Synthesis of novel sulfonyl-stabilized phosphorus ylides, and the kinetics and mechanism of their conventional and flash vacuum pyrolysis reactions

Article abstract of DOI:10.1139/v05-210

Nine substituted sulfonyl-stabilized phosphorus ylides were prepared by treating their intermediate ylide analogues with phenylmethanesulfonyl fluoride. The stoichiometric ratio of the reactants for each preparation needed to be adjusted according to the basicity of each ylide intermediate. The nine ylide compounds were then subjected to conventional (sealed-tube) gas-phase pyrolysis at 470-545 K. The pyrolytic reactions were homogeneous and obeyed a first-order rate equation. The values of the Arrhenius log A (s^-1) and E _a (kJ mol^-1) obtained for these reactions averaged 11.12 ± 2.00 and 131.8 ± 24.4, respectively. Analysis of the pyrolysates from conventional pyrolysis and from flash vacuum pyrolysis at 600 K showed the products to be complex mixtures of triphenylphosphine, triphenylphosphine oxide, triphenylphosphine sulfide, and symmetric and unsymmetric alkenes. Conventional pyrolysis also gave novel mixed sulfones and, for the p-methoxyaryl substituent, p-anisaldehyde. The products of the reactions under study are explained on the basis of a mechanism involving a sulfonyl carbene intermediate, and the reaction mechanism is used to rationalize the kinetic results and molecular reactivities.

Full text of DOI:10.1139/v05-210

1543
Synthesis of novel sulfonyl-stabilized phosphorus
ylides, and the kinetics and mechanism of their
conventional and flash vacuum pyrolysis
reactions1
Rasha F. Al-Bashir, Nouria A. Al-Awadi, and Osman M.E. El-Dusouqui
Abstract: Nine substituted sulfonyl-stabilized phosphorus ylides were prepared by treating their intermediate ylide ana-
logues with phenylmethanesulfonyl fluoride. The stoichiometric ratio of the reactants for each preparation needed to be
adjusted according to the basicity of each ylide intermediate. The nine ylide compounds were then subjected to conven-
tional (sealed-tube) gas-phase pyrolysis at 470–545 K. The pyrolytic reactions were homogeneous and obeyed a first-
order rate equation. The values of the Arrhenius log A (s–1) and Ea (kJ mol–1) obtained for these reactions averaged
11.12 2.00 and 131.8 24.4, respectively. Analysis of the pyrolysates from conventional pyrolysis and from flash
vacuum pyrolysis at 600 K showed the products to be complex mixtures of triphenylphosphine, triphenylphosphine ox-
ide, triphenylphosphine sulfide, and symmetric and unsymmetric alkenes. Conventional pyrolysis also gave novel mixed
sulfones and, for the p-methoxyaryl substituent, p-anisaldehyde. The products of the reactions under study are ex-
plained on the basis of a mechanism involving a sulfonyl carbene intermediate, and the reaction mechanism is used to
rationalize the kinetic results and molecular reactivities.
Key words: ylides, synthesis, pyrolysis, kinetics, mechanism.
Résumé : La réaction d’analogues d’ylures intermédiaires avec le fluorure de phénylméthanesulfonyle a permis de pré-
parer neuf ylures de phosphores substitués, stabilisés par un groupe sulfonyle. Le rapport stoechiométrique des réactifs
nécessaires pour chacune des préparations a été ajusté en fonction de la basicité de chaque ylure intermédiaire. On a
ensuite soumis chacun des neuf ylures à une pyrolyse à phase gazeuse, en tube scellé, à des températures allant de 470
à 545 K. Les réactions pyrolytiques sont homogènes et obéissent à une équation de vitesse du premier ordre. Les va-
leurs moyennes pour les paramètres d’Arrhenius, log A (s–1) et Ea (kJ mol–1), obtenues pour ces réactions sont respecti-
vement de 11,12 2,00 et de 131,8 24,4. L’analyse des produits de pyrolyse conventionnelle et de pyrolyse éclair
sous vide à 600 K montrent que les produits correspondent à des mélanges complexes comprenant de la triphénylphos-
phine, de l’oxyde de triphénylphosphine, de sulfure de triphénylphosphine ainsi que des alcènes symétriques et non sy-
métriques. La pyrolyse conventionnelle conduit aussi à de nouvelles sulfones mixtes et, dans le cas du substituant p-
méthoxyaryle, à du p-anisaldéhyde. Les produits des réactions obtenus dans cette étude sont expliqués sur la base d’un
mécanisme impliquant un intermédiaire sulfonylcarbène et on utilise le mécanisme réactionnel pour rationaliser les ré-
sultats cinétiques et les réactivités molaires.
Mots clés : ylures, synthèse, pyrolyse, cinétique, mécanisme.
[Traduit par la Rédaction] Al-Bashir et al. 1553
Introduction
react with the designated sulfonyl fluoride (RSO2F) to form
the target ylide (1–4). In the present study, this procedure
was found, however, not to be uniform and straightforward,
as the stoichiometric ratio of the reactants (QS:BuLi:RSO2F)
needed to be adjusted according to the basic strength of the
ylide intermediate formed in the first step. Besides, it has
been noted that α-sulfonyl ylides cannot be prepared by
treatment of the intermediate ylides with sulfonyl chloride
derivatives, since this procedure results in the formation of
α-chloro ylides instead of the target sulfonyl-stabilized
phosphorus ylides (4). Hence, sulfonyl fluorides were used
instead.
Reports on the synthesis of sulfonyl-stabilized phosphorus
ylides suggest two formal steps in the preparation: first, a
base, butyl lithium (BuLi), reacts with the appropriate qua-
ternary phosphonium halide salt (QS) in a nitrogen atmo-
sphere to give an intermediate ylide, which then proceeds to
Received 9 May 1005. Published on the NRC Research Press
Web site at http://canjchem.nrc.ca on 25 November 2005.
R.F. Al-Bashir, N.A. Al-Awadi,2 and O.M.E. El-Dusouqui.
Department of Chemistry, University of Kuwait, P.O. Box
5969, Safat 13060, Kuwait.
Aitken et al. (1) have shown that flash vacuum pyrolysis
at 600 K of sulfonyl-stabilized phosphorus ylides gave Ph3P,
Ph3PO, Ph3PS, and alkenes (either symmetric or unsym-
metric). These products are consistent with the formation of
1This article is part of a Special Issue dedicated to organic
reaction mechanisms.
2Corresponding author (e-mail: nouria@kuc01.kuniv.edu.kw).
Can. J. Chem. 83: 1543–1553 (2005)
doi: 10.1139/V05-210
© 2005 NRC Canada

1544
Can. J. Chem. Vol. 83, 2005
Scheme 1. Reaction pathway for ylides 3–9.
Ph3P+CH2G
X
Ph3P
XCH2G
+
Step 1
THF
Room temp.
2 Ph3P CHG
Ylide intermediate
2 Ph3PCH2G + 2 BuLi
X
Step 2
THF
Room temp.
(a) Ph3P CHG
+ PhCH2SO2F
Ph3P CHG
Ylide intermediate
(as reactant)
F
SO2CH2Ph
Transylidation
Ph3P CG
SO2CH2Ph
Target ylide
(b) Ph3P CHG
Ph3P CHG
+
F
SO2CH2Ph
Ylide intermediate
( as base)
Fluoride salt
X: Cl or Br
G: Phenyl or substituted phenyl group
a sulfonyl carbene intermediate. The phosphorus oxides and
sulfides can be accounted for by the separate extrusion of
Ph3P and SO2, which then partly combine to give Ph3PO and
Ph3PS, and the validity of this was confirmed by control ex-
periments (1). The sulfonyl-stabilized ylides were obtained
as stable, high-melting solids with characteristic spectral data
including diagnostic 31P NMR signals at δ 16.9–21.7 ppm.
