Asian Journal of Chemistry; Vol. 32, No. 2 (2020), 339-341
A
SIAN
J
OURNAL OF HEMISTRY
C
Catalytic Hydrogenation of Cinnamic Acid and Salicylic Acid
1
,2,*
1
SUNIL B. SHINDE
and RAJ M. DESHPANDE
1
2
National Chemical Laboratory, Dr. Homibaba Road, Pune-411007, India
Post Graduate Department of Chemistry, Sir Parashurambahu College (Affiliated to Savitribai Phule Pune University), Pune-411030, India
*
Corresponding author: E-mail: sbs1977@gmail.com
Received: 12 August 2019; Accepted: 27 September 2019;
Published online: 30 December 2019;
AJC-19723
Hydrogenation of cinnamic acid and salicylic acid was carried out using 5 %Ru/C, 5 % Pd/C and Ru-Sn/Al
MPa of hydrogen partial pressure. Ru-Sn/Al catalyst was found to be active for hydrogenation -COOH group to give cinnamyl
alcohol. The selectivity to cinnamyl alcohol was low (15 %) as absolute inhibition of C=C bond hydrogenation in cinnamic acid is challenging.
%Pd/C catalyst was found to hydrogenate C=C bond and aromatic ring in cinnamic acid. 5 %Ru/C catalyst was found to be least
2
O
3
catalyst at 493 K and 6.89
2
O
3
5
selective catalyst as it hydrogenated C=C bond, aromatic ring and -COOH group in cinnamic acid. Hydrogenation of salicylic acid is not
possible at 493 K as decarboxylation of salicylic acid occurs.
Keywords:Hydrogenation, Cinnamic acid, Chemoselectivity, Ru-Sn/Al
2
3
O .
mic acid is investigated but selective hydrogenation of -COOH
group is not deeply studied [7]. Hydrogenation of -COOH,
C=O & C=C groups are well investigated individually for diffe-
rent compounds like acetylene, ethylene, aldehydes, ketone
and succinic acid. Hydrogenating C=O bond in carboxylic acid
is tough relative to aldehyde and ketone [8]. Similarly hydro-
genation of C=C is rapid in case of alkene than benzene. Chemo-
selective hydrogenation of -COOH group in presence of aromatic
ring is studied for benzoic acid, phthalic acid, isophthalic acid
and terephthalic acid [9,10].
In this article, we have carried out hydrogenation of
cinnamic acid and salicylic acid. Cinnamic acid has -COOH
group, C=C bond & aromatic ring available for hydrogenation
whereas salicylic acid has -COOH and aromatic ring. Here
study related to hydrogenation of cinnamic acid was carried
out to understand the selectivity of Pd, Ru & Ru-Sn catalyst
for different functional groups present in cinnamic acid. Hydro-
genation of salicylic acid was carried to observe hydrogenation
of -COOH, aromatic ring and hydrogenolysis of -OH group
present in salicylic acid. Hydrogenolysis of salicylic acid is
considered here as hydrogenolysis of -OH is reported in literature
[11]. Product distribution for hydrogenation of cinnamic acid
and salicylic acid with Ru, Pd and Ru-Sn based catalyst is
also reported in this article.
INTRODUCTION
The organic compounds which can be hydrogenated are
alkenes, alkynes, aliphatic aldehydes and ketones, aromatic
aldehydes and ketones, sugars, esters, anhydrides and carbo-
xylic acids, nitriles and nitro compounds [1]. Compared to
hydrogenation of nitro, aromatic ring, aldehyde, and ketonic
functional groups, hydrogenation of carboxylic acids largely
entails extreme reaction conditions like high temperature and
high hydrogen pressure [2]. Different types of selectivity obser-
ved for hydrogenation reactions are chemoselectivity, regio-
selectivity, stereoselectivity and enantioselectivity [3]. The
activation energy for hydrogenation of various functional
groups is different and also dependent on the steric surroun-
dings nearby the functional group [4]. For unsaturated carboxy-
lic acids, it is difficult to selectively reduce carboxylic group
in the presence of a C=C bond as the activation energy for
hydrogenation of C=C is lower as compared to -COOH group
[
3]. In organic moieties where C=C is not conjugated with the
carbonyl group, discriminate hydrogenation of carbonyl group
to the unsaturated alcohol takes place without difficulty, parti-
cularly when the double bond is highly substituted, similar
study for hydrogenation of substituted cinnamic acids has also
been reported [5,6]. Hydrogenation C=C double bond in cinna-
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