Anhydride hydrolysis measurement

The freezing point of trimellitic anhydride, the maximum temperature reached during crystallization of a molten sample, is a measure of the product purity. Impurities and trimellitic acid formed by hydrolysis depress the freezing point. 

Figure 4-12. Stopped-flow study of the pyridine-catalyzed hydrolysis of acetic anhydride, showing the formation and decay of the acetylpyridinium ion intermediate. Initial concentrations were 0.087 M pyridine, 2.1 x im M acetic anhydride the pH was 5.5 ionic strength, 1.0 M temperature, 25 C. Five hundred data points tabsorbance at 280 nm) were measured in I s. The smooth curve is a ht to Eq. (3-27). Source Data of D. Khossravi and S.-F. Hsu, University of Wisconsin.

The rotations were measured in chloroform solution, a fact which is not stated in the original article. The hydrolysis curves for aqueous solution of difructose anhydride III indicate that the rotation in water of the resulting trimethyl-D-fructose is also within this range. 

The polyfructosans, in contrast to the difructose anhydrides, are readily hydrolyzed in acid solution. Schlubach and his associates86 have measured the rates of hydrolysis of a large number of polyfructosans. The time required for 50% hydrolysis to take place in N sulfuric acid solution at 20° is recorded in Table III. These results are based on... 

If di-D-fructose anhydride II has formula XIX, a mixture of 1,3,4-and 1,4,6-trimethyl-D-fructoses would be present in the hydrolytic product. Such a mixture would have a specific rotation of — 10° to — 20° (water) in contrast to the value of + 25 to + 30 found by McDonald and Jackson.76 The rotation of 1,4,6-trimethyl-D-fructose was measured by Montgomery76 in chloroform (+ 29.7°), but it has not been measured directly in water. However, the hydrolysis data of McDonald and Jackson76 for hexamethyl-di-D-fructose anhydride III show that 1,4,6-trimethyl-D-fructose has about the same rotation in water as in chloroform. The argument thus appears to exclude structure XIX. 

Reference reaction is attack on 2,4-dinitrophenyl acetate by RCOO- of pK, 2.4 (k2 = 3.3 x 10-3 s-1 based on a short extrapolation using P = 1.0 Jencks and Gilchrist, 1968). The reaction measured is the subsequent hydrolysis of the mixed anhydride the observed value thus sets only a lower limit for EM (Fersht and Kirby, 1967b, 1968a)... 

Super or near-critical water is being studied to develop alternatives to environmentally hazardous organic solvents. Venardou et al. utilized Raman spectroscopy to monitor the hydrolysis of acetonitrile in near-critical water without a catalyst, and determined the rate constant, activation energy, impact of experimental parameters, and mechanism [119,120]. Widjaja et al. tracked the hydrolysis of acetic anhydride to form acetic acid in water and used BTEM to identify the pure components and their relative concentrations [121]. The advantage of this approach is that it does not use separate calibration experiments, but stiU enables identihcation of the reaction components, even minor, unknown species or interference signals, and generates relative concentration profiles. It may be possible to convert relative measurements into absolute concentrations with additional information. 

Bunton and Perry294 measured the rates of hydrolysis of acetic, benzoic, mesitoic, acetic-benzoic and acetic-mesitoic anhydrides in aqueous dioxan. They found that the hydrolyses of acetic, acetic-benzoic and benzoic an-... 

As indicated in Equation 8.3, qtot is not generally simply equal to the reaction heat-flow rate qReact (see Equation 8.4) but is affected by other physical or chemical processes which have heat changes, e.g. mixing or phase changes. As will be shown in Section 8.3, even for a simple reaction such as the hydrolysis of acetic anhydride, a significant heat of mixing occurs which must be taken into account. Furthermore, it should always be kept in mind that the qtot values determined by a reaction calorimeter also contain measurement errors such as base line drifts, time distortions or ambient temperature influences. 

