Mass spectrometric study on O(S)-alkyl N,N-dimethylamino alkylphosphonates (alkylphosphonothiolates) for chemical weapons convention verification purposes

Article abstract of DOI:10.1016/j.ijms.2012.03.006

Modified microsynthesis of O(S)-alkyl N,N-dimethylamino alkylphosphonates (alkylphosphonothiolates) which are included in schedule 2 of Chemical Weapons Convention (CWC) annex of chemicals, is reported. Retention indices and electron ionization mass spect

Full text of DOI:10.1016/j.ijms.2012.03.006

International Journal of Mass Spectrometry 319–320 (2012) 9–16
Contents lists available at SciVerse ScienceDirect
International Journal of Mass Spectrometry
journal homepage: www.elsevier.com/locate/ijms
Mass spectrometric study on O(S)-alkyl N,N-dimethylamino alkylphosphonates
(alkylphosphonothiolates) for Chemical Weapons Convention verification
purposes
Hamdollah Saeidiana,∗, Davood Ashrafib, Mansour Sarabadanib, Mohammad Taghi Naserib,
Mehran Babrib,∗
a Department of Science, Payame Noor University (PNU), Zanjan, Iran
b Defense Chemical Research Lab (DCRL), P.O. Box 31585-1461, Karaj, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Modified microsynthesis of O(S)-alkyl N,N-dimethylamino alkylphosphonates (alkylphosphonothiolates)
which are included in schedule 2 of Chemical Weapons Convention (CWC) annex of chemicals, is reported.
Retention indices and electron ionization mass spectral data with fragmentation routes for these chem-
icals are also given. Mass spectrometric studies revealed that their fragmentations were dominated by
alkene elimination, McLafferty rearrangement, ␣-cleavage, amine elimination, etc. Conclusions were con-
firmed using MS/MS experiments, fragment ions of deuterated analogs and density functional theory
calculations.
Received 9 February 2012
Received in revised form 20 March 2012
Accepted 20 March 2012
Available online 31 March 2012
Keywords:
Mass spectrometry
Chemical Weapons Convention
Alkylphosphonate
Alkylphosphonothiolate
DFT calculation
© 2012 Elsevier B.V. All rights reserved.
Fragmentation
1. Introduction
mass spectra of the CW agents, their precursors and degrada-
tion products such as N,N-dialkylaminoethanols, alkylphospho-
The CWC prohibits the production, storage and use of chem-
ical weapons (CWs), and stated that all member states must
destroy all the CWs over a fixed period of time [1]. Millions of
chemicals are listed in CWC annex of chemicals in three distinct
schedules. On the other hand, the CWC verification also includes
identification of degradation products of CWC chemicals. Such
large number of CWC-related chemicals puts more complexity
to the analytical activities under CWC verification requirements
which need unambiguous identification of chemicals in complex
environmental samples. Mass spectrometry with gas chromatog-
raphy inlet provides key technique for analysis of the CWC-related
chemicals [2]. For successful identification of the CWC-related
chemicals in real samples or samples of OPCW official proficiency
tests (PTs) [3], the availability of mass spectra and interpreta-
tion skills are essential requirements. Actually, it is impossible to
have a collection of mass spectral data of all CWC-related chem-
icals. However, spectra of a class of chemicals tend to be similar.
In recent years, some studies have been reported which include
nates, N,N-dialkylphosphoramidates, sulfur and nitrogen mustard,
methylphosphonites, N,N-dialkylaminoethane-2-sulfonic acids, N-
oxides of aminoethanols, N,N-dialkylaminoethane-2-thiols, alkyl
methylphosphoric acids [4–14]. One of the CWC-related chemicals
is O(S)-alkyl N,N-dimethylamino alkylphosphonates (alkylphos-
phonothiolates). To the best of our knowledge, there is no data in
mass spectral libraries for such compounds. The general structure
of these chemicals is shown below.
O
P
H3C
N
O(S)R1
H3C
R2
All these chemicals are placed in the CWC as schedule
2.B.4, which includes all compounds with phosphorus bonded
to methyl, ethyl, isopropyl, or propyl moieties. The microsyn-
thesis and understanding of mass spectral data for these
compounds are of immense help to those involved in the ver-
ification analysis of the CWC-related chemicals. Herein, we
wish to report a general microsynthesis protocol for a pool of
the O(S)-alkyl N,N-dimethylamino alkylphosphonates (alkylphos-
phonothiolate) 5 (Fig. 1). Electron ionization mass spectra of
N,N-dimethyl alkylphosphoramidic chlorides 3 and O(S)-alkyl
∗
Corresponding authors.