Here, we report the results of a study on the kinetics and re-
action product of thermolysis of nine substituted sulfonyl-
stabilized phosphorus ylides using conventional (sealed-tube
(ST); static) pyrolysis (CP), and compare the products of re-
action with those from flash vacuum pyrolysis (FVP). The
kinetic investigation also provides a novel insight into mo-
lecular reactivities and the effects of substituents on the py-
rolysis of stabilized phosphorus ylides.
The nine ylide compounds under study are derivatives
of [(benzylsulfonyl)methylene](triphenyl)phosphorane
(Ph3P=C(G)SO2CH2Ph) in which the substituent (G) is: p-
CNC6H4 (1), p-NO2C6H4 (2), m-NO2C6H4 (3), p-ClC6H4 (4),
m-ClC6H4 (5), C6H5 (6), p-CH3C6H4 (7), p-CH3OC6H4 (8),
and CH3 (9), respectively.
step 2b. The electron-withdrawing substituents (CN and p-
NO2) of the phenyl group in ylides 1 and 2, respectively,
will decrease the protophilic character of the multiple bond
of these ylides relative to that of ylides 3–9, and so the
amount of BuLi base had to be doubled to avoid formation
of excess ylide intermediate and to provide the base required
in step 2b (Scheme 2). Accordingly, the reactant ratio of
quaternary phosphonium halide salt
:
BuLi
:
phenylmethanesulfonyl fluoride was adjusted to 1:2:1.
Attempts to synthesize ylide 1 (G = p-CNC6H4) using the
ratio of 2:2:1 failed to give any ylide product. Besides, it is
of interest to note that the reactant ratio of 1:2:1, which gave
ylide 2 (G = p-NO2C6H4) in 72% yield, failed to give ylide 3
(G = m-NO2C6H4), which, however, was obtained in 65%
yield when the reactant ratio of 2:2:1 was used instead; this
same ratio was also used for ylides 3–9. The present find-
ings indicate that the basicity of the ylide intermediate ob-
tained in the initial step of the reaction determines whether
the intermediate ylide is basic enough to act as the proton
scavenger in the transylidation reaction, or that the stronger
BuLi base is needed to complete the reaction. The
stoichiomeric ratio of the reactants as well as the % yield of
the target ylides correlate well with the expected relative
basicities of the intermediate ylides as judged by the elec-
tron-donating and electron-withdrawing effect of the group
in substituent G.
Results and discussion
Synthesis
Synthesis of ylides 3–9 according to literature procedures
(1) required the ratio of the reactants, quaternary phos-
phonium halide salt (Ph3P+CH2GX–) : BuLi : phenyl-
methanesulfonyl fluoride (PhCH2SO2F), to be 2:2:1; as these
reactions involve transylidation to regenerate one molecule
of quaternary phosphonium fluoride salt (Scheme 1). In
these cases, the basicity of the ylide intermediate formed in
step 1 is high enough for it to act also as the base needed to
abstract the proton from the quaternary phosphonium salt
formed in step 2a to give the target ylide in transylidation
Pyrolysates and reaction mechanism
Reaction products for complete pyrolysis were obtained
for all nine substrates (i) in a FVP (flow) reactor at 600 K,
and (ii) in a sealed-tube pyrolyser (static method) at temper-
atures exceeding those used in the kinetic investigations. The
static-method reactions (CP reaction) were allowed ample
residence time to ensure maximum pyrolysis. The constitu-
ents of the pyrolysates obtained by this method were isolated
© 2005 NRC Canada

Al-Bashir et al.
1545
Scheme 2. Reaction pathway for ylides 1 and 2.
Step I
THF
Room temp.
Ph3P CHG
Ph3PCH2GX
+ BuLi
Ylide intermediate
Step II
THF
Room temp.
(a) Ph3P CHG
Ylide intermediate
+
PhCH2SO2F
Ph3P CHG
F
SO2CH2Ph
THF
Room temp.
(b) Ph3P CHG
F
Ph3P CG
SO2CH2Ph
+
BuLi
SO2CH2Ph
Target ylide
Scheme 3. Composition of the products of gas-phase pyrolysis of ylides 1–9.
Ph3PO
Ph3PS
Ph3P
GHC CHG PhHC CHPh
+
SO2
Ph3P
+
+
+
CG
SO2CH2Ph
GHC CHPh
+
+
GCH SO CH Ph
CH3O
PhCH2CH2Ph
CHO
+
+
+
2
2
2
CH2 CH2
+
using preparative liquid chromatography (PLC) and ana-
lyzed using GC–MS, FT-IR, and H NMR techniques. The
nitrobenzyl)benzylsulfone, isolated by CP only, was prop-
erly characterized and identified.
1
pyrolysates from FVP were collected in a cold trap. FVP
and CP gave identical products of Ph3P, Ph3PO, Ph3PS, and
alkenes (symmetric and unsymmetric) (Scheme 3). How-
ever, static pyrolysis of the ylides followed by PLC gave
better separation and isolation profiles of alkenes, and al-
lowed the identification of more reaction products, including
p-anisaldehyde and mixed sulfones, which were not detected
in the pyrolysates from FVP. It is noteworthy that the static
(sealed-tube) method provides longer residence time for
novel pyrolytic reaction pathways. Identification and charac-
terization of the constituents of the pyrolysates are detailed
in the Experimental section.
[(Benzylsulfonyl)(3-nitrophenyl)methylene](triphenyl)-
phosphorane (ylide 3)
The analysis of the products of reaction of this ylide
showed a mixture of two alkenes: trans-3-nitrostilbene (ma-
jor fraction) and trans-stilbene; the latter identified only
through the static method. Besides, (3-nitrobenzyl)benzyl
sulfone was isolated and clearly identified as a novel com-
pound using the static pyrolysis technique.
[(Benzylsulfonyl)(4-chlorophenyl)methylene](triphenyl)-
phosphorane (ylide 4)
The spectral analysis (1H NMR, IR, and MS) of the prod-
ucts proved the presence of 4,4′-dichlorostilbene, which was
separated in a pure form by PLC. Both trans-4-chloro-
stilbene and trans-stilbene were present as well in small
[(Benzylsulfonyl)(4-cyanophenyl)methylene](triphenyl)-
phosphorane (ylide 1)
The analysis of the pyrolysates — separated as oils —
showed 4-cynostilbene, which was separated in pure form on
PLC. trans-Stilbene and novel trans-4,4′-dicyanostilbene were
also isolated in a very pure state as well from a separate
fraction. In a third fraction, (4-cyanobenzyl)benzyl sulfone
identified for the first time in the present study, was isolated
as a novel sulfone only by CP.
1
amounts. The H NMR for trans-4-chlorostilbene in CDCl3
showed signals (5) at δ 6.83 (1H, d, J = 16.4 Hz), 6.91 (1H,
d, J = 16.4 Hz), 7.07–7.42 (9H, m). MS m/z: 216 (34%
abundance) molecular ion, 215 (17%), 214 (100%) base
peak, 179 (45%), 178 (59%). Novel (4-chlorobenzyl)benzyl
sulfone obtained by the static technique was separated as a
pure fraction on PLC.
[(Benzylsulfonyl)(4-nitrophenyl)methylene](triphenyl)-
phosphorane (ylide 2)
Analysis by H NMR, IR, and MS showed a mixture of
[(Benzylsulfonyl)(3-chlorophenyl)methylene](tri-
phenyl)phosphorane (ylide 5)
1
alkenes, namely, trans-4-nitrostilbene and trans-stilbene,
Reaction product separation on PLC showed 3-
chlorostilbene, 3,3′-dichlorostilbene, and trans-stilbene. H
1
both clearly identified.
A
major fraction, novel (4-
© 2005 NRC Canada

1546
Can. J. Chem. Vol. 83, 2005
Scheme 4. Generation and further reaction of the sulfonyl carbene intermediate of ylides 1–8.
