Acetyl Value

Fig. 1. Acetyl value and combined acetic acid for acetate esters of cellulose. Designations are as follows CA = acetate(DS = 2.4) CELL = cellulose(DS = 0) CTA = triacetate(DS = 3.0). Combined acetic acid (%) = 6005(DS)/( 159.1 + 43.04(DS)) acetyl value...

Secondary Acetate Processes. There is no commercial process to directiy produce secondary cellulose acetate sufficientiy soluble in acetone to produce fiber. Hence, the cellulose is completely acetylated to the triacetate during the dissolution step and then hydrolyzed to the required acetyl value. 

R. R. Miller - has examined six typical samples ot Wisconsin oils, and gives the following figures lor the cstur and acetylation values, which do not indicate so great a variation as the above figures. In the eater determination, the resells for saponiricetion in thirty minutes... 

Acetyl values from fully acetylated xylan preparations indicate a D. P. of about 100 or greater. The theoretical acetyl value for a fully acetylated xylan molecule of infinite size is 39.8%. As the molecule decreases in length, its acetyl content increases because of the increasing proportion of triacetyl-bearing end units. Assuming an accuracy of 0.1% for the acetyl determination, a noticeable deviation from theory would be apparent in acetylated xylan of less than D. P. 100. 

Solution Viscosity and Acetyl Value. For cellulose triacetate, the values of [ln /C] C = 0.1% in a 90 to 10 volume mixture of methylene chloride-methanol at 25°C. were measured and denoted as inherent viscosity (I. V.) (deciliters per gram). 

Acetyl values were determined by base hydrolysis of the acetyl groups of a weighed sample, followed by back-titration to determine the number of milliequivalents of acetic acid. 

Acetyl Values and Solution Viscosities of the Residues. Acetyl values are summarized in Table I. In nearly all cases the irradiated samples had higher acetyl values than the original ones. 

Chitin is classically a linear polymer of /3-d-(1 - 4)-linked 2-acetamido-2-deoxy-D-glucosyl residues. However, after comparing chitin isolated from different sources, it became evident that substantial variations in solubility, molecular weight, acetyl values, and specific rotation occur among samples. It would appear that chitin is not a single, polymeric entity, but rather, a family of closely related products derived from natural chitin-protein complexes.209... 

N-Acetyl glucosaminidase, V, 61 Acetyl phosphate, III, 237 Acetyl propionyl. See 2,3-Propanedione. Acetyl value, determination of, for starch acetates, I, 290 Acetylation, of cellulose, I, 311 rates for various cellulosic fibers, V, 122, 123... 

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. 

The acetyl value is defined as the number of mg of potassium hydroxide required to neutralize the acetic acid obtained by saponifying 1 g of the acetylated sample. 

Saponification Weigh accurately from 2 to 2.5 g each of the acetylated oil and of the original, untreated sample into separate 250-mL Erlenmeyer flasks. Add to each flask 25.0 mL of 0.5 N alcoholic potassium hydroxide, and continue as directed in the Procedure under Saponification Value, in this Appendix, beginning with Connect an air condenser.. .. Record the saponification value of the untreated sample as S, and that of the acetylized oil as S, then calculate the acetyl value of the sample by the formula... 

Proceed as directed under Acetyl Value, in this Appendix, but calculate the hydroxyl value by the formula... 

It should be borne in mind in these cases that while mixed acetic anhydride and sulfuric acid produce acetylation, they also bring about acetolysis which may result in severe depolymerization of the starch molecules. The occurrence of degradation is evident from the fact that the resulting acetates have acetyl values in excess of the theoretical value of 44.78%, and from the finding of glucose pentaacetate among the reaction products whenever low temperatures or low sulfuric acid concentrations are not employed. 

It should be observed that slight depolymerization or incomplete acetylation of the starch acetate molecule leads to products possessing a much wider degree of solubility. For example, at low acetyl values (0-26%), starch acetates are said to be water-soluble. -" However, if the starch molecules are undegraded, it is probable that the water-soluble range does not extend to products containing more than fi-15% acetyl groups. 

The air-dried leaves gave about 0.5 per cent of a light yellow oil, specific gravity at 15°/15, 0.9181, optical rotation -i-337 , refractive index 1.489, ester value 20, acetyl value 3.5. This oil contained 5 to 10 per cent of ci-pinene, 20 to 25 per cent of h-a-phellandrene, 10 to 15 per cent of cineole, sesquiterpenes 30 to 40 per cent, sesquiterpene alcohols 5 to 10 per with traces of aldehydes, phenols and esters. 

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