Aminolyses of 4-Nitrophenyl Phenyl Carbonate and Thionocarbonate:  Effect of Modification of Electrophilic Center from CO to CS on Reactivity and Mechanism

• Published in: Journal of organic chemistry Vol. 71; no. 6; pp. 2302 - 2306
• Main Authors: Um, Ik-Hwan, Kim, Eun Young, Park, Hye-Ran, Jeon, Sang-Eun
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 17.03.2006
• Subjects: Carbonates - chemical synthesis; Carbonates - chemistry; Chemistry; Exact sciences and technology; Kinetics and mechanisms; Molecular Structure; Nitro Compounds - chemical synthesis; Nitro Compounds - chemistry; Organic chemistry; Reactivity and mechanisms; Stereoisomerism; Sulfhydryl Compounds - chemistry; Nitro compound; Nucleophilic reaction; Organic carbonate; Stepwise mechanism; Chemical substitution; Thione; Brönsted function; Reaction mechanism; Kinetics; Rate constant; Chemical reactivity; Nucleophilic substitution; Primary amine
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo052417z

A kinetic study is reported for nucleophilic substitution reactions of 4-nitrophenyl phenyl carbonate (5) and 4-nitrophenyl phenyl thionocarbonate (6) with a series of primary amines. The thiono compound 6 is less reactive than its oxygen analogue 5 toward strongly basic amines but is more reactive toward weakly basic CF3CH2NH2. The Brønsted-type plots obtained from the aminolyses of 5 and 6 are curved downwardly. The reactions are proposed to proceed through a stepwise mechanism with a change in the RDS on the basis of the curved Brønsted-type plots. The microscopic rate constants (k 1 and k 2/k - 1 ratio) associated with the current aminolyses are consistent with the proposed reaction mechanism. The replacement of the CO bond in 5 by a polarizable CS group results in a decrease in the k 1 value but an increase in the k 2/k - 1 ratio. Besides, such a modification of the electrophilic center causes a decrease in pK a°, defined as the pK a at the curvature center of curved Brønsted-type plots, but does not alter the reaction mechanism. The larger k 2/k - 1 ratio for the reactions of 6 compared to those of 5 is proposed to be responsible for the decreased pK a° value.