Acetyl Value and its Determination

Determination of acetyl content has been the commonest means for the characterization of a starch acetate. Quantitative determinations of the acetyl content of starch acetates may be made by several procedures, each of which involves an initial saponification of the acetyl groups. 

One suitable analytical procedure is a modification of the Eberstadt method developed primarily for use with cellulose acetates. By this procedure, the sample is swollen with warm 75% alcohol and then 

A second procedure involves the transesterification of a dry starch acetate in anhydrous methanol using sodium methoxide as a catalyst. 

Another similar procedure has been developed in which p-toluene-sulfonic acid is added to the reaction flask prior to the distillation of the methyl acetate. 

Since all of these methods involve heterogeneous saponifications, the physical condition of the sample is an important variable. Best results are therefore obtained if a finely divided or fluffy sample is used. 

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Rate constants for the mercuration of selenophene and its 2-bromo, 2-carboethoxy, 2-acetyl, and 2-nitro derivatives under the conditions employed by Motoyama et al.,121 have been determined at various temperatures by Yur ev and his co-workers.304 The selenophene derivatives were mercurated from 1.5 to 3 times more rapidly than the corresponding thiophene derivatives. A straight line is obtained in the Hammett plot with ap+ constants, with a p value of — 5.7 at 25°. 

Many of the tests described involve physical properties such as refractive index, viscosity or melting point of the fat, of the fatty acids or of the lead salts of the fatty acids. However, there were also many chemical tests such as Reichert, Polenske, iodine, saponification and acetyl values. These all gave information as to the composition of the fat, some information as to fatty acid composition, others as to other non-glyceride components of the fat. Thus the iodine value is a measure of unsaturated fatty acids in the fat, now obtainable in more detail from a fatty acid profile. Similarly the Reichert value is a measure of volatile fatty acids soluble in water. For most purposes this means butyric acid, and so the modem equivalent is the determination of butyric acid in the oil. The modem method for milk-fat analysis is thus carrying out the analysis in a similar way to the Reichert determination, but uses a technique that is less dependent on the exact conditions of the analysis and is thus less likely to be subject to operator error. The Reichert value could be useful, in theory, even if milk fat was not present. Lewkowitsch notes that some other oils do give high values. Porpoise jaw oil has a value almost twice that of milk fat, while some other oils also have significant values. It is unlikely that one would have come across much porpoise jaw oil even in 1904, and even less likely today. 

MSAS from P. patulum was separated from the FAS via sucrose gradient centrifugation [121,122] and thus shown to constitute a distinct multifunctional enzymatic system. It was purified to homogeneity and found to be a 190 kDa multifunctional enzyme [22,120]. The enzyme was more stable in the presence of its substrates and at mildly basic pH values. The pH optimum of the enzyme was 7.6 and apparent K values for its substrates were 10 pM (acetyl-CoA), 7 pM (malonyl CoA), and 12 pM (NADPH) [115,120,123]. The rate for triacetate lactone formation in the absence of NADPH was determined to be ten-fold lower than for 6-MSA formation (Fig. 5) [120]. Analogous to FASs and peptide synthetases, 4 -phosphopantetheine is a covalently bound cofactor of 6-MSAS [124]. Likewise, iodoacetamide and N-ethylmaleimide were found to inactivate the enzyme, suggesting the presence of catalytic sulfhydryl residues in 6-MSAS [124]. Furthermore, in the presence of malonyl CoA and NADPH, low concentrations of iodoacetamide convert 6-MSAS into a malonyl CoA decarboxylase. Without external addition of acetyl-CoA, 6-MSAS decarboxylates the malonyl group and the derived acetyl moiety is used as a starter unit for the formation of 6-MSA [125]. 

The urinary excretion pattern of the 11-oxy-17-OS during the first few days bears more resemblance to that found in adults (Table 10), but again paper chromatography shows other compounds with similar polarity to be present (C6). The rate of excretion of a major unknown substance is given in Table 10, and it will be seen that the urinary content of this and of the known compounds rapidly decline over the first few days. The results shown were determined by scanning paper chromatograms stained with Zimmermann reagent. Identification of the named steroids was not complete and consisted of a comparison of 1 / values in various solvent systems before and after acetylation of the compounds. 

The deacetylation process involves the removal of acetyl groups from chltln molecules. The DAC is defined as the average number of glucosamine units per 100 monomers expressed as a percentage. It determines the content of free amino groups [-NH2] in the chitosan and is one of the most important chemical characteristics that influence the physicochemical properties, biological properties, antibacterial activity, and applications of chitosan. In other words, DAC value determines the functionality, reactivity, polarity, and water solubility of the polymer. Chitin does not dissolve in dilute acetic acid. When chitin is deacetylated to a certain degree ( 60% deacetylation] where it becomes soluble in the acid, it is referred to as chitosan [18, 21]. 

DFT studies of the hydrolysis of acetyl and chloroacetyl chloride and of variously substituted benzoyl chlorides supported an S 2 mechanism. An extended Grunwald-Winstein equation correlation for the specific rates of solvolysis of 3,4,5-trimethoxybenzoyl chloride gave sensitivities towards changes in solvent nucleophilic-ity (/-value) of 0.29 and solvent ionizing power (m-value) of 0.54. The low m-value allowed specific rates to be determined in highly ionizing fiuoroalcohol/H20 mixtures. A parallel correlation of the specific rates of solvolysis of 2,4,6-trichlorobenzoyl chloride revealed that solvolyses in 100% and 90% ethanol or methanol did not appreciably follow the ionization pathway indicated for solvolyses in the other solvents and it was proposed that, despite the two or//to-substituents, the addition-elimination pathway had become dominant. ... 

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