Meurer Eduardo C, Sparrapan Regina, Tomazela Daniela M, Eberlin Marcos N, Augusti Rodinei
Institute of Chemistry, State University of Campinas, UNICAMP, Campinas, Brazil.
J Am Soc Mass Spectrom. 2005 Oct;16(10):1602-7. doi: 10.1016/j.jasms.2005.05.011.
Gas-phase reactions of several acylium and thioacylium ions, that is H2C=N-C+=O, H2C=N-C+=S, O=C=N-C+=O, S=C=N-C+=O, H3C-C+=O, and (CH3)2N-C+=O, with both a model isocyanate and isothiocyanate, that is, C2H5-N=C=O and C2H5-N=C=S, were investigated using tandem-in-space pentaquadrupole mass spectrometry. In these reactions, the formation of mono- and double-addition products is observed concurrently with proton transfer products. The double-addition products are far more favored in reactions with ethyl isocyanate, whereas the reactions with ethyl isothiocyanate form, preferentially, either the mono-addition product or proton transfer products, or both. Retro-addition dominates the low-energy collision-induced dissociation of the mono- and double-addition products with reformation of the corresponding reactant ions. Ab initio calculations at Becke3LYP//6-311 + G(d,p) level indicate that cyclization is favored for the double-addition products and that products equivalent to those synthesized in solution, that is, of 3,4-dihydro-2,4-dioxo-2H-1,3,5-oxadiazinium ions and sulfur analogs, are formed.
利用空间串联五极杆质谱研究了几种酰鎓离子和硫代酰鎓离子（即H2C=N-C+=O、H2C=N-C+=S、O=C=N-C+=O、S=C=N-C+=O、H3C-C+=O和(CH3)2N-C+=O）与模型异氰酸酯和异硫氰酸酯（即C2H5-N=C=O和C2H5-N=C=S）的气相反应。在这些反应中，单加成产物和双加成产物的形成与质子转移产物同时被观察到。双加成产物在与异氰酸乙酯的反应中更占优势，而与异硫氰酸乙酯的反应则优先形成单加成产物或质子转移产物，或两者皆有。逆加成主导了单加成产物和双加成产物的低能碰撞诱导解离，并重新形成相应的反应物离子。在Becke3LYP//6-311 + G(d,p)水平上的从头算计算表明，双加成产物有利于环化，并且形成了与在溶液中合成的产物相当的产物，即3,4-二氢-2,4-二氧代-2H-1,3,5-恶二嗪鎓离子及其硫类似物。
