• Bulletin of the Korean Chemical Society
• /
• 제30권4호
• /
• pp.797-802
• /
• 2009

Potential of acetates and related compounds in glacial acetic acid as a catalyst for aldol-type condensation reactions was examined. Reactions of cycloalkanones or selected heteroaromatics with aldehydes in presence of 10 mol% of various acetates in acetic acid afforded ${\alpha},{\alpha}$'-bis(substituted-benzylidene)cycloalkanones and substituted-benzylidene-mackinazolinones, respectively, in good yields. Among the compounds tested, ammonium acetate is the best and effective especially towards the reactions of mackinazolinone and aliphatic aldehydes to afford 6-alkylidenemackinazolinones.

• Bulletin of the Korean Chemical Society
• /
• 제27권1호
• /
• pp.106-110
• /
• 2006

Photocatalytic electron transfer reactions of aryl benzyl sulfides using 2,4,6 triphenylpyrilium tetrafluoroborate ($TP^+BF_4^-$) resulted in the oxidation of these sulfides to the corresponding sulfoxides and also in most cases in the C-S bond cleavage of them along with formation of aromatic aldehydes. In these reactions, the formation of sulfide radical cation has been proposed, which undergoes either oxidation to the corresponding sulfoxide or C-S bond cleavage to the formation of aromatic aldehydes. The further oxidation of sulfoxides to sulfones has not been observed. The influence of substrate structures on the reaction pathways as well as the role of $O_2$ in this respect is discussed.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2013년도 추계 학술논문 발표대회
• /
• pp.154-155
• /
• 2013

The aim of this work is to have a better knowledge of reactions that take place in a cement paste, blast furnace slag mixed cement paste and fly ash mixed cement paste and know about the change in chemical components exposed to elevated temperature. The results show that the dehydration reactions appeared differently in the each admixture mixed cement paste and can be used as tracers for determining the temperature history of concrete after a fire exposure.

• Bulletin of the Korean Chemical Society
• /
• 제12권1호
• /
• pp.101-103
• /
• 1991

The kinetic isotope effects (KIE) are determined for the reactions of benzyl benzenesulfonates (BBS), ethyl benzenesulfonates (EBS) and phenacyl benzensulfonates (PAB) with deuterated benzylamine nucleophiles. The inverse secondary ${\alpha}$-deuterium KIE observed were somewhat smaller than those for the corresponding reactions with aniline nucleophiles. The primary $KIE_s$ obtained with PAB were slightly greater than those for the corresponding reactions with anilines, which suggested that the inverse secondary KIE is decreased due to a relatively earlier transition state for bond-making with little change in the hydrogen bonding strength to the carbonyl oxygen.

• Bulletin of the Korean Chemical Society
• /
• 제22권7호
• /
• pp.739-742
• /
• 2001

Reactions of [Cp*Ir(η3-CH2CHCHPh)(NCMe)]OTf (1) with HC≡CR (R = H, CH2OH) in the presence of bases, B (B=NEt3, PPh3, AsPh3) produce stable Cp*Ir-η3-allyl-alkenyl compounds [Cp*Ir(η3-CH2CHCHPh)(-CH=CH-+B)]OTf (2) and [Cp*Ir(η3-CH2CHCHPh)(-C(CH2OH)=CH- +PPh3)]OTf (3), respectively in high yields. Cp*Ir-η3-allyl-alkynyl compounds Cp*Ir(η3-CH2CHCHPh(-C≡C-R') (4) and Cp*(η3-CH2CHCHPh)Ir-C≡C-p-C6H4-C≡C-Ir(η3-CH2CHCHPh)Cp* (5) have been prepared from reactions of 1 with HC≡CR'(R' = C6H5, p-C6H4CH3, C3H5, C6H9) and HC≡C-p-C6H4-C≡CH in the presence of NEt3.

• Bulletin of the Korean Chemical Society
• /
• 제18권7호
• /
• pp.749-754
• /
• 1997

Rate constants have been measured spectrophotometrically for the reactions of alkali metal ethoxides (EtOM) with S-p-nitrophenyl 2-thiofuroate (1b) and 2-thiophenethiocarboxylate (2b) in absolute ethanol at 25.0±0.1 ℃. 1b is observed to be more reactive than 2b toward all the EtOM studied. The reactivity of EtOM is in the order EtOK > EtONa > EtO- > EtOLi for both substrates, indicating that K+ and Na+ behave as a catalyst while Li+ acts as an inhibitor in the present system. Equilibrium association constants of alkali metal ions with the transition state (KaTS) have been calculated from the known equilibrium association constants of alkali metal ion with ethoxide ion (Ka) and the rate constants for the reactions of EtOM with 1b and 2b. The catalytic effect (KaTS/Ka) is larger for the reaction of 1b than 2b, and decreases with decreasing the size of the alkali metal ions. Formation of 5-membered chelation at the transition state appears to be responsible for the catalytic effect.

