Synthesis and characterization of different types of epoxide-based Mannich polyols from low-cost cashew nut shell liquid

Article abstract of DOI:10.1007/s11164-013-1034-2

Cashew nut shell liquid (CNSL) is a natural aromatic organic oil consisting of phenolic compounds with interesting structures. Extraction of CNSL was performed in a Soxhlet apparatus. The major (90 %) component of CNSL is anacardic acid, which is easily decarboxylated to cardanol (10 %) by use of conventional methods. In this paper we describe a three-step synthesis of Mannich polyols for rigid foams. The first step is synthesis of N-(2-hydroxyethyl)-1,3-oxazolidine (the Mannich precursor) by condensation of paraformaldehyde and diethanolamine. The second step involves synthesis of the Mannich base phenolic ring of cardanol by reaction with N-(2-hydroxyethyl)-1,3- oxazolidine. The third step is alkoxylation. The synthesized polyols were characterized by FTIR and ¹H NMR spectroscopy and thin-layer chromatography. Springer Science+Business Media Dordrecht 2013.

Full text of DOI:10.1007/s11164-013-1034-2

Res Chem Intermed
DOI 10.1007/s11164-013-1034-2
Synthesis and characterization of different types
of epoxide-based Mannich polyols from low-cost cashew
nut shell liquid
•
Tejas S. Gandhi Mayank R. Patel
Bharatkumar Z. Dholakiya
•
Received: 7 November 2012 / Accepted: 8 January 2013
Ó Springer Science+Business Media Dordrecht 2013
Abstract Cashew nut shell liquid (CNSL) is a natural aromatic organic oil con-
sisting of phenolic compounds with interesting structures. Extraction of CNSL was
performed in a Soxhlet apparatus. The major (90 %) component of CNSL is ana-
cardic acid, which is easily decarboxylated to cardanol (10 %) by use of conven-
tional methods. In this paper we describe a three-step synthesis of Mannich polyols
for rigid foams. The first step is synthesis of N-(2-hydroxyethyl)-1,3-oxazolidine
(the Mannich precursor) by condensation of paraformaldehyde and diethanolamine.
The second step involves synthesis of the Mannich base phenolic ring of cardanol
by reaction with N-(2-hydroxyethyl)-1,3-oxazolidine. The third step is alkoxylation.
The synthesized polyols were characterized by FTIR and 1H NMR spectroscopy and
thin-layer chromatography.
Keywords Cashew nut shell liquid Á Mannich precursor Á Mannich base Á
Mannich polyols
T. S. Gandhi Á B. Z. Dholakiya (&)
Department of Applied Chemistry, Sardar Vallabhbhai National Institute of Technology (SVNIT),
Surat 395007, Gujarat, India
e-mail: bharat281173@gmail.com
T. S. Gandhi
e-mail: tejsvnit.ac.in@gmail.com
M. R. Patel
Chemical Sciences Department, N. V. Patel College of Pure & Applied Sciences, Vallabh
Vidyanagar 388120, Gujarat, India
123

