Fragmentation of pyrazolecarbaldehyde thio- and dithioacetals under electron impact and chemical ionization

Article abstract of DOI:10.1134/S1070428011120116

The mass spectra of 1-substituted 3,5-dimethyl-1H-pyrazole-4-carbaldehyde bis(2-hydroxyethyl) dithioacetals and thioacetals were studied for the first time. The main fragmentation pathways of their molecular ions generated under electron impact and chemic

Full text of DOI:10.1134/S1070428011120116

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2011, Vol. 47, No. 12, pp. 1851–1858. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © L.V. Klyba, L.K. Papernaya, E.R. Sanzheeva, A.A. Shatrova, E.V. Rudyakova, G.G. Levkovskaya, 2011, published in Zhurnal
Organicheskoi Khimii, 2011, Vol. 47, No. 12, pp. 1813–1822.
Dedicated to Full Member of the Russian Academy of Sciences
M.G. Voronkov on his 90th anniversary
Fragmentation of Pyrazolecarbaldehyde Thio- and Dithioacetals
under Electron Impact and Chemical Ionization
L. V. Klyba, L. K. Papernaya, E. R. Sanzheeva, A. A. Shatrova,
E. V. Rudyakova, and G. G. Levkovskaya
Favorskii Irkutsk Institute of Chemistry, Siberian Division, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
e-mail: papern@irioch.irk.ru
Received June 6, 2011
Abstract—The mass spectra of 1-substituted 3,5-dimethyl-1H-pyrazole-4-carbaldehyde bis(2-hydroxyethyl)
dithioacetals and thioacetals were studied for the first time. The main fragmentation pathways of their
molecular ions generated under electron impact and chemical ionization were similar. Primary decomposition
of the molecular ions of bis(2-hydroxyethyl) dithioacetals involves elimination of 2-sulfanylethanol molecule
with formation of the corresponding 1,3-oxathiolane radical cation. Fragmentation of the molecular ions [M]+ ·
and [M + H]+ derived from 2-(3,5-dimethyl-1H-pyrazol-4-yl)-1,4,6-oxadithiocanes includes cleavage of the
eight-membered heteroring and elimination of C4H9OS·. Substituents in the heteroring of pyrazolecarbalde-
hydes inhibit decomposition processes related to the aldehyde group.
DOI: 10.1134/S1070428011120116
Compounds containing a pyrazole fragment are
used as components of many medicines possessing
anti-inflammatory, antidiabetic, analgesic, and other
kinds of pharmacological activity [1, 2]. In addition,
they are highly effective pesticides, in particular
insectoacaricides [3], and are successfully used in the
synthesis of coordination compounds as efficient cata-
lysts [4]. Therefore, pyrazole derivatives attract strong
interest. Pyrazolecarbaldehydes open wide prospects in
further modification and synthesis of pyrazole deriva-
tives which could exhibit biological activity and be
useful as dyes, fluorophores, etc. From the viewpoint
of practical application of pyrazole derivatives in
human activity, of particular importance is their iden-
tification by instrumental methods which could ensure
reliable determination of their concentration in various
media.
In continuation of our studies in the field of synthe-
sis and properties of functionalized pyrazoles, in the
present work we examined the behavior of previously
unknown pyrazolylcarbaldehyde bis(2-hydroxyethyl)
dithioacetals Ia–Ie, pyrazolyl-substituted 1,4,6-oxadi-
thiocanes IIa–IIe and 1,3-oxathiolanes IIIa–IIIe, and
pyrazolecarbaldehydes IVa–IVe under electron impact
(EI) and chemical ionization with a view to reveal
analytical ions ensuring their reliable mass spectro-
metric identification. The complete mass spectra (EI)
of all compounds I–IV are given in Table 1.
The presence in molecules I and II of a labile
dithioacetal functionality in addition to a pyrazole ring
makes them interesting models for both chemical and
mass spectrometric studies. Moreover, these com-
pounds may equally be regarded as functionally substi-
tuted pyrazoles and dithioacetals derived from 2-sul-
fanylethanol and the corresponding pyrazolecarbalde-
hyde. Therefore, their fragmentation under electron
O
OH
S
S
S
RCHO
OH
O
R
R
S
S
R
Ia–Ie
IIa–IIe
IIIa–IIIe
IVa–IVe
Me
R =
;
N
Me
N
X
X = Me (a), Pr (b), i-Pr (c), CH2=CHCH2 (d), PhCH2 (e).
1851

KLYBA et al.
1852
Table 1. Complete electron impact mass spectra of pyrazolecarbaldehyde bis(2-hydroxyethyl) dithioacetals Ia–Ie, pyrazolyl-
substituted 1,4,6-oxadithiocanes IIa–IIe and 1,3-oxathiolanes IIIa–IIIe, and pyrazolecarbaldehydes IVa–IVe
Compound
m/z (Irel, %)a
no.
