N
X
C
O
N
S
Hal
Solvents
Natural
Products
P Si
C
C
C C
C
C
412
8 Mass Spectrometry
8.10.2 Sulfides and Disulfides
Aliphatic Sulfides [1]
Fragmentation: Loss of alkyl radicals by cleavage of the C–C bond next to S (the
largest group being lost preferably) and of the C–S bond, followed by alkene and
H 2 S elimination. Alkene elimination from M +· to form the corresponding thiol ions.
In contrast to thiols and cyclic sulfides, no H 2 S or HS · elimination from M +· .
alk–SH
alk–S
+
– R
.
– alkene
–
. CR 3
C
S
R
R
R
alk
C R
R
R +
– alk-S
.
alk–S=CR 2
– alkene
H S=CR 2
+
+
alk
S
R
– R
.
S
alk
– alkene
S
H
+
+
m/z 61
+ .
+ .
+ .
In general, the H rearrangements are nonspecific. The transfer of secondary H
predominates over that of primary H.
ESI-MS/MS: Cleavage of a C–S bond producing an alkyl cation or a protonated
thiol:
[R 1 SR 2 + H] +
[R 1 ] + + R 2 SH
[R 1 SR 2 + H] +
[R 1 SH + H] + + [R 2 - H]
Ion series: Sulfur-containing aliphatic fragments, C n H 2n+1 S (m/z 47, 61, 75, 89, …).
The hydrocarbon fragments may dominate in long-chain sulfides.
Intensities: Intensive peaks in the lower mass range. Characteristic local maxima
from S-containing fragments, C n H 2n+1 S (m/z 47, 61, 75, 89, …).
Molecular ion: Usually strong. Characteristic 34 S isotope peak at [M+2] +· and
[frag+2] for S-containing fragments (4.5% per S atom).
Alkyl Vinyl Sulfides
Fragmentation: Loss of alkyl radicals (Δm 15, 29, 43, …). Elimination of
thioethanol (Δm 62) after triple H rearrangement. Dominant m/z 60 (CH 3 CH=S +· )
accompanied by m/z 61 (CH 3 CH 2 S + ).
Ion series: Sulfur-containing unsaturated aliphatic fragments, C n H 2n-1 S (m/z 45,
59, 73, …). Unsaturated hydrocarbon ions, C n H 2n (m/z 42, 56, 70, …) and C n H 2n-2
(m/z 40, 54, 68, …)
Intensities: Intensive peaks evenly distributed over the whole mass range.
Molecular ion: Of medium intensity. Characteristic 34 S isotope peak at [M+2] +· and
[frag+2] for S-containing fragments (4.5% per S atom).