T. S. Gandhi et al.
Introduction
Cashew nut shell liquid (CNSL) is an product extracted from cashew nut tree fruits.
The cashew nut tree (Anacardium occidentale) is native to Brazil. The top 10
countries growing cashew trees are Vietnam (28 % of total world production), India
(25 %), Nigeria (10 %), Brazil (8 %), Tanzania, Indonesia, Guinea-Bissau, Ivory
Coast, Mozambique, and Benin. The cashew nut tree has a fruit with a very
interesting structure. The nut, which is attached to the cashew apple, has two
shells—a hard inner shell and an outer shell. Between these two shells, in a
honeycomb structure, is an oil known as CNSL [1, 2]. CNSL is an amber-colored,
poisonous, viscous oil obtained as a byproduct of the cashew nut. Three methods are
generally used for extraction of CNSL from cashew nuts—mechanical, roasting,
and solvent extraction in a Soxhlet apparatus. CNSL is an organic aromatic oil
containing a variety of natural phenolic components (Fig. 1). The major component
(approx. 90 %) is anacardic acid; the oil also contains 10 % cardol. Anacardic acid
is a natural phenol with a long hydrocarbon chain of 15 carbon atoms in the meta
position and a carboxyl group attached to the ortho position. Anacardic acid can be
converted to cardanol by (conventional) de-carboxylation, as shown in Fig. 2 [3].
Cardanol has many applications, for example use in epoxy resins, phenol–
formaldehyde resins, nonionic surfactants, and polyurethanes [4–14].
In this study we report a three-step synthesis of Mannich polyols for rigid
polyurethane foams. The first step is synthesis of the Mannich precursor, N-(2-
hydroxyethyl)-1,3-oxazolidine, by simple condensation of formaldehyde (the most
used carbonyl compound) and diethanolamine. The second step involves synthesis
of the Mannich base by reaction of the Mannich precursor with cardanol. The third
step is alkoxylation of the Mannich base with different oxide derivatives to furnish
the Mannich polyether polyols. These polyether polyols can be directly used for
rigid foam formulations without supplementary purification [15, 16]. After the
alkoxylation (different types of oxide) the Mannich bases can be used as polyol
components in reactions with a variety of isocyanates, for example toluene
diisocyanate or biphenyl methane diisocyanate (Fig. 3), to obtain rigid polyurethane
foams with good physical–mechanical, thermal, and fire resistance properties [16,
17].
Experimental procedures
Materials
Cashew nut shells (CNS) were obtained from Gujarat Cashew Industry (Kutch).
CNSL was obtained from CNS by Soxhlet extraction. Cardanol was obtained by de-
carboxylation of CNSL. Diethanolamine, paraformaldehyde powder 95 %, and
8-hydroxyquinoline were purchased from Sigma–Aldrich. Chloroethanol, potassium
hydroxide, and epichlorohydrin were obtained from Merck, India. Styrene oxide
was obtained from KDAC Chem, Vadodara, India.
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Synthesis and characterization of different types of epoxide
Fig. 1 Major phenolic components of cashew nut shell liquid
Fig. 2 Thermal de-carboxylation of anacardic acid to cardanol
Synthesis of epoxides 3
Synthesis of ethylene oxide
Gaseous ethylene oxide 3 was obtained by reaction between chloroethanol (100 g)
and potassium hydroxide (68.32 g) at ambient temperature for 1 h in the mole ratio
1:1 (Scheme 1). The resulting product was absorbed in methanol [18].
123

T. S. Gandhi et al.
Fig. 3 Different types of isocyanate
Synthesis of 2-((m-tolyloxy)methyl)oxirane 12 and 4-((oxirane-2-
yl)methoxy)quinoline 13
Epoxides were prepared by reaction of aromatic phenols 9 or 10 with epichloro-
hydrin 11, in alkaline medium, with tetrabutylammonium bromide (TBAB) as
phase-transfer catalyst, in the mole ratio 1:2:1, as shown in Scheme 3. The reaction
was performed in a two-necked, 250-ml, round-bottomed flask, with m-cresol (5 g)
or 8-hydroxyquinoline (5 g), epichlorohydrin (9.02, 6.71 g), and TBAB (0.52,
0.62 g). The reaction mixture was heated under reflux at 90 °C for 3 h. The reaction
progress was monitored by TLC. On completion of the reaction the mixture was
poured into water and extracted with ethyl acetate. Finally, solvent was removed
under reduced pressure to furnish the final product 12 or 13.
Synthesis of N-(2-hydroxyethyl)-1,3-oxazolidine (Mannich precursor) 6
and Mannich bases 8a and 8b
N-(2-Hydroxyethyl)-1,3-oxazolidine 6 was synthesized by reaction of paraformal-
dehyde 4 with diethanolamine 5 in the mole ratio 1:1, as shown in Scheme 2. The
reaction was performed in a 250-ml, round-bottomed flask, with diethanolamine
Scheme 1 Synthesis of ethylene oxide. Reaction and condition A room temperature, 1h
123