276 (<1) [M]+ ·, 277 (<1) [M + 1]+, 199 (9), 198 (32), 197 (4), 156 (7), 153 (7), 147 (6), 144 (4), 143 (4), 141
Ia
(7), 139 (22), 138 (51), 137 (100),123 (5), 111 (3), 110 (3), 109 (5), 82 (4), 81 (3), 79 (4), 78 (12), 69 (3), 68
(3), 67 (5), 66 (14), 65 (7), 63 (3), 62 (3), 61 (8), 60 (32), 59 (18), 58 (7), 57 (4), 56 (33), 55 (4), 54 (4), 53 (6),
52 (4), 50 (3), 49 (3), 48 (15), 47 (24), 46 (12), 45 (34), 44 (10)
304 (<1) [M]+·, 305 (6) [M + 1]+, 229 (6), 228 (15), 227 (100), 226 (38), 225 (9), 183 (5), 181 (6), 167 (19), 166
Ib
(19), 165 (14), 151 (22), 139 (8), 138 (17), 137 (37), 125 (8), 124 (52), 123 (38), 110 (3), 109 (7), 97 (7), 89
(6), 82 (8), 80 (5), 78 (7), 68 (3), 67 (4), 66 (3), 65 (4), 61 (13), 60 (21), 59 (12), 58 (3), 54 (3), 53 (3), 52 (3),
48 (10), 47 (16), 46 (5), 45 (19), 44 (5)
304 (<1) [M]+·, 305 (9) [M + 1]+, 228 (14), 227 (100), 226 (18), 225 (6), 185 (10), 181 (4), 167 (8), 166 (11),
Ic
165 (7), 151 (18), 141 (4), 139 (7), 138 (3), 137 (3), 125 (5), 124 (21), 123 (28), 109 (9), 97 (7), 89 (6), 82 (3),
78 (7), 68 (3), 67 (3), 66 (3), 65 (3), 61 (10), 60 (8), 59 (9), 52 (3), 48 (4), 47 (9), 46 (4), 45 (22)
302 (<1) [M]+·, 303 (1) [M + 1]+, 227 (4), 226 (12), 225 (72), 224 (63), 223 (11), 181 (5), 180 (2), 179 (9), 166
Id
(3), 165 (32), 164 (71), 163 (100), 150 (3), 149 (27), 147 (5), 139 (3)138 (3), 137 (15), 136 (6), 135 (16), 124
(3), 123 (18), 122 (9), 121 (10), 120 (3), 119 (3), 118 (3), 109 (8), 108 (6), 107 (3), 106 (3), 97 (4), 95 (8), 94
(11), 93 (3), 92 (3), 89 (5), 82 (7), 81 (7), 80 (7), 79 (4), 78 (12), 77 (4), 69 (3), 68 (5), 67 (8), 66 (7), 65 (8),
63 (3), 62 (3), 61 (16), 60 (37), 59 (22), 58 (5), 57 (3), 56 (7), 55 (9), 54 (6), 53 (6), 52 (5), 51 (4), 49 (3), 48
(16), 47 (26), 46 (9), 46 (34), 44 (8)
352 (<1) [M]+·, 276 (4), 275 (84), 274 (100), 273 (7), 230 (6), 229 (6), 215 (11), 214 (56), 213 (75), 200 (4),
Ie
199 (29), 197 (3), 186 (4), 185 (29), 171 (3), 137 (5), 123 (5), 122 (5), 92 (9), 91 (100), 89 (10), 82 (3), 78
(13), 77 (3), 66 (4), 65 (28), 63 (5), 61 (14), 60 (8), 59 (11), 58 (3), 55 (3), 52 (3), 51 (6), 48 (4), 47 (8), 46 (3),
45 (18), 43 (3)
260 (2) [M + 2]+·, 259 (9) [M + 1]+, 258 (10) [M]+·, 156 (5), 155 (7), 154 (100), 153 (45), 139 (4), 138 (3), 137
IIa
(5), 123 (5), 111 (2), 109 (3), 91 (4), 80 (2), 66 (4), 56 (6)
289 (3), 288 (5) [M + 2] +·, 287 (21) [M + 1]+, 286 (9) [M]+·, 184 (5), 183 (9), 182 (100), 181 (11), 167 (15), 154
IIb
(5), 153 (4), 152 (4), 151 (3), 149 (10), 141 (4), 140 (9), 139 (17), 124 (4), 123 (4), 109 (4), 97 (4),
89 (3)
288 (5) [M + 2] +·, 287 (21) [M + 1]+, 286 (8) [M]+·, 184 (4), 183 (8), 182 (100), 181 (9), 167 (13), 149 (10),
IIc
140 (9), 139 (16), 123 (5), 109 (3)
286 (3) [M + 2] +·, 285 (16) [M + 1]+, 284 (10) [M]+·, 182 (5), 181 (15), 180 (100), 179 (23), 165 (7), 153 (7),
IId
152 (4), 147 (30), 139 (5), 138 (6), 106 (3), 89 (3), 80 (2), 59 (3)
335 (7) [M + 1]+, 334 (3) [M]+ ·, 232 (5), 231 (17), 230 (100), 229 (23), 215 (7), 214 (3), 199 (5), 197 (8), 185
IIe
(3), 1677 (3), 156 (4), 139 (3), 92 (4), 91 (42), 65 (3)
199 (11) [M + 1]+, 198 (18) [M]+·, 163 (11), 153 (2), 139 (5), 138 (92), 137 (100), 110 (5), 99 (3), 85 (12), 83
IIIa