E-mail addresses: dcrl@isiran-net.com, h porkaleh@yahoo.com (H. Saeidian).
1387-3806/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ijms.2012.03.006

10
H. Saeidian et al. / International Journal of Mass Spectrometry 319–320 (2012) 9–16
N,N-dimethylamino alkylphosphonates (alkylphosphonothiolate)
5 with possible fragmentation routes are also investigated by
MS/MS experiments, fragment ions of deuterated analogs and
energy calculations.
2.4. General procedure for the microsynthesis of O-alkyl
N,N-dimethylamino alkylphosphonates
To a solution of dimethylamine hydrochloride 1 (0.2 mmol)
and alkyl (methyl, ethyl and n-propyl) phosphonic dichlorides 2
(0.2 mmol) in CH2Cl2 (300 ␮L), triethylamine (0.6 mmol) in CH2Cl2
(300 ␮L) was added dropwise, while stirring. The reaction mix-
ture was stirred at ambient temperature for 10 min then alcohol 4
(0.2 mmol) in CH2Cl2 (300 ␮L) was added dropwise to the solution.
The mixture was stirred for an additional 10 min. Triethylamine
hydrochloride salt was filtered off and the resulting solution was
analyzed by GC/MS.
2. Experimental
2.1. Reagents and chemicals
Dimethylamine, triethylamine and all the alcohols/thiols
required for the microsynthesis of O(S)-alkyl N,N-dimethylamino
alkylphosphonates (alkylphosphonothiolates) were purchased
from Sigma–Aldrich, Fluka and Merck companies and were used as
received. Alkyl (methyl, ethyl and n-propyl) phosphonic dichlorides
were synthesized in-house by the existing method [15].
2.5. General procedure for the microsynthesis of S-alkyl
N,N-dimethylamino alkylphosphonothiolates
To a solution of dimethylamine hydrochloride 1 (0.2 mmol)
and alkyl (methyl, ethyl and n-propyl) phosphonic dichlorides 2
(0.2 mmol) in CH2Cl2 (300 ␮L), triethylamine (0.4 mmol) in CH2Cl2
(300 ␮L) was added dropwise, while stirring. The reaction mix-
ture was stirred at ambient temperature for 10 min. Triethylamine
hydrochloride salt was filtered off and the resulting solution was
added dropwise to a solution of sodium thiolate 4 in 300 ␮L CH2Cl2.
The mixture was stirred for 10 min at ambient temperature. The
resulting precipitate was filtered off and the solution was analyzed
by GC/MS.
2.2. GC/MS and GC/MS/MS analysis
The GC/MS analyses were performed by an Agilent 6890N gas
chromatography equipped with a 5973 mass selective detector. HP-
5MS capillary column of length 30 m, 320 ␮m i.d. and 0.25 ␮m film
thickness and helium as carrier gas at constant flow of 1.8 mL min−1
were used. The oven temperature was set at 40 ◦C for 3 min and then
was increased to 280 ◦C (6 min) with ramp 10 ◦C/min. The sam-
ples were injected in splitless mode at an injection temperature of
250 ◦C. The temperatures of the EI source and analyzer were kept
at 230 and 150 ◦C, respectively. The scan range was 35–500 amu.
GC/MS/MS analyses were performed with an Agilent 7890N gas
chromatography interfaced to a 7000A Triple Quadruple mass spec-
trometer. The GC conditions were the same as mentioned above.
The MS/MS analyses were carried out using nitrogen as collision
gas, at collision energy of 10 eV and a source temperature of 180 ◦C.
3. Results and discussion
3.1. Synthesis
The microsynthesis of the O(S)-alkyl N,N-dimethylamino
alkylphosphonates (alkylphosphonothiolates) 5 generally involves
two steps: the initial addition of dimethylamine hydrochloride 1
to alkylphosphonic dichlorides 2 in the presence of triethylamine
as a base to form N,N-dimethyl alkylphosphoramidic chlorides 3
and subsequently reaction with alcohols/sodium thiolates 4 to yield
desired products 5 (Fig. 1).
In synthesis of tabun family, straightforward route for prepa-
ration of N,N-dimethylphosphoramidic chloride is the reaction of
anhydrous gaseous dimethylamine with phosphoryl chloride [18].
This procedure suffers from reaction conditions such as using of an
excess of phosphoryl chloride. On the other hand, handling and use
of a stoichiometric amount of gaseous dimethylamine is difficult.
Another method consists of introduction a single dimethylamino
group to phosphorus atom, under harsh condition by refluxing
dimethylamine hydrochloride in an excess of phosphoryl chloride
for 20 h [19]. It is evident that development of an efficient protocol
is required to access N,N-dimethyl alkylphosphoramidic chlorides.
