Methyl- or ethyl esters

B) Benzylamtdes (see (a) above) can often be prepared directly from the ester, particularly if a methyl or ethyl ester. Usually works best with esters of aromatic acids. (M.ps., pp. 543 545.)... 

The reaction (which is essentially the direct aminolysis of esters with benzylamine) proceeds readily when R is methyl or ethyl. Esters of higher alcohols should preferably be subjected to a preliminary methano-lysis by treatment with sodium methoxide in methanol ... 

Place 1 0 ml. of hydrazine hydrate (CAUTION corrosive chemical) in a test-tube fitted with a short refiux condenser. Add 10 g. of the methyl or ethyl ester dropwise (or portionwise) and heat the mixture gently under refiux for 15 minutes. Then add just enough absolute ethanol through the condenser to produce a clear solution, refiux for a further 2-3 hours, distil oflF the ethyl alcohol, and cool. Filter oflF the crystals of the acid hydrazide, and recrystallise from ethanol, dilute ethanol or from water. 

Section 27 16 Carboxyl groups are normally protected as benzyl methyl or ethyl esters Hydrolysis m dilute base is normally used to deprotect methyl and ethyl esters Benzyl protecting groups are removed by hydrogenolysis... 

Dichloroacetic acid is produced in the laboratory by the reaction of chloral hydrate [302-17-0] with sodium cyanide (31). It has been manufactured by the chlorination of acetic and chloroacetic acids (32), reduction of trichloroacetic acid (33), hydrolysis of pentachloroethane [76-01-7] (34), and hydrolysis of dichloroacetyl chloride. Due to similar boiling points, the separation of dichloroacetic acid from chloroacetic acid is not practical by conventional distillation. However, this separation has been accompHshed by the addition of a eotropeforming hydrocarbons such as bromoben2ene (35) or by distillation of the methyl or ethyl ester. 

Some peptides have special tastes. L-Aspartyl phenylalanine methyl ester is very sweet and is used as an artificial sweetener (see Sweeteners). In contrast, some oligopeptides (such as L-ornithinyltaurine HQ. and L-oriuthinyl-jB-alariine HQ), and glycine methyl or ethyl ester HQ have been found to have a very salty taste (27). 

The most common impurities are the corresponding acid and hydroxy compound (i.e. alcohol or phenol), and water. A liquid ester from a carboxylic acid is washed with 2N sodium carbonate or sodium hydroxide to remove acid material, then shaken with calcium chloride to remove ethyl or methyl alcohols (if it is a methyl or ethyl ester). It is dried with potassium carbonate or magnesium sulfate, and distilled. Fractional distillation then removes residual traces of hydroxy compounds. This method does not apply to esters of inorganic acids (e.g. dimethyl sulfate) which are more readily hydrolysed in aqueous solution when heat is generated in the neutralisation of the excess acid. In such cases, several fractional distillations, preferably under vacuum, are usually sufficient. 

Section 27.16 Carboxyl groups are normally protected as benzyl, methyl, or ethyl esters. 

In a penicillin synthesis, the carboxyl group was protected as a / -bromophenacyl ester that was cleaved by nucleophilic displacement (PhSK, DMF, 20°, 30 min, 64% yield). Hydrogenolysis of a benzyl ester was difficult (perhaps because of catalyst poisoning by sulfur) basic hydrolysis of methyl or ethyl esters led to attack at the /3-lactam ring. ... 

The Diels-Alder reactions of the methyl or ethyl ester of benzenesulfonylindole-2-acrylic acid with several l-alkoxycarbonyl-l,2-dihydropyridines are reported and only a single stereoisomer was obtained, as in the case of l-methoxy(ethoxy)-carbonyl-1,2-dihydropyridines. However, when the Diels-Alder reaction of 17 was carried out with 8g[R = (CHsjsC], a mixture of two stereoisomers 18gand25were obtained in a 1 1 ratio (65% total yield). The bulky rerr-butyl group creates sufficient steric interference with the indole ring to cause the loss of stereochemistry ... 

Derivatization Dissolve less than 1 mg of methyl or ethyl ester in 1 ml of freshly distilled pyrrolidine and 0.1 ml of acetic acid. Heat the mixture in a sealed or capped tube (able to withstand high temperatures) at 100° for 30 min. Cool the reaction mixture to room temperature and add 2 ml of methylene chloride. Wash the methylene chloride extract with dilute HC1, followed by ion exchange water. Dry the methylene chloride extract with anhydrous magnesium sulfate.1... 

