Vol. 31, No. 5 (2019)
Catalytic Hydrogenation Products of Aromatic and Aliphatic Dicarboxylic Acids 1141
OH
OH
O
O
H
O
O
2
+
O
O
+
Ru-Sn/Al O , 493 K
2
3
O
O
H
H
O
Hexahydro phthalide
18 %
1,2-Cyclohexane dicarboxylic acid anhydride
52 %
1,2-Cyclohexane dicarboxylic acid
Conversion = 50 %
1,2-Cyclohexane dimethanol
30 %
Scheme-XI: Hydrogenation of 1,2-CDCA with Ru-Sn/Al2O3 catalyst
Hydrogenation of cyclohexane dicarboxylic acids with
5 % Ru/C, 5 % Pd/C and 5 %Ru-29 %Sn/Al2O3 (Sn/Ru atomic
ratio 5) catalyst: Cyclohexane dicarboxylic acids are hydro-
genation products of terephthalic acid, isophthalic acid and
phthalic acid [15-17]. Hence the activity of 5 % Ru/C, 5 % Pd/
C and Ru-Sn/Al2O3 catalyst for hydrogenation of cyclohexane
dicarboxylic acids was assessed. Hydrogenation reactions were
carried out under reaction conditions mentioned in Table-1.
Hydrogenation of 1,4-CDCA, 1,3-CDCA and 1, 2-CDCA
with 5 % Ru/C catalyst yielded only over hydrogenation products.
5 % Pd/C catalyst was also found to be inactive for the hydro-
genation of 1,4-CDCA, 1,3-CDCA and 1,2-CDCA under the
reaction conditions mentioned in Table-1. This is because Pd/
C is inactive for hydrogenation of carboxylic group.
The only catalyst which selectivelyhydrogenated 1,2-CDCA,
1,3-CDCA and 1,4-CDCA to corresponding 1,2-cyclohexane,
1,3-cyclohexane and 1,4-cyclohexane dimethanol respectively
was Ru-Sn/Al2O3. The product distribution for hydrogenation
with Ru-Sn/Al2O3 catalyst is shown in Schemes XI-XIII for
1,2; 1,3 and 1,4-cyclohexane dicarboxylic acid respectively.
with 14 % and 40 % conversion of 1,3-CDCA and 1,4-CDCA
respectively.
Conclusion
Hydrogenation of aromatic dicarboxylic acids like tere-
phthalic acid and isophthalic acid gave 100 % selectivity to
respective cyclohexane dicarboxylic acid with 5 % Pd/C
catalyst. 5 % Ru/C catalyst was observed to be a very active
catalyst for hydrogenation of dicarboxylic acids and gave
overhydrogenation products at 493 K. At lower temperature
(453 K) the selectivity for cyclohexane dicarboxylic acids was
increased. Hydrogenation of phthalic acid with Ru-Sn/Al2O3
catalyst was observed to give phthalide instead of 1,2-benzene
dimethanol or 2-hydroxy methyl benzoic acid. Hydrogenation
of cyclohexane dicarboxylic acids like 1,4-cyclohexane dicar-
boxylic acid, 1,3-cyclohexane dicarboxylic acid and 1,2-cyclo-
hexane dicarboxylic acid was studied using the catalysts Pd/C,
Ru/C and Ru-Sn/Al2O3. Ru-Sn/Al2O3 catalyst selectively hydro-
genated the carboxylic group of these cyclohexane dicarbo-
xylic acids to give cyclohexane dimethanol. The selectivity of
1,2-cyclohexane dimethanol formed from hydrogenation of
1,2-cyclohexane dicarboxylic was low (30 %) due to dehydra-
tion of 1,2-cyclohexane dicarboxylic acid to give 1,2-cyclo-
hexane dicarboxylic acid anhydride. The screening of the
catalysts showed that with proper choice of catalysts it was
possible to achieve selectivity towards desired products.
HO
HO
O
H
2
Ru-Sn/Al
O , 493 K
3
2
O
OH
OH
CONFLICT OF INTEREST
1,3-Cyclohexane dimethanol
100 %
1,3-Cyclohexane dicarboxylic acid
Conversion = 14 %
The authors declare that there is no conflict of interests
regarding the publication of this article.
Scheme-XII: Hydrogenation of 1,3-CDCA with Ru-Sn/Al2O3 catalyst
HO
O
HO
REFERENCES
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H
2
Ru-Sn/Al O , 493 K
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2
3
O
OH
OH
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1,4-Cyclohexane dicarboxylic acid
Conversion = 40 %
1,4-Cyclohexane dimethanol
100 %
Scheme-XIII: Hydrogenation of 1,4-CDCA with Ru-Sn/Al2O3 catalyst
5. M. Toba, S. Tanaka, S. Niwa, F. Mizukami, Z. Koppány, L. Guczi, K.-
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As seen in Schemes II-XIII, hydrogenation of 1,2-CDCA
gives 18 % hexahydro phthalide, 52 % 1,2-cyclohexane dicar-
boxylic acid anhydride and 30 % 1,2-cyclohexane dimethanol,
at a 1,2-CDCA conversion of 50 %.
Hydrogenation of 1,3-CDCA and 1,4-CDCA with Ru-
Sn/Al2O3 gives 100 % 1,3 and 1,4-cyclohexane dimethanol
https://doi.org/10.1039/C6CY00335D.