A synthetic route to 4-alkyl-α-methylhydrocinnamylaldehydes

Article abstract of DOI:10.1007/s11164-016-2782-6

The 4-Alkyl-α-methylhydrocinnamylaldehydes (alkyl-isopropyl, isobutyl, methyl) are frequently used fragrances with desired floral (lilac, cyclamen, lily-of-the-valley) scent. These substances are valued for their good stability in basic solution and, therefore, are frequently used in soaps, detergents, or shampoos. These substances are synthesized by a two-step synthesis involving base catalyzed aldol condensation of 4-alkylbenzaldehyde with propanal followed by selective hydrogenation of the C=C bond. In aldol condensation, selectivity is decreased by formation of undesired products of propanal autocondensation 2-methylpent-2-enal. In this work the reaction conditions for homogenous catalyzed aldol condensation of 4-isobutylbenzadehyde with propanal were tested (catalyst type and amount, molar ratio of reactants, solvent type). Reaction conditions giving the best results (92% conversion, 79% selectivity) were adapted to other 4-alkyl-α-methylcinnamylaldehydes preparation with similar results. In the second step—hydrogenation of aldol product different types of catalyst (nickel, cobalt, palladium or Adkins catalyst), and also different solvents, were tested. Hydrogenation conditions leading to the highest yield (72% selectivity at 95% conversion) were adapted to other 4-alkylhydrocinnamyladehydes with similar results.

Full text of DOI:10.1007/s11164-016-2782-6

Res Chem Intermed
DOI 10.1007/s11164-016-2782-6
A synthetic route to 4-alkyl-a-
methylhydrocinnamylaldehydes
1
Eva Vrbkova Eliska Vyskocilova
1
•
•
´
ˇ
ˇ
´
Martin Rott1 Martin Zapletal1 Libor Cerveny
1
ˇ
•
•
´
Received: 25 May 2016 / Accepted: 8 October 2016
Ó Springer Science+Business Media Dordrecht 2016
Abstract The 4-Alkyl-a-methylhydrocinnamylaldehydes (alkyl-isopropyl, iso-
butyl, methyl) are frequently used fragrances with desired floral (lilac, cyclamen,
lily-of-the-valley) scent. These substances are valued for their good stability in basic
solution and, therefore, are frequently used in soaps, detergents, or shampoos. These
substances are synthesized by a two-step synthesis involving base catalyzed aldol
condensation of 4-alkylbenzaldehyde with propanal followed by selective hydro-
genation of the C=C bond. In aldol condensation, selectivity is decreased by for-
mation of undesired products of propanal autocondensation 2-methylpent-2-enal. In
this work the reaction conditions for homogenous catalyzed aldol condensation of
4-isobutylbenzadehyde with propanal were tested (catalyst type and amount, molar
ratio of reactants, solvent type). Reaction conditions giving the best results (92%
conversion, 79% selectivity) were adapted to other 4-alkyl-a-methylcinnamy-
laldehydes preparation with similar results. In the second step—hydrogenation of
aldol product different types of catalyst (nickel, cobalt, palladium or Adkins cata-
lyst), and also different solvents, were tested. Hydrogenation conditions leading to
the highest yield (72% selectivity at 95% conversion) were adapted to other
4-alkylhydrocinnamyladehydes with similar results.
Keywords Cyclamen aldehyde Á Silvial Á Aldol condensation Á Hydrogenation Á
4-Alkyl-a-methylhydrocinnamylaldehyde
´
Eva Vrbkova
eva.vrbkova@vscht.cz
&
1
Department of Organic Technology, University of Chemistry and Technology Prague,
´
Technicka 5, 166 28 Prague, Czech Republic
123

