일치환 Bezaldehyde의 Semicarbazone 생성 반응에 관한 연구

• 영문명: Studies on the Semicarbazone Formation of Mono substituted Benzaldehydes
• 발행기관: 한국응용과학기술학회 (구.한국유화학회)
• 저자명: Kim Yong In(金容仁) Kim Chang Mean(金昌勉)
• 간행물 정보: 『한국응용과학기술학회지』한국유화학회지 제7권 제1호, 93~105쪽, 전체 13쪽
• 주제분류: 공학 > 화학공학
• 파일형태: PDF
• 발행일자: 1990.05.30

영문 초록

Semicarbazone formation of nine monosubstituted benzaldehydes was studied kinetically in 20% methanol buffer solution at 15, 25, 35, and 45℃. The rate of p-nitrobenzaldehyde semicarbazone formation is 2.7 times as fast as that of benzaldehyde, while p-hvdroxybenzaldehyde is 3.6 times as slow as that of benzaldehyde. Activation energies for p-chlorobenzaldehyde, benzaldehyde, p-methylbenzaldehyde, p-methoxybenzaldshyde, p-hydroxybenzaldehyde, and p-dimethylaminobenzaldehyde semicarbazone formation are calculated as 5.80, 6.19, 6.57, 7.06, 8.03, and 6.46 kcal/mol respectively. It is concluded from the effect of ionic strength that the reaction is affected by not ions but neutral molecules involving hydrogen bonding between oxygen atom of carbonyl group and hydrogen atom of acid-catalyst, and concerted attack of the necleophilic reagent, free base on carbonyl compound. Also, the effect of solvent composition is small in 20% and 50% methanol (and ethanol) aqueous solutions. The ρ-σ plots for the rates of semicarbazone formation at pH 7.1 show a linear ρ-σ relationship (ρ=0.14), in contrast to that at pH 2.75 and pH 5.4 corresponding to ρ-σ correlations reparted by Jencks. The rate of semicarbazone formation at pH 5.4 show a relationship which is convex upward, resulting in a break in the curve but at pH 2.75, slight difference from a linear relationship. As a result of studying citric acid catalysis, second-order rate constants increase linearly with citric acid concentration and show a 2 times increase as the catalyst concentration is varied from 0.025 to 0.1 mol/1 at pH 2,9, but slight increase at pH 5.3. The rate-determining step is addition below pH 5 but is dehydration between pH 5 and 7. Conclusively, the rate-determining step of the reaction changes from dehydration to addition in respect to hydrogen ion activity near pH 5. The ortho: para rate ratio of the hydroxybenzaldehydes for semicarbazone formation is about 17 at 15℃. It is concluded that the results constitute strong evidence in favor of greater stabilization of p- than o-hydroxybenzaldehyde by substituent which donate electrons by resonance and is due to hydrogen bonding between the carbon-bound hydrogen of the-CHO group and the oxygen atom of the substituent.

목차

ABSTRACT

I. 서론

II. 실험

III. 실험결과 및 고찰

IV. 결론

문헌