Kinetics and mechanism of the alkaline hydrolysis of securinine.
The hydroxide ion-catalyzed hydrolysis of securinine involves the ring opening of the lactone moiety. The rate of hydrolysis is insensitive to the ionic strength. The observed pseudo-first-order rate constants reveal a decrease of approximately 4-fold due to the increase in the MeCN content from 4 to 50% (v/v) in mixed aqueous solvent. The temperature dependence of the rate of hydrolysis follows the Eyring equation, which yields delta H* and delta S* as 11.0 kcal mol-1 and -34.5 cal deg-1 mol-1, respectively. The hydroxyl carboxylate product of the alkaline hydrolysis of securinine is shown to undergo cyclization in acidic medium to yield securinine. The observed pseudo-first-order rate constants for cyclization increase linearly with an increase in [H+]. The change in the content of MeCN from 3.8 to 47.2% (v/v) in mixed aqueous solvents does not show an effect on the rate of the cyclization reaction. The most plausible mechanisms for alkaline hydrolysis and acid cyclization reactions are also discussed.
Lajis
N H
NH
Department of Chemistry, Universiti Pertanian Malaysia, Selangor Darul Ehsan.
Noor
H M
HM
Khan
M N
MN
D000470:Alkaloids / Q000737:chemistry*; D001381:Azepines; D000697:Central Nervous System Stimulants / Q000737:chemistry*; D003500:Cyclization; D006207:Half-Life; D006576:Heterocyclic Compounds, 4 or More Rings; D006572:Heterocyclic Compounds, Bridged-Ring; D006868:Hydrolysis; D007700:Kinetics; D007783:Lactones; D010880:Piperidines; D012972:Sodium Hydroxide; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature
D000470:Alkaloids; D001381:Azepines; D000697:Central Nervous System Stimulants; D006576:Heterocyclic Compounds, 4 or More Rings; D006572:Heterocyclic Compounds, Bridged-Ring; D007783:Lactones; D010880:Piperidines; D012972:Sodium Hydroxide; C000785:securinine