Saponifications

Saponification procedures can be applied to the determination of ester groups in polymers. A copolymer of ethylene and vinyl acetate has the following structure which, upon hydrolysis in the presence of potassium hydroxide/p-toluene sulfonic acid catalyst [32, 33] reacts as follows  

Excess potassium hydroxide is then determined by titration with standard acetic acid, and the vinyl acetate content of the polymer calculated from the amount of potassium hydroxide consumed. 

Esposito and Swann [34] described a technique involving methanolysis of a polyester resin with lithium methoxide as a catalyst the methyl esters formed were separated from polyols and identified by gas chromatography  

This method was recently improved by Percival [35] using sodium methoxide as a catalyst and injecting the reaction mixture of the transesterification directly into the gas chromatograph (without preliminary separation). 

The hydrolysis of esters in the presence of bases is called saponification. Sample reaction 24-11 

Fats are carboxylic acid esters of glycerol. When these esters are hydrolyzed, carboxylic acids with long hydrocarbon chains called fatty acids are formed, along with the parent alcohol (glycerol). 

Which of the following most readily undergoes hydrolysis among the acid derivatives given below  

Which of the following is the major product of the reaction of an acid chloride with an alcohol  

The reaction of an ester with Grignard reagent (excess) in the presence of an aqueous acid results in  

This is a group of cyclic polyethers which are used as phase transfer catalysts. These have been used for esterifications, saponifications, anhydride formation, oxidations, aromatic substitution reactions, elimination reactions, displacement reactions, generation of carbenes, alkylations etc. Some of the examples are as follows  

CH3CH2, CH3CH2CH2, CeHs, 2-CH3C6H4, 2,4,6-trimethylbenzoyl, 4-t-butyl 

Hydrolysis of glycerides (fats) in a basic medium produces glycerol (glycerine) and a mixture of salts of long chained carboxylic acids (fatty acids). 

when heated with a solution of NaOH or KOH are hydrolyzed. After the hydrolysis, glycerine and long chained carboxylic acids salts are left, this mixture is soap and the process is called saponification. Soaps are basic salts which are formed by weak fatty acids and strong bases. For this reason, soap solutions show basic properties. Saponification is the reverse process of esterification. 

When NaOH is used in the saponification process, a solid soap is produced but when KOH is used, a molten soft soap is produced. 

Soap micelles absorb grease molecules into their interiors so that the grease is suspended in the water and can be washed away. 

Water soluble stains on the surface of clothes can easily be cleaned using water. If our hands get covered in salt, for example, it is enough to wash them with plenty of water. However, water isn t so effective at getting rid of oily stains. 

When an EVA copolymer is saponified, ethylene vinyl alcohol (EVOH) units are introduced (17,18). EVOH copolymers are excellent in melt moldability, gas barrier properties, oil resistance, antistatic property and mechanical strength, and are used as various types of packages in the form of a film, a sheet, a container, etc. 

In these packages, visible imperfections generated at the time of molding, e.g., discoloration, fish eyes, rough surface, etc., are significant problems that need to be addressed. Thus, several improvements in the process of producing an EVOH have been proposed. 

In the saponification of an EVA copolymer, usually an alkali catalyst is used. The alkali catalyst acts as a catalyst for the transesterification between EVA and an alcohol. It is known that in a process where saponification proceeds mainly with this transesterification, when water is present in the reaction system, the alkali catalyst is consumed, and the reaction rate of the saponification decreases. 

This arises, because water accelerates the direct saponification reaction between the EVA and the alkali catalyst. Moreover, water also accelerates the reaction between an acetic acid ester formed as a byproduct in the transesterification and the alkali catalyst. 

Therefore, attempts to fix this problem have focused exclusively on the removal of water from the reaction system. However, this procedure results in visible imperfections in products molded from the EVOH. Actually, the appearance of an EVOH molded product can be improved by adding trace amounts of water - which is conventionally removed as a catalyst poison (17). 

Acrylics can be somewhat sensitive to alkali environments — such as those which can be created by zinc surfaces [5], This sensitivity is nowhere near as severe as those of alkyds and is easily avoided by proper choice of copolymers. 

FIGURE 2.5 Depiction of an acrylate (left) and a methacrylate (right) polymer molecule. 

Poly(methyl methacrylate) is quite resistant to alkaline saponification the problem lies with the polyacrylates [6], However, acrylic emulsion polymers cannot be composed solely of methyl methacrylate because the resulting polymer would have a minimum film formation temperature of over 100°C. Forming a film at room temperature with methyl methacrylate would require unacceptably high amounts of external plasticizers or coalescing solvents. For paint formulations, acrylic emulsion polymers must be copolymerized with acrylate monomers. 

