酸性酯交换-气相色谱-质谱法同时测定植物油中氯丙二醇酯和缩水甘油酯

建立了一种气相色谱-质谱同时测定植物油中3-氯丙二醇酯、2-氯丙二醇酯和缩水甘油酯的方法.称取0.25 g样品,依次加入内标工作液、四氢呋喃和酸性溴化钠溶液,50℃水浴反应15 min,加入6 g/L碳酸氢钠溶液终止反应,使用正己烷提取,上层液经氮气吹干后用四氢呋喃溶解.随后加入1.8％(v/v)硫酸-甲醇溶液于40℃...     

The determination of wax esters in lube oil by infrared spectrometry

A simple and rapid method for estimating the content of wax esters in lubricating oils has been developed through the use of isopropanol extraction to concentrate the wax esters. The ratio of the absorption bands at 1740 and 1385 cm^-1 can be used directly for the determination of wax esters in lube oil samples. The method can be satisfactorily applied at levels down to 1 %, with an overall deviation of less than 10 %; for samples containing as low as 0.5 %, the procedure can be used semi-quantitatively with an error of about 20 %. This infrared method can also be used to determine marine and sulfurized wax esters.     

Analysis of amino acids as formamidene butyl esters by electrospray ionization tandem mass spectrometry.

Amino acid formamidene butyl esters are optimally prepared by heating amino acids with dimethylformamide dimethylacetal (DMF-DMA) for 2 minutes at 65 degrees C and then with n-butanol/hydrogen chloride for 15 minutes at 65 degrees C. The formamidene butyl esters of simple alpha-amino acids and beta-amino acids afford between 1.1 and 20 times the signal intensity of the corresponding butyl esters during electrospray ionization tandem mass spectral analysis. Complex alpha-amino acids, such as ornithine, arginine and citrulline, and gamma-amino acids are better analyzed as butyl esters. Secondary alpha-amino acids, such as proline and sarcosine, give a mixture of two iminium salts with the DMF-DMA derivatization method. A derivative incorporating two molecules of the amino acid predominates at higher derivatization temperatures. Contrary to a previous report, N-formylamino acids were not detected. The presence of secondary amino acids in amino acid mixtures, derivatized as formamidene butyl esters, affords derivatives that incorporate two different amino acids. The new formamidene butylation method is unlikely to replace the butylation procedure used by neonatal blood spot screening programs for amino acid disorders, since a much poorer response was obtained with formamidene butyl esters of arginine and citrulline, important in the diagnosis of arginase deficiency and citrullinaemia.     

Facile synthesis of diphenylmethyl esters from 2-diphenylmethoxypyridine using catalytic boron trifluoride·diethyl etherate

A practical method for the direct preparation of diphenylmethyl (DPM) esters from 2-diphenylmethoxypyridine is described. The reaction was readily performed in the presence of a catalytic amount of boron trifluoride-diethyl etherate at room temperature. Using this reaction protocol, various carboxylic acids were converted to DPM esters with high yields. This method is highly effective for the protection of carboxylic acids and the synthesis of DPM esters, and offers a promising approach for facile esterification of a variety of carboxylic acids.     

Rhodium(I)-catalyzed carboxylation of aryl- and alkenylboronic esters with CO2

When the esters of arylboronic acids with 2,2-dimethylpropan-1,3-diol were treated with a catalytic amount of [Rh(OH)(cod)]2 in the presence of 1,3-bis(diphenylphosphino)propane and CsF in dioxane at 60 degrees C under carbon dioxide atmosphere, the benzoic acid derivatives were obtained in good yields. Reactions of alkenylboronic esters also proceeded under similar conditions to give alpha,beta-unsaturated carboxylic acids. As these boronic esters are now easily available through coupling or direct borylation reactions, this method would be a useful method for the preparation of various functionalized aryl- and alkenyl-carboxylic acids.     

Direct asymmetric intramolecular alkylation of beta-alkoxy-alpha-amino esters via memory of chirality

The intramolecular alpha-alkylation of beta-alkoxy-alpha-amino esters derived from L-serine proceeded predominantly over beta-elimination. When beta-alkoxy-alpha-amino esters were treated with powdered CsOH in DMSO at 20 degrees C, alpha-alkoxymethyl cyclic amino esters were obtained in up to 94% ee. Optically active THF amino acids were synthesized for the first time by the present method.     