Mass spectra of pyrrolidine derivatives of methyl or ethyl esters The molecular ions are intense with characteristic fragment ions at m/zs 70, 98, and 113. The position of the double bond can be determined by locating two peaks that differ by 12 mass units. A relatively intense peak should be observed 26 m/z units higher than the lower mass peak. The double bond lies between the two peaks that are separated by 26 Daltons. 

Pyrrolidine derivative of monounsaturated methyl or ethyl ester for determining the double bond position. 

Alternatively, secondary and tertiary carboxylic acid methyl or ethyl esters react (6) with two equivalents of trimethylsilylmethy] lithium (prepared in pentane) to give /1-ketosilanesingood (80-96%) yield. Primary esters also give /3-ketosilanes, but in lower (45%) yield. 

Because Me3SiCl 14 is almost inert to lithium organic compounds or Grignard reagents in non-polar solvents, formation of tertiary alcohols on addition of MeLi or n-BuLi to free carboxylic acids [127] or their methyl or ethyl esters [128] in THF... 

Perphosphate esters (e.g., methyl or ethyl esters) or amides can be used for oxidative gel breaking [1066]. Whereas the salts of the perphosphate ion interfere with the action of the crosslinkers, the esters and amides of perphosphate do not. Fracturing fluids that contain these breakers are useful for fracturing... 

These specific polymerizabilities of MMA and ethyl methacrylate are not due to their reactivities. According to literature (29), the propagating and terminating reaction constants, kp and kp, are shown in Table 7. Butylester is usually more reactive than methyl or ethyl ester. 

Here, the concept of the hard and soft HA and monomers may be reasonably applied. As Fig. 10 shows, n-butyl esters are much harder than methyl or ethyl ester. Accordingly, n-butyl methacrylate and acrylate were too hard to be incorporated into the soft HA formed by PVPA or starch. 

Isolation of individual amino acids started about 1820 by 1904 all of the naturally occurring amino acids in proteins had been isolated except methionine (Mueller, 1922) and threonine (Rose, 1937). One of the earliest methods for the separation of amino acids was through the differential volatility of their methyl or ethyl esters (Emil Fischer, 1901). This approach led to the discovery of valine, proline, and hydroxyproline. [In the 1970s Fischer s method was modified for microanalysis of proteins, separating the amino acid esters by gas phase chromatography. Separation is now usually performed by hplc (high pressure liquid chromatography).]... 

Virtually all that tested positive are methyl or ethyl esters of phosphoric or thiophosphoric acids, and are electrophilic and mutagenic (e.g., dichlorvos, tetrachlorvinphos Figure 14.12). 

Acids, (a) Carboxylic Liquid carboxylic acids are first freed from neutral and basic impurities by dissolving them in aqueous alkali and extracting with ethyl ether. (The pH of the solution should be at least three units above the PKa of the acid). The aqueous phase is then acidified to a pH at least three units below the pK of the acid and again extracted with ether. The extract is dried with magnesium sulphate or sodium sulphate and the ether is distilled off. The acid is fractionally distilled through an efficient column. It can be further purified by conversion to its methyl or ethyl ester (see p. 52) which is then fractionally distilled. Hydrolysis yields the original acid which is again purified as above. 

Methylthiourea has been prepared from methyl isothiocyanate and ammonia in alcoholic 1 or aqueous2 solution, from methylammonium thiocyanate,3 and by heating the methyl or ethyl ester of A-methyldithiocarbamic acid with alcoholic ammonia.4... 

Several synthetic methods for the reduction of a-amino esters have also been reported. The reduction of methyl or ethyl esters by diisobutylaluminum hydride (DIBAL-H) at low temperature (—78 °C) has been described as useful for the preparation of a-amino aldehydes. 1118 20 Again, this method suffers from overreduction. Reductive methods involving mild reductive agents have been described. The reduction of phenyl esters 6 21 (readily prepared from the corresponding amino acid 5) with lithium tri-ferf-butoxyaluminum hydride is efficient for the preparation of various Boc-a-amino aldehydes including Na-Boc-7V J-nitroargininal and A7a-Boc-W"-Z-argininal (Scheme 5). 

Esterification of sulfonic acids.1 Sulfonic acids are converted into methyl or ethyl esters on reaction with trimethyl or triethyl orthoformate. Yields are >80% in esterification of arenesulfonic acids, but are somewhat lower in the reaction of alkanesulfonic acids because of volatility of the products. 

N 24.78%. Two isomers are described in the literature 2,4-Dinitrobenzoic Acid Hydrazide (2,4 -Dinitrobenzoic Acid Hydrazide), orn-yel cryst (from abs ale), mp 231-3° was prepd in small quant by treating the methyl or ethyl ester of 2,4 -dinitrobenzoic acid with hydrazine sulfare(Ref 3)... 

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