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Kinetics of reaction between meta-substituted long chain alkyl phenols and formaldehyde.

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Die Angewandte Makromolekulare Chemie 24 (1972) 163-169 ( N r . 341)
From the Regional Research Laboratory, Hyderabad/India
Kinetics of Reaction between Meta-substituted
Long Chain Alkyl Phenols and Formaldehyde
By N. HEMALATHA
ISAIAH,
M. YASEEN,and J. S. AGGARWAL
(Eingegangen am 22. Dezember 1971)
SUMMARY:
The reaction between formaldehyde and long chain alkyl phenols as cardanol
and 3-pentadecylphenol is found to be of second order, when it is studied in dioxanwater (1 :1) system in presence of catalyst hydroxide sodium as at 28, 50 and 70°C.
Individual methylols were separated and identified by thin layer chromatography.
The long alkyl chain in the meta-position of the phenolic nuclei sterically hinders
the reactivity of 2-position at 28OC, but a t higher temperatures i. e. 50 and 70°C
this position gets activated resulting in the formation of various methylols.
ZUSAMMENFASSUNG :
Die Reaktion zwischen Formaldehyd und langkettigen Alkylphenolen wie Car&no1 und 3-Pentadecylphenol verliiuft in Dioxan/Wasser (1:l ) in Gegenwart von
Natriumhydroxid als Katalysator bei 28, 50 und 70°C nach der zweiten Ordnung.
Einzelne Methylole wurden isoliert und durch Diinnschichtchromatographie identifiziert. Die lange Alkylkette in der Metastellung des Phenolrings erniedrigt bei
28 "C die Reaktionsfahigkeit in der 2-Stellung durch sterische Hinderung, dagegen
wird diese Stellung bei hoheren Temperaturen (50, 70°C) aktiviert, woraus die Bildung verschiedener Methylole resultiert.
Introduction
I n the initial stages of phenol/formaldehyde reactions, various methylols
are expect.ed t o be formed depending upon the nature of the phenols used.
Exhaustive literature on the kinetics of reaction between simple or short chain
substituted phenols and formaldehyde elucidate the mechanism involved in
these reactions leading to the formation of complex resinous products. However,
not much information is available on the kinetics of reaction between long
chain alkyl phenols and formaldehyde.
Recently chromatographic techniques have been used widely t o study the
and KRISHNASreaction kinetics of phenol/formaldehydel-6 systems. BAKSHI
WAMY7 were t h e fist t o study t h e reaction kinetics of cardanol and 3-pentadecylphenol with paraformaldehyde without a n y solvent and they inferred
163
N. HEMALATHA
ISAIAH,
M. YASEEN,
and J. S. AGGARWAL
t h a t these reactions followed first order rate laws. In the present work the
kinetics of reaction between long chain alkyl phenols and formaldehyde was
studied in waterldioxan solvent system making a judicious choice of reaction
conditions like mole ratio of reactants, temperature and catalysts.
Experimental
Materials
Double distilled cardanol, bp : 220-221 OC/2 mm Hg, specific gravity at 30 "C:
0.934, acid value (phenolic acidity): 5.0, iodine value : 255.0, and hydroxyl value:
193.5, was used. 3-Pentadecylphenol, mp 52.5"C, was prepared in the laboratory*.
Formalin (40 Yo) (containing less than 2 yo methanol), dioxan, hydroxylamine
hydrochloride, sodium hydroxide, and sulphuric acid were of A. R. Grade.
Dioxan-water solvent system
The insolubility of long chain alkyl phenols in water or aqueous alkali necessitated the use of a non-aqueous-solvent/watersystem. Alcohols and ketones which
are completely mixible with water are not used because they may cause side reactions like the formation of acetals between alcohols and formaldehyde or condensation reactions between ketones in presence of alkali. The alternate solvent chosen
is dioxan which is completely mixible with water and does not interfere with the
reactants. The solution of formaldehyde and phenol in dioxanlwater (1: 1) system
remained clear up to 50 yo conversion in alkali catalysed reactions. For comparative
evalution, a few reactions were also carried out with acid catalyst using the same
solvent system.
