American Journal of Applied Science and Technology
124
https://theusajournals.com/index.php/ajast
VOLUME
Vol.05 Issue 06 2025
PAGE NO.
124-127
10.37547/ajast/Volume05Issue06-27
Condensation And Polymerization Of Some Lower
Aldehydes And The Influence Of Acid And Basic
Groups Of The Catalyst On The Reaction Rate
Shavkat Shayimovich Oblokulov
Bukhara State Medical Institute named after Abu Ali ibn Sino, Uzbekistan
Received:
27 April 2025;
Accepted:
23 May 2025;
Published:
29 June 2025
Abstract:
Acidic or basic catalytic systems, as well as zeolite-type catalysts are used for condensation and
polymerization reactions of ethyl and unsaturated carbonyl compounds. Reactions involving lower aldehydes, as a
rule, are carried out in the gas-phase variant and have rather low selectivity and conversion of reagents. This
problem is partially solved by recirculation of unreacted reagents. The most promising way to solve the problem of
selectivity and activity is selective carrying out of the reaction under conditions of homogeneous catalysis with
varying acid-base properties of the catalyst and reaction medium.
Keywords:
Crotonic aldehyde, acetaldehyde, homo-condensation, polymerization, propionic aldehyde,
polycrotonic aldehyde, oligomers, IR spectrometer.
Introduction:
The present approach would allow such
transformations to be carried out selectively.
Therefore, the objectives of the present work are as
follows:
1.
Development of new homogeneous-catalytic
systems to realize the condensation of lower
aldehydes.
2.
Study of the influence of acid-base properties
of catalytic systems on the selectivity of
croton aldehyde polymerization and aldol
condensation of lower aldehydes. Study of
the influence of acid and basic components
on the selectivity of aldol condensation in the
presence of bifunctional systems.
3.
Establishment of optimal conditions for the
realization of selective method of liquid-
phase preparation of polycrotonic aldehyde.
4.
Study of liquid-phase homo-condensation of
acetaldehyde for selective production of
croton aldehyde.
5.
Study of sequential homo-condensation of
lower aldehydes using acetaldehyde as an
example. Development of a method for
obtaining a certain set of products.
Verification of the possibility of realization of
the above systems in reactions involving
crotonic aldehyde.
6.
Croton aldehyde (2-butenal) is a reactive
compound. To obtain polycrotonic aldehyde
use NaOH and study the rate of
polymerization.
Unsaturated aldehydes are reactive compounds.
Polymers obtained on their basis retain double bonds
and aldehyde groups, on which various chemical
transformations are possible in order to obtain new
polymers.
Species from such unsaturated aldehydes as
acrolein are widely used in industry. Crotonic
aldehyde, on the other hand, is a poorly studied
aldehyde. Croton aldehyde is an irritant, is included
in the list of particularly dangerous substances.
Widespread in nature. It is found in some foods, such
as soybean oil. Croton aldehyde belongs to unstable
compounds, gradually oxidizes in air. This substance
is a strong lacrimator.
American Journal of Applied Science and Technology
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American Journal of Applied Science and Technology (ISSN: 2771-2745)
Obtaining polymers from croton aldehyde is of
practical interest due to its availability as a waste
product of acetic aldehyde production. In the
literature there are some studies in the field of
polymerization of this monomer. However, few
studies have been carried out. This is due to the fact
that in crotonic aldehyde the double bond is
symmetrically substituted, which leads to difficulties
in its polymerization.
Experimental part
A given amount of freshly distilled croton aldehyde at
100 0C was placed in a three-neck flask equipped with
a thermometer, a reflux condenser and a dropping
funnel with a magnetic stirrer. Then an aqueous
solution of NaOH was introduced into the flask using
a drop funnel. Polymerization was carried out at 30-
80 0C.
Polymerization of croton aldehyde
Crotonic aldehyde (CA) -140 grams, initiator NaOH, polymerization time -3 h.
