García-Río L, Leis J R, Moreira J A, Norberto F
Departamento de Química Física, Facultad de Química, Universidad de Santiago, 15706 Santiago, Spain.
J Org Chem. 2001 Jan 26;66(2):381-90. doi: 10.1021/jo0006730.
We have studied the nitroso group transfer from substituted N-methyl-N-nitrosobenzenesulfonamides to primary and secondary amines, observing that the rate of the reaction increases as a consequence of the presence of electron withdrawing groups on the aromatic ring of the nitrosating agents. The rate constants determined for the nitroso group transfer, ktr, give good Bronsted-type relationships between log ktr (rate constant for nitroso group transfer) and pKaR2NH2+ and pKaleaving group. The study of the nitrosation processes of secondary amines catalyzed by ONSCN and denitrosation catalyzed by SCN-, in combination with the formation equilibrium of ONSCN, has enabled us to calculate the value of the equilibrium constant for the loss of the NO+ group from a protonated N-nitrosamine (pKNOR2N+HNO), which can be defined by analogy with pKaR2NH2+. The value of pKNOX-NO for the loss of the NO+ group from an N-methyl-N-nitrosobenzenesulfonamide was obtained in a similar way. By using values of delta pKNO = pKNOR2N+HNO - pKNOX-NO, we were able to calculate the equilibrium constant for the nitroso group transfer and characterize the transition state. On the basis of Bronsted-type correlations, we have obtained values of beta nuclnorm and alpha lgnorm approximately equal to 0.55, showing a perfectly balanced transition state. In terms of the Marcus theory, the calculation of the intrinsic barriers for the nitroso group transfer reaction shows that the presence of electron withdrawing groups on the aromatic ring of the N-methyl-N-nitrosobenzenesulfonamides does not cause these barriers to vary.
我们研究了取代的N-甲基-N-亚硝基苯磺酰胺中硝基的转移至伯胺和仲胺的过程，观察到由于亚硝化剂芳环上存在吸电子基团，反应速率增加。所测定的硝基转移速率常数ktr，在log ktr（硝基转移速率常数）与pKaR2NH2+和离去基团的pKa之间呈现出良好的布朗斯特型关系。对由ONSCN催化的仲胺亚硝化过程以及由SCN-催化的脱亚硝化过程的研究，结合ONSCN的形成平衡，使我们能够计算质子化N-亚硝胺失去NO+基团的平衡常数（pKNOR2N+HNO），其可类似于pKaR2NH2+进行定义。以类似方式获得了N-甲基-N-亚硝基苯磺酰胺失去NO+基团的pKNOX-NO值。通过使用ΔpKNO = pKNOR2N+HNO - pKNOX-NO的值，我们能够计算硝基转移的平衡常数并表征过渡态。基于布朗斯特型相关性，我们得到了βnuclnorm和αlgnorm的值约等于0.55，表明过渡态完全平衡。根据马库斯理论，硝基转移反应本征能垒的计算表明，N-甲基-N-亚硝基苯磺酰胺芳环上吸电子基团的存在并不会导致这些能垒发生变化。
