Kinetics and quantification of the electrophilic reactivities of substituted thiophenes and structure‐reactivity relationships

Abstract

Second-order rate constants (k 1 ) have been measured spectrophotometrically for reactions of 2-methoxy-3-X-5-nitrothiophene 1a-c (X = NO 2 , CN, and COCH 3 ) with secondary cyclic amines (pyrrolidine 2a, piperidine 2b, and morpholine 2c) in CH 3 CN and 91:9 (v/v) CH 3 OH/CH 3 CN at 20 • C. The experimental data show that the rate constants (k 1 ) values exhibit good correlation with the parameters of nucphilicity (N) of the amines 2a-c and are consistent with the Mayr's relationship log k (20 • C) = s(E + N). We have shown that the electrophilicity parameters E derived for 1a-c and those reported previously for the thiophenes 1d-g (X = SO 2 CH 3 , CO 2 CH 3 , CONH 2 , and H) are linearly related to the pK a values for their gem-dimethoxy complexes in methanol. Using this correlation, we successfully evaluated the electrophilicity E values of 12 structurally diverse electrophiles in methanol for the first time. In addition, a satisfactory linear correlation (r 2 = 0.9726) between the experimental (log k exp ) and the calculated (log k calcd ) values for the -complexation reactions of these 12 electrophiles with methoxide ion in methanol has been observed and discussed. K E Y W O R D S electrophilicity parameters, kinetics, Mayr relationship, substituted thiophenes 2 EXPERIMENTAL MaterialsThe thiophenes 1 was prepared, as previously described. 7,8 All the amines 2 (morpholine, piperidine and pyrrolidine) were commercial products (Merck, Darmstadt-Germany) and were redistilled before use whenever necessary.Acetonitrile and methanol HPLC grade >99.9% (Merck, Darmstadt-Germany) were available of the highest quality and used without further purification.All spectrophotometric measurements were carried out using a spectrophotometer (UV-1650 Shimadzu, Japan) equipped with a Peltier temperature controller (model TCC-240 A), which is able to keep to temperature within 0.1 K. 582

Electrophilic reactivities of 7‐L‐4‐nitrobenzofurazans in σ‐complexation processes: Kinetic studies and structure–reactivity relationships

“…It is interesting to note that the slopes close to unity (1.02 and 1.08) obtained in this work indicates that equation (1) is applicable to these reactions 7‐10,15‐19 . According to equations (3) and (4), the electrophilicity parameter E values of −8.46 and −9.52 are thus obtained for benzofurazans 1 and 2 , respectively.…”

SNAr reactions of substituted pyridines with secondary amines in aqueous solution: Kinetic and reactivity indices in density functional theory

“…When the relation k −1 ≪ k 2 + k 3 [NuH] 0 is satisfied, Equation is rewritten as Equation , suggesting that the formation of the intermediate zwitterion ZH is the rate‐limiting step of the uncatalyzed reaction: …”

Electrophilicities of 4‐Nitrobenzochalcogenadiazoles

“…In all cases, the agreement between calculated and experimental rate constants is remarkably good because Eq. (1) usually predicts rate constants of polar organic reactions within a factor of 10–100 . Follet and co‐workers have shown that Eq.…”

“…(1) usually predicts rate constants of polar organic reactions within a factor of 10-100. [16,21,35,[44][45][46][47][48][49][50][51][52][53][54] Follet and co-workers [46] have shown that Eq. (1) predicts the rate constants for reactions of indol-3-ylmethylium ions with various phosphines and pyridines in dichloromethane solutions at 20°C within a factor of 0.33-87.2.…”