Fragmentation mechanisms in mass spectrometry of Chemical Weapons Convention related spiro alkylphosphonates and alkyldioxaphosphinane oxides

Article abstract of DOI:10.1016/j.ijms.2014.06.003

The availability of mass spectra and interpretation skills are essential for unambiguous identification of the Chemical Weapons Convention (CWC)-related compounds. This paper examines electron ionization (EI) and electrospray ionization (ESI) mass spectral fragmentation routes of spiro alkylphosphonates I and 5,5-bis(chloromethyl)-2-alkyl-1,3,2-dioxaphosphinane 2-oxides II as compounds which are covered under CWC schedule 2.B.4. Mass spectrometric studies revealed some fragmentation pathways, such as elimination of alkyl(oxo)phosphane oxide (RPO₂), chlorine, chloromethylene, alkene, HCl, and H₂O, α-cleavage and McLafferty-type and hydrogen rearrangements. The proposed fragmentation processes include some new fragmentation patterns, such as isomerization of cations to stabilized carbocations and oxocarbocations, and elimination of formaldehyde and alkoxy through concerted retro [2 + 2] cycloaddition reaction and 1,2 PO alkyl shift. Structures of fragments were confirmed using EI-MS and MS/MS analysis of the deuterated analogs. The results will make a contribution to the Organization for the Prohibition of Chemical Weapons (OPCW) Central Analytical Database (OCAD) which may be used for the detection and identification of CWC-related compounds during on-site inspection and OPCW proficiency tests.

Full text of DOI:10.1016/j.ijms.2014.06.003

G Model
MASPEC 15193 1–12
International Journal of Mass Spectrometry xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
International Journal of Mass Spectrometry
journal homepage: www.elsevier.com/locate/ijms
1
2
3
Fragmentation mechanisms in mass spectrometry of Chemical
Weapons Convention related spiro alkylphosphonates and
alkyldioxaphosphinane oxides
a,
b,
c
b
4
5
Q1
Hamid Saeidian *, Mehran Babri *, Zohreh Mirjafary , Mohammad Taghi Naseri ,
b
b
b
Mansour Sarabadani , Davood Ashrafi , Seyyed Sajjad Mousavi Faraz
Department of Science, Payame Noor University (PNU), P.O Box 19395-4697, Tehran, Iran
Defense Chemical Research Lab (DCRL), P.O. Box 31585-1461, Karaj, Iran
Department of Chemistry, Science and Research Branch Islamic Azad University, Tehran, Iran
6
7
8
a
b
c
A R T I C L E I N F O
A B S T R A C T
Article history:
The availability of mass spectra and interpretation skills are essential for unambiguous identification of
the Chemical Weapons Convention (CWC)-related compounds. This paper examines electron ionization
Received 23 February 2014
Received in revised form 25 May 2014
Accepted 2 June 2014
(EI) and electrospray ionization (ESI) mass spectral fragmentation routes of spiro alkylphosphonates I
and 5,5-bis(chloromethyl)-2-alkyl-1,3,2-dioxaphosphinane 2-oxides II as compounds which are covered
under CWC schedule 2.B.4. Mass spectrometric studies revealed some fragmentation pathways, such as
Available online xxx
elimination of alkyl(oxo)phosphane oxide (RPO
2 2
), chlorine, chloromethylene, alkene, HCl, and H O,
Keywords:
a
-cleavage and McLafferty-type and hydrogen rearrangements. The proposed fragmentation processes
Mass spectrometry
Spiro alkylphoshonates
McLafferty rearrangements
Cycloaddition
Microsynthesis
Chemical Weapons Convention
include some new fragmentation patterns, such as isomerization of cations to stabilized carbocations and
oxocarbocations, and elimination of formaldehyde and alkoxy through concerted retro [2 + 2]
cycloaddition reaction and 1,2 P ꢀꢀ O alkyl shift. Structures of fragments were confirmed using EI-MS
and MS/MS analysis of the deuterated analogs. The results will make a contribution to the Organization
for the Prohibition of Chemical Weapons (OPCW) Central Analytical Database (OCAD) which may be used
for the detection and identification of CWC-related compounds during on-site inspection and OPCW
proficiency tests.
ã 2014 Published by Elsevier B.V.
