Carbanion Intermediates in Aqueous Acid
J . Org. Chem., Vol. 63, No. 3, 1998 811
min. The reaction mixture was stirred for 3.5 h; workup with
dichloromethane followed by washing with ice cold water and
HCl (10%), drying, and evaporation of the organic phase
followed by fractional distillation gave 4 (2.8 g, 62%) as a clear
Though carbanion formation with water (rather than
hydroxide ion) acting as the base is well-precedented in,
for example, the ionization in water of such very strong
carbon acids as 2-(dicyanomethylene)-1,1,3,3-tetracyano-
propane12 and tris(methylsulfonyl)methane,13 the hy-
drolysis of 1 is to the best of our knowledge the first
clearly demonstrated example of reversible and irrevers-
ible E1cB reactions induced by water. We were fortunate
in this instance to be able to induce H-D exchange under
acidic conditions, and hence to observe the alteration in
the reaction from (E1cB)irr to (E1cB)rev, thereby providing
an easy way to distinguish the (E1cB)irr and E2 processes.
liquid. 1H NMR δ 3.15 (s), 13C NMR δ 38.0, 63.6 (4 × 5, J CF
)
38.1 Hz, J CD ) 23.4 Hz), 121.2 (q, J ) 277.5 Hz), 19F NMR δ
-74.47 (s). A solution of sodium thiocyanate (3.6 g, 44.4 mmol)
in DMF (25 mL) was heated till the head temperature reached
150 °C (6 mL of DMF collected). To the cooled reaction mixture
was added 4 (2 g, 11.1 mmol), and the reaction mixture slowly
distilled over a period of 2 h. The distillate was taken up in
pentane (100 mL), and the solution was washed with water
(4 × 50 mL). The pentane layer was dried over anhydrous
MgSO4 and the solvent carefully distilled off to give 5 (600
mg, 37.8%) as a light yellow liquid; 19F NMR δ -66.7 (s).
Conversion of 5 to 6 followed the preparation of 1; 5 (520 mg,
3.63 mmol) gave 6 (355 mg, 53%) as a clear liquid. The 1H
NMR spectrum showed only signals due to the presence of
traces of DMF; 19F NMR δ -62.36 (s).
Exp er im en ta l Section
Laboratory procedures, spectra determination, and pH-stat
rate measurements were carried out as previously described,14
except that a Neslab ULT-80 low-temperature bath circulator
was used for rate measuurements at 1.0 °C. 2,2,2-Trifluoro-
ethanesulfonyl chloride (1) was either purchased from Aldrich
Chemical Co. Inc. and used as supplied, or prepared by the
following variation on the literature15 procedure. Aqueous 6
M HCl (20 mL) in an ice bath was saturated with Cl2, and
CF3CH2SCN15 (1.81 g, 12.8 mmol) was quickly added to the
stirred solution. The reaction mixture was stirred for 8 min
with a constant flow of Cl2. Workup, followed by distillation
under reduced pressure, gave 1 (1.28 g, 53%) as a clear liquid.
1H NMR δ 4.43 (q, J ) 8 Hz, 2H); 19F NMR δ -62.09 (t, J )
8 Hz); reported 1H NMR (neat) δ 4.37 (q, J ) 9 Hz, 2H).16
Authentic 2,2,2-trifluoroethanesulfonic acid was prepared by
stirring a mixture of 1 (283 mg, 1.55 mmol) and water (5 mL)
for 1.5 h and then removing the water under reduced pressure
P r od u cts of Deu ter iolysis of 1 a n d Hyd r olysis of 6. In
D2O. A sample of 1 (10 mg, 0.055 mmol) in CD3CN:D2O, 20:
80, after 15 min showed 1H, 13C, and 19F NMR signals
-
assignable almost entirely to monodeutrated CF3CHDSO3
,
with a small amount (e2%) of CF3CH2SO3-. Similar spectra
-
were obtained for the reaction in pH 2-7 range; CF3CHDSO3
1H NMR (D2O/DSS) δ 3.86 (qt, J ) 9 Hz, J ) 2.3 Hz, 1H);
13C NMR (D2O/DSS) δ 54.9 (qt, J ) 30 Hz, J ) 21 Hz), 125.3
(q, J ) 275.5 Hz); 19F NMR (D2O/CFCl3) δ -63.49 (d, J ) 9
Hz). In H2O. Similar reaction of 6 (10 mg, 0.054 mmol) in
CD3CN:H2O, 20:80, mixtures in pH range 2-7 after 15 min
:
showed signals assignable mostly to CF3CHDSO3- and a trace
-
of CF3CD2SO3
.
