• Korean Chemical Engineering Research
• /
• 제57권2호
• /
• pp.164-171
• /
• 2019

The protonation parameters, dissociation constants ($pK_{BH^+}$) of conjugate acid, slope values (m, ${\phi}$ and $m^*$) and correlation coefficients (r) of hydroxamic acids were determined by Hammett acidity function method, Bunnett-Olsen method and excess acidity method in hydrochloric and perchloric acid solutions. Effect of acid concentration on partition and percentage protonation was also studied. $pK_{BH^+}$ values show that hydroxamic acids do not behave as Hammett bases, but hydroxamic acids behave as weak bases in strong acidic solutions. The values of $pK_{BH^+}$ obtained through Bunnett-Olsen method and excess acidity method were compared with the Hammett acidity function. ChemAxon's MarvinSketch 6.1.5 software was also used for determining $pK_a$, pI and microspecies distribution (%) of hydroxamic acids with pH. Hydrogen donor and acceptor values and logD were also obtained. The results show that N-p-chlorophenyl-4-bromobenzohydroxamic acid has the highest $pK_a$ and lowest logD values. On the contrary, N-phenyl-3,5-dinitrobenzohydroxamic acid has lowest the $pK_a$ and highest logD values.

• Bulletin of the Korean Chemical Society
• /
• 제15권9호
• /
• pp.782-785
• /
• 1994

The dissociation kinetics of linear polyaminopolycarboxylate complexes of lanthanide ions (L$n^{3+}: Ce^{3+},\;Eu^{3+}\;and\;Yb^{3+}$) has been studied in an aqueous solution of 0.10 M (NaCl$O_4$) at 25.0${\pm}0.1^{\circ}C$ using Cu(II) ions as a scavenger. The dissociation rates of acid-catalyzed pathway decrease in the order Ln(EPDTA$)^- > Ln(DPOT)^- > In(TMDTA)^- > Ln(MPDTA)^- > Ln(EDTA)^- > Ln(PDTA)^- > Ln(DCTA)^-$ according to the present and literature data. An increase in the N-Ln-N chelate ring from 5 to 6 and substitution of two methyl groups, one ethyl and hydroxyl group on a chelate ring carbon of these ligands leads to a decrease in kinetic stabilities of the complexes. The substitution of one methyl group and cyclohexyl ring on a ring carbon, however, results in a significant increase in the kinetic stability of the resulting $Ln^{3+}$ complexes. Individual reaction steps taking place for each system, with different copper, acetate buffer concentration and pH dependence, are also discussed.

• 한국환경과학회지
• /
• 제20권6호
• /
• pp.687-700
• /
• 2011

A new $N_3-O_2$ pentadentate ligand, H-BHPT, was synthesized. Hydrochloric acid salts of Br-BHPT, Cl-BHPT, $CH_3O$-BHPT and $CH_3$-BHPT, having Br-, Cl-, $CH_{3-}$ and $CH_3O-$ substituents at the para position of the phenol hydroxyl group of H-BHPT were synthesized. Hydrochloric acid salts of 3OH-BHPT and 4OH-BHPT, having different position of the phenol hydroxyl group of H-BHPT were also synthesized. The synthesis of each ligand was confirmed by C. H. N. atomic analysis and $^1H$ NMR, $^{13}C$ NMR, UV-visible, and mass spectra. The calculated proton dissociation constants ($log{K_n}^H$) of the phenol hydroxyl group and secondary amine group of the synthesized $N_3-O_2$ ligands showed five steps of the proton dissociations. The order of the overall proton dissociation constants ($log{\beta}_p$) of the ligands was Br-BHPT < Cl-BHPT < H-BHPT < $CH_3O$-BHPT < $CH_3$-BHPT. The order agreed with that of Hammett substituent constants (${\delta}_p$). However, dissociation steps of 3OH-BHPT were four and that of 4OH-BHPT was three. The calculated stability constants ($logK_{ML}$) between the ligands and transition metal ions agreed with the order of $log{\beta}_p$ values of the ligands. The order of the stability constants between the transition metal ions with the synthesized ligands was Co(II) < Ni(II) < Cu(II) > Zn(II) > Cd(II) > Pb(II). The order agreed well with that of the Iriving-Williams.

• 대한화학회지
• /
• 제10권3호
• /
• pp.119-128
• /
• 1966

The glass electrode was empirically calibrated in methanol-and 2-propanol-water mixed solvents, by means of which the pH-meter reading could be converted to stoichiometric hydrogen ion concentration. The thermodynamic dissociation constants of hydrogen cupferrate in methanol-and 2-propanol-water solution were potentiometrically determined with the changes in composition of organic solvents at 0.01 and 0.05 of the ionic strength and 25$^{\circ}C$. The empirical formula of the constants with mole fraction (n) of the organic solvent are as follow: methanol-water solution $pK_a$= 2.24n + 4.29 at ${\mu}$ = 0.01 n = 0.0476∼0.642 $pK_a$ = 2.35n + 4.38 at ${\mu}$ = 0.05 n= 0.0446~0.642 2-propanol-water solution $pK_a$= 5.50n + 4.48 at ${\mu}$ = 0.05 n = 0.0253~0.259 The relationships between $pK_a$ of acetic acid, propionic acid and HCup and dielectric constant of some mixed solvents were discussed. It would be considered that the factors effecting $pK_a$ value of weak acid in mixed-solvent are not only dielectric constants but acid-base character and solvation effect of the solvent, etc.

