Highly efficient and recyclable alkylammonium hydrosulfate catalyst for formation of bisphenol F by condensation of phenol with formaldehyde

Article abstract of DOI:10.1039/c6ra07385a

Several C₁-C₄ alkylammonium hydrosulfates [R₃NH][HSO₄] have been conveniently prepared from the cheap raw materials sulfuric acid and alkylamines. Their acidities were measured by chemical titration and determined using UV-vis spectroscopy with a basic indicator 4-nitroaniline. The catalytic performance of these hydrosulfates for the condensation of phenol with formaldehyde to bisphenol F (BPF) was evaluated in detail on a batch reactor. The results indicated that the proposed catalysts are very active for such condensation due to its homogeneous catalysis characteristics in reaction conditions. Among the catalysts examined, [H₃NCH₂CH₂NH₃][HSO₄]₂ shows the best catalytic performance and it can achieve a complete conversion of formaldehyde, providing a higher than 90% selectivity for BPF under the optimal conditions. Furthermore, the catalyst can be recovered from the reaction mixture via an azeotropic distillation with cyclohexane to remove water and then filtration and used repeatedly six times almost without loss of activity, showing an excellent reusability. It is suggested that the present catalytic process combines the characteristics of a homogenized reaction and heterogenized recovery so might provide a highly-efficient, environmentally-friendly and low-cost route for synthesis of bisphenol F.

Full text of DOI:10.1039/c6ra07385a

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Highly efficient and recyclable alkylammonium hydrosulfate
catalyst for formation of bisphenol F by condensation of phenol
with formaldehyde
Received 00th January 20xx,
Accepted 00th January 20xx
Jiafu Xiao, a Hua Huang, a, b Weijian Xiang, a Wei Liao, a Junyi Liu, a, b Xichun She, b Qiong Xu, a Zaihui
Fu, a Steven Robert Kirk a and Dulin Yina,*
DOI: 10.1039/x0xx00000x
www.rsc.org/
Several C1-C4 alkylammonium hydrosulfates [R3NH][HSO4] have been conveniently prepared from the cheap raw materials
sulfuric acid and alkylamines, their acidities were measured by chemical titration and determined using UV/Vis
spectroscopy with a basic indicator 4-nitroanline. The catalytic performance of these hydrosulfates for the condensation of
phenol with formaldehyde to bisphenol F (BPF) was evaluated in detail on a batch reactor. The results indicated that the
proposed catalysts are very active for such condensation due to its homogeneous catalysis characteristics in reaction
condition. Among the catalysts examined, [H3NCH2CH2NH3][HSO4]2 shows the best catalytic performance and it can achieve
a complete conversion of formaldehyde, providing a higher than 90% selectivity for the BPF under the optimal conditions.
Furthermore, the catalyst can be recovered from reaction mixture via an azeotropic distillation with cyclohexane to
remove water and then filtration and used repeatedly for six times almost without loss of activity, showing an excellent
reusability. It is suggested that the present catalytic process combines the characters of homogenized reaction and
heterogenized recovery might provide a highly-efficient, environmentally-friendly and low-cost route for synthesis of
bisphenol F.
[10]
impregnated on fumed silica [9], montmorillonite K10
or
1. Introduction
activated-bentonite[11]
,
Cesium-substituted DTP-based solid
[12]
composite catalysts xCsTPA–ZTP
and mesoporous M (Al, Zr, Al–
Bisphenol F (BPF) is a common name for a mixture of p,p'-
dihydroxyphenolmethane, o,p'-dihydroxyphenolmethane and o,o'-
dihydroxyphenolmethane, often used as a raw material for the
synthesis of low viscosity epoxy resins, polyester and polycarbonate
resins. It is also used as a modifier and stabilizer for phenolic resins,
etc. In the last several decades [1], BPF has attracted considerable
attention due to its attractive applications compared with Bisphenol
A. BPF is conventionally prepared by condensation of phenol with
formaldehyde using some liquid mineral acids (phosphoric acid or
sulfuric acid) as catalysts [2-5], which has several disadvantages of
separation, recycling, treatment of spent acids, and equipment
corrosion. In order to overcome the drawbacks of homogeneous
catalysis, some recyclable solid acids have been employed to
develop a heterogeneous catalysis process for the synthesis of
bisphenol F, they include aluminum-grafted MCM-41 molecular
[14]
Zr)-SBA-15[13]
.