P r oced u r e for Hyd r olysis Ra te Mea su r em en ts. Aque-
ous KCl (50 mL, 0.05 M) solution was brought to 1 °C and the
desired pH using 0.1 M H2SO4 or 0.1 M NaOH. To the above
stirred solution was added a solution of 1 (or 6) (3.72 mg, 0.02
mmol) in THF (50 µL), and the pH of the solution was kept
constant with NaOH (0.1 M). The rate of hydrolysis was
monitored by recording the volume of the titrant (NaOH)
added with time. Plots of ln(V∞ - Vt) versus time were
constructed from the volume of sodium hydroxide titrant
added. The pseudo-first-order rate constants were then
obtained from the slopes of straight lines; the results are
shown in Figure 1 and listed in Table S1 (see also Table 1).
The pH-stat measurements at 4.5 °C were carried out similarly
except that a mixture of CH3CN (10 mL) and aqueous KCl
solution was kept at 4.5 °C in a Haake FJ constant temper-
ature circulating bath, and a solution of 1 (3.11 mg, 0.017
mmol) in dry CH3CN was used for each run.
1
leaving tresic acid as a clear liquid (202 mg, 80%); H NMR
(D2O/DSS) δ 3.88 (q, J ) 10 Hz, 2H); 19F NMR δ -63.4 (t, J )
10 Hz); reported16 1H NMR (D2O) δ 3.87 (q, J ) 10 Hz, 2H).
2,2,2-Tr iflu or oeth a n esu lfon yl-1,1-d 2 Ch lor id e (6). Ben-
zyl trifluoroacetate (2) (15 g, 73.5 mmol) from a literature
preparation17 (in 80% yield) was added dropwise to a slurry
of LiAlD4 (2 g, 48 mmol) in dry ether (80 mL) under N2, over
a period of 40 min, and the mixture was stirred for 1 h at rt.
Excess reducing agent was destroyed by dropwise addition of
water, followed by addition of 20% H2SO4 (50 mL). The
reaction mixture was extracted with dichloromethane (200
mL). Fractional distillation using a Vigreux column (12 cm)
gave fractions that contained 3 (5 g, 67%) with a little diethyl
ether. 1H NMR δ 3.5 (br, s, OH); 19F NMR δ -77.86 (s).
Triethylamine (3.08 g, 30.4 mmol) was added to a stirred
solution of 3 (2.7 g, 26.5 mmol) in dry ether (75 mL) in an ice
bath, and methanesulfonyl chloride (3.34 g, 29 mmol) was
added dropwise from an addition funnel over a period of 15
Ack n ow led gm en t. We thank the Natural Sciences
and Engineering Research Council of Canada for finan-
cial support of this study.
(12) Middleton, W. J .; Little, E. L.; Coffman, D. D.; Engelhardt, V.
A. J . Am. Chem. Soc. 1958, 80, 2795-2806.
(13) Schwartzenbach, G.; Felder, E.; Helv. Chim. Acta 1944, 27,
1701-1711.
Su p p or tin g In for m a tion Ava ila ble: Rate constants for
the hydrolysis of 1 and 6 at 1 °C and of 1 in H2O:CH3CN 80:
20 at 4.5 °C (1 page). This material is contained in libraries
on microfiche, immediately follows this article in the microfilm
version of the journal, and can be ordered from the ACS; see
any current masthead page for ordering information.
(14) King, J . F.; Gill, M. S. J . Org. Chem. 1996, 61, 7250-7255.
(15) Crossland, R. K.; Wells, W. E.; Shiner, V. J ., J r. J . Am. Chem.
Soc. 1971, 93, 4217-4219.
(16) Bunyagidj, C.; Piotrowska, H.; Aldridge, M. H. J . Org. Chem.
1981, 46, 3335-3336.
(17) Oliverio, V. T.; Sawicki, E. J . Org. Chem. 1955, 20, 363-367.
J O971872V