Ester sulfonates titration

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]. 

Carboxylic and sulfonic acid groups import acidity to organic compounds. Most carboxylic acids and sulfuric acids are readily dissolved in water, and their titration with a base is straightforward. If solubility in water is not sufficient, the acid can be dissolved in ethanol and titrated with aqueous base. Aliphatic amines and many saturated cyclic amines can be titrated directly with a solution of a strong acid. Esters are determined by saponification with a measured quantity of standard base. The excess base is titrated with standard acid. 

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. 

In these procedures, the hydroxyl-containing polymer is reacted with an excess of a standard non-aqueous solution of acetic anhydride or phthalic anhydride, sometimes in the presence of a catalyst such as p-toluene sulfonic acid. After ester formation is complete, an excess of water is added to convert excess anhydride to the free carboxylic acid. The acid is titrated with aqueous or alcoholic standard potassium hydroxide to the phenol phthalein end-point to determine unconsumed acid. A blank run is carried out in which the sample is omitted. The hydroxyl... 

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]. 

Titration at alkaline pH. The two-phase titration is performed twice at pH 9, using bromcresol green and then phenol red to indicate the titration end point. With bromcresol green, only the a-sulfo fatty acid methyl ester is determined. With phenol red, the total of sulfonate and carboxylate groups is determined. The difference between these values and that for total sulfonate (determined by titration to the methylene blue end point) yields the carboxylate content. If soap is present, its concentration must be subtracted to determine a-sulfo fatty acid (120,121). 

In general, phosphate esters will respond poorly if at all to the paired-ion procedures used to determine sulfate and sulfonate anionic surfactants by titration or spectrophotometry. This is presumably due to their hydrophilicity. Some success has been reported with individual products of higher lipophile character, such as didodecyl phosphate (123). 

Saponification for four hours will decompose a-sulfo fatty acid methyl esters so that they can no longer be titrated by the standard two-phase procedure, either in acidic or basic media. A one-hour saponification will cleave the ester, but will remove only about 20% of the sulfonate group, so that these compounds are still titrated. Reflux with HCl has no effect. On the other hand, reflux with either acid or base will decompose fatty alcohol sul-foacetates so that they are no longer titratible (35). 

So far it has been assumed, without any proof, that sulfonic groups in SPPO are attached to aromatic rings. In principle, sulfonic groups could also be attached to methyl groups as in case of other modified PPO polymers, for example, carboxylated PPO or methyl ester carboxylated PPO [22]. Acid-base and conductimetric titrations do not allow distinguishing between aryl and methyl substituted PPO. On the other hand, proton nuclear magnetic resonance ( H NMR) and infrared (IR) spectroscopy provide more information on the structure of SPPO. These techniques can also be used for determination of the DS of SPPO. 

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