Kinetics and mechanism for pyridine N-oxide carboxaldehyde phenylhydrazone formation

Kinetics and Mechanism for Oxime Formation from 4-Pyridinecarboxaldehyde N-Oxide

“…do Amaral et al 6 investigated the kinetics and mechanism of phenylhydrazone formation from 4-pyridinecarboxaldehyde N-oxide; 6 in this study two breaks in the rate-pH profile under acidic and neutral conditions were found. The authors interpreted these results as follows: the first break at pH 5-6, as a change in the rate-determining step from carbinolamine dehydration to stepwise carbinolamine formation, whereas the second break at pH 1-2, as a change in the mechanism of carbinolamine formation from stepwise to concerted.…”

“…18 Under conditions of ratedetermining carbinolamine dehydration, the product of the equilibrium constant for carbinolamine formation and the rate constant for carbinolamine dehydration, K add k H + , measures the order of reactivity of hydroxylamine versus phenylhydrazine K add k H + = 10.34 x 10 5 M -2 s -1 (Phenylhydrazone formation). 6 K add k H + = 7.59 x10 5 M -2 s -1 (this work)…”

“…The kinetics and mechanism for oxime formation from 4-pyridinecarboxaldehyde N-oxide, was undertaken to get a true understanding of the mechanism and catalysis for imine formation from this substrate; this aldehyde is very activated for addition of nucleophiles given its high degree of hydration. 5 Up to now, there has been only one report 6 explaining the reaction mechanism with a similar nucleophile, however, it does not demonstrate clearly the slow rate-determining-step of the process in the different pH-regions studied. Therefore, in our opinion, it is necessary for the kinetics community to establish the detailed mechanism of imine formation from this substrate.…”

Construction of double dynamic covalent bond crosslinked hydrogel based on water-soluble block polymers

“…目前通过对材料在分子层面的设计, . 酰腙键在 pH>2时即可形成, 但在不同的pH条件下其形成机理 不同, 如酸性条件下, 酸催化作用使酰腙键表现出较 高的动态性 [22] , 而在中性和弱碱性条件下, 酰腙键发 生动态"锁定" [23~25] . Patrickios等 [26] 在研究酰腙键交联 的基于改性四聚乙二醇的凝胶时指出, 在2.0~12.5的…”