Synthesis, thermal reactivity, and kinetics of stabilized phosphorus ylides, part 2: [(Arylcarbamoyl) (cyano)-methylene] triphenylphos-phoranes and their thiocarbamoyl analogues

Article abstract of DOI:10.1002/kin.20170

A series of five cyano(arylcarbamoyl) phosphorus ylides 2 and five cyano-(arylthiocarbamoyl) phosphorus ylides 3 are prepared and fully characterized. Pyrolytic reaction products of a representative example of each type obtained by flash vacuum pyrolysis technique show that they undergo thermal extrusion of Ph₃PO or Ph₃PS. Kinetic study of the gas-phase pyrolysis of each ylide by static method shows that these reactions are unimolecular and first order with no significant substituent effect, but the thiocarbamoyl ylides 3 react 40-65 times more rapidly than their carbamoyl analogues 2.

Full text of DOI:10.1002/kin.20170

Synthesis, Thermal
Reactivity, and Kinetics
of Stabilized Phosphorus
Ylides, Part 2:
[(Arylcarbamoyl)(cyano)-
methylene]triphenylphos-
phoranes and Their
Thiocarbamoyl Analogues
R. ALAN AITKEN,1 NOURIA A. AL-AWADI,2 OSMAN M. E. EL-DUSOUQUI,2
DORCAS M. M. FARRELL,1 AJITH KUMAR2
1School of Chemistry, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9ST, UK
2Department of Chemistry, Kuwait University, PO Box 5969, Safat 13060, Kuwait
Received 18 August 2005; revised 6 December 2005; accepted 7 December 2005
DOI 10.1002/kin.20170
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: A series of five cyano(arylcarbamoyl) phosphorus ylides 2 and five cyano-
(arylthiocarbamoyl) phosphorus ylides 3 are prepared and fully characterized. Pyrolytic reac-
tion products of a representative example of each type obtained by flash vacuum pyrolysis
technique show that they undergo thermal extrusion of Ph3PO or Ph3PS. Kinetic study of the
gas-phase pyrolysis of each ylide by static method shows that these reactions are unimolecular
and first order with no significant substituent effect, but the thiocarbamoyl ylides 3 react 40–65
times more rapidly than their carbamoyl analogues 2. ꢀ 2006 Wiley Periodicals, Inc. Int J Chem
C
Kinet 38: 496–502, 2006
INTRODUCTION
In a series of recent papers, one of us has described
the thermal extrusion of Ph3PO from oxo-stabilized
phosphorus ylides using the technique of flash vacuum
pyrolysis (FVP) as a general and preparatively useful
Correspondence to: Nouria A. Al-Awadi; e-mail: nouria@kuc01.
kuniv.edu.kw.
Contract grant sponsor: University of Kuwait.
Contract grant number: SC 03/99.
2006 Wiley Periodicals, Inc.
c
ꢀ

SYNTHESIS, THERMAL REACTIVITY, AND KINETICS OF STABILIZED PHOSPHORUS YLIDES
497
route for synthesis of alkynes [1–3]. In these studies,
no attempt was made to examine the kinetics of the
processes involved and indeed until recently the ther-
molysis of phosphorus ylides has not previously been
examined from the kinetic point of view [4]. We re-
cently reported kinetic data for the thermolysis of a
range of ꢀ,ꢁ-dioxo ylides [5], and in Part 1 of this series
[6] we presented a detailed kinetic study of substituted
benzoyl/arylcarbamoyl ylides and their thiocarbamoyl
analogues. Although this did give useful mechanistic
information, the process involved turned out to be sim-
ply reversion to the starting materials from which the
ylides were formed. Wehavelookedforrelatedsystems
in which more interesting thermal reactions might oc-
cur, and in this paper we describe the synthesis and
characterization of a series of 10 ylides stabilized by a
cyano and arylcarbamoyl or arylthiocarbamoyl group
together with a study of their thermal reactivity using
both FVP product studies and kinetic measurements.
informative with a consistent pattern of phosphorus
coupling observed. The one bond-coupling constants
to the ylide carbon of around 145 Hz for compounds 2
and 160 Hz for compounds 3 are remarkably high com-
pared to the values of 100–125 Hz normally observed
for stabilized ylides, but values of 140–145 Hz have
previously been observed for the cyano dithiocarboxy-
late ylides 4 [15]. More significantly from the point
of view of the likely pyrolysis behavior, the coupling
from phosphorus to the carbonyl carbon in compounds
2 was generally 9 Hz. On the basis of our extensive pre-
vious studies in ylide pyrolysis [16–24], the fact that
this value is below 10–12 Hz can be taken to indicate
a high contribution to the structure from the resonance
form 5 and therefore that the pyrolysis is likely to result
in extrusion of Ph3PO. For thiocarbonyl ylides such as
3, there have not been sufficient pyrolysis studies to
allow such a cutoff value to be established.