´
E. Vrbkova et al.
Introduction
The 3-(4-isopropylphenyl)-2-methylpropanal (cyclamen aldehyde), 3-(4-isobutyl-
phenyl)-2-methylpropanal (cyclamen homo aldehyde, Silvial) and 3-(4-methylphe-
nyl)-2-methylpropanal (Jasmorange) are compounds widely used in, e.g., soaps,
detergents, and shampoos because of their good stability in basic solutions and also
in perfumes for their floral (lilac, lily-of-the-valley, cyclamen) and muguet notes.
These fragrances are used to surrogate the frequently used cheap analogue of these
compounds 3-(4-tertbutylphenyl)-2-methylpropanal (lily aldehyde), which has been
classified as a possible mutagenic agent [1]. All mentioned compounds are
synthesized by aldol condensation of propanal and appropriate 4-alkylbenzaldehyde
followed by selective hydrogenation of a double C–C bond to corresponding 3-(4-
alkylphenyl)-2-methylpropanal (Fig. 1). The first step of aldol condensation is
usually homogeneously catalyzed by inorganic hydroxides (NaOH, KOH) [2–4] or
sodium methoxide [5], and this reaction gives the desired product but also a product
of propanal autocondensation—2-methylpent-2-enal. The second step—hydrogena-
tion, can be catalyzed by wide range of metal catalysts such as palladium supported
on charcoal or alumina [4, 6–8], nickel catalyst [7–9] or rhodium catalyst [8].
basic cat.
a
b
H2
H2
R - isopropyl
isobutyl
d
c
H2
H2
e
Fig. 1 Aldol condensation of 4-alkylbenzaldehyde with propanal followed by hydrogenation of cross-
aldol condensation product [3-(4-alkylfenyl)-2-methylprop-2-enal (a); 2-methylpent-2-enal (b); 3-(4-
alkylphenyl)-2-methylpropanal (c); 3-(4-alkylphenyl)-2-methylprop-2-en-1-ol (d); 3-(4-alkylphenyl)-2-
methylpropan-1-ol (e)]
123

A synthetic route to 4-alkyl-a-methylhydrocinnamylaldehydes
Hydrogenation gives three possible products— the desired 3-(4-alkylphenyl)-2-
methylpropanal, the undesired 3-(4-alkylphenyl)-2-methylprop-2-en-1-ol. and the
product of subsequent hydrogenation of the desired product’s carbonyl group 3-(4-
alkylphenyl)-2-methylpropan-1-ol. The 3-(4-Alkylphenyl)-2-methylprop-2-en-1-ol
can be isomerized to the desired product [10].
The 3-(4-Alkylphenyl)-2-methylpropanal molecule is optically active. In all
cases, R isomer is responsible for the pleasant scent, S isomer is described as a little
musty [11]. The racemic mixture is used in applications due to economic reasons
and also because the unfavorable smell of S isomer is almost entirely suppressed in
the mixture. Nevertheless, some syntheses leading to non-racemic R isomer of
cyclamen aldehyde have been reported in the past five years [11–13].
Results for aldol condensation of 4-isopropylbenzaldehyde with propanal were
already reported by the authors [14]. Study of aldol condensation of 4-isobutylben-
zaldehyde with propanal is not available in the literature; therefore, we performed
detailed study of reaction conditions’ influence on the reaction course. The goal was to
get reaction conditions, which would be applicable to aldol condensation of different
4-alkyl substituted benzaldehydes with propanal. Usage of different palladium and
nickel catalysts was also tested in aldol product hydrogenation.
Experimental
The 4-isopropylbenzaldehyde (Acros), 4-isobutylbenzaldehyde (TCI), 4-tertbuty-
laldehyde (Chemical Point UG), 4-methylbenzaldehyde (Sigma Aldrich), potassium
and sodium hydroxide (Penta), sodium methoxide (Sigma Aldrich), methanol,
ethanol, n-propylalcohol, n-butanol, isopropylalcohol, acetonitrile, N,N’-dimethyl-
formamide, ethylacetate, and tetrahydrofurane (all solvents were from Penta) were
used from commercial sources and used without further purification. Propanal
(Sigma Aldrich) was freshly distilled before reaction (b.p. 46 °C). Different
palladium and nickel catalysts (Table 1) were used for hydrogenation.
Aldol condensation
In a typical experiment the flask was charged with the solvent and the catalyst, then
4-isobutylbenzadehyde (iBB) was added. The total amount of propanal was added
dropwise to the mixture in three portions at the 0th, 30th and 60th min of the reaction.
Except for monitoring the influence of temperature, all experiments were performed at
room temperature (25 °C). When a higher temperature was used, the flask was equipped
with a condenser. Samples were neutralized by acetic acid, diluted with ethanol,
centrifuged and analyzed. At the end of the reaction, the reaction mixture was neutralized
using acetic acid, washed with water, extracted using diethylether and evaporated.
Example of isolation of pure unsaturated aldehyde (forcyclamen aldehyde)
Reaction mixture was distilled using a laboratory rectification column filled with
oriented packing Sulzer DX (efficiency 10 theoretical levels). The column was
123

