Esters separation

HCOOCHjCHj. Colourless liquid with the odour of peach-kernels b.p. 54 C, Prepared by boiling ethanol and methanoic acid in the presence of a little sulphuric acid the product is diluted with water and the insoluble ester separated and distilled. Used as a fumigant and larvicide for dried fruits, tobacco and foodstuffs. It is also used in the synthesis of aldehydes. 

Place I g. of powdered 3,5-dinitrobenzoyl chloride in a small conical flask, add 2 5 ml. of dry methanol, and warm on a water-bath until the solid has dissolved. Cool and filter off the 3,5-dinitrobenzoate which has separated. Recrystallise from ethanol or petroleum (b.p. 60-80°). The ester separates in colourless crystals, m.p. 108°. Yield,... 

Method 1. Reflux a mixture of pure nicotinic acid (Section V,22), 84 g. (105 ml.) of absolute ethanol and 90 g. (50 ml.) of concentrated sulphuric acid in a flask for 4 hours on a steam bath. Cool the solution and pour it slowly and with stirring on to 200 g. of crushed ice. Add sufficient ammonia solution to render the resulting solution strongly alkaline generally, some ester separates as an oil but most of it remains dissolved in the alkaline solution. Extract the solution with five 25 ml. portions of ether, dry the combined ethereal extracts with anhydrous magnesium sulphate, remove the ether and distil under reduced pressure. The ethyl nicotinate passes over at 117-118°/ 6 mm. the yield is 34 g. The b.p. under normal pressure is 222-224°. 

Purification. Purification problems are primarily solved by two methods continuous vacuum fractionation and chemical combination to yield a high boiling ester, separation of the noncombining impurities by distillation, and hydrolysis of the ester. Although the product produced by continuous vacuum fractionation satisfies most needs, shows no impurities by glc, is odor-acceptable, and thus is used to produce most of the PEA for commercial use, for highest requirements chemical purification by the borate ester is required. 

To aid in determining the number of carboxyl groups, prepare a derivative using trideuterated Methyl-8 (Pierce cat. no. 49200), using the same procedure previously given. Inject 1-2 pd of the trideuterated methyl ester separately or mix equal portions of the nondeuterated methyl ester with the trideuterated methyl ester, and inject 2 pd immediately into the GC/MS system. From the mass difference, it is easy to determine the number of carboxyl groups present. 

Although menthyl esters, especially 19, are most often used to prepare sulfoxides, esters derived from optically active alcohols other than menthol have been prepared . Ridley and Smal prepared arenesulfmic esters of 1,2 5,6-di-O-cyclohexylidene-a-D-glucofuranose. Unfortunately, these diastereomers were oils, except for the mesityl derivative, with the major epimer having configuration R at sulfur and so they offered no advantage over the menthyl esters. Separation of the epimers by chromatography failed. 

The solution is now poured and rinsed into a moderate-sized (500-750 c.c.) separating funnel containing 100 g. of ice, and the acid is buffered by slowly adding finely powdered sodium carbonate. The ester separates as an oil and is taken up in ether, but the funnel must not be stoppered and shaken until evolution of carbon dioxide has ceased. Extraction with ether is repeated and the combined 1 Annalen, 1882, 215, 1. 

In a i-l. three-necked flask fitted with a fetirrer and thermometer are placed 93 g. (0.5 mole) of dodecanol (Note 1) and 158 g. (2 moles) of pyridine. The flask is surrounded by a water bath sufficiently cold to lower the temperature of the mixture to io°. At this temperature 105 g. (0.55 mole) of />-toluenesul-fonyl chloride is added in portions over a twenty- to thirty-minute period, or at such a rate that the temperature does not exceed 20° at any time. The mixture is then stirred for three hours at a temperature below 20°, after which it is diluted with 300 cc. of hydrochloric acid (sp.gr. 1.19) in 11. of ice water. The ester which crystallizes is collected on a chilled Buchner funnel and sucked as dry as possible. The solid is transferred to a 600-cc. beaker, 250--300 cc. of methyl alcohol is added, and the mixture is warmed on the steam bath until the ester melts. It is then cooled in a freezing mixture while being stirred continuously the ester separates in a fairly fine state. It is then collected on a chilled funnel and allowed to dry in the air, preferably at a temperature, below 20°. The yield of ester is 152-156 g. (88-90 per cent of the theoretical amount based upon the dodecanol used). It melts at 20-250 (Note 2) and is sufficiently pure for most purposes. 