• Bulletin of the Korean Chemical Society
• /
• 제33권11호
• /
• pp.3618-3624
• /
• 2012

Photodissociation dynamics of propiolic acid ($HC{\equiv}C-COOH$) at 212 nm in the gas phase was investigated by measuring rotationally resolved laser-induced fluorescence spectra of OH ($^2{\Pi}$) radicals exclusively produced in the ground electronic state. From the spectra, internal energies of OH and total translational energy of products were determined. The electronic transition at 212 nm responsible for OH dissociation was assigned as the ${\pi}_{C{\equiv}C}{\rightarrow}{\pi}^*{_{C=O}}$ transition by time-dependent density functional theory calculations. Potential energy surfaces of both the ground and electronically excited states were obtained employing quantum chemical calculations. It was suggested that the dissociation of OH from propiolic acid excited at 212 nm should take place along the $S_1/T_1$ potential energy surfaces after internal conversion and/or intersystem crossing from the initially populated $S_2$ state based upon the potential energy calculations and model calculations for energy partitioning of the available energy among products.

• Corrosion Science and Technology
• /
• 제7권4호
• /
• pp.237-242
• /
• 2008

Physical properties of water, such as dielectric constant and ionic product, significantly vary with the density of water. In the supercritical conditions, since density of water widely varies with pressure, pressure has a strong influence on physical properties of water. Dielectric constant represents a character of water as a solvent, which determines solubility of an inorganic compound including metal oxides. Dissociation equilibrium of an acid is also strongly dependent on water density. Dissociation constant of acid rises with increased density of water, resulting in drop of pH. Density of water and the density-related physical properties of water, therefore, are the major governing factors of corrosion and environmentally assisted cracking of metals in supercritical aqueous solutions. This paper discusses importance of "physical properties of water" in understanding corrosion and cracking behavior of alloys in supercritical water environments, based on experimental data and estimated solubility of metal oxides. It has been pointed out that the water density can have significant effects on stress corrosion cracking (SCC) susceptibility of metals in supercritical water, when dissolution of metal plays the key role in the cracking phenomena.

• Bulletin of the Korean Chemical Society
• /
• 제35권3호
• /
• pp.770-774
• /
• 2014

The bond dissociation energy (BDE) of the chemical bond between the carbon and oxygen atoms of a simple TEMPO-derivative is calculated by employing the density functional theory, the $2^{nd}$ order M${\phi}$ller-Plesset (MP2) perturbation theory, and complete basis set (CBS) methods. We find that BDE of the positive ion of the TEMPO-derivative is larger at least by 7 kcal/mol than that of the negative ion, which implies that the dissociation reaction rate of the positive ion should be slower than that of the negative ion. Such theoretical predictions are contrary to the results of our previous experiments (Anal. Chem. 2013, 85, 7044), in which the larger energy was required for negative o-TEMPO-Bz-C(O)-peptides to undergo the dissociation reactions than for the positive ones. By comparing our theoretical results to those of the experiments, we conclude that the dissociation reaction of o-TEMPO-Bz-C(O)-peptide should occur in a complicated fashion with a charge, either positive or negative, probably being located on the amino acid residues of the peptide.

• 대한화학회지
• /
• 제9권1호
• /
• pp.33-36
• /
• 1965

5-Acetyl-8-hydroxyquinoline 의 酸解離定數를 $25^{\circ}C({\mu}$=0.1)에서 分光光度法과 pH滴定法에 依하여 測定하였다. 두 方法에 의하여 얻은 $pK_1$은 近似하게 一致하였으며 pK값은 8-hydroxyquinoline의 該當 pK값보다 작다. 그것은 acetyl group의 芳香族環에 대한 電子吸引性에 基因한 結果라고 생각한다.

• 대한화학회지
• /
• 제31권5호
• /
• pp.400-405
• /
• 1987

세가지 아미노산 즉 글리신, 알라닌 및 트립토판의 두가지 해리상수를 전도도법을 이용하여 온도(15 ~ 35$^{\circ}$C)와 압력(1~2,500bar)을 변화시키면서 측정하였다. 두가지 해리상수는 온도가 높아지면 모두 증가했으나 압력이 높아지면 첫째 해리상수는 증가하고 둘째 해리상수는 트립토판을 제외하면 감소하였다. 이와같은 현상은 반응의 열역학적 성질을 이용하여 설명하였으며 나아가서 반응의 특성을 알아보기 위해서 Hammett의 법칙을 적용하고 반응의 치환기 상수와 압력에 따른 반응상수를 계산하였다. 아미노산의 해리상수의 특성을 치환 효과로 설명하였고 반응의 유형을 반응상수로서 알아보았다.

• 대한화학회지
• /
• 제30권2호
• /
• pp.145-151
• /
• 1986

3-CN, 4-CN, $3-NH_2$ 및 $4-NH_2$ 치환피리딘의 해리상수를 온도(15 ∼ 40${\circ}C$)와 압력(1-2500bar)을 변화시키면서 측정하였다. 측정방법은 전도도법을 적용했으나 낮은 해리상수를 가진 물질에서도 적용되는 피리딘류의 염용액의 전도도를 측정하므로 계산가능한 방법을 모색하여 응용하였다. 이 방법은 어떤 조건에서의 해리상수를 알고 있어야 하는 것과 실험값을 외삽하여 피리딘염의 전도도를 알아야 하는 번거로움도 있으나 측정이 가능하다는 것을 확인할 수 있다. 이들 치환체의 해리상수는 온도가 증가하면 커지고 압력이 높아지면 해리상수는 작아진다는 것을 알 수 있었다. 또 반응의 열역학적 성질을 계산하여 반응성도 고찰하였다.