(11), 82 (10), 80 (3), 79 (3), 69 (4), 66 (21), 65 (6), 60 (10), 59 (10), 53 (4), 49 (3), 48 (5), 47 (28), 46 (7),
45 (5)
227 (8) [M + 1]+, 226 (60) [M]+·, 181 (12), 167 (16), 166 (43), 165 (14), 152 (5), 151 (57), 140 (3), 139 (10),
IIIb
138 (8), 137 (7), 125 (11), 124 (51), 123 (100), 114 (3), 96 (6), 95 (7), 83 (4), 82 (13), 81 (6), 80 (13), 69 (4),
68 (7), 59 (10), 57 (3), 56 (3), 55 (3), 54 (3, 53 (3), 52 (3), 51 (4)
227 (6) [M + 1]+, 226 (36) [M]+·, 225 (7), 211 (3), 181 (5), 167 (19), 166 (61), 165 (14), 152 (7), 151 (53), 138
IIIc
(8), 137 (11), 125 (11), 124 (58), 123 (100), 109 (3), 108 (3), 94 (4), 82 (8), 65 (6), 61 (5), 60 (6), 59 (7), 58
(5), 45 (8)
225 (9) [M + 1]+, 224 (28) [M]+·, 223 (5), 179 (11), 165 (29), 164 (49), 163 (91), 149 (20), 137 (14), 136 (4),
IIId
135 (12), 123 (20), 122 (9), 121 (8), 120 (7), 108 (6), 94 (11), 82 (11), 80 (12), 79 (6), 78 (4), 68 (4), 67 (6),
66 (12), 65 (10), 60 (10), 59 (9), 58 (8), 57 (3), 56 (5), 55 (4), 54 (5)
275 (6) [M + 1]+, 274 (17) [M]+·, 273 (3), 215 (15), 214 (21), 213 (38), 200 (3), 199 (32), 186 (4), 185 (15), 171
IIIe
(6), 151 (3), 144 (3), 137 (3), 123 (3), 122 (4), 92 (8), 91 (100), 65 (27), 63 (5), 60 (12)
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 12 2011

FRAGMENTATION OF PYRAZOLECARBALDEHYDE THIO- AND DITHIOACETALS
Table 1. (Contd.)
1853
Compound
no.
m/z (Irel, %)a
138 (55) [M]+·, 137 (100) [M – 1]+, 85 (9), 84 (4), 83 (33), 82 (7), 81 (5), 79 (5), 68 (3), 67 (3), 66 (4), 65 (3),
59 (4), 56 (12), 49 (4), 48 (5), 47 (6), 47 (7)
167 (7) [M + 1]+, 166 (66) [M]+·, 165 (4), 164 (7), 152 (5), 151 (34), 138 (4), 137 (5), 125 (12), 124 (27), 123
(100), 96 (4), 95 (7), 85 (10), 83 (27), 82 (4), 81 (3), 67 (7), 65 (5), 54 (5), 48 (7), 47 (8)
IVa
IVb
IVc
167 (7) [M + 1]+, 166 (93) [M]+·, 165 (5), 152 (3), 151 (58), 138 (5), 136 (3), 126 (3), 125 (5), 124 (38), 123
(100), 110 (3), 97 (3), 96 (4), 85 (20), 83 (32), 82 (4), 76 (3), 68 (10), 67 (9), 66 (8), 65 (6), 54 (8), 49 (10),
48 (9)
165 (22) [M + 1]+, 164 (100) [M]+·, 163 (89), 149 (11), 137 (17), 136 (4), 135 (13), 124 (4), 123 (26), 122 (7),
121 (8), 109 (5), 108 (8), 106 (3), 95 (8), 94 (13), 93 (3), 82 (14), 81 (7), 80 (8), 69 (9), 68 (8), 67 (10), 65
(13), 56 (5), 55 (4), 54 (5), 53 (3)
216 (5) [M + 2]+, 215 (29) [M + 1]+, 214 (84) [M]+·, 213 (37) [M – 1]+, 200 (5), 199 (39), 186 (5), 185 (16), 172
IVd
IVe
(2), 171 (8), 158 (5), 145 (5), 137 (5), 124 (6), 123 (5), 107 (3), 92 (8), 91 (100), 89 (4), 65 (26)
a
Ion peaks with a relative intensity of less than 3% were omitted.
impact can follow pathways typical of both classes of
compounds or take a quite different pathway.
acetals [7]. The molecular ion decomposes in statu
nascendi via cleavage of the acetal C–S bond with
elimination of C2H5S· radical or C2H6OS molecule
(Scheme 2). The [M – C2H5OS]+ ion can have structure
A or A′, and the [M – C2H6OS]+· radical cation, struc-
ture B or B′. Further decomposition of these ions
involves expulsion of sulfur-containing radical C2H5S·
with formation of ions C and D (Table 2). This frag-
mentation path is energetically favorable if the [M –
C2H6OS]+ · ion has the structure of 1,3-oxathiolane
radical cation B and [M – C2H5OS]+ is protonated
1,3-oxathiolane A.
