• 제목/요약/키워드: basicity

검색결과 196건 처리시간 0.028초

A Mechanistic Study on Addition Reactions of Alicyclic Amines to 3-Butyn-2-one

  • 음익환;이정숙;육성민
    • Bulletin of the Korean Chemical Society
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    • 제19권7호
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    • pp.776-779
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    • 1998
  • Second-order rate constants have been measured spectrophotometrically for the addition reaction of a series of alicyclic amines to 3-butyn-2-one to yield their respective enamines at 25.0 'C. The reactivity of the amines increases with increasing the basicity of the amines. However, the Bronsted-type plot obtained exhibits a downward curvature as the basicity of the amines increases, i.e. βnuc decreases from 0.3 for low basic amines (pKa < 9) and to 0.1 for highly basic amines (pKa > 9). Such a curvature in the Bronsted-type plot is clearly indicative of a change in the reaction mechanism or transition state structure. From the corresponding reactions run in D2O, the magnitude of kinetic isotope effect (KIE) has been calculated to be about 0.8 for highly basic amines and 1.21 for weakly basic amines. The difference in the magnitude of KIE also supports a change in the reaction mechanism or transition state structure upon changing the basicity of the amines. Furthermore, the small KIE clearly suggests that H+ transfer is not involved in the rate-determining step, i.e. the addition reaction is considered to proceed via a stepwise mechanism in which the attack of the amines to the acetylene is the rate-determining step. The curvature in the Bronsted-type plot has been attributed to a change in the degree of bond formation between the amine and the acetylene.

A Kinetic Study for the Reaction of 2,4-Dinitrophenyl Benzoate with Secondary Cyclic Amines

  • 엄익환;김명진;민지숙;권동숙
    • Bulletin of the Korean Chemical Society
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    • 제18권5호
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    • pp.523-527
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    • 1997
  • Apparent second-order rate constants (kapp) have been measured spectrophotometrically for the reaction of 2,4-dinitrophenyl benzoate (DNPB) with 6 secondary cyclic amines in H2O containing 20 mole% DMSO at 25.0±0.1 ℃. The Bronsted-type plot (log kapp vs. pKa) shows a break at pKa near 9.1, e.g. two straight lines with βapp values of 0.67 and 0.44 for the low basic (pKa < 9.1) and the highly basic (pKa > 9.1) amines, respectively. Using an estimated k2 value of 3×109 sec-1, all the other microconstants (k1, k-1 and K) involved in the present aminolysis have been calculated. The k value decreases with increasing the basicity of amines while k1 and K values increase with increasing the amine basicity, as expected. Good linear Bronsted-type plots have been obtained for these microconstants of the present aminolysis of DNPB. The magnitudes of the slope of the Bronsted-type plots, k1 and k-1 have been calculated to be 0.43 and - 0.24, respectively, indicating the k-1 step is about two folds less sensitive than the k1 step to the amine basicity. The K value has been calculated to be 0.66, which appears to be much smaller than the one for other aminolyses showing general base catalysis. The small K value has been attributed to the absence of general base catalysis in the present aminolysis of DNPB.

二中心 H${\u}$ckel 法의 應用 脂肪族 아민의 염기도 [Ⅰ] (Application of Two Centre HTEX>$\''{u}$ckel Method for Basicity of the Aliphatic Amines)

  • 박병각;이무상;홍영석
    • 대한화학회지
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    • 제15권3호
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    • pp.147-152
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    • 1971
  • On the baisis of the calculations by the two centre Huckel method for sigma electron system, the electronic structure of the various aliphatic amines including ammonia, and the relationship between the observed $pK_b$ and the change in the sigma electronic energy, ${\Delta}E{\sigma}$ in the course of protonation are discussed. A parallelism is observed between the $pK_b$ and the calculated ${\Delta}E{\sigma}$ of the amines. Also, it is observed that the electron densities of hydrogen atom directly bonded to nitrogen of the amines, likewise have a linear relationship with the $pK_b$. Therefore, the basicity of the aliphatic amines may be estimated qualitatively by means of the two center Huckel method.

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SLAG 박리성 평가 방법에 대한 고찰 (A study on the evaluation method for slag detachability)

  • 우유철;김희진
    • Journal of Welding and Joining
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    • 제5권1호
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    • pp.57-63
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    • 1987
  • A method which can be used for evaluating slag detachability is proposed in this study. The proposed method was intended to get an absolute value for slag detachability, to give consistent value for a given welded joint, and finally to be simple to test. With a test fig made in this study, an impact by dropping a steel ball (13Kg in weight) is applied on the back side of an as-welded plate having a slag layer on the weld bead. Such impact applied forces the slag to drop off from the bead surface. In order to make a quantitative evaluation the amount of slag removed was measured with increasing the number of drops. Using this method six kinds of fluxes were evaluated in terms of the effects of flux type, basicity and weding variables on the slag detachability. As an initial result of this test, it was found that welding heat input affects the detachability significantly. Most importantly the evaluation made using the presently proposed method gives the same order of ranking as that of the actual practice done by a welder.

