Cycling of waste fusel alcohols from sugar cane industries using supercritical carbon dioxide

Article abstract of DOI:10.1039/c5ra16346c

The present study describes the clean synthesis of non-phosgene organic carbonates (NPOCs) from a selective multicomponent reaction with two important by-products from sugar and alcohol industries, namely, fusel alcohols and carbon dioxide, in the presence of 1,8-diazabicycloundecene (DBU), 1,5-diazabicyclo[4.3.0]-non-5-ene (DBN) or 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]-pyrimidine (TBD) and an alkylating agent. The bases were used for the nucleophilic activation of the alcohols. The synthesis of carbonates was carried out without solvent and confirmed by GC-MS with EI ionization mode, ¹H- and ¹³C-NMR and FT-IR analysis. The carbonates were obtained in excellent yields. Crude fusel alcohol can be converted to alkylcarbonates. The proposed methodology can also be employed to convert other hydroxylated compounds into carbonates.

Full text of DOI:10.1039/c5ra16346c

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Cycling of waste fusel alcohols from sugar cane
industries using supercritical carbon dioxide†
Cite this: RSC Adv., 2015, 5, 81515
F. S. Pereira, L. J. Pereira, D. F. A. Credito, L. H. V. Girao, A. H. S. Idehara
´
˜
*
and E. R. P. Gonzalez
´
The present study describes the clean synthesis of non-phosgene organic carbonates (NPOCs) from a
selective multicomponent reaction with two important by-products from sugar and alcohol industries,
namely, fusel alcohols and carbon dioxide, in the presence of 1,8-diazabicycloundecene (DBU), 1,5-
diazabicyclo[4.3.0]-non-5-ene (DBN) or 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]-pyrimidine (TBD) and
an alkylating agent. The bases were used for the nucleophilic activation of the alcohols. The synthesis of
carbonates was carried out without solvent and confirmed by GC-MS with EI ionization mode, 1H- and
13C-NMR and FT-IR analysis. The carbonates were obtained in excellent yields. Crude fusel alcohol can
be converted to alkylcarbonates. The proposed methodology can also be employed to convert other
hydroxylated compounds into carbonates.
Received 13th August 2015
Accepted 8th September 2015
DOI: 10.1039/c5ra16346c
www.rsc.org/advances
development of synthetic methods for the formation of organic
carbonates from fusel alcohols by the capture and xation of
Introduction
carbon dioxide has become of great importance, seeking an
efficient, clean and low-cost synthesis.
Fusel alcohol is one of the by-products of sugar and alcohol
industries; however, these industries generate large amounts of
by-products and waste, which cause impact on the environ-
ment.1,2 2.5 litres of fusel alcohol is obtained per 1000 litres of
ethanol produced. Brazil stands out for having a great number
of sugar and alcohol industries; it produced 23.6 billion litres of
ethanol in the 2012 harvest.3 Therefore, the production of fusel
alcohol was approximately 59 million gallons. Fusel alcohol is
basically composed of approximately 15% isobutyl and 45%
isopentyl alcohols, among other compounds such as acids,
esters and aldehydes.1 The perspective for the growth of ethanol
production is large and, consequently, the generation of fusel
alcohols will also increase.
Due to the high content of alcohols, several studies have
been reported that use them as sustainable materials. The
synthesis of lauric, stearic, benzoic and phthalic esters was
performed by the direct esterication of fusel alcohol with
carboxylic acids, using a free-solvent microwave activation
method and p-TsOH or H3PW12O40 (HPW) as catalyst.5 Fusel
alcohol and coconut cream were used as starting materials for
the biosynthesis of ethyl-, butyl-, isobutyl- and isoamyl- octa-
noates (avor-active octanoic acid esters) using lipase palatase
as the biocatalyst.6
The potential of reactive distillation for the valorization of
fusel alcohols and increase their reaction with acetic acid has
been reported, which separates the esters in their pure form.