Bildung von Estern und Lactonen durch Silberionen-Katalyse

A mild and efficient method for the preparation of esters has been found in the silver ion induced reaction of alcohols with 2-pyridyl esters of thiocarboxylic S-acids. Examples are given to show the utility of this push button activation for the rapid formation of macrocyclic lactones and esters at room temperature under non-basic conditions.     

Quantification of trace fatty acid methyl esters in diesel fuel by using multidimensional gas chromatography with electron and chemical ionization mass spectrometry

Measurement of contamination of marine and naval diesel fuels (arising from product mixing or adulteration) with biodiesel or fatty acid methyl esters can be problematic, especially at very low levels. A suitable solution for this task for trace amounts of individual fatty acid methyl esters with resolution and quantification can be achieved by using a multidimensional gas chromatographic approach with electron and chemical ionization mass spectrometric detection. A unique column set comprising a 100 m methyl‐siloxane nonpolar first dimension column and high‐temperature ionic liquid column in the second dimension enabled identification of individual fatty acid methyl esters at below the lowest concentrations required to be reported in a diesel fuel matrix. Detection limits for individual fatty acid methyl esters compounds ranged from 0.5 to 5.0 mg/L, with excellent linearity up to 5000 mg/L and repeatability of the method from 1.3 to 3.2%. The method was applied to the analysis of diesel fuel samples with suspected biodiesel contamination. Contamination at 568 mg/L was calculated for an unknown sample and interpretation of the results permitted the determination of a likely source of the contamination.     

用裂解色谱法鉴定羧酸酯的结构

研究了用裂解气相色谱法鉴定羧酸酯结构的方法。对一些一元酸酯和二元酸酯进行了普通裂解和与碱石灰混合后的裂解,依据裂解产物可确定酯的母体酸和母体醇。直接从薄层板上取分离后的组分,不用去除吸附剂就能进行鉴定,可用于常见羧酸酯的剖析工作。     

A mild,chemoselective, one-pot synthesis of δ-keto α-cyano esters by organocatalysis

A sequential condensation of α-cyano esters, aldehydes, and ketones with catalytic amount of pyrrolidine/HOAc at room temperature has been developed. This method offers a chemoselective, one-pot cascade access to δ-keto α-cyano esters with moderate to good yields under mild conditions.     

Micro-determination of total phthalate esters in biological samples by gas-liquid chromatography.

A method was investigated in which all of the phthalate esters in biological samples were determined as phthalic acid by gas-liquid chromatography. The method is based on the separation of phthalate esters from the sample with n-hexane, saponification of the esters with an alkaline ethanolic solution to give phthalic acid, purification of the acid by extraction with diethyl ether and column chromatography using silica gel, and conversion of the acid into bis(2,2,2-trifluoroethyl) phthalate with a 2,2,2-trifluoroethanol solution containing boron trifluoride. The derivative obtained is highly sensitive to an electron-capture detector, giving a sensitivity of 0.1 pg. Biological samples fortified with di(2-ethylhexyl) phthalate at levels of 5-100 ppb were analyzed, with recoveries of 70-100%.     

The methyl group as a source of structural diversity in heterocyclic chemistry: side chain functionalization of picolines and related heterocycles

The reaction of 2-picoline at the methyl group with NDA and KDA followed by dimethyldisulfide trapping furnished, respectively, dithioacetals and trithioortho esters with high selectivity. The method was successfully applied to other methyl-substituted pyridines, quinolines, and pyrazines. Dithioketals were prepared by a one-pot procedure involving the reaction of metalated 2-picoline with 2 equiv of dimethyldisulfide followed by in situ trapping with a second electrophile. All of the generated thio-substituted compounds were efficiently transformed in presence of mercury salts or under oxidizing conditions to other functional groups comprising aldehydes, ketones, ketals, thiol esters, orthoesters, and esters.     

麻疯油转酯化产物的高效液相色谱分析

建立了高效液相色谱法同时测定麻疯油转酯化产物中4种主要脂肪酸甲酯的分析方法。样品经膜处理后用丙酮溶解,采用Hypersil ODS(C18)色谱柱进行分离。以乙腈为流动相进行等度洗脱,内标法定量,同时对色谱条件进行优化。结果表明,在优化的色谱条件下4种脂肪酸甲酯在10 min内得到良好的分离,标准曲线的线性相关系数均达到0.999以上,平均回收率为96%~98%,重现性相对标准偏差为7.2%~10.2%,重复性相对标准偏差为0.31%~2.02%。与气相色谱法相比,该方法具有较高的灵敏度,可用于麻疯油转酯化产物中脂肪酸甲酯含量的测定,为麻疯油转酯化反应制备生物柴油的定性定量分析提供了参考依据。     

An Improved Method for the Efficient Conversion of Unstaurated Alcohols,Ethers and Esters to Their Corresponding Aldehydes,Ketones, Enol Ethers and Enol Esters

Catalytic conversion of unsaturated alcohols to their corresponding aldehydes and ketones with nonacarbonyl diiron in benzene at 40–50 C are performed efficiently in high yields. The efficient preparation of some enol ethers and also preperation of a few esters from their corresponding unsaturated ethers and esters are also performed by this method.     

