Solubility of the cosolutes 4-hydroxybenzoic acid and its alkyl esters (‘alkylparabens’) in aqueous urea: evidence for 1 : 1 cosolute–urea association in solution and evaluation of the methylene group contribution to the free energy of association

1992 ◽  
Vol 88 (7) ◽  
pp. 971-977 ◽  
Author(s):  
Geoffrey Dempsey ◽  
Philip Molyneux
Keyword(s):  
Free Energy ◽  
Group Contribution ◽  
Hydroxybenzoic Acid ◽  
Alkyl Esters ◽  
Aqueous Urea ◽  
Methylene Group

p-Hydroxybenzoic Acid Alkyl Esters inAndrographis paniculataHerbs, Commercial Extracts, and Formulated Products

2003 ◽  
Vol 51 (2) ◽  
pp. 524-529 ◽  
Author(s):  
Wenkui Li ◽  
Yongkai Sun ◽  
Joy Joseph ◽  
John F. Fitzloff ◽  
Harry H. S. Fong ◽  
...  
Keyword(s):  
Hydroxybenzoic Acid ◽  
Alkyl Esters

Vanadium(V) oxyanions. The dependence of vanadate alkyl ester formation on the pKa of the parent alcohols

1988 ◽  
Vol 66 (9) ◽  
pp. 2294-2298 ◽  
Author(s):  
Alan S. Tracey ◽  
Bruno Galeffi ◽  
Soroush Mahjour
Keyword(s):  
Aqueous Solution ◽  
Nuclear Magnetic Resonance ◽  
Free Energy ◽  
Resonance Spectroscopy ◽  
Linear Free Energy Relationship ◽  
Alkyl Esters ◽  
Linear Free Energy ◽  
Ester Formation ◽  
Interesting Correlation ◽  
Extra Electron

The interaction of vanadate (VO4H21−) with a variety of alkyl alcohol's (ROH) covering about seven pKa units of acidity have been studied in aqueous solution by 51V nuclear magnetic resonance spectroscopy. A linear free energy relationship between the equilibrium constant for the formation of the vanadate monoester (HOVO3R1−) and the acidity of the alcohol was established at 23 °C. The correlation was found to be [Formula: see text] where K = [HOVO3R1−]/[VO4H21−][ROH]. This correlation was shown not to extend to ligands with π-bonding capability such as phenols or phosphates, where the products are highly favoured relative to the alkyl esters. An interesting correlation between pKa values of the product esters and the pKa of the parent alcohols was also observed. It was found that below a [Formula: see text] of about 15 the pKa values of the esters were essentially constant. However, above this value of 15 the pKa of the ester was found to increase rapidly with an increase in pKa of the alcohol. This result may indicate that the electron accepting ability of the metal is exhausted with the higher pKa alcohols, and the extra electron density is transferred to the oxygens, thus causing an increase in pKa of the ester.

Investigation and Analytical Applications of the Reaction of N1-Methylnicotinamide and Active Methylene Containing Drugs

2020 ◽  
Vol 17 ◽  
Author(s):  
Heba A. Elsebaie ◽  
Mervat H. Elhamamsy ◽  
Khaled M. Elokely ◽  
Mohammed A. Eldawy
Keyword(s):  
Quality Control ◽  
Free Energy ◽  
Spectral Analysis ◽  
Quantitative Analysis ◽  
Geometry Optimization ◽  
Fluorescent Product ◽  
Spectrofluorometric Method ◽  
Active Methylene ◽  
Methylene Group

Background: The reaction between N1-methylnicotinamide iodide (NMNI) and the active methylene group containing compounds yields a fluorescent product, which can be used in the quantitative determination of certain drugs. Objective: The objective is to develop, adapt and validate a simple spectrofluorometric method for the quantitative analysis of modafinil 1, budesonide 2, allicin 3 and florfenicol 4. Results: A C4 cyclization pathway was confirmed for the formation of the fluorophore. The spectrofluorometric method showed good linearity (R2= 0.996-0.999) over concentrations of 1-50 ng/mL, 0.5-5 ng/mL, 60-150 pg/mL, and 1-15 ng/mL of the standard solutions of 1, 2, 3, and 4, respectively. Methods: Spectral analysis (elemental analysis, 1H, 13C NMR, MS), computational methods (geometry optimization, Gibbs free energy and pKa calculations) and spectrofluorometric approaches were conducted. Conclusion: The proposed method is simple and suitable for quality control and assurance studies

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