+
+
7500 J. Am. Chem. Soc., Vol. 118, No. 32, 1996
Block et al.
1
H), 1.90 (dd, J ) 7.0, 1.6 Hz, 3 H), 1.18 (s, 9 H); 13C NMR (CDCl
3
)
13C NMR (CDCl
3
) δ 163.67, 148.41, 138.74, 124.96, 122.42, 61.32,
+
δ 139.21, 131.79, 54.80, 22.56, 15.76; EI-MS same as (E)-9b. Anal.
Calcd (found) for C 14OS: C, 57.49 (57.28); H, 9.65 (9.90).
-Methyl-2-propyl Vinyl Sulfoxide (9c). To a THF solution of
dCHMgBr (prepared from 0.5 mol each of CH dCHBr and Mg
14.01; EI-MS, m/z (rel intensity) 174 (M , 14), 59 (100). Anal. Calcd
(found) for C H O S: C, 48.26 (48.58); H, 5.79 (6.07).
7 10 3
7
H
2
Gas-Phase Pyrolysis of 9c. The pyrolysis apparatus consisted of a
25 cm quartz tube fitted with 14/20 joints containing a thermocouple
held against the outside of the tube by a strip of asbestos. The asbestos
was covered with coiled nichrome wire wrapped the length of the tube,
and this in turn was covered with layers of glass wool and asbestos. A
sample of 2 g of 9c maintained at 30 °C was evaporated during 13 h
through the tube, heated to 400 °C, at a pressure of 0.01 mmHg. In a
CH
2
2
turnings using 350 mL of dry THF and decanting the clear supernatant
liquid away from accumulated white salts) at -10 °C internal
temperature under argon in a 1 L three-necked flask was added dropwise
a solution of 2-methyl-2-propanesulfinyl chloride (51 g, 0.37 mol) in
THF (125 mL). The brown solution was concentrated in Vacuo, and
the thick brown residue was treated with saturated aqueous NH
mL) and 1 N HCl (10 mL) and then extracted with CHCl
mL). The extract was dried (MgSO ), filtered, and concentrated in
5
3
Cl (50
trap cooled by liquid N
2
a colorless, lachrymatory pyrolysate collected.
4
1
(2 × 100
H NMR analysis showed this product to consist of isobutene and 95:5
(Z)/(E) ethanethial S-oxide (5a).
3
4
Vacuo and the residue was distilled to afford 9c (16 g, 35% yield) as
a colorless liquid: bp 65-70 °C/2 mmHg, IR (νmax, neat) 1600 (CdC)
Gas-Phase Pyrolysis of 9b. Using the procedure described above,
pyrolysis of 9b afforded a mixture of isobutene and 97:3 (Z)-/(E)-
propanethial S-oxide (5b; by NMR analysis).
-
1
1
and 1050 cm (SdO), H NMR (CDCl ) δ 6.59 (dd, J ) 9.9, 16.6
3
Hz, 1 H), 6.09 (d, J ) 16.5 Hz, 1 H), 6.04 (d, J ) 10.0 Hz, 1 H), 1.24
Liquid-Phase Pyrolysis of 9b. In a 5 mL flask fitted with a short
path distillation head cooled with circulating ice water was placed 0.5
g of 9b. The flask was heated at 110 °C for 3 h whereupon ca. 0.1
mL of colorless liquid was collected in the receiving flask. Analysis
1
3
(
(
(
s, 9 H); C NMR (CDCl
3
) δ 136.46, 123.46, 54.46, 22.61; MS m/z
, 25), 57(100). Anal. Calcd
+
rel intensity) 132 (M , 6), 76 (P - C
found) for C
4
H
8
6
H12OS: C, 54.50 (54.48); H, 9.15 (9.29).