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Acid and Base Properties of Chemical-Treated Natural Zeolite

  • Lee, Jae-Young;Shim, Mi-Ja;Kim, Sang-Woo
    • 한국재료학회지
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    • 제5권5호
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    • pp.620-624
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    • 1995
  • To study the acid and base properties of chemical-treated natural zeolite, FT-IR analysis was performed by the adsorption of pyridne and pyrrole and thermo-gravimetric analysis was done by the adsorption of NH$_{3}$. These solid catalysts have two acid sites, which are related to the Bronsted and Lewis acid sites, respectively. HIC-treatment led to the increased acidity and the maintained basicity.Acidity of NaHO-treatment samples also increased with thr NaOH-treatment but basicity decreased. The p-xylene selectivity on the chemical-treatment zelite was higher than that on the untreated zeolite.

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턴디쉬용 MgO Coating 재의 손상에 미치는 Flux의 영향 (Effect of Fluxes on the Wear of MgO Coating Materials for Tundish)

  • 홍기곤;박재원;김효준
    • 한국세라믹학회지
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    • 제34권7호
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    • pp.677-684
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    • 1997
  • The effects of fluxes on MgO coating materials for tundish were investigated. As the number of charge in continuous casting was increased, the basicity of tundish slag was decreased due to the increase of silica formed by dissolution from rice hull. As a result, the wear of magnesia lining was increased. In aggregates of MgO coating materials, magnesioferrite was formed by the reaction between magnesia and ferric oxide formed by the oxidation of molten steel, while matrix parts of MgO coating materials were worn by CaO-Al2O3-SiO2 compounds. Silica in rice hull extracted to the molten slag reduced basicity of slag and formed forsterite in the result of its reaction with magnesia lining. Also, fayalite was formed from the reaction between silica and ferric oxide and it caused the increment of magnesia lining's wear. The wear of magnesia lining by flux of CaO-SiO2 was larger than that of Cao-Al2O3 and calcia in the flux increased the wear of magnesia lining through the formation of rankinite.

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폐주물사를 첨가한 전로슬랙의 개질특성에 관한 연구 (A Study on the Properties of Converter Slag Modified by Addition of Waste Foundry Sand)

  • 김영환;김종학;고인용
    • 자원리싸이클링
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    • 제8권1호
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    • pp.44-51
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    • 1999
  • 전로슬랙에 폐주물사($SiO_2$원)와 탄소를 첨가하여 환원 . 용해함으로써얻은 개질슬랙의 기본적인 물성을 조사하였다. 염기도에 따라 철의 회수율이 크게 영향을 받음을 알 수 있었다. 염기도를 1.34로 조절하고 환원하여 철을 분리 회수한 후, 서냉하여 얻은 개질슬랙의 주요 물성치(비중, 흡수율, 경도 및 압축강도)들은 천연골재와 유사한 값을 보인다.

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The Effect of Solvation and Polarizability on the $\alpha$-Effect: Nucleophilic Substitution Reactions of p-Nitrophenyl Benzoate with Various Anionic Nucleophiles

  • 엄익환
    • Bulletin of the Korean Chemical Society
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    • 제13권6호
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    • pp.632-636
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    • 1992
  • Second-order rate constants have been determined spectrophotometrically for nucleophilic substitution reactions of p-nitrophenyl benzoate with various anionic nucleophiles including 6 ${\alpha}$ -effect nucleophiles. The logarithmic second-order rate constants for the aryloxides give a good Bronsted correlation with the respective basicity while the ones for p-chlorothiophenoxide and hydroxide exhibit significantly positive and negative deviations, respectivity, from the Bronsted linear line. The deviations are attributed to a solvation effect rather than a change in the reaction mechanism. The ${\alpha}$-effect nucleophiles except highly basic ones demonstrate significantly higher nucleophilicity (the ${\alpha}$ -effect) than would be predicted from the respective basicity. The effect of solvation and polarizability appears to be important for the ${\alpha}$-effect as well as for the reaction rate.

전이금속촉매를 사용한 DFP 분해 성능 연구 (Decomposition Studies of DFP Using Transition Metal Catalysts)

  • 계영식;정근홍;정우영
    • 공업화학
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    • 제21권1호
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    • pp.1-5
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    • 2010
  • Cu(II)와 diamine, aminothiol 그리고 dithiol과의 착물을 합성하여, 동일한 조건 하에서 DFP 분해반응성을 평가하였다. 실험결과 Lewis basicity가 높은 유기물질일수록 DFP의 분해반응을 촉진시키는 것으로 나타났다. N donor인 diamine에 비해 전자를 더 잘 제공하는 S donor를 가진 aminothiol과 결합된 Cu(II) 착물이 DFP의 가수분해 반응에 약 3배 정도 효과적인 것으로 분석되었다. Lewis basicity가 더 높은 dithiol 리간드를 사용한 경우 Cu(II)(1,2-ethane dithiol)$(NO_3)_2$의 난용성으로 인해 heterogeneous 조건하에서 반응속도를 측정하였음에도 homogeneous 조건하에서 측정한 Cu(II) (ethylenediamine)$(NO_3)_2$ 반응보다 약 1.6배 효과적이었다. DFP 분해에 대한 제올라이트의 반응성 평가에서 NaY의 경우 DFP 가수분해 반응을 촉진시키지 못하였으며, RuNaY는 DFP분해 반응이 Cu(II)-organic complex의 반응성에 비해서는 효과가 떨어지는 것으로 관찰되었다.