RESULTS AND DISCUSSION
Analysis of Pyrolysates
Although the interaction of stabilized ylides, including
Ph3P CHCN 1, with phenyl isocyanate was first re-
ported in 1959 [7], there has since been little work on
the resulting adducts [8–11], and this is also the case
with the corresponding isothiocyanate adducts [12–
14]. A series of five carbamoyl ylides 2 were prepared
by treatment of 1 with the appropriate aryl isocyanates
in CH2Cl2, and similar reaction with isothiocyanates
gave the thiocarbamoyl ylides 3 (see Scheme 1). The
products were all stable high-melting solids which gave
satisfactory analytical data and showed 31P NMR sig-
nals at from +22.6 to 22.7 for 2 and from +14.8 to 15.7
for 3. The 13C NMR spectra (Table I) were particularly
In Part 1, we showed that the early observation that
compounds 6 revert to the starting components (see
Scheme 2) from which they are formed upon heating
in boiling toluene [25,26] applies in general to ylides of
this type and their thiocarbamoyl analogues [6]. Since
the mechanism of this process involves interaction be-
tween the RCO carbonyl and NH, it seemed likely that
this would not happen when RCO is replaced by CN
and indeed this turned out to be the case. When ylide
2a was subjected to FVP, reaction was completed at
the relatively low temperature of 500◦C to give, at the
furnace exit, a solid identified as Ph3PO and, in the
cold trap, a liquid which was found to be mainly ani-
line (see Scheme 3). Ylide 3a behaved similarly to give
Ph3PSandaniline. Thus, itseemsthat, asexpectedfrom
the low value of 2 JP−CO, Ph3PO/S has been eliminated
but the resulting cyano-ynamine 7 has fragmented un-
der the conditions used to give aniline and gaseous
by-products. Compounds with the cyano-ynamine
Scheme 1
Scheme 2

498
AITKEN ET AL.
Part 1 [6], is attributed both to C S being weaker than
C O and to the greater nucleophilicity of sulfur than
oxygen.
EXPERIMENTAL
Synthesis
Scheme 3
Melting points were recorded on a Reichert hot-stage
microscope and are uncorrected. Infrared spectra were
recorded as Nujol mulls on a Perkin-Elmer 1420
instrument. NMR spectra were obtained for 1H at
300 MHz and for 13C at 75 MHz using a Bruker AM300
instrument and for 31P at 121 MHz using a Varian
Gemini 2000 instrument. All spectra were run on so-
lutions in CDCl3 unless otherwise stated with internal
structure are known [27], but they might be expected
to be thermally unstable. Although various ynamines
have been generated under FVP conditions, and those
with an NH present undergo isomerization to keten-
imines [28,29], it appears that the presence of a CN
group changes this reactivity in favor of radical frag-
mentation to give aniline as the only isolable product.
Once the nature of the pyrolysis process was estab-
lished, the kinetics were determined for all the com-
pounds except 2e which did not behave well in HPLC
and so failed to give satisfactory kinetic results. Kinetic
data, Arrhenius parameters, and rate coefficients of re-
action at 600 K are summarized in Table I.
1
Me4Si as reference for H and 13C and external 85%
H3PO4 for 31P. Chemical shifts are reported in ppm
to high frequency of the reference, and coupling con-
stants J are in Hz. Mass spectra were obtained on an
AEI/Kratos MS-50 spectrometer using electron impact
at 70 eV.
