1189-05-5Relevant articles and documents
The influence of conventional heating and microwave irradiation on the resolution of (RS)-sec-butylamine catalyzed by free or immobilized lipases
Pilissa?o, Cristiane,De Oliveira Carvalho, Patri?cia,Da Grac?a Nascimento, Maria
, p. 1688 - 1697 (2013/01/15)
The lipases CAL-B, PSL, PSL-C, PSL-D, and A. niger lipase, free or immobilized in starch (obtained from two types of yam, known in Brazil as cara? (Discorea alata L.) and inhame (Colocasia esculenta (L.) Schott) or gelatin films, were used in the acylation of (RS)-sec-butylamine with different acyl donors in various organic solvents applying conventional heating (CH) or microwave (MW) irradiation. In the case of free A. niger lipase, the conversion degrees were three times higher using MW irradiation when compared to conventional heating at 35 °C. Using free A. niger lipase, the (R)-amide was obtained with a conversion degree of 21percent, resulting in eep > 99percent and E-value (enantioselectivity value) > 200, in 1 min of reaction under MW irradiation. When the A. niger lipase was immobilized in yam starch films, the (R)-amide was obtained in moderate conversions of 8-25percent after 3 or 5 min of reaction under MW irradiation, but with higher selectivity (eep > 99percent and E > 200) in comparison with the free form (conversion degree of 45percent, eep 81percent and E value of 18).
Ester Aminolysis: New Reaction Series for the Quantitative Measurement of Steric Effects
DeTar, DeLos F.,Delahunty, Claire
, p. 2734 - 2739 (2007/10/02)
Further development of theoretical methods for computing steric effects on chemical reactivity requires a large body of new reliable quantitative data for calibration and for testing.We report here on design criteria for reaction series suitable for obtaining these data and on a successful implementation that shows promise of providing access to a particularly broad range of steric hindrance and which additionally has shown a new form of steric hindrance.The series examined in the present study is ester aminolysis in the form RCOOC6H4NO2-p + R'NH2 in acetonitrile solution.A primary purpose of the examination has been to ascertain whether aminolysis may be a useful general series or whether known or unexpected complications might render it unsuitable.We have measured rate constants for a matrix of reactions using five different R groups and four different R' groups, each reaction at a series of concentrations of amine.This is the first systematic study of the sumultaneous action of steric hindrance effects in both the acylating agent and the entering nucleophile.The reactions showed both a second-order term k2 and a relatively less important third-order term k32.The Taft equation was applied to subsets of the rate constants.For each amine there were data for a set of esters for which the R group was the variable.The slopes ρs for these sets were nearly unity.For each ester there were corresponding data for a series of amine reactions in which R' was the variable.These sets also gave good correlations, but the slopes ρs' were considerably larger, about 2.3.This unusually large difference in response to structural effects in the acylating agent and in the nucleophile is unexpected and appears to arise from a new type of steric hindrance.An obvious explanation based on bond lengths proves to be quantitatively insufficient; that explanation postulates that there is greater hindrance for the amine because the C-N bond is short in comparison with the C-C bond.The difference may be due instead to a requirement for special orientation within the transition state, a matter currently under theoretical investigation.The k2 and the k3 sets gave similar correlations, an important finding in at least two respects.It means that steric effects are well-defined in this example of ester aminolysis, and it means also that the extra molecule of amine is far enough from the reaction center so that no additional steric hindrance results.The reactions observed in the present study cover a range of 5 powers of 10 in relative rate constants.Preliminary studies with other examples of aminolysis suggest that a range of relative rate constants covering well in excess of 12 powers of 10 should be observable.
Alkylation of Nitriles with Gaseous Carbenium Ions. The Ritter Reaction in the Dilute Gas State
Cacace, Fulvio,Ciranni, Giovanna,Giacomello, Pierluigi
, p. 2258 - 2261 (2007/10/02)
Radiolytically formed carbenium ions, such as sec-C3H7+, sec-C4H9+, and t-C4H9+, react in the gas phase with model aliphatic and aromatic nitriles yielding the corresponding nitrilium ions.The latter undergo efficient condensation with water that eventually leads to the formation of the corresponding N-alkylamides.The mechanism is analogous to the Ritter reaction in solution.The reactivity and selectivity of the gas-phase electrophilic attack on nitriles has been deduced from competition experiments under conditions that largely exclude the effects of solvation, ion pairing, etc., which complicate the interpretation of solution-chemistry measurements.