1
by H NMR spectroscopy identified the distillate as principally
FT-MW Spectroscopic Methods. Pyrolysis precursors 9b or 9c
acetaldehyde.
were placed in a stainless-steel trap pressurized to 20 psi with 4:1 Ne/
He. The output mixture from the trap was flowed by way of a 1 mm
id quartz capillary tube through a 30.5 cm furnace region maintained
at 350 °C. A continuous flow of products was maintained by passing
the furnace effluent through one port of a dual flow pulsed valve
(E,Z)-Ethanethial S-Oxide (5a). Following the procedure detailed
51
for the preparation of 5b, ethanesulfinyl chloride (prepared in 94%
yield from ethyl thioacetate5 ) was treated with Et
1b
3 3
N in CFCl at -78
°C (4 h) to -20 °C (overnight). Isolation of 5a was achieved in a
manner similar to that for 6 except that the final trap-to-trap distillation
2
3
(
described previously ) and a bubbler before being exhausted into a
1
13
hood. A precision double-ended micrometer needle valve located
between the pulsed-solenoid valve and the exhaust hood allowed the
pressure in the gas line to be adjusted between 1 and 30 psi while
maintaining the gas flow at 2-5 mL/min. Spectra were most intense
when the precursors of 5a,b were heated to 50 and 60 °C, respectively.
Spectral searches were initiated when transitions of the coproduct
isobutene were observed. With this flow system, it normally took 4-8
h of conditioning of the gas lines leading from the furnace to the pulse
valve in order to see spectral transitions of 5a,b. The deuteration
was conducted at -40 °C/0.001 mmHg. See Table 1 for H, C, and
7
1
O NMR data.
(E,Z)-2-Methylpropanethial S-Oxide (5d). Following the proce-
dure described for the preparation of 5b, 2-methyl-1-propanesulfinyl
5
1
chloride (prepared in 95% yield from (Z)-2-methyl-1-propyl
thioacetate5 ) was treated with Et
1b
3 3
N in CFCl at -40 °C (6 h) to -20
°C (overnight). Isolation of 5d was achieved as described for 5b except
that the final trap-to-trap distillation was conducted at -25 to -30
1
13
17
°C/0.001 mmHg. See Table 1 for H, C, and O NMR data.
(E,Z)-2,2-Dimethylpropanethial S-Oxide (5e). 2,2-Dimethyl-1-
propanesulfinyl chloride (5.1 g, 33 mmol; prepared in 83% yield by
experiments using the precursors were done by putting D
2
O (99.9%
D; ca. 20 mL) into a 6 L steel cylinder, pressurizing it with Ar or the
Ne/He mixture, and flowing this gas through the precursor trap and
into the furnace as described above.
chlorination of bis(2,2-dimethyl-1-propyl) disulfide54 in Ac
O; the
2
sulfinyl chloride had bp 35-45 °C/0.2 mmHg; IR (νmax) 1140 cm-
1
1
and H NMR (CDCl
3
) 3.53 (s, 2 H), and 1.18 (s, 9 H)) was treated at
N (3.3 g, 33 mmol) in CFCl (125 mL) and kept at
15 °C for 2 days. The nonlachrymatory, rather unstable product was
The procedure for observing the LF directly from the onion also
utilized the flow nozzle. A 4:1 Ne/He stream was used to purge a
standard drying tube, which had an outlet coupled to a 30.5 cm tube
leading into the pulse nozzle. While purging, a yellow onion was
macerated in a kitchen food processor. Then, a toggle valve was closed
to isolate the nozzle and the onion mash was placed in the drying tube
while maintaining a slow Ne/He flow through the tube. The spec-
-
10 °C with Et
-
3
3
isolated as above with purification by distillation at 10-15 °C/0.01
1
13
17
mmHg. See Table 1 for H, C, and O NMR data.
trans-3,4-Diethyl-1,2-dithietane 1,1-Dioxide (12a). A sample of
freshly distilled 5b was dissolved in twice its volume of freshly dried
benzene. The mixture was transferred to a 5 mL vial, flushed with
dry argon, stoppered tightly with a rubber septum, and kept in the dark
at 5 °C. Several samples were prepared in the same manner, and the
progress of the reaction was followed daily by NMR analysis. The
samples turned deep yellow after 7 days and NMR analysis showed
complete decomposition of 5b. The yellow solution, now devoid of
lachrymatory properties, was concentrated in Vacuo leaving a yellow
trometer was tuned to rotational transitions of (Z)-5b and (E)-5b,2
4a
and the spectrum appeared as soon as the toggle valve leading to the
nozzle was opened. The intensity of the transition varied considerable
from one onion to the next, as well as over time. Figure 1 illustrates
the best signal to noise obtained for the J ) 404-303 transition of (Z)-
2
4a
5
b at 16783.7989 MHz.