The solid acids
used are, however, easily
deactivated during reaction because polycondensates formed from
the consecutive condensation of bisphenol F with formaldehyde
were deposited inside their pores. As a result, a complicated
regeneration process including reflux process with organic solvent,
then an additional calcination or activated process to remove such
sediments inside the catalyst’s pores, is required to recover the
activity of catalyst.
Recently, some Ionic liquid acids have attracted substantial
attention due to their special physical and chemical properties [15-19]
.
A thermoregulated phase-separable reaction system based on
a
series of water-soluble imidazolium- based Brønsted acids as
catalysts was designed to achieve the highly efficient synthesis of
bisphenol, which should be attribute to its advantage in combing
homogenous catalytic reaction with heterogenous separation of
catalyst. Only part of the catalyst used, however, can be separated
in this system and separation of the residual water-soluble catalyst
still needs to be extracted with water from reaction mixtures and
further improved in efficiency.
sieves[6-7] H-beta zeolite[8]
, , dodecatungstophosphoric acid(DTP)
In order to further decrease the cost of catalyst and improve
its catalysis and recovery efficiencies, we attempt to establish a
highly efficient catalysis system with the characteristics of
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homogenized reaction and heterogenized catalyst recovery for the Triethylammonium sulfate [Et3NH][HSO4]. 1H NMR (DMSO-d6): δ
condensation of phenol with formaldehyde to BPF. In that, a series (ppm) 1.19 (t, 9H), 3.09 (m, 6H), 9.39 (s, 1H). Thermal
of alkylammonium hydrosulfates prepared via cheap alkylamines decomposition point: 285◦C, Melting point: 90 ◦C.
and sulfuric acid as raw materials are used to homogeneously
Tripropylammonium sulfate [Pr3NH][HSO4]. 1H NMR (DMSO-d6): δ
catalyze the condensation. After reaction, they can be recovered
(ppm) 0.91 (t, 9H), 1.63 (m, 6H), 2.99 (m, 6H), 9.26 (s, 1H). Thermal
from the reaction mixture via the removal of water using
decomposition point: 256◦C, Melting point: 88◦C.
cyclohexane's azeotropic distillation and then filtration. Herein, we
would report some initial results obtained from employing this
Tributylammonium sulfate [Bu3NH][HSO4].1H NMR (DMSO-d6): δ
catalytic process for highly efficient synthesis of BPF.
(ppm) 0.92(t, 9H), 1.33 (m, 6H), 1.59 (m, 6H), 3.01 (m, 6H), 9.32 (s,
1H). Thermal decomposition point: 258◦C, Melting point: 80◦C.
2. Experimental
Ethane-1,2-diaminium hydrogen sulfate [H3NCH2CH2NH3][HSO4]2. 1H
2.1 Chemicals and Materials
NMR (DMSO-d6): δ (ppm) 3.04 (s, 4H), 7.87 (m, 6H). Thermal
decomposition point: 346◦C, Melting point: 86◦C.
The starting materials phenol, formaldehyde, trimethylamine,
triethylamine, N-butylamine, N-tripropylamine, sulfuric acid,
Propane-1,2-diaminium hydrogen sulfate [H3NCH2(CH3)CHNH3]
ethylenediamine, 1, 2-Propanediamine, phenolphthalein, sodium
[HSO4]2.1H NMR (DMSO-d6): δ (ppm) 1.26 (d, 3H), 2.93(m, 2H),
hydroxide, acetylacetone and 4-Nitroaniline were AC grade, while
3.08(m, 1H), 7.99 (m, 6H). Thermal decomposition point: 322◦C,
the potassium hydrogen phthalate was GC grade and purchased
Melting point: 82◦C.
from Sinopharm chemical Reagent Co., Ltd. Bisphenol F (99%)
standard was received from Alfa Aesar. All chemicals were used as
2.3 Measurement of acidity of alkylammonium hydrosulfates
received without any purification process.
