Chiappe Cinzia, Pieraccini Daniela, Saullo Paola
Dipartimento di Chimica Bioorganica e Biofarmacia, via Bonanno 33, 56126 Pisa, Italy.
J Org Chem. 2003 Aug 22;68(17):6710-5. doi: 10.1021/jo026838h.
Room-temperature ionic liquids have been used as environmentally benign solvents for the preparation of primary and secondary alkyl azides and nitriles under solid-RTIL phase-transfer conditions. The reaction of primary, secondary, and tertiary halides or tosylates with KCN and NaN(3) has been investigated in three ionic liquids ([bmim][PF(6)], [bmim][N(Tf)(2)], and [hpyr] [N(Tf)(2)]). The observed nucleofugacity scales for the reaction of NaN(3) are similar to those reported for the same process in cyclohexane, indicating that in these solvents it is possible to evidence the intrinsic ability to depart of leaving groups. Changes in the nature of the IL cation or anion determine significant modifications in reactivity of the investigated substrates. Reactivity has been interpreted considering a gradual shift of the mechanism from concerted S(N)2 (primary substrates) to stepwise S(N)1 (tertiary substrate, 3), through the nucleophilically assisted formation of an ion pair intermediate, in the case of 2d.
室温离子液体已被用作环境友好型溶剂，用于在固-室温离子液体相转移条件下制备伯烷基叠氮化物和仲烷基叠氮化物以及腈。在三种离子液体（[bmim][PF₆]、[bmim][N(Tf)₂]和[hpyr][N(Tf)₂]）中研究了伯、仲、叔卤化物或甲苯磺酸盐与KCN和NaN₃的反应。观察到的NaN₃反应的离去倾向标度与在环己烷中相同过程报道的标度相似，这表明在这些溶剂中有可能证明离去基团离去的内在能力。离子液体阳离子或阴离子性质的变化决定了所研究底物反应性的显著改变。对于2d的情况，考虑到反应机理从协同的S(N)2（伯底物）逐渐转变为分步的S(N)1（叔底物，3），通过亲核辅助形成离子对中间体来解释反应性。
