Kinetics and Mechanism of the Pyridinolysis of Dimethyl Isothiocyanophosphate in Acetonitrile

어디까리,이해황 대한화학회 2012 Bulletin of the Korean Chemical Society Vol.33 No.7

The kinetics and mechanism of the pyridinolysis (XC5H4N) of dimethyl isothiocyanophosphate are investigated in acetonitrile at 55.0 oC. The Hammett and Brönsted plots for substituent X variations in the nucleophiles exhibit two discrete slopes with a break region between X = 3-Ac and 4-Ac. These are interpreted to indicate a mechanistic change at the break region from a concerted to a stepwise mechanism with a rate-limiting expulsion of the isothiocyanate leaving group from the intermediate. The relatively large βX values imply much greater fraction of frontside nucleophilic attack TSf than that of backside attack TSb. The steric effects of the two ligands play an important role to determine the pyridinolysis rates of isothiocyanophosphates.

Significant Substituent Effects on Pyridinolysis of Aryl Ethyl Chlorophosphates in Acetonitrile

어디까리,이해황 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.5

The substituent effects on the pyridinolysis (XC5H4N) of Y-aryl ethyl chlorophosphates are investigated in acetonitrile at 35.0 oC. The two strong π-acceptor substituents, X = 4-Ac and 4-CN in the X-pyridines, exhibit large positive deviations from the Hammett plots but little positive deviations from the Brönsted plots. The substituent Y effects on the rates are really significant and the Hammett plots for substituent Y variations in the substrates invariably change from biphasic concave downwards via isokinetic at X = H to biphasic concave upwards with a break point at Y = 3-Me as the pyridine becomes less basic. These are interpreted to indicate a mechanistic change at the break point from a stepwise mechanism with a rate-limiting bond formation (ρXY = –6.26) for Y = (4-MeO, 4-Me, 3-Me) to with a rate-limiting leaving group expulsion from the intermediate (ρXY = +5.47) for Y = (4-Me, H, 3-MeO). The exceptionally large magnitudes of ρXY values imply frontside nucleophilic attack transition state.

Kinetics and Mechanism of the Benzylaminolysis of O,O-Diphenyl S-Aryl Phosphorothioates in Dimethyl Sulfoxide

어디까리,이해황 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.5

Kinetic studies of the reactions of O,O-diphenyl Z-S-aryl phosphorothioates with X-benzylamines have been carried out in dimethyl sulfoxide at 55.0 °C. The Hammett (log k_2 vs σX) and Brönsted [log k_2 vs pK_a(X)] plots for substituent X variations in the nucleophiles are biphasic concave downwards with a maximum point at X =H, and the unusual positive ρX and negative βX values are obtained for the strongly basic benzylamines. The sign of the cross-interaction constant (ρXZ) is negative for both the strongly and weakly basic nucleophiles. Greater magnitude of ρXZ value is observed with the weakly basic nucleophiles (ρXZ = −2.35) compared to with the strongly basic nucleophiles (ρXZ = −0.03). The deuterium kinetic isotope effects (k_H/k_D) involving deuterated benzylamines [XC_6H_4CH_2ND_2] are primary normal (k_H/k_D > 1). The proposed mechanism is a concerted SN2involving a frontside nucleophilic attack with a hydrogen bonded, four-center-type transition state for both the strongly and weakly basic nucleophiles. The unusual positive ρX and negative βX values with the strongly basic benzylamines are rationalized by through-space interaction between the π-clouds of the electron-rich phenyl ring of benzylamine and the phenyl ring of the leaving group thiophenoxide

Nucleophilic Substitution Reactions of N-Methyl α-Bromoacetanilides with Benzylamines in Dimethyl Sulfoxide