A traditional acid-base titration was used to determine the
acidic amount of the alkylammonium hydrosulfates, 1mmol
2.2 Synthesis and characterization of alkylammonium
alkylammonium hydrosulfates was dissolved in 20mL distilled
hydrosulfates
water, then titrated by the calibrated 0.05mol/L NaOH solution and
phenolphthalein as an indicator. The acid amount of catalyst could
According to the reported preparation of the simple ammonium
be obtained based on the consumption amount of NaOH solution.
[21-22]
based acid catalysts
, the synthesis of alkylammonium
hydrosulfates was modified. A 100ml round-bottomed glass reactor
equipped with reflux condenser and thermometer was
The Brønsted acidic strength of catalysts was evaluated by
Hammett acidity functions and UV/Vis spectroscopy with a basic
indicator reported by Thomazeau [23]. According to Thomazeau’s
method, the protonation extent of the basic indicator 4-Nitroaniline
(named I) in ionic water was determined. The molar concentration
of the unprotonated indicator base may be represented by [I] and
[IH+] is the molar concentrations of the protonated indicator base in
a solution; pK(I)aq is the pKa value of the indicator base in aqueous
solution(pK(I)aq = 0.99). The resulting Hammett function H0 was
defined as
a
a
immersed in a recirculating heated oil-bath. 0.1mol sulfuric acid
was dropped slowly into the 0.1mol alkylamine at 20˚C for
60min.The mixture was then stirred for an additional 120 min at 60
˚C to ensure the reaction finished completely. Finally, the resulting
reaction solution was completely evaporated to dryness at 70 ˚C
under vacuum (5 mm Hg) to yield the white solid product.
The 1H NMR spectra of the synthesized alkylammonium
hydrosulfates were recorded with a 500 MHz Bruker spectrometer
in DMSO-d6 calibrated with tetramethylsilane (TMS) as the internal
reference. Thermogravimetric analysis of the samples under
nitrogen flow was conducted in a Netzsch-STA409PC thermal
gravimetric analyzer. During the analysis, the temperature was
increased from room temperature to 800˚C at a heating rate of 10
˚C /min. Melting point was determined by a WRS-1B digital melting
point apparatus at a linear heating rate of 1 ˚C /min.
H0=pK (I) aq + log ([I]/ [IH+])
(1)
2.4 Catalyst evaluation
The condensation of phenol with formaldehyde catalyzed by
different alkylammonium hydrosulfates catalysts were carried out
in a 50ml magnetically stirred round-bottomed flask equipped with
a reflux condenser and a thermometer. In a typical condensation
reaction, 100 mmol phenol, 10 mmol aqueous formaldehyde (37%)
and 0.5mmol catalyst were added into the reactor, which then was
heated to 70˚C for 2h. The products were determined with the
external standard method using an Agilent 1100 HPLC equipped
with a Venusil C18 (4.6mm ×250mm); a methanol –water (65:35)
mixture was used as mobile phase and solvent. The unreacted
formaldehyde was determined using the Shimadzu UV-2450
The detailed 1H NMR data, melting point and thermal
decomposition point of alkylammonium hydrosulfates are shown
below:
Trimethylammonium sulfate [Me3NH][HSO4].1H NMR (DMSO-d6): δ
(ppm) 2.77 (s, 9H), 9.37 (s, 1H). Thermal decomposition point: 324◦C,
Melting point: 125◦C.
