• Journal of the Korean Society of Safety
• /
• v.16 no.2
• /
• pp.75-79
• /
• 2001

For handling and storage of reactive chemicals, the hazard evaluations have been extremely important. In the chemical industry, the most concerns are focused on the thermal harzards such as runaway reactions and thermal decompositions, which are mostly governed by thermodynamics and reaction kinetics or these reactive chemical in the system. This study no investigated the thermal decomposition characteristics of nitrophenylhydrazine isomers by using differential scanning calorimeter(DSC) and accelerating rate calorimeter(ARC). Experimental results showed that exothermic onset-temperatures in nitrophenylhydrazine(NPH) isomers were about 160-$210^{\circ}C$ by DSC and 100-$150^{\circ}C$ by ARC. The decomposition temperature acquired by ARC was about 50-$60^{\circ}C$ lower than that by DSC. Reaction heats were about 40-100cal/g by DSC and 330-750ca1/g by ARC. While ortho isomer of NPH show two distinct exothermic peaks, para isomer shows a single peak in DSC curves. The first exothermic peak for 2-NPH is mainly due to intramolecular dehydration forming 1-hydroxybenzotriazole(HOBT) and the second exothermic peak is mainly due to the decomposition of HOBT formed in the first step of decomposition. The exothermin peak in the DSC curve for 4-NPH is mainly due to dissociation of hydrazino and nitro groups.

• Bulletin of the Korean Chemical Society
• /
• v.20 no.3
• /
• pp.355-361
• /
• 1999

To improve the volatility and stability of lead complexes, the principle of stabilization by saturating the metal coordination sphere by intramolecular coordination through a β-diketonates with an ethereal group has was tested. Several new lead complexes with alkoxyalkyl-substituted β-diketonates, Pb(R1C(O)CHC(O)(CH2)3OR2)2(Rl=t-Bu, Me, OMe, i-Pr, R2=Me, Et), or carboxylate, Pb(OC(O)(CH2)3OEt)2, were prepared by the reaction between Pb(OAc)2 and corresponding alkoxyalkyl-substituted β-diketonates, and they were found to have a viscous liquid phase. The nature of the head (β-diketonate or carboxylate) or tails and substituents of β-diketonates appeared not to be important for the formation of the liquid phase. It is worth mentioning that Pb(OAc)2, which has limited use due to its low solubility, was successfully adopted as a starting material for the preparation of new lead complexes. Easy hydrolysis, reaction with HCl, and 13C NMR spectra indicated that tail portions were not coordinated to the metal as a copper derivative, Cu(t-BuC(O)CHC(O)(CH2)3OMe)2. All these complexes were not volatile enough for the MOCVD experiments, but a methyl derivative, Pb(MeC(O)CHC(O)(CH2)3OEt)2, showed some sublimation. The methoxy derivative, Pb(MeOC(O)CHC(O)(CH2)3OEt)2, was thermally unstable due to possible equilibrium between species coordinating with a keto oxygen atom and an ethereal atom of a methoxy group, which was confirmed by IR and 13C NMR spectra.

• Bulletin of the Korean Chemical Society
• /
• v.35 no.2
• /
• pp.436-440
• /
• 2014

The ${\alpha}$-Effect; Ground state; Transition state; Intramolecular H-bonding; Yukawa-Tsuno plot; Second-order rate constants for aminolysis of 2-chloro-4-nitrophenyl X-substituted-benzoates (1a-h) have been measured spectrophotometrically in 80 mol % $H_2O/20$ mol % DMSO at $25.0^{\circ}C$. The Br${\emptyset}$nsted-type plot for the reactions of 2-chloro-4-nitrophenyl benzoate (1d) with a series of primary amines curves downward, which has been taken as evidence for a stepwise mechanism with a change in rate-determining step (RDS). The Hammett plots for the reactions of 1a-h with hydrazine and glycylglycine are nonlinear while the Yukawa-Tsuno plots exhibit excellent linearity with ${\rho}_X=1.22-1.35$ and ${\gamma}= 0.57-0.59$, indicating that the nonlinear Hammett plots are not due to a change in RDS but are caused by stabilization of substrates possessing an electron-donating group (EDG) through resonance interactions between the EDG and C=O bond of the substrates. The ${\alpha}$-effect exhibited by hydrazine increases as the substituent X changes from a strong EDG to a strong electron-withdrawing group (EWG). It has been concluded that destabilization of hydrazine through the electronic repulsion between the adjacent nonbonding electrons is not solely responsible for the substituent dependent ${\alpha}$-effect but stabilization of the transition state is also a plausible origin of the ${\alpha}$-effect.

• Journal of the Korean Chemical Society
• /
• v.40 no.4
• /
• pp.254-263
• /
• 1996

Five cobalt(Ⅲ) complexes were synthesized from bi- or tridentate nitrogen ligands. Catalytic actions of these complexes for hydrolyses of p-nitrophenyl picolinate, p-nitrophenyl nicotinate, and p-nitrophenyl isonicotinate were investigated by a spectrophotometric method. p-Nitrophenyl picolinate showed the most senstive reaction among three substrates by these catalysts. Aquohydroxo Co(Ⅲ) complexes raised as much as 21∼40 times the rate of hydrolysis of p-nitrophenyl picolinate at pH 6.5. Activities of complexes were in the order: Co(ibpn)(OH)2(OH2) > Co(aepn)(OH)2(OH2) > Co(tn)2(OH)(OH2) > Co (bpy)2(OH)(OH2) > Co(dien)(OH)2(OH2). Catalytic hydrolysis was postulated to proceed through a intramolecular general base catalysis path which is mixed by a partial intramolecular nucleophilic catalysis.