2.3. Computational details
All geometry optimizations and frequency calculations of all
species were carried out using the Gaussian 03 program [16]. Den-
sity functional theory with the Becke three parameters hybrid
functional (DFT-B3LYP) calculations were performed with a 6-
311++G (2d, 2p) basis set for all atoms. Vibrational frequencies are
calculated at the same level to ensure that each stationary point is
a real minimum. Harmonic-oscillator approximation is also used
for the thermodynamic partition functions. After geometry opti-
mization and frequency calculations, zero-point energies (ZPEs)
and thermal corrections are obtained at 298 K. Bond dissociation
enthalpy (BDE) of P O and P S bond was extracted from enthalpies
as calculated by Gaussian 03 (BDE = −ꢀH = −((H2 + H3) − H1) which
H is the enthalpy of species [17].
Fig. 1. Synthesis route of O(S)-alkyl N,N-dimethylamino alkylphosphonates (alkylphosphonothiolates) 5.

H. Saeidian et al. / International Journal of Mass Spectrometry 319–320 (2012) 9–16
11
O
H3C
N
P
Cl
H3C
R2
3
O
P
H3C
H2C
O
P
O
P
H3C
H3C
OH
P
OH
P
H3C
H3C
O
P
H3C
H3C
N
Cl
N
R2
N
Cl
R2
Cl
N
Cl
R2
Cl
R2
F
C
D
E
B
A
H
N
H3C
CH2
H3C
H3C
H
N
P
OH
G
H2C
N
CH2
N
H3C
CH2
m/z 42
m/z 43
Fig. 2. Plausible fragmentation ions of N,N-dimethyl alkylphosphoramidic chlorides 3.
Dropwise addition of triethylamine to dimethylamine hydrochlo-
ride gently produced dimethylamine in dichloromethane solution
which then reacted with alkylphosphonic dichlorides to form N,N-
dimethyl alkylphosphoramidic chlorides. The GC/MS analysis of
the mixture in the initial step clearly indicated the formation of
N,N-dimethyl alkylphosphoramidic chloride. It should be men-
tioned that N,N-dimethyl alkylphosphoramidic chlorides 3 are also
included in CWC, schedule 2.B.4. Subsequently, conversion of 3
to the corresponding O(S)-alkyl N,N-dimethylamino alkylphospho-
nates (alkylphosphonothiolates) 5 was observed within 10 min. The
main feature of this microsynthetic protocol is the immediate syn-
thesis of the CWC-related chemicals under mild conditions.
Expected isotopic ratios of chlorine containing fragments were
observed, as is evident from the relative abundances listed in
Table 1. With these encouraging results, attention was focused
on the spectra of O(S)-alkyl N,N-dimethylamino alkylphosphonates
(alkylphosphonothiolates) 5. Major EI fragment ions of these com-
pounds as well as their retention indices (RI) are given in Table 2
and the plausible fragmentation routes of 5 are illustrated in Fig. 3.
Retention indices were calculated according to the Van Den Dool
and Kratz formula [20].
EI-MS spectra of the title chemicals also exhibited some isobaric
ions (hence indistinguishable), as listed in Table 2. Presence of these
ions in the spectra of other homologous indicates both mechanisms.
Mass spectral appearance of these compounds is influenced by the
alkyl groups on phosphorous and oxygen/sulfur (Fig. 4). The most
important fragmentation in mass spectra of 5 was McLafferty rear-
rangement of alkyl group on oxygen/sulfur (Fig. 5), which led to
ion [A]. The alkyl is left as an alkene. For O-methyl and O-phenyl
analogs (Table 2, entries 1, 11, 19, 36, 37 and 38), formation of
allylic or vinyllic group is not possible. Consequently, spectra for
these chemicals are distinct (Table 2). This supported the proposed
mechanism for the formation of [A]. Formation of ion [B] from 5 is
through loss of alkyl radical on oxygen/sulfur.