9
23
1
. Introduction
weapons in 2013. Mass spectrometry coupled with gas chroma-
tography (GC/MS) provides a key analytical technique for the
2
4
1
1
1
1
1
1
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All activities related to the production, development, stock-
piling and use of chemical weapons are forbidden by the Chemical
Weapons Convention (CWC), which came into force on 29 April
unambiguous identification of scheduled chemicals during profi-
ciency tests (PTs) and off- and/or on-site analyses [1]. For
unequivocal identification of CWC-related compounds in real
samples or PTs, the availability of mass spectra and interpretation
skills are essential requirements. Due to the extreme toxicity of
CWC-related compounds, there is limited number of research on
such compounds. In recent years, some research results have been
reported which contains microsynthesis and interpretation of
mass spectra of CWC-related compounds [2–7], but to our
knowledge there is no mass spectral fragmentation study for
spiro alkylphosphonate compounds I and 5,5-bis(chloromethyl)-2-
alkyl-1,3,2-dioxaphosphinane 2-oxides II. These compounds are
covered under CWC schedule 2.B.4 as well as all compounds with
phosphorus bonded to a methyl, ethyl, isopropyl, or propyl
moieties. The studied compounds are the reaction products of
alkylphosphonic dichlorides with pentaerythritol. Mass spectra of
such compounds might be of interest to OPCW. It should be
mentioned that pentaerythritol is a versatile building block for the
27
28
1997. Chemical warfare agents (CWAs) were used during World
29
War I, the Iran–Iraq war and subsequently in some terrorist attacks
in Japan. Recently sarin, as nerve agent, was used during the Syria
conflict. These tragic events show that monitoring and analysis of
CWAs, their precursors and degradation/reaction products is an
important part of verification activities in support of CWC. The
state parties to CWC have established the Organization for the
Prohibition of Chemical Weapons (OPCW) to achieve the objective
and purpose of CWC. It is interesting to note that OPCW received
the Nobel peace prize for its extensive efforts to eliminate chemical
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37
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Q2
*
Corresponding authors at: Department of Science, Payame Noor University
(
PNU), P.O. Box 19395-4697, Tehran, Iran.
E-mail address: h_porkaleh@yahoo.com (H. Saeidian).
http://dx.doi.org/10.1016/j.ijms.2014.06.003
387-3806/ã 2014 Published by Elsevier B.V.
1
Please cite this article in press as: H. Saeidian, et al., Fragmentation mechanisms in mass spectrometry of Chemical Weapons Convention
related spiro alkylphosphonates and alkyldioxaphosphinane oxides, Int. J. Mass Spectrom. (2014), http://dx.doi.org/10.1016/j.ijms.2014.06.003

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preparation of many polyfunctionalized compounds such as the
explosive pentaerythritol tetranitrate and pentaerythritol tetraa-
crylate [8]. As continuation of our mass spectral fragmentations
studies on CWC-related compounds [9–12], it was concluded that
detailed studies on a class of spiro alkylphosphonate I and 5,5-bis
software (NIST, Gaithersburg, MD, USA) were used to calculate
retention indices of the synthesized compounds. An alkane
8
mixture [octane (C ) to tetracosane (C24)] was used for retention
indices calculations.
89
(
chloromethyl)-2-alkyl-1,3,2-dioxaphosphinane 2-oxides II were
2.3. ESI-MS and ESI-MS–MS analysis
necessary. This paper describes a study on a general microsyn-
thesis procedure for a few title compounds (Scheme 1). Subse-
quently, electron ionization (EI) and electrospray ionization (ESI)
mass spectra of these compounds, with possible fragmentation
routes, were investigated via analysis of fragment ions of
deuterated analogs and MS–MS experiments.
90
91
92
93
94
LC/MS analysis was performed on an Agilent 1200 LC system
(Agilent Technologies, Inc., Waldbronn, Germany) equipped with
Agilent 6410 triple quadrupole tandem mass spectrometer and
managed by a Mass Hunter workstation (Agilent Technologies Inc.,
CA, Santa Clara, USA). The column used for separation was an
9
5
Agilent rapid resolution HT zorbax SB-C18 (3 ꢂ150 mm, 3.5
mm)
5
5
5
6
96
97
98
2. Experimental
(Agilent Technologies Inc., Santa Clara, CA, USA). The column
ꢁ
temperature was set at 25 C. A gradient mobile phase of (A) water
2.1. Reagents and chemicals
plus 20 mM formic acid and (B) acetonitrile plus 20 mM formic acid
was used. The initial condition was set at 5% of B. The following
solvent gradient was applied: from 95% A and 5% B to 5% A and 95%
9
9
5
5
5
6
6
7
8
9
0
1
100
101
102
103
104
All chemicals required for the microsynthesis of spiro
alkylphosphonates were purchased from Sigma–Aldrich (St. Louis,
MO, USA), Fluka (Neu-Ulm, Germany), and Merck (Darmstadt,
Germany), and were used as received. Alkylphosphonic dichlorides
were synthesized by use of a method described elsewhere [13,14].
B within 20 min, hold for 10 min. Flow rate was set at 0.25 mL
ꢀ1
min and 4
m
L of samples were injected using ALS autosampler
(Agilent Technologies, Inc., Waldbronn, Germany). The electro-
spray ionization (ESI) and fragmentor voltages were set at 4000
and 60 V, respectively. The ultra-high pure nitrogen was used as the
nebulizer, drying and collision gas. The heated capillary tempera-
1
05
6
2
106
107
108
109
110
2.2. GC/MS and GC/MS–MS analysis
ꢁ
ture was maintained at 300 C. The drying gas flow rate and
6
6
6
6
6
6
6
7
7
7
7
7
7
7
7
7
7
8
8
8
8
8
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
ꢀ1
GC/MS analyses were performed using an Agilent 6890 N gas
nebulizer gas pressure were 10 L min and 40 psi, respectively.
chromatograph equipped with a 5973 quadrupole mass selective
detector, MSD, (Agilent Technologies, Inc., Santa Clara, CA, USA), a
HP-5MS (5% phenyl, 95% dimethylpolysiloxane, Agilent’s J&W
Mass spectra were obtained by scanning from m/z > 80 to 1000
with 0.5 s scan time.