• YAKHAK HOEJI
• /
• v.40 no.4
• /
• pp.382-386
• /
• 1996

The compound of the 6,7-dichloroquinoline-5,8-dione has two asymmetric chloro radicals at the position of the C6 and C7. When the compound reacts with ethyl acetoacetate in the presence of sodium ethoxide, it is considered that C6 and/or C7 position of the compound can be substitued. The exact substitued position of the product (I) could not be identified by the NMR analysis in our experiment. Therefore, we synthesized the 3-ethoxycarbonyl-2-methyl-1-N-propyl pyridino(2,3f)indole-4,9-dione by reaction of the product (I) with propylamine via intramolecular cyclization to identify the substitued position of the product (I) using the X-ray crystallographic structure analysis. The result demonstrates that the position of nucleophilic substitution of the product (I) is at the position of the C6.

• Bulletin of the Korean Chemical Society
• /
• v.26 no.2
• /
• pp.273-277
• /
• 2005

Dynamic resolution of $\alpha$-bromo tertiary acetamides in asymmetric nucleophilic substitution reaction is described. Intermolecular substitution of $\alpha$-bromo tertiary acetamides with dibenzylamine in the presence of TBAI and $Et_3N$ gave the dipeptide analogues 7-10 with high stereoselectivities up to 90 : 10 dr. Also, cyclic dipeptide analogues 20-29 were produced by the intramolecular nucleophilic cyclization of $\alpha$-bromo tertiary acetamides with low stereoselectivities in 84-42% yields.

• Bulletin of the Korean Chemical Society
• /
• v.29 no.2
• /
• pp.357-362
• /
• 2008

A method for synthesizing o-carborane substituted tetrahydroisoquinolines containing a polar functional group such as sulfamide, sulfonic, or phosphoric acid on the nitrogen atom of the piperidine ring, starting from arylethylamine, N-(2-arylethyl)sulfamide, N-(2-arylethyl)sulfamic acid or 2-arylethylamidophosphate, is described. In vitro studies showed the desired compounds 10, 15, 19, and 25 synthesized accumulate to high levels in B-16 melanoma cells with low cytotoxicity.

• Bulletin of the Korean Chemical Society
• /
• v.29 no.5
• /
• pp.1018-1024
• /
• 2008

Photolysis of 2-(pentamethyldisilanyloxy)phenylpentamethyldisilane 1 in methanol provides five photoproducts 3, 4, 5, 6, and 7. Compounds 3 and 4 were probably formed from the methanol addition reactions of silene intermediate 2 and the formation of 5, 6, and 7 can best be explained by the nucleophilic attack of methanol to silicon atom in pentamethyldisilanyloxy or pentamethyldisilanyl group of the photoexcited state of 1. Irradiation of 1 in n-hexane gives a photoproduct 6 via silyl radical intermediate 8 and a novel intramolecular cyclization photoproduct 11 via silene 9 and silyl radical intermediate 10. Irradiation of 1 in deaerated methylene chloride in the presence of acetone affords a novel photoproduct 11 and phenol 7 but the expected photoproducts from the reaction of the silene intermediate with acetone were not obtained.

• YAKHAK HOEJI
• /
• v.33 no.4
• /
• pp.246-252
• /
• 1989

2-Amino-1-N-methyl benzamide, 2-N-benzyl amino benzamide, 2-N-phenyl amino benzamide of 2-amino benzamide derivatives were reacted with ${\alpha}-bromo$ acetaldehyde diethyl acetal in basic condition. 2-N-alkylated products were prepared from 2-amino-1-N-methyl benzamide and 2-N-phenyl amino benzamide. 1-N-benzyl-1.4-benzodiazepin-5-one was prerpared from 2-N-benzyl aminobenzamide via intramolecular cyclization. However, 2-amino-1-N-methyl benzamide with sodium amide did not react to 1.4-benzodiazepin-5-one derivative but 3-methyl-quinazoline-2.4-dione was obtained.

• Animal cells and systems
• /
• v.2 no.2
• /
• pp.243-248
• /
• 1998

We have partially sequenced glutaminyl cyclases from several mammalian and one avian species and found that the two cysteine residues of the human glutaminyl cyclase are completely conserved. The mammalian glutaminyl cyclase has been reported to possess reactive thiols (Busby, Jr, et aI., 1987, J BioI Chern 262, 8532-8536). Mutagenesis of these cysteine residues, however, resulted in only a slight decrease in enzyme activity. Likewise, the recombinant human enzyme was completely resistant to attempted chemical modification of the putative reactive thiols. Although the human glutaminyl cyclase did not appear to have reactive thiols, it was sensitive to diethylpyrocarbonate and acetylimidazole, indicating the presence of functionally important histidine and tyrosine residues which could act as acid/base catalysts. Almost identical deuterium solvent isotope effect (1.2 vs 1.3) upon the reaction by the human and papaya enzymes, respectively, provides an evidence both animal and plant glutaminyl cyclases catalyze pyroglutamyl-peptide formation by intramolecular cyclization.