´
E. Vrbkova et al.
Table 1 List of used
hydrogenation catalysts
Denotation Type
Name
Producer
K1
5% Pd/SiO2
Escat 1351
Stream
chemicals
K2
K3
K4
3% Pd/C
K-0224
K-0251
MPT3 W
Heraeus
Heraeus
5% Pd/c-Al2O3
3% Pd/C
Su¨d
Chemie
K5
K6
5% Pd/C
5% Pd/C
K-0227
Heraeus
MPT5 W
Su¨d
Chemie
K7
K8
3% Pd/C
3% Pd/C
Noblemax
100
Su¨d
Chemie
Noblemax
100
T-4811
Su¨d
Chemie
K9
3% Pd/C
Noblemax
100
T-4810
Su¨d
Chemie
K10
70% NiO/SiO2
Nisat 320
Su¨d
Chemie
K11
K12
89% Ni, 9% Al, 2% Mn Acticat 1200 Cattaloy
83% NiO/SiO2 Nisat 330 Su¨d
Chemie
Su¨d
Chemie
Su¨d
Chemie
Su¨d
Chemie
Su¨d
Chemie
K13
K14
K15
K16
79% NiO, 3% ZrO2/SiO2 Nisat 340
18% CoO/Al2O3
G6861
G99B0
47% CuO, 46% Cr2O3,
4% MnO, 22% BaO
74% NiO, 2% ZrO2/SiO2 G69
equipped with an electrically heated boiler. In order to prevent heat loss, the column
mantle was also heated. Reflux ratio was set exactly (10–15). Rectification was
carried out under low pressure (1.5–1.9 kPa). Fractions with boiling point were in
the range of 137–138 °C and contained 97% of the desired forcylamenaldehyde.
Hydrogenation
Hydrogenations were performed in an autoclave (volume 160 ml; Parr). Fractions
containing 80–97% of 3-(4-alkylphenyl)-2-methylprop-2-enal were used for
hydrogenation. The autoclave was filled with an appropriate amount of catalyst
(1 wt.% in case of Pd catalysts, 10 wt.% in case of other catalysts, Table 1), 10 g of
3-(4-alkylphenyl)-2-methylprop-2-enal and 90 ml of solvent, isopropylalcohol.
Samples taken during the reaction were centrifuged and analyzed.
123

A synthetic route to 4-alkyl-a-methylhydrocinnamylaldehydes
Both samples from aldol condensation and hydrogenation were analyzed using a
Shimadzu GC 17A chromatograph fitted with a nonpolar column ZB-5 (60 m,
0.32 mm diameter, 0.25 lm i.d. film) and FID. Composition of the reaction mixture
was also monitored using a GC–MS Shimadzu 2010 fitted with a nonpolar column.
Results and discussion
Aldol condensation
Results for aldol condensation of 4-isopropylbenzaldehyde with propanal were
already reported by the authors [14]. This reaction was performed under the following
conditions: catalyst 33% methanolic solution of sodium methoxide, molar ratio
4-isopropylbenzadehyde:sodium methoxide:propanal 1:0.05:1, 25 °C, solvent metha-
nol, 180 min of reaction (92% selectivity to forcyclamen aldehyde, 90% conversion
of 4-isopropylbenzaldehyde, i.e., a 83% theoretic yield of desired product).
In aldol condensation of 4-isobutylbenzaldehyde (iBB) with propanal (PA), three
catalysts were tested: sodium methoxide (reaction conditions used in [14] resulted in
iBB conversion of about 50% in 5 h), sodium hydroxide (36% water and 19%
methanolic solution) and potassium hydroxide (36% water solution). Because of
higher iBB conversion (about 80% in 5 h) in case of inorganic hydroxides, only
inorganic hydroxides were tested (Table 2, entry 1–10) in the following experiments.
Overall higher conversions at a comparable time of iBB were obtained using
sodium hydroxide comparing potassium hydroxide. In both cases, iBB conversion
(i.e., reaction rate) increased with increasing hydroxide amount in the range
Table 2 Reaction results using different reaction conditions (methanol:iBB = 1:1 vol., 25 °C, 5 h,
iBB = 4-isobutylbenzadehyde, PA = propanal)
Entry Catalyst
Molar ratio
catalyst:iBB
Molar ratio
iBB:PA
iBB
conversion
(%)
Selectivity to cross-aldol
product (%)
1
36% Water sol.
NaOH
0.05:1
0.075:1
0.1:1
1:1.1
10
88
92
76
83
15
55
71
61
58
66
100
91
86
94
92
91
79
87
85
78
87
2
3
4
0.15:1
0.2:1
5
6
36% Water sol.
KOH
0.05:1
0.075:1
0.1:1
7
8
9
0.15:1
0.2:1
10
11
19% Methanolic
sol. NaOH
0.1:1
12
13
36% Water sol.
NaOH
2:1
3:1
93
87
75
68
123