Experienc
e №
NaOH
moles
NaOH:CА
moles
H
2
O
ml
t
0
C
Output
%
1
0,25
1:8
200
30
5
2
0,25
1:8
200
50
4
3
0,25
1:8
200
80
3
4
0,1
1:20
40
30
60
5
0,05
1:40
40
30
74
6
0,025
1:80
40
30
82
7
0,005
1:400
40
40
70
The table shows the results of croton aldehyde
polymerization
depending
on
the
initiator
concentration at a constant amount of monomer. In
experiments 1-3, the reaction mixture at the end of
the process was stratified into aqueous and organic
phases. The polymer was precipitated from the
aqueous phase with acetone and from the organic
phase with water. The separated powders were
washed and dried to constant weight. In other
experiments, the reaction mass at the end of the
process contained no liquid phase.
Carbonyl groups in the obtained products were
determined according to the method [6], carboxylate
hydroxyl and double bonds - according to the
methods [7]. The spectra of the obtained compounds
were taken on SHIMADZU (IR), Tesla BS-567 A (NMR)
spectrometers.
Found C-65.16-65.73% H-8,06-8,08%
C-68.6% H-8.5% (69:9) was calculated for (C4H6O)n
The products isolated in Experiments 4-6 and from
the organic phase 1-3 are, in contrast to those
previously described, light orange powders. They are
soluble in organic solvents (acetone, pyridine, etc.)
but insoluble in water. The softening point of this
powder is 120-130 0C. Molecular mass determined by
measuring the thermal effects of condensation is 580-
600. The obtained compounds are oligomers with
coefficient of polymerization 8-9. The IR spectra of
the oligomers show absorption bands of aldehyde
groups (1950 cm-1), C-C double bonds (1500, 1100
cm-1) and hydroxyl groups (1100, 650 cm-1).
The presence of aldehyde groups in the oligomers of
polycrotonic
aldehyde
is
conditioned
by
polymerization of the monomer along the double
bond to form links
-C(CH3) -CH(CHO) - (A)
Double bonds in oligomers are the result of
polymerization over the aldehyde group to form the
links
-CH(CH=CH-CH3)-O- (B)
Hydroxyl groups should be attributed to the hydrate
form of the aldehyde groups in the links (A)
-C(CH3) -CH(CH(OH)2) - (C)
Quantification of aldehyde and hydroxyl groups and
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American Journal of Applied Science and Technology (ISSN: 2771-2745)
double bonds showed that the structures A,B,C are in
the ratio of 3:2:1.
Studies of the aqueous phase showed that it
contains the products of croton aldehyde
transformation, which differ from the oligomers
isolated from the organic phase both in
physicochemical properties and composition. They
are white powders with a decomposition
temperature of 130-140 0C, which are soluble in
water but insoluble in organic solvents. IR spectra of
water-soluble compounds contain additionally
absorption bands of carboxylate groups and do not
contain absorption bands of aldehyde groups.
Comparative studies of acetaldehyde homo-
condensation in the presence of a number of catalytic
systems used in the study of cross-condensation were
carried out to identify general regularities and
differences in the condensation reactions.
The main purpose of studying acetaldehyde homo-
condensation was to determine the influence of the
basic properties of the catalyst on the conversion,
composition and yield of homo-condensation
products.
Studies
of
acetaldehyde
homo-
condensation were carried out in the presence of
amines in various solvents.
The yield of crotonic aldehyde increases with
decreasing amine basicity, and the conversion
increases with increasing solvent basicity. Studies of
acetaldehyde homo-condensation in the presence of
amine salts were also carried out.
With increasing basicity of amine salts in a polar
solvent, the conversion of reagents increases with a
simultaneous decrease in selectivity for 2-butenal. At
the same time, the yield of polycondensation
products with higher molecular weight increases. The
structure of amine salts and the size of substituents
also
significantly
affect
the
process.
For
monosubstituted amine salts, the selectivity for 2-
butenal
increases,
but
the
conversion
of
acetaldehyde is lower than for salts with two
substituents. Increasing the size of the substituent
promoted the formation of 2-butenal while
maintaining sufficiently close values for the
conversion of acetaldehyde.
The homo-condensation of acetaldehyde in the
presence of various amino acids has been studied.
In the presence of amino acids, regardless of the
nature of the solvent, the reaction proceeds with high
yields and selectivity in the whole range investigated.
The influence of solvents on the reaction has also
been studied. In basic solvents a significant amount of
products of sequential condensation of acetaldehyde
is formed. The same tendency is observed with
increasing basicity of the catalyst. In nonpolar
solvents (toluene) crotonic aldehyde is selectively
formed (except for salts of secondary amines).