The total ion chromatograms of dithioacetals Ia–Ie
(injector, interface, and ion source temperatures were
equal to 200°C) contained four peaks. The mass spec-
trum of the first peak (m/z 78) matched the reference
spectrum of 2-sulfanylethanol (V) [5]. The mass spec-
trum of the second peak was typical of the correspond-
ing pyrazolecarbaldehyde IV. The other two peaks
with different retention times but the same molecular
weight were assigned to 1,3-oxathiolanes III. Presum-
ably, bis(2-hydroxyethyl) dithioacetals Ia–Ie under-
went partial thermal decomposition upon chromatog-
raphy (Scheme 1). It should be noted that thermolysis
of bis(2-hydroxyethyl) dithioacetal Ia–Ie with forma-
tion of pyrazolecarbaldehyde and 2-sulfanylethanol is
a reverse process to their formation in solution [6].
In the electron impact mass spectra of compounds
Ia–Ie introduced directly into the ion source, the
intensity of the molecular ion peaks was less than 1%.
An exception was compound Ib which displayed in the
mass spectrum a weak [M + H]+ peak with m/z 305
(6%). The primary fragmentation of bis(2-hydroxy-
ethyl) dithioacetals Ia–Ie follows a path typical of
The above assumption was confirmed by studying
the mass spectra of 1,3-oxathiolanes IIIa–IIIe. These
compounds under electron impact displayed strong
molecular ion peaks (Table 1, Scheme 3), which is typ-
ical of 2-aryl-1,3-oxathiolanes and oxathianes [8, 9]. In
the fragmentation of unsubstituted 1,3-oxathiolane,
its 2-alkyl derivatives, and 1,3-oxathiane, the charge
resides mainly on sulfur-containing fragments. There-
fore, [M – CHO]+, [M – CH2O]+·, and [HCS]+ ions are
the most abundant. By contrast, the main fragmenta-
tion pathway of pyrazolyl-substituted 1,3-oxathiolanes
IIIa–IIIe is elimination of sulfur-containing fragment
Scheme 1.
S
OH
OH
+
HS
HS
O
OH
R
S
≥150°C
IIIa–IIIe
V
V
OH
R
S
RCHO
+ 2
Ia–Ie
IVa–IVe
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KLYBA et al.
1854
Table 2. Principal ions in the electron impact mass spectra of pyrazolecarbaldehyde bis(2-hydroxyethyl) dithioacetals Ia–Ie
m/z (Irel, %)
Ion
Ia
Ib
Ic
Id
Ie
M+
276 (<1)
277 (<1)
199 (9)
304 (<1)
305 (6)
304 (<1)
305 (9)
227 (100)
226 (18)
166 (11)
165 (7)
137 (3)
000 (6)
000 (7)
000 (8)
00 (10)
302 (<1)
303 (1)
352 (<1)
353 (–)
[M + H]+
[M – C2H5OS]+, A, A′
[M – C2H6OS]+, B, B′
[A – C2H5S] +·, C
[B – C2H5S]+, D
[R]+
[C3H5 OS]+, m/z 89
[C2H6OS]+ ·, m/z 78
[C3H4S]+ ·, m/z 60
[C2H5S]+, m/z 61
227 (100)
226 (38)
166 (19)
165 (14)
137 (37)
000 0(6)
000 0(7)
000 (21)
000 (13)
225 (72)
224 (63)
164 (71)
163 (100)
135 (16)
000 0(5)
000 (12)
000 (37)
000 (16)
275 (84)
274 (100)
214 (56)
213 (75)
185 (29)
000 (10)
000 (13)
0000 (8)
000 (14)
198 (33)
138 (51)
137 (100)
109 (5)
000 (1)
000 (12)
000 (32)
000 (8)
from [M]+· with formation of [M – C2H4S]+· radical
cation (C, Scheme 3). Analogous pattern was observed
for fragmentation of nitrobenzaldehyde thioacetals [6].
It should be noted that introduction of a strong elec-
tron-withdrawing substituent dramatically reduced the
stability of the molecular ion, and the corresponding
peak was almost not observed in the mass spectra.
molecular ion [M]+· of 1,3-oxathiolanes IIIa–IIIe with
formation of [M – C2H5O]+ ion (E) is a minor pathway.
Presumably, the reason is higher electronegativity of
the oxygen atom.