G
G
G
Ph3P
Ph3P
Ph3P
C
O2S
SO2CH2Ph
O2S
CH2Ph
CH2Ph
1-8
Intramolecular
CH insertion
Hydrogen
abstraction
(ii)
(i)
G
G
O2S
SO2
Ph
O2S
CH2Ph
Mixed sulfone
GCH CHPh
PhCH CHPh
GCH CHG
Metathesis
NMR for trans-3,3′-dichlorostilbene in CDCl3 showed diag-
nostic signals (6) at δ 7.03 (2H, s), 7.32–7.42 (8H, m), and
for trans-3-chlorostilbene (7) at δ 6.85 (1H, d, J = 16.5 Hz),
6.92 (1H, d, J = 16.5 Hz), 7.11–7.42 (9H, m). (3-
Chlorobenzyl)benzyl sulfone was also isolated for the first
time in this study using CP.
the overall pyrolysate composition, a feasible reaction mech-
anism is proposed to account for the product of the gas-
phase pyrolytic reaction of the sulfonyl-stabilized phospho-
rus ylides (1–9) under study. The mechanism involves the
formation and further reaction of a sulfonyl carbene interme-
diate (1).
It is to be noted that FVP does not give the sulfone prod-
ucts.
In the case of ylides 1–8 (Scheme 4): (i) The carbene in-
termediate obtained reacts by an intramolecular CH insertion
process to give thiirane dioxide, followed by loss of SO2,
alkene metathesis, and the partial reaction of Ph3P with SO2
to give Ph3PO and Ph3PS; (ii) the carbene intermediate ab-
stracts hydrogen in a novel reaction, observed only in pyrol-
ysis by the static method of ylides 1–5 (all with an electron-
withdrawing group in substituent G), to give mixed sulfones
(Scheme 4). It is to be noted that for ylide 6 (G = Ph) and
ylides 7 and 8 (electron-donating groups in G) no such
sulfone products were detected in the pyrolysates. The for-
mation of 4-methoxybenzaldehyde (p-anisaldehyde) by ylide
8 involves a novel route in which the carbene centre seems
to abstract O and H possibly through a free radical pathway
to give the aldehyde. An earlier study on the pyrolysis of
arylsulphonyl-stabilized phosphorus ylides reports aldehyde
formation for substrates in which the aryl substituent is an o-
methoxyphenyl group (1).
Ylides 6, 7, and 9
The FVP at 600 K of these ylides has been studied before
(1). In each case a mixture of Ph3P, Ph3PO, and Ph3PS was
produced together with various alkenes, exactly as observed
in the present study for ylides 1–5. Static pyrolysis of these
ylides gave products identical to those obtained through FVP.
[(Benzylsulfonyl)(4-methoxyphenyl)methylene](triphenyl)-
phosphorane (ylide 8)
The spectral analysis of the products by both FVP and the
static method showed trans-methoxystilbene; δH (CDCl3)
(6): 4.01 (3H, s), 6.88 (2H, d, J = 8.5 Hz), 6.98 (1H, d, J =
16.3 Hz), 7.08 (1H, d, J = 16.3 Hz), 7.10–7.55 (m, 7H). MS
m/z: 210 (M+·, 22% abundance) molecular ion, 209 (100%)
base peak, and fragment ions at 194 (12%), 195 (6%), 165
(33%), 166 (10%), 152 (6%), 135 (16%), 121 (33%).
In a separate fraction, trans-4,4′-dimethoxystilbene was
identified; δH (CDCl3) (8): 3.86 (6H, s), 6.91 (4H, d, J =
6.85 Hz), 6.95 (2H, s), 7.45 (4H, d, J = 6.85 Hz). MS m/z:
240 (M+·, 100%), molecular ion and base peak, fragment
ions (9) at 226 (18%), 225 (49%), 165 (45%), 153 (28%),
152 (32%), 120 (12%). Besides, trans-stilbene was also iso-
lated in a third fraction, but the sulfone fraction could not be
identified even on using CP. Instead, 4-methoxybenzy-
aldehyde (p-anisaldehyde) was isolated in a very pure state.
According to these results, the composition of the prod-
ucts of the gas-phase pyrolysis of the substituted sulfonyl-
stabilized ylides (1–9) was as shown in Scheme 3. Based on
When G = CH3 (ylide 9), literature reports (1, 3) suggest
two pathways (Scheme 5) for the reaction of the sulfonyl
carbene intermediates.
Kinetic analysis
The kinetic data of the pyrolytic gas-phase elimination re-
actions of the nine ylides (1–9) under study are given in Ta-
ble 1. Each rate constant at any given temperature represents
an average from a set of three values obtained in three sepa-
rate kinetic runs conducted at the same temperature. The
agreement among the values of the rate constant in each set
is within 2%. Each kinetic run was monitored until 90%–
95% of the reaction was completed, and the range of 44
© 2005 NRC Canada

Al-Bashir et al.
1547
Scheme 5. Reaction pathway of ylide 9.
G
CH3
1,2-H shift
CH insertion
O2S
O2S
O2S
Ph
CH2Ph
CH2Ph
9
SO2
SO2
H2C CH
Gases
PhCH2
CH3CH CHPh
Dimerization
PhCH2CH2Ph
Table 1. Rate constants (k, s–1), Arrhenius log A and Ea, entropies of activation (∆S‡), and rate constants at 500 K of the gas-phase py-
rolysis of sulfonyl-stabilized phosphorus ylides (1–9).
T
(K)
104k
log A
Ea
104k500 K
∆S5‡00 K
Ylide
G
(s–1)
(s–1)
(kJ mol–1)
(s–1)
(J K–1 mol–1)
2.899
–55.62
p-CNC6H4
1
495.4
502.4
515.0
520.4
526.2
533.2
10.11 0.26
13.12 0.25
8.63 0.08
129.4 2.51
156.1 2.43
113.4 0.79
3.93
6.41
6.11
4.737
9.194
13.53
18.87
27.08
2
3
487.0
2.368
+1.895
–84.10
p-NO2C6H4
494.8
502.4
509.4
516.6
529.4
492.4
4.313
8.705
13.19
20.00
53.36
3.939
m-NO2C6H4
499.2
507.0
513.8
520.6
527.8
534.8
494.8
5.745
8.680
12.50
17.90
25.72
34.74
2.748
4
5
8.65 0.18
7.67 0.15
115.6 1.84
107.4 1.55
3.78
2.88
–83.64
–102.3
p-ClC6H4
502.6
509.7
523.4
538.2
544.8
494.2
4.502
6.269
13.62
26.17
37.59
2.122
m-ClC6H4
506.2
515.6
522.5
530.0
536.2
543.7
500.8
3.942
6.116
9.016
12.92
15.91
22.88
5.527
6
9.75 0.06
124.7 0.63
5.32
–62.61
C6H5
508.4
516.2
524.2
8.917
13.39
21.17
© 2005 NRC Canada

1548
Can. J. Chem. Vol. 83, 2005
Table 1 (concluded).
T
(K)
104k
log A
Ea
104k500 K
∆S5‡00 K
Ylide
G
(s–1)
(s–1)
(kJ mol–1)
(s–1)
(J K–1 mol–1)
531.4
539.0
545.2
479.2
31.64
46.49
63.72
3.656
7
9.13 0.14
115.3 1.34
134.0 3.26
12.0
12.5
–74.54
–28.53
p-CH3C6H4
493.8
501.6
509.4
524.0
475.0
8.356
12.74
20.14
43.28
2.190
8
9
11.53 0.34
p-CH3OC6H4
483.0
491.6
498.2
505.0
512.2
520.4
470.4
3.882
6.849
10.95
19.03
25.11
47.33
3.194
8.43 0.14
107.4 1.25
16.2×10–4
–87.95
CH3
476.4
483.6
490.4
497.2
504.4
511.8
4.366
6.871
9.945
14.14
20.54
28.52
6 K over which the reactions were followed is in accord
with the temperature range deemed necessary for reliable ki-
netic analysis of thermal gas-phase elimination reactions
(10, 11). Arrhenius parameters were obtained using the re-
sults from Table 1. The Arrhenius plots were linear over the
studied temperature and reaction range, with correlation co-
Fig. 1. Arrhenius plot for the pyrolysis of ylide 1.