In the reactions of homo-aldol condensation of
acetaldehyde in the presence of amino acids, the
ratio of homo-interaction products corresponds to
the experiments performed in the presence of
formaldehyde.
For reactions in the presence of amine salts, the
same patterns are observed, but in the presence of
formaldehyde, the main route of interaction is cross-
condensation.
It should be noted that at high conversion of
acetaldehyde, over 95%, the amount of polyenal
increases compared to the yield of 2-butenal, this fact
indicates the series-parallel character of the reaction
of acetaldehyde homo-condensation. On the basis of
this fact, we can conclude that in the realization of
cross-condensation
of
acetaldehyde
and
formaldehyde it is necessary to control the formation
of reaction products and exclude the possibility of
complete consumption of formaldehyde. At homo-
condensation the formation of the dimerization
product of propionic aldehyde 2-methyl-2-pentenal
(69.3 %), as well as the oligomerization product of
propenal - tributylacetylcitrate and polyenals of
different structure was observed.
In the reaction of propionic aldehyde and
formaldehyde, 2-methyl-2-propanal (29.4%) and the
by-product of the side homo-condensation of
propionic aldehyde 2-methyl-2-pentenal (17.3%)
were formed. Mainly the formation of polyenals of
different structures, over 50 %, was observed.
In the aldol condensation of propionic aldehyde
and acetaldehyde a significant number of reactions
occur, approximately in equal proportions formed
products of cross-condensation - 2-pentenal (19.7%),
homo-condensation of propionic aldehyde - 2-
methyl-2-pentenal (1.5%), and homo-condensation
of acetaldehyde - 2-butenal (19.6%). In all cases of
cross-condensation of propionic aldehyde, the
formation of cyclic ketones, enones and lactones was
observed. This reaction is of exceptional interest for
further development of a method for the selective
preparation of aldehydes and alcohols of branched
structure.
The obtained data on yields and selectivity of
reactions in the presence of acid-base systems can be
explained within the framework of mechanisms of
substrate activation by different types of catalysts.
With an acid catalyst, the initial step is the acid-
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American Journal of Applied Science and Technology (ISSN: 2771-2745)
catalyzed conversion of acetaldehyde to enol. The
acid activates the substrate by protonating it,
increasing the electrophilicity of the carbonyl carbon
atom.
In the presence of both acid and basic catalysts,
acetaldehyde homo-condensation reaction leading to
the formation of 2-butenal is possible.
The reaction rate is determined by the electron
density on the a- carbon atom. The activation of the
substrate also depends on the electron density on the
a-carbon atom. Since in 2-butenal methyl fragment
and the presence of a double bond significantly
increase the electron density, it will be the most
active substrate in this reaction, but at the initial
stage, when its concentration is low, occurs mainly
the reaction of homo interactions, which is reflected
in the yield of reaction products.
At high values of acetaldehyde conversion the
amount of 2-butenal decreases, and the amount of
heavier products of sequential condensation
increases, so at acetaldehyde conversion approaching
100 % the yield of 2-butenal and heavier product
2,4,6-octatrienal is 4 % and 81.3 %, respectively.
In the case of sequential interaction, in addition to
condensation of the initial substrates, interaction of
reaction products with the reactant is possible, since
2-ethyl-2-butenal conjugated aldehyde of branched
structure. In the presence of acetaldehyde in the
system with formaldehyde, a more preferable
mechanism of activation of the latter occurs. The
homo-condensation product of formaldehyde in such
a system is practically not formed, which was
confirmed by analyzing the composition of reaction
products by derivative chromatography. The cross-
condensation reaction of acetaldehyde with
formaldehyde leads to the formation of acrolein, a
valuable monomer for the chemical, pharmaceutical,
and polymer industries. The currently developed
approaches to the reaction in the gas phase using
basic heterogeneous catalysts are certainly available
and technologically attractive in terms of catalyst
cheapness, ease of apparatus design, but have a
number of significant disadvantages: the inability to
fully regenerate the catalyst and control the
selectivity of the process. The formation of reaction
by-products requires significant energy consumption
for their separation, which overrides the benefit from
the use of cheap catalysts.
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