The deuteration of the LF was done in the
O (ca. 20 mL) was added to the food
same manner except that D
2
-3
oil. The oil was subjected to molecular distillation (50 °C, 10 mmHg)
yielding a practically colorless, clear liquid with a strong onion-like
odor. GC analysis showed a single major product with a retention
time of 9.45 min at 140 °C (3 mm × 1.2 m, 10% Apiezon
L/Chromosorb W column): HRMS molecular weight m/z 180.0278
processor and blended with the onion. The J ) 404-303 transition of
at 16674.3963 MHz was monitored.24a
Z)-5b-d
1
(
FVP-Mass Spectroscopic Study of 9c. At 200-250 °C new species
m/z 76 (C SO) and 56 (C ) were produced as the parent molecule
2
H
4
4 8
H
ion m/z 132 disappeared. The decomposition appeared to be clean in
this temperature range.
Trapping of Ethenesulfenic Acid (2e) in Solution as Ethyl (E)-
(
Calcd for C
6
H
12
O
2
S
2
: 180.0279); UV λmax (C
2 5
H OH or hexane) at
-1
ca. 280 (ꢀ 100, sh); IR (νmax, neat) 1139, 1133 cm (SO
2
). See Table
1
13
17
1
for H, C, and O NMR data.
trans-4,5-Diethyl-1,3-dithiolane-2-thione (trans-14). cis-3,4-Ep-
oxyhexane (8 g, 80 mmol; bp 78-79 °C), prepared in 80% yield by
3
-(Vinylsulfinyl)acrylate (10). A solution of 9c (1 g; 7.5 mmol) in
ethyl propiolate (38 mmol) was refluxed under Ar for 20 h. The
reaction mixture was concentrated in vacuo and subjected to column
55
peracetic acid oxidation at 0 °C of cis-3-hexene in CH
added to a stirred solution of potassium methyl xanthate (11.2 g, 0.2
mol KOH; 18.24 g, 0.24 mol CS ; 75 mL of CH OH) and the mixture
was stored at 25 °C for 6 days. Treatment of the mixture with water
2 2
Cl , was slowly
chromatography (silica gel; CH
2 2 2 2
Cl followed by 1:19 EtOAc/CH Cl )
giving 10 (0.384 g, 29% yield), a yellow liquid; IR (νmax, neat) 1724
-
1
1
2
3
(
(
CdO), 1620 (CdC), 1293 (C-O) and 1074 cm (SdO), H NMR
CDCl ) δ 7.48 (d, J ) 14.9 Hz, 1 H), 6.60 (dd, J ) 16.5, 9.6 Hz, 1
3
H), 6.55 (d, J ) 15.0 Hz, 1 H), 6.09 (d, J ) 16.6 Hz, 1 H), 5.93 (d, J
9.9 Hz, 1H), 4.20 (q, J ) 7.1 Hz, 2 H), 1.26 (t, J ) 7.1 Hz, 3 H);
(
54) (a) Tanner, D. D.; Browlee, B. G. Can. J. Chem. 1973, 51, 3366.
(b) Bordwell, F. G.; Pitt, B. M.; Knell, M. J. Am. Chem. Soc. 1951, 73,
004.
(55) Reif, D. J.; House, H. O. Org. Syn. 1963, 4, 860.
)
5
(53) Block, E.; O’Connor, J. J. Am. Chem. Soc. 1974, 96, 3921.