Acrylics can be successfully formulated for coating zinc or other potentially alkali surfaces, if careful attention is given to the types of monomer used for copolymerization. 

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Fats are hydrolysed to glycerol and fatty acids by boiling with acids and alkalis, by superheated steam and by the action of lipases. If alkalis are used for hydrolysis, the fatty acids combine with the alkalis to form soaps. Alkaline hydrolysis is therefore sometimes called saponification. 

In organic chemistry the term is used to describe the conversion of an ester to an acid and an alcohol (saponification), the addition of the elements of water to a molecule, e.g. the conversion of a nitrile to an amide... 

Saponification (number) NFT60-110 ISO 6293 ASTM D 94 Reaction with potash and analysis of excess... 

An interesting early paper is that on the saponification of I -monostearin mono-layers, found to be independent of surface pressure [307]. 

A selection of important anionic surfactants is displayed in table C2.3.1. Carboxylic acid salts or tire soaps are tire best known anionic surfactants. These materials were originally derived from animal fats by saponification. The ionized carboxyl group provides tire anionic charge. Examples witlr hydrocarbon chains of fewer tlran ten carbon atoms are too soluble and tliose witlr chains longer tlran 20 carbon atoms are too insoluble to be useful in aqueous applications. They may be prepared witlr cations otlrer tlran sodium. 

Hydrolysis (or saponification) of n-butyl acetate. Boil 4-5 g. of n-butyl acetate (Section 111,95) with 50 ml. of 10 per cent, sodium hydroxide solution under reflux until the odour of the ester can no longer be detected (about 1 hour). Set the condenser for downward distiUation and coUect the first 10 ml. of distillate. Saturate it with potassium carbonate, aUow to stand for 5 minutes, and withdraw all the Uquid into a small pipette or dropper pipette. AUow the lower layer of carbonate solution to run slowly into a test-tube, and place the upper layer into a small test-tube or weighing bottle. Dry the alcohol with about one quarter of its buUr of anhydrous potassium carbonate. Remove the alcohol with a dropper pipette and divide it into two parts use one portion for the determination of the b.p. by the Siwoloboff method (Section 11,12) and convert the other portion into the 3 5-dinitrobenzoate (Section III, 27) and determine the m.p. 

It is frequently advisable in the routine examination of an ester, and before any derivatives are considered, to determine the saponification equivalent of the ester. In order to ensure that complete hydrolysis takes place in a comparatively short time, the quantitative saponi fication is conducted with a standardised alcoholic solution of caustic alkali—preferably potassium hydroxide since the potassium salts of organic acids are usuaUy more soluble than the sodium salts. A knowledge of the b.p. and the saponification equivalent of the unknown ester would provide the basis for a fairly accurate approximation of the size of the ester molecule. It must, however, be borne in mind that certain structures may effect the values of the equivalent thus aliphatic halo genated esters may consume alkali because of hydrolysis of part of the halogen during the determination, nitro esters may be reduced by the alkaline hydrolysis medium, etc. 

The saponiflcatlon equivalent or the equivalent weight of an ester is that weight in grams of the ester from which one equivalent weight of acid is obtainable by hydrolysis, or that quantity which reacts with one equivalent of alkali. The saponification equivalent is determined in practice by treating a known weight of the ester with a known quantity of caustic alkali used in excess. The residual alkali is then readily determined by titration of the reaction mixture with a standard acid. The amount of alkafi that has reacted with the ester is thus obtained the equivalent can then be readily calculated. 

The experimental details already given for the detection and characterisation of aliphatic esters (determination of saponification equivalents h3 diolysis Section 111,106) apply equally to aromatic esters. A sfight modification in the procediu-e for isolating the products of hydrolysis is necessary for i)henolic (or phenyl) esters since the alkaline solution will contain hoth the alkali phenate and the alkali salt of the organic acid upon acidification, both the phenol and the acid will be hberated. Two methods may be used for separating the phenol and the acid ... 

When the compound for identification fails to respond to test 4 (aldehyde or ketone), the next class reactions to apply are the hydroxatnic acid teat and saponification, i.e., hydrolysis in alkaline solution. These are the class reactions for esters and anhydrides the rarely-encountered lactones react similarly. 

An ester is converted upon saponification into an alcohol and the salt of an acid, or the salts of both an acid and a phenol if it is an ester of a phenol. An anhydride upon hydrolysis yields only a salt of an acid. 