Thus the electron impact mass spectra of bis(2-hy-
droxyethyl) ditihoacetals Ia–Ie (upon direct sample ad-
mission into the ion source) completely coincide with
the spectra of the corresponding 1,3-oxathiolanes IIIa–
IIIe. This indicates that primary fragmentation of the
molecular ion of Ia–Ie gives rise to 1,3-oxathiolane
radical cation via elimination of C2H6OS molecule.
Further decomposition pattern of ion C completely
coincides with that typical of the molecular ions of
pyrazolecarbaldehydes IVa–IVe (see below). Elimina-
tion of oxygen-containing fragment C2H5O· from the
Scheme 2.
R
SC2H4OH
H
A'
+·
[C2H6OS]
m/z 78
·
–C2H5OS
+·
O
S
·
·
–C2H5S
R
R
H
O
H
R
R
+·
OH
A
C
S
+·
OH
S
R
S
C
O
Ia–Ie, M+·
–C2H5S
O
B
D
–C2H6OS
+·
[R–C
≡
SC2H4OH]
B'
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 12 2011

FRAGMENTATION OF PYRAZOLECARBALDEHYDE THIO- AND DITHIOACETALS
1855
Scheme 3.
latter has the structure of protonated pyrazolecarbalde-
+·
hyde IVa–IVe (Scheme 5).
+·
O
S
R
C
S
·
Scheme 5.
–C2H4O
–C2H4S
R
H
O
R
S
S
CH5
E
IIIa–IIIe, M+·
C
R
OH
–CH4
–C2H4S
O
O
R
R
H
m/z 153 (2)
181 (12)
181 (5)
198 (18)
226 (60)
226 (36)
224 (28)
274 (17)
138 (92) (a)
166 (43) (b)
166 (61) (c)
164 (49) (d)
214 (21) (e)
IIIa–IIIe
F
179 (11)
229 (–)
The two other fragment ions with m/z 89 and 61
(Table 4) can be formed as a result of decomposition
of [M + H]+ or ionization via anion abstraction
(Scheme 6).
The chemical ionization mass spectra of bis(2-hy-
droxyethyl) dithioacetals Ia–Ie were also very similar
to the positive ion chemical ionization (PICI) spectra
of 1,3-oxathiolanes IIIa–IIIe. As under electron im-
pact, expulsion of 2-sulfanylethanol molecule (V) from
the molecular ion of bis(2-hydroxyethyl) dithioacetal
Ia–Ie gives the corresponding protonated 1,3-oxathio-
lane IIIa–IIIe (Scheme 4, Table 3).
Scheme 6.
S
S
or
+ HR + CH4
O
O
S
CH5
m/z 89
O
R
C2H5S+
+
RCHO + CH4
IIIa–IIIe
Scheme 4.
m/z 61
OH
S
S
CH5
Apart from the above ions, the PICI mass spectra
contained fairly intense peaks of cluster ions [M +
C2H5]+ and [M + C3H5]+ formed by electrophilic addi-
tion. These ions, as well as [M + H]+, readily lose
C2H4S molecule, yielding two important characteristic
ions [(M + C2H5) – C2H4S]+ and [(M + C3H5) – C2H4S]+
(Tables 3, 4).
OH
–C2H6OS
O
R
S
R
H
Ia–Ie
+
HSCH2CH2OH + CH4
V
In the PICI spectra of 1,3-oxathiolanes IIIa–IIIe
the molecular ions [M + H]+ are fairly abundant
(Table 4). The most typical fragmentation pathway (as
under electron impact) involves elimination of C2H4S
molecule with formation of ion F. Most probably, the
We can conclude that the main fragmentation path-
ways of the molecular ions of pyrazolecarbaldehyde
dithioacetals I and pyrazolyl-substituted 1,3-oxathio-
lanes III under electron impact and chemical ioniza-
Table 3. Positive ion chemical ionization mass spectra of pyrazolecarbaldehyde bis(2-hydroxyethyl) dithioacetals Ia–Ie
(reactant gas methane)
m/z (Irel, %)
Ion
Ia
Ib
Ica
Id
Ieb
[M – C2H5OS]+, A
[A + C2H5]+
[A + C3H5]+
[(A + C2H5) – C2H4S]+
[(A + C3H5) – C2H4S]+
[A – C2H4S]+
199 (73)
227 (12)
239 (5)
227 (100)
255 (15)
267 (5)
227 (85)
255 (10)
267 (2)
225 (100)
253 (12)
265 (4)
275 (20)
303 (2)
315 (–)
243 (20)
255 (2)
215 (100)
–
167 (25)
179 (5)
195 (15)
207 (3)
195 (20)
207 (5)
193 (12)
205 (4)
139 (100)
000 (13)
000 (20)
167 (55)
000 (10)
000 (8)
167 (100)
000 (15)
000 (18)
165 (80)
000 (15)
000 (12)
[C3H5OS], m/z 89
[C2H5OS], m/z 61
000 (25)
a
m/z 125 (3) [(A – C2H4S) – C3H6]+ (Ic).
b
m/z 91 (17) [C7H7]+, 119 (5) [C7H7N2]+ (Ie).
