ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2019, Vol. 93, No. 12, pp. 2566–2569. © Pleiades Publishing, Ltd., 2019.
Russian Text © The Author(s), 2019, published in Zhurnal Fizicheskoi Khimii, 2019, Vol. 93, No. 12, pp. 1917–1920.
SHORT
COMMUNICATIONS
Selective Hydrogenation of Citral on Pt-Containing Catalysts
at Room Temperature and Atmospheric Pressure
K. V. Vikanovaa,* and E. A. Redinaa
aZelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia
*e-mail: ks.vikanova@gmail.com
Received May 8, 2019; revised May 8, 2019; accepted May 14, 2019
Abstract—It is shown that the 1% Pt/CeO2–ZrO2 (1% Pt/CZ) catalytic system allows selective hydrogena-
tion of citral with a 94% conversion and a selectivity towards unsaturated alcohols of 59% at room tempera-
ture and atmospheric pressure. The effect of addition of alkali to the reaction mixture on the yield of the target
products is studied, and the optimum conditions of the reaction are determined.
Keywords: citral, selective hydrogenation, production of nerol and geraniol, platinum, cerium–zirconium
oxide
DOI: 10.1134/S0036024419120318
INTRODUCTION
since such catalytic systems require harsh conditions
to carry out the hydrogenation reaction. Under such
conditions, the C=C bond is inevitably hydrogenated,
The popularity of the processes of conversion of
bioavailable materials is constantly growing. In pro- resulting in low selectivity towards desired products
[4, 5].
Systems with noble metals known for their activity
cessing natural substrates, we can obtain valuable
compounds that are subsequently used in different
fields of science and industry. Citral is a naturally
occurring aldehyde. It was found in substantial quan-
tities in the essential oils of lemongrass, lemon, lime,
lemon balm, and verbena [1]. Citral belongs to the
class of monoterpene acyclic carbonyl compounds
and has two C=C bonds in its structure. One of the
double bonds is conjugated with the carbonyl group,
while the other is isolated. Therefore, we can obtain a
wide range of possible products via the conversion of
citral. Among the other hydrogenation products, the
products of selective reduction of the carbonyl group
(isomeric alcohols nerol and geraniol) are of the great-
est value, since they are widely used in pharmaceuti-
cals, perfumes, food industry, and organic synthesis
[2]. In addition, the selective reduction of the C=O
bond presents a challenge for researchers, since the
hydrogenation of the C=C bond is thermodynami-
in hydrogenation reactions would seem to be the ones
most attractive and promising for the above reaction.
Anantan et al. studied catalytic systems containing
platinum, gold, palladium, and ruthenium supported
on TiO2 [6]. The maximum yield of unsaturated alco-
hols (65%) was observed using platinum-containing
catalysts. However, this result was achieved at a tem-
perature of 90°C and a pressure of 100 atm—rather
harsh conditions for carrying out the reaction in the
presence of noble metals. High selectivity towards
unsaturated alcohols was observed using a Pd–Sn
bimetallic catalyst. However, the observed increase in
selectivity when Pd was doped with tin was mainly due
to a reduction in catalytic activity, since high selectiv-
ity with respect to unsaturated alcohols (>80%) was
achieved at conversion below 20% [7]. At the same
time, monometallic palladium systems are highly
active under the chosen reaction conditions (140°C,
cally more favorable than reduction of the carbonyl 70 atm), but products of selective carbonyl group
hydrogenation do not form [7]. Carrying out the reac-
tion at a lower temperature or pressure results in a con-
siderable drop in the yield of nerol and geraniol. The
use of a Pt–Fe/MWCNT bimetallic catalytic system
allows to obtain nerol and geraniol with a yield of 60%.
However, increased hydrogen pressure and an elevated
temperature (20 atm, 80°С) are also required to
group [3].
Due to the complexity and high practical impor-
tance of the selective hydrogenation of the citral car-
bonyl group conjugated with the C=C bond, a great
number of works are devoted to the selective prepara-
tion of isomeric alcohols nerol and geraniol. Non-
noble metal catalysts are rarely used in this reaction, achieve citral conversion of more than 50% [8]. High
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