• Bulletin of the Korean Chemical Society
• /
• 제16권9호
• /
• pp.827-831
• /
• 1995

Kinetic studies on the reactions of five secondary acylic alkyl arenesulfonates with anilines are carried out in acetonitrile at 65.0 ℃. The magnitude of ρXZ determined (ρXZ=0.12-0.13) is slightly greater than that for the alicyclic series (ρXZ=0.11) under the same experimental condition. Ab initio MO results are found to support the slightly tighter transition state expected from the greater magnitude of ρXZ for the acyclic series. Despite the small variations, the magnitude of ρXZ and the theoretical transition state tightness remain relatively constant for the secondary carbon centers. Secondary kinetic isotope effects involving deuterated aniline nucleophiles show a successively smaller kH/kD(<1.0) value for a more sterically crowded reaction center carbon. This is in accord with the later transition state for bond-making predicted by the Bell-Evans-Polanyi principle for the more endothermic nucleophilic substitution reaction. Further support is provided by the results of the AM1 MO calculations on the reactions of secondary alkyl benzenesulfonates with chloride nucleophile.

• Bulletin of the Korean Chemical Society
• /
• 제17권9호
• /
• pp.849-853
• /
• 1996

Hetero Dieis-Alder reactions containing phosphorus atom at various positions of diene and dienophile as well as standard Dieis-Alder reaction between ethylene and cis-l,3-butadiene have been studied using ab initio method. Activation energy showed a good linear relationship with the FMO energy gap between diene and dienophile, which can be normally used to explain Dieis-Alder reactivity. Since π-bond cleavage and σ-bonds formation occur concertedly at the TS, geometrical distortion of diene and dienophile from the reactant to the transition state is the source of barrier. Based on the linear correlations between activation barrier and deformation energy, and between deformation energy and π-bond order change, it was concluded that the activation barrier arises mainly from the breakage of π-bonds in diene and dienophile. Stabilization due to favorable orbital interaction is relatively small. The geometrical distortions raise MO levels of the TS, which is the origin of the activation energy. The lower barrier for the reactions of phosphorus containing dienophile (reactions C, D, and E) can be explained by the electronegativity effect of the phosphorus atom.

• Bulletin of the Korean Chemical Society
• /
• 제15권11호
• /
• pp.985-990
• /
• 1994

Cross-interaction constants, ${\rho}^e_{XY}$, ${\rho}_{YZ}$ and ${\rho}_{XZ}$ are defined using observed rate constant, k_N=(k_1/k_{-1})k_2=Kk_2$, for the stepwise carbonyl addition reactions involving the rate-limiting breakdown of a tetrahedral intermediate $(T^{\pm})$. Abundant experimental evidence in the literature enables us to determine signs for the three constants for such mechanism, ${\rho}^e_{XY}$>0, ${\rho}_{YZ}$<0 and ${\rho}_{XZ}$0. These are in contrast to those for the concerted $S_N2$ mechanism, ${\rho}_{XY}$<0, ${\rho}_{YZ}$>0 and ${\rho}_{XZ}$, and provide useful mechanistic criteria. In the light of these criteria, mechanisms of some nucleophilic reactions of carbonyl compounds are re-examined.

• Bulletin of the Korean Chemical Society
• /
• 제22권4호
• /
• pp.383-387
• /
• 2001

The kinetics and mechanism of the reactions of thiophenyl dimethylacetates (TDA) and trimethylacetates (TTA) with benzylamines in acetonitrile are studied. The reactions are first order in both the amine and the substrate. Relatively large values of ${\beta}X(\betanuc$ = 1.1-1.5; TDA and 1.1-1.5; TTA) and ${\beta}Z({\beta}lg$ = -1.8~-2.0; DTA and -1.3~-1.6; TTA) for benzylamines, significantly large kH/kD values (=1.2-1.5; DTA and 1.2-1.5; TTA) involving deuterated benzylamines, and large ${\rho}XZ$ (=0.82; TDA and 1.05; TTA) values are interpreted to indicate stepwise acyl transfer mechanism, but with the hydrogen bonded four center type transition state for benzylamine. The relatively greater magnitudes of ${\rho}XZ$ and the secondary kinetic isotope effects involving deuterated nucleophiles are in line with the proposed mechanism.