2 | J. Name., 2012, 00, 1-3
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spectrophotometer using an acetylacetone spectrophotometric Table 1 Amount of H+ of different alkylammonium hydrosulfates
method [24]. The catalytic activities of these hydrosulfates were
H+(mmol )
evaluated in terms of formaldehyde conversion and the selectivity
Catalyst
Amount(mmol)
1.01
of bisphenol F and its isomer distribution，which were calculated
[Me3NH][HSO4]
1.00
as below:
[Et3NH][HSO4]
[Pr3NH][HSO4]
[Bu3NH][HSO4]
1.00
1.00
1.01
0.50
0.98
1.00
0.99
1.02
Conversion % = ꢂꢃꢄꢅꢆ ꢃꢇ ꢈꢅꢉꢊꢋꢅꢌ ꢇꢃꢈꢂꢉꢄꢌꢅꢍꢎꢌꢅ × 100
ꢀ2ꢁ
ꢀ ꢁ
ꢀ
ꢁ
ꢂꢃꢄꢅꢆ ꢃꢇ ꢇꢃꢈꢂꢉꢄꢌꢅꢍꢎꢌꢅ
[H3NCH2CH2NH3][HSO4]2
ꢂꢃꢄꢅꢆ ꢃꢇ ꢏꢐꢆꢑꢍꢅꢒꢃꢄꢆ ꢓ
[H3NCH2CH(CH3)NH3][HSO4]2
0.51
1.04
ꢀ
ꢁ
=
Selectivity %
× 100
3
∑
ꢂꢃꢄꢅꢆ ꢃꢇ ꢉꢄꢄ ꢑꢈꢃꢌꢔꢊꢋꢆ
2.5 Catalyst reusability
When the condensation reaction proceeded until free
formaldehyde was no longer detected, the reflux condenser was
replaced by a water separator and 10ml cyclohexane was added
into the condensation reaction mixture, which was then held at 70
˚C for 30min, during which the white solid precipitated from liquid
mixture. The resulting solid was then easily separated by a hot
filtration higher than 40˚C to yield the recovered catalyst. And the
cyclohexane layered from the liquid mixture was easily recovered
3. Results and discussion
3.1 Characterization of alkylammonium hydrosulfates
The detailed 1H NMR spectra shown in Fig. 1–6(see ESI†) indicate
that the prepared catalysts were consistent with the molecular
structures of these alkylammonium hydrosulfates. The acid-base
titration results shown in Table
1
indicate that these
by
a
decantation separation.
The recovered catalyst and
alkylammonium hydrosulfates in water could be ionized to yield the
protons to be almost equal to their theoretical ones, illustrating
that they have very high quality. The thermal decomposition point
of alkylammonium hydrosulfates higher than 250 ˚C suggests that
these catalysts have a good thermal stability.
cyclohexane were directly reused in the next run. The amount of
residual catalyst in the liquid phase composed of phenols was
roughly measured using a DDS-307 Conductivity Meter equipped
with
a
DJS-1C Conductance electrode. And its accurate
measurement was achieved using SPECTROBLUE inductively
coupled plasma optical emission spectrometry (ICP-OES) with the
standard curve method [25-26]. 0.5g liquid composed of phenols was
dissolved in ultra-pure water and diluted to 50mL in a volumetric
flask. An Optima SPECTROBLUE ICP-OES purged with argon was
operated at 1.4 kW RF power. The nebulizer, auxiliary and plasma
gas flow rates were 0.8, 0.8 and 12 L min-1, respectively. The sulfur
Fig.1 is the detailed absorption spectra of 4-nitroaniline in the
presence of alkylammonium hydrosulfates. In that,
a strong
absorption band at λmax= 375 nm is found in an UV-vis spectrum of
4-nitroaniline, and the intensity of such band obviously decreases in
the presence of alkylammonium hydrosulfates, which should be
due to a protonated effect.
emission signal was registered at 180.731 nm with a 0.1
s
integration time. The observed sulfur emission intensity was due to Furthermore, the decaying degree of such band is influenced by the
residual hydrosulfate, the calculation of residual rate shown as hydrosulfates and follows an increasing sequence of
below:
[H3NCH2CH2NH3][HSO4]2
>
[H3NCH2(CH3)CHNH3][HSO4]2
>
[Me3NH][HSO4] > [Et3NH][HSO4] > [Bu3NH][HSO4] > [Pr3NH][HSO4]
.