3.2. Mass spectra analyses
As shown in Fig. 2, the ion [A] is formed by the hydrogen radical
loss from molecular ion of 3 through ␣-cleavage. The molecular ion
also fragmented to [B] ([M−Cl]+) by elimination of chlorine radical
as expected. The ion [B] has the second highest relative abun-
dance in the mass spectra of N,N-dimethyl alkylphosphoramidic
chlorides 3. Ions [C] and [D] were formed through cleavage of
N,N-dimethylamino and CH3
N CH2 respectively from the molec-
The fragment [C] can be formed from molecular ion. It is worth
to note that relative intensity of [C] for alkylphosphonates depends
on the size of alkyl group. The larger alkyl group (≥C4) leads to
intense peak for ion [C]. In such cases, this ion peak is the highest or
the second highest peak in the spectra. Formation of ion [C] can be
explained by McLafferty + 1 rearrangement that involves an initial
hydrogen migration (1,5 C O H shift) to the oxygen-bearing radi-
cal site, leading to a distonic species. An ion and a neutral species
are produced after single bond cleavage. Then a hydrogen atom is
transferred from the neutral molecule to the radical cation, yielding
a cation and a stable radical fragment. This may explain why this
mechanism is favorable with larger alkyl groups (≥C4). Indeed, in
such cases, stable allylic radicals are expelled [21] (Fig. 6).
ular ion. Ion [E] is formed via cleavage of P-alkyl bond from 3.
Ion [F] is formed by the loss of alkene involving hydrogen trans-
fer from P-alkyl group to P O group. It is interesting to note that,
isobaric fragment ions [D] and [E] of the N,N-dimethyl propylphos-
phoramidic chloride are indistinguishable but the presence of ions
[D] and [E] in the mass spectra of the other homologous, indicates
operation of both mechanisms. On the other hand, the product ion
scan of ion at m/z 126 in spectrum of N,N-dimethyl propylphos-
phoramidic chloride by MS/MS showed that it further fragmented
to most relative intense ions m/z 42, 44 and 83 which indicates
preference of ␣-cleavage of alkyl radical from molecular ion over
␣-cleavage of N,N-dimethylamino substituent. Ion [G] was formed
by elimination of a chlorine radical from [F]. The base peak [H]
was produced from N,N-dimethylamino group which fragmented
to ions m/z 42 and 43 by hydrogen loss.
No formation of [C] from O-methyl and O-phenyl analogs could
confirm this proposed fragmentation. It is interesting to note that,

12
H. Saeidian et al. / International Journal of Mass Spectrometry 319–320 (2012) 9–16
O
P
H3C
H3C
N
XR1
R2
5
X = O, S
McLafferty
OH
- R1
-alkene
McLafferty+1
-XR1
-aldehyde /thioaldehde
-R2
X
P
O
P
X
P
OH
OH
H3C
N
H3C
H3C
O
P
O
P
H3C
H3C
OH
P XR1
H3C
H3C
H3C
H3C
H3C
H3C
H3C
R2
N
N
R2
N
O
N
P
XH
N
XR1
N
N
P
R2
or
H3C
H3C
H
R2
C
H3C
R2
R2
A
H3C
B
D
E
E'
F
G
-R1XH
O
H2C
H3C
M
N
P
m/z 90
-N(C2H6)
-CH3 (if X = O)
alpha-cleavage
-H (if X = O, R1<5)
O
P
R2
O
P
O
P
O
H3C
H2C
O
O
P
R2
H
N
H
H3C
H3C
H3C
H3C
H3C
N
XR1
N
P XR1
R2
N
X
XR1
XH
N
P
OH
H3C
N
XH
R2
R2
P
CH2
H2C
or
H3C
alkyl
H
I
J
K
L
L'
m/z 92
M m/z 44
Fig. 3. Proposed fragmentation routes for O(S)-alkyl N,N-dimethylamino alkylphosphonates (alkylphosphonothiolates) 5.
Fig. 4. Representative EI-MS mass spectra of 5.
Fig. 5. McLafferty rearrangement on chemical 5.

H. Saeidian et al. / International Journal of Mass Spectrometry 319–320 (2012) 9–16
13
Table 1
GC/MS data of N,N-dimethyl alkylphosphonamidic chlorides 3.
Structure
Retention index (RI)
M•+
Fragment ions (% relative abundances)
[A]
[B]
[C]
[D]
[E]
[F]
[G]
[H]
44
O
P
H3C
N
Cl
H3C
CH3
141
(14)
143
(4)
140
(4)
142
(2)
106
(48)
–
97
(12)
99
98
126
(7)
128
(2)
–
–
–
–
–
–
(9)
100
(3)
(100)
–
–
1095
1164
1243
(6)
O
H3C
N
P
Cl
H3C
C2H5
155
(13)
157
(4)
154
(3)
156
(2)
120
(38)
–
111
(6)
113
(4.)
