An expeditious Kabbe condensation reaction for the synthesis of 2,2-dialkyl and 2-spiro-chroman-4(1H)-ones has been developed using pyrrolidine-butanoic acid in DMSO as bifunctional organocatalyst. Unlike existing methods, this reaction proceeds at room temperature with high yields, rendering it an attractive method to synthesize a vast variety of privileged 4-chromones. 相似文献
Potential host systems based on a rigid 1,8‐diethynylanthracendiyl backbone were synthesised by treatment of 1,8‐diethynylanthracene with the Group 13 trialkyls AlMe3, GaMe3, InMe3, AlEt3 and GaEt3. The resulting products were characterised by IR and multinuclear NMR spectroscopy, elemental analyses and determination of their crystal structures by X‐ray diffraction. The compounds are dimeric in the solid state and comprise two M2C2 heterocycles. Depending on the steric demand of the alkyl substituents at the metal atom, different types of binding modes were observed, which can be classified to lie between the ideals of side‐on coordination with almost linear primary M? C?C units and the 3c–2e coordination with symmetrically bridging alkynyl units in M‐C‐M bonds. As a solution in THF the dimers are broken into monomers and some are found to undergo ligand scrambling reactions. 相似文献
Three of a kind : Vicinal tricarbonyl compounds undergo C? C cleavage mediated by ferric ions (see scheme). The observed cleavage of ninhydrin and dehydroascorbic acid has relevance for amino acid detection and the metabolism of vitamin C.
A simple spectrophotometric assay for the quantification of lactulose in pharmaceutical preparations was developed. The method
is based on hydrolysis of lactulose under acidic conditions. The hydrolyzed product reacts with resorcinol, giving absorption
peaks at 398 and 480 nm. Both absorption wavelengths can be used for the determination of lactulose. The limit of detection
of lactulose at 398 nm and 480 nm was 0.075 μg mL−1 and 0.65 μg mL−1, respectively. The calibration was linear in the range of 5–25 μg mL−1. Analytical conditions were optimized, and the method was validated for analysis of pharmaceutical preparations. The determined
amount of lactulose was found to be in good agreement with labeled claims in commercial products. The proposed method is economical,
convenient, and suitable for the quantification of lactulose in pharmaceutical preparations.
The text was submitted by the authors in English. 相似文献
2,4‐Dichlorophenoxy acetic acid herbicide is spectrophotometrically determined by diazotization method in a flow injection assembly. The method is based on base hydrolysis of herbicides. The hydrolyzed product 2,4‐dichlorophenol is reacted with diazotized sulfanilic acid. The absorbance of the resulting coloured product was measured at 480 nm. The calibration graph is linear over the range of 0.2–20 μgmL?1, with a relative standard deviation of (RSD) of 7.2% and sample throughput of 90 samples h?1. The % recovery for determination of 2,4‐dichlorophenoxy acetic acid was found to be 92.0–95.3%. The method is easy, simple and faster than the established chromatographic method. The method was applied for determination of 2,4‐dichlorophenoxy acetic acid herbicide in commercial formulations and for residue determination in fruits and food samples. 相似文献
A flow injection spectrophotometric method is proposed for the determination of bromoxynil herbicide. Bromoxynil was hydrolyzed with HCl and the resulting product, 3,5-dibromo-4-hydroxyaniline, was diazotized with nitrite and coupled with aniline. The absorbance of the azo dye was measured at 500 nm. The conditions were optimized for diazotization using FIA. The range of linearity was found to be 0.01 to 5 ppm with a molar absorptivity of 1.27 x 10(5) L mol(-1) cm(-1). The % recovery for the determination of bromoxynil was found to be 91%. The sampling frequency was 80 samples per hour for FIA. The method is simple, fast, and has been successfully applied to the determination of bromoxynil in commercial formulations and food samples. 相似文献
A single crystalline enantiomer of 2-(2-thioxothiazolidin-3-yl)thiazole 5 has been isolated as the major product of the pyrolysis of 3-(2-thiazolin-2-yl)thiazolidine-2-thione 3 (n = 1); the latter isolated as the sole product of the reaction between thiazolidine-2-thione 2 (n = 1) and diethyl azodicarboxylate (DEAD) in benzene. 相似文献