Enantio-differentiating hydrogenation of 2-octanone over modified nickel catalysts prepared by an in situ modification

Article abstract of DOI:10.1246/bcsj.75.2695

The enantio-differentiating hydrogenation of 2-octanone was carried out over a tartaric acid-modified reduced nickel catalyst. It was shown that the in situ modification of the Ni surface was available for the hydrogenation of 2-octanone in the presence of a large amount of pivalic acid in the reaction media. An optical yield of 74% was attained with the in situ modified reduced Ni catalyst.

Full text of DOI:10.1246/bcsj.75.2695

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Bull. Chem. Soc. Jpn., 75, 2695–2696 (2002) 2695
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because the pre-modification process in an aqueous solution in
advance of hydrogenation can be omitted, and the in situ mod-
ification does not produce a waste modification solution con-
taining Ni ions. The possibility of applying the in situ modifi-
cation to the hydrogenation of 2-ocatanone is of significant in-
terest, because the reaction media is an acidic organic solution
containing a large amount of pivalic acid, while pre-modifica-
tion was carried out in an aqueous solution. In this paper, we
report on the hydrogenation of 2-octanone over an in situ mod-
ified reduced Ni catalyst. The parameters affecting the optical
yield were examined.
Figure 1 shows the effect of the amount of TA added to the
reaction media on the optical yield. A reduced Ni catalyst was
prepared by the reduction of NiO at 623 K in a hydrogen
stream. The optical yield increased significantly with the addi-
tion of 2 mg of TA, and gradually increased with up to a 10-mg
addition of TA. Figure 2 shows the effect of the NaBr amount
Enantio-Differentiating
Hydrogenation of 2-Octanone over
Modified Nickel Catalysts Prepared
by an In Situ Modification
02
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SJA8
09-2673
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T. Osawa et al.
Tsutomu Osawa,* Nobuyo Ozaki, Tadao Harada,†
and Osamu Takayasu
Faculty of Science, Toyama University,
3190 Gofuku, Toyama 930-8555
02
†Faculty of Science and Technology, Ryukoku University,
Seta, Otsu 520-2194
02
1
(Received June 10, 2002)
The enantio-differentiating hydrogenation of 2-oc-
tanone was carried out over a tartaric acid-modified reduced
nickel catalyst. It was shown that the in situ modification of
the Ni surface was available for the hydrogenation of 2-oc-
tanone in the presence of a large amount of pivalic acid in the
reaction media. An optical yield of 74% was attained with
the in situ modified reduced Ni catalyst.
An (R,R)-tartaric acid (TA)–NaBr-modified Ni catalyst was
conventionally prepared by immersing a Ni catalyst in an
aqueous solution of pH 3.2 containing TA and NaBr at 373 K
before the hydrogenation reaction (pre-modification). This
pre-modified catalyst hydrogenates two kinds of prochiral
ketones with high optical yields. That is, they are β-function-
alized ketones and dialkyl ketones.1–3 The feature of the reac-
tion medium for attaining high optical yields for the hydroge-
nation of dialkyl ketones was different from that for the β-
functionalized ketones. An acidic mixture of pivalic acid and
tetrahydrofuran (THF) was needed for the hydrogenation of
dialkyl ketones, while THF was used for the hydrogenation of
β-functionalized ketones.4 Although the addition of pivalic
acid to the reaction media greatly increased the optical yield
for the hydrogenation of 2-octanone, pivalic acid produced the
desorption of Na ions from the TA–NaBr-pre-modified Raney
Ni (RNi) catalyst; this decreased the enantio-differentiating
ability of the catalyst for repeated runs (the first run, 59% opti-
cal yield; the second run, 4%; the third run, 0%).5 We recently
reported that the use of a reduced Ni catalyst prepared by the
reduction of NiO enabled the application of an in situ modifi-
cation (TA and NaBr were directly added to the reaction me-
dia) to the enantio-differentiating hydrogenation of methyl ac-
etoacetate, and that the in situ modified reduced Ni catalyst
gave a 90% optical yield.6 The added TA and NaBr were ad-
sorbed on the nickel surface during the initial stage of the reac-
tion and created an enantio-differentiating catalyst. The in situ
modification has greater advantages compared with pre-modi-
fication, especially for industrial applications of this catalyst,
Fig. 1. Effect of the in situ added TA on the optical yield
NaBr 1.5 mg, Hydrogenation 373 K.
Fig. 2. Effect of the in situ added NaBr on the optical yield
and the hydrogenation rate
TA 10 mg, Hydrogenation 373 K.

