Thioacylium ions

The silicon analogues of the acylium and thioacylium ions are believed to be generated under electron-impact ionization. For example, CH3 i = 0 is suggested to be formed via reactions 90120 and 91102, and CH3 i = S from 204106 (reaction 92). 

Gas-phase synthesis of 3,4-dihydro-2,4-dioxo-277-l,3,5-oxadiazinium ions (16 X = Y = O) via cyclization of acylium (17 X = O) and thioacylium ions (17 X = S) with isocyanates (18 Y = O) and isothiocyanates (18 Y = S) has been investigated using tandem-in-space pentaquadrupole mass spectrometry (MS) <2005JAM1602>. The formation of single (19) and double (20) addition products in these reactions was observed to occur concurrently with proton transfer. The products of double addition have been observed to be favored in reactions with ethyl isocyanate, whereas the reactions with ethyl isothiocyanate formed preferentially either the single-addition product or proton-transfer products, or both. Furthermore, ab initio calculations at the Becke3LYP//6-311- -G(dp) level indicate that cyclization of the double addition products is favored and 3,4-dihydro-2,4-dioxo-277-l,3,5-oxadiazinium ions (16 X = Y = 0) are formed (Scheme 2) <2005JAM1602>. 

Gas-phase reactions of acylium and thioacylium ions with isocyanate and isothiocyanate were investigated by MS <2005JAM1602>. The use of liquid chromatography/mass spectrometry (LC/MS) for the confirmation and quantification of thiomethoxam has been reported <2005ANA21>. 

With the help of a combination of selective dissolution and chromatographic separation, several of the cyclic ethers have been separated and isolated <2003OL3745>. Though not of synthetic value, gas-phase cyclization reactions of acylium ions with nitriles, forming 1,3,5-oxadiazinium ions 375 by double nitrile addition followed by cyclization, have been reported (Scheme 75) <2001MI445>. Similarly, the gas-phase reactions of acylium and thioacylium ions with isocyanates (18 Y = 0) and isothiocyanates (18 Y = S) have been reported to result in oxadiazinium (16 X = 0) and thiadiazinium (16 X = S) salts, respectively (see Scheme 2) <2005JAM1602>. 

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