112
(7)
114
(2)
126
(18)
128
(6)
127
(3)
129
(1)
92
(27)
–
44
(100)
–
–
–
–
O
H3C
N
P
Cl
H3C
n-C3H7
169
(13)
171
(4)
168
(1)
170
(1)
134
(22)
–
125
(2)
127
(24)
126a
(24)
128a
(8)
126a
(24)
128a
(8)
127
(24)
129
(7)
92
(41)
–
44
(100)
–
–
–
–
a
Isobaric ions.
relative intensity of ion [C] in O-propyl is higher than O-isopropyl
analogs (entries 3, 4, 13 and 14, Table 2). This difference may be
used for identification of propyl and isopropyl moieties on these
chemicals. Ion [D] in mass spectra of 5 is formed by the elimi-
nation of O(S)-alkyl radical from molecular ion. It is important to
note that the base peak for the most alkylphosphonothiolates is
ion [D] (entries 24–34, Table 2). On the other hand, bond dissoci-
ation enthalpy (BDE) of P O bond in O-ethyl N,N-dimethylamino
methylphosphonate (entry 2, Table 2), as calculated by Gaussian
03, was found to be higher by 107 kJ mol−1 than of BDE of P S bond
in S-ethyl N,N-dimethylamino methylphosphonothiolate (entry 24,
Table 2). The higher relative intensity of ion [D] for alkylphospho-
nothiolates than alkylphosphonates and BDE calculations showed
that P S bond cleavage in alkylphosphonothiolates requires less
energy than P O bond cleavage in alkylphosphonates. Low inten-
sity ion [E]/[Eꢀ] for alkylphosphonates was formed through loss of
aldehyde/ketone from molecular ion [5]. In contrast, the relative
intensity of ion [E]/[Eꢀ] for alkylphosphonothiolates with loss of
thioaldehyde/thioketone is moderate. For O-phenyl derivative loss
of an aldehyde molecular is not possible (Table 2, entry 36). It is
interesting to note that fragment ion [E]/[Eꢀ] was ascribed to two
possible structures shown in Fig. 7. Formation of ion [E]/[Eꢀ] can
be explained by hydrogen migration involving oxygen and phos-
phorus atoms. The free energy of the [CH3-P(N(CH3)2)OH]•+, as
calculated by Gaussian 03, was found to be lower by 58 kJ mol−1
than that of the [CH3-PO(N(CH3)2)H]•+, indicating the former as
the preferred structure rather than the later.
The formation of ion [F] was attributed to loss of alkene from the
molecular ion. Support for this route was provided by precursor ion
scan of ion m/z 153 in S-ethyl N,N-dimethylamino propylphospho-
nothiolate spectrum (entry 32, Table 2) and analysis of mass spectra
of deuterated analogs. Ion [F] was not observed in mass spectrum
Fig. 6. Proposed mechanism for formation of ion [C].

14
H. Saeidian et al. / International Journal of Mass Spectrometry 319–320 (2012) 9–16
Table 2
GC/MS data of O(S)-alkyl N,N-dimethylamino alkylphosphonates (alkylphosphonothiolates) 5.
•+
Entry
Substituent
Retention
index (RI)
M
Fragment ions (% relative abundances)
XR
R
[A]
[B]
[C]
[D]
[E’]
[F]
[G]
[H]
[I]
[J]
[K]
[L]
[M]
1
2
a
a
a
1
OCH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
933
137
(38)
151
(28)
165
(10)
165
(23)
179
(7)
179
(2)
193
(6)
193
(2)
207
(3)
–
–
123
(2)
123
(7)
123
(17)
123
(9)
123
(14)
123
(10)
123
(10)
123
(8)
122
–
–
124
(1)
106