-2.438
-2.638
-2.838
-3.038
-3.238
-3.438
-3.638
efficients of the order of 0.990
plot is given in Fig.
0.009. A representative
for [(benzylsulphonyl)(4-
1
cyanophenyl)methylene](triphenyl)phosphorane (ylide 1),
with a correlation coefficient of 0.999. Arrhenius log A (s–1),
∆S‡ (J K–1 mol–1), the energy of activation (Ea, kJ mol–1),
and the first-order rate constants (k, s–1) of the pyrolysis re-
actions at 500 K are recorded in Table 1. The values for ∆S‡
(J K–1 mol–1) are negative or small (positive) suggesting
higher structural organization and the formation of an or-
dered transition state.
1.856 1.876 1.896 1.916 1.936 1.956 1.976 1.996 2.016 2.036
1000/T
2. Introducing p-methyl and p-methoxy groups into the ar-
omatic ring ylides 7 and 8 respectively, has increased
the rate of pyrolysis by almost 2.3 times for both ylides;
this could be explained in terms of the electron-donating
nature of these substituents and their influence on the
carbene intermediate suggested (Schemes 4 and 5).
3. When electron-withdrawing substituents (p-Cl, m-Cl,
and p-CN) were introduced into ylides 4, 5, and 7, re-
spectively, the reactivity was reduced; this indicates that
these substituents destabilize the carbene intermediate.
4. Introducing the nitro group at the para and meta posi-
tions of ylides 3 and 4, respectively, resulted in no
change on the reactivity compared to ylide 6 (G =
C6H5); this unique behaviour of the nitro group in the
gas-phase thermal elimination reactions of organic com-
pounds has been reported in other studies (12).
Molecular reactivities and substituent effects
The first-order rate constants at 500 K of the gas-phase
pyrolytic reactions of ylides 1–9 and the rate constant ratio
(relative rate, krel) of the ylides are summarized in Table 2.
The main features of the kinetic results are as follows:
1. The rate of pyrolysis of ylide 9, where G = CH3, is ca. 3
times faster than the rate of pyrolysis of ylide 6, where
G = C6H5; this represents the highiest increment in reac-
tivity in the series of ylides under consideration and is
attributed to the fact that the reactive carbene intermedi-
ate of ylide 9 can react either by 1,3-H insertion or 1,2-
H insertion followed by the elimination of SO2. The
pyrolysates 1-phenylpropene and dibenzyl prove the
possibility of both modes of insertion, where G is the
aromatic phenyl group, the carbene intermediate can re-
act only by 1,3-insertion.
© 2005 NRC Canada

Al-Bashir et al.
1549
Scheme 6. Carbene intermediate stabilization by conjugative in-
Table 2. Rate constants (k, s–1) at 500 K and the rate constant
ratio (relative rate, krel) of the pyrolysis of sulfonyl-stabilized
phosphorus ylides (1–9).
teraction with sulfonyl groups.
G
G
Ylide
G
104 k (s–1)
3.926
6.406
6.109
3.782
2.881
5.317
12.00
12.48
16.17
krel
p-CNC6H4
p-NO2C6H4
m-NO2C6H4
p-ClC6H4
m-ClC6H4
C6H5
CH2Ph
S
1
2
3
4
5
6
7
8
9
0.738
1.20
1.15
0.711
0.542
1.00
2.26
2.35
3.04
CH2Ph
O
S
O
O
O
ylides 2 and 6–9 were prepared following literature proce-
dures (1, 3). The general procedure A for the synthesis of
ylides 1 and 2, and procedure B for the preparation of ylides
3–9 are described hereafter.
p-CH3C6H4
p-CH3OC6H4
CH3
Synthesis
5. It is important to note that these sulfonyl carbene inter-
mediates are already stabilized by conjugative interac-
tion with the sulfonyl group (Scheme 6), and this might
be the reason behind the relatively small substituent ef-
fects obtained.
These features of the kinetic results support the reaction
pathways suggested and that the formation of the carbene in-
termediate is the rate-controlling step.
Procedure A
In the synthesis of ylides 1 and 2, a solution of 1.6 mol/L
BuLi in hexane (7.5 mmol) was slowly added from a syringe
to a stirred suspension of the corresponding quaternary phos-
phonium salt (7.5 mmol) in dry THF (50 mL) at room tem-
perature under nitrogen. The mixture was stirred for about
1 h, and then an equivalent amount of phenylmethanesulf-
onyl fluoride (7.5 mmol) in dry THF (ca. 5 mL) was added
all at once. The reaction mixture was stirred further for 5 h,
followed by the addition of another portion of BuLi in hex-
ane (7.5 mmol). The crude material was dissolved in di-
chloromethane (100 mL), washed with water (3 × 75 mL),
dried, and concentrated under vacuum. The residual oil was
triturated with a suitable solvent to obtain the pure ylide.
Experimental
Materials, techniques, and instrumentation
The required quaternary phosphonium salts were prepared
by the reaction of the appropriate alkyl halide with tri-
phenylphosphine in boiling toluene. The phenylmethane-
sulfonyl fluoride, BuLi, and dry THF are commercially
available from Aldrich. Further drying of THF was made by
distillation from potassium benzophenone ketyl under N2.
The ylides and the constituents of their pyrolysates were
Procedure B
For the preparation of ylides 3–9, a suspension of the ap-
propriate quaternary phosphonium salt (15 mmol) in dry
THF (100 mL) was stirred at room temperature under nitro-
gen while a solution of 1.6 mol/L BuLi in hexane
(15.6 mmol) was slowly added from a syringe. The mixture
was stirred further for about 1 h, and then a solution of
phenylmethanesulfonyl fluoride (7.5 mmol) in dry THF
(10 mL) was added dropwise to the ylide solution. The mix-
ture was kept stirring overnight, and the reaction mixture
was then filtered and the filtrate was evaporated. The residue
was dissolved in dichloromethane (150 mL) and washed with
water (3 × 75 mL), dried and the solvent evaporated (1, 3).
A problem encountered in the preparation of stabilized
ylides in general, and in the synthesis of the present ylides,
they were often difficult to crystallize in pure form from the
oils obtained following the evaporation step. Since the prod-
ucts hydrolyzed when chromatography was attempted, and
decomposed on sublimation, the safer option was their
trituration with suitable solvents to obtain the pure ylides
(13).
1
characterized using GC–MS, FT-IR, H NMR, 13C NMR,
and 31P NMR spectroscopy. Instrumentation included a
Finnigan Mat INCOSXL for GC–MS studies, a PerkinElmer
2000 spectrometer for FT-IR, and a Bruker DPX 400 spec-
trometer for the NMR analysis. Kinetic runs and pyrolysates
preparation for reaction product analysis using a sealed-tube
pyrolyser (conventional static pyrolysis) were conducted in a
Chemical Data System (CDS) custom-made pyrolyzer com-
prising an insulated aluminum block fitted with a platinum-
resistance thermometer and thermocouple connected to a
Comark microprocessor thermometer. The temperature of
the aluminum block was controlled by a digital Eurotherm
093 precision temperature regulator. Aluminum was chosen
for its low temperature gradient and resistance to elevated
temperatures. HPLC analysis of kinetic runs was carried out
on a Waters prope (pump model 515 and UV detector model
2487).
FVP was conducted in a fused-quartz tube, which was
housed in a sublimation oven. The latter was connected to a
hot zone pyrolyzer under low pressure ending with a U-
shaped trap cooled in liquid nitrogen.