The experiment was performed on a laboratory-scale reactive
distillation column, and a simulation model was validated.7
Other studies presented some data regarding the uncatalyzed
esterication of fusel alcohols with acetic, propionic and butyric
acids. The formation rates of the butyric acid esters were found
to be higher than those of acetic acid and propionic acid esters.8
Among the methods used for the preparation of carbonates,
the reaction of phosgene with diols9 involves highly toxic and
corrosive products such as carbon monoxide and hydrochloric
acid. New methods for the synthesis of carbonates that consider
the utilization of carbon dioxide as raw material10,11 can be an
alternative to replace phosgene and its related compounds.12–14
Organic carbonates can be used as solvents15,16 or reagents17 in
the chemical industry18 and medicinal chemistry.19 They can
also be used as fuel additives.20,21
Over the last few years, the concentration of greenhouse
gases has increased because of the increase in industrial
activities, agriculture and transport, mainly due to the use of
fossil fuels. The greenhouse gas emissions from sugarcane
harvest systems are an issue of national concern.4
Thus, to minimize the environmental impacts caused by the
by-products (fusel alcohols and CO2) and for recycling them, the
ˆ
Universidade Estadual Paulista – Faculdade de Ciencias e Tecnologia, Departamento
´
´
´
´
ˆ
de Fısica, Quımica e Biologia – Laboratorio de Quımica Organica Fina C.P. 467,
Presidente Prudente, 19060-900, SP, Brazil. E-mail: eperez@fct.unesp.br
† Electronic supplementary information (ESI) available: Mass spectra of isopentyl
alcohol, isobutyl alcohol, crude fusel alcohol, DBU, carbonates from DBN,
carbonates
from
TBD,
2,4-dichlorobenzyl
isopentyl
carbonate,
2,4-dichlorobenzyl isobutyl carbonate, isononyl alcohol, butyl-isononyl
carbonate and cholesterol-butyl carbonate; 1H and 13C NMR spectra of the
carbonates; FTIR spectra of crude fusel oil and the corresponding NPOCs. See
DOI: 10.1039/c5ra16346c
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Fang and Fujimoto22 reported the synthesis of dimethyl phosgene organic carbonates. The multi-component selective
carbonate from carbon dioxide and methanol using base reaction utilized two important by-products from sugar and
catalysis in the presence of the promoter CH3I, which is alcohol industries, the pre-activated alcohols from fusel oil
considered a toxic reagent. The synthesis was carried out at high and pressurized CO2, as starting materials, with an alkylating
ꢀ
temperatures of 80–100 C for 2 h. The results showed that at agent. 1,8-Diazabicycloundecene (DBU), 1,5-diazabicyclo[4.3.0]-
ꢀ
100 C, dimethyl ether was detected as a by-product but when non-5-ene (DBN) or 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]-
the temperature was decreased to 80 ꢀC, the formation of the by- pyrimidine (TBD) were used as agents for the initial nucleo-
product decreased drastically, while the yield of DMC remained philic activation of starting alcohols. The protocol was also
at a constant level. The synthesis of carbonates was also investigated for other hydroxylated compounds. The formation
reported by Yamazaki et al.23 The synthetic procedure for dialkyl of alkyl carbonates was performed at low temperatures in short
1
carbonates occurred under 1 atm pressure of CO2 using an reaction times and conrmed by GC-MS, H and 13C-NMR and
alcohol, Cs2CO3 and CH2Cl2 as the solvent. The syntheses were FT-IR techniques.
ꢀ
performed at 100 C with 12 h of reaction time. However, high
Scheme 1 shows the proposed mechanism for the formation
temperatures, long reaction times, toxic solvents and an of alkyl carbonates via the capture and xation of CO2 with
expensive catalyst were employed in this study. alcohols using the amidine base DBU as promoter and the
Amidine and guanidine bases have been used as catalysts in alkylating agent butyl bromide (BuBr).
reactions involving the use of carbon dioxide as proton transfer
reagents.24–29 These bases have been used as nucleophiles for
CO2 xation to afford bicarbonate or zwitterionic adducts.28–30
The amidine DBU has been investigated to activate and
transfer the carbon dioxide molecule to amines28,29 due to its
basicity and nucleophilicity.31 DBU has also been used as a
nucleophile in its reaction with phosphorochloridates to form
DBU–phosphorus intermediates via N–P bond formation.32
Copolymers bearing DBU and DBN and copolymers derived
from 4-chloromethylstyrene were able to x carbon dioxide
under atmospheric pressure.33
Experimental
Materials and reagents
˜
Fusel oil was obtained from a sugar and alcohol industry of Sao
Paulo State. All the reagents were of analytical grade and used
without further purication.