(12)
106
(24)
106
(42)
106
(49)
106
(42)
106
(63)
106
(31)
106
(56)
106
(23)
106
(18)
120
(3)
120
(16)
120
(29)
120
(33)
120
(27)
120
(18)
120
(15)
120
(12)
134
(2)
107
(<1)
107
(3)
107
(3)
107
(5)
107
(3)
107
(4)
107
(2)
107
(4)
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
122
108
(<1)
108
(28)
108
(18)
108
(14)
108
(14)
108
(10)
108
(8)
108
(8)
108
(5)
108
(3)
108
(11)
108
(81)
108
(53)
108
(39)
108
(37)
108
(19)
108
(12)
108
(8)
93
(61)
122
79
(37)
79
(20)
79
(8)
79
(6)
79
(6)
79
(4)
79
(4)
79
(4)
79
(2)
79
(2)
93
(1)
93
(39)
93
(8)
93
(4)
93
(4)
93
136
(4)
150
(<1)
164
(<1)
164
(<1)
–
44
(100)
44
(100)
44
(100)
44
(100)
44
(100)
44
(100)
44
(72)
44
(93)
44
(47)
44
(39)
44
(100)
44
(100)
44
(100)
44
(100)
44
(86)
44
(61)
44
(51)
44
(39)
44
(100)
44
(100)
44
(100)
44
(98)
44
(66)
44
(30)
44
(29)
44
(28)
44
(27)
44
(31)
44
(30)
44
(28)
44
(29)
44
3
3
3
3
3
3
3
3
3
3
3
(21)
122
(9)
(21)
(21)
a
a
a
a
2
OC
H
1096
1177
1119
1270
1204
1366
1288
1469
1569
1118
1158
1245
1185
1338
1440
1540
1640
1184
1236
1327
1414
1514
1290
1376
1479
1582
1360
1443
1547
1641
1431
1519
1618
1179
1529
1080
1104
136
(2)
150
(1)
150
(5)
–
107
(3)
121
(<1)
121
(<1)
–
–
–
–
–
–
–
–
–
–
–
–
107
(30)
136
(2)
150
(1)
150
(5)
–
2
5
a
a
a
a
3
n-OC
H
122
(14)
122
(21)
122
(15)
122
(12)
122
(11)
122
(11)
122
(8)
124
(47)
124
(10)
124
(95)
124
(58)
124
(100)
124
(100)
124
(100)
124
(100)
–
3
7
4
i-OC
H
3
7
5
n-OC
2-OC
n-OC
2-OC
n-OC
n-OC
H
4
4
5
5
6
7
9
–
–
–
a
a
a
a
6
H
H
H
H
H
164
(3)
178
164
(3)
178
178
(<1)
–
–
–
–
–
–
–
9
7
11
11
13
15
(<1)
(<1)
a
a
8
178
(3)
178
(3)
a
a
9
107
(1)
107
(1)
–
–
–
–
192
192
(<1)
–
(<1)
–
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
221
(2)
123
(7)
–
–
137
(9)
122
(7)
–
–
–
a
a
OCH
C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
151
(44)
165
(45)
179
(15)
179
(25)
193
(7)
207
(5)
221
(3)
235
(2)
165
(43)
179
(38)
193
(17)
207
(7)
221
(5)
167
(26)
181
(6)
195
(3)
209
(1)
181
(36)
195
(7)
209
(4)
136
(3)
121
(<1)
123
(8)
137
(9)
151
(1)
151
(1)
165
(1)
–
–
–
–
–
–
123
(43)
137
(41)
151
(27)
165
(8)
179
(3)
–
–
–
–
–
–
–
–
153
(10)
167
(1)
181
(<1)
–
–
153
(25)
167
(44)
181
(8)
–
–
–
–
–
–
126
(4)
122
(71)
136
(3)
150
(1)
164
(<1)
164
(3)
–
150
(4)
164
(1)
178
(<1)
178
(<1)
–
–
–
–
–
3
2
2
2
2
2
2
2
2
5
5
5
5
5
5
5
5
–
138
(1)
a
a
a
a
a
a
OC
H
136
121
(3)
136
(30)
150
(11)
150
(<1)
164
(6)
121
(3)
2
5
(30)
136
(9)
136
(20)
136
(10)
136
(8)
n-OC
H
137
(9)
138
(50)
138
(11)
138
(100)
138
(100)
138
(100)
138
(100)
–
121
(2)
121
(6)
121
(2)
121
(1)
121
(1)
121
(1)
–
–
–
–
135
(1)
135
(2)
135
(<1)
135
(<1)
149
(<1)
–
–
–
–
–
3
7
i-OC
H
137
(14)
137
(11)
137
(7)
137
(8)
137
(8)
3
7
n-OC
n-OC
n-OC
n-OC
H
H
H
H
4
5
6
7
9
–
178
(3)
192
(3)
192
(<1)
206
(<1)
–
11
13
15
(2)
93
(2)
93
136
(7)
–
–
–
136
(5)
206
(3)
–
–
150
(5)
(1)
107
(<1)
107
(13)
107
(7)
107
(4)
107
(1)
95
(11)
95
(8)
95
(6)
95
(4)
109
(12)
109
(8)
109
(7)
109
(5)
123
(6)
123
(6)
123
(5)
–
a
a
OCH
n-C
n-C
n-C
n-C
n-C
H
–
–
150
