Aminolyses of aryl diphenylphosphinates and diphenylphosphinothioates: effect of modification of electrophilic center from P=O to P=S.
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.
Um
Ik-Hwan
IH
Division of Nano Sciences and Department of Chemistry, Ewha Womans University, Seoul 120-750, Korea. ihum@ewha.ac.kr
Akhtar
Kalsoom
K
Shin
Young-Hee
YH
Han
Jeong-Yoon
JY
D000588:Amines / Q000737:chemistry*; D004583:Electrons; D007700:Kinetics; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry*; D010721:Phosphinic Acids / Q000737:chemistry*; D010758:Phosphorus / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry*
D000588:Amines; D010721:Phosphinic Acids; D013438:Sulfhydryl Compounds; D010758:Phosphorus; D013455:Sulfur; D010100:Oxygen