Kinetic procedure
I n alkali catalysed reactions, 0.1 M solutions of reactants and the catalyst were
taken in equimolar proportions, whereas in acid catalysed reactions reactants were
in equimolar and the catalyst was in half molar proportions. Requisite amounts
of the solution of reactants and the catalyst in separate containers were placed in a
thermostat ( f 0.1 "C). When reactants attained the temperature of the bath they
were quickly transferred to a three necked flask fitted with reflux condenser, mercury sealed glass stirrer and sampling device. Aliquot portions ( 5 ml) taken out
from the reaction mixture immediately and at every half an hour intervals were
transferred into a 250 ml conical flask and chilled with ice cold distilled water for
the determination of initial and subsequent concentrations of formaldehyde. The rate
of disappearance of formaldehyde in the reaction mixture was estimated by the
hydroxylamine hydrochloride methods. The rate data was substituted in various
equations for the determination of the order of reaction. The data at three temperatures were found to fit in the equation of the second order of reaction within experimental limits.
Simultaneously a t every half an hour intervals 1 ml of the reaction mixture was
withdrawn and transferred into a separate test tube kept in ice for thin layer
164
Reaction of Alkyl Phenols and Formaldehyde
chromatographic (TLC) analysis. The solution of the reaction mixture drawn a t
various intervals was just acidified with dilute acetic acid and dissolved in ether.
These solutions were spotted on silica gel G plates (250 p thick coating on 20 x 20 cm
glass plates which were dried at 110°C and stored in a desiccator) along with the
mixture of authentic synthesised methylolslo. Plates were developed in the solvent
system petroleum ether (60-80 "C) : ethyl ether : dimethylformamide : glacial
acetic acid (75: 85: 5 : 1, v/v), sprayed with sulphuric acid and charred at 120-130°C
for visualisation. The identification of methylols was carried out as described
earlierll.
Results and Discussion
The kinetic data of alkali catalysed reactions between cardanol and formaldehyde a t 28, 50 and 70°C is plotted in Fig. 1. When the rate of disappearance
x
of formaldehyde at different temperatures is expressed in terms of
a (a-x)
and plotted against time, most of the points representing this relationship fall
X
6-
0
3C
60
90
TIME
Fig. 1.
I20
150
IN MINUTES
180
210
240
Sodium hydroxide catalysed cardanol/formaldehyde reaction.
165
N. HEMALATHA
ISAIAH,
M. YASEEN,
and J. S. AQGARWAL
on a straight line. This observation shows that the rate constant of alkali
catalysed reactions between cardanol and formaldehyde a t three different
temperatures follows the equation of second order reaction. The rate kinetics
of reaction between 3-pentadecylphenol and formaldehyde, catalysed by sodium hydroxide follows the same order of reaction a t different temperatures as
it is observed in the case of cardanol (Fig. 2).
I If-
:
0.9
-
\
o
Fig. 2.
30
eo
90
120
TIME IN MIN.
150
teo
/*
210
240
Sodium hydroxide catalysed 3-pentadecylphenol/formaldehydereaction.
The acid catalysed reactions between these long chain alkyl substituted
phenols and formaldehyde are comparatively so slow that a t 28 "C no measurable amounts of formaldehyde reacted could be detected. For this reason the
kinetic data of the acid catalysed reaction a t 28°C is not reported here. Even
a t 50 and 70°C the rate constants of acid catalysed reactions are about one
fifth of those found in alkali catalysed reactions (Table 1). I n the presence of
acid cat,alyst some separation of reaction mixture has been observed but for
166
Reaction of Alkyl Phenols and Formaldehyde
comparison a few reactions were carried out in the same waterldioxan solvent
system. Hence no definite conclusion could be drawn from acid catalysed
reactions in present studies.
Table 1. Second order rate constants of reactions between phenol and formaldehyde and energy of activation values.
Phenol
Catalyst
28°C
Cardanol
3-Pentadecylphenol
m-Cresol
50°C
70°C
Sodium hydroxide
Sulphuric acid
Sodium hydroxide
Sulphuric acid
Sodium hydroxide
The rate constants of 3-pentadecylphenol and formaldehyde reactions both
in presence of acid and alkali catalysts are slightly greater than those of cardanol-formaldehyde reactions under identical conditions (Table 1). These
observations indicate that saturation of side chain slightly enhance the rate
of reaction, but this effect is not found so significant. The energy of activation
determined for alkali catalysed reactions also shows that a comparatively lower
amount of energy is required to activate the reactions of saturated long chain
alkyl phenols than the unsaturated ones.
