Mechanisms saponification

The mechanisms by which an alkaline cleaner removes the soil are saponification, emulsification, and dispersion. These mechanisms can operate independently or in combination. Saponification occurs when alkaline salts react with fatty components of the soil, forming a soluble soap compound. 

On the basis of the general mechanism for basic ester hydrolysis shown in Figure 20.5, write an analogous sequence of steps for the saponification of ethyl benzoate. 

Lormetazepam (84) is readily synthesized by Polonovski rearrangement of benzodiazepine oxide derivative by heating with acetic anhydride followed by saponification of the resulting rearranged ester.The mechanism of this rearrangement to... 

The mechanism shown in Figure 21.7 is supported by isotope-labeling studies. When ethyl propanoate labeled with lsO in the ether-like oxygen is hydrolyzed in aqueous NaOH, the l80 label shows up exclusively in the ethanol product. None of the label remains with the propanoic acid, indicating that saponification occurs by cleavage of the C-OR bond rather than the CO—R bond. 

Mechanism of base-induced ester hydrolysis (saponification). 

The removal of organics by industrial detergent cleaners. These products employ several mechanisms, depending on the formulation, but tend to include dissolution (using nonaqueous solvents such as kerosene, petroleum spirits, and naphtha, saponification, by caustic, or emulsification by nonionic detergents. 

The sirup and the crystalline acid (VIII), when oxidized with sodium periodate, gave the same aldehydes as those produced by the oxidation of the ester from D-glucose (II) and its saponification product (XXX), respectively. Hence, the mechanism of the reaction of D-galactose is the same as that of D-glucose and D-mannose. Moreover, the approximate yield from... 

Saponification (base hydrolysis) follows a simpler mechanism (see Figure 12-35). 

Anionic polymerization proceeds by acyl-oxygen cleavage for almost all lactones, consistent with the mechanism for alkaline saponification of esters [Duda and Penczek, 2001 Hofman et al., 1985 Kricheldorf et al., 1988], For example, initiation by methoxide ion proceeds as... 

Synthesis of the thymidine derivative relies on the older two-step insertion of fluorine. Thus, the hydroxyl group in 3 -deoxythymidine benzoate (51-1) is first converted to the mesylate (51-2). Reaction with potassium fluoride in hydrogen fluoride replaces the mesylate by fluorine (51-3). The fact that this reaction, as that above, proceeds with retention of the configuration mles out simple displacement as the mechanism for this transform. The presence of the methyl group at position 5 negates the need for the chlorination step. Saponification then affords the antiviral agent alovudine (51-4) [52]. 

The chemistry used to prepare the antischistosomal hydroxyquinolines provided the initial entry to this series. Thus, addition-elimination of aminopicoline (38-1) to EMME (38-2) gives the corresponding enamino ester (38-3). Thermal cyclization of that intermediate leads to the hydroxyquinoline (38-4). Reaction of the ambident anion from that compound leads to alkylation via the keto tautomer and thus the formation of the Al-alkylated derivative (38-5). Saponification of the ester then gives nalidixic acid (38-6) [44]. It has incidentally been shown that the presence of the strong Michael acceptor function in this series plays a little role in the mechanism of action in these compounds. 

Problem 16.40 Write mechanisms for the reactions of RCOOR with (a) aqueous OH" to form RCOO and R OH (saponification), (b) NH, to form RCONH, (c) R OH in acid, HA, to form a new ester RCOOR" (transesterification Section 16.6). ... 

The second synthetic approach to oidiolactone C (61) is summarized in Scheme 20. This route also commences with the ozonolysis of trans-communic acid 180. Now, when this compound was exposed to ozone in excess, keto aldehyde 187 was obtained in 76% yield. The key step in this approach was the y-lactone closure via chemoselective reduction of the lactone moiety on compound 189 through a SN2 mechanism. Compound 189 could be prepared by saponification of the corresponding methyl ester with sodium propanethiolate. Once the primary alcohol is oxidized, the completion of the synthesis of key lactone 103 only requires the allylic oxidation of the C-17 methyl with concomitant closure of the 8-lactone. This conversion was achieved with Se02 in refluxing acetic acid to give 103 in 51% yield. 

Alkali is a frequent cause of eye bums as again confirmed in a recent study of Midelfarth [22], Alkali reacts with the tissue surface by concentration and time-dependent dissolution of the Upid membranes of epithelial cells the chemical mechanism is saponification of lipids with loss of all membranous barriers. Lipid saponification of membranous lipids starts at a pH over 11 [23]. 

A solution of 200 g. (3.57 moles) of potassium hydroxide (Note 1) in 200 cc. of water is placed in a 2-1. round-bottom flask fitted with a reflux condenser, a mechanical stirrer and a separatory funnel. The stirrer is started and to the hot solution 200 g. (0.92 mole) of ethyl sec.-butylmalonate (Note 2) is added slowly. The solution refluxes gently due to the heat of saponification. After all of the sec.-butylmalonic ester has been added, the solution is refluxed gently for two hours. The solution is diluted with 200 cc. of water and 200 cc. of liquid is then distilled from the solution. This is done in order to remove all of the alcohol formed during the saponification (Note 3). 

There are basically two mechanisms to convert the fatty acids in a complex lipid to fatty acid methyl esters (FAMEs) methylation following hydrolysis of the fatty acids from the complex lipids, or direct transesterification. The first mechanism involves saponification (alkaline hydrolysis) in which the ester bond is cleaved between the fatty acid and the glycerol moiety (e.g., triacylglycerols and phospholipids) under heat and in the presence of an alkali (usually sodium hydroxide), followed by methylation performed in the presence of an acidic catalyst in methanol. Direct transesterification is usually a one-step reaction involving alkaline or acidic catalysts. 

A Bac2 mechanism is proposed for die saponification of ethyl benzoate in ethanol-water.37 The reactions of aryl benzoates in absolute ethanol with ethoxide, aryloxides and acetophenone oximates occur via a stepwise mechanism in which the formation of the tetrahedral intermediate is rate determining.38 A stepwise mechanism is also supported for the reactions of /7-nitrophenyl-substituted benzoates with hydroxide and / -chlorophcnoxidc. The evidence comes from breaks in Hammett plots as the acyl... 

Saponification of the bicyclic p-lactam 21 to yield 22 has been employed by Corey [65] as an experimental evidence of the mechanism-based design of... 

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) ... 

The saponification of organotriethoxysilane is carried out in enameled reactor 14 with an agitator and a water vapour jacket. First the reactor is filled from batch box 13 with 42% caustic soda and with a metered amount of water. After the dissolution is complete, the alkali solution receives organotriethoxysilane from batch box 12 at a temperature below 60 °C. The contents of the apparatus are agitated for 1 hour the mixture is sampled to determine the NaOFl content, solid residue and density. The prepared liquid is filtered through brass mesh in nutsch filter 15 into settling box 16. In the settling box the product is separated from mechanical impurities (it is settled for at least 24 hours), filtered in pressure filter 17 and poured into containers. 

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