Synthesis and characterization of different types of epoxide
Scheme 2 Synthesis of N-(2-hydroxyethyl)-1,3-oxazolidine and Mannich base. Reaction and condition
B 50 °C, 2 h, C 70 °C, 2.5 h
(10 g) and paraformaldehyde (2.855 g), by means of a condensation reaction. The
reaction temperature was maintained at 50 °C for 2 h in a water bath. The water was
then distilled from the reaction mixture. The reactivity of N-(2-hydroxyethyl)-1,3-
oxazolidine is explained by the equilibrium between the cyclic form and the open-
chain form, as shown in Fig. 4. The N-(2-hydroxyethyl)-1,3 oxazolidine structure
was confirmed by the IR spectrum.
Mannich bases 8a and 8b were synthesized by reaction of cardanol (3-
pentadecylphenol) 7 and the Mannich precursor (N-(2-hydroxyethyl)-1,3-oxazoli-
dine) 6 in the mole ratio 1:1. The reaction was performed in a two-necked, 250-ml,
round-bottomed flask containing N-(2-hydroxyethyl)-1,3-oxazolidine by stepwise
addition of cardanol (25.81 g). The reaction mixture was heated under reflux at
70 °C for 2.5 h. The resulting products 8a and 8b were viscous, brown–amber
liquids. The structures of the Mannich bases were confirmed by the IR and 1H NMR
spectra.
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T. S. Gandhi et al.
Scheme 3 Synthesis of different epoxides. Reaction and condition D, E 90 °C, 3 h, TBAB
Fig. 4 Cyclic and open-chain forms of N-(2-hydroxyethyl)-1,3-oxazolidine.
Synthesis of Mannich polyols 16(a), 16(b)–19(a), 19(b)
The Mannich polyether polyols 16a and 16b were synthesized by reaction of
Mannich bases 8a and 8b and methanolic ethylene oxide 14 in the mole ratio 1:2 at
100 °C under auto-generated pressure (50 Psi) in a closed system for 3 h [19, 20].
The other Mannich polyether polyols, 17a, 17b–19a, 19b were synthesized by
reaction of Mannich bases 8a and 8b with different synthesized epoxides 12, 13, and
15, with K2CO3 as catalyst and n-butanol as a solvent in the mole ratio 1:2:1:1, as
shown in Scheme 4. All types of epoxide are reactive with nucleophiles such as N,
S, and O Mannich bases contain –OH, and nucleophilic attach on the epoxide ring in
the presence of basic catalyst gives the Mannich polyols. The reaction was
123

Synthesis and characterization of different types of epoxide
performed in a two-necked, 250-ml, round-bottomed flask containing ((m-
tolyloxy)methyl)oxirane (8.44 g), 8-((oxirane-2-yl)methoxy)quinoline (10.34 g) or
styrene-oxide (6.17 g) with stepwise addition of the Mannich base (10 g) in the
presence of basic catalyst K2CO3 (3.54 g) and n-butanol as a solvent (1.85 g). The
reaction mixture was heated under reflux at 100 °C for 3 h. The progress of the
reaction was monitored by TLC. The structures of the final products were confirmed
1
by the H NMR and IR spectra.
Characterization
1H NMR spectra were recorded with an Hitachi 500-MHz spectrometer. Infrared
spectra were recorded with a Jasco FT-IR spectrometer by the KBr pellet method.
The method for hydroxyl group determination, using acetic anhydride, is described
in detail in ASTM E222 [21].
The IR spectrum of N-(2-hydroxyethyl)-1,3-oxazolidine contained strong
absorption at (m, cm-1): 1,654 (C=N imine group).
The IR spectrum of the Mannich base from cardanol contained peaks at (m,
cm-1): 3,349 (–OH), 2,925 (–C=C–), 2,854 (–C–H), 1,584 (phenyl ring), 1,378
(–C–N), 1,274 (–C–O), and 1,074 (conjugated double bond). The 1H NMR spectrum
(400 MHz, DMSO) of the Mannich base from cardanol contained peaks at (d, ppm):
1.53–1.56 (3H, –CH3), 2.56–3.75 (2H, =N–CH2), 5.29–5.38 (6H–C=C–), 6.5 (1H–
Ar–OH), and 6.5–7.87 (Ar–H).
The IR spectrum of the Mannich polyol formed by reaction of the Mannich base
with 2-((m-tolyloxy)methyl)oxirane contained peaks at (m, cm-1): 3,348 (–OH),
3,009 (–C–H–), 2,925 (–C–C–), 2,854 (–C=C–), 1,585 (phenyl ring), 1,455 (–C–N,
1
1,260 (–C–O), 1,082 (–C=C–). The H NMR spectrum (400 MHz, DMSO) of the
Mannich polyol formed by reaction of the Mannich base with 2-((m-tolyl-
oxy)methyl)oxirane contained peaks at (d, ppm): 1.29–1.54 (3H, –CH3),
2.64–3.45 (Ar–OR), 3.58–3.83 (2H, =N–CH2), 5.3–5.38 (–C=C–), 5.38–6.73 (Ar–
H), and 6.73–7.91 (phenyl ring).
The IR spectrum of the Mannich polyol formed by reaction of the Mannich base with
8-((oxiran-2-yl)methoxy)quinoline contained peaks at (m cm-1): 3,293 (–OH), 3,008
(–C–H), 2,925 (–C–C–), 2,853 (–C=C–), 1,652 (phenyl ring), 1,456 (–C–N), 1,267 (–C–
O–), and 1,080 (conjugated double bond). The1H NMR spectrum (400 MHz DMSO) of
the Mannich polyol formed by reaction of the Mannich base with 8-((oxiran-2-
yl)methoxy)quinoline contained peaks at (d, ppm): 1.33–1.38 ppm (3–H,–CH3),
2.47–2.80 (Ar–OH), 3.45–3.76 (2H, =N–CH2), 5.32–5.38 (conjugated double bond),
5.39–6.86 (Ar–H), and 6.54–7.9 (naphthalene ring).
The IR spectrum of the Mannich polyol formed by reaction of the Mannich base
with styrene oxide contained peaks at (m cm-1): 3,369 (–OH), 3,008 (–C–H), 2,926
(–C–C–), 2,854 (–C=C–), 1,452 (–C–N), 1,581 (phenyl ring), and 1,045 (conjugated
1
double bond). The H NMR spectrum (400 MHz DMSO) of the Mannich polyol
formed by reaction of the Mannich base with styrene oxide contained peaks at
(d, ppm): 1.33–1.45 (3-H,–CH3), 2.5–2.75 (Ar–OR), 3.42–3.54 (2H,=N–CH2),
123

