Aminolyses of Aryl Diphenylphosphinates and Diphenylphosphinothioates:  Effect of Modification of Electrophilic Center from PO to PS

Abstract

A kinetic study is reported for aminolysis of aryl diphenylphosphinothioates (2a-i). The phosphinothioates 2a-i are less reactive than aryl diphenylphosphinates (1a-i), the oxygen analogues of 2a-i, regardless of the basicity of the leaving aryloxides or the attacking amines. The Yukawa-Tsuno plot for the reactions of 2b-i with piperidine exhibits good linearity with a small r value (r=0.28), indicating that the leaving group departs at the rate-determining step with a small degree of bond fission. Reactions of 2,4-dinitrophenyl diphenylphosphinothioate (2a) with alicyclic secondary amines result in a good linear Brønsted-type plot with betanuc=0.52, implying that the reactions proceed through a concerted mechanism. The betanuc value determined for the reactions of 2a is slightly larger than that reported for the corresponding reactions of 2,4-dinitrophenyl diphenylphosphinate (1a, i.e., betanuc=0.38), suggesting that reactions of 2a proceed through a tighter transition state (TS) than that of 1a. The reaction of 2a with piperidine exhibits a ca. 0.4 kcal/mol more favorable enthalpy of activation (DeltaH) than that of 1a. On the contrary, the entropy of activation at 25.0 degrees C (TDeltaS) is ca. 1.5 kcal/mol more unfavorable for the reaction of 2a than for that of 1a. This result supports the proposal that the reaction of 2a proceeds through a tighter TS than that of 1a and explains why 2a-i are less reactive than 1a-i.

Alkali Metal Ion Catalysis and Inhibition in Nucleophilic Substitution Reactions of 3,4-Dinitrophenyl Diphenylphosphinothioate with Alkali Metal Ethoxides in Anhydrous Ethanol: Effect of Changing Electrophilic Center from P=O to P=S

“…Compound 9 was readily prepared as described previously from the reaction of diphenylphosphinodithioic acid with 3,4-dinitrophenol in the presence of 4-(dimethylamino)-pyridine and N,N-dicyclohexylcarbodiimide in methylene chloride. 17 The crude compound 9 was purified by column chromatography. The stock solutions of EtOM were prepared by dissolving the respective alkali metal in anhydrous ethanol under N 2 and stored in the refrigerator.…”

Kinetic Study on Aminolysis of Y-Substituted-Phenyl X-Substituted-Benzoates: Effects of Substituents X and Y on Reactivity and Reaction Mechanism

“…[1][2][3][4][5][6][7][8][9][10][11] Many factors have been suggested to affect reactivity and reaction mechanism (e.g., the nature of electrophilic center, reaction medium, substituents, amine basicity, etc.). [2][3][4][5][6][7][8][9][10][11] Aminolysis of P=O and P=S centered esters (e.g., 4-nitrophenyl diphenylphosphinate and diphenylphosphinothioate) has been reported to proceed through a concerted mechanism on the basis of a linear Brønsted-type plot with  nuc = 0.5 ± 0.1. 6,7 In contrast, aminolysis of C=O centered esters has generally been reported to proceed through a stepwise mechanism, in which the rate-determining step (RDS) is dependent on the basicity of the incoming amine and the leaving-group.…”

“…[2][3][4][5][6][7][8][9][10][11] Aminolysis of P=O and P=S centered esters (e.g., 4-nitrophenyl diphenylphosphinate and diphenylphosphinothioate) has been reported to proceed through a concerted mechanism on the basis of a linear Brønsted-type plot with  nuc = 0.5 ± 0.1. 6,7 In contrast, aminolysis of C=O centered esters has generally been reported to proceed through a stepwise mechanism, in which the rate-determining step (RDS) is dependent on the basicity of the incoming amine and the leaving-group. [2][3][4][5][6][7][8][9][10][11] It is now firmly understood that RDS changes from breakdown of a zwitterionic tetrahedral intermediate (T ± ) to its formation as the incoming amine becomes more basic than the leaving group (or the leaving group is less basic than the amine) by 4-5 pK a units.…”

“…6,7 In contrast, aminolysis of C=O centered esters has generally been reported to proceed through a stepwise mechanism, in which the rate-determining step (RDS) is dependent on the basicity of the incoming amine and the leaving-group. [2][3][4][5][6][7][8][9][10][11] It is now firmly understood that RDS changes from breakdown of a zwitterionic tetrahedral intermediate (T ± ) to its formation as the incoming amine becomes more basic than the leaving group (or the leaving group is less basic than the amine) by 4-5 pK a units.…”

Reactions of 4-Nitrophenyl 2-Thiophenecarboxylates with R2NH/R2NH2+in 20 mol % DMSO (aq). Effects of 5-Thienyl Substituent and Base Strength

“…[7][8][9] The aminolysis can also proceed via a zwitterionic tetrahedral intermediate. [14][15][16][17] In contrast, much less is known about the corresponding acyl transfer reactions involving heterocyclic aromatic compounds.…”