Characterization
Ylides 2 and 6–9 were gratefully received from Dr. Alan
Aitken, University of St. Andrews, St. Andrews, Fife UK.
The ylides were purified, recrystallized from dichloro-
methane–ether (ylide 2), ethylacetate (ylides 6–9), and char-
acterized before use.
Synthesis and characterization of ylides (1–9)
The details of the synthesis of the novel sulfonyl-
stabilized ylides 1 and 3–5 are given in the following, while
© 2005 NRC Canada

1550
Can. J. Chem. Vol. 83, 2005
[(Benzylsulfonyl)(4-cyanophenyl)methylene](triphenyl)-
phosphorane (1)
[(Benzylsulfonyl)(3-nitrophenyl)methylene](triphenyl)-
phosphorane (3)
The quaternary salt, 3-nitrobenzyltriphenylphosphonium
chloride (Ph3P+CH2m-NO2-C6H4Cl–), was prepared by
refluxing 10.49 g (0.04 mol) of triphenylphosphine and 6.9 g
(0.04 mol) of 3-nitrobenzyl chloride in 30 mL benzene for
28 h. After cooling, the solid was collected and washed with
diethyl ether to obtain 11 g (~63%) of the salt; mp 255–
258 °C (16). 1H NMR (CDCl3) δH: 6.08 (2H, d, J =
15.2 Hz), 7.29 (1H, t, J = 8 Hz), 7.58–7.64 (7H, m), 7.74–
7.76 (3H, m), 7.84–7.89 (6H, m), 7.95 (1H, d, J = 8 Hz),
8.04 (1H, d, J = 8 Hz). 13C NMR (CDCl3) (JP-C) δC: 30.18
(d, J = 46.8 Hz, P-CH2), 118.01 (d, J = 85.4 Hz, C-1 of P-
Ph), 123.41 (d, J = 3.4 Hz), 126.17 (d, J = 5 Hz), 130.31 (d,
J = 3 Hz), 130.81 (d, J = 12.5 Hz, C-3 of P-Ph), 131.17 (d,
J = 19.6 Hz), 134.98 (d, J = 10 Hz, C-2 of P-Ph), 135.65 (d,
J = 3 Hz, C-4 of P-Ph), 139.41 (d, J = 5.4 Hz), 148.14 (d,
J = 3.6 Hz). 31P NMR (CDCl3) δP: 25.55. MS m/z: 398
(M+· – Cl–). Anal. calcd. for C25H21ClNO2P (%): C 69.20, H
4.84, N 3.23; found: C 69.14, H 4.86, N 3.32.
The quaternary phosphonium salt, 4-cyanobenzyltri-
phenylphosphonium bromide (Ph3P+CH2p-NCC6H4Br–),
was prepared by refluxing 10.49 g of triphenylphosphine
(0.04 mol) and 7.84 g (0.04 mol) of α-bromo-p-toluenitrile
in 60 mL toluene for 18 h to get 11 g (ca. 60%) of the salt;
mp 326–329 °C (14). 1H NMR (CDCl3) (15) δH: 5.92 (2H, d,
J = 15.6 Hz), 7.32 (2H, d, J = 8 Hz), 7.43 (2H, dd, J = 2.3,
8.2 Hz), 7.57–7.61 (6H, m), 7.73–7.83 (9H, m). 13C NMR
(DMSO) (JP-C) δC: 29.17 (d, J = 46.6 Hz, P-CH2), 112.22 (d,
J = 3.8 Hz), 118.50 (d, J = 85.3 Hz, C-1 of P-Ph), 119.37 (d,
J = 2 Hz), 131.26 (d, J = 12.5 Hz, C-3 of P-Ph), 132.80 (d,
J = 5.4 Hz), 133.64 (d, J = 3 Hz, C-4 of P-Ph), 135.09 (d,
J = 10 Hz, C-2 of P-Ph), 135.15 (d, J = 8.2 Hz), 136.32 (d,
J = 2.7 Hz). 31P NMR (CDCl3) δP: 25.12. Anal. calcd. for
C26H21BrNP (%): C 68.12, H 4.58, N 3.06; found: C 68.10,
H 4.63, N 3.17.
The target ylide 1 was prepared by treating the obtained
salt with BuLi followed by phenylmethanesulfonyl fluoride
in a 1:2:1 ratio, as shown in procedure B. The yellow mate-
rial that remained after evaporation of the solvent was
triturated with diethyl ether to afford a solid material, which
was recrystallized from acetonitrile to give 1.80 g of yellow
crystals (ca. 45%); mp 276–278 °C. IR υmax (cm–1): 2216,
The target ylide 3 was obtained by treating the salt with
BuLi followed by the addition of phenylmethanesulfonyl
fluoride in a 2:2:1 ratio, as per procedure A. The residual oil
was triturated and recrystallized from ethyl acetate to give
2.68 g of yellow crystals (ca. 65%) of the target ylide: mp
233–235 °C. IR υmax (cm–1): 1518, 1438, 1340, 1276, 1257,
1
1594, 1285, 1263, 1177, 1141, 1101, 994, 695, 544, 514. H
1
1100, 1012, 997, 745, 693, 551. H NMR (CDCl3) δH: 3.95
NMR (CDCl3) δH: 3.88 (2H, s), 6.95 (2H, d, J = 8 Hz), 7.09
(2H, d, J = 8 Hz), 7.16 (2H, d, J = 8 Hz), 7.25–7.28
(2H, m), 7.30–7.34 (1H, m), 7.40–7.45 (6H, m), 7.54–7.61
(9H, m). 13C NMR (CDCl3) (JP-C) δC: 51.3 (d, J = 126 Hz,
P=C), 62.9 (CH2), 106.5 (CϵN), 120.13, 126.55 (d, J =
92 Hz, C-1 of P-Ph), 128.37, 128.77, 129.10 (d, J = 12 Hz,
C-3 of P-Ph), 131.17 (2C), 131.46 (d, J = 9 Hz), 132.37 (d,
J = 5.4 Hz), 132.67 (d, J = 3 Hz, C-4 of P-Ph), 132,46 (d,
J = 9.7 Hz), 134.48 (d, J = 10 Hz, C-2 of P-Ph), 142.65 (d,
J = 9.5 Hz). 31P NMR (CDCl3) δP: 19.36. MS m/z: 531 (M+·,
2), 440 (25), 392 (14), 376 (16), 277 (18), 262 (68), 183
(55), 105 (100). Anal. calcd. for C33H26NO2PS (%): C
74.58, H 4.90, N 2.64, S 6.03; found: C 74.71, H 5.12, N
3.01, S 5.68.
(2H, s), 7.13–7.17 (3H, m), 7.23–7.27 (3H, m), 7.40–7.44
(6H, m), 7.51–7.61 (10H, m), 7.63–7.65 (1H, m), 7.73–7.75
(1H, m). 13C NMR (CDCl3) (JP-C) δC: 48.71 (d, J = 128 Hz,
P=C), 62.7 (CH2), 119.40 (d, J = 1 Hz), 126.47 (d, J =
92 Hz, C-1 of P-Ph), 127.87, 128.12, 128.33, 128.39 (d, J =
3.7 Hz), 128.69 (d, J = 12 Hz, C-3 of P-Ph), 130.79, 130.97,
132.16 (d, J = 3 Hz, C-4 of P-Ph), 133.97 (d, J = 10 Hz, C-2
of P-Ph), 137.81 (d, J = 10 Hz), 140.18 (d, J = 4.5 Hz),
147.20. 31P NMR (CDCl3) δP: 20.3. MS m/z: 551 (M+·, 2),
461 (12), 412 (8), 396 (10), 277 (60), 262 (100), 201 (15),
183 (84), 108 (38), 91 (96). Anal. calcd. for C32H26NO4PS
(%): C 69.69, H 4.72, N 2.54, S 5.81; found: C 69.80, H
4.82, N 2.50, S 5.46.