This procedure has been used successfully for many years in the preparation of ethyl laurate, caprylate, and myristate by the alcoholysis of cocoanut oil (1 kg.) in ethanol (1900 g.) with hydrogen chloride (50 g.) as a catalyst.3 The method differs slightly from the one described above. The alcoholysis is complete after fifteen or twenty hours, and the solution is then neutralized to methyl orange with barium carbonate. The mixture is added to an equal volume of a saturated sodium chloride solution, whereupon 1100-1300 g. of the mixture of crude ethyl esters separates. This mixture of esters is washed with water and fractionated as described above. The yields are approximately 50 g. of ethyl caprylate, 350 g. of ethyl laurate, and 60 g. of ethyl myristate from 1000 g. of cocoanut oil. 

Ethyl-cyanacetic ester. Ill parts of the above ester is added and dissolved in a solution of 92 parts sodium in 1,500 parts of dry ethanol. 750 parts of ethyl iodide are gradually added to the mixture, while it boils gently under reflux. Filter the sodium iodide that forms from the solution and distill off the alcohol. After adding water to the residue the ester separates and is purified by vacuum distillation. Collect the fraction around 125° at 4 mm. 

After standing for one hour, the solution is poured into a large dish and the carbon tetrachloride and unused bromine allowed to evaporate spontaneously (Note 3). The dibromo ester separates in large crystals which form a solid cake in the bottom of the dish (Note 4). This cake is broken up and spread in a thin layer on a large Buchner funnel and subjected to suction until all traces of bromine have disappeared. The white crystals are then dried by pressing between large filter papers. The yield of crude dibromo ester is 280-285 g. (83-87 per cent of the theoretical amount). It melts 65-71 °. 

Haken has considered the applicability of "Rohrschneider/ McReynolds constants" for the classification of stationary phases for the separation of fatty esters (13). He concluded that the approach was limited since the measurements used to determine the aforementioned "constants" are made at 100°C and most fatty acid methyl ester separations are carried out at about 200°C. He had previously shown significant variation in the, what will now be called, Rohrschneider/McReynolds coefficients, with temperature (14). Polar polysiloxanes such as XF-1150 demonstrated greatest variability in the coefficients and nonpolar types such as SE-30 demonstrated least variation. Supina pointed out that the X factor in the McReynolds coefficients should be indicative of extent of interaction with olefinic substituents (15). Figure 9.5 demonstrates the utility of this approach the 18 3 and 20 0 methyl esters are used as markers for the consideration of... 

Purification. Purification problems are primarily solved by two methods continuous vacuum fractionation and chemical combination to yield a high boiling ester, separation of the noncombining impurities by distillation, and hydrolysis of the ester. 

J. C. S., 67, 600.)—This method is used when an ester is not easily obtained by the usual methods owing to steric hindrance or some such cause. The silver salt and alkyl iodide are heated or shaken together with or without an inert solvent, benzene, etc. The precipitated silver halide is filtered off, and the ester separated from the filtrate by distillation or some other method. 

The third category is the basis of many commonly used methods. In general, the steps in this category are solvent extraction to remove the lipid fraction, saponification, methylation to fatty acid esters, separation using chromatographic columns and GC analysis. Martin-Hemandez... 

GC-MS characterization of indomethacin has been reported using trimethylsilyl esters separated on SE-52 liquid phase(51). The same paper also reports precision and accuracy using an electron capture detector, which for plasma was 92+19%(5ng/ml) and 96+1.5%(1000ng/ml). For aqueous humors, the values were 97+5.6% and 99+2.2%,respectively. 

After completing the nitration by warming on the water-bath for twenty miuutes, the mixture is poured into water, and the mixed o- and p-nitro-esters separated by digestion with a little alcohol, in which only the ortho-compound dissolves. The substance may then be obtained in a pure state by pouring the alcoholic solution into cold water and filtering. 

A colorless solution is obtained from which the tin is removed by precipitation with hydrogen sulfide. On addition of sodium carbonate solution, 3-Amino-4-propoxybenzoic acid 2-(diethylamino)ethyl ester separates as an oil. When treated with one equivalent of hydrochloric acid it forms a hydrochloride, which is readily soluble in water and crystallizes from a mixture of absolute alcohol and ethyl acetate in white prisms MP 182.0-183.3°C. 

Peng W-J (2008) Extraction process for formyl-substituted fatty acid triglyceride ester separation and catalyst recovery. WO 2008/156993... 

Fatty acids have so far been analysed by CEC either as the free acids or as phenacyl- or methyl esters. Aqueous acetonitrile (50 mM) at pH 6 (9 1 v/v) was shown to be the optimal mobile phase [191]. It is generally known that in reversed-phase chromatography free fatty acids and fatty acid methyl esters separate according to the partition number, which is defined as the carbon number minus twice the number of double bonds. A double bond reduces the retention time by the equivalent... 

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