From the data presented in Table II it is clear that the
nature of the substituent X does not significantly affect
the rate of reaction. The relative rates of gas-phase py-
rolysis of the substrates are recorded in Table III. The
greater reactivity of the thiocarbamoyl ylides 3 over
their carbamoyl analogues 2, a feature also noted in
(Cyanomethylene)triphenylphosphorane 1 was pre-
pared using a literature method [30] as follows. A
solution of triphenylphosphine (26.2 g, 0.1 mol) and
chloroacetonitrile (7.6 g, 0.1 mol) in ethyl acetate
(20cm3)washeatedunderrefluxfor90min. Theresult-
ing precipitate was filtered off and washed with diethyl
Table I 13C NMR Spectra of Ylides 2 and 3, δC (JP
)
C
P-Phenyl
X
P C
C N
C O/S
C-1
C-2
C-3
C-4
Aryl Signals
2a
2b
2c
2d
2e
3a
3b
3c
3d
3e
H
33.7
(146)
35.4
(144)
33.9
(145)
33.3
(146)
33.0
(146)
49.6
(162)
53.0
(159)
50.0
123.1
(15)
122.3
(15)
122.9
(16)
123.3
(16)
123.4
(21)
120.9
(21)
120.2
(20)
120.8
(20)
167.6
(9)
167.6
(10)
167.5
(9)
167.5
(9)
167.4
(9)
189.6
(15)
189.3
(16)
189.7
(15)
123.9
(95)
123.3
(95)
123.8
(95)
124.1
(95)
124.1
(95)
124.6
(96)
123.6
(96)
124.3
(97)
133.6
(10)
133.6
(10)
133.6
(10)
133.6
(10)
133.7
(10)
133.7
(10)
133.7
(10)
133.7
(10)
129.1
(13)
129.3
(13)
129.1
(13)
129.1
(13)
129.1
(13)
128.9
(13)
129.1
(13)
129.0
(13)
133.0
(2)
133.3
(3)
133.1
(2)
132.9
(2)
133.0
(2)
132.6
(2)
133.0
(2)
132.7
(2)
139.6 (4ry), 128.7 (2CH),
122.7 (CH), 119.3 (2CH)
145.5 (4ry), 142.0 (4ry),
124.9 (2CH), 118.1 (2CH)
137.8(4ry), 128.6 (2CH),
127.3 (4ry), 120.4 (2CH)
136.5 (4ry), 132.1 (4ry), 129.2
(2CH), 119.3 (2CH), 20.7
155.4 (4ry), 132.3 (4ry), 121.2
(2CH), 114.0 (2CH), 55.5
139.4 (4ry), 128.4 (2CH),
125.1 (CH), 123.9 (2CH)
145.5 (4ry), 143.3 (4ry), 124.3
(2CH), 121.9 (2CH)
138.0 (4ry), 130.2, 128.4
(2CH), 125.2 (2CH)
136.8 (4ry), 135.0 (4ry), 129.0
(2CH), 124.3 (2CH), 21.0
157.2 (4ry), 132.4 (4ry), 126.3
(2CH), 113.6 (2CH), 55.4
NO2
Cl
Me
OMe
H
NO2
Cl
(161)
49.0
(162)
48.5
Me
OMe
121.1
(21)
121.1
(21)
189.8
(15)
190.1
(15)
124.8
(97)
124.7
(97)
133.7
(10)
133.7
(10)
128.9
(13)
128.9
(13)
132.5
(3)
132.5
(2)
(162)

SYNTHESIS, THERMAL REACTIVITY, AND KINETICS OF STABILIZED PHOSPHORUS YLIDES
499
Table II Kinetic Data for the Gas-Phase Elimination Reaction of 2 and 3
X
H
104 k (s−1) at T (K)
log10 A (s−1
)
Ea (kJ mol−1
)
Correlation
0.997
2a
0.38
421.3
1.47
444.0
3.05
457.0
1.62
446.6
0.74
390.2
1.71
407.6
0.74
399.2
1.94
409.2
1.47
409.1
0.96
3.16
5.31 16.88 26.00
13.36 0.67 143.64 5.77
12.70 0.76 140.55 6.75
12.94 0.18 144.09 1.66
13.53 1.19 147.88 10.65
433.2 442.6 452.6 464.4 470.3
3.32 10.17 26.19
453.0 469.2 479.2
2b NO2
2c Cl
2d Me
0.998
0.999
0.994
0.998
0.997
0.994
0.999
0.997
5.40