111
Scientific) capillary column of (30 m, 320
m
m i.d. and 0.25
m
m film
2.4. NMR analysis
thickness), and helium as carrier gas at constant flow of 1.8 mL
ꢀ1
ꢁ
112
113
114
min . The oven temperature was set at 40 C for 3 min and then
A Bruker (Avance DRX-250 MHz, Germany) NMR instrument
ꢁ
ꢁ
ꢁ
1
31
13
was increased to 280 C with ramp of 10 C/min and held at 280 C
for 6 min. The samples were injected in splitless mode at an
injection temperature of 250 C. The temperatures of the EI source
was employed for H, P and C NMR experiments. All spectra
were recorded at ambient temperature using CDCl as a solvent.
3
ꢁ
ꢁ
115
and analyzer were kept at 230 and 150 C, respectively. The scan
2. 5. General procedure for microsynthesis of spiro alkylphosphonates I
range was m/z > 35–500. GC/MS–MS analyses were performed
using an Agilent 7890 N gas chromatograph interfaced to a 7000 A
triple quadruple mass spectrometer (Agilent Technologies, Inc.,
Wilmington, DE, USA). GC conditions were as noted above. The
ionization energy was set at 70 eV in both MS spectrometers. MS–
MS analyses were carried out using nitrogen as collision gas, at
116
117
118
119
120
121
122
123
124
125
Pentaerythritol (0.30 mmol) and triethylamine or pyridine
(0.65 mmol) in 500
with stirring, to
dichloride, in 500
m
a
2 2
L CH Cl or pyridine were added dropwise,
solution of 0.60 mmol alkylphosphonic
ꢁ
m
L CH
2
Cl
2
at 0–5 C. The reaction mixture
was stirred for 4 h. The resulting precipitate was removed by
filtration and the solution analyzed by GC/MS or GC/MS–MS as
required. For separation of spiro methylphosphonate 1a (entry 1a,
Table 1) from mixture, after completion of the reaction, the
ꢁ
collision energy of 10 eV and source temperature of 230 C. CI-MS
experiments also were done on 5973 MSD using isobutane as
reagent gas. The scan range was set at m/z > 70–500. Other
instrumental conditions were as EI experiments. Automated mass
spectral deconvolution and identification system (AMDIS)
mixture was poured into ice cold H
2
O and stirred for 15 min, then
the mixture was saturated with brine. Subsequently, extraction
Scheme 1. Microsynthesis route of spiro alkylphosphonates I and 5,5-bis(chloromethyl)-2-alkyl-1,3,2-dioxaphosphinane 2-oxides II.
Please cite this article in press as: H. Saeidian, et al., Fragmentation mechanisms in mass spectrometry of Chemical Weapons Convention
related spiro alkylphosphonates and alkyldioxaphosphinane oxides, Int. J. Mass Spectrom. (2014), http://dx.doi.org/10.1016/j.ijms.2014.06.003

G Model
MASPEC 15193 1–12
H. Saeidian et al. / International Journal of Mass Spectrometry xxx (2014) xxx–xxx
3
Table 1
GC/EI–MS data of spiro alkylphosphonates I.
