophilic part of the molecules to be directed toward the solution. 

Inspection of Table II, Group III indicates that the terpolymer sensitivity increases with increasing oxime ester concentration, a result which parallels that for the copolymers (Group I). P(M-OM-CN) (69 16 15), the most sensitive material prepared, is 85 times more sensitive than the parent PMMA. Note that the effect on the sensitivity of incorporation of methacrylonitrile is an additive one, i.e., each terpolymer is roughly 2-3 times more sensitive than its corresponding copolymer. 

The electron beam sensitivities of a random sample of co- and terpolymers were also determined, and were found to be essentially equal to that of PMMA. The value of 5X10 C/cm was largely invariant with oxime ester concentration, and the presence of methacrylonitrile had no effect (12). 

The ultimate levels of esters in fresh and stored apples are determined by the amount of precursors for ester formation, e.g. lipids, which are influenced by cultivar, growing conditions, harvest maturity and storage conditions [47]. In Fuji apples, acetate ester concentrations increase during maturation, 2-methyl-butyl acetate being the major ester component in the volatile compound profile... 

If an amine P-NH2 is used in the aqueous solution, one obtains RCONHP instead of RCOOH. Rates of cleavage of three acyl nitrophenyl esters were followed by the appearance of p-nitrophenolate ion as reflected by increased absorbances at 400 nm. The reaction was carried out at pH 9.0, in 0.02 M tris(hydroxymethyl)aminomethane buffer, at 25°C. Rate constants were determined from measurements under pseudo-first-order conditions, with the residue molarity of primary amine present in approximately tenfold excess. First-order rate graphs were linear for at least 80% of the reaction. With nitrophenyl acetate and nitrophenyl caproate, the initial ester concentration was 6.66xlO 5M. With nitrophenyl laur-ate at this concentration, aminolysis by polymer was too fast to follow and, therefore, both substrate and amine were diluted tenfold for rate measurements. 

It is apparent that an increase in the substrate-to-catalyst ratio dramatically decreases the catalytic efficiency for the pNPOAc reactions, but affects to a much lower extent the POAc reaction. This is easily understood with reference to Table 5.3. Since in the reaction of pN POAc the rate-determining step is mainly deacetylation, an increase in ester concentration causes a proportional increase in the rate of background methanolysis, but hardly affects the rate of deacetylation, with the result that catalytic efficiency varies inversely to ester concentration. Conversely, the reaction of POAc approaches a situation in which acetylation of the catalyst is rate determining, which implies that both acetylation and background reactions increase on increasing ester concentration. 

This sieve effect cannot be considered statically as a factor that only determines the amount of accessible acid groups in the resin in such a way that the boundary between the accessible and non-accessible groups would be sharp. It must be treated dynamically, i.e. the rates of the diffusion of reactants into the polymer mass must be taken into account. With the use of the Thiele s concept about the diffusion into catalyst pores, the effectiveness factors, Thiele moduli and effective diffusion coefficients can be determined from the effect of the catalyst particle size. The apparent rates of the methyl and ethyl acetate hydrolysis [490] were corrected for the effect of diffusion in the resin by the use of the effectiveness factors, the difference in ester concentration between swollen resin phase and bulk solution being taken into account. The intrinsic rate coefficients, kintly... 

Figure 5. Ratio of borate esters to borate anion as a function of global free ligand concentration. The borate ester concentration was observed directly with "B NMR, and the borate anion concentration was calculated from the solution pH and the free boron concentration. Standard errors are shown based on multiple fits to individual "B NMR spectra. As the free ligand concentration is also calculated (by difference) from the "B NMR spectra, its standard error is shown as well. The model prediction of this ratio, which is identical to the classical law of mass action, is shown as a solid line.