´
E. Vrbkova et al.
0.05–0.1:1 (5 h). In the range 0.1–0.2:1, the initial reaction rate was higher with
increasing amount of catalyst, but the total achieved conversion in 5 h was lower,
due to the faster consumption of propanal by the autocondensation reaction. The
products of the Canizzaro reaction of iBB (isobutylbenzoic acid), which could
neutralize the catalyst, was not detected in the reaction mixture.
In this heterogeneous system (two liquid phases), the selectivity decreased with
an increasing amount of water in the reaction mixture—it complicates the reactant
transfer to catalyst. Due to the presence of a water solution of hydroxide, the
reaction mixture consists of two phases that may limit the reaction rate; therefore,
the usage of methanolic solution of sodium hydroxide was also tested (Table 2,
entry 3 and 11, 19% concentration was caused by limited solubility of sodium
hydroxide in methanol). In this case the selectivity to desired product remained the
same (compared to the water solution), but the reaction rate was significantly lower
(92% conversion in case of water solution vs. 65% conversion in case of methanolic
solution). For all these reasons, sodium hydroxide water solution was chosen to be
the catalyst in further reactions.
It should be mentioned that the only undesired product in the reaction mixture was
formed by propanal autocondensation (2-methylpent-2-enal). This product decreased
selectivity significantly as it was visible after testing the influence of the reactant
molar ratio (Table 2, entry 3, 12–13) on reaction course. At the same conversion of
iBB, the selectivity to desired product decreased with increasing PA amount in the
reaction mixture due to the expected increased formation of 2-methylpent-2-enal.
Initial reaction rate was increasing with increasing amounts of propanal.
Another tested reaction parameter was the influence of solvent type (Table 3) on
the reaction course, relative yield was chosen to compare reaction results with
different solvents. The highest relative yield was obtained using methanol;
satisfactory results were also obtained using n-C2-C4 alcohols. Usage of other
Table 3 Influence of the
Solvent
iBB Selectivity to
conversion 2-methyl-3-(4-
Relative
yield
(%)
solvent type on reaction course
(36% water solution of NaOH,
NaOH: IBB: PA = 0.1:1:1.1
molar, solvent:IBB = 1:1 vol.,
25 °C, 5 h)
(%)
iso-
butylphenyl)prop-
2-enal (%)
Water
19
92
70
72
38
68
44
5
44
86
92
94
53
87
72
75
51
8
79
65
67
20
59
32
4
Methanol
Ethanol
n-Propylalcohol
i-Propylalcohol
n-Butanol
Acetonitrile
Ethyl acetate
N,N0-
58
30
Dimethylformamide
Tetrahydrofurane
None
33
57
61
65
20
37
123