0
+ꢃ
Entry
R
R
M
Fragment ions (% relative abundances)
[
A]
256 241
7)
[B]
[C]
[D]
[E] [F]
[G]
[H]
[I]
[J]
[K]
[L]
[M]
[N]
[O]
[P]
1a
1b
1c
1d
1e
1f
Me
Me
Me
Me
225
(1)
242
(ꢀ)
178
(12)
181
(17)
192
(17)
197
(15)
206
(36)
178,
181
(18),
(ꢀ)
187 175 157
148
97
79
(44)
82
(53)
93
(32)
98
(27)
107
(30)
119
(8)
122
(3)
160
(100)
163
(100)
174
(100)
179
(100)
188
(100)
160, 174 131,
(100),
(57)
131
(10)
134
(7)
145
(13)
150
(10)
159
(13)
181
(2)
184
(ꢀ)
195
(1)
200
(1)
209
(1)
211
(12)
214
(6)
225
(32)
230
(27)
244
(1)
211,
225
(ꢀ),
(20)
211,
244
(ꢀ),
(ꢀ)
159
(11)
162
(7)
(
(10) (18) (78) (49)
193 181 163 151
(5) (17) (100) (31)
215 203 185 162
(7) (26) (61) (34)
225 213 195 167
(7) (24) (54) (29)
243 231 213 176
(5) (35) (46) (18)
(37)
100
(24)
111
(53)
116
(39)
125
(81)
262 244
(2)
284 255
228
(ꢀ)
246
(ꢀ)
(
d
3
)
(d
Et
3
)
Et
239
(1)
256
(5)
133
(12)
138
(3)
147
(17)
119,
133
(4),
(14)
173
(16)
178
(10)
187
(18)
159,
173
(12),
(13)
159,
187
(12),
(5)
(
8)
Et
Et
(d
294 260
(3)
312 269
244
(1)
253
(4)
225,
239
(20),
(7)
262
(2)
(
d
5
)
5
)
n-Pr
n-Pr
270
(77)
242,
256
(22),
(ꢀ)
(
30)
270 241,
55
Me
Et
201 189 171
(ꢀ) (ꢀ) (4)
148,
162
(24),
(39)
148,
97, 111 79, 93
(40),
(37)
181,
195
2
(
(
(24),
(24)
145
(9), (8) (ꢀ),
11),
4)
(4)
1
1
g
Me
Et
n-Pr
n-Pr
284 241,
69
225,
253
(21),
(ꢀ)
242,
270
(22),
(ꢀ)
178,
206
(17),
(4)
192,
206
(22),
(9)
215 203 185
(8) (38) (79) 176
(24),
97, 125 79, 107 119,
(40),
(37)
160, 188 131,
(100),
(57)
181,
209
(ꢀ),
(ꢀ)
2
(24),
(9)
147
(4),
(19)
159
(9),
(12)
(
(
13),
7)
(12)
162,
h
298 255,
69
239,
253
(17),
(2)
256,
270
(36),
(10)
229 217 199
(6) (31) (54) 176
111, 125 93, 107 133,
(46),
(27)
174, 188 145,
(100),
(28)
195,
209
(ꢀ),
(ꢀ)
225,
244
(8), (ꢀ) (11),
173,
187
2
(30),
(14)
147
(11),
(10)
149
(13),
(5)
(
(
13),
7)
(19),
(32)
(10)
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
26
157
158
with acetonitrile (5 ꢂ1 mL) then dry the organic phase with
Na SO and concentration under vacuum, afforded the desired
spiro methylphosphonate 1a with 89% yield with up 97% purity as
indicated by GC/MS and NMR analysis.
It should be mentioned that in this reaction 5,5-bis(chlor-
omethyl)-2-alkyl-1,3,2-dioxaphosphinane 2-oxides II are also
formed as indicated by the GC/MS results. These compounds are
also covered under CWC schedule 2.B.4. Therefore, EI-MS
compounds with possible fragmentation routes were also investi-
gated. It is interesting to note that reaction of pentaerythritol with
alkylphosphonic dichlorides in pyridine as base and solvent
yielded only spiro alkylphosphonates I with high yield (upto
3. Results and discussion
3.1. Mass spectrometric analyses
27 Q4
28
2
4
29
30
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
3.1.1. 1. GC/MS and GC/MS–MS analyses of spiro alkylphoshonates I
Major EI fragment ions of spiro alkylphosphonates I are given in
Scheme 2 and Table 1. The molecular ions (M ) of spiro
alkylphosphonates I are not observed in their mass spectra
(Fig. 2). CI-MS of spiro alkylphosphonates I was performed to
the proposed structures (Supplementary material).
31
32
+ꢃ
33
34 Q5
35
36
0
Ion [A], the result of direct elimination of an alkyl (R or R )
37
+ꢃ
radical from M , was observed for all these compounds (Table 1),
38
80–90%). In the case of methylphosphonic dichlorides (entry 1a,
with relative abundance <30%. Spectra of deuterated analogs (1b,
39
Table 1), spiro methylphosphonate 1a was separated from reaction
and 1d) and spiro alkylphosphonates bearing different alkyl (R and
40
1
13
31
0
mixture and was fully characterized by H, C and P NMR and
chemical ionization (CI)-MS analysis.
R , 1f–1h) clearly show the ions corresponding to this fragment.
41
Interesting fragment ion [B] can arise through two possible
fragmentation pathways. (1) Elimination of oxygen atom from [A]
42
1
13
31
The H, C and P NMR spectra of 1a clearly indicated the
43
1
0
0
ꢃ
formation of spiro methylphosphonate (Fig. 1). The H NMR
or (2) 1,2 P ꢀꢀ O alkyl (R or R ) shift then elimination of R(R )O from
44
+ꢃ
spectrum of 1a consisted of a doublet (JHP = 17.5 Hz) for the methyl
M
(Scheme 3) [15,16].
45
0
protons at
d
= 1.56–1.63 ppm, and a multiplet peak (
d
= 4.01–
Expulsion of the alkyl group (R or R ) on phosphorus atom as an
46
4
.54 ppm) for the methylene protons, which are diastereotopic and
alkene gave ion [C] with relative abundance in the range 2–77%.