ꢕꢅꢐꢖꢍꢋ ꢃꢇ ꢈꢅꢆꢐꢌꢔꢉꢄ ꢊꢉꢋꢉꢄꢎꢆꢋ
ꢕꢅꢐꢖꢍꢋ ꢃꢇ ꢉꢌꢌꢅꢌ ꢊꢉꢋꢉꢄꢎꢆꢋ
ꢀ
ꢁ
ꢀ ꢁ
4
Residual rate % =
× 100
Table 2 Acidities of different alkylammonium hydrosulfates and their catalytic performance
Catalyst
H0
Formaldehyde
conversion at a
Bisphenol
selectivity at a
BPF isomer distribution
at a period of 15min（%）
period of 15min (%) period of 15min (%)
p,p'-BPF
35.3
o,p'-BPF
44.4
o,o'-BPF
[Me3NH][HSO4]
[Et3NH][HSO4]
[Pr3NH][HSO4]
[Bu3NH][HSO4]
1.48
1.73
1.81
1.78
89.5
67.7
57.9
62.2
89.8
89.1
88.9
89.7
20.3
23.2
22.8
23.4
28.1
48.7
28.4
48.8
28.2
48.4
[H3NCH2CH2NH3][HSO4]2
1.38
96.7
90.1
36.9
43.2
19.9
20.1
[H3NCH2CH(CH3)NH3][HSO4]2
1.47
93.6
89.9
36.5
43.4
Reaction conditions: phenol/formaldehyde, 10 mol mol-1; catalyst (HSO4 ) /formaldehyde, 0.05mol mol-1; temperature=70 ˚C
-
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Fig.2 Formaldehyde conversion at different time over different
alkylammonium hydrosulfates. Reaction conditions: phenol/
formaldehyde, 10 mol mol-1; catalyst /formaldehyde, 0.05mol mol-1;
temperature, 70˚C
Fig.1 UV-vis absorption spectra in water. Hydrosulfates
concentration, 20 mmol L-1; 4-Nitroaniline, 5 mg L-1
This can be indicative of an acid strength order of the hydrosulfates
(inversely proportional to H0 value, see Table 2). The acidic strength
of these hydrosulfates seems to be relative to alkyl chains of their
quaternary ammoniums and obviously decreases when the alkyl
carbon atom of hydrosulfate is more than 3.
with a decrease in the selectivity for other two isomers (o,p'-BPF
from 48.8 to 43.2%, and o,o'-BPF from 22.8 to 19.9%), indicating
that the stronger acidity of catalyst is favourable of accelerating the
formation of p,p'-BPF. The above results indicate that
[H3NCH2CH2NH3][HSO4]2 seems to be the optimum catalyst for
formation of bisphenol
formaldehyde
F
from condensation of phenol with
3.2 Catalytic performance of alkylammonium
hydrosulfates
.
Table 2 lists the data for the hydrosulfates-catalyzed condensation
of phenol with formaldehyde. It is seen from Table 2 that these
hydrosulfates are very active for this reaction, which can give rise to
57-97 % formaldehyde conversion at 15 min with approximately
90% selectivity for BPF. Notably, three hydrosulfates with H0 value
of lower than 1.5 exhibits by much higher catalytic activity
compared to the other ones with relatively high H0 value. Time-
dependence of formaldehyde conversion shown in Fig.2 also
illustrates that the catalytic rate of hydrosulfates is basically
consistent with their acidity and the stronger acidity of
hydrosulfates is more conducive to accelerate this condensation.
