Anhydride groups, determination

The free maleic acid content in maleic anhydride is determined by direct potentiometric titration (166). The procedure involves the use of a tertiary amine, A/-ethylpipetidine [766-09-6J, as a titrant. A tertiary amine is chosen as a titrant since it is nonreactive with anhydrides (166,167). The titration is conducted in an anhydrous solvent system. Only one of the carboxyhc acid groups is titrated by this procedure. The second hydrogen s dissociation constant is too weak to titrate (166). This test method is not only used to determine the latent acid content in refined maleic acid, but also as a measure of the sample exposure to moisture during shipping. 

Monomer Reactivity. The poly(amic acid) groups are formed by nucleophilic substitution by an amino group at a carbonyl carbon of an anhydride group. Therefore, the electrophilicity of the dianhydride is expected to be one of the most important parameters used to determine the reaction rate. There is a close relationship between the reaction rates and the electron affinities, of dianhydrides (12). These were independendy deterrnined by polarography. Stmctures and electron affinities of various dianhydrides are shown in Table 1. 

In films cured initially at 175°C, determination by infrared spectroscopy of the concentration of anhydride groups indicated that all potential cross-linking groups had reacted. 

Exercise 22-30 a. In the nitration of para-cymene by ethanoyl nitrate in ethanoic anhydride, the observed product composition at 0° is 41 % 5 and 6, 41 % 3, 8% 4, and 10% of 4-nitromethylbenzene. Use these results to determine the relative reactivities of the para-cymene ring carbons towards N02 . Give your answer relative to C3 as unity (C3 is the carbon next to the isopropyl group). Determine the relative reactivities based on the data obtained in Equation 22-1. How does neglect of ipso substitution affect calculation of relative reactivities of the ring carbons b. Write a mechanism for the solvolytic conversion of 5 and 6 to 3. 

Details are given of the solution polymerisation of styrene-maleic anhydride copolymers with surfaces containing functional arrhydride groups of differerrt percerrtage. Ampicillin was bound to the anhydride groups and spectroscopically characterised. The in vitro release rate of Ampicillin was established together with the determination of its antimicrobial activity. 13 refs. 

Recently Heitz et at. 20) have used cationic oligomerization of THF in the presence of acetic anhydride to calculate K, and K. They have assumed that the distribution of the oligomers carrying acetoxy end groups, determined by gpc, corresponds to the distribution of the living oligomers. The GPC chromatogram is shown in Fig. 2.1. 

Determinations of grafted anhydride groups were carried out on the automatic titration assembly Titroprocessor produced by Metrohm. 

In Fig. 13.4, the concentration of the amine end groups (determined by po-tentiometric end-group titrations) after blocking with succinic anhydride in CO2/IO mol% 1,4-dioxane is given vs time. 

Weigh the product and calculate the percent yield. Determine the melting point and obtain an infrared spectrum. Compare your results to those listed in the literature (The Aldrich Library ofIR Spectra and/or SciFinder Scholar). What characteristic absorptions do you observe for the anhydride group in the carbonyl region of the spectrum ... 

Van Houwelingen [8] discussed the determination of anhydride groups in a resin derived from octadecene-1 and maleic anhydride. 

A suitable method for determining the anhydride group is titration with aqueous potassium hydroxide in pyridine after previous esterification of the carboxyl group with diazomethane. This esterification is carried out in diethyl ether methanol (9 + 1). After methylation, which takes about 10 minutes for 0.5 g of sample, solvents are removed by evaporation and a portion of the derivatised polymer is dissolved in pyridine and titrated. In the IR spectra of the resin before and after methylation, the absorption band of the acid group at 1710 cm (5.84 pm) disappears and a carbonyl band of the ester at 7104 cm (5.74 pm) is formed. The acid content of the sample is found from the difference in titres of an unmethylated and a methylated product. 

Functional Group Analysis. The total hydroxyl content of lignin is determined by acetylation with an acetic anhydride—pyridine reagent followed by saponification of the acetate, and followed by titration of the resulting acetic acid with a standard 0.05 W sodium hydroxide solution. Either the Kuhn-Roth (35) or the modified Bethge-Liadstrom (36) procedure may be used to determine the total hydroxyl content. The aUphatic hydroxyl content is determined by the difference between the total and phenoHc hydroxyl contents. 

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