Reaction kinetics of m-cresol and formaldehyde in presence of an alkali
catalyst shows a fairly fast rate of reaction compared to the reactions of long
chain m-substituted phenols described above. The fast rate of reaction of the
former is due to the inductive effect of single methyl group in the m-position,
whereas this effect goes on decreasing with the increasing number of carbon
atoms in the side chain of the latter.
The reactivities of the various substituted phenols are governed not only
by the free-o- or p-positions but also by the nature and position of the substituent in the phenolic nuclei. Steric factors also affect the orientation of the
methylol groups to a particular position in the phenolic nuclei. I n reaction
rate studies catalysed by alkali, it is generally reported that the p-position of
the phenol has a slightly greater affinity for formaldehyde than o-position.
But in the present study with these m-substituted long chain alkyl phenols,
the 6-0-position with respect to phenolic hydroxyl group is preferentially
167
N. HEMALATHA
ISAIAH,
M. YASEEN,
and J. S. AGGARWAL
attacked a t all the temperatures whereas 2-0- and 4-p-positions are sterically
hindered. These are further illustrated by thin layer chromatographic studies.
Thin-layer Chromatographic Results
Products formed in 3-pentadecylphenol/formaldehyde alkali catalysed
reaction a t 28°C showed the formation of only 6- and 4-monomethylols and
4,6-dimethylol along with the unconverted parent phenol with Rf x 100
values of 46.0, 36.0, 24.0 and 98.0 respectively. The appearance of 2-methyl01
was not noticed a t this temperature even a t the end of 4 hours of the reaction.
I n the reaction, 6-methyl01 appears first and its concentration increases with
time; 4-methylol later followed by the formation of 4,6-&methylol in detectable quantities and their concentrations increase with the time. These observations show the higher reactivity of the 6-o-position compared to the
4-p-position since it is sterically hindered.
Products formed in alkali catalysed 3-pentadecylphenol/formaldehyde
reactions a t 50 and 70 "C showed eight distinct spots after one hour corresponding to the unconverted parent phenol, 2-, 6-, 2,6-, 4-,2,4-, 4,6- and 2,4,6methylols in the decreasing order of Rf x 100 values 98, 50, 46, 41,36, 34,24
and 8.4 respectively. It is evident that a t these temperatures the 2-0-position
becomes reactive resulting in the formation of all the theoretically possible
methylol derivatives from 3-pentadecylphenol. This observation has not been
reported so far.
Cardanol, 3-pentadecylphenol or their methylol derivatives possess the same
migration characteristics on thin layers of silica gel G under conditions described above. Therefore the synthetic methylols of 3-pentadecylphenol were used
as model samples for the identification of methylol derivatives formed in
alkali catalysed cardanol/formaldehyde reactions. TLC analysis of alkali catalysed cardanol-formaldehyde reaction products a t temperatures 28, 50 and
70 "C show exactly similar results as obtained from 3-pentadecylphenol.
b
J. H. FREEMAN
and C. W. LEWIS,J. Amer. Chem. SOC.76 (1954) 2080.
L. M. YEDDANAPALLI,
V. V. GOPALKRISHNA,
and A. K. KURIAKOSE,
J. Sci.
Ind. Res., Sect. B 19 (1960) 25.
L. M. YEDDANAPALLI
and V. V. GOPALAKRISHNA,
Makromolekulare Chem. 32
C
L. M. YEDDANAPALLI
and A. K. KURIAKOSE,
J. Sci. Ind. Res., Sect. B 18 (1959)
1
2a
(1959) 112.
467.
3
4
5
J. REESE,Kunststoffe 45 (1955) 137.
J. H. FREEMAN,
Anal. Chem. 24 (1952) 2001.
S. H. BAKSHI
and N. KRISHNASWAMY,
J. Chromatogr. 9 (1962) 395.
168
Reaction of A l k y l Phenols a n d Formaldehyde
6
7
8
9
lo
l1
S. H. BAKSHI
and N. KRISHNASWAMY,
Indian J . Chem. 4 (1966) 320.
S. H . BAKSHIand N. KRISHNASWAMY,
Indian. J. Chem. 3 (1965) 503.
D. WASSERMAN
and C. R. DAWSON,
Ind. Eng. Chem. 37 (1945) 396.
B. W. NORDLANDER,
Oil. Paint, Drug Reptr. 130 (1936) 3, 27.
N. HEMALATHA,
R. SUBBARAO
and J. S. AGGARWAL,
Ind. J. Technol. (in press).
N. HEMALATHA
and J. S. AGGARWAL,
J. Chromatogr. (in press).
169
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