This indicates that the stronger acidity of hydrosulfates is more
conducive to accelerate this condensation. Table 2 further shows
that acidity of the catalyst plays an adjusting effect on the
distribution of BPF isomers, when the H0 value of hydrosulfates is
reduced from 1.81 to 1.38, the selectivity of p,p'- BPF gradually
-
Fig.3 Effect of Catalyst (HSO4 )/formaldehyde mole ratio on
formaldehyde conversion, bisphenol F selectivity and its isomers
distribution. Reaction conditions: phenol/formaldehyde, 10 mol
mol-1; temperature, 70˚C; reaction time, 2h
increases
from
28.4
to
36.9%,
along
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Fig.5 Effect of phenol/formaldehyde mole ratio on formaldehyde
conversion, bisphenol F selectivity and its isomers distribution.
Fig.4 Effect of temperature on formaldehyde conversion, bisphenol
F selectivity and its isomers distribution .Reaction conditions:
-
Reaction conditions: catalyst (HSO4 )/ formaldehyde, 0.05mol mol-1;
-
phenol/formaldehyde, 10 mol mol-1; catalyst (HSO4 )/ formaldehyde,
reaction time, 2h; temperature 70 ˚C
0.05mol mol-1; reaction time, 2h
The results shown in Fig. 5 reveal that the mole ratio of phenol to
formaldehyde has no significant effect on formaldehyde conversion
and the distribution for bisphenol F isomers, but can exert a definite
In the following experiments, the effect of various parameters
including the amount of catalyst, reaction temperature and time,
phenol/ formaldehyde mole ratio on this condensation was checked
in details using the best [H3NCH2CH2NH3][HSO4]2 as a catalyst and
the results are shown in Figs.3-6. It is seen from Fig.3 that
formaldehyde conversion clearly increases with an increase in the
amount of catalyst Fig. 4 (catalyst/formaldehyde mole ratio from
0.002 to 0.01), with a further increase in the amount of catalyst
(catalyst/formaldehyde ratio from 0.05 to 1.00) yielding a very slow
increase in formaldehyde conversion. Moreover, the selectivity for
bisphenol F and the distribution for BPF isomers remain almost
unchanged over the entire range of catalyst concentration.
Moreover, the selectivity for bisphenol F and the distribution for
BPF isomers remain almost unchanged over the entire range of the
amount of catalyst.
effect on the selectivity for bisphenols F. With the increase of
phenol/formaldehyde mole ratio from 5:1 to 10:1, the bisphenol F
selectivity increase from 79.0% to 90.7%. After that, the selectivity
is nearly unchanged with further increasing such ratio.
The effect of reaction time on condensation reaction is presented in
Fig. 6. With an increase in the reaction time, the formaldehyde
conversion and the selectivity of o,o'-BPF increase slightly, while
bisphenol F selectivity and the amount of p,p'-BPF and o,p'-BPF
decrease slightly.
As shown in Fig. 4, increasing the reaction temperature from 50 to
70˚C resulting in a slow increase in formaldehyde conversion
from 88.8 to 99.9%. After that, the improved effect of
temperature on the conversion is nearly negligible. In the
temperature examined, the selectivity for bisphenol F is hardly
influenced by temperature. Notably, with the increase of reaction
temperature from 50 to 90˚C, the amount of p, p’-BPF is reduced
from 35.2 to 29.9%, along with a slight increase in other two
isomers p, p’-BPF and o, o’-BPF. This may imply that o, p’-isomer
and o, o’-isomer assigned to have a higher thermodynamic stability
than p, p’-isomer, which was reported by Jana using aluminium-
[7]
.