7.25 11.86 21.49 38.37
464.0 468.8 474.4 481.6 490.0
5.79 12.38 35.11
458.9 471.8 482.5
3a
H
1.16
397.0 406.8 414.0 421.0 429.0 435.0
4.66 8.51 18.51 32.79
419.8 426.8 438.0 447.6
2.08 4.48 6.37 15.90
409.4 418.4 426.2 436.6
3.65 5.41 10.85 19.24
418.9 426.1 434.9 443.4
3.47 4.48 7.92 12.27 22.57
420.0 426.0 433.6 441.5 448.4
2.64
5.09
7.76 12.56 17.94 34.59 9.71 0.33 103.56 2.63
444.2
3b NO2
3c Cl
3d Me
3e OMe
10.70 0.37 112.75 3.00
11.51 0.47 119.26 3.79
9.20 0.49 101.38 4.06
9.27 0.49 102.66 4.07
ether to afford (cyanomethyl)triphenylphosphonium
chloride (22 g, 65}) as colorless crystals, mp 268–
270◦C. This material was suspended in dry CH2Cl2
(300 cm3) and stirred while triethylamine (16.5 g,
0.165 mol) was added over 15 min. The mixture was
stirred for a further 30 min and then washed thoroughly
with water, dried, and evaporated to give the desired
ylide 1 (15.5 g, 79%) as beige crystals, mp 195–197◦C
(lit. [31], 190–192◦C); δH 7.8–7.4 (15H, m, Ph) and
1.65 (1H, br s, CH); δC 132.8 (d, J = 11 Hz, 6 × C-2
of P-Ph), 132.8 (3 × C-4 of P-Ph), 129.2 (d, J = 13 Hz,
6 × C-3 of P-Ph), 127.5 (d, J = 92 Hz, 3 × C-1 of P-Ph)
and −2.1 (d, J = 137 Hz, P C); δP + 23.4.
dropwise. After stirring for 2 h, the mixture was evap-
orated and the solid residue recrystallized from ethyl
acetate to give the product.
Characterization of Ylides 2a–e and 3a–e
[(Cyano)(phenylcarbamoyl)methylene]triphenylpho-
sphorane 2a. Using phenyl isocyanate gave colorless
prisms (3.78 g, 90%), mp 214–216◦C (lit. [7], 205–
206◦C) (Found: C, 76.9; H, 5.0; N, 6.4. C27H21N2OP
requires C, 77.1; H, 5.0; N, 6.7%); ꢂmax/ cm−1 (KBr):
3287, 2163, 1622, 1590, 1522, 1438, 1315, 1238, 1209,
1108, 753, 692; δH 7.80 (1H, br s), 7.70–7.40 (15H, m),
7.32–7.10 (3H, m), 7.00–6.90 (2H, m); δC see Table I;
δP +22.6; m/z 420 (M+, 10%), 328 (M+−ArNH, 70),
300 (6), 277 (100), 262 (20), 212 (25), 93 (90).
The aromatic isocyanates and isothiocyanates were
commercially available and were used without further
purification.
A solution of the ylide 1 (3.01 g, 10 mmol) in
CH2Cl2 (50 cm3) was stirred at room temperature (RT),
while a solution of the appropriate isocyanate or isoth-
iocyanate (10 mmol) in CH2Cl2 (10 cm3) was added
[(Cyano)(4-nitrophenylcarbamoyl)methylene]tri-
phenylphosphorane 2b. Using 4-nitrophenyl iso-
cyanate gave brown crystals (2.60 g, 56%), mp 246–
248◦C (Found: C, 69.5; H, 4.1; N, 8.9. C27H20N3O3P
requires C, 69.7; H, 4.3; N, 9.0%); νmax/cm−1: 3406,
2167, 1639, 1596, 1529, 1438, 1330, 1302, 1243,
1202, 1174, 1110, 856, 752, 722, 696; δH 8.08 (2H,
half AB pattern, J = 9 Hz) and 7.75–7.50 (17H, m);
δC see Table I; δP +22.7; m/z 465 (M+, 1%), 368 (2),
329 (24), 328 (M+−ArNH, 100), 183 (20), 69 (23).
