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1.
Trimethyl phosphite selectively removes the N-1-oxygen in N-(3-methyl-2-quinoxaloyl) L-α-amino ester-1,4-dioxides, whereas it removes the N-4-oxygen in the corresponding series of dioxides lacking the C3-Me. This selectivity reversal reflects the relative strength of the intrahydrogen-bridging to the N-1-oxygen. The monoxides having the favourable N-oxygen are not reduced to the quinoxalines, implying that the reagent requires doubling of the N-oxide function for deoxygenation. However, alkaline sodium dithionite removes the N-1-oxygen in both series of the amino acid-dioxides, as well as in the parent quinoxaline-2-carboxylic acid-dioxides, a result that contradicts the report stating removal of the N-4-oxygen. The N-oxygenated quinoxalinium ion ( 145 or 159) prevails in the MS of the 4-oxides, but it is not observed (<1%) for the isomeric 1-oxides. 1H NMR, 13C NMR and UV spectral data also offer diagnostic criteria for differentiation between the isomeric 1- and 4-oxides. Aryl-heteryl “interaction” (as revealed by 1H NMR, though not by 13C NMR in the aromatic amino ester dioxides) is not manifested in the corresponding monoxides. 相似文献
2.
A new analytical solution is introduced for the effect of viscous dissipation on mixed convection flow and heat transfer about an isothermal vertical wall embedded in Darcy and non-Darcy porous media with uniform free stream velocity. The effect of viscous dissipation on mixed convection in both regimes has been analyzed for both the aiding and opposing flows using Gebhart number, Ge
x
=gx/c
p. The governing parameters are Re, Ra, Pe and Ge
x
. The case of Re=0 corresponds to Darcy mixed convection region and Re/Pe is identified as the mixed convection governing parameter, Ra=0 leading to pure forced convection. A good agreement was found between the numerical and analytical solutions. It was found from the Nusselt number results that viscous dissipation lowers the heat transfer rate in both Darcy and Forchheimer flow regimes for aiding as well as opposing flows. 相似文献
3.
Diacyl chlorides react with dialkylcyanamide in the presence of a Lewis acid to give amino-substituted bis-1,3,5-oxadiazinium salts in excellent yields. A mechanism leads to the formation of the product has been postulated. All new compounds have been characterized by 1H-nmr, 13C-nmr, ir-spectroscopy and elemental analysis. 相似文献
4.
Shkoor M. Tashtoush H. Al-Talib M. Mhaidat I. Al-Hiari Y. Kasabri V. Alalawi S. 《Russian Journal of Organic Chemistry》2021,57(7):1141-1151
Russian Journal of Organic Chemistry - A series of 1,3 and 1,4-bis[5-(R-sulfanyl)-1,2,4-triazol-3-yl)benzene derivatives were synthesized by the reaction of isophthalic and terephthalic acid... 相似文献
5.
6.
Heat transfer characteristics of a non-Newtonian fluid on a power-law stretched surface of variable temperature with suction
or injection were investigated. Similarity solutions of the laminar boundary layer equations describing heat transfer and
fluid flow in a quiescent fluid were obtained and solved numerically. Velocity and temperature profiles as well as the Nusselt
number, Nu, were studied for two thermal boundary conditions; uniform surface temperature and variable surface temperature,
for different parameters; Prandtl number Pr, temperature exponent b, velocity exponent m, injection parameter d and power-law index n. It was found that decreasing injection parameter d, and power-law index n and increasing Prandtl number Pr and surface temperature exponent b enhance the heat transfer coefficient.
Received on 27 April 2000 相似文献
7.
Amjad M. Qandil Aiman A. Obaidat Muaadh A. Mohammed Ali Bashar M. Al-Taani Bassam M. Tashtoush Nawzat D. Al-Jbour Mayyas M. Al Remawi Khaldoun A. Al-Sou’od Adnan A. Badwan 《Journal of solution chemistry》2009,38(6):695-712
Complexation between ibuprofen and low molecular weight chitosan (LMWC) was studied. LMWC was prepared from high molecular
weight chitosan using the acid hydrolysis method. The complexes were investigated by using DSC, FT-IR and liquid-state 1H-NMR. Molecular mechanics (MM) calculations were used to give insight into the stoichiometry of the interaction of chitosan
with ibuprofen. The results showed that complexation of ibuprofen with LMWC involves ionic interaction between the ammonium
group of LMWC and the carboxylate anion of ibuprofen. It was also shown that it is more efficient to prepare the complexes
using lower concentration solutions of the polymer. These results were supported by molecular mechanics calculations. The
experimental results may explain the discrepancies in the literature where, in many studies, the concentration of chitosan
and its low average molecular weight were not considered to be important factors in the complexation process. 相似文献
8.
Mahmoud Al‐Talib Hasan Tashtoush Areej Al‐Ghoul Burkhard Ziemer Ulrich Koert 《Journal of heterocyclic chemistry》2005,42(2):287-288
Phenylmalonic acid dihydrazide reacted with 2,4‐pentanedione to give, unexpectedly, 5,7‐dimethyl‐1,3‐dioxo‐2‐phenyl‐2,3‐dihydro‐1H‐pyrazolo[1,2‐a]pyrazole‐4‐ylium 5. The structure of the product is confirmed by X‐ray crystallography. 相似文献
9.
A. M. Qandil B. M. Tashtoush B. M. Al-Taani S. M. Al-Nabulsi F. Al-Zogoul 《Chromatographia》2008,67(3-4):287-291
A simple, rapid and selective RP-HPLC method was developed and validated for the determination of ketorolac and five piperazinylalkyl
ester prodrugs. A binary isocratic mobile phase composed of a mixture of 65:35 (v/v) 0.02 M phosphate buffer (pH 5.4) and acetonitrile was used on a C18 column (125 × 4 mm, 5 μm). The injection volume was 25 μL and the detection wavelength was 314 nm and the flow rate was 1.5 mL min−1. The method exhibited excellent linearity with R
2 of no less than 0.999 and intra-assay and inter-assay precision that were less than the maximum amount allowed according
to Horwitz equation. The accuracy was found to be within the allowed ±15%. The limits of detection for the analytes were between
0.060 and 0.220 μg mL−1 and the limits of quantification were between 0.183 and 0.667 μg mL−1. This method was used successfully for the study of the solubility, stability and partition coefficients of piperazinylalkyl
ester prodrugs of ketorolac. 相似文献
10.
Bassam M. Tashtoush Amjad M. Qandil Elaine L. Jacobson Myron K. Jacobson 《Chromatographia》2008,68(1-2):135-138
Octyl nicotinate is an ester prodrug which is under development for delivery of nicotinic acid to skin for treatment and prevention of dermatological conditions that involve skin barrier impairment such as chronic photodamage and atopic dermatitis or for mitigating skin barrier impairment that results from therapy such as retinoids or steroids. We report here an isocratic RF-LC method with water/acetonitrile (10:90, v/v) as a mobile phase, for the rapid analysis of octyl nicotinate in aqueous solutions. The method was validated in terms of linearity, precision, accuracy and mean recovery of octyl nicotinate from skin homogenate ranging from 98.8 to 102.6%. Separation and quantification of amounts as low as 0.25 μg mL?1 octyl nicotinate was accomplished. The kinetic of degradation of octyl nicotinate in aqueous solution at 310, 333, 343, and 353 K was studied. The hydrolysis rate constants for degradation of octyl nicotinate in phosphate buffer and skin homogenate were reported. This method will be effective for routine analysis of octyl nicotinate stability in different formulations in future studies. 相似文献