Unreacted anhydride

In the blank titration, the acetic anhydride is hydrolyzed to give 2 mol of acetic acid per mole of AC2O. In a sample titration, each unreacted anhydride molecule likewise yields two of acetic acid, but each reacted AC2O molecule yields only one... 

The acetylation is ordinarily carried out by mixing the sample with a carefully measured volume of acetic anhydride in pyridine. After heating, water is added to hydrolyze the unreacted anhydride ... 

The anhydride-epoxide reaction is complex because of the possibility of several reactions occurring simultaneously. Thus, appreciable etherification can result in undesirable amounts of unreacted anhydride and half-acid ester in the cured resin. On the basis of experimental results, Arnold (11) has suggested that for optimum properties anhydride to epoxide ratios of 1 1 are needed for tertiary amine catalysts, and 0.85 1 for no catalyst. 

Upon completion of the esterification reaction, the triester, or totally esterified cellulose, is transferred to a hydrolysis reactor and combined with water to destroy unreacted anhydrides and to effect hydrolysis. The reaction is carried out at elevated temperatures under the influence of sulfuric acid catalysis and continued until control measurements indicate the desired hydroxyl content of the ester has been attained. The hydrolysis reaction is terminated by the addition of magnesium carbonate, which neutralizes the sulfuric acid, releases carbon dioxide, and forms insoluble magnesium sulfate crystals that are subsequently removed during the filtration process. 

The Dp of prepolymers was affected by the nature of the monomer, the ratio between the monomer and acetic anhydride, and the reaction time. Short oligomers of 1-2 monomer units were prepared from the reaction of the diacid monomer with acetyl chloride in chlorinated hydrocarbon solution in the presence of an acid acceptor. Prepolymers were also prepared using propionic anhydride and butyric anhydride. However, these reagents boil at a higher temperature than acetic anhydride thus requiring vigorous conditions to remove the unreacted anhydride and acids by vacuum evaporation. Acetic acid mixed anhydride prepolymers were prepared also from the reaction of the diacid monomers with ketene [30],... 

Studies have been made of PEST/PO/styrene copolymer blend compatibilization in which a copolymer may be formed between polyester alcohol end-groups and pendent anhydride functionality on a styrene copolymer (Table 5.27). Because the alcohol-anhydride reaction is reversible (with the equilibrium lying on the side of unreacted anhydride), only a relatively small amount of copolymer may be formed. In consequence, the dispersed phase polymer may not be well stabilized against coalescence upon further thermal treatment [Sun et al., 1996]. Alternatively, at least some copolymer may be formed by a degradative mechanism through transesterification between PEST main-chain linkages and a low concentration of pendent acid groups in anhydride-functionalized styrene copolymer (see Section 5.7.12.5). 

Blends containing PA and an anhydride-modified polyphenylene sulfide have been prepared by Kadoi et al. (1996). For example, PPS was extruded with either maleic anhydride, itaconic anhydride, or succinic anhydride to form a PPS shown to have carbonyl incorporation by FTIR after selective solvent extraction to remove unreacted anhydride. Blends of modified PPS and PA-66 were extruded at 290-310 °C and molded to provide test parts with improved properties compared to blends with unmodified PPS. 

Turning now to chemical methods used for stereochemical studies of carotenoids the modified Horeau method (32) has been successfully used to confirm the configuration of (2/ )- 3, 3-caroten-2-ol [(33), R=H] (38) and to establish the configuration of aleuriaxanthin (36) (34). However, no conclusive results could be obtained for plectaniaxanthin [(35), R = R =H] (28). In principle the Horeau method is based on partial resolution of racemic and meso a-phenylbutyric anhydride by means of an optically active secondary alcohol, which readts preferentially with one diastereomer. The unreacted anhydride is quantitatively determined by an appropriate procedure (32, 68, 94). 

The principal property measured in polyols is hydroxyl content. According to ASTM D4274-88, hydroxyl group content is determined by acetylation and the excess of acid is back titrated with a base. The acetylating agent is usually a solution of acetic anhydride in pyridine. Acetylation is carried out at 100 °C. Unreacted anhydride is then converted with water into acid and titrated with 1 N NaOH. Hydroxyl content is usually expressed as hydroxyl number (OH number), which is defined as the number of milligrams of KOH (Mkoh = 56.11) used for titration of one gram of the sample. 

The anhydride-epoxy reaction is complex because of the possibility of several reactions occurring simultaneously. Appreciable etherification can result in undesirable amounts of unreacted anhydride... 

A decrease in the anhydride concentration is indicated by decreases in intensity of the vibrations at 1860, 1080 and 918 cm . An increase in the concentration of carboxyl groups is indicated by the increases in the intensities of the bands at 1712 cm (C=0), 1395 cm (O—H) and 1195 cm (C—O). These spectral results reflect the initial hydrolysis of the unreacted anhydride (approximately 5% of the initial anhydrides) to the diacid, which is in part leached from the sample by the water. As shown in Fig. 4.5, the water induces some of the diacid molecules to react with the epoxy groups. 

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