1005789-34-3Relevant academic research and scientific papers
Nucleophilic Addition to Olefins. 15. Solvent and Substituent Effects on the Hydrolysis of Benzylidenemalononitriles in Basic Me2SO-Water Solutions
Bernasconi, Claude F.,Fox, John P.,Kanavarioti, Anastassia,Panda, Markandeswar
, p. 2372 - 2381 (1986)
Benzylidenemalononitriles hydrolyze to ArCHO and CH(CN)2- in basic solution.A kinetic study of this reaction with the parent compound and with the 4-NMe2, 4-OMe, 3-CL, 4-CN, and 4-NO2 derivatives in water and in 30percent, 50percent, 60percent, and 70percent aqueous Me2SO is reported.In water nucleophilic addition of OH- to the olefin (k1OH, Scheme I), to form ArCH(OH)C(CN)2- (TOH-) is rate limiting with all substrates.In the Me2SO-containing solvents, the formation of TOH- at high becomes faster than its conversion to products.This allows separate measurement of the rate of product formation.The major pathways for this latter process involve rate-limiting intramolecular proton switch (ki, Scheme II) and rate-limiting carbon protonation of the dianonic intermediate ArCH(O-)C(CN)2- (TO2-) by water (k6H2O, Scheme II); the most "obvious" pathway through rate-limiting carbon protonation of TOH- by water (k2H2O) is insignificant, but carbon protonation of TOH- by piperidinium ion (k2BH) is important.At very high base concentration, there is a further change to rate-limiting breakdown of ArCH(O-)CH(CN)2 (TO-( (k4) for the 3-Cl and 4-NO2 derivatives but not for the other substrates.The intramolecular proton switch (ki) is best understood as a concerted proton transfer with a transition state that includes a water bridge.Two kinetically equivalent alternatives involve carbon protonation of TO2- by H3O+, with transition stabilisation by hydrogen bonding between H3O+ and O-, and carbon protonation TOH- by water, with transition-state stabilization by hydrogen bonding between the hydroxy group of TOH- and the incipient hydroxide ion.Both alternatives can be excluded because they cannot account for the high ki values.On the basis of the substituent and solvent effects on the rate (k1OH) and equilibrium constants (k1OH) of OH- addition, the following conclusions are drawn: (1) There is an imbalance between the polar substituent effect (ρnor) and the response of k1OH to the decreased solvation of OH- in the Me2SO-containing solvens (βnuc,sol).This may be attributed to a combination of factors, such as a lag in the resonance stabilization of the C(CN)2- moiety in TOH-, an early desolvation of the OH- ion, and an electrostatic interaction in the transition state between the residual negative charge on the attacking OH- and the aryl substituent. (2) The ρ(k1OH) values depend very little on solvent effect on k1OH (βnuc,sol) depends very little on the aryl substituent.This indicates that the cross-correlation coefficient pxs = δρ(k1OH)/δ log γOH- = δβnuc,sol/δ? ca. 0, with γOH- being the solvent activity coefficient for the transfer of OH- from water to Me2SO-water mixtures.
The Ever-surprising chemistry of boron: Enhanced acidity of phosphine·boranes
Hurtado, Marcela,Yanez, Manuel,Herrero, Rebeca,Guerrero, Andres,Juan Z. Davalos,Jose-Luis, M. Abboud,Khater, Brahim,Guillemin, Jean-Claude
supporting information; experimental part, p. 4622 - 4629 (2009/12/29)
The gas-phase acidity of a series of phosphines and their corresponding phosphine·borane derivatives was measured by FT-ICR techniques. BH 3 attachment leads to a substantial increase of the intrinsic acidity of the system (from 80 to 110 kJ mol-1). This acidity-enhancing effect of BH3 is enormous, between 13 and 18 orders of magnitude in terms of ionization constants. This indicates that the enhancement of the acidity of protic acids by Lewis acids usually observed in solution also occurs in the gas phase. High- level DFT calculations reveal that this acidity enhancement is essentially due to stronger stabilization of the anion with respect to the neutral species on BH3 association, due to a stronger electron donor ability of P in the anion and better dispersion of the negative charge in the system when the BH3 group is present. Our study also shows that deprotonation of ClCH2PH2 and ClCH 2PH2·BH3 is followed by chloride departure. For the latter compound deprotonation at the BH3 group is found to be more favorable than PH2 deprotonation, and the subsequent loss of Cl- is kinetically favored with respect to loss of Cl - in a typical SN2 process. Hence, ClCH2PH 2·BH3 is the only phosphine·borane adduct included in this study which behaves as a boron acid rather than as a phosphorus acid.
Mechanism and structure-reactivity correlation in the retroaldol reaction of substituted benzylidenemalononitriles with hydroxide ion
Shunmugasundaram,Jawahar,Srinivasan
, p. 789 - 791 (2007/10/03)
The kinetics of retroaldol reaction of benzylidene-malononitrile and para-substituted benzylidenemalononitriles with hydroxide ion in 90% methanol-10% water (v/v) mixture have been carried out. The reaction is first order with respect to both benzylidenemalononitrile and hydroxide ion. The rate of the reaction increases with increase in water content in the reaction medium and it is not much affected by the change in ionic strength. Addition of acrylonitrile has no influence on the rate of the reaction. On the basis of the kinetic observations, a suitable mechanism involving the nucleophilic attack of the hydroxide ion on the α-carbon atom and the subsequent cleavage of Cα-Cβ bond is proposed. Effect of substituents on the rate of the reaction shows that electron-attracting substituents accelerate the reaction rate while electron-donating substituents retard it. Satisfactory Hammett correlation has been observed.
Nucleophilic Addition to Olefins. 9. Kinetics of the Reaction of Benzylidenemalononitrili with Malononitrile Anion
Bernasconi, Claude F.,Zitomer, Janie L.,Fox, John P.,Howard, Keith A.
, p. 482 - 486 (2007/10/02)
The rates of the reversible addition of - to benzylidenemalononitrile, to form -, have been measured in water and in 50percent Me2SO - 50percent water.In water at 20 deg C, k1 = 2.30*1E5 M-1 s-1, k-1 = 5.95 s-1, and K1 = 3.86*1E4 M-1.In 50percent Me2SO - 50percent water at 20 deg C, k1 = 9.50*1E5 M-1 s-1, k-1 = 6.52 s-1, and K1 = 1.45*1E5 M-1.The pKa of the adduct is about 5 pK units lower than that of malononitrile.K1 for the addition of - is much higher than K1 for piperidine addition, despite the slightly lower proton basicity of -.This reflects the common observation that the carbon basicity of carbanions is higher than that of amines.The intrinsic rate contante for nucleophilic attack by - appears to be somewhat smaller than for amine attack, just as the intrinsic rate constant for protonation of - is lower than for the protonation of amines.This is not unexpected, since structural factors should affect the coordination of bases with Lewis acids in a similar way as coordination with the proton.The change from water to 50percent Me2SO - 50percent water has the effect of increasing k1 by a slighthly larger factor (4.13) than K1 (3.75).This implies that the intrinsic rate constant is higher in the less aqueous solvent, which is consistent with the notion that solvent reorganization contributes to the intrinsic barrier of the reaction.