T. S. Gandhi et al.
Scheme 4 Synthesis of Mannich polyols. Reaction and condition F 100 °C, 3 h and 50 Psi and G, H and
1–100 °C, 3 h
5.30–5.31 (conjugated double bond), 6.68–7.1 (Ar–H), and 7.30–7.33 (phenyl
ring).
Results and discussion
This new method, based on oxazolidine chemistry, involves very reactive species of
oxazolidines obtained by reaction of diethanolamine and paraformaldehyde.
Oxazolidine is a low-viscosity light yellow liquid. The IR spectrum of oxazolidine
indicates strong absorption at 1,654 cm-1 (C=N imine group), proving the existence
of the mentioned equilibrium between the cyclic structure and the open-chain
123

Synthesis and characterization of different types of epoxide
Table 1 Characteristics of cashew Mannich polyols form Mannich base
No. Type of Mannich Mannich precursor/Mannich base
(mol mol-1
Hydroxyl number
(mg KOH g-1
)
Color of
liquid
polyol
)
1
2
MP-1
MP-2
2/1
2/1
412
687
Brown
Dark
brown
3
4
MP-3
MP-4
2/1
2/1
309
807
Light
brown
Dark
brown
structure [22]. The Mannich base with cardanol is characterized by low viscosity
and can be used as a polyol for synthesis of rigid polyurethanes. It is well known
that the phenolic hydroxyl reacts extremely slowly with isocyanates [15]. By
alkoxylation of Mannich bases with different types of oxide, the phenolic hydroxyl
is converted to an aliphatic hydroxyl of good reactivity in reaction with isocyanates.
Mannich polyols were obtained by ethoxylation of the synthesized Mannich bases.
Ethoxylation by use of EO-to-Mannich base mole ratios of 2:1, gives trifunctional
polyols designated cashew Mannich polyols. The structures of all the synthesized
compounds (different types of polyol) were confirmed by IR and 1H NMR
spectroscopy. All polyols had the same functional groups and hydroxyl values, and
all were brown (Table 1).
Conclusion
The Mannich polyols obtained in this work are, because of high amine–tertiary
nitrogen contact, reactive in the foaming process, with catalytic effect in reaction in
the of hydroxyl groups with isocyanates. The synthesized Mannich polyols can be
used for the production of rigid polyurethane foams without any purification step
and are recommended for use in formulations for spraying rigid polyurethanes foam.
The rigid polyurethane foams obtained with these Mannich polyols have higher
physical–mechanical properties, thermalstability, and flame resistance.
Acknowledgments The author wish to thank the Department of Applied Chemistry, SVNIT, Surat, for
providing laboratory facilities, and Gujarat Cashew Industrial (Kutch, Gujarat, India), for providing the
initial product. Analytical facilities provided by the Centre of Excellence, Vapi, Gujarat, India, and
Punjab University, Chandigarh, India, are gratefully acknowledged.
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