Formationof[C]inmassspectralofcompoundsbearingR = n-Pr take
place through the McLafferty-type rearrangement. McLafferty
rearrangement is a skeletal rearrangement, meaning formation of
47
1
1
13
would exhibit different peak in the H spectrum. H-decoupled
NMR spectrum of 1a showed 3 distinct resonances in agreement
with the proposed structure, at = 8.63–10.86 ppm a doublet
resonance ( JCP = 139.40 Hz) for carbon of methyl moieties, a triplet
resonance ( JCP = 4.83 Hz) for spiro carbon (quaternary carbon)
between
Hz) at
of 1a showed a distinct resonance at
spectrum of 1a clearly showed the presence of ion [M + H] , m/
z > 257.
C
48
49
d
50
1
3
an allylic group is not possible for R = CH analogs [17]. Conse-
51
3
quently, spectra for these compounds are distinct from the other
spiro alkylphosphonates. As ethyl analogs can not form allylic
radicals, formation of ion [C] from ethyl analogs is not possible via
the McLafferty-type rearrangement. Instead, neutral loss of
ethylene is possible from ethyl analogs via a hydrogen migration
(1,4C ꢀꢀ O H shift) to the oxygen-bearing cation radical site.
52
2
d
= 37.33–37.49 ppm and a doublet resonance ( JCP = 6.17
53
31
d
= 66.49–66.59 ppm for carbon of methylene. The P NMR
= 27.93. CI-MS mass
54
d
55
+
56
Please cite this article in press as: H. Saeidian, et al., Fragmentation mechanisms in mass spectrometry of Chemical Weapons Convention
related spiro alkylphosphonates and alkyldioxaphosphinane oxides, Int. J. Mass Spectrom. (2014), http://dx.doi.org/10.1016/j.ijms.2014.06.003

G Model
MASPEC 15193 1–12
4
H. Saeidian et al. / International Journal of Mass Spectrometry xxx (2014) xxx–xxx
Fig. 1. 1H, 13C and 31P NMR spectra of spiro methylphosphonate 1a.
1
1
86
87
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
Fragment ion [D] is attributed to oxetane spiro ion by the
cycloaddition reaction (Scheme 5) [18]. Fragmentation of ion [H]
for 1a (m/z > 148) leads to product ions m/z > 42, 70, 97, 119 and 133
(Scheme 5). The proposed structural assignments in Scheme 5 are
supported by deuterium-labeling studies, which show the forma-
tion of corresponding ions to these fragments. The product ion scan
of m/z > 151 in mass spectrum of 1b revealed further disintegration
to product ions m/z > 42, 70, 100, 121 and 133 (Fig. 3). All EI-MS
spectra of I show fragment ion at m/z > 133.
Fragment ion [K] was formed by expulsion of formyl (CHO)
radical from [H]. As shown in Scheme 6, elimination formyl radical
from [H] can be explained by hydrogen migration from carbon to
oxygen of PQO group.
elimination of a neutral alkyl(oxo)phosphane oxide (RPO
2
) from M
1
88
89
90
91
92
93
94
95
96
97
98
99
00
+ꢃ
(
Scheme 4). The peak of this ion is visible in the deuterated spiro
1
1
1
1
1
1
1
1
1
1
1
2
alkylphosphonates I EI-MS spectra.
Ions [E] and [F] were generated from M by some hydrogen
rearrangements. The loss of H O from [F] gave rise to ion [G] with
+ꢃ
2
relative high abundances >46%. The product ion scan of [G] for
spiro methylphosphonate 1a revealed further fragmentation to [J]
with m/z > 79. The product ion spectrum of [G] at m/z > 163 in spiro
methyl(d3) phosphonate 1b mass spectrum, supports the struc-
tural assignment for [G] and [J] (Supplementary material, Fig. 28S
and 29 S). Proposed fragmentation for the formation high intensity
ion [H] involves two steps: elimination of a neutral alkyl(oxo)
Fragment ion at m/z > 133 was formed by cleavage of the P ꢀꢀ R
bond in ion [H] which is observable in all mass spectra of spiro
alkylphosphonates I. It should be mentioned that the fragment
+ꢃ
phosphane oxide (RPO
2
) from M which gave ion [D] then
expulsion of formaldehyde from [D] via a concerted retro [2 + 2]
Please cite this article in press as: H. Saeidian, et al., Fragmentation mechanisms in mass spectrometry of Chemical Weapons Convention
related spiro alkylphosphonates and alkyldioxaphosphinane oxides, Int. J. Mass Spectrom. (2014), http://dx.doi.org/10.1016/j.ijms.2014.06.003

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H. Saeidian et al. / International Journal of Mass Spectrometry xxx (2014) xxx–xxx
5
Scheme 2. Proposed EI-MS fragmentation routes for spiro alkylphosphonates I.
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
233
234
235
ions at m/z > 42 and 70 are also present in mass spectrum of
pentaerythritol (Supplementary material, Fig. 27S). Elimination of
an alkylphosphonic acid molecule from the molecular ion of spiro
alkylphosphonates gave rise to ion [L] as base peak in all EI mass
spectra of I. Further fragmentation of [L] in mass spectrum of 1a
and 1b at m/z > 160 and 163, respectively showed product ions at
m/z > 81, 82 and ion [M] (Supplementary material, Fig. 30S).