Saponification of esters. Aqueous sodium hydroxide method. To hydrolyse an ester of an alcohol, reflux 5-6 g. with 50 ml. of 20 per cent, sodium hydroxide solution for 1-2 hours or until the ester layer disappears. Distil the alkahne mixture and collect about 6 ml. of distillate. This will contain any volatile alcohol formed in the saponification. If the alcohol does not separate, i.e., is water-soluble, saturate the distillate with sohd potassium carbonate an upper layer of alcohol is then usually formed. (The alcohol may be subsequently identified as the 3 5-dinitrobenzoate see Section 111,27,2.) Cool the residual alkahne mixture, and acidify it with dilute sulphuric acid. If no crystalline acid is precipitated, the acid may frequently be isolated by ether extraction, or it may be distilled from the acidified solution and isolated from (or investigated in) the distfllate. (The acid may be subsequently identified, e.g., as the S benzyl wo-thiuronium salt see Section 111,85,2.)... 

The addition of about 0-2 g. of an emulsifying agent, such as sodium lauryl or oleyl sulphate, assists in reducing the time required for complete saponification a large flask should be used since there is usually considerable foaming. 

The determination of the saponification equivalent of an ester by the alcohohc potassium hydroxide method is described in Section 111,106 an alternative procedure using diethylene glycol is given below. This constant should be determined if possible in the prehminary examination, since a knowledge of its value together with the boihng point provides a basis for a fairly good approximation of the size of the ester molecule. 

Determination of the Saponification Equivalent of an Ester BY THE Diethylene Glycol Method... 

Cydopentane reagents used in synthesis are usually derived from cyclopentanone (R.A. Ellison, 1973). Classically they are made by base-catalyzed intramolecular aldol or ester condensations (see also p. 55). An important example is 2-methylcydopentane-l,3-dione. It is synthesized by intramolecular acylation of diethyl propionylsucdnate dianion followed by saponification and decarboxylation. This cyclization only worked with potassium t-butoxide in boiling xylene (R. Bucourt, 1965). Faster routes to this diketone start with succinic acid or its anhydride. A Friedel-Crafts acylation with 2-acetoxy-2-butene in nitrobenzene or with pro-pionyl chloride in nitromethane leads to acylated adducts, which are deacylated in aqueous acids (V.J. Grenda, 1967 L.E. Schick, 1969). A new promising route to substituted cyclopent-2-enones makes use of intermediate 5-nitro-l,3-diones (D. Seebach, 1977). 

Erlenmeyer et al. showed that it is possible to realize a moderated saponification of diethyl 4,5 thiazoledicarboxylate in mild conditions with an ethanolic potassium solution. The attack begins at the 5-position, and finally monoesters in the 4-position are obtained (Scheme 9) (17). 

Ester hydrolysis in base is called saponification, which means soap making Over 2000 years ago the Phoenicians made soap by heating animal fat with wood ashes Animal fat is rich m glycerol triesters and wood ashes are a source of potassium car bonate Basic hydrolysis of the fats produced a mixture of long chain carboxylic acids as their potassium salts... 

Potassium and sodium salts of long chain carboxylic acids form micelles that dissolve grease (Section 19 5) and have cleansing properties The carboxylic acids obtained by saponification of fats are called fatty acids... 

In an extension of the work described m the preceding section Bender showed that basic ester hydrolysis was not concerted and like acid hydrolysis took place by way of a tetrahedral intermediate The nature of the experiment was the same and the results were similar to those observed m the acid catalyzed reaction Ethyl benzoate enriched m 0 at the carbonyl oxygen was subjected to hydrolysis m base and samples were isolated before saponification was complete The recovered ethyl benzoate was found to have lost a por tion of Its isotopic label consistent with the formation of a tetrahedral intermediate... 

In base the tetrahedral intermediate is formed m a manner analogous to that pro posed for ester saponification Steps 1 and 2 m Figure 20 8 show the formation of the tetrahedral intermediate m the basic hydrolysis of amides In step 3 the basic ammo group of the tetrahedral intermediate abstracts a proton from water and m step 4 the derived ammonium ion dissociates Conversion of the carboxylic acid to its corresponding carboxylate anion m step 5 completes the process and renders the overall reaction irreversible... 

Section 20 11 Ester hydrolysis m basic solution is called saponification and proceeds through the same tetrahedral intermediate (Figure 20 5) as m acid catalyzed hydrolysis Unlike acid catalyzed hydrolysis saponification is irreversible because the carboxylic acid is deprotonated under the reac tion conditions... 

The saponification of 0 labeled ethyl propanoate was desenbed in Section 20 11 as one of the significant expenments that demonstrated acyl-oxygen cleavage in ester hydrolysis The 0 labeled ethyl propanoate used in this expenment was prepared from 0 labeled ethyl alcohol which in turn was obtained from acetaldehyde and 0 enriched water Wnte a senes of equations... 

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