Saponification with alkali

In our laboratory we have used two methods, both of which involve saponification with alkali to yield methanol. The released methanol can be analyzed colorimetrically after oxidation to formaldehyde with potassium permanganate, and reaction of the formaldehyde with pentan-2,4-dione, to yield a chromophore with Amax 412 nm (Wood and Siddiqui, 1971). Alternatively, the methanol produced can be converted to its nitrite ester by reaction with sodium nitrite and analyzed by GLC (Litchman and Upton, 1972 Versteeg, 1979). For the latter procedure to be reliable, careful timing of the reactions is required (Litchman and Upton, 1972). 

The 0-acetyl content of a cell wall preparation of polysaccharide can readily be determined after saponification with alkali by colorimetric or GLC methods. 

Instead of the not necessarily harmless saponification with alkali, in 1973 M.A. Barton and her associates proposed an elegant procedure cleavage of the peptide from the supporting polymer by intramolecularly catalyzed transesterification of the (benzyl) ester bond with dimethylaminoethanol followed by the anchimerically assisted hydrolysis of the peptide dimethylaminoethyl ester. 

Saponification with alkali generally used for the removal of methyl and ethyl esters is avoided if instead of simple alkyl esters rather benzyl esters or tert.butyl esters are applied for the protection of carboxyl groups. In addition to acid catalyzed esterification benzyl esters can also be secured by the reaction of cesium salts of (blocked) amino acids with benzyl chloride ... 

The carboxyl group is esterified in the process and has to be deblocked by saponification with alkali to allow its activation for subsequent incorporation. Deprotection of the imidazole can be achieved by catalytic hydrogenation although sometimes difficulties are encountered in this step. An alternative method of debenzylation, treatment with acetic acid, must be carried out at fairly high temperature. More acid sensitivity is shown by the im-trityl derivative while the diphenyl-4-pyridylmethyl group is acid resistant ... 

The degree of blockiness in the structure of partially hydrolysed, poly(vinyl acetate) depends on the method of hydrolysis. Saponification with alkali gives vinyl acetate-alcohol copolymers with a highly blocked structure, transesterification with methanolic methoxides gives intermediate blockiness, and acid-catalysed equilibrium hydrolysis gives near-random copolymers. These structures respond differently in iodination analyses. ... 

The xanthophylls and carotenes of plants are examined conveniently after removal of the chlorophylls by saponification with alkali. For this saponification, add 10 ml of 30% potassium hydroxide in methanol to the centrifuged acetone or methanol extract in the separatory funnel. After 30 min with occasional swirling, add 40 ml of cold petroleum ether (20-40°C)-diethyl ether (1 1) plus 100 ml of 10% aqueous sodium chloride solution. Wash the resultant upper golden-yellow layer with water and take to dryness as above. Prepare the sample solution by dissolving the residue in 1 ml of petroleum ether (60-110°C)-diethyl ether (1 1). This saponification procedure should not be employed with plant extracts containing xanthophylls that are decomposed by alkalies, as are fucoxanthin from diatoms and brown algae and peridinin from dinoflagellates. 

The general test for esters (including lactones) and anhydrides is saponification with alkali. Ethers will remain unaffected under the experimental conditions chosen, but aldehydes may be decomposed. See Problem 17. 

The decomposition of fats can he effected in many ways, eitlier by saponification with alkalies or alka-1 7J. 

The reactions involved in the various methods for carrying out this process are theoretically as follows — ((/) In tlic saponification with alkalies, e.g. with lime —... 

Acylglycerols can be hydrolyzed by heating with acid or base or by treatment with lipases. Hydrolysis with alkali is called saponification and yields salts of free fatty acids and glycerol. This is how soap (a metal salt of an acid derived from fat) was made by our ancestors. One method used potassium hydroxide potash) leached from wood ashes to hydrolyze animal fat (mostly triacylglycerols). (The tendency of such soaps to be precipitated by Mg and Ca ions in hard water makes them less useful than modern detergents.) When the fatty acids esterified at the first and third carbons of glycerol are different, the sec-... 

Fractional saponification, with the use of varying amounts of caustic alkali, will also reveal the presence of terpinyl acetate. 

Acetylation.—Gitronellal may be quantitatively estimated by the ordinary acetylation process i when the aldehyde is quantitatively converted into isopulegyl acetate, which is then determined by saponification with potash in the ordinary way. Dupont and Labaume have attempted to base a method for the separation of geraniol from citronellal in citron-ella oils on the fact that the citronellal oxime formed by shaking with hydroxylamine solution at the ordinary temperature is not converted into an ester by subsequent acetylation, but into the nitrile of citronellic acid which is stable towards" alkali during the saponification process. 

Saponification of Esters or Lactones and Reaction of Persilylated Amides and Lactams with Alkali I 71... 

The basic process is that of reacting fat stocks with alkali to form soap (direct saponification) and glycerin, followed by washing to remove the glycerin. Two methods of direct saponification are in common use kettle method and continuous saponification). An alternative method is splitting fat stocks with water (hydrolysis) to form fatty acids and glycerine, followed by neutralization of the fatty acids with alkali,... 

Saponification, Resinous Substances.—Resin oils are not saponifiable, except for such part of the resinous substances as they may contain as impurities (especially in the crude oils) these combine with alkali and are detectable by the acid number see preceding paragraph) and by the saponification number, determined as in fatty oils see Vol. I, p. 375). 

The mechanism of this type of reaction, originally elucidated by Kruck (94), is related to the simple addition of the nucleophile observed with alkali alkoxides. In the present case the following reactions, in which the saponification step is also of preparative significance (99, 102), have been observed (45) ... 

Glycerides can also be hydrolyzed by treatment with alkali (saponification). After acidification and extraction, the free fatty acids are recovered as alkali salts (soaps). 

There are no significant differences between ethyl and methyl esters concerning synthesis or cleavage. Related protocols of the methyl esters (see Section 2.2.1.1.1.1) are, therefore, applied to the ethyl esters. The usefulness of ethyl esters is somewhat limited by the difficulties encountered in their saponification. Hydrolysis with alkali is feasible, but ethyl esters are less sensitive to nucleophilic attack than methyl esters. Aminolysis and hydrazinolysis as well as cleavage of the alkyl-oxygen bond with lithium iodide in pyridineb l proceed several times slower in the case of ethyl esters. Mild enzyme-catalyzed hydrolysis by trypsin and chymotrypsin,t 2° 2 1 or by carboxypeptidase remains an attractive alternative. 

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