[(Benzylsulfonyl)(4-chlorophenyl)methylene](triphenyl)-
phosphorane (4)
[(Benzylsulfonyl)(4-nitrophenyl)methylene](triphenyl)-
phosphorane (2)
The quaternary salt, 4-chlorobenzyltriphenylphosphonium
chloride (Ph3P+CH2p-Cl-C6H4Cl–), was prepared by
refluxing 10.49 g triphenylphosphine (0.04 mol) and 6.5 g 4-
chlorobenzyl chloride (0.04 mol) in 70 mL toluene for 21 h.
After cooling, the solid was filtered and washed with diethyl
ether to obtain 13.15 g (ca. 78%) of the salt: mp 290–293 °C
(17, 18). 1H NMR (CDCl3) (15) δH: 5.71 (2H, d, J =
14.8 Hz), 7.0 (2H, d, J = 8 Hz), 7.11–7.12 (2H, m), 7.55–
Obtained by treating the obtained salt with BuLi followed
by phenylmethanesulfonyl fluoride in a 1:2:1 ratio. Yield:
72%, mp 275 to 276 °C (3). IR υmax (cm–1): 1582, 1490,
1
1334, 1284, 1264, 1142, 1107, 992, 936, 695 (3). H NMR
(CDCl3) δH (3): 3.86 (2H, s), 6.84 (2H, d, J = 8.9 Hz), 7.11
(2H, d, J = 7.1 Hz), 7.29–7.34 (3H, m), 7.43–7.48 (6H, m),
7.56–7.66 (9H, m), 7.71 (2H, d, J = 8.8 Hz). 13C NMR
(CDCl3) (JP-C) δC: 54.03 (d, J = 124 Hz, P=C), 63.10,
123.10, 126.00 (d, J = 92 Hz, C-1 of P-Ph), 128.55, 128.87,
129.29 (d, J = 12 Hz, C-3 of P-Ph), 130.53 (d, J = 6 Hz),
131.00, 131.52, 132.93 (d, J = 3 Hz, C-4 of P-Ph), 134.63
(d, J = 10 Hz, C-2 of P-Ph), 143.11, 145.81 (d, J = 10 Hz).
31P NMR (CDCl3) δP: 19.21. MS m/z: 551 (M+·, 20), 460
(38), 412 (18), 396 (16), 277 (85), 262 (100), 201 (22), 183
(96), 108 (36), 91 (85). Anal. calcd. for C32H26NO4PS (%):
C 69.69, H 4.74, N 2.54, S 5.81; found: C 69.49, H 4.80, N
2.70, S 5.28.
7.59 (6H m), 7.69–7.80 (9H, m). 13C NMR (CDCl3) (JP-C
)
δC: 30.11 (d, J = 46.2 Hz, P-CH2), 118.40 (d, J = 85 Hz, C-1
of P-Ph), 126.99 (d, J = 6.9 Hz), 129.26 (d, J = 3.2 Hz, C-4
of P-Ph), 130.61 (d, J = 12.5 Hz, C-3 of P-Ph), 133.69 (d,
J = 5.4 Hz), 134.75 (d, J = 4.7 Hz), 135.06 (d, J = 10 Hz, C-
2 of P-Ph), 135.38. 31P NMR (CDCl3) δP: 24.79. MS m/z:
389/387 (M+· + 2/M+· – Cl–). Anal. calcd. for C25H21Cl2P (%):
C 70.92, H 4.96; found: C 70.90, H 5.02.
The target ylide 4 was prepared by treating the salt with
BuLi followed by phenylmethanesulfonyl fluoride in a 2:2:1
© 2005 NRC Canada

Al-Bashir et al.
1551
ratio, as shown in procedure A. The obtained colourless ma-
terial was recrystallized from ethyl acetate to give 2.59 g
(ca. 64%) of the ylide: mp 232–234 °C. IR υmax (cm–1):
1584, 1485, 1436, 1269, 1104, 1018, 935, 757, 732, 694,
by phenylmethanesulfonyl fluoride in a 2:2:1 ratio. Yield:
78%; mp 210–212 °C (1, 3). IR υmax (cm–1): 1590, 1484,
1
1435, 1266, 1240, 1094, 1021, 939, 708, 692, 545, 526. H
NMR (CDCl3) (1) δH: 4.00 (2H, s), 7.03–7.15 (4H, m),
7.26–7.37 (12H, m), 7.47–7.54 (9H, m). 13C NMR (CDCl3)
(JP-C) (1) δC: 46.80 (d, J = 129 Hz, P=C), 61.83 (CH2),
125.85 (d, J = 2 Hz), 127.91, 128.09 (d, J = 92 Hz, C-1 of
P-Ph), 128.13, 128.50, 128.73 (d, J = 12 Hz, C-3 of P-Ph),
131.70, 131.94 (d, J = 3 Hz, C-4 of P-Ph), 134.27 (d, J =
10 Hz, C-2 of P-Ph), 135.20 (d, J = 9 Hz), 135.29 (d, J =
9 Hz), 135.94 (d, J = 4 Hz). 31P NMR (CDCl3) δP: 19.61 (1).
MS m/z: 506 (M+·, 60), 416 (57), 415 (48), 368 (64), 351
(90), 273 (18), 165 (64), 105 (100). Anal. calcd. for
C32H27O2PS (%): C 75.89, H 5.34, S 6.32; found: C 75.85,
H 5.44, S 6.21.
1
542. H NMR (CDCl3) δH: 3.97 (2H, s), 6.98 (2H, d, J =
8 Hz), 7.05–7.15 (4H, m), 7.27–7.30 (2H, m), 7.35–7.39
(7H, m), 7.48–7.53 (9H, m). 13C NMR (CDCl3) (JP-C) δC:
46.6 (d, J = 129 Hz, P=C), 62.06 (CH2), 127.68 (d, J =
92 Hz, C-1 of P-Ph), 128.05 (2C), 128.17 (d, J = 1.4 Hz),
128.63, 128.68 (d, J = 1.9 Hz), 128.89 (d, J = 12 Hz, C-3 of
P-Ph), 131.61, 131.69, 132.18 (d, J = 3 Hz, C-4 of P-Ph),
134.16 (d, J = 3.6 Hz), 134.28 (d, J = 10 Hz, C-2 of P-Ph),
136.63 (d, J = 4 Hz). 31P NMR (CDCl3) δP: 19.61. MS m/z:
542/540 (M+· + 2/M+·, 35/60%), 415 (30), 401 (45), 385
(80), 351 (40), 277 (100), 262 (75), 201 (45), 199 (42), 183
(80), 139 (58), 1 (64). Anal. calcd. for C32H26ClO2PS (%): C
71.04, H 4.81, S 5.92; found: C 71.21, H 4.92, S 6.03.
[(Benzylsulfonyl)(4-methylphenyl)methylene](triphenyl)-
phosphorane (7)
[(Benzylsulfonyl)(3-chlorophenyl)methylene](triphenyl)-
phosphorane (5)
Obtained by treating the obtained salt with BuLi followed
by phenylmethanesulfonyl fluoride in a 2:2:1 ratio. Yield:
74%; mp 186–189 °C (1). IR υmax (cm–1): 1625, 1502, 1483,
1435, 1264, 1244, 1144, 1106, 1094, 1043, 1028, 935, 864,
788, 754, 714, 694 (1). 1H NMR (CDCl3) (1) δH: 2.24
(3H, s), 3.99 (2H, s), 6.87 (2H, d, J = 8 Hz), 7.13–7.16
(4H, m), 7.24–7.36 (9H, m), 7.45–7.52 (9H, m). 13C NMR
(CDCl3) (JP-C) δC: 21.5 (CH3), 46.6 (d, J = 129 Hz, P=C),
61.6 (CH2), 128.30 (d, J = 92 Hz, C-1 of P-Ph), 128.58 (d,
J = 12 Hz, C-3 of P-Ph), 128.63, 128.75, 128.97 (d, J =
1 Hz), 131.73, 131.86 (d, J = 3 Hz, C-4 of P-Ph), 131.96,
132.01, 134.26 (d, J = 10 Hz, C-2 of P-Ph), 135.63 (d, J =
2 Hz), 136.11 (d, J = 4 Hz). 31P NMR (CDCl3) δP: 19.49.
MS m/z: 520 (M+·, 60), 429 (50), 416 (5), 380.7 (40), 365
(100), 277 (5), 262 (30), 165 (65), 119 (90), 91 (75). Anal.
calcd. for C33H29O2PS (%): C 76.15, H 5.58, S 6.15; found:
C 76.17, H 5.64, S 5.79.
