Generation of New Nitrile N-Sulfides (NCCNS, R₂NCNS, H₃CSCNS, and ClCNS) as Ions and Neutrals in the Gas Phase:  Tandem Mass Spectrometry, Flash Vacuum Pyrolysis, and ab Initio MO Study

Abstract

1,2,5-Thiadiazoles 1−5 bearing CN, CONH2, SCH3, and Cl substituents have been investigated under electron impact conditions. Collisional activation (CA) and neutralization−reionization (NR) mass spectrometries have allowed the identification of new nitrile N-sulfides (NCCNS, H2NCNS, H3CSCNS, and ClCNS) as ions or neutrals in the gas phase of a mass spectrometer. These results were supported by chemical ionization experiments of nitriles using carbon disulfide as the reagent gas, flash vacuum pyrolysis experiments, and ab initio molecular orbital calculations at the G2(MP2,SVP) level. The neutral nitrile N-sulfides are found by experiment and theory to be observable species in the gas phase. All the cations are potential energy minima, and their calculated fragmentation energies are in accord with experimental observations.

Experimental and theoretical study of the gas-phase interaction between ionized nitrile sulfides and pyridine

“…The calculated ionization energy of NCCNS (10.05 eV) [21] is in keeping with the observation of a very efficient charge exchange process (33% of the main beam ϩ 57% for protonated pyridine). When energetically allowed, the charge exchange reaction is known to present a very high efficiency because the measured reaction rate can be very close to the collision rate constant [27].…”

“…Mass-selected m/z 93 radical cations, 35 Cl-C §N ϩ -S • , prepared by dissociative ionization of 3,4-dichloro-1,2,5-thiadiazole [21], react in the rf-only quadrupole cell with neutral pyridine by (i) charge exchange reaction (m/z 79, ionized pyridine), (ii) by S •ϩ (m/z 111), (iii) Cl ϩ (m/z 114), (iv) CNS ϩ (m/z 137) transfers to pyridine, and (v) by addition of ClCNS •ϩ , followed by the loss of an hydrogen atom (m/z 171), see Figure 1a and Table 1. The m/z 111 and 114 products were easily identified on the basis of previous MS/MS studies, as their consecutive CA spectra were in keeping with the fragmentation expected for pyridine N-thioxide [19] and pyridine N-chloride [22]) molecular ions, respectively.…”

“…The calculated ionization energy of cyanogen chloride sulfide (IE ϭ 8.79) [21] is significantly lower than the IE of pyridine (9.25 eV) [23]. Therefore, the unexpected observation of the charge exchange reaction can be attributed to the lack of efficient thermalization of the reactive ions prior to the reaction.…”

“…Mass-selected m/z 84 radical cations, NC-C §N ϩ -S • , prepared by dissociative ionization of 3,4-dicyano-1,2,5-thiadiazole [21], also react with neutral pyridine in the quadrupole cell by (i) charge exchange reaction (m/z 79) and subsequent production of protonated pyridine (m/z 80), (ii) NC ϩ cation transfer (m/z 105), (iii) ionized sulfur atom transfer (m/z 111), and (iv) cycloaddition reaction (m/z 162), see Table 1 and Figure 5. The calculated ionization energy of NCCNS (10.05 eV) [21] is in keeping with the observation of a very efficient charge exchange process (33% of the main beam ϩ 57% for protonated pyridine).…”

First Isolation and Spectroscopic Observation of Thiofulminic acid (HCNS)

“…[2,3] The existence of HCNS and other simple nitrile sulfide derivatives was established only indirectly on the timescale of microseconds by neutralizationreionization mass spectrometry. [3,6,7] UV irradiation of the precursor 1,2,5-thiadiazole [8] at 254 nm evidently led to the formation of HCNS in cryogenic Ar and Kr matrices (Scheme 1). After photolysis new and strong absorption bands were observed in the IR spectrum ( Figure 1).…”