CATALYTIC REACTIONS OF HOMO- AND CROSS-CONDENSATION
Table 1. The yield of products of crotonic condensation involving propanal
1033
Product yield, %
Reactants
Polyenals
with various structures
2
-methyl-2-pentenal 2-pentenal 2-methyl-propenal C4 C6 C8
Propanal
Propanal + methanal
Propanal + ethanal
69
17
12
–
–
20
–
30
–
–
–
19
–
–
4
–
–
3
31
53
42
C is 2-butenal, C is 2,4-hexadienal, and C is 2,4,6-octatrienal. Conditions: C(CH CH CHO) = 4.02–5.15 mol/L, C(CH O) =
4
6
8
3
2
2
4
.05 mol/L, C(CH CHO) = 4.17 mol/L, the catalyst is PhNH · HCl, the solvent is DMAA, T = 125°C, and τ = 3 h.
3 2 r
tions of homo- and cross-condensation of formaldehyde
The reagent-grade substances used as a solvent
and acetaldehyde were studied [7, 8]. The aim of this (water, toluene, N,N'-dimethylacetamide, and pyri-
work is to acquire data on the homocondensation of pro- dine) were purified according to standard procedures
panal and its cross-condensation with methanal and [9]. The catalysts, namely, amines, salts of amines,
ethanal in the presence of benzoyl derivatives of amino and amino acids (Reakhim) were dried over P O
2 5
acids and aniline hydrochloride C H NH · HCl.
using a vacuum drying oven. Methanal, ethanal, and
6
5
2
propanal were purchased from Aldrich. The ethanal
trimerization product paraldehyde was separated via
fractional distillation.
EXPERIMENTAL
The experiments were carried out in static steel and
glass thick-walled autoclaves (Aldrich) at 25 and obtained according to standard procedures and puri-
Esters and benzoyl derivatives of amino acids were
1
25°C for 3 and 24 h, respectively. Water, toluene, fied via recrystallization from ethanol [9].
N,N'-dimethylacetamide (DMAA) were used as a sol-
vent. A weighed amount of a solvent was placed into
the autoclave, a required amount of an aldehyde was
added, and a catalyst was introduced into the obtained
RESULTS AND DISCUSSION
In this study, several condensation reactions were
solution. The process is accompanied by the change in investigated, namely, propanal cross-condensations
the color of the reaction solution from pale yellow to with methanal and ethanal and homocondensation of
black depending on the catalytic system used.
propanal.
In the case of homocondensation of two propanal
molecules, the formation of an intermediate product,
-methyl-3-hydroxypentanal, is observed which then
undergoes dehydration to form 2-methyl-2-pentenal
Scheme 1, Table 1).
The choice of DMAA is determined by a number of
factors, namely, it is a solvent with a high boiling
point, which ensures the progress of the reaction in the
liquid phase at 125°C and is a good proton acceptor
able to promote the activation of formaldehyde via the
formation of the iminium cation.
2
(
O
O
The products were identified and quantified via:
+
H C
3
H C
3
—gas–liquid chromatography: a Kristall 2000М
H
H
chromatograph; a ZB-5 capillary column (Zebron)
with a length of 30 m, a diameter of 0.32 mm, and a
film thickness of 0.50 μm; and a flame ionization
detector. The detection conditions were as follows: the
linear velocity of the carrier gas of 25 cm/s and the
FID temperature of 250°C. The internal standard was
n-heptane;
OH O
O
H3C
H3C
H −
H2O
H
CH3
CH3
Scheme 1. The scheme of formation
of 2-methyl-2-pentenal.
—
gas
chromatography–mass
spectrometry:
The formation of 2-methyl-2-propenal was
an Agilent Technologies 6890GC GC–MS spectrom- observed in the cross-condensation reactions of pro-
eter with a 5973 MS mass selective detector and an panal and methanal (Scheme 2).
HP-5MS capillary column. The column temperature
O
O
O
was programmed as follows: holding at 70°C (5 min),
heating at a rate of 15°C/min to 250°C, and holding at
H C
2
+
H C
3
2
−H O
H
H
H
2
2
2
50°C for 10 min. The injector temperature was
50°C, and the temperature of the interface was
60°C. The carrier gas was helium. The linear velocity
H
CH3
Scheme 2. The scheme of formation
of 2-methyl-2-propenal.
of the carrier gas was 25 cm/s. The results were pro-
cessed using the program ChemStation G1701DA Ver.
D00.00.38. The internal standard was n-heptane.
In the case of interaction of propanal and ethanal,
2-pentenal is formed in two stages (the formation of 3-
PETROLEUM CHEMISTRY Vol. 58 No. 12 2018