A synthetic route to 4-alkyl-a-methylhydrocinnamylaldehydes
solvents did not offer satisfactory results, which was probably influenced by
solubility of NaOH in these solvents. In case of aprotic solvents, acetonitrile,
tetrahydrofurane and the N,N0-dimethylformamide homoconjugation of sodium
hydroxide occurred, which caused suppression of hydroxide protonation and
dissociation [15]. In the case of these three solvents, hydroxide was probably
present only in the water phase compared to other alcoholic solvents, where the
dissociated hydroxide was present also in alcohol. Ethyl acetate was shown to be an
inappropriate type of solvent, because it reacted with hydroxide and formed ethanol
and sodium acetate. In the case of water, 4-isobutylbenzaldehyde conversion was
very low and selectivity to desired product was also low, due to the faster formation
of undesired 2-methylpent-2-enal.
The use of hydroxide as a catalyst was also tested in the case of other 4-alkyl
substituted benzaldehydes with propanal (Table 4). It is obvious, that hydroxide can
be successfully used as a catalyst in this reaction, although in the case of
4-isopropylbenzaldehyde, it could produce better results with sodium methoxide.
Hydrogenation
Hydrogenation of aldol condensation products was performed to obtain the desired
fragrant product—saturated aldehyde (Fig. 2, I.). In this reaction a side product—
unsaturated alcohol (II.) can occur. Both these products—saturated aldehyde (I.) and
Table 4 Results of aldol condensation of 4-alkylbenzaldehydes with propanal (36% water solution of
NaOH, NaOH:4-alkylbenzaldehyde:PA = 0.1:1:1.1 molar, methanol:4-alkylbenzaldehyde = 1:1 vol.,
25 °C, 5 h)
Substituent in para 4-Alkylbenzaldehyde
conversion (%)
Selectivity to 2-methyl-3-(4-
alkylphenyl)prop-2-enal (%)
Relative
yield (%)
position
None
96
95
91
92
87
88
89
83
86
83
84
85
76
79
72
Methyl
isopropyl
isobutyl
tertbutyl
I.
III.
II.
Fig. 2 Scheme of hydrogenation (R = methyl, isopropyl, isobutyl, tertbutyl): saturated aldehyde (I.),
unsaturated alcohol (II.), saturated alcohol (III.)
123

´
E. Vrbkova et al.
unsaturated alcohol (II.)— can occur following hydrogenation to saturated alcohol
(III.). Reaction conditions strongly influence the final composition of the reaction
mixture. According to the literature, palladium and nickel-based catalysts were
chosen to perform these experiments.
To confirm that hydrogenation was heterogeneously catalyzed, the catalyst 83%
NiO (K12, 120 °C, 8 MPa, solvent methanol) was chosen. Reaction was stopped
after 60 min, depressurized and cooled to room temperature.The reaction mixture
was removed from the autoclave, the catalyst was filtered and the reaction mixture
was inserted back into the autoclave, pressurized and heated to desired temperature.
No change in reaction mixture was observed after 60 min; therefore, we declared
that the reaction was heterogeneously catalyzed. We also used atomic absorption
spectroscopy to confirm that no nickel was leached into the reaction mixture during
hydrogenation.
Influence of catalyst type
At first palladium catalysts were tested in hydrogenation (Table 5, entry 1–9) of
3-(4-isopropylphenyl)-2-methylprop-2-enal (forcyclamen aldehyde) to obtain the
desired saturated aldehyde—cyclamen aldehyde. The maximal selectivity to the
desired cyclamen aldehyde was the highest (61%) at 95% forcyclamen aldehyde
conversion with Pd/Al2O3 catalyst (Table 5, entry 3), which was probably caused by
the fact that this catalyst was the only one with Al2O3 support. Reactions catalyzed
by other palladium catalysts possessed lower selectivity (Table 5, entry 1–2 and
4–9) and formation of subsequent saturated alcohol – cyclamen alcohol was higher.
In the case of catalysts K4 and K6 (same catalyst producer) when using higher Pd
loading, the reaction rate increased, on the other hand, the selectivity to cyclamen
aldehyde decreased on the same conversion level (Table 5, entry 1–9). Acidity of
the three types of used solid supports (active charcoal, SiO2, Al2O3) strongly
influenced hydrogenation result—the catalyst with the least acidic solid support—
SiO2 (K1), offered the best selectivity at 95% conversion. The catalyst supported on
middle acidic solid support—SiO2 (K1), gave the second best selectivity at 95%
conversion. Hydrogenations catalyzed by catalyst with the most acid solid
support—active charcoal (K5), resulted in the worst selectivities. K7, K8 and K9
were the catalysts offered by one producer with comparable properties that were
confirmed in these experiments.
Other used catalysts were the catalysts with significantly lower activity
comparing to palladium catalysts—nickel, cobalt or Adkins catalysts (Table 5,
entry 10–16). With these catalysts, slightly higher selectivity to desired product was
obtained—up to 67% selectivity to desired saturated aldehyde at 95% conversion
(Table 5, entry 10–16). An exception was Adkins catalyst (Table 5, entry 15)—
which preferably catalyzed hydrogenation to other intermediate—unsaturated
alcohol (forcyclamen alcohol) with 68% selectivity at 95% conversion. In other
cases saturated alcohol was the main product that decreased the selectivity. For
comparison, a highly active Raney-nickel catalyst was also tested, but as it was
assumed saturated alcohol was the main product of the reaction. In this case the
123