2696 Bull. Chem. Soc. Jpn., 75, No. 12 (2002)
© 2002 The Chemical Society of Japan
(Wako Pure Chemical Industry Co., Ltd.) were reduced in a hy-
drogen stream at 623 K for 1 h before use. TA and an aqueous so-
lution of NaBr (in 50 µL distilled water) were added to the reac-
tion mixture of 2-octanone (4.1 g), THF (10 mL), and pivalic acid
(8.2 g). The hydrogenation of 2-octanone was carried out over re-
duced nickel at 333 to 373 K and at an initial hydrogen pressure of
9 MPa. For repeated use of the catalyst, it was separated from the
reaction mixture and washed three times with THF. The hydroge-
nation was carried out without the addition of TA and NaBr after
the second run. The optical yield of the reaction was determined
by polarimetry. The specific optical rotation of the optically pure
(S)-2-octanol was +9.76° (neat).
on the optical yield and hydrogenation rate. The addition of
appropriate amounts of TA (10 mg) and NaBr (1.5 mg) gave a
70% optical yield for hydrogenation at 373 K. When the hy-
drogenation temperature was lowered to 333 K, the optical
yield increased to 74% (NaBr: 1.5 mg). These results indicat-
ed that TA and NaBr added to the reaction media were ad-
sorbed on the Ni surface during the initial stage of the reaction
to create an enantio-differentiating catalyst in spite of the pres-
ence of a large amount of pivalic acid in the reaction media.
The amount of NaBr also affected the hydrogenation rate. The
rate increased with the increase in the amount up to 1.5 mg of
NaBr, and then decreased. The repeated use of the in situ mod-
ified reduced Ni for the hydrogenation of 2-octanone was also
investigated. An optical yield of 62% was maintained after the
third run at 373 K (the first run, 67% optical yield; the second
run, 67%; the third run; 62%). A distinct improvement in the
durability compared with the case of the pre-modified RNi can
be attributed to the combination of the in situ modification and
the reduced Ni catalyst, analogous to the hydrogenation of me-
thyl acetoacetate.7 Because the surface of the reduced Ni has a
more regularly arranged Ni domain than that of RNi,8 TA and
NaBr would be more stably adsorbed on the reduced Ni than
on RNi. The in situ-modified reduced Ni is a promising cata-
lyst for practical applications of the enantio-differentiating hy-
drogenation of dialkyl ketones.
References
1
A. Tai and T. Harada, “Tailored Metal Catalysts,” Reidel,
Dordrecht (1986), p. 265 and references therein.
G. Webb and P.B. Wells, Catal. Today, 12, 319 (1992), and
references therein.
2
3
T. Osawa, T. Harada, and O. Takayasu, Topics in Catalysis,
13, 155 (2000), and references therein.
4
(1984).
5
(1987).
6
T. Osawa and T. Harada, Bull. Chem. Soc. Jpn., 57, 1518
T. Osawa and T. Harada, Bull. Chem. Soc. Jpn., 60, 1277
T. Osawa, Y. Hayashi, A. Ozawa, T. Harada, and O.
Takayasu, J. Mol. Catal. A: Chemical, 169, 289 (2001).
T. Osawa, S. Sakai, K. Deguchi, T. Harada, and O.
Takayasu, J. Mol. Catal. A: Chemical, 185, 65 (2002).
Y. Nitta, F. Sekine, T. Imanaka, and S. Teranishi, Bull.
Chem. Soc. Jpn., 54, 980 (1981).
Experimental
7
A typical enantio-differentiating hydrogenation of 2-octanone
over an in situ modified reduced nickel catalyst was carried out as
follows: six grams of commercially available nickel(Ⅱ) oxide
8