• Transactions of the Korean hydrogen and new energy society
• /
• v.19 no.1
• /
• pp.56-63
• /
• 2008

In this study, thermochemical degradation of hemicellulose by Acetone-Solvolysis, the effects of reaction temperature, conversion yield, degradation properties and degradation products were investigated. Experiments were performed in a tube reactor by varying reaction temperature from $200{\circ}C$ to $400{\circ}C$ at 40 min of reaction time. The liquid products from pyrolysis-liquefaction of hemicellulose contained various kinds of ketones. ketones, as 4-methyl-3-penten-2-one, 3-methylene-2-pentanone, 22,6-dimethyl-2, 5-heptadien-4-one, 4-methyl-2-pentanone, 5-methyl-2-hexanone, 3,5,5-trimethyl-2-cyclohexen-1-one, and bezenes. as 1,4-dimethylbenzene, 1-methyl-2-(1-methylethyl)-benzene, 1,4-dimethyl-2-(2-methylpropyl)benzene, 4-secbutyl-ethyl benzene, could be used as high-octane-value fuels and fuel additives. Combustion heating value of liquid products from thermochemical conversion processes of hemicellulose was in the range of $6,680{\sim}7,170cal/g$. After 40min of reaction at $400{\circ}C$ in Acetone-Solvolysis of hemicellulose, the energy yield and mass yield was as high as 72.2% and 41.2g oil/100g raw material, respectively.

• Korean Chemical Engineering Research
• /
• v.51 no.6
• /
• pp.716-726
• /
• 2013

Enzymatic acylations catalyzed by hydrolytic enzymes, along with enzymatic hydrolysis, are established reactions in the synthesis of fine chemicals such as chiral intermediates and polymerizations in the industry. Those reactions have been carried out mostly in organic media due to the thermodynamic limitations. Recently, there have been reports on enzymatic acylations in aqueous media. They have dealt with the elucidation of reaction mechanisms of hydrolases and acyl transferases based on their X-ray structures, homology comparison of the two kinds of enzymes, substrate engineering of acyl donors and computational design of acyl transferases for enzymatic acylations in aqueous media. Enzymatic acylations play an important role in the combinatorial synthesis of natural products such as polyketides and nonribosomal peptides. In this review, the historic developments of enzymatic acylations and industrial examples are described briefly. In addition, recent developments of enzymatic acylations in the modification of natural products and their prospects will be discussed.

• Journal of the Korean Chemical Society
• /
• v.37 no.6
• /
• pp.618-625
• /
• 1993

Rate constants of hydrolysis of N-(benzoyl)-C-(N-methylanilino)imidoylchlorides were determined by UV spectrophotometry in 50% (v/v) aqueous methanol at 25$^{\circ}C$. On the basis of rate equation, substituent effect, solvent effect, salt effect, thermodynamic parameters and hydrolysis product analysis, it may be concluded that the hydrolysis of N-(benzoyl)-C-(N-methylanilino)imidoylchlorides proceed through $S_N$1 mechanism via azocarbonium ion intermediate in the range of from pH 3.0 to pH 10.0, while above pH 10.0 and below pH 3.0 the hydrolysis proceeds through nucleophilic addition-elimination (A$d_{N-E}$) mechanism.

• Korean Chemical Engineering Research
• /
• v.44 no.3
• /
• pp.235-242
• /
• 2006

Spray pyrosysis is a process to prepare particles and films by evaporating and decomposing droplets of precursor solutions in the order of 1-10 micrometer in diameter. Key elements of the spray pyrolysis process include precursor, solvent, droplet generator, and reactor. Various combination of these 4 elements produces wide range of particles and films. In general. the current status of the spray pyrolysis technology is not quite promising for commercial success. However, this process will be feasible to produce multicomponent functional materials of controlled morphology. In this paper, current status of the spray pyrolysis technology is introduced with the emphasis of production of fluorescence particles.

• Journal of the Korean Chemical Society
• /
• v.24 no.5
• /
• pp.342-346
• /
• 1980

Rates and activation parameters have been determined for the solvolysis of N, N-dimethylsulfamoyl chloride in aqueous binaries of MeOH, EtOH, $(Me)_2CO$ and MeCN. Various solvent effect correlation showed that the solvolysis proceeded via the dissociative $S_n2$ mechanism.