High-performance liquid chromatographic determination of cholesteryl esters in the blood of obese children.

The serum of obese children and adolescents was analyzed for cholesteryl esters. The test substances were first separated from the sample matrix by solvent extraction and thin-layer chromatography and then resolved in a reversed-phase high-performance liquid chromatographic system involving a Separon SGX C18 column and a mobile phase of 2-propanol-acetonitrile (40:60, v/v), with ultraviolet detection at 206 nm. Cholesterol and 10-cholesteryl esters could be separated and determined within ca. 25 min at a flow-rate of 1 ml/min. The method was applied to a study of the effect of external conditions (physical stress, diet) on the content of cholesteryl esters in a test group of obese boys and girls aged from 13 to 16 years. The analyses have demonstrated that the above conditions do not affect the concentrations of the individual cholesteryl esters, although the total cholesterol concentration decreased significantly after spa treatment.     

β-Cyclodextrin as an efficient catalyst for the one-pot synthesis of 1-aminophosphonic esters in water

A simple, efficient, and general method has been developed for the one-pot synthesis of α-aminophosphonic esters in water using β-cyclodextrin as an efficient catalyst. α-Aminophosphonic esters were obtained in good yields (45-82%) and purity under mild conditions by the reaction of diethyl phosphite with a mixture of aldehyde and amine in water at reflux.     

High-pressure transesterification of sterically hindered esters

A mild, rapid, and efficient method for the solvolysis of sterically hindered esters under high pressure is described. Transesterification is carried out in the presence of DBU at room temperature and at a pressure of 10 kbar to give quantitative conversions within short reaction times. The substrates examined included aromatic and aliphatic esters of sterically hindered alcohols and phenols. An optically pure benzyl ester of phenylalanine was chosen to study racemization of the amino acid esters under high-pressure reaction conditions.     

Determination of organophosphate esters in air samples by dynamic sonication-assisted solvent extraction coupled on-line with large-volume injection gas chromatography utilizing a programmed-temperature vaporizer

An on-line method for the determination of airborne organophosphate esters based on dynamic sonication-assisted solvent extraction and large-volume injection (LVI) gas chromatography with nitrogen-phosphorous detection is introduced. The LVI is performed with a programmed-temperature vaporizer. The entire extracted fraction of 800 microl (hexane-methyl-tert.-butyl ether, 7:3, v/v) is introduced directly into the GC system without any clean-up step following extraction. The extraction and analysis step were completed in less than 15 min. The limit of detection of the investigated organophosphate esters was established to be in the range of 5-32 pg/filter. The correlation coefficients (r2) were investigated in the linear range study of the entire system and established to be approximately 0.9900 for all the investigated organophosphates esters. Applications of the method was demonstrated with the extraction of air samples collected onto glass fiber filters from different indoor environments. Six organophosphate esters were found at the levels 0.4-138 ng/m3.     

Direct determination of tocopherols in paprika and paprika oleoresin by liquid chromatography

A method for the determination of tocopherols and tocopherol esters, quantified as tocopherol acetate, in paprika and paprika oleoresin is reported. Paprika samples were extracted with ethyl acetate and aliquots of the extracts were directly injected into a liquid chromatograph. Reverse phase high-performance liquid chromatography with spectrophotometric detection at 280 nm was used. Gradient elution was applied, allowing the determination of tocopherols and tocopherol esters in the presence of carotenoids. The method does not need previous separation steps, so is useful for the routine determination of vitamin E in commercial samples.     

Quantitative determination of esters by saponification in dimethyl sulphoxide

A method is given for the quantitative determination of esters which makes use of the unusually rapid rate of their alkaline hydrolysis in aqueous dimethyl sulphoxide medium. Only 5 min heating on a steam-bath is needed for quantitative hydrolysis of most esters, and many react completely in 5 min at room temperature. When hydrolysis is complete, the excess of base is titrated with standard acid, using a visual indicator.