The quaternary salt, 3-chlorobenzyltriphenylphosphonium
chloride (Ph3P+CH2m-Cl-C6H4Cl–), was prepared by
refluxing 10.49 g of triphenylphosphine (0.04 mol) with
6.44 g of 3-chlorobenzyl chloride (0.04 mol) in benzene for
48 h to obtain 13.90 g (ca. 82%) of the salt: mp 320–323 °C
1
(19). H NMR (CDCl3) δH: 5.66 (2H, d, J = 15.2 Hz), 6.87
(1H, d, J = 2 Hz), 7.02 (1H, t, J = 8 Hz), 7.12 (1H, d, J =
7.6 Hz), 7.15 (1H, d, J = 7.6 Hz), 7.57–7.61 (6H, m), 7.71–
7.81 (9H, m). 13C NMR (CDCl3) (JP-C) δC : 30.62 (d, J =
46.5 Hz, P-CH2), 118.30 (d, J = 85.40 Hz, C-1 of P-Ph),
128.91 (d, J = 3.8 Hz), 130.35 (d, J = 8.4 Hz), 130.55 (d,
J = 3.3 Hz, C-4 of P-Ph), 130.70 (d, J = 12.5 Hz, C-3 of P-
Ph), 130.76, 131.73 (d, J = 5.3 Hz), 134.72 (d, J = 3.8 Hz),
134.98 (d, J = 10 Hz, C-2 of P-Ph), 135.51 (d, J = 2.7 Hz).
31P NMR (CDCl3) δP: 25.05. MS m/z: 389/387 (M+· + 2/M+· –
Cl–). Anal. calcd. for C25H21Cl2P (%): C 70.92, H 4.96;
found: C 70.96, H 4.96.
[(Benzylsulfonyl)(4-methoxyphenyl)methylene](triphenyl)-
phosphorane (8)
Obtained by treating the obtained salt with BuLi followed
The target ylide 5 was prepared by treating the obtained
salt with BuLi and phenylmethanesulfonyl fluoride accord-
ing to procedure A, in a 2:2:1 ratio. The obtained colorless
material was recrystallized from ethyl acetate to obtain
3.25 g of the pure colorless crystals (ca. 80%) of the target
ylide mp 216–218 °C. IR υmax(cm–1): 1584, 1436, 1270,
1103, 811, 760, 542, 503. 1H NMR (CDCl3) δH: 3.99
(2H, s), 6.90–7.00 (2H, m), 7.04 (1H, s), 7.10–7.15 (2H, m),
7.25–7.31 (4H, m), 7.37–7.40 (6H, m), 7.48–7.55 (9H, m).
13C NMR (CDCl3) (JP-C) δC: 47.5 (d, J = 129 Hz, P=C),
62.29 (CH2), 125.6 (d, J = 2 Hz), 127.53 (d, J = 92 Hz, C-1
of P-Ph), 128.13, 128.64, 128.71, 128.89 (d, J = 12 Hz, C-3
of P-Ph), 128.98, 131.59 (d, J = 2.1 Hz), 132.06 (d, J =
2.9 Hz), 132.24 (d, J = 3 Hz, C-4 of P-Ph), 134.17, 134.30
(d, J = 10 Hz, C-2 of P-Ph), 134.89 (d, J = 4.1 Hz), 137.7
(d, J = 9 Hz). 31P NMR (CDCl3) δP: 19.84. MS m/z: 542/540
(M+· + 2/M+·, 8/18%), 451/449 (37/35Cl – M+ – PhCH2, 35/100),
401 (50), 385 (85), 351 (40), 262 (46), 241 (40), 183 (85),
165 (78), 139 (75). Anal. calcd. for C32H26ClO2PS (%): C
71.04, H 4.81, S 5.92; found: C 71.17, H 4.96, S 5.66.
by phenylmethanesulfonyl fluoride in a 2:2:1 ratio. Yield:
86%; mp 193–195 °C (3). IR
1438, 1242, 1095, 1049, 750, 694 (3). H NMR (CDCl3) (3)
υmax
(cm–1): 2829, 1598, 1503,
1
δ
H: 3.75 (3H, s), 4.13 (2H, s), 6.62 (2H, d, J = 8 Hz), 7.16–
7.18 (4H, m), 7.27–7.29 (2H, m), 7.32–7.35 (7H, m), 7.45–
7.50 (9H, m). 13C NMR (CDCl3) (JP-C
)
δ
C: 45.85 (d, J =
129 Hz, P=C), 55.61 (CH3), 61.55 (CH2), 113.72, 126.97 (d,
J = 8.4 Hz), 127.86, 128.28 (d, J = 92 Hz, C-1 of P-Ph),
128.60, 128.71 (d, J = 12 Hz, C-3 of P-Ph), 131.70, 131.87
(d, J = 3 Hz, C-4 of P-Ph), 132.04, 134.20 (d, J = 10 Hz, C-
2 of P-Ph), 137.94 (d, J = 3 Hz), 158.35 (d, J = 2 Hz). 31P
NMR (CDCl ) : 19.80. MS m/z: 536 (M+·, 40), 397.1 (25),
δP
3
365 (30), 381 (100), 278 (50), 262 (55), 183 (70), 152 (40),
121 (50), 91 (75). Anal. calcd. for C33H29O3PS (%): C
73.88, H 5.41, S 5.97; found: C 73.80, H 5.51, S 5.55.
[(Benzylsulfonyl)(methyl)methylene](triphenyl)phosphorane
(9)
Obtained by treating the obtained salt with BuLi followed
[(Benzylsulfonyl)(phenyl)methylene](triphenyl)phosphorane
(6)
Obtained by treating the obtained salt with BuLi followed
by phenylmethanesulfonyl fluoride in a 2:2:1 ratio. Yield:
1
62%; mp 170–172 °C (1). H NMR (CDCl3) (1) δH: 1.58
(3H, d, J = 14 Hz), 3.97 (2H, s), 7.27 (5H, s), 7.7–7.4
© 2005 NRC Canada

1552
Can. J. Chem. Vol. 83, 2005
Table 3. Conditions for kinetics and HPLC analysis of sulfonyl-stabilized phosphorus ylides 1–9 (Ph3P=CGSO2CH2Ph).
Ylide
G
Internal standard
UV detector (λ, nm)
T range (K)
Eluent (CH3CN:H2O)
p-CNC6H4
p-NO2C6H4
m-NO2C6H4
p-ClC6H4
m-ClC6H4
C6H5
1
2
3
4
5
6
7
8
9
1,2,4-Trichlorobenzene
Chlorobenzene
256
210
256
256
256
210
256
256
210
495–533
487–529
492–535
495–545
494–544
501–545
479–524
475–520
470–512
60:40+0.1% AcOH
70:30
Chlorobenzene
70:30
Chlorobenzene
70:30
Chlorobenzene
70:30
1,3-Dichlorobenzene
Chlorobenzene
62:38
60:40+0.1% AcOH
60:40+0.1% AcOH
60:40+0.1% AcOH
p-CH3C6H4
p-CH3OC6H4
CH3
Chlorobenzene
1,2,4-Trichlorobenzene
(15H, m). 31P NMR (CDCl3) (1) δP: 20.8. Anal. calcd. for
C27H25O2PS (%): C 72.97, H 5.63, S 7.21; found: C 72.68,
H 5.42, S 6.98.
