Syntheses for 2-(pyridyl N-oxide) methylphosphonic acid, 1-H, and 2-(pyridyl N-oxide) hydroxymethylphosphonic acid, 4-H, are described, and the crystal structures of both ligands are presented. Combination of these ligands with freshly prepared erbium hydroxide results in the formation of the isostructural complexes Er(L(-))(3)(LH).8H(2)O. The crystal structure determinations of the complexes show that extensive hydrogen bonding links the individual eight coordinate Er(L(-))(3)(LH) molecular units into a 3-D structure. 相似文献
Ruthenium complexes have been shown to perform efficient transfer hydrogenation reactions between alcohols and alkenes; in combination with an in situ Wittig reaction, indirect formation of C-C bonds has been achieved from alcohols. 相似文献
The reaction of UCl4 with KO-2,6-Cl2C6H3 in tetrahydrofuran results in the preparation of the title compound. The six-coordinate complex possesses pseudo-octahedral geometry about uranium, with U-O(phenoxide) bond lengths in the range 2.161(11) to 2.178(10) Å and U-O(THF) bond lengths of 2.467(10) and 2.475(11) Å. This complex crystallizes in the monoclinic space group P21/n (a = 11.169(2), b = 11.588(2), c = 35.119(5) Å, = 92.11(1)°, V = 4542.2(13) Å3, and Z = 4). 相似文献
The flash pyrolysis of glycerin was investigated by the use of isotopic labeling with 13C, in conjunction with GC/MS analysis of the products. The formation of acetaldehyde and acrolein was shown to occur by unimolecular reaction. Acetaldehyde was found to be produced by at least two competing mechanisms. Mechanism “A” delivered C-2 of glycerin to the carbonyl group of acetaldehyde, whereas mechanism “B” delivered C-2 of glycerin to the methyl group of acetaldehyde. Formaldehyde was exclusively derived from C-1 or C-3 by either mechanism. The partition between the two mechanistic paths was found to be influenced by the presence of potassium salts and acids, but not by the presence of benzoyl peroxide or galvanoxyl. Mechanism “A” is postulated to be a concerted cyclic version of the Grob Fragmentation, proceeding through an intermediate which is hydrogen-bonded between the 1- and 3-hydroxyl groups to simultaneously generate enol-acetaldehyde, formaldehyde and H2O. Mechanism “B” as favored by the presence of alkali is postulated to involve hydrogen-bonding between adjacent hydroxyl groups and to be an alkaline version of the pinacol rearrangement followed by retro-aldol fragmentation of the intermediary 3-oxopropoxide anion. These mechanistic classes are both fundamentally important, not only for their effect on glycerin, but for being able to provide numerous means of initial pyrolytic carbon–carbon bond breakage along carbohydrate carbon-chains, given the numerous 1,2,3-triol interactions that are possible. Further nomenclature is introduced to refine the distinctions among isotopomers and isotopologs (ipsomer, ipsolog, naturalomer, “nominal” isotopolog, ubiquilog), as extensions of a concept previously adopted by IUPAC. 相似文献
A convenient synthesis of alkyl-substituted ethyl nicotinates 8 was devised, using 3-cyano-2(1H)-pyridones 4. These were converted to the corresponding 2-bromo-3-cyanopyridines 5 with boiling phosphorus tribromide. The resulting 5 were smoothly debrominated to 3-cyanopyridines 6 with zinc dust in boiling ethanolic acetic acid. The nitrile function was hydrolyzed in boiling 6N hydrochloric acid, and the resulting nicotinic acid hydrochlorides 7 esterified with refluxing triethyl orthoformate, to give the ethyl nicotinates 8. A modified formylation of 2-butanone led to the sodium salt of 2-methyl-3-oxobutanal ( 3a ) of enhanced purity. 相似文献
Two bis(mu-methoxo)dichromium(III) complexes, [L(Se)(2)Cr(2)(mu-OCH(3))(2)(CH(3)OH)(2)] 1 and [L(Se)(2)Cr(2)(mu-OCH(3))(2)(CH(3)OH)(CH(3)O)](-) 2, where L(Se) represents the dianion of 2,2'-selenobis(4,6-di-tert-butylphenol), have been reported to demonstrate the effect of hydrogen bonding on the exchange coupling interactions between the chromium(III) centers. The corresponding sulfur analogue of the ligand, i.e., 2,2'-thiobis(4,6-di-tert-butylphenol), also yields the analogous [L(S)(2)Cr(2)(mu-OCH(3))(2)(CH(3)OH)(2)] 3 and [L(S)(2)Cr(2)(mu-OCH(3))(2)(CH(3)O)(CH(3)OH)](-) 4, which exhibit similar exchange coupling parameters. An acid-base dependent equilibrium between 1 and 2 or 3 and 4 has been established by electronic spectral measurements. 相似文献
A new method for the sequential determination of attapulgite and nifuroxazide in pharmaceutical formulations by first- and second-derivative spectrophotometry, respectively, has been developed. In order to obtain the optimal conditions for nifuroxazide stability, studies of solvent, light, and temperature effects were performed. The results show that a previous hydrolysis of 2 h in 1.0 x 10(-1)M NaOH solution is necessary in order to obtain stable compounds for analytical purposes. Subsequently, the first- and second-derivative spectra were evaluated directly in the same samples. The sequential determination of the drugs can be performed using the zero-crossing method; the attapulgite determination was carried out using the first derivative at 278.0 nm and the nifuroxazide determination, using the second derivative at 282.0 nm. The determination ranges were 5.7 x 10(-6)-1.0 x 10(-4) and 3.7 x 10(-8) -1.2 x 10(-4)M for attapulgite and nifuroxazide, respectively. Repeatability (relative standard deviation) values of 1.2 and 3.0% were observed for attapulgite and nifuroxazide, respectively. The ingredients commonly found in commercial pharmaceutical formulations do not interfere. The proposed method was applied to the determination of these drugs in tablets. Further, infrared spectroscopy and cyclic voltammetry studies were carried out in order to obtain knowledge of the decomposition products of nifuroxazide. 相似文献
Full characterization of complex reaction mixtures is necessary to understand mechanisms, optimize yields, and elucidate secondary reaction pathways. Molecular-level information for species in such mixtures can be readily obtained by coupling mass spectrometry imaging (MSI) with thin layer chromatography (TLC) separations. User-guided investigation of imaging data for mixture components with known m/z values is generally straightforward; however, spot detection for unknowns is highly tedious, and limits the applicability of MSI in conjunction with TLC. To accelerate imaging data mining, we developed DetectTLC, an approach that automatically identifies m/z values exhibiting TLC spot-like regions in MS molecular images. Furthermore, DetectTLC can also spatially match m/z values for spots acquired during alternating high and low collision-energy scans, pairing product ions with precursors to enhance structural identification. As an example, DetectTLC is applied to the identification and structural confirmation of unknown, yet significant, products of abiotic pyrazinone and aminopyrazine nucleoside analog synthesis.