Stability of cation cyclopropyl due to aromaticity is driving force
for formation of ion [M]. Mass spectra of deuterated analogs (1b
and 1d) clearly show the corresponding ions to [L] and [M]. Loss of
formaldehyde from fragment ion [A] can result in an interesting
fragment [O] [19]. The product ion scan of ion [O] at m/z > 211 in
mass spectrum of 1a revealed further fragmentation to product
ions at m/z > 181, 159, 133, 79 and 53 (Fig. 4). Elimination of
formaldehyde from [O] yielded fragment ion [N] at m/z > 181 for 1a
and m/z > 184 for 1b. Ion [P] was also observed in product ion scan
of ion m/z > 214 in mass spectrum of 1b. Fragment ion at m/z > 53 is
stable cation. The stabilization of carbocation at m/z > 53 by
cyclopropyl substituent, is a result of the interaction of electrons in
the cyclopropyl C ꢀꢀ C bonds with the positive carbon [18].
236
237
238
239
240
241
242
243
244
245
246
247
248
3.1.2. LC/MS and LC/MS–MS analyses of spiro alkylphoshonates I
The sipro methylphosphonate 1a formed relative moderate
+
intensity [M + H] under positive ion ESI conditions. The most
+
abundant ions in ESI-MS are observed at m/z > 279 as ion [M + Na]
+
and at m/z > 535 as [2M + Na] . Tandem mass spectrum of the
[M + H] ion (m/z > 257) is shown in Fig. 5. The most abundant
+
product ion is observed at m/z > 83. The general fragmentation
+
pathway of the [M + H] of 1a is summarized in Scheme 7. ESI
fragmentation pattern is similar to EI fragmentation pattern.
3 2
Elimination of a neutral methyl(oxo)phosphane oxide (CH PO )
+
and a methylphosphonic acid molecule from [M + H] result in an
ion at m/z > 179 and 161 corresponding to ions [D] and [L] in EI-MS
of 1a, respectively. Formation of the ion at m/z > 149 can be
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related spiro alkylphosphonates and alkyldioxaphosphinane oxides, Int. J. Mass Spectrom. (2014), http://dx.doi.org/10.1016/j.ijms.2014.06.003

G Model
MASPEC 15193 1–12
6
H. Saeidian et al. / International Journal of Mass Spectrometry xxx (2014) xxx–xxx
Fig. 2. Representative EI mass spectra of spiro ethylphosphonate 1c and deuterated analog 1d.
Scheme 3. Proposed mechanisms for formation of ion [B].
O
O
O
O
O
(
R')R
O
(R')R
O
O
O
P
P
P
O
P
+
O
R(R' )
O
R(R')
oxetane spiro [D]
alkyl(oxo)phosphane oxide
Scheme 4. Fragmentation mechanism for formation of ion [D].
2
2
2
2
2
2
49
50
51
52
53
54
explained by direct elimination of formaldehyde from ion at m/
z > 179 by a concerted process. This proposed mechanism is similar
to that envisaged to explain the formation of ion [H] in EI
fragmentation of spiro alkylphosphonates. The proposed fragmen-
tation pathways of the [M + H] of 1a in Scheme 7 are supported by
analysis of ESI mass spectrum of the deuterated analog 1b (Fig. 5)
255
256
257
258
259
3.1.3. GC/MS and GC/MS–MS analyses of 5,5-bis(chloromethyl)-2-
alkyl-1,3,2-dioxaphosphinane 2-oxides II
Prominent EI fragment ions of 5,5-bis(chloromethyl)-2-alkyl-
1,3,2-dioxaphosphinane 2-oxides II are listed in Table 2 and their
corresponding structures are shown in Scheme 8. Expected
+
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related spiro alkylphosphonates and alkyldioxaphosphinane oxides, Int. J. Mass Spectrom. (2014), http://dx.doi.org/10.1016/j.ijms.2014.06.003

G Model
MASPEC 15193 1–12
H. Saeidian et al. / International Journal of Mass Spectrometry xxx (2014) xxx–xxx
7
O
O
O
(
R')R
O
(
R')R
O
P
O
retro [2+2]
P
cycloaddition
O
O
oxetane spiro [D]
[
H]
CID
- C
H
H
-
CHO
O
OH
P
-
R(R')
(
R')R
P
O
(R')R
OH
HO
O
[
K]
m/z 42
OH
m/z 70
O
O
[
I]
O
P
m/z 133
Scheme 5. Proposed fragmentation pathways of ion [H] for the spiro alkylphosphonates.
Fig. 3. Product ion spectra of m/z 148 and 151 from 1a and deuterated analog 1b, respectively.
H
H
O
O
O
O
O
O
HO
HO
(R')R
P
1,4 C-O H shift
P
-CHO
P
P
(
R')R
(
R')R
(
R')R
O
HO
[
H]
[K]
Scheme 6. Proposed mechanism for formation of ion [K] from [H].
