Cyclization reactions of acylium and thioacylium ions with isocyanates and isothiocyanates: gas phase synthesis of 3,4-dihydro-2,4-dioxo-2H-1,3,5-oxadiazinium ions.
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.
Meurer
Eduardo C
EC
Institute of Chemistry, State University of Campinas, UNICAMP, Campinas, Brazil.
Sparrapan
Regina
R
Tomazela
Daniela M
DM
Eberlin
Marcos N
MN
Augusti
Rodinei
R
D000080:Acetals / Q000032:analysis / Q000737:chemistry*; D000465:Algorithms; D005740:Gases / Q000032:analysis / Q000737:chemistry*; D007477:Ions; D017953:Isocyanates; D017879:Isothiocyanates; D044367:Phase Transition; D011724:Pyridazines / Q000032:analysis / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
D000080:Acetals; D005740:Gases; D007477:Ions; D017953:Isocyanates; D017879:Isothiocyanates; D011724:Pyridazines; C037152:isothiocyanic acid; C062482:pyridazine