Procedure for obtaining isobutyl and isopentyl alcohols from
fusel oil
The catalyst can be later recovered as a free base. It has been
reported that a recovery of about 75% of DBU was achieved and
it was reutilized once again for the synthesis of N-cyclohexyl
ethyl carbamate with reproducible yield and purity.12
The present study describes an efficient and eco-friendly
procedure for the conversion of fusel alcohols and CO2, the
by-products from sugarcane and ethanol industries, to non-
The fusel oil is composed of a number of main alcohols such as
ethyl, propyl, butyl, isobutyl, and isopentyl alcohols. Other
compounds identied were hexyl acetate, methyl benzoate as
well as the octanoic, decanoic, dodecanoic and pentadecanoic
acids.
For the separation of alcohols from fusel oil, a conventional
fractional distillation system was used. 100 mL of fusel oil was
distilled and each sample was collected in the following
temperature ranges: rst fraction at 80–85 ꢀC, second fraction at
ꢀ
87–90 C, and third at 106–129 ꢀC.
Procedure for the synthesis of alkyl carbonates from isobutyl,
isopentyl and isononyl alcohols
The general procedure for the synthesis of alkyl carbonates
involves adding 10 mmol (1.5 g) of the nucleophilic activator
DBU, DBN or TBD to a solution containing 10 mmol of alcohol
under stirring for 30 minutes at 25 ꢀC for partial deprotonation
of the alcohol. Subsequently, the reaction mixture was trans-
ferred to a Parr Autoclave reactor tted with a stainless steel
vessel with a 50 mL capacity. 10 mL of acetonitrile (CH3CN) and
20 mmol (2.74 g) of the alkylating agent (butyl bromide) or
(3.91 g) 2,4-dichlorobenzyl chloride were added for the
formation of an alkyl carbonate. The reaction time was 1 h
under pressurized CO2 (68 mmol) at 80 bar and 40 ꢀC. This
pressure value was maintained during the entire reaction time.
The remaining starting products and solvent were evaporated
under reduced pressure and the product was washed with
chloroform and distilled water (3 ꢁ 10 mL) to remove the base
that was in the form of an unstable white salt. This salt was
Scheme 1 Capture and fixation of CO2 with isolated fusel alcohols
promoted by DBU using an alkylating agent.
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solubilized in a solution of K2CO3 and the base was recovered
by extraction with EtOAc.12
GC-FID analysis was carried out on a Shimadzu apparatus,
GC-2010 model, equipped with a ame ionization detector. A
To investigate the role of the solvent, the synthesis was also capillary Rtx-Wax column (30 m length, 0.25 mm diameter and
studied without the use of either CH3CN or any common 0.25 mm thick) was used. The operational parameters used
ꢀ
organic solvent; instead, 10 mL of the starting alcohol was used were as follows: column temperatureꢂo1f 50 C was maintained
in excess. In both cases, the product was obtained as a brown for 5 minꢂ, 1then increased at 2 ꢀC min up to 100 ꢀC for 3 min,
oil.
5 ꢀC min to 190 ꢀC for 30 minutes and 5 ꢀC minꢂ1 to 220 ꢀC
until the end of the analysis at 69.4 kPa. The injector and
detector were kept at 250 ꢀC and 250 ꢀC, respectively. The
carrier gas ow (N2) was 0.87 mL minꢂ1 with a linear velocity of
23.4 cm sꢂ1. The injection mode was 1 : 15 and injection
volume was 1 mL.
The remaining alkylating agent 2,4-dichlorobenzyl chloride
was quantied by a calibration curve using the GC-FID with
Restek Rtx-WAX column. The calibration curve was obtained by
dilutions of a stock solution of the analyte in methanol (5.0 mol
Lꢂ1). The curve was constructed using ve points of concen-
trations in the range of 0.2–1.0 mol Lꢂ1. The calibration curve
for the remaining alkylating agent was obtained using linear
regression, plotting the area of the analyte versus analyte
concentration.
General procedure for the synthesis of alkyl carbonates from
fusel alcohols
For the reaction with crude fusel alcohol, 10 mmol (1.5 g) of
DBU was added to a round-bottom ask containing 3 g of fusel
alcohol and stirred for 30 min at 25 ꢀC. Then, the reaction
mixture was transferred to a Parr Autoclave reactor tted with a
stainless steel vessel of 50 mL capacity. 20 mmol (2.74 g) of
alkylating agent (butyl bromide) was added for the formation of
the alkyl carbonates. The reaction time was 1 h under pressur-
ized CO2 (68 mmol) at 80 bar and 40 ꢀC. The reaction was
studied without the use of an organic solvent. The product was
obtained as a light yellow oil.
