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L. Appelbaum et al. / Journal of Organometallic Chemistry 592 (1999) 240–250
Only negligible current is observed, no loss of tetralin,
nor any oxidation was detected after 3 h.
formation was followed in the course of CPE on HPLC
based on calibration graphs. Between 9 and 10 samples
were taken at predetermined times in each run. Te-
tralone gives a strong HPLC signal as compared to
tetralin, tetralol and other products, due to the high
response factor of the UV detector.
GC–MS from reactions 2–3 shows m/z (%): te-
tralin=132(46), 117(12), 115(12), 104(100), 91(4); 1,2-
dihydronaphthalene 131(54), 130(100), 129(35), 119(27),
115(19), 91(4); 1-tetralol 148(42), 147(38), 131(19),
130(100), 129(38), 120(92), 119(54), 115(23), 105(42),
104(8), 91(58); 1-tetralone 146(69), 131(15), 118(100),
115(12), 104(4), 90(65); 1-acetamidotetralin (identified
by GC–MS only): 189(7), 146(13), 131(16), 130(100),
129(25), 119(11), 118(4), 117(2), 115(11), 91(7) (from
reaction 3, trace amount).
Acetamidotetralin m/z 189 was found in uncatalyzed
direct reactions at high potential. Chlorotetralin was
detected in trace amounts in one catalyzed run only
(out of ten), and identified by GC–MS only. Tetralin
itself contains trace impurities m/z=130 m/z=128
presumably 2,3-dihydronaphthalene and naphthalene.
Electrolysis of 3; A ‘H-shaped’ cell with a fritted
glass separator was used with Pt electrodes as above
with 90 ml acetonitrile solutions of TBAP 0.1 M in
each compartment. Compound 3, 2.5×10−5 mol
(2.8×10−4 M) was added to the anode compartment
and electrolyzed at 1.4 V (Ag ꢀ AgBF4) for 3 h, under a
steady current of 130 mA. Altogether, 1.4 C was passed.
The solution was scanned by CV at predetermined
times. There was no change in 3. The cell was reversed
and with 3 in the catholyte its concentration dropped
rapidly with build up of the reversible CV signal of 1.
Over 2 h, the current dropped from 250 to 60 mA,
during which, 0.6 C were passed.
4.3.2. Direct CPE at high potential — reaction 2 (a)
non-catalyzed
Reaction was run at 1.9 V (see Fig. 7). LiClO4 was
0.1 M, [3]=0, tetralin quantity was 44×10−5 mol.
Reaction time was 4 h, charge passed 22×10−5 F,
tetralin converted was 7×10−5 mol (15.9%), current
efficiency for two 1 e steps is therefore ꢁ64%. Initial
rate is d[Tetralin]/dt=5×10−7 mol min−1, calculated
as an average over the first 30 min.
4.3.3. Direct CPE at high potential — reaction 2 (b)
catalyzed
CPE, was carried out direct, at 1.9 V in the presence
of 3. Reaction 8: initial quantities were: 3 2.5×10−5
mol, tetralin 45×10−5 mol. Reaction time was 4 h,
charge passed 41.4×10−5 F, tetralin converted 17×
10−5 mol (37.7%), current efficiency 82%. Initial rate
over first 30 min. d[Tetralin]/dt=3.10−5 mol min−1
.
4.3.4. Indirect CPE-catalyzed, low potential —
reaction 3
At 1.4 V (see Fig. 7). LiClO4 0.1 M, Quantities in the
sample: 3=2.5×10−5 mol, tetralin 45×10−5 mol
(initial). Reaction time 4 h, charge passed 26.3×10−5
F, tetralin converted 13×10−5 mol (29%) (by HPLC),
current efficiency ꢁ98%. Reaction time 5.3 h: 29×
10−5 mol (final), (35.5% converted), hence 16×10−5
mol consumed, charge passed 31.7 C (32.86×10−5 F).
Current efficiency for two 1 e steps is 98%. Initial rate
(first 30 min), d[Tetralin]/dt=1.5×10−6 mol min−1
.
Reaction under the same conditions with 0.1 M TBAP
instead of LiClO4 shows 21.6% conversion after 4 h, 28
C (29×10−5 F), a current efficiency of 65%. The
composition of a sample of isolated products mixture
after 5.3 h, is given in the results section.
4.5. X-ray structure determination of 2 and 3
Crystal data and other details of the structural deter-
mination are collected in Table 2 Data collections were
carried out with an Enraf–Nonius CAD4 automatic
4.3.5. Effect of water
Reaction under the same conditions as reaction 3,
with 0.1 M TBAP and increasing concentrations of
water to 0.1 M (untreated acetonitrile has 0.03%, 0.017
M water), shows 16.5% conversion after 4 h, 23 C
(24×10−5 F), a current efficiency of 61%.
,
diffractometer (ꢀ−2q scan, u=0.71096 A, variable
scan time 45 s), controlled by a PC fitted with a
low-temperature equipment. The cell parameters were
obtained from a least-squares treatment of the SET4
setting angles of 25 reflections in the range of 12.7°B
2qB24.2° for 2 and 10.16°B2qB26.4° for 3. Reflec-
tions were scanned with variable scan time, depending
on intensities, with 2/3 of the time used for scanning the
peak and 1/6 measuring each the left and the right
background. The intensities of three check reflections
monitored every 2 h showed only statistical fluctuations
during the data collection. The orientation of the crys-
tal was checked every 200 intensity measurements by
scanning three strong reflections well distributed in
reciprocal space. A new orientation matrix would have
4.4. Products from CPE
Tetralone is the main product, accompanied by 5–
20% tetralol depending on run and reaction time. Te-
tralol is an intermediate and oxidizes to tetralone.
Dihydronaphthalene and naphthalene are in small
amounts in the low potential runs. Tetralin, tetralol,
tetralone and 1,2-dihydronaphthalene were identified
by HPLC and GC–MS and compared with authentic
samples (Aldrich). Tetralin conversion and tetralone