Search results for "Formate"
showing 10 items of 111 documents
Reactions of electron-rich heterocycles with orthocarboxylic acid derivatives.11. Reactions of carbazole and 4-methoxycarbazole with triethyl orthofo…
1988
Carbazole (1a) and 4-methoxycarbazole (1b) can be regioselectively functionalized by reaction with triethyl orthoformate. Whereas the reaction of 1a with the ortho ester furnishes the amide acetal 2, the new carbazole derivatives 4–10 are formed, depending on the reaction conditions, in the electrophilic substitution of 1b. The products of this reaction sequence provide a contribution to studies on the mechanism of the transformation of 1b to tris-carbazolylmethane 5. Compound 5 represents a new, three-bladed propeller in the triheteroarylmethane series.
Chiral determination of amphetamine and related compounds using chloroformates for derivatization and high-performance liquid chromatography
1999
The enantiomeric determination of amphetamine and various amphetamine-type compounds by liquid chromatography after chiral derivatization with 9-fluorenylmethyl chloroformate-L-proline (FMOC-L-Pro) is reported. The results obtained were compared with those achieved after achiral derivatization with 9-fluorenylmethyl chloroformate and subsequent separation of the derivatives on a beta-cyclodextrin chiral stationary phase. Conditions for the derivatization of amphetamines with FMOC-L-Pro were investigated, including the effect of the derivatization reagent concentration, pH and reaction time, using amphetamine, ephedrine and pseudoephedrine as model compounds. On the basis of these studies, p…
Analysis of pyridoquinoline derivatives by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry
2001
A method using liquid chromatography/atmospheric pressure chemical ionization mass spectrometry (LC/APCI-MS) has been developed for the characterization and determination of pyridoquinoline derivatives 4,6-bis(dimethylaminoethylamino)-2,8,10-trimethylpyrido[3,2-g]quinoline, 4,6-bis(dimethylaminoethoxy)-2,8,10-trimethylpyrido[3,2-g]quinoline and 4,6-bis[(dimethylaminoethyl)thio]-2,8,10-trimethylpyrido[3,2-g] quinoline, all with potential antitumor properties. LC separation was performed on a conventional C18 column using a binary mobile phase composed of acetonitrile and 50 mM aqueous ammonium formate at pH 3. The APCI mass spectra obtained showed that proton addition giving [M + H]+ was the…
Characterization of bile acids and fatty acids from ox bile in oil paintings by gas chromatography?mass spectrometry*1
2004
Characterization of ox bile, traditionally used in painting, is of interest in the fields of archaeometry and conservation and restoration of works of art. Bile acids, fatty acids (F), and cholesterol found in ox bile have been identified using a derivatization method that combines the formation of ethyl esters from the carboxylic groups and the trimethylsilyl ethers from hydroxyl groups. This method of analysis is consistent with these others proposed by the authors to analyze drying oils, proteins, and diterpenic resins usually used as binders and varnishes by the painters. Bile acids from binary samples such as animal glue/ox bile, casein/ox bile and Arabic gum/ox bile have been successf…
Liquid chromatographic determination of aliphatic amines in water using solid support assisted derivatization with 9-fluorenylmethyl chloroformate
2002
A simple and sensitive method has been developed for the liquid chromatographic determination of short-chain aliphatic amines in water. Analytes are retained in solid-phase extraction (SPE) cartridges, and then derivatized by drawing an aliquot of the fluorogeneic reagent 9-fluorenylmethyl chloroformate (FMOC) through the cartridges. After a certain reaction time the derivatives formed are desorbed with acetonitrile. The collected extracts are then chromatographed on a LiChrospher 100 RP18 125 mm×4 mm i.d., 5 μm, column using an acetonitrile-water gradient. The influence of experimental conditions (SPE material, volume of sample, concentration of FMOC, time of reaction and pH) has been inve…
Suppression of pigment interference in the gas chromatographic analysis of proteinaceous binding media in paintings with EDTA.
2004
A method to suppress the interference of pigments in the analysis of proteinaceous media used in paintings is presented in this paper. This method is based on the formation of metallic ion-ethylenediaminetetraacetic acid (EDTA) complexes previous to the derivatisation process, using ethyl chloroformate (ECF), to transform the amino acids in N(O,S)-ethoxycarbonyl (EOC) ethyl esters. Test specimens, containing different proteinaceous media such as albumin, porcine gelatine and casein mixed with lead white, chalk, verdigris and raw Sienna have been prepared for carrying out this study. Different pH conditions have been probed for the different pigments studied. Values of peak area ratio of ami…
Identification of diterpenes in canvas painting varnishes by gas chromatography-mass spectrometry with combined derivatisation.
2004
A derivatisation method that combines the formation of ethyl esters from the carboxylic groups and trimethylsilyl ethers from hydroxyl groups of the components of diterpenic resins is presented in this paper. This methodology involves two experimental steps: (1) formation of ethyl esters using ethyl chloroformate; and (2) the esterified compounds are lead to react with trimethylsilylimidazole to form the corresponding trimethylsilyl ethers. The main advantage of the proposed method is the possibility of performing simultaneously the analysis of amino acids from proteins, fatty acids from drying oils, and diterpenic compounds from natural resins usually found in works of art. This methodolog…
Study of Burseraceae resins used in binding media and varnishes from artworks by gas chromatography–mass spectrometry and pyrolysis-gas chromatograph…
2005
In the present work, a study attempting to characterize the Manila elemi and Mexican copal resins from the Burseraceae family, which are used as components of varnishes and binding media of artworks, has been carried out. A new GC-MS method involving the use of methyl chloroformate as derivatisation reagent has been proposed. A second method which uses pyrolysis-GC-MS and hexamethyldisilazane as derivatization reagent has also been applied. Characterization of the main components of the mono-, sesqui- and triterpenoid fractions occurring in the raw materials has been achieved. Both alpha- and beta-amyrin have been established as the major triterpenoid compounds occurring in these resins tog…
Separation of the enantiomers of primary and secondary amphetamines by liquid chromatography after derivatization with (−)-1-(9-fluorenyl)ethyl chlor…
2003
The chiral reagent (−)-1-(9-fluorenyl)ethyl chloroformate (FLEC) has been evaluated for the enantioselective analysis of amphetamines by liquid chromatography. For separation of the FLEC diastereomers conventional reversed-phase conditions were used. The conditions affording the best enantiomeric resolution and sensitivity were determined for amphetamine, methamphetamine, ephedrine, pseudoephedrine, 3,4-methylenedioxyamphetamine (MDA), 3,4-methylenedioxymethamphetamine (MDMA), and 3,4-methylenedioxyethylamphetamine (MDE). All the amphetamines assayed could be separated with resolution factors ranging from 0.91 to 1.92. Although FLEC is typically used as a fluorogenic reagent, it was shown t…
Enantiomeric separation of chiral phenoxy acid herbicides by electrokinetic chromatography. Application to the determination of analyte-selector appa…
2001
The enantiomeric resolution of chiral phenoxy acid herbicides was performed by electrokinetic chromatography using a cyclodextrin as chiral pseudophase (CD-EKC). A systematic evaluation of several neutral and charged cyclodextrins was made. Among the cyclodextrins tested, (2-hydroxy)propyl beta-cyclodextrin (HP-beta-CD) was found to be the most appropriate for the enantioseparation of phenoxy acids. The influence of some experimental conditions, such as nature and pH of the background electrolyte, chiral selector concentration, and temperature, on the enantiomeric separation of phenoxy acids was also studied. The use of a 50 mM electrolyte solution in ammonium formate at pH 5 and a temperat…