N
X
C
O
N
S
Hal
Solvents
Natural
Products
P Si
C
C
C C
C
C
414
8 Mass Spectrometry
8.10.3 Sulfoxides and Sulfones
Aliphatic Sulfoxides [4,5]
Fragmentation: Most fragments are produced after rearrangement with nonspecific H transfer to the O atom and subsequent OH · elimination to yield [M-17] +
or alkene elimination to [M-alkene] +· , followed by OH · , SOH · (giving alk + ions), or
alk · elimination (yielding CH 2 =S–OH + , m/z 63).
S
R
2
O
R
1
H
SH
R
2
OH
R
1
+
S
R
2
R
1
+
– O H
.
S
OH
R
1
CH 2 =S-O H
m/z 63
R-CH 2
m/z 29, 43, 57
S
R
1
+
– OH
.
+
+
– R
.
– SO H
.
S
R
2
OH
R
1
+
– CH 2 =CHR
2
+ .
.
+ .
.
ESI-MS/MS: Elimination of an alkyl radical.
Ion series: Characteristic ion at m/z 63 (CH 2 =S–OH + ) as well as alkyl and alkenyl
fragments, C n H 2n+1 (29, 43, 57, 71, …) and C n H 2n-1 (27, 41, 55, 69, …).
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).
Alkyl Aryl and Diaryl Sulfoxides [4,5]
Fragmentation: Most fragments of methyl aryl sulfoxides are produced, after
rearrangement to CH 3 S–O–ar +· , by elimination of CH 2 S (yielding [M-46] +· , a
phenol), of CO (to [M-28] +· ), and of CH 3
· (to [M-15] + ). The latter ion loses CO to
give the thiapyranyl cation (m/z 97 if ar is phenyl).
S
O
O
S
[M -28]
+ .
O H
[M -15]
+
m/z 125
S +
m /z 97
– CO
– CO
– CH 2 S
–
. CH 3
+ .
+ .
+ .
m /z 112
The skeletal rearrangement is not relevant for the fragmentation of higher alkyl aryl
sulfoxides. Here, direct cleavage of the C–S bonds and McLafferty rearrangements
dominate.
For diaryl sulfoxides, elimination of SO (to give [M-48] +· ) as well as of O, OH · , and
CHO · (yielding [M-16] +· , [M-17] + , and [M-29] + , respectively). After rearrangement to sulfenates, cleavage of the S–O bond to produce ar–S + and ar–O + ions,