A synthetic route to 4-alkyl-a-methylhydrocinnamylaldehydes
Table 5 Forcyclamen aldehyde (FCA) results using different reaction conditions
Entry Catalyst
Catalyst Temp. Pressure Solvent
(MPa)
Selectivity to
cyclamenaldehyde (%)
amount (°C)
(wt%)
at 50% at 95%
FCA FCA
conversion conversion
1
5%Pd/SiO2(K1)
1
60
3
Methanol
48
43
60
37
44
28
50
50
42
76
0
44
39
61
37
42
23
33
31
26
66
8
2
3%Pd/C(K2)
3
5%Pd/Al2O3(K3)
3%Pd/C(K4)
4
5
5%Pd/C(K5)
6
5%Pd/C(K6)
7
3%Pd/C(K7)
8
3%Pd/C(K8)
9
3%Pd/C(K9)
10
11
12
13
14
15
16
17
18
19
20
21
22
70% NiO(K10)
Ra-Ni(K11)
10
120
8
83% NiO(K12)
79% NiO(K13)
18% CoO(K14)
Adkins(K15)
80
82
78
11
65
70
86
64
78
67
53
45
0
74% NiO(K16)
83% NiO(K12)
83% NiO(K12)
83% NiO(K12)
83% NiO(K12)
83% NiO(K12)
83% NiO(K12)
52
57
67
62
66
72
67
Hexane
1,4-Dioxane
Toluene
Tetrahydrofurane
1-Methoxypropanol 81
isopropylalcohol 80
decrease of catalyst amount to the level used in the case of rare metal catalysts
(1 wt%) would decrease the reaction rate and increase the selectivity.
Influence of solvent type
Several types of solvents were used to perform the reaction using nickel catalyst
(Table 5, entry 12 and 17–22). No straight trend concerning solvent polarity or
basicity was observed. Resulting selectivities to desired cyclamen aldehyde ranged
from 57 to 72% in 95% forcyclamen aldehyde conversion. The most significant
difference was in the reaction time to reach 95% focyclamen aldehyde conversion
(Table 6), which was probably caused simultaneously by different boiling point of
solvents and hydrogen solubility in these solvents.
The reaction conditions for one palladium (3 MPa, 60 °C, isopropylalcohol,
1 wt% of catalyst 5% Pd-Al2O3 K-0251,) and one nickel catalyst (8 MPa, 120 °C,
isopropylalcohol, 10 wt% of catalyst NISAT 330) were chosen to perform reactions
(Table 7) with other 3-(4-alkylphenyl)-2-methylprop-2-enals (alkyl = methyl,
123

