Acetyl content, analytical determinations

Specifications and Analytical Methods. The commercial material is specified as 97% minimum purity, determined by gas chromatography or acetylation. Moisture is specified at 0.05% maximum (Kad-Fischer titration). Formaldehyde content is determined by bisulfite titration. 

After prolonged degassing of a large batch of PPG, analyses showed that its hydroxyl, unsaturation, and water contents were 0.97 meq/g, 0.033 meq/g, and 0.0035%, respectively. The hydroxyl content was determined by an acetylation method, carried out with acetic anhydride (10). The amounts of unsaturation and water were determined by the mecuric acetate and Karl Fischer methods (10), respectively. The obtained analytical results indicate that the number-average molecular weight of the dihydroxy material is 2062, provided its molecular weight is arbitrarily assumed to be twice that of the monohydroxy material, and that the mole fraction of the monohydroxy poly (propylene oxide) is 0.066. This value corresponds to a number-average functionality of 1.93 for the PPG. 

Considerable effort in the past few years has been devoted to the development and the study of rapid and efficient analytical methods for the determination of functionality in coal and coal derived products (2-11). The determination of phenol and alcohol moieties by acetylation has been used routinely for several years (1,3-7). Recently several groups have used silylation in combination with Infrared,(10) proton NMR (2) and atomic adsorption spectroscopy (3) to determine phenolic and alcoholic content of coal and coal derived products. Triethylborane activated by pivalic acid has been used very recently as a reagent for the determination of hydroxyl groups in lignites (11). 

The new MALDI-MS based analytical procedures described in this chapter have been employed successfully for (i) determining the accurate molar mass and molar mass distribution for different types of xylans and glucomannans, (ii) characterizing the distribution of uronic acid residues in hard- and softwood xylans and (iii) determining the content and distribution of 0-acetyl substituents in xylans and glucomannans. 

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