(5)
–
–
150
122
(63)
136
(21)
108
(1)
121
(14)
–
164
(1)
178
(<1)
192
(<1)
206
(<1)
–
–
–
–
–
–
–
–
–
–
–
–
–
3
3
3
3
3
3
7
7
7
7
7
–
OC
H
H
H
H
H
151
(2)
151
(27)
151
(9)
151
(8)
139
(5)
139
(31)
139
(29)
139
(27)
153
(10)
153
(43)
153
(37)
153
(30)
167
(4)
167
(44)
167
(32)
123
(4)
–
152
(<1)
152
(45)
152
(100)
152
(100)
–
–
140
(7)
140
(14)
140
(12)
154
(1)
–
–
108
(76)
108
(60)
108
(89)
108
(25)
124
(6)
124
(6)
124
(5)
124
(4)
124
(30)
124
(30)
124
(26)
124
(22)
124
(23)
124
(27)
124
(25)
108
(8)
164
(3)
178
(1)
192
(1)
2
5
–
a
a
a
a
n-OC
n-OC
n-OC
H
H
H
134
(22)
134
(21)
134
(15)
106
(100)
106
(100)
106
(100)
106
(100)
120
(100)
120
(100)
120
(100)
120
(100)
134
(83)
134
(94)
134
(100)
106
(59)
106
(100)
106
(3)
150
(12)
164
(5)
149
(<1)
163
(<1)
–
–
123
(1)
137
(<1)
151
(<1)
165
(<1)
137
(1)
151
(<1)
165
(<1)
179
(<1)
151
(1)
165
(<1)
–
–
119
(8)
155
(3)
96
(40)
110
(16)
3
4
5
7
(12)
150
(7)
9
150
(5)
135
(1)
178
(3)
152
(<1)
–
206
(1)
11
a
a
SC
H
CH
CH
CH
CH
138
(1)
107
(25)
107
(22)
107
(25)
107
(41)
121
(30)
121
(23)
121
(26)
121
(43)
135
(21)
135
(18)
135
(24)
107
(12)
–
152
2
5
3
(<1)
–
n-SC
n-SC
n-SC
H
138
(<1)
138
(<1)
138
(<1)
3
4
5
7
3
3
3
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
H
9
H
11
–
a
a
a
a
SC
H
C
C
C
C
H
H
H
H
152
(7)
152
(7)
2
5
2
2
2
2
5
n-SC
n-SC
n-SC
H
H
H
152
(1)
154
(7)
166
(1)
3
4
5
7
5
5
5
–
–
–
–
–
–
–
–
152
(<1)
152
(<1)
166
(2)
154
(15)
154
(12)
168
(<1)
168
(6)
168
(14)
124
(2)
–
–
–
–
–
–
180
(1)
9
223
(1)
195
(18)
209
(5)
194
(<1)
152
(4)
11
SC
H
n-C
n-C
n-C
H
2
5
3
3
3
7
7
7
(28)
44
(27)
44
(25)
44
(98)
44
(59)
44
(100)
44
a
a
a
a
n-SC
H
H
H
H
166
(3)
166
(3)
3
4
7
–
–
–
–
–
–
n-SC
223
(2)
166
(1)
180
(1)
9
a
a
a
OC
H
CH
CH
CH
163
(19)
199
(35)
140
(20)
154
(19)
122
(100)
122
(<1)
122
(<1)
–
148
(6)
184
148
(6)
162
(1)
198
(3)
139
(2)
153
(2)
3
5
3
–
79
(<1)
79
(1)
93
a
OPh
108
(1)
109
(<1)
109
(16)
184
3
3
–
–
–
–
–
(10)
(10)
a
a
OCD
108
(<1)
–
125
(11)
125
(36)
125
(11)
139
(1)
3
3
OCD
C
H
–
–
2
5
–
–
–
(1)
(100)
a
Isobaric ions.

H. Saeidian et al. / International Journal of Mass Spectrometry 319–320 (2012) 9–16
15
Fig. 7. Proposed mechanism for formation of ions [E]/[Eꢀ].
of O-methyl-d3 N,N-dimethylamino methylphosphonates but it
was presented in spectrum of O-methyl-d3 N,N-dimethylamino
ethylphosphonates m/z 126. Direct cleavage of the P-alkyl bond
from the molecular ion led to ion [G]. Spectra of deuterated analogs
showed m/z 125 corresponding to this fragment. Subsequently, ion
[G] was fragmented to m/z 90 by elimination of alcohol/thiol from
ion [G]. It is interesting to note that, ion [G] could be comprised
of three possible resonance structures. Free energy difference
between structure (2) and (3) is low (1 kJ mol−1). However, the
free energy of structure (1) was calculated to be 54 and 56 kJ mol−1
higher than that structure (2) and (3) respectively. This revealed
relative preference of formation of resonating forms (2) and (3)
over (1) (Fig. 8).