Fig. 4. Product ion spectra of m/z 211 and 214 from 1a and deuterated analog 1b, respectively.
2
2
2
2
2
2
2
2
60
61
62
63
64
65
66
67
268
269
270
271
272
273
274
275
isotopic ratios of chlorine containing fragments were observed, as
is evident from the relative abundances listed in Table 2. Loss of a
chlorine radical from M gave rise to ion [A] as base peak in all
compounds II, except the compound bearing n-Pr moiety (entry 2d,
Table 2)
Product ion scan of chloronium ion [A] in spectra of ethyl(d )
5
derivatives (entry 2c, Table 2) at m/z > 216 revealed high relative
abundance product ions [B, C, D, J, K] and product ions at m/z > 83
and 101. Elimination of formaldehyde as a neutral molecule from
ion [A] yielded ion [C] as base peak in molecular ion spectrum of 2c
(Fig. 6). Formation of interesting ion [D] from M and/or ion [A]
can be explained in the proposed mechanism shown in Scheme 9.
This assignment is base on the observation of ion [D] in all mass
spectra of II along with 2c, the presence of expected isotopic ratio
of chlorine for [D] in all mass spectra and CID spectrum of ion [D]
from 2c. The CID spectrum of ion [D] at m/z > 134 for 2c includes the
+ꢃ
+ꢃ
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related spiro alkylphosphonates and alkyldioxaphosphinane oxides, Int. J. Mass Spectrom. (2014), http://dx.doi.org/10.1016/j.ijms.2014.06.003

G Model
MASPEC 15193 1–12
8
H. Saeidian et al. / International Journal of Mass Spectrometry xxx (2014) xxx–xxx
Fig. 5. ESI-MS and ESI-MS/MS spectra of protonated spiro methylphosphonate 1a and deuterated analog 1b.
2
2
2
2
2
2
2
2
2
2
76
286
287
288
289
290
291
292
293
294
295
product ions at m/z > 116 and 98 corresponding to exclusion of H
and HCl from ion [D], respectively (Fig. 6). The first step in the
proposed mechanism for formation of [D] is involved,
rearrangement process which afford the intermediate 1 as a
stabilized cyclic oxocarbocation. Stability of 1 is the major driving
force for this rearrangement. Then a cation and neutral alkyl-
phosphonochloridic acid (ion-neutral complex) [20] are produced
by McLafferty rearrangement. Migration of a hydrogen atom to the
neutral alkylphosphonochloridic acid resulted in fragment ion [D]
2
O
Ion [E] (Scheme 8) as a chloronium ion was formed by the loss of
chloromethylene radical from M . It appears relatively in high
77
+ꢃ
78
a
abundance in the range of 46–77%. This peak is the base peak or the
second highest peak in EI-MS of compounds bearing Et or n-Pr
substitutes (Table 2). Elimination of HCl from [E] yielded ion [F]
with moderate relative abundance. Spectrum of deuterated analog
also (entry 2c, Table 2) shows the ions corresponding to [E] and [F].
The proposed assignment is further supported by CID spectra of [E]
from 2a and 2c at m/z > 183 and 202 (Supplementary material,
Fig. 31S).
79
80
81
82
83
84 Q6
85
(
Fig. 7).
H
O
O
O
O
H C
O
3
P
P
O
CH3
[M+H] m/z 257
-
CH PO
-CH PH O
2 3
3
2
3
H
H
H
O
H
H
O
P
O
O
P
O
O
P
P
H C
OH
H C
3
O
H C
3
O
O
3
H C
3
O
O
O
OH
m/z 97
m/z 179
m/z 161
m/z 149
m/z 83
-
CH O
2
Scheme 7. General fragmentation pattern of [M + H]+ of spiro methylphosphonate 1a.
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related spiro alkylphosphonates and alkyldioxaphosphinane oxides, Int. J. Mass Spectrom. (2014), http://dx.doi.org/10.1016/j.ijms.2014.06.003

G Model
MASPEC 15193 1–12
H. Saeidian et al. / International Journal of Mass Spectrometry xxx (2014) xxx–xxx
9
Table 2
GC/MS data of 5,5-bis(chloromethyl)-2-alkyl-1,3,2-dioxaphosphinane 2-oxides II.