grafted MCM-41 molecular sieves as catalyst
Fig.6 Effect of reaction time on formaldehyde conversion, bisphenol
F selectivity and its isomers distribution. Reaction conditions:
phenol/formaldehyde, 10 mol mol-1; temperature, 70˚C
;
catalyst
-
(HSO4 )/ formaldehyde, 0.05mol mol-1
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repeatedly
for
Table 3 Electric conductivity (σ) of mixture and catalyst residual rate
in reuse
recycle
time
σ of reaction
mixture at 70˚C
(us/cm)
σ of phenols Catalyst
sulfur
phase at
25˚C
(us/cm)
0.22
0.21
0.23
0.21
0.22
0.21
residual concentra
rate (%)
tion
(ppm)
0.19
0.17
0.21
0.20
0.20
0.18
1
2
3
4
5
6
48.7
47.8
48.4
47.9
47.7
47.4
0.21a
0.54
0.51
0.66
0.52
0.56
0.53
phenol
----
Fig.7 Results of catalyst recycling experiments. Reaction conditions:
phenol/formaldehyde ratio, 10mol mol-1; catalyst/ formaldehyde
ratio, 0.05 mol mol-1; temperature,70 ˚C; reaction time, 2h
a -phenol being crystal state at 25˚C (phenol melts point 40.8 ˚C).
Finally, the catalyst’s recovery rate and repeatability were checked
using the [H3NCH2CH2NH3][HSO4]2 as a catalyst under the conditions
described in the experimental section and the obtained results are
presented in Table 3 and Fig.7. Table 3 shows that after the catalyst
was separated, the measured electro-conductivity of the liquid
phase of phenols is close to the electro-conductivity of pure liquid
phenol, but drastically less than electro-conductivity of the reaction
mixture without separating catalyst, indicating that the residue of
catalyst is negligible with such detection method. And the residual
rate of catalyst in the liquid of phase phenols determined using the
accurate ICP-OES method is in the range of 0.51 to 0.66%, and
thereby estimating that the average recovery rate of catalyst is
close to 99.5%. Fig. 7 shows that when the catalyst was used
6 times, formaldehyde conversion, bisphenol selectivity and isomer
distribution in each recycling run are nearly unchanged compared
to those obtained in the first run, this indicates that the catalyst still
remained efficient catalytic performance after seven cycle times.
3.3 The plausible mechanism for formation of
bisphenol F
A
plausible mechanism of condensation of phenol and
formaldehyde to BPF is presented in scheme.1.
Scheme 1. Plausible mechanism of condensation of phenol and formaldehyde to BPF
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ARTICLE
10 A. C. Garade, V. S. Kshirsagar, R. B. Mane, A. A. Ghalwadkar,
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A carbocation CH2OH+ is formed by protonation of formaldehyde
-
with H+ released by HSO4 in ethane-1, 2- diaminium hydrogen
sulfate. An electrophilic substitution reaction occur on phenol with
the formation of two intermediates I(a) and I(b) as the first step,
then the short-lived intermediates I (b) and I (a) deprotonates fast
to form II (a) 2-hydroxybenzylalcohol and II (b) 4-hydroxybenzyl The
protonation of alcohol II (a) and II (b) initially produced form the
carbocation III (a) and III (b) respectively. A complexation of the
electrophile carbocation III (a) and III (b) with the π electron system
of another phenol molecule generates three intermediates
IV(a),IV(b) and IV(c): these unstable intermediates then eliminate a
proton, resulting in final formation of BPF (V(a) o,o'-BPF, V(b) o,p'-
BPF and V(c) p,p'-BPF).
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Conclusions
In this work, a series of water-soluble alkylammonium hydrosulfates
have been synthesized conveniently and used for acid-catalyzed
condensation of phenol with formaldehyde to bisphenol F. The
proposed catalysts are efficient for such reaction, and can achieve
formaldehyde conversion of 99.9% and a selectivity of bisphenol F
above 89.5% with 33.3% p,p'-BPF, 44.9% o,p'-BPF and 21.8% o,o'-
BPF under the optical reaction condition. Furthermore, this type of
hydrosulfates can be highly-efficiently recovered and reused for 6
times without any change in catalytic performance. The present
catalysis system may be regarded as an environmentally friendly
method for the industrial synthesis of bisphenol F at low cost.
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This Work is supported by the Graduate Innovation Fund of Hunan
province (NO. CX2014B170).
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DOI: 10.1039/C6RA07385A
The alkylammonium hydrosulfates are soluble at reaction temperature and easily separated at
room temperature with excellent reusability.