279 (2), 219 (2), 218 (18), 217 (10), 216 (32), 127 (50), 126
(18), 125 (100), 91 (100).
Ylide 5
Characterization of novel products of the pyrolysis of
ylides 1–4
(3-Chlorobenzyl)benzyl sulfone (3-ClC6H4CH2SO2CH2C6H5)
IR υmax (cm–1): 1598, 1476, 1318, 1118, 904, 728, 648,
1
609. H NMR (CDCl3) δH : 4.09 (2H, s), 4.19 (2H, s), 7.29
Ylide 1
(1H, d, J = 8 Hz), 7.35 (2H, d, J = 8 Hz), 7.37–7.45
(6H, m). MS m/z: 283 (6), 281 (M+· + 1, 18), 218 (18), 217
(14), 216 (30), 183 (8), 181 (22), 157 (15), 155 (10), 127
(24), 125 (50).
trans-4,4′-Dicyanostilbene (p-NCC6H4CH=CHC6H4CN-p)
1
IR υmax (cm–1): 2224, 949, 773. H NMR (CDCl3) δH:
7.21 (2H, s), 7.63 (4H, d, J = 8 Hz), 7.69 (4H, d, J = 8 Hz).
MS m/z: 231 (18), 230 (M+·, 100), 229 (44), 228 (13), 215
(15), 202 (12).
Kinetic measurements and product analysis
Stock solution (7 mL) was prepared by dissolving 6–
10 mg of the ylide in acetonitrile as the solvent to give a
concentration of 1000–2000 ppm. Internal standard was then
added, the amount of which was adjusted to give the desired
peak area ratio of ylide to standard (2.5:1). The solvent and
the internal standard were selected because both are stable
under the conditions of pyrolysis and they do not react with
either ylide or product. The internal standards used in this
study were chlorobenzene, 1,3-dichlorobenzene, and 1,2,4-
trichlorobenzene. Each mixture was filtered before use to
ensure a homogenous solution.
The weight ratio of the ylide with respect to the internal
standard was calculated from the ratio of the ylide peak area
to the peak area of the internal standard. The kinetic rate
was obtained by tracing the rate of disappearance of the
ylide with respect to the internal standard as follows:
An aliquot part (0.2 mL) of each solution containing the
ylide and the internal standard was pipetted into the reaction
tube, and the tube was placed in the pyrolyzer for 6 min un-
der nonthermal conditions. A sample was analyzed using the
HPLC probe with the UV detector at a wavelength of 256 or
210 nm, and the standardization value (Ao) was then calcu-
lated. Several HPLC measurements were obtained with an
accuracy of ≥2%. The temperature of the pyrolysis block
was then raised until approximately 10% pyrolysis was
deemed to occur over 900 s. This process was repeated after
each 10–15 °C rise in the temperature of the pyrolyzer until
>90% pyrolysis was achieved. The relative ratios of the inte-
gration values of the sample and the internal standard (A) at
the pyrolysis temperature were then calculated. At least
three kinetic runs were carried out at each reaction tempera-
ture following each 10–15 °C rise in the pyrolyzer tempera-
ture to ensure reproducible values of A. Treatment of the
(4-Cyanobenzyl)benzyl sulfone (4-NCC6H4CH2SO2CH2C6H5)
IR υmax (cm–1): 2229, 1731, 1664, 1496, 1313, 1120, 773,
1
644. H NMR (CDCl3) δH: 4.15 (2H, s), 4.24 (2H, s), 7.41–
7.50 (7H, m), 7.70 (2H, d, J = 8 Hz). MS m/z: 271 (M+·, 13),
207 (40), 206 (34), 130 (11), 116 (49).
Ylide 2
(4-Nitrobenzyl)benzyl sulfone (4-NO2C6H4CH2SO2CH2C6H5)
1
IR υmax (cm–1): 1525, 1349, 1296, 1116, 907, 730. H
NMR (CDCl3) δH: 4.20 (s, 2H), 4.26 (s, 2H), 7.44–7.48 (m,
5H), 7.55 (d, 2H, J = 8.8 Hz), 8.27 (d, 2H, J = 8.7 Hz).
Ylide 3
(3-Nitrobenzyl)benzyl sulfone (3-NO2C6H4CH2SO2CH2C6H5)
IR υmax (cm–1): 1528, 1352, 1320, 1256, 1118, 1077, 815,
1
699, 641. H NMR(CDCl3) δH: 4.2 (2H, s), 4.28 (2H, s),
7.43–7.48 (5H, m), 7.61 (1H, t, J = 8 Hz), 7.76 (1H, d, J =
7.7 Hz), 8.18 (1H, brs), 8.28 (1H, dd, J = 1, 8.2 Hz). 13C
NMR (CDCl3) + DEPT135 δC: 57.01 (CH2), 59.81 (CH2),
124.43, 126.33, 127.62, 129.4, 129.73, 129.89, 130.36,
131.09, 137.43, 145.5. MS m/z: 291 (M+·, 3), 227 (8), 178
(24), 165 (32), 152 (14), 105 (62).
Ylide 4
(4-Chlorobenzyl)benzyl sulfone (4-ClC6H4CH2SO2CH2C6H5)
1
IR υmax (cm–1): 1492, 1300, 1116, 902, 724. H NMR
(CDCl3) δH: 4.10 (2H, s), 4.18 (2H, s), 7.32 (2H, d, J =
8.4 Hz), 7.38–7.45 (7H, m). 13C NMR (CDCl3) + DEPT135
δC: 57.4 (CH2), 58.8 (CH2), 126.2, 127.8, 129.5, 129.6,
129.6, 131.2, 132.6, 135.8. MS m/z: 282 (2), 280 (M+·, 6),
© 2005 NRC Canada

Al-Bashir et al.
1553
8. H. Ndayikengurukiye, S. Jacobs, and W. Tachelet. Tetrahe-
dron, 53, 13811 (1997).
kinetic data and calculation of Arrhenius parameters and re-
action rate constants have been detailed elsewhere (10, 20,
21). The conditions for kinetic and HPLC analyses of the
ylides 1–9 are summarized in Table 3.
9. Mass Spectrometry Data Centre. Eight peak index of mass
spectra. 4th ed. Royal Society of Chemistry, Cambridge. 1991.
10. N.A. Al-Awadi, M.H. Elnagdi, K. Kaul, S. Ilingovan, and
O.M.E. El-Dusouqui. J. Phys. Org. Chem. 12, 1 (1999).
11. R. Taylor. In The chemistry of functional groups: Supplement
B. Edited by S. Patai. John Wiley, Chichester. 1979. p. 876.
12. H.H. Dib, N.A. Al-Awadi, Y.A. Ibrahim, and O.M.E. El-
Dusouqui. Tetrahedron, 59, 9455 (2003).
13. R.A. Aitken, J.I.G. Cadogan, and I. Gosney. Phosphorus, sul-
fur and silicon. Vol. 101. OPA, Amsterdam. 1995. p. 281.
14. A. Mylona, J. Nikokavouras, and I.M. Takakis. J. Chem. Res.
Miniprint, 12, 3514 (1986).
Acknowledgements
One of the authors (R.F.A.) wishes to thank the College of
Graduate Studies, Kuwait University for a PhD candidacy.
Kuwait University Research Grant SC 01/99 and ANALAB
and SAF Grant Nos. GS 01/01 and GS 03/01 are gratefully
acknowledged.
15. C. Imrie, T.A. Modro, E.R. Rohwer, and C.C.P. Wagener. J.
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© 2005 NRC Canada