Ester group titration

When a mixture of phosphoric acid and phosphoric acid esters is titrated with a sodium hydroxide solution two potential jumps can be observed. The first jump results from the acid group of the diester, the first neutralization step of the monoester, and the first neutralization step of free phosphoric acid. The second potential jump is caused by the second neutralization steps of the monoester and of the free phosphoric acid. The third step of neutralization of the free phosphoric acid cannot be covered by this method. Titration of acid esters can only be used for the determination of mono- and diesters of phosphoric acid when the amount of free phosphoric acid is separately ascertained. 

Extraction and Identification. Identification of PE as the clearing enzyme in citrus juices progressed rapidly after MacDonnell et al. (17) reported on cation requirement for extraction and solubilization of the enzyme from various portions of the fruit. PE was assayed by the method introduced by Kertesz (18) and modified by Lineweaver and Ballou (19). The method involved measuring the rate at which the methyl ester groups in the pectin molecule are hydrolyzed by titrating the free carboxyl groups with 0.1N NaOH as they are formed. One unit of PE was defined as the amount of enzyme which will hydrolyze 1 meq carboxyl groups per min from a 0.5% solution of pectin in 0.15M NaCl at pH 7.5, 30°C (86°F). McDonnell et al. (17) showed that the enzyme... 

The copolymers of ChMAA-n with A-m and MA-m were obtained by polymerization in benzene in the presence of DAA. The composition of the copol3naers was determined by the ratio of optical densities of the 1,740 cm-l (C=sO modes in an ester group) and 1.650cm" (CaO modes in an amide group) absorption bands. The results of turbidimetric titration of polymers in benzene indicate that the copolymers are homogeneous in... 

The ester cannot be determined by saponification because this slowly removes the sulphonate group as well as hydrolysing the ester group. It can be determined by acid hydrolysis followed by measurement of the a-sulphonated carboxylate salt produced, either by potentiometric titration of the weak acid or by two-phase titration with benzethonium chloride. Both procedures measure the a-sulphonated ester plus the unsulphonated ester. If the latter is present at a significant level, it can be determined (section 5.11.2) and corrected for. 

Consider what other functional groups are present which might offer a route to any of the components, e.g. hydroxyl groups (hydroxyl value), free acidic or basic groups that can be titrated, ester groups (saponification value) or polyalkenoxy chains (colorimetry, NaTPB titration of barium complexes), etc. 

When the hemiacetal hydroxyl of a 2-0-tosyl or 2-0-mesyl aldose is unsubstituted, titration with dilute alkali at room temperature eliminates the sulfonic ester grouping and provides the related epimeric sugar in good yield 6 a, 226a), The epimerization presumably proceeds through an intermediate 1,2-epoxide. 

Ester groups occur in a wide range of polymers (e.g., polyethylene terephthalate) and in copolymers such as, for example, ethylene vinyl acetate. The classical chemical method for the determination of ester groups, namely, saponification, can be applied to some types of polymer. For example, copolymers of vinyl esters and esters of vinyl esters and esters of acrylic acid, can be saponified in a sealed tube with 2 M sodium hydroxide. The free acids from the vinyl esters were determined by potentiometric titration or gas chromatography. The alcohols formed by the hydrolysis of the acrylate esters were determined by gas chromatography. Vinyl acetate ethylene copolymers can be determined by saponification with 1 N ethanolic potassium hydroxide at 80 C for 3 hours and back titration with standard acid or by saponification with p-toluene sulfonic acid and back titration with standard acetic acid [49, 50]. 

Although two isomeric esters are theoretically possible, the main product is the 2-ester (formulated above) traces of the isomeric l-ester are eliminated during purification. These derivatives possess a free carboxyl group their equivalent weights may therefore be determined by titration with standard alkali and thus serve as an additional check upon the identity of the compound. 

The amount of the ester sulfonates, besides the mono- and disalt of the a-sulfo fatty acid, can be calculated by two titrations, one in the acid and one in the basic range. In the basic range both sulfonates and carbocylate functionalities are negatively charged and titrated with the cationic surfactant hyamine. In acid medium the RCOOH group is protonated and no longer available for the titration. Since hyamine-methylene blue (acid conditions) titrates only sulfonate and hyamine-phenol red (basic conditions) determines both sulfonates and carbo-cylates, substraction of the titration value with phenol red from the double value of the titration with methylene blue yields only the a-sulfo fatty acid ester. This is the only species of the three which has merely the sulfonate function [106]. 

Acidity of the reaction mixes after incubation increased as the activity of the probe ro —se during determination of pectinesterase activity of the samples.1t was caused by the for—mation of carboxyl groups as a result of pectin ester bonds hydrolysis under pectinesterase ac—tion.That is why kinetic characteristics of substrate hydrolysis were measured according to the speed of pectin hydrolysis by continuously recorded titration of the free carboxyl groups (11). 

Another example of interest with regard to the reaction mechanism is the analysis of epoxy groups. Durbetaki60 titrated a-epoxy compounds with HBr (cf., p. 260) in glacial acetic acid with crystal violet as indicator, but the method was slow for glycidyl esters, CH2—CHCH2OOCR. As it concerns a two-step... 

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