어디까리,이해황 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.3

Kinetic studies of the reactions of N-methyl-Y-α-bromoacetanilides with substituted X-benzylamines have been carried out in dimethyl sulfoxide at 25.0 ^oC. The Hammett plots for substituent X variations in the nucleophiles (log k_N vs σ_X) are slightly biphasic concave upwards/downwards, while the Brönsted plots (log k_N vs pK_a) are biphasic concave downwards with breakpoints at X = H. The Hammett plots for substituent Y variations in the substrates (log k_N vs σ_Y) are biphasic concave upwards/downwards with breakpoints at Y = H. The cross-interaction constant ρ_(XY) values are all negative: ρ_(XY) = −0.32 for X = Y = electron-donating; −0.22for X = electron-withdrawing and Y = electron-donating; −1.80 for X = electron-donating and Y = electronwithdrawing;−1.43 for X = Y = electron-withdrawing substituents. Deuterated kinetic isotope effects are primary normal (k_H/k_D > 1) for Y = electron-donating, while secondary inverse (k_H/k_D < 1) for Y = electronwithdrawing substituent. The proposed mechanisms of the benzylaminolyses of N-methyl-Y-α-bromoacetanilides are a concerted mechanism with a five membered ring TS involving hydrogen bonding between hydrogen (deuterium) atom in N-H(D) and oxygen atom in C = O for Y = electron-donating, while a concerted mechanism with an enolate-like TS in which the nucleophile attacks the α-carbon for Y = electronwithdrawing substituents.

Kinetics and Mechanism of the Benzylaminolysis of O,O-Diethyl S-Aryl Phosphorothioates in Dimethyl Sulfoxide

어디까리,이해황 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.10

The reactions of O,O-diethyl Z-S-aryl phosphorothioates with X-benzylamines are kinetically investigated in dimethyl sulfoxide at 85.0 °C. The Hammett (log k_2 vs σX) and Brönsted [log k_2 vs pK_a(X)] plots are biphasic concave downwards for substituent X variations in the nucleophiles with a break point at X = H. The signs of the cross-interaction constants (ρXZ) are positive for both the strongly and weakly basic nucleophiles. Considerably great magnitude of ρXZ (= 6.56) value is observed with the weakly basic nucleophiles, while ρXZ = 0.91 with the strongly basic nucleophiles. Proposed reaction mechanism is a stepwise process with a ratelimiting leaving group expulsion from the intermediate involving a backside nucleophilic attack with the strongly basic nucleophiles and a frontside attack with the weakly basic nucleophiles. The kinetic results are compared with those of the benzylaminolysis of O,O-diphenyl Z-S-aryl phosphorothioates.

Kinetics and Mechanism of the Pyridinolysis of Aryl Ethyl Chlorothiophosphates in Acetonitrile

어디까리,이해황 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.11

The nucleophilic substitution reactions of Y-aryl ethyl chlorothiophosphates with X-pyridines are studied kinetically in acetonitrile at 55.0 ºC. The Hammett and Brönsted plots for substituent X variations in the nucleophiles exhibit biphasic concave upwards with a break point at X = 3-Me. The substituents of X = 4-CN and 4-Ac show great positive deviations from both the Hammett and Brönsted plots. The Hammett plots for substituent Y variations in the substrates exhibit biphasic concave upwards with a minimum point at Y = H. The obtained values of the cross-interaction constants (ρXY) are all null in spite of the biphasic free energy correlations for both substituent X and Y variations, since the ρX values with both the strongly and weakly basic pyridines are almost constant. A stepwise mechanism with a rate-limiting leaving group departure from the intermediate is proposed where the distance between X and Y does not vary from the intermediate to the second transition state. A frontside attack is proposed with the strongly basic pyridines based on the considerably great magnitudes of ρX and βX values and a backside attack is proposed with the weakly basic pyridines based on the relatively small magnitudes of ρX and βX. The positive deviations of the two strong π-acceptor parasubstituents,X = 4-Ac and 4-CN, from both the Hammett and Brönsted plots are rationalized by the great extents of bond formation and breaking.