The analysis was carried out on a Shimadzu apparatus,
model GC-2010, equipped with a ame ionization detector. The
operation parameters used were as ꢂfo1llows: column tempera-
ture of 50 ꢀC for 8 min, then 2 ꢀC min up to 100 ꢀC for 3 min, 5
ꢀC min to 190 C for 30 minutes and 5 C min to 230 C
until the end of analysis at 79.9 kPa. The injector and detector
were kept at 250 ꢀC and 250 ꢀC, respectively. The carrier gas ow
(N2) was 0.87 mL minꢂ1 with a linear velocity of 23.4 cm sꢂ1. The
injection mode was 1 : 15 and injection volume was 1 mL.
1H and 13C NMR analyses were recorded on a Bruker DRX400
Ultra Shield NMR spectrometer, 400 MHz, at 25 ꢀC. The solvent
used in the experiments was CDCl3.
Procedure for the synthesis of alkyl carbonate from
cholesterol
For the synthesis of cholesteryl-butyl carbonate, 5 mmol of
cholesterol was solubilized in 10 mL of dichloromethane, and
10 mmol (1.5 g) of DBU with 0.5 mmol of tetraethylammonium
bromide (TEAB) was added to this solution with stirring for
30 min at 25 ꢀC for the partial deprotonation of the alcohol. The
reagent TEAB was used in this procedure to enhance the cata-
lytic activity for an efficient deprotonation of hydroxyl group.
Subsequently, the reaction mixture was transferred to a Parr
Autoclave reactor tted with a stainless steel vessel of 50 mL
capacity. 20 mmol (2.74 g) of alkylating agent (butyl bromide)
was added for the formation of the alkyl carbonate. The reaction
time was 6 h under pressurized CO2 (68 mmol) at 80 bar and 40
ꢀC. The product was obtained as a light yellow oil.
ꢂ1
ꢂ1
ꢀ
ꢀ
ꢀ
FT-IR analyses were performed on a Bruker spectropho-
tometer, Model Vector 22, KBr pellets. Spectra were recorded at
23 ꢀC in the 4000–400 cmꢂ1 range at a resolution of 4 cmꢂ1 and
120 scans.
1
Butyl-isopentyl and butyl-isobutyl carbonates. H-NMR (500
Characterization
MHz, CDCl3): d 4.13 (2H), 3.90 (2H), 1.98 (1H), 1.66 (2H), 1.42
GC-MS analyses were performed using a gas chromatograph (2H), 0.94 (9H). 13C-NMR (500 MHz, CDCl3): d 155.4, 73.9, 67.7,
equipped with an Rtx-Wax column (30 m length, 0.25 mm 30.6, 27.7, 18.9, 13.6. IR nmax 2959, 2872, 1750, 1059 cmꢂ1. GC-
diameter and 0.25 mm thick). Operational conditions for the MS: [C5H10O3 + H]+ of m/z 118, [C4H9 + H]+ of m/z 57, [C3H6 + H]+
analysis of butyl-isopentyl and butyl-isobutyl carbonates: of m/z 41.
detector temperature 250 ꢀC, injector temperature 250 ꢀC,
2,4-Dichlorobenzyl-isopentyl
and
2,4-dichlorobenzyl-
injection mode 1 : 15, injection volume 1 mL, ow of carrier gas isobutyl carbonates. 1H-NMR (500 MHz, CDCl3): d 7.40 (2H),
(He) 0.80 mL minꢂ1. The heating ramp was initiated at 50 C, 7.25 (2H), 5.22 (2H), 4.20 (2H), 1.72 (1H), 1.58 (2H), 0.94 (6H).
ꢀ
held at this temperature for 5 min, then increased at 4 ꢀC minꢂ1 13C-NMR (500 MHz, CDCl3): d 154.9, 134.9, 131.8, 130.6, 129.4,
up to 100 ꢀC for 3 min, 2 ꢀC minꢂ1 to 110 ꢀC for 5 minutes and 127.2, 67.1, 65.9, 37.2, 24.7, 22.4. IR nmax 3458, 2999, 2872, 1750,
10 C min to 230 C until the end of the analysis. The oper- 1650, 1255 cmꢂ1. GC-MS: [C8H6Cl2O3 + H]+ of m/z 220, [C7H5Cl2
ational conditions for the analysis of fusel alcohols and the + H]+ of m/z 159, [C3H7 + H]+ of m/z 43.