´
E. Vrbkova et al.
Table 6 Time to reach 95%
forcyclamen aldehyde
conversion using different
solvents
Solvent
Time to 95%
conversion (min)
Hexan
195
290
185
225
125
135
95
1,4-Dioxane
Toluene
Tetrahydrofuran
1-Methoxypropanol
isopropanol
Methanol
Table 7 Hydrogenation results
using different substrates
Metal
type
Substituent in para
position
Selectivity to unsaturated
aldehyde (%)
50%
conversion
95%
conversion
Palladium None
Methyl
58
56
60
62
57
85
90
80
81
78
60
61
61
59
58
76
79
67
76
66
isopropyl
isobutyl
tertbutyl
None
Nickel
Methyl
isopropyl
isobutyl
tertbutyl
isobutyl, tertbutyl) and with 3-phenyl-2-methylprop-2enal. In the case of palladium
catalyst almost the same results (in the range of measurement error) were obtained
for all substrates. In the case of nickel catalyst, the hydrogenation of methyl,
isobutyl and non-substituted substrates resulted in slightly higher selectivity to
desired product in comparison with isopropyl and tertbutyl substituted substrates.
Conclusion
The first part of this work was dealing with aldol condensation of 4-isobutylben-
zaldehyde and propanal giving desired 3-(4-isobutylphenyl)-2-methyl-prop-2-enal.
The influence of several reaction conditions (e.g., catalyst type and amount, molar
ratio, solvent type) was tested. The best result—92% 4-isobutylbenzaldehyde
conversion and 79% selectivity to desired 3-(4-isobutylphenyl)-2-methylprop-2-
enal were obtained under the following conditions—solvent methanol, 36% water
solution of NaOH, NaOH:iBB:PA = 0.1:1:1.1 molar, solvent:IBB = 1:1 vol.,
25 °C, and 5 h. These conditions are applicable to aldol condensation of other
4-alkylsubstituted benzaldehydes with propanal.
123

A synthetic route to 4-alkyl-a-methylhydrocinnamylaldehydes
The second part of this work was dealing with hydrogenation of prepared 3-(4-
isopropylphenyl)-2-methylprop-2-enal giving 3-(4-isopropylphenyl)-2-methyl-
propanal using several types of catalysts (nickel, cobalt or Adkins and palladium
catalysts). Overall the best result—72% yield at 95% 3-(4-isopropylphenyl)-2-
methylprop-2-enal conversion was obtained using 1-methoxypropanol as solvent
(catalyst Ni-NISAT330, 8 MPa, 120 °C). Results of hydrogenation of other para
substituted substrates showed that this way is adaptable to these substrates too.
Acknowledgements A word of thanks to the Ministry of education, youth and sports for financial
support from specific university research (MSMT No 20-SVV/2016).
References
1. U. Huchel et al. DE102009001570A1, Henkel (2010)
2. C. Kohlpaintner et al. Ullmann’s encyclopedia of industrial chemistry, Aldehydes, Aliphatic and
Araliphatic. (Wiley, New York, 2013)
3. A. Knorr, A. Weissenborn, US1844013, Winthrop chemical company (1932)
4. M.S Carpenter, J.W.M. Easter, US2875131 A, Givaudan Corp. (1959)
5. J. Therre et al. US6723883 B1, Basf (2004)
6. W. Jia, CN1315316 A, Yongquan Science and Technology Development Co., Ltd (2001)
7. S.Y. Shiaou, A. Ko, J. Chin. Chem. Soc. 53, 1539 (2006)
8. A.M. Pak, Zh. Prikl. Khim. 59(5), 1135 (1986)
9. D.V. Sokolskii, A.M. Pak, S.R. Konuspaev, M.A. Ginzburg, S.M. Turganbaeva, A.P. Pogorelskii,
Izv. Akad. Nauk Kaz. SSR Ser. Khim. 4, 26 (1980)
´
10. H. Cherkaouia, M. Soufiaouib, R. Gree, Tetrahedron 57(2), 2379 (2001)
11. M. Kawasaki, M. Goto, D. Hu, N. Toyooka, T. Kometani, J. Mol. Catal. B Enzym. 96, 27 (2013)
12. D. Limnios, C.G. Kokotos, RSC Adv. 3, 4496 (2013)
13. V. Beghetto, U. Matteolia, A. Scrivantia, M. Bertoldinia, Sci. Ca’Foscari 1, 20 (2012)
14. E. Vrbkova, T. Skypala, E. Vyskocilova, L. Cerveny, Res. Chem. Intermed. 41(12), 9195 (2015)
´
ˇ ´
´
ˇ ˇ
´
15. R. Knob, V. Pauk, V. Maier, Vybrane aspekty uzitı nevodnych rozpoustedel v analyticke chemii.
http://ach.upol.cz/user-files/files/nevodna_rozpoustedla2.pdf. Accessed 11 May 2016
123