78109-13-4Relevant academic research and scientific papers
Mechanism of the Aminolysis of Alkyl Benzimidates
Gilbert, Hiram F.,Jencks, William P.
, p. 6769 - 6779 (1982)
The aminolysis of a series of ring- and alkyl-substituted benzimidates proceeds through a mechanism involving the formation and decomposition of a tetrahedral intermediate as evidenced by a change in rate-determining step with changing pH.On the alkaline side of the pH-rate profile, formation of the tetrahedral intermediate from the free amine and protonated benzimidate is rate determining.Structure reactivity correlations for this step show a late (intermediate-like) transition state with βnuc = 0.61, β0 = -0.47 (for O-substituted benzimidates), and ρ = 1.49.There is no evidence for a kinetically significant proton-transfer step.The addition of water to alkyl benzimidates follows β0 = -0.56.On the acidic side of the pH-rate profile for aminolysis, the breakdown of the intermediate with expulsion of alcohol is the rate-determining step, as evidenced by the observation of an exchange reaction of methoxyamine for ammonia.The neutral tetrahedral intermediate (T0) partitions between acid-catalyzed expulsion of alcohol, ammonia, and methoxyamine with partition ratios of approximately 1/1/300, respectively.The expulsion of alcohol also occurs by a spontaneous (water catalyzed) reaction characterized by β0 = -1.30 and ρ = -0.01, suggesting a late (product-like) transition state for this reaction.The expulsion of alcohol through a general-acid-catalyzed reaction is characterized by relatively low Broensted α values of 0.40-0.49.The decrease in α with decreasing pK of the leaving alcohol can be described by an interaction coefficient pxy' = 1/c5 = δα/δpK1g = 0.05.This reaction can be described on a structure-reactivity diagram by a diagonal reaction coordinate that represents concerted proton transfer and C-O bond cleavage in the transition state.The effect of structure on the direction of acid-catalyzed expulsion of alcohols and amines from addition compounds is reviewed briefly.
Mechanisms of acid-catalyzed Z/E isomerization of imines
Johnson, James E.,Morales, Nora M.,Gorczyca, Andrea M.,Dolliver, Debra D.,McAllister, Michael A.
, p. 7979 - 7985 (2007/10/03)
The kinetics and mechanism of acid-catalyzed Z/E isomerization of O-methylbenzohydroximoyl chloride (1Za and 1Ea), methyl O-methylbenzohydroximate (1Zb and 1Eb), ethyl O-methylbenzohydroximate (1Zc and 1Ec and five para and meta substituted derivatives),
Mechanisms of Alkoxide Substitution Reactions at the Carbon-Nitrogen Double Bond. Stereoelectronic Control during Nucleophilic Substitution
Johnson, James Elver,Nalley, Elizabeth Ann,Weidig, Charles,Arfan, Mohammed
, p. 3623 - 3629 (2007/10/02)
The stereochemistry and mechanisms of the alkoxide substitution reactions of O-methylbenzohydroximoyl chlorides (1 and 2) and alkyl O-methylbenzohydroximates (3 and 4) have been investigated.The reactions of the (Z)-hydroximoyl chlorides 1 with alkoxides in 10percent methanol-90percent Me2SO proceed with >= 95percent retention of configuration to give the (Z)-hydroximates 3.The alkoxide reactions of the (E)-hydroximoyl chlorides 2 are usually less stereospecific and give >= 77percent of the substitution product (4), corresponding to retention of configuration.The reactions of the hydroximoyl chlorides 1a and 2a with methoxide ion follow second-order kinetics and have approximately the same rate constants.The reaction of the hydroximoyl bromide 1h with methoxide is only 2.2 times faster than that of the chloride 1a.The methoxide substitution rates of five (Z)-hydroximoyl chlorides (1a, 1d-g) give a Hammett correlation with ? with a ρ value of 1.90.These observations are consistent with a mechanism in which a hydroximoyl chloride (1) undergoes rate-determining nucleophilic attack by methoxide to form a tetrahedral intermediate which rapidly loses chloride ion to give the hydroximate 3.The (Z)-hydroximate 3e undergoes a methoxide substitution reaction to give 4e but at a considerably slower rate than the (Z)-hydroximoyl chloride 1a (k(1a)/k(3e) = 53).The second-order rate constant for the reaction of the (Z)-hydroximate 3e with methoxide is about 300 times greater than the rate constant for the reaction of the (E)-hydroximate 4e with methoxide.The reaction of methoxide with the (E)-hydroximate 4e initially produces mainly the Z product 3a, but the product distribution changes with time, and eventually the E isomer 4a predominates.The change in product distribution during the course of this reaction is due to a methoxide-catalyzed isomerization of 3a to 4a.The stereochemistry and relative rates of the reactions of 1-4 with methoxide ion are interpreted in terms of Deslongchamp's theory of stereoelectronic control.It is suggested that stereoelectronically controlled loss of chloride ion from the tetrahedral intermediate 12 (from the reaction of 1a with methoxide ion) is faster than either loss of methoxide ion to give starting material or stereomutation.In the tetrahedral intermediate 13 (from 2a), stereomutation to 12 and 14 and stereoelectronically controlled loss of chloride ion from 12 and 14 are faster processes than loss of methoxide ion from 13.The tetrahedral intermediate 15 (from 3e) undergoes stereoelectronically controlled loss of methoxide or ethoxide ion faster than it undergoes stereomutation.In the case of the intermediate 17 (from 4e), stereoelectronically controlled loss of methoxide ion to give starting material is faster than stereomutation.