• Journal of Life Science
• /
• v.27 no.11
• /
• pp.1381-1392
• /
• 2017

This review described solvent-tolerant lipases and their potential industrial, biotechnological and environmental impacts. Although organic solvent-tolerant lipase was first reported in organic solvent-tolerant bacterium, many organic solvent-tolerant lipases are in not only solvent-tolerant bacteria but also solvent-intolerant bacterial and fungal strains, such as the well-known Bacillus, Pseudomonas, Streptomyces and Aspergillus strains. As these lipases are not easily inactivated in organic solvents, there is no need to immobilize them in order to prevent an enzyme inactivation by solvents. Therefore, the solvent-tolerant lipases have the potential to be used in many biotechnological and biotransformation processes. With the solvent-tolerant lipases, a large number insoluble substrates become soluble, various chemical reactions that are initially impossible in water systems become practical, synthesis reactions (instead of hydrolysis) are possible, side reactions caused by water are suppressed, and the possibility of chemoselective, regioselective and enantioselective transformations in solvent and non-aqueous systems is increased. Furthermore, the recovery and reuse of enzymes is possible without immobilization, and the stabilities of the lipases improve in solvent and non-aqueous systems. Therefore, lipases with organic-solvent tolerances have attracted much attention in regards to applying them as biocatalysts to biotransformation processes using solvent and non-aqueous systems.

• Journal of the Korean Chemical Society
• /
• v.22 no.3
• /
• pp.150-157
• /
• 1978

The rate constants for the hydrolysis of the derivatives of N-(p-nitrophenyl)-benzohydrazonyl azide (p-$CH_3,\;p-CH_3O,\;p-NO_2$, p-Cl, p-Br) have been determined by UV spectrophotometry in 50% dioxane-water at $25^{\cicr}C$ and a rate equation which can be applied over wide pH range was obtained. Below pH 5, the rate of hydrolysis of hydrazonyl azides is accelerated by electron-donating group ($\rho$ = -0.47), whereas at the pH values greater than 7, the $\rho$-value is 0.68. The effect of salt, solvent, substituent and azide ion on the rate of hydrolysis are rationalized in terms of $S_N1$ and $S_N2$ mechanism; below pH 5, the hydrolysis proceed through $S_N1$, however, above pH 7, the hydrolysis is started by the attack of hydroxide ion and in the range of pH 5∼7, these two reactions occur competitively.

• Journal of Life Science
• /
• v.13 no.6
• /
• pp.788-793
• /
• 2003

Production of chiral phenyl oxirane by Rhodosporidium toruloides SJ-4 was investigated. Racemic phenyl oxirane was kinetically resolved by enantioselective hydrolysis reaction by epoxide hydrolase of R. toruloides in two-phase hollow-fiber reactor system. Dodecane with high concentration of the racemic substrate passed through the lumen side and cell suspension was recirculated through the shell side of the hollow fiber reactor For the removal of phenyl-1, 2-ethandiol to reduce the product inhibition to biocatalysts, another hollow-fiber reactor was employed to extract the diol. Racemic phenyl oxirane up to 300 mM was enantioselectively resolved with high enantiopurity (>99% ee) in hollow-fiber reactor system.

• Journal of the Korean Chemical Society
• /
• v.24 no.5
• /
• pp.347-355
• /
• 1980

The rate constants for the reaction of ${\alpha}$-naphthalene carbonyl chloride and ${\beta}$-naphthalene carbonyl chloride have been determined in methanol-acetonitrile and methanol-acetone. The rate constant of ${\alpha}$-naphtalene carbonyl chloride is higher than that of ${\beta}$-naphthalene carbonyl chloride. This behavior is consistent with Dewar's number, Nr and also Streitwieser's value ${\sigma}^+$. Since in the transition state carbonyl carbon is transformed to$sp^3$, no peri-hydrogen effect was observed.

• Journal of the Korean Chemical Society
• /
• v.43 no.5
• /
• pp.505-510
• /
• 1999

$TiO_2$ powders were prepared via hydrolysis of titanium n-butoxide in n-butanol and hydrolysis mechanism of titanium n-butoxide was studied using UV-Vis spectrometer. Hydrolysis reactions were controlled to proceed to pseudo-first order reaction in the presence of excess water. The phases of $TiO_2$ powders, prepared under the these conditions, were identified by XRD and reaction rates were calculated by Gugggenheim method. Prepared powders were noncrystalline states in their initial stage of formation but transformed to crystalline rutile structure by heating. Reaction mechanism of titanium n-butoxide was proposed as Interchange-Associative(Ia) mechanism, based on the data of n-value and termodynamic parameters which were determined from the rate constants.