J IRAN CHEM SOC (2012) 9:529–534
531
(d, 6H, 2Me, J = 7.35 Hz), 1.10 (m, 4H, 2 CH2), 4.02
(m, 2H, –OCH), 6.27 (s, 2H, –CH=CH–). Anal. Calcd for
C12H20O4: C, 63.14; H, 8.83%. Found (%): C, 63.16; H,
8.85.
Trans di-iso-butyl maleate (3b): FT-IR (KBr, cm-1):
1,724 (C=O), 1,635 (C=C), 1,217 (C–O). 1H NMR
Results and discussions
According the report of Li et al. [8], dioctyl phthalate can
be prepared via the esterification of phthalic anhydride with
octyl alcohol in the presence of acidic functionalized ionic
liquid. They also used the neutral ionic liquids for this
reaction and lower yield of dioctyl phthalate was prepared
under these conditions. According our earlier reports,
phosphinite ionic liquid, IL-OPPh2, can act as a weak
Lewis base catalyst [18, 19]. So, as decribed in ‘‘Intro-
duction’’, the catalytic behavior of this ionic liquid in the
well-known acid catalyze esterification reaction surprised
us. To investigate the scope and limitation of IL-OPPh2 for
the esterification reaction, various alcohols were used in the
reaction with maleic and phthalic anhydrides. Phosphinite
ionic liquid was synthesized according to Iranpoor and co-
worker’s reported work [17]. To examine its activity, the
esterification reaction of maleic anhydride was reacted with
two equivalent of benzyl alcohol at room temperature in
the absence of any additives. The experimental results
revealed that this ionic liquid, exhibits a very high activity.
During the course of our further optimization of the reac-
tion conditions, when using one half equivalent of ionic
liquid in toluene as solvent, the reactions were generally
completed in a matter of hours, but the time, as expected,
was inversely proportional to the temperature. A toluene
reflux temperature was found to be optimal. We also
examined this procedure in the presence of phosphinite
ionic liquid without any solvent. Good yield of diester
product was isolated at 100 °C under these conditions.
Thus, the optimized reaction conditions for this esterifica-
tion reaction are the phosphinite ionic liquid (excess
amount) and 100 °C for 12–15 h. To study the versatility
of this procedure, the esterification of maleic and phthalic
anhydrides with phenol, and various primary, secondary
and tertiary alcohols was examined. The results are listed
in Table 1. It shows that the yields of diesters from primary
and secondary alcohols with both the phthalic and maleic
anhydrides were satisfactory under the present reaction
conditions. For the primary and secondary alcohols such as
n-octanol, n-butanol, benzyl alcohol, 1-phenyl ethanol,
isopropanol and cyclohexanol, excellent yields of diester
products were isolated from the reaction with both of
maleic and phthalic anhydrides under the optimized reac-
tion conditions (Table 1). On the other hand, the esterifi-
cation of the relatively hindered tertiary alcohols such as
tert-butanol and 2-phenyl-2-propanol with both of maleic
and phthalic anhydride was not preceded significantly and
only the reactants were isolated after 24 h stirring of the
reaction mixture under optimized conditions. We also
examined the reaction of phenol and p-cresol with maleic
and phthalic anhydrides and no ester or diester products
were prepared after 24 h stirring of the reaction mixture
(400 MHz, CDCl3)
d (ppm): 0.97 (t, 6H, 2Me,
J = 7.25 Hz), 1.01 (d, 6H, 2Me, J = 7.36 Hz), 1.09 (m,
4H, 2 CH2), 4.02 (m, 2H, –OCH), 6.31 (s, 2H, –CH=CH–).
Anal. Calcd for C12H20O4: C, 63.14; H, 8.83%. Found (%):
C, 63.2; H, 8.87.
Di-iso-butyl phthalate (5b): FT-IR (KBr, cm-1): 1,718
1
(C=O), 1,631 (C=C), 1,215 (C–O). H NMR (400 MHz,
CDCl3) d (ppm): 0.95 (t, 6H, 2Me, J = 7.33 Hz), 0.99
(d, 6H, 2Me, J = 7.39 Hz), 1.10 (m, 4H, 2 CH2), 4.09 (m,
2H, –OCH), 7.28–7.33 (m, 2H, Ar–H), 7.35–7.38 (m, 2H,
Ar–H). Anal. Calcd for C16H22O4: C, 69.04; H, 7.97%.
Found (%): C, 69.15; H, 8.01.
Cis di-cyclohexyl maleate (2f): FT-IR (KBr, cm-1):
1,721 (C=O), 1,648 (C=C), 1,230 (C–O). 1H NMR
(400 MHz, CDCl3) d (ppm): 1.05 (m, 20H, cyclohexyl
protons), 4.09 (m, 2H, –OCH2), 6.31 (s, 2H, –CH=CH–).
Anal. Calcd for C16H24O4: C, 68.54; H, 8.63%. Found (%):
C, 68.56; H, 8.64.
Trans di-cyclohexyl maleate (3f): FT-IR (KBr, cm-1):
1,726 (C=O), 1,650 (C=C), 1,233 (C–O). 1H NMR
(400 MHz, CDCl3) d (ppm): 1.02 (m, 20H, cyclohexyl
protons), 3.98 (m, 2H, –OCH2), 6.29 (s, 2H, –CH=CH–).
Anal. Calcd for C16H24O4: C, 68.54; H, 8.63%. Found (%):
C, 68.57; H, 8.66.
Di-cyclohexyl phthalate (5f): FT-IR (KBr, cm-1): 1,732
1
(C=O), 1,641 (C=C), 1,227 (C–O). H NMR (400 MHz,
CDCl3) d (ppm): 1.04 (m, 20H, cyclohexyl protons), 4.11
(m, 2H, –OCH2), 7.21 (s, 2H, Ar–H), 7.32 (s, 2H, Ar–H).
Anal. Calcd for C20H26O4: C, 72.70; H, 7.93%. Found (%):
C, 72.73; H, 7.95.
Cis dibenzyl maleate (2g): FT-IR (KBr, cm-1): 1,732
1
(C=O), 1,638 (C=C), 1,225 (C–O). H NMR (400 MHz,
CDCl3) d (ppm): 5.17 (s, 4H, –OCH2), 6.32 (s, 2H,
–CH=CH–), 7.34–7.41 (m, 10H, Ar–H). Anal. Calcd for
C18H16O4: C, 72.96; H, 5.44%. Found (%): C, 72.94; H, 5.45.
Trans dibenzyl maleate (3g): FT-IR (KBr, cm-1): 1,725
1
(C=O), 1,640 (C=C), 1,231 (C–O). H NMR (400 MHz,
CDCl3) d (ppm): 5.09 (s, 4H, –OCH2), 6.30 (s, 2H,
–CH=CH–), 7.31–7.38 (m, 10H, Ar–H). Anal. Calcd for
C18H16O4: C, 72.96; H, 5.44%. Found (%): C, 72.97; H,
5.46.
Dibenzyl phthalate (5g): FT-IR (KBr, cm-1): 1,718
1
(C=O), 1,638 (C=C), 1,229 (C–O). H NMR (400 MHz,
CDCl3) d (ppm): 5.21 (s, 4H, –OCH2), 7.21–7.25 (m, 2H,
Ar–H), 7.27–7.31 (m, 2H, Ar–H), 7.36–7.43 (m, 10H,
Ar–H). Anal. Calcd for C22H18O4: C, 76.29; H, 5.24%.
Found (%): C, 76.33; H, 5.27.
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