Entry
R
Fragment ions (% relative abundances)
[
A]
197, 199
100), (32)
211, 213
100), (33)
216, 218
100), (33)
225, 227
74), (24)
[B]
[C]
[D]
[E]
[F]
[G]
[H]
[I]
[J]
[K]
2
2
2
2
a
b
c
Me
Et
97
167, 169
(25), (8)
181, 183
(38), (15)
186, 188
(41), (13)
195, 197
(23), (20)
115, 117
(13), (5)
129, 131
(17), (6)
134, 136
(21), (10)
143, 145
(12), (4)
183, 185
(46), (16)
197, 199
(94), (31)
202, 204
(94), (30)
211, 213
147
(34)
161
(60)
166
(60)
175
(27)
79
(51)
93
(50)
98
(53)
107
–
88
(26)
88
(23)
88
(22)
88
217
–
131
(9)
145
(8)
150
(9)
159
(3)
161
(11)
175
(13)
180
(12)
189
(7)
(
(18)
111
(18)
116
(6)
125
–
217
(1)
217
(9)
217
(2)
(
Et(d
5
)
(
d
n-Pr
(
(100), (33)
(18)
Scheme 8. Proposed EI-MS fragmentation routes for 5,5-bis(chloromethyl)-2-alkyl-1,3,2-dioxaphosphinane 2-oxides II.
Please cite this article in press as: H. Saeidian, et al., Fragmentation mechanisms in mass spectrometry of Chemical Weapons Convention
related spiro alkylphosphonates and alkyldioxaphosphinane oxides, Int. J. Mass Spectrom. (2014), http://dx.doi.org/10.1016/j.ijms.2014.06.003

G Model
MASPEC 15193 1–12
10
H. Saeidian et al. / International Journal of Mass Spectrometry xxx (2014) xxx–xxx
Fig. 6. EI-MS and product ion spectra of the ions at m/z 216 and 134 from 2c.
2
2
2
2
3
3
3
3
3
3
3
3
3
3
3
3
3
3
96
314
The ion [F] fragmented to ion [G], as shown by CID spectra of [F]
4. Conclusion
97
from 2a and 2c at m/z > 147 and 166, respectively (Supplementary
material, Fig. 32S and 33S). Cation-radical ion [H] as 2-methyl-
idenepropane-1,3-diol were present in all compounds II. It should
be noted that this fragment is not observable in EI-MS of spiro
alkylphosphonates I. On the other hand, EI-MS of pentaerythritol
also show the ion [H] (Supplementary material, Fig. 27S). Direct
98
315
316
317
318
319
320
321
322
323
This investigation reported the microsynthesis and NMR, EI-MS
and ESI-MS analyses of some spiro alkylphosphonates I and
alkyldioxaphosphinane oxides II. Important fragmentations and
disintegrations that rationalized the formation of most of the
characteristic fragment ions were McLafferty-type rearrange-
ments, alkyl and hydrogen shifts, HCl, chlorine and formaldehyde
eliminations and a-cleavage. Fragmentation ion product struc-
tures were proved using MS/MS experiments and investigation of
MS spectra of deuterated analogs.
99
00
01
02
03
ꢃ
+ꢃ
elimination of alkyl (R ) radical by a-cleavage from M gave rise to
04
ion [I] in relative low abundance <10. When the alkyl group is
05
+ꢃ
methyl, M was not disintegrated to ion [I] (entry 2a, Table 2).
06 Q7
07
+ꢃ
Formation of ion [K] from M can be explained by a step-wise
mechanism involving loss of a chlorine radical then elimination of
HCl. The proposed step-wise fragmentation is further supported
from CID spectra of ion [A] from 2a and 2c (Fig. 6). It is interesting
to note that fragment ion [K] is a very stable fragment. It can be
08
324
Appendix A. Supplementary data
09
10
325
326
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.ijms.2014.06.003.
11
0
isomerized to stabilized carbocation ion [K ] (Scheme 10). There is
12
a favorable orbital overlap between the filled cyclopropane bent
13
0
bonds and the empty p-orbital in [K ] [18].
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G Model
MASPEC 15193 1–12
H. Saeidian et al. / International Journal of Mass Spectrometry xxx (2014) xxx–xxx
11
O
O
R
O
O
O
CH2
O
R
O
R
O
P
Cl
P
P
O
Cl
chloronium ion [A]
Cl
H
H
O
R
R
-
O
O
O
1
,2 C-C H shift
P
P
O
O
Cl
Cl
R
Oxocarbocation 1
McLafferty rearrangement
OH
OH
R
O
Hydrogen transfer
O
P
+
P
+
O
OH
Cl
Cl
H
m/z 83
[D]
cation-neutral complex
cation-neutral complex
Scheme 9. Proposed mechanism for formation of ion [D] in EI-MS of II.
Fig. 7. Product ion spectrum of m/z 202 from 2c.
H
O
O
O
O
O
R
O
O
O
R
O
R
P
P
P
[
K]
[K']
bisected conformation
Scheme 10. Stabilization of ion [K] by favorable orbital overlap between the filled cyclopropane bent bonds and the empty p-orbital.
3
27
[4] B. Papoušková, P. Bedná ꢀr , J. Stýskala, J. Hlavá c9 , P. Barták, K. Lemr, J. Mass
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Please cite this article in press as: H. Saeidian, et al., Fragmentation mechanisms in mass spectrometry of Chemical Weapons Convention
related spiro alkylphosphonates and alkyldioxaphosphinane oxides, Int. J. Mass Spectrom. (2014), http://dx.doi.org/10.1016/j.ijms.2014.06.003