Kinetics and Mechanism of the Pyridinolysis of S-Aryl Phenyl Phosphonochloridothioates in Acetonitrile

어디까리,룸비니,이해황 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.10

Kinetic studies on the reactions of Y-S-aryl phenyl phosphonochloridothioates with X-pyridines have been carried out in MeCN at 55.0 ºC. The Hammett and Brönsted plots for substituent X variations in the nucleophiles are biphasic concave upwards with a break point at X = H. The Hammett plots for substituent Y variations in the substrates are biphasic concave upwards with a break point at Y = H, and the sign of ρY is changed from unusual negative (ρY < 0) with the weaker electrophiles to positive (ρY > 0) with the stronger electrophiles. The stepwise mechanism is proposed on the basis of the ρX, βX, and ρXY values as follows: a ratelimiting leaving group departure from the intermediate involving a frontside attack and product-like TS for the stronger nucleophiles and weaker electrophiles; a rate-limiting leaving group departure from the intermediate involving a backside attack and product-like TS for the weaker nucleophiles and electrophiles; a rate-limiting bond formation involving a frontside attack for the stronger nucleophiles and electrophiles; a rate-limiting bond formation involving a backside attack for the weaker nucleophiles and stronger electrophiles. The substituent effects of X and Y on the pyridinolysis mechanisms of R1R2P(=S)Cl-type substrates are discussed.

Transition State Variation in the Anilinolysis of O-Aryl Phenyl Phosphonochloridothioates in Acetonitrile

어디까리,룸비니,Shuchismita Dey,이해황 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.8

The nucleophilic substitution reactions of Y-O-aryl phenyl phosphonochloridothioates with substituted anilines (XC_6H_4NH_2) and deuterated anilines (XC_6H_4ND_2) are kinetically investigated in acetonitrile at 55.0oC. The deuterium kinetic isotope effects (DKIEs) invariably increase from an extremely large secondary inverse (kH/kD = 0.439; min) to a primary normal (kH/kD = 1.34; max) as both substituents of nucleophile (X)and substrate (Y) change from electron-donating to electron-withdrawing. These results are opposite to the DKIEs on Y-O-aryl methyl phosphonochloridothioates, and can be rationalized by the gradual transition state (TS) variation from backside to frontside attack. The trigonal bipyramidal pentacoordinate TS is proposed for a backside attack, while the hydrogen-bonded, four-center-type TS is proposed for a frontside attack. The negative values of the cross-interaction constants (ρXY(H) = −0.38 for XC_6H_4NH_2 and ρXY(D) = −0.29 for XC_6H_4ND_2) indicate that the reactions proceed by a concerted S_N2 mechanism.

Kinetics and Mechanism of the Pyridinolysis of Methyl Phenyl Phosphinic Chloride in Acetonitrile

이해황,어디까리 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.6

The pyridinolysis of methyl phenyl phosphinic chloride is investigated kinetically in acetonitrile at –20.0 ^oC. The Hammett and Brönsted plots for substituent X variations in the nucleophiles are biphasic concave downwards with a break point at X = H, and unusual positive ρX (= 2.94) and negative βX (= –0.48) values are obtained for the strongly basic nucleophiles. A stepwise mechanism with a rate-limiting step change from bond breaking for the weakly basic pyridines to bond formation for the strongly basic pyridines is proposed on the basis of biphasic concave downward Hammett and Brönsted plots. Unusual positive ρ_X and negative β_X values are rationalized by the isokinetic relationship. The pyridinolyses and anilinolyses of four R_1R_2P(=O)Cl-type substrates, dimethyl, diethyl, methyl phenyl, and diphenyl phosphinic chlorides in acetonitrile are compared to obtain systematic information on phosphoryl transfer reaction mechanism. The combination of the two ligands,Me and Ph, shows unexpected kinetic results for both the anilinolysis and pyridinolysis: greatest magnitude of k_H/k_D (= 2.10) involving deuterated anilines [XC_6H_4NH_2(D_2)] for the anilinolysis, and exceptionally fast rate and biphasic concave downward free energy correlation for the pyridinolysis.

Mechanistic Study on the Aminolysis of Chlorophosphates in Solvent: Concerted or Stepwise?

김찬경,Nasir Shahzad,어디까리,조형진 대한화학회 2017 Bulletin of the Korean Chemical Society Vol.38 No.8