Acetyl number

Acetyl-saure, /. acetic acid, -schwefelsaure, /, acetylsulfuric acid. -senfSl, n. acetyl mustard oil, -zahl,/. acetyl number. 

Other Determinations.—These include determinations of the saponification, iodine and acetyl numbers and are made by the ordinary methods (see Vol. I Fatty Substances). As regards the iodine number, as factis is only slowly soluble in chloroform, it must be left in contact with the latter for at least 12 hours with frequent agitation, before the iodine solution is added further, since factis retains iodine tenaciously, long and vigorous shaking is necessary in the final titration. 

Acetyl Number It is defined as the amount in millilitres of potassium hydroxide solution required to neutralise the acetic acid obtained by saponification of 1 gm of fat or oil after acetylation. Some fatty acids contain hydroxyl groups. In order to determine the proportion of these, they are acetylated by means of acetic anhydride. This results in the introduction of acetyl groups in the place of free hydroxyl groups. The acetic acid in combination with fat can be determined by titration of the liberated acetic acid from acetylated fat or oil with standard alkali. Acetyl number is thus a measure of the number of hydroxyl groups present in fat or oil. 

The acetyl value is the number of mg of KOH required to neutralize the acetic acid produced by the hydrolysis of 1 g of acetylated fat and is a measure of free hydroxyl groups present in the oil. The acetyl number of peanut oil (8.5-9.5) is lower than other vegetable oils but higher than coconut oil, palm oil, and the animal fats and oils. 

Acetyl number (value) n. Number of milligrams of potassium hydroxide required to neutralize the acetic acid set free from 1 g of an acetylated compound when the latter is subjected to hydrolysis. 

For the determination of the number of acetyl groups in pentacetyl-glucose, see p. 456,... 

The excess of unchanged acetic anhydride is then hydrolysed by the addition of water, and the total free acetic acid estimated by titration with standard NaOH solution. Simultaneously a control experiment is performed identical with the above except that the alcohol is omitted. The difference in the volumes of NaOH solution required in the two experiments is equivalent to the difference in the amount of acetic add formed, i.e., to the acetic acid used in the actual acetylation. If the molecular weight of the alcohol is known, the number of hydroxyl groups can then be calculated. 

This method is precisely similar to the previous method used for the estimation of the number of hydroxyl groups in a polyhydric alcohol. A known weight of aniline is heated with a mixture of acetic anhydride and pyridine until acetylation is complete the excess of acetic anhydride remaining is... 

Estimation of the Number of Acetyl Groups in an Acetyl Ester. 

I. DETERMINATION OF NUMBER OF ACETYL GROUPS IN TRIACETIN (TRIACETYL-GLYCEROL) C3H6(O COCH3)3. Molecular Weight, 218. 

Under these first-order conditions the rates of nitration of a number of compounds with acetyl nitrate in acetic anhydride have been determined. The data show that the rates of nitration of compounds bearing activating substituents reach a limit by analogy with the similar phenomenon shown in nitration in aqueous sulphuric and perchloric acids ( 2.5) and in solutions of nitric acid in sulpholan and nitro-methane ( 3.3), this limit has been taken to be the rate of encounter of the nitrating entity with the aromatic molecule. 

Acetyl coenzyme A is the biosynthetic precursor to the fatty acids, which most often occur naturally as esters Fats and oils are glycerol esters of long chain carboxylic acids Typically these chains are unbranched and contain even numbers of carbon atoms... 

Fatty acids derived from animal and vegetable sources generally contain an even number of carbon atoms siace they are biochemically derived by condensation of two carbon units through acetyl or malonyl coenzyme A. However, odd-numbered and branched fatty acid chains are observed ia small concentrations ia natural triglycerides, particularly mminant animal fats through propionyl and methylmalonyl coenzyme respectively. The glycerol backbone is derived by biospeciftc reduction of dihydroxyacetone. 

Acetylation of hydroxyl groups and esterification of carboxyl groups have been observed ia a limited number of cases but, ia geaeral, have ao preparative advantage over chemical methods. By comparison, phosphorylation has been useful ia the preparatioa of modified purine and pyrimidine mononucleotides from their corresponding nucleosides, eg, 6-thioguanosiae [85-31-4] (51) (97). 

The hydroxyl number can be deterrnined in a number of ways such as acetylation, phthalation, reaction with phenyl isocyanate, and ir and nmr methods. An imidazole-catalyzed phthalation has been used to measure the hydroxyl number for a number of commercial polyether polyols and compared (favorably) to ASTM D2849 (uncatalyzed phthalation) (99). The uncatalyzed method requires two hours at 98°C compared to 15 minutes at the same temperature. 

Garyophyllene. (-)-CaryophyUene can be isolated from Indian turpentine and has been used to prepare a number of woody aroma products. The epoxides are produced by reaction with peracids. Acetylation of caryophyUene also gives a usehil methyl ketone (180) (Fig. 8). Acid-catalyzed rearrangement of caryophyUene in the presence of acetic acid gives a mixture of esters, which are related to caryolan-l-ol and clovan-2-ol (181). 

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