α-Bromobenzaldehyde-p-nitrophenylhydrazone의 알카리 가수분해 반응 메카니즘 = Kinetics and Mechanism of Alkaline Hydrolysis of α-Bromobenzaldehyde-p-nitrophenylhydrazone

다국어 초록 (Multilingual Abstract)

The rate constants for the hydrolysis of the derivatives of α-bromobenzaldehyde-p-nitro-phenylhydrazone (p-H, p-OCH_3, p-Cl, p-NO_2) at various pH have been determined by UV spectrophotometry in 50% dioxane at 25℃ and the following rate equations which can be applied over wide pH range were obtained. i. e.
α-bromobenzaldehyde-p-nitrophenylhydrazone;
kobs.=1.25×10 exp (-7) + 7.92×10 exp (-11)/〔H^+〕+1.51×10 exp (-7)
α-bromo-p-chlorobenzaldehyde-p-nitrophenylhydrazone;
kobs.=1.06×10 exp (-7) + 1.08×10 exp (-10)/〔H^+〕+1.45×10 exp (-7)
α-bromo-p-methoxybenzaldehyde-p-nitrophenylhydrazone;
kobs.=1.79×10 exp (-7) + 1.40×10 exp (-10)/〔H^+〕+4.08×10 exp (-7)
α-bromo-p-nitrobenzaldehyde-p-nitrophenylhydrazone;
kobs.=7.10×10 exp (-8) + 2.89×10 exp (-10)/〔H^+〕+2.37×10 exp (-7)
Below pH 2, the rate of hydrolysis of α-bromobenzaldehyde-p-nitrophenylhydrazone is accelerated by electron-donating group (ρ=-0.91). Above pH 5, however, this reaction is slowded down by electron-attracting group (ρ=0.37).
From the rate equation and the effect of solvent and substituent upon the rate of reaction, below pH 2, the hydrolysis proceed through SN_1 mechanism. Above pH 5, the hydrolysis proceed through 1.3-dipolar ion mechanism.
And in the range of pH 2∼5 these two reactions occur competitively.