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KLYBA et al.
1856
Table 4. Positive ion chemical ionization mass spectra of 2-pyrazolyl-1,3-oxathiolanes IIIa–IIIe (reactant gas methane)
m/z (Irel, %)
Ion
IIIa
IIIb
IIIc
IIId
IIIe
M+·
198 (6)
226 (2)
227 (12)
255 (3)
267 (1)
195 (11)
207 (4)
167 (100)
000 (3)
000 (18)
226 (8)
224 (5)
274 (3)
275 (21)
303 (3)
315 (1)
243 (15)
255 (4)
215 (100)
000 (4)
000 (17)
[M + H]+
199 (77)
227 (7)
227 (65)
255 (9)
225 (61)
253 (10)
265 (3)
[M + C2H5]+
[M + C3H5]+
[(M + C2H5) – C2H4S]+
[(M + C3H5) – C2H4S]+
[(M + H) – C2H4S]+
[C3H5OS]+, m/z 89
[C2H5S]+, m/z 61
239 (4)
267 (3)
167 (11)
179 (3)
195 (12)
207 (4)
193 (12)
205 (4)
139 (100)
000 (12)
000 (15)
167 (100)
000 (13)
000 (17)
165 (100)
000 (13)
000 (19)
Table 5. Positive ion chemical ionization mass spectra of pyrazolecarbaldehydes IVa–IVe (reactant gas methane)
m/z (Irel, %)
Ion
IVa
IVb
IVc
IVd
IVe
M+·
138 (6)
139 (100)
167 (15)
179 (4)
111 (3)
166 (5)
166 (6)
164 (10)
165 (100)
193 (16)
205 (5)
214 (15)
215 (100)
243 (12)
255 (4)
–
[M + H]+
[M + C2H5]+
[M + C3H5]+
[M – CHO]+
167 (100)
195 (13)
207 (4)
167 (100)
195 (17)
207 (6)
125 (3)
125 (5)
137 (4)
tion are similar. In both cases, the molecular ions of
bis(2-hydroxyethyl) dithioacetals I are unstable, and
they rapidly decompose to give the corresponding
1,3-oxathiolane III radical cation. There exists strong
analogy between thermal decomposition of compounds
Ia–Ie and IIIa–IIIe and fragmentation of their molec-
ular ions under mass spectrometric analysis.
peak was observed in the spectrum of IVe. The mass
spectra (EI) of IVa–IVe lacked [M – CHO]+ ion peak.
In addition, aldehydes IVa–IVe displayed in the PICI
spectra peaks from [M + H]+ ions (100%) and fairly
intense peaks from cluster ions [M + Alk]+. Thus sub-
stituents in the heteroring of aldehydes IVa–IVe inhibit
fragmentation processes typical of alicyclic aldehydes.
Pyrazolecarbaldehydes IVa–IVe displayed in the
electron impact mass spectra a strong peak from the
molecular ion (Table 1), which is typical of com-
pounds containing an aromatic ring [9]. The main
fragmentation pathway is determined by the presence
of a heteroaromatic ring and is related to cleavage of
C–C and C–N bonds with formation of [M – Me]+ and
[M – X]+ ions. As might be expected, compound IVd
decomposes mainly following a path typical of alkyl-
benzenes [9], and the base peak in the spectrum is that
corresponding to [C7H7]+ (m/z 91).
Unlike bis(2-hydroxyethyl) dithioacetals Ia–Ie, the
electron impact mass spectra of pyrazolyl-substituted
oxadithiocanes IIa–IIe contained weak molecular ion
peaks (Irel 3–10%, Table 1) and [M + H]+ peaks (Irel 7–
Scheme 7.
+·
O
S
R
C
S
·
·
–C4H9OS
–CS
S
R
IIa–IIe, M+·
G
R+
Pyrazolecarbaldehydes IVa–IVe readily undergo
protonation in the gas phase. In their chemical ioniza-
tion mass spectra (reactant gas methane) peaks of
protonated molecular ions have the maximal intensity
(Table 5). The PICI mass spectra of IVa–IVd con-
tained the only fragment ion peak [M – CHO]+; no such
OH
S
+·
[RCHS]
–C4H9OS
–HCS
S
R
M + H+
H
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 12 2011

FRAGMENTATION OF PYRAZOLECARBALDEHYDE THIO- AND DITHIOACETALS
1857
21%, Table 1). The latter are likely to appear due to the
presence of traces of water in the ion source. The main
fragmentation pathway of [M]+· and [M + H]+ is cleav-
age of the eight-membered heteroring with elimina-
tion of C4H9OS · and formation of ions G and H
(Scheme 7). This pattern is typical of 1,3-diselenanes
of the thiophene series [10] but is different from the
decomposition of 1,4,6-oxadithiocane which mainly
loses H2S2 species (Scheme 8) [11].
peaks formed as a result of electrophilic addition and
peaks of ions arising from elimination of C2H4S mole-
cule from the above ions (Table 6).
Scheme 10.