As pointed out in Section 8.2, most physical and chemical processes, not just the chemical transformation of reactants into products, are accompanied by heat effects. Thus, if calorimetry is used as an analytical tool and such additional processes take place before, during, or after a chemical reaction, it is necessary to separate their effects from that of the chemical reaction in the measured heat-flow signals. In the following, we illustrate the basic principles involved in applying calorimetry combined with IR-ATR spectroscopy to the determination of kinetic and thermodynamic parameters of chemical reactions. We shall show how the combination of the two techniques provides extra information that helps in identifying processes additional to the chemical reaction which is the primary focus of the investigation. The hydrolysis of acetic anhydride is shown in Scheme 8.1, and the postulated pseudo-first-order kinetic model for the reaction carried out in 0.1 M aqueous hydrochloric acid is shown in Equation 8.22 ... 

Fig. 8.4 Heat flow rate (qtot) forthe hydrolysis of acetic anhydride measured at25,40 and 55°C. Reprinted in modified form with permission [18]. 

Fig. 8.5 Hydrolysis of acetic anhydride investigated separately at Tr = 25°C (a) by calorimetry and (b) by infrared spectroscopy. Graph (a) shows measured and simulated reaction power graph (b) shows measured and simulated concentration-time curves of acetic anhydride. The simulated curve is from the kinetic parameters obtained from the calorimetric measurements, and is compared with the one determined by the IR measurements at 1139 cm-1. Reprinted in modified form with permission [18],...

F]DGal, 119, a useful tracer to measure galactose metabolism in the liver with PET162b, has been synthesized by 18F ion displacement from a triflate163-165. The protected carbohydrate 120 has been oxidized163 and then reduced by LAH to give the talose derivative 121 which, in turn with triflic anhydride and pyridine, furnished the triflate intermediate 122. [18F]fluoride displacement on the latter and deprotection by acid hydrolysis yielded 119, in 30% r.y. in 90 minutes. 

Chemical Analysis. The copolymers were acetylated by refluxing with acetic anhydride in pyridine, and the hydroxyl content was estimated by titration with alkali of the acetic acid produced during acetylation and by hydrolysis of excess anhydride. The procedure adopted was based on that described by Sorensen and Campbell (33). The results of the analyses are given in Table A. At the three lower concentrations of hydroxyl groups all results were averaged from five or more measurements. 

Regenass [10] reviews a number of uses for heat flow calorimetry, particularly process development. The hydrolysis of acetic anhydride and the isomerization of trimethyl phosphite are used to illustrate how the technique can be used for process development. Kaarlsen and Villadsen [11,12] provide reviews of isothermal reaction calorimeters that have a sample volume of at least 0.1 L and are used to measure the rate of evolution of heat at a constant reaction temperature. Bourne et al. [13] show that the plant-scale heat transfer coefficient can be estimated rapidly and accurately from a few runs in a heat flow calorimeter. 

Trypsin was named more than 100 years ago. It and chymotrypsin were among the first enzymes to be crystallized, have their amino acid sequences determined, and have their three-dimensional structure outlined by x-ray diffraction. Furthermore, both enzymes hydrolyze not only proteins and peptides but a variety of synthetic esters, amides, and anhydrides whose hydrolysis rates can be measured conveniently, precisely and, in some instances, extremely rapidly. As a result, few enzymes have received more attention from those concerned with enzyme kinetics and reaction mechanisms. The techniques developed by the pioneers in these various fields have enabled other serine proteases to be characterized rapidly, and the literature on this group of enzymes has become immense. It might be concluded that knowledge of serine proteases is approaching completeness and that little remains but to fill in minor details. 

Figure 32.2 Cell surface peptide hydrolysis (A) and amino acid oxidation (B) using the fluorescent compound Lucifer "Vellow Anhydride (LYA)-tetraalanine and lysine, respectively. Fluorescent products are measured along with the added tracer hy high performance liquid chromatography (HPLC) and products can be further degraded or taken up by cells.

Cephalothin can be determined by means of the colored complex formed on the addition of a ferric reagent to the corresponding hy-droxamic acid produced by treatment with hy-droxylamine. The method used is essentially the same.as the procedure described for penicillins. The ferric hydroxamate procedure is not specific for cephalothin or penicillins. For example, many amides, esters, and anhydrides form hydroxamic acids when reacted with hydroxyl-amine. This type of interference is eliminated by the blank determination wherein cephalothin is rendered incapable of forming hydroxamic acid by use of basic hydrolysis or enzymatic hydrolysis with cephalosporinase. Since cephalothin degradation products having an intact (3-lactam ring react as well as the parent compound, the method measures total 3-lactam content. ... 

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