Chemistry Letters 2001
231
Interestingly, this reaction proceeded without a radical ini-
tiator, AIBN (2,2'-azobisisobutyronitrile). When AIBN was
added to the reaction mixture, no good reproducibility of the
reaction rates was obtained. It is plausible that oxygen, present
in the solvent and/or argon, plays a role as a radical initiator. A
minor amount (28 % of ethylbenzene) of phenethyl alcohol was
6
found in the product. The production rate of phenethyl alcohol
is also accelerated by the magnetic field in the same order as
that of ethylbenzene.
The present experiments may have an intrinsic drawback.
The reaction rate of S'0T was determined by the NMR instru-
ment; the sample might have been affected by the magnetic
field during measurement of the spectrum. Therefore, the reac-
tion course was investigated by HPLC.
One of the two NMR tubes containing C H solutions of
6
6
TBTH (179 µmol) and m-methoxybenzyl bromide (149 µmol)
was placed in the NMR probe (35 °C; S''9.4T) and another in the
water bath (35 °C; S'' ). The tubes were capped instead of
0
T
sealed. The reaction course was monitored by taking out 10 µL
portions of the mixture and analyzing them by HPLC
The authors are indebted to Prof. Yoshifumi Tanimoto of
Hiroshima University for discussion.
(LiChrosorb®, hexane : AcOEt = 99.8 : 0.2, UV: 260 nm). The
yield (X) of 3-methoxytoluene was calculated according to X =
B/(A+B), where A and B were the peak intensities of m-
methoxybenzyl bromide and 3-methoxytoluene, respectively.
The HPLC analysis (Figure 3) indicates that the magnetic
field increases the reaction rate (K9.4T/0T = 1.7) as well. The
average enhancement of the reaction rate, obtained after repeat-
ing 20 experiments, was K9.4T/0T = 1.58 ± 0.16.
On the other hand, when the butyltin hydride reduction of
phenethyl iodide was performed in the presence of 0.4 T mag-
netic field (a neodymium magnet), no acceleration is observed.
The substitution reaction of phenethyl methanesulfonate
References and Notes
1
2
3
4
5
R. De, Y. Fujiwara, B. Zhang, and Y. Tanimoto, Bull.
Chem. Soc. Jpn., 73, 1573 (2000).
R. Nakagaki and K. Mutai, Bull. Chem. Soc. Jpn., 69, 261
(1996).
R. Nakagaki, M. Yamaoka, O, Takahashi, Y. Fujiwara, and
Y. Tanimoto, J. Phys. Chem. A, 101, 556 (1997).
Y. Fujiwara, K. Yoda, T. Tomonari, T. Aoki, Y. Akimoto,
and Y. Tanimoto, Bull. Chem. Soc. Jpn., 72, 1705 (1999).
It was found that the tin hydride reduction proceeded in a
moderate rate at 35 °C. Therefore, the NMR probe was
heated at this temperature.
with sodium iodide in acetone-d was not accelerate by the
6
magnetic field (9.4 T), either.
The acceleration mechanism of the magnetic effect on the
present reaction is not clear so far, and experiments to study the
mechanism to interpret the present findings are in progress.
6
Even though evacuation and filling with argon of the NMR
tube were repeated several times, the yield of the phenethyl
alcohol did not change. It seems that a considerable
amount of oxygen is tightly trapped in the benzene.