Table III Rate Constants and Relative Rates at 400 K
in the Gas Phase
2
3
k(2)
k(3)
X
106k (s−1
)
104k (s−1
)
krel
=
H
NO2
Cl
Me
OMe
4.01
2.22
1.33
1.66
–
1.54
0.95
0.87
0.92
0.74
38
43
65
55
–
[(4-Chlorophenylcarbamoyl)(cyano)methylene]tri-
phenylphosphorane 2c. Using 4-chlorophenyl isocya-
nate gave colorless crystals (2.77 g, 61%), mp 231–
232◦C (Found: C, 71.3; H, 4.4; N, 5.9. C27H20ClN2OP

500
AITKEN ET AL.
requires C, 71.3; H, 4.4; N, 6.2%); νmax/cm−1: 3285,
2178, 1611, 1584, 1518, 1308, 1239, 1104, 826, 748,
720, 694; δH 7.75–7.45 (15H, m), 7.40, 7.18 (4H,
AB pattern, J = 9 Hz); δC see Table I; δP +22.6;
m/z 456 (37Cl − M+, 1%), 454 (35Cl − M+, 3), 328
(M+−ArNH, 100), 183 (25), 91 (15).
[(4-Chlorophenylthiocarbamoyl)(cyano)methylene]-
triphenylphosphorane 3c. Using 4-chlorophenyl
isothiocyanate gave colorless crystals (2.96 g, 63%),
mp 212–214◦C (Found: C, 68.8; H, 4.2; N, 5.8.
C27H20ClN2PS requires C, 68.9; H, 4.3; N, 5.9%);
νmax/cm−1: 3432, 3235, 2164, 1588, 1525, 1490,
1314, 1284, 1236, 1110, 832, 726, 689; δH 8.45 (1H,
br s), 7.85–7.65 (6H, m), 7.65–7.40 (11H, m), 7.22
(2H, half AB pattern, J = 9 Hz); δC see Table I; δP
+15.1; m/z 472 (37Cl−M+, 3%), 470 (35Cl−M+, 10),
437 (7), 363 (12), 361 (31), 344 (45), 294 (85), 262
(25), 183 (100).
[(Cyano)(4-methylphenylcarbamoyl)methylene]tri-
phenylphosphorane
2d. Using
4-methylphenyl
isocyanate gave colorless crystals (2.04 g, 47%),
mp 228–230◦C (Found: C, 77.6; H, 5.3; N, 6.6.
C28H23N2OP requires C, 77.4; H, 5.3; N, 6.4%);
νmax/cm−1: 3296, 2171, 1618, 1590, 1523, 1436,
1316, 1222, 1105, 815, 746, 716, 690; δH 7.75–7.45
(15H, m), 7.33, 7.04 (4H, AB pattern, J = 9 Hz), 2.28
(3H, s); δC see Table I; δP +22.6; m/z 434 (M+, 6%),
328 (M+−ArNH, 100), 183 (16), 165 (6), 77 (7).
[(Cyano)(4-methylphenylthiocarbamoyl)methylene]-
triphenylphosphorane 3d. Using 4-methylphenyl
isothiocyanate gave colorless crystals (2.07 g, 46%),
mp 214–216◦C (Found: C, 74.7; H, 5.1; N, 6.0.
C28H23N2PS requires C, 74.6; H, 5.1; N, 6.2%);
νmax/cm−1: 3436, 3236, 2164, 1590, 1526, 1315,
1110, 957, 714, 693; δH 8.47 (1H, br s), 7.85–7.70
(6H, m), 7.65–7.45 (9H, m), 7.45, 7.12 (4H, AB
pattern, J = 9 Hz), 2.30 (3H, s); δC see Table I; δP
+14.8; m/z 450 (M+, 40%), 417 (55), 344 (90), 341
(100), 294 (25), 262 (30), 183 (86).
[(Cyano)(4-methoxyphenylcarbamoyl)methylene]tri-
phenylphosphorane 2e. Using 4-methoxyphenyl
isocyanate gave yellow crystals (1.22 g, 27%),
mp 223–225◦C (Found: C, 74.9; H, 5.0; N, 5.6.
C28H23N2O2P requires C, 74.7; H, 5.1; N, 6.2%);
νmax/cm−1: 3295, 2167, 1608, 1594, 1529, 1510, 1313,
1217, 1108, 1034, 828, 720, 694; δH 7.75–7.60 (9H,
m), 7.60–7.45 (6H, m), 7.35, 6.78 (4H, AB pattern,
J = 9 Hz), 3.76 (3H, s); δC see Table I; δP +22.6; m/z
450 (M+, 7%), 328 (M+−ArNH, 100), 183 (17), 49
(16).