O
CH5
+·
S
M + H
–CH4
S
R
IIa–IIe
100%
S
+·
Scheme 8.
S
H
+·
O
Me
H
·
CH3
+
+·
[M – H2S2]
·
–C4H9OS
·
–X
S
Me
N
Me
N
N
X
N
H
S
m/z 150 (3)
m/z 84 (100)
We can conclude that a combination of chemical
ionization and electron impact mass spectra ensures
more reliable determination of molecular weight and
structure of compounds under study and increases the
validity of their identification.
It is known that elimination of HS· and HS2· radicals
is characteristic of fragmentation of all 2-aryl-1,3-di-
thianes [8]. The presence of a heteroaromatic ring in
molecules IIa–IIe completely suppresses these proc-
esses, as well as elimination of H2S2; however, charac-
teristic is the second series of ions arising from expul-
sion of the X substituent from the pyrazole ring in ion
H (Scheme 9, Table 1)
EXPERIMENTAL
Pyrazolecarbaldehyde bis(2-hydroxyethyl) dithio-
acetals Ia–Ie were obtained by dehydrochlorination
with aqueous ammonia of the corresponding dithio-
acetal salts synthesized from pyrazolecarbaldehydes
and 2-sulfanylethanol at a ratio of 1:2 [12]. Pyrazolyl-
1,4,6-oxadithiocanes IIa–IIe were synthesized by
reaction of aldehydes IVa–IVe with 2,2′-oxydiethane-
thiol at room temperature according to the procedure
described in [12]. 2-Pyrazolyl-1,3-oxathiolanes IIIa–
IIIe were isolated by column chromatography (silica
gel, 0.060–0.2 mm; diethyl ether–methanol, 25:1)
from the reaction mixtures obtained by reaction of
pyrazolecarbaldehydes with an equimolar amount of
2-sulfanylethanol in the presence of Me3SiCl. Alde-
hydes IVa–IVe were synthesized by Vilsmeier–Haack
formylation [13] of the corresponding 1,3,5-trisubsti-
tuted pyrazoles which were prepared in turn by alkyla-
tion of 3,5-dimethyl-1H-pyrazole with alkyl halides,
allyl bromide, and benzyl chloride under the conditions
reported for alkylation of indoles [14].
Scheme 9.
+·
S
S
H
N
Me
H
·
–X
Me
N
Me
N
X
N
H
H
J
Analogous channels of decomposition of the mo-
lecular ions of 5-pyrazolyl-substituted 1,4,6-oxadi-
thiocanes IIa–IIe were also observed upon chemical
ionization using methane as reactant gas. Unlike
chemical ionization mass spectra of bis(2-hydroxy-
ethyl) dithioacetals Ia–Ie, the base peak in the spectra
of compounds IIa–IIe was that corresponding to the
protonated molecular ion. The latter then decomposes
via elimination of C4H9OS· radical with formation of
odd-electron pyrazolecarbothialdehyde ion, which is
quite untypical of chemical ionization. The subsequent
fragmentation of pyrazolecarbothialdehyde ion follows
general relations found for five-membered heteroaro-
matic structures [9] (Scheme 10).
The electron impact mass spectra were recorded on
a Shimadzu QP-5050A mass spectrometer (quadrupole
mass analyzer, a.m.u. range 34–650 D). Samples were
introduced using a DI-50 direct inlet probe. The ion
source and direct inlet probe temperatures were select-
ed to ensure high-quality mass spectrum and avoid
thermal decomposition of the substrate. Chromato-
In addition, the PICI spectra of all oxadithiocanes
IIa–IIe contained [M + C2H5]+ and [M + C3H5]+ ion
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 12 2011

KLYBA et al.
1858
Table 6. Positive ion chemical ionization mass spectra of 5-pyrazolyl-1,4,6-oxadithiocanes IIa–IIe (reactant gas methane)
m/z (Irel, %)
Ion
IIa
IIb
IIc
IId
IIe
[M + H]+
259 (100)
287 (24)
299 (7)
227 (5)
199 (3)
154 (15)
000 (–)
139 (4)
287 (100)
315 (21)
327 (6)
287 (100)
315 (20)
327 (7)
285 (100)
313 (20)
325 (8)
335 (100)
363 (20)
375 (8)
303 (2)
275 (5)
230 (20)
000 (8)
215 (7)
[M + C2H5]+
[M + C3H5]+
[(M + C2H5) – C2H4S]+
[(M + H) – C2H4S]+·
[(M + H) – C4H9OS]+.
[C5H9OS2]+ ·, m/z 149
[(M + H) – C4H9OS – Me]+
255 (4)
255 (5)
253 (1)
227 (1)
227 (1)
225 (1)
182 (22)
000 (12)
167 (15)
182 (20)
000 (10)
167 (13)
180 (15)
000 (15)
165 (7)
7. Budzikiewicz, H., Djerassi, C., and Williams, D.H.,
Mass Spectrometry of Organic Compounds, San
Francisco: Holden-Day, 1967.
graphic separation was performed using an SPB-5
capillary column (60 m×0.25 mm×0.25 μm), carrier
gas helium, flow rate 0.7 ml/min, inlet pressure
280 kPa, split ratio 1:2; injector temperature 250°C,
ion source temperature 200°C, oven temperature pro-
gramming from 60 to 250°C at a rate of 10 deg/min.