Direct evidence that hydrolysis reactions going by the Aac1 mechanism are kinetically first-order can be obtained, at least in principle, for reactions in strongly acidic solution, because the activity of water varies significantly with the acid concentration. Graham and Hughes 7 showed that the hydrolysis of methyl benzoate in sulphuric acid at 20°C is first-order with respect to ester concentration, but zeroth-order with respect to water in concentrations up to 1 M. Leisten6 showed further that the first-order rate coefficient for this reaction is almost independent of the initial concentration of the ester, and thus ruled out the possibility that a bimolecular attack by bisulphate ion is involved, since the ester is completely protonated in 100% sulphuric acid and tfe concentration of bisulphate ion depends on the concentration of the ester, viz. 

Though not reported in Table III, a peak for phenethyl alcohol emerged in the gas chromatograms of the ester concentrates of the later brandy fractions and increased in size into the tails fractions. Phenethyl alcohol is barely detectable, if at all, in corresponding concentrates of continuous still brandies. 

A synthesis of the 3-methylthiopyran-2-one (337) is based on the formation of a 2 1 adduct (336) between methyl propynoate and DMSO which occurs at high ester concentrations (Scheme 102) (66CB1558). Upon heating, cyclization occurs with the overall loss of methoxymethane. Only a small amount of dimethyl furan-2,4-dioate is formed in this reaction, but a furan is the sole product from dimethyl butynedioate and DMSO. 

The relative rate of amide and ester formation depends on the nature of the zeolite but we observe generally a rapid stabilization of the amide concentration while the ester concentration shows a linear dependence against tii.ie. A typical example is described for a HM (Si/A1 =8) (Fig. 3). The signi-... 

Fig. 4 LC-GC-FID chromatograms for typical olive oils. The nearly complete absence of wax esters (esters 40-esters 46) and very low concentrations of steryl esters indicate a high-quality extra virgin oil. The concentration of free stigmasterol is low. C24-26-OH, fatty alcohols. In lampante oils, more wax esters and steryl esters are found. The concentration of stigmasterol increases more than campesterol if the oil was prepared from olives of low quality. Run at the same sensitivity, chromatograms of solvent-extracted oils are completely overloaded. The refined extraction oil was diluted 1 5 before running the chromatogram shown. Wax ester and steryl ester concentrations are very high. (From Ref. 34, p. 626.)...

Cao, Y. et al. (2004) Predictive relationships for the effects of triglyceride ester concentration and water uptake on solubility and partitioning of small molecules into lipid vehicldsPharm. Sci., 93 2768-2779. 

To avoid difficulties related to the growth of pressure in a sealed vessels as well as temperature measurement, the esterification reaction of acetic acid with propanol was carried out in an open vessel under reflux conditions. It was found that ester concentrations during the course of the reaction were comparable under both conventional and microwave conditions [20]. In a similar reaction (i.e., the esterification of trimethylben-zoic acid with propanol), the kinetic parameters of the reaction under the Arrhenius law were estimated for conventional conditions. Then ester concentrations were calculated theoretically and compared with the results obtained for the reaction under microwave conditions. It was found that the theoretical values correlated well with the experimental results so microwave irradiation did not influence the rate of the reaction [21]. 

An estimation of ester concentrations and rate constants for some polyesters and vinyl esters crosslinked by styrene is given in Table 14.3. To compare with linear polymers r(100°C) 8x 10-5molkg-1 day-1, so that K 2 x 10 5 day 1 for bisphenol A polycarbonate ([E]0 4mol kg-1), and r(100°C) 8.45 x 10-3 molkg-1 day-1, so that K 1.6x 10-3 day-1 for poly(ethylene terephthalate) ([E]0 5.20molkg-1). 

For preparation of a wide range of acyl derivatives of trypsinlike enzymes, the 4-amidinophenyl benzoates proved appropriate, and using these fools preparation of acyl enzymes is relatively easy. In the first step the enzyme is acylatcd in the presence of excessive ester concentrations. Thereafter deacylation is stopped by lowering pH and temperature. Ultimately, the acyl enzyme is isolated from the... 

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