[(Cyano)(4-methoxyphenylthiocarbamoyl)methylene]
triphenylphosphorane 3e. Using 4-methoxyphenyl
isothiocyanate gave colorless crystals (2.19 g, 47%),
mp 190–192◦C (Found: C, 72.1; H, 4.9; N, 5.8.
C28H23N2OPS requires C, 72.1; H, 5.0; N, 6.0%);
νmax/cm−1: 3437, 3258, 2160, 1524, 1510, 1313,
1237, 1110, 1040, 956, 721, 691; δH 8.42 (1H, br s),
7.85–7.70 (6H, m), 7.65–7.45 (9H, m), 7.43, 6.85 (4H,
AB pattern, J = 9 Hz), 3.87 (3H, s); δC see Table I; δP
+14.8; m/z 466 (M+, 26%), 433 (25), 357 (80), 344
(100), 294 (68), 262 (30), 183 (90), 108 (25).
[(Cyano)(phenylthiocarbamoyl)methylene]triphenyl-
phosphorane 3a. Using phenyl isothiocyanate gave
pale yellow flakes (4.14 g, 95%), mp 206–208◦C
(Found: C, 74.0; H, 4.7; N, 6.15; S, 6.8. C27H21N2PS
requires C, 74.3; H, 4.9; N, 6.4; S, 7.3%); νmax/cm−1
(KBr): 3433, 3264, 2165, 1593, 1525, 1497, 1440,
1315, 1270, 1109, 746, 691; δH 8.52 (1H, br s),
7.85–7.70 (6H, m), 7.65–7.45 (9H, m), 7.35–7.25 (3H,
m), 7.15–7.05 (2H, m); δC see Table I; δP +14.9; m/z
436 (M+, 12%), 403 (14), 344 (32), 327 (50), 294
(50), 277 (65), 262 (50), 183 (100).
Procedure for Product Analysis by Flash
Vacuum Pyrolysis
The sample was volatilized from a tube in a Bu¨chi
Kugelrohr oven through a 30 cm × 2.5 cm horizontal
fused quartz tube. This was heated externally by a Car-
bolite Eurotherm tube furnace MTF-12/38A at a tem-
perature of 500◦C, the temperature being monitored
by a Pt/Pt–13%Rh thermocouple situated at the center
of the furnace. The products were collected in a U-
shaped trap cooled in liquid nitrogen. The whole sys-
tem was maintained at a pressure of 10−2 Torr by an
Edwards model E2M5 high capacity rotary oil pump,
the pressure being measured by a Pirani gauge situ-
ated between the cold trap and the pump. Under these
conditions, the contact time in the hot zone was esti-
mated to be ≈10 ms. Yields were estimated by adding
[(Cyano)(4-nitrophenylthiocarbamoyl)methylene]tri-
phenylphosphorane 3b. Using 4-nitrophenyl isoth-
iocyanate gave pale yellow crystals (3.51 g, 73%),
mp 217–219◦C (Found: C, 67.5; H, 4.4; N, 8.8.
C27H20N3O2PS requires C, 67.3; H, 4.2; N, 8.7%);
νmax/cm−1: 3430, 2186, 1592, 1514, 1304, 1260,
1240, 1107, 850, 752, 714, 685; δH 8.80 (1H, br s),
8.15, 7.92 (4H, AB pattern, J = 9 Hz), 7.85–7.70 (6H,
m), 7.70–7.50 (9H, m); δC see Table I; δP +15.7; m/z
481 (M+, 20%), 448 (10), 372 (65), 368 (30), 344
(65), 183 (75), 91 (90), 57 (100).

SYNTHESIS, THERMAL REACTIVITY, AND KINETICS OF STABILIZED PHOSPHORUS YLIDES
501
an accurately weighed quantity of a standard such as
CH2Cl2 or MeCN to the NMR solutions and comparing
integrals.
compounds were detected by UV absorbance at 210 or
256 nm. Concentrations for each run were calculated
based on the ratio of the substrate peak area to the peak
area of the internal standard detected using a Waters
intergrator. Peaks assigned to the substrates and stan-
dards were cleanly separated from each other and from
theproducts. Analyticaluncertaintyinthepeakareade-
termination is estimated as 2%. Rate constants were
determined from the equation (k = −1/t ln(At /A0)),
where t is the reaction time, A0 is the initial concen-
tration, and At is the concentration after time t. For
purposes of calculating rate constants, the lowest tem-
perature examined was that at which approximately
10% pyrolysis occurs over 900 s. The reaction temper-
ature was then increased in intervals of 10–15 K un-
til approximately 90% conversion was observed. The
relative ratios of the integration values of the sample
and the internal standard (A) at the pyrolysis temper-
ature were then calculated. A minimum of three ki-
netic runs were carried out at each 10–15◦C rise in the
temperature of the pyrolyzer to ensure reproducibility.