Fragment ion [H] could be generated from the molecular ion
with the loss of alkyl on oxygen/sulfur atom and cleavage of the P-
alkyl bond. The product ion scan of ion [H] in mass spectrum of the
O-ethyl N,N-dimethylamino propylphosphonate (m/z 108, entry 20,
Table 2) revealed that it further fragmented to ions m/z 43, 44
and 65. Direct elimination of N,N-dimethylamino substituent from
the molecular ion gave fragment [I]. This particular fragmentation
was not common in alkylphosphonate analogs with larger O-alkyl
group (>C4); but it was observed for most of alkylphosphonothio-
lates. Despite of alkylphosphonothiolates (entries 24–34, Table 2)
cleavage of a methyl radical from N,N-dimethylamino group is a
common fragmentation mode which resulted ion [J] in the major-
ity of alkylphosphonates. Fragmentation of deuterated analogs also
showed this ion. Loss of N,N-dimethylamino group and alkyl on
oxygen/sulfur from the molecular ion were attributed to formation
of ion [K], which was observed in all the compounds. Formation
of ion [L]/[Lꢀ] took place by ␣-cleavage a hydrogen radical from
the molecular ion. Loss of hydrogen radical was possible by two
routes, first from the N,N-dimethylamino group and second from
the C H bond cleavage of the X-alkyl group. Thus [L] and [Lꢀ] were
isobaric. These ions were distinguished when the EI-MS of deuter-
ated analogs were recorded. Spectra of deuterated O-methyl-d3
N,N-dimethylamino methylphosphonates and O-methyl-d3 N,N-
dimethylamino ethylphosphonates showed only [M−H]+ (m/z 139
and m/z 153, respectively). This supported the loss of hydrogen
radical from the N,N-dimethylamino group. Furthermore the free
energy of structure [L] was calculated to be 100 kJ mol−1 lower than
[Lꢀ]. This clearly indicates preference of formation of structure [L]
over [Lꢀ].
Fig. 8. Possible resonance structures of [G].
the nerve gas sarin, except that it contains a P N instead of P
F
bond. Comparison of mass spectrometry data of them should be
useful for the identification and analysis of chemicals that are
relevant to the CWC. EI-MS of O-isopropyl N,N-dimethylamino
methylphosphonate shows some similarities and differences with
sarin. The most difference is the presence of M•+ with relative
moderate abundance in the mass spectrum of the O-isopropyl
N,N-dimethylamino methylphosphonate, but M•+ of sarin was not
observed in its mass spectrum. The elimination of an alkyl radical
via ␣-cleavage and P N cleavage were observed in all mass spectra
of O(S)-alkyl N,N-dimethylamino alkylphosphonates (alkylphos-
phonothiolates), while no corresponding P CH3 fragmentation and
P
F bond cleavage were observed in sarin. On the other hand, loss
of an allyl radical (M-C3H5) is demonstrated in the mass spectra of
O(S)-alkyl N,N-dimethylamino alkylphosphonates (alkylphospho-
nothiolates) and sarin that gave rise to the ions at m/z 124 and
99 respectively. Similarly, the McLafferty rearrangement of iso-
propyl moiety on oxygen was observed in the mass spectra of both
chemicals. It is interesting to note that, the second highest peak in
the spectrum of O-isopropyl N,N-dimethylamino methylphospho-
nate is ion at m/z 106 that generated by elimination of O-isopropyl
radical from molecular ion, while low relative intensity of cor-
responding fragment in mass spectrum of sarin (m/z 81) was
observed.
4. Conclusions
An improved process for microsynthesis of O(S)-alkyl N,N-
dimethylamino alkylphosphonates (alkylphosphonothiolates) and
their electron ionization mass spectrometric data were pre-
sented in this paper. The title chemicals synthesized under mild
conditions. GC retention indices as well as mass spectral data
with proposed fragmentation routes for 41 chemicals (3, 27
and 11 chemicals of N,N-dimethyl alkylphosphoramidic chlorides,
O-alkyl N,N-dimethylamino alkylphosphonates and S-alkyl N,N-
dimethylamino alkylphosphonothiolates, respectively) are also
Finally, it is worth to note that O-isopropyl N,N-dimethylamino
methylphosphonate (entry 4, Table 2) is structurally similar to

16
H. Saeidian et al. / International Journal of Mass Spectrometry 319–320 (2012) 9–16
given. These data could be useful for successful detection and iden-
tification of the CWC-related chemicals in real sample or during
OPCW proficiency tests.
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Appendix A. Supplementary data
[14] J.C. Ingram, A.D. Appelhans, G.S. Groenewold, Int. J. Mass Spectrom. Ion Pro-
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Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.ijms.2012.03.006.
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