8. Pasto, D.J., J. Heterocycl. Chem., 1969, vol. 6, p. 175;
Bowie, J.H. and White, P.Y., Org. Mass Spectrom.,
1972, vol. 6, p. 317; Bowie, J.H., White, P.Y., and
Blumenthal, T., Org. Mass Spectrom., 1987, vol. 22,
p. 541; Bowie, J.H. and White, P.Y., Org. Mass Spec-
trom., 1969, vol. 2, p. 611.
The chemical ionization mass spectra (positive ion
detection) were obtained on an Agilent 5975C instru-
ment using methane as reactant gas. Samples were
introduced through an Agilent 6890N chromatograph
(HP-5MS capillary column, 30 m×0.25 mm×0.25 μm;
carrier gas helium, constant flow rate).
9. Zaikin, V.G., Varlamov, A.V., Mikaya, A.I., and Prosta-
kov, N.S., Osnovy mass-spektrometrii organicheskikh
soedinenii (Principles of Mass Spectrometry of Organic
Compounds), Moscow: MAIK, 2001, p. 286; Budzikie-
wicz, H., Djerassi, C., and Williams, D.H., Interpreta-
tion of Mass Spectra of Organic Compounds, San
Francisco: Holden-Day, 1964.
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 10-03-00256a).
10. Papernaya, L.K., Levanova, E.P., Sukhomazova, E.N.,
Albanov, A.I., Klyba, L.V., and Deryagina, E.N., Russ.
J. Org. Chem., 2004, vol. 40, p. 441; Papernaya, L.K.,
Levanova, E.P., Sukhomazova, E.N., Klyba, L.V., Zhan-
chipova, E.R., Albanov, A.I., Korchevin, N.A., and
Deryagina, E.N., Russ. J. Gen. Chem., 2006, vol. 76,
p. 1123.
REFERENCES
1. Elguero, J., Goya, P., Jagerovic, N., and Silva, A.M.S.,
Targets in Heterocyclic Systems. Chemistry and Prop-
erties, Attanasi, O.A. and Spinelli, D., Eds., Rome: Italian
Soc. Chem., 2002, vol. 6, p. 53.
11. Lee, J.-H., Jeong, H.J., Jin, C.K., Jang, C.H.,
Kim, M.K., Yoon, Y.-J., and Lee, S.-G., Bull. Korean
Chem. Soc., 2005, vol. 26, p. 811.
2. Katrizky, A.R., Wang, M., Zhang, S., Voronkov, M.V.,
and Steel, P.J., J. Org. Chem., 2001, vol. 66, p. 6787.
3. Grapov, A.F., Usp. Khim., 1999, vol. 68, p. 773.
12. Papernaya, L.K., Shatrova, A.A., Albanov, A.I., Rudya-
kova, E.V., and Levkovskaya, G.G., Russ. J. Org. Chem.,
2011, vol. 47, p. 468.
4. Sonley, M.P., Burns, C.T., and Jordan, R.F., Organo-
metallics, 2007, vol. 26, p. 6750; Dias, H.V.R., Diyaba-
lange, H.V.K., Rawashdeh-Omary, M.A., Frazman, M.A.,
and Omary, M.A., J. Am. Chem. Soc., 2003, vol. 125,
p. 12072.
13. Pawer, A. and Patil, A.A., Indian J. Chem., 1994,
vol. 33, p. 156; Malhotra, M., Falt-Hansen, B., and
Becher, J., J. Heterocycl. Chem., 1991, vol. 28, p. 1837.
5. Mass Spectral Library (NIST 05); CAS no. 60–24–2.
14. Pozharskii, A.F., Anisimova, V.A., and Tsupak, E.B.,
Prakticheskie raboty po khimii geterotsiklov (Labora-
tory Works on the Chemistry of Heterocycles), Rostov-
on-Don: Rostov. Gos. Univ., 1988, p. 22; Suvo-
rov, N.N., Smushkevich, Yu.I., Velezheva, V.S., Rozh-
kov, V.S., and Simakov, S.V., Khim. Geterotsikl.
Soedin., 1976, p. 191.
6. Papernaya, L.K., Shatrova, A.A., Klyba, L.V., and Zhan-
chipova, E.R., Abstracts of Papers, III Mezhdunarodnaya
konferentsiya “Khimiya geterotsiklicheskikh soedinenii,”
posvyashchennaya 95-letiyu so dnya rozhdeniya profes-
sora A.N. Kosta (IIIrd Int. Conf. “Chemistry of Hetero-
cyclic Compounds” Dedicated to 95th Anniversary of
Prof. A.N. Kost), Moscow, 2010, p. 157.
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