The standard deviation of the rate values reported in
Table I is between 1.4 × 10−4 and 1.2 × 10−5. Temper-
ature was controlled by means of an Eurotherm 093
precision temperature regulator set to provide 0.1 in-
cremental change achieved by a digital switch which
gives an overall temperature output. A platinum resis-
tance thermocouple is connected from the other end to
a comark microprocessor thermometer to read the ac-
tual pyrolysis temperature. Reactions were ascertained
to be homogeneous and free from surface effects and
radical pathways in auxiliary experiments in which the
tubes were packed with quartz helices so as to increase
the surface area by approximately six-fold [32,33]. The
rates at 600 K are calculated using the kinetic equation
for first-order reactions:
Pyrolysis of 2a (100 mg) at 500◦C gave two frac-
tions. A colorless solid at the furnace exit proved to be
Ph3PO (70%); δC 132.5 (d, J = 104 Hz, C-1), 132.1 (d,
J = 10 Hz, C-2), 131.1 (d, J = 2 Hz, C-4), 128.7 (d,
J = 12 Hz, C-3); δP +28.2; m/z 277 (M+ − H, 100%),
201 (40), 199 (36), 183 (62), 93 (70), 77 (45). The dark
colored liquid in the cold trap consisted mainly of ani-
line (∼50%); δH (CD3SOCD3) 7.03 (2H, t, J = 8 Hz),
6.59 (2H, d, J = 8 Hz), 6.51 (1H, t, J = 8 Hz), 5.00
(2H, br s); m/z 93 (M+, 100%), 66 (50), 65 (45).
Pyrolysis of 3a (100 mg) at 500◦C gave two frac-
tions. A colorless solid at the furnace exit proved to be
Ph3PS (80%); δC 132.8 (d, J = 85 Hz, C-1), 132.3 (d,
J = 11 Hz, C-2), 131.6 (d, J = 2 Hz, C-4), 128.5 (d,
J = 12 Hz, C-3); δP +43.2; m/z 294 (M+, 100%), 262
(50), 183 (80), 77 (50). The dark colored liquid in the
cold trap consisted mainly of aniline (∼40%); δH 7.10
(2H, t, J = 8 Hz), 6.67 (1H, t, J = 8 Hz), 6.61 (2H,
d, J = 8 Hz), 3.55 (2H, br s); δC 129.3 (2C), 118.6
(1C), 115.1 (2C); m/z 93 (M+, 100%), 66 (50), 65
(45).
Kinetic Runs and Data Analysis
Stock solution (7 mL) was prepared by dissolving 6–
10 mg of the substrate in acetonitrile as 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 substrate to standard
(2.5:1). The solvent (acetonitrile) and the internal stan-
dard (chlorobenzene) were selected because both are
stable under the conditions of pyrolysis, and because
they do not react with either substrate or product. Each
reaction mixture was filtered to ensure that a homoge-
neous solution was obtained.
The weight ratio of the substrate with respect to
the internal standard was calculated from the ratio of
the substrate peak area to the peak area of the internal
standard. The kinetic rate was obtained by tracing the
rate of disappearance of the substrate with respect to
the internal standard as follows.
Ea
log k = log A −
4.575T
Treatment of the kinetic data has been detailed else-
where [34–36].
ACKNOWLEDGMENT
An aliquot part (0.2 mL) of each solution contain-
ing the substrate and the internal standard was pipetted
into Pyrex reaction tube (15 mm i.d., 18 mm o.d., 120
mm length, volume 21.2 mL) which was then placed
in liquid nitrogen in order to freeze the contents of the
tube, then sealed under vacuum (6 × 10−2 mbar), and
then placed in the pyrolyzer for 6 min under nonthermal
conditions. The reaction tube was then opened, and a
sample was transferred by microsyringe directly from
the tube, injected and analyzed using HPLC probe. The
The facilities of ANALAB and SAF are gratefully
acknowledged.
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