ꢂ1
ꢀ
ꢀ
NPOCs from fusel alcohols: detector temperature 250 ꢀC,
Butyl-isononyl carbonate. IR nmax 3436, 2925, 2858, 1750,
injector temperature 250 ꢀC, injection mode 1 : 15, injection 1644, 1257, 1054 cmꢂ1. GC-MS: [C10H19O3 + H]+ of m/z 187,
volume 1 mL, ow of carrier gas (He) 1.00 mL minꢂ1. The [C8H15O3 + H]+ of m/z 159, [C4H9 + H]+ of m/z 57.
heating ramp was initiated at 50 ꢀC, held at this temperature for
Cholesteryl-butyl carbonate. IR nmax 3440, 2940, 2868, 1745,
5 min, then increased at 2 ꢀC minꢂ1 up to 100 ꢂꢀC1 for 3 min, 5 ꢀC 1634, 1250 cmꢂ1. GC-MS: [C27H45 + H]+ of m/z 368, [C11H15 + H]+
minꢂ1 to 190 ꢀC for 30 minutes and 5 ꢀC min to 220 ꢀC until of m/z 147, [C4H9 + H]+ of m/z 57.
the end of the analysis.
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Table
2
Chromatographic conversion (%) of butyl-isopentyl and
Results and discussion
butyl-isobutyl carbonates from preliminary experiments (1 h, 80 bar)
The initial experiments were carried out to study the synthesis
of alkyl carbonates using butyl bromide as the alkylating agent
T (ꢀC)
Butyl-isopentyl carbonate
Butyl-isobutyl carbonate
and DBU as the nucleophilic activator. An excess of alcohol was 25
92%
94%
85%
65%
80%
96%
61%
75%
40
used for substitution of any common organic solvent, and the
60a
synthesis was performed for the rst time in 1, 2, 3 and 6 h. The
80a
ꢀ
temperature was xed at 40 C and CO2 was pressurized at 80
a
Remaining percentage to reach 100% was starting alcohol.
bar (both the temperature and pressure are close to CO2
supercritical conditions).18 Table 1 shows the chromatographic
conversion obtained for the synthesized alkyl carbonates. The
chromatographic yield was calculated by area integration of the
alcohols and carbonates peaks from the chromatograms. The
yield of carbonates aer 1 h of reaction time at 40 ꢀC was quite
quantitative; therefore, this value was used for the subsequent
experiments. Further increase in the reaction time did not
improve the yields signicantly. In addition, at reaction times
lesser than 1 h, no carbonate was formed.
syntheses of carbonates (NPOCs) can be performed from a one-
pot capture of CO2 with fusel alcohols under clean conditions
using an excess of fusel alcohols without solvents, which is a
relevant advance to a green chemistry procedure.
Fig. 1a displays the chromatogram obtained from the
synthesis of butyl-isopentyl carbonate under the determined
ꢀ
optimal experimental conditions, 25 C and 80 bar of CO2 for
Having established the optimal reaction time, the next step
was to investigate the inuence of the variation of reaction
temperature on the yield of the carbonates. Thus, the syntheses
were carried out at four different temperature values ranging
from 25 to 80 ꢀC. For butyl-isopentyl and butyl-isobutyl
carbonates, 40 ꢀC was found to be the optimal temperature
for the reaction (Table 2). In the chromatograms of the
carbonates, no by-products were observed at higher tempera-
tures. The decrease in yield with temperatures higher than 40 ꢀC
could be associated to the presence of adventitious water in the
reaction media, which could partially hydrolyze the carbonate
intermediates.
The effect of some other experimental conditions was also
examined. Reactions were performed without the nucleophilic
activator or promoter (DBU) and the alkylating agent (butyl
bromide). Non-supercritical pressure (10 bar) and constant CO2
ow at normal pressure were also investigated. All the experi-
ments were carried out without the use of a solvent. The results
of this study are reported in Table 3. Both carbonates were
obtained in low yield when the reaction was carried out at 10
bar, in which the pressure is directly related to the rate of
reaction, expressed by the activation volume in the system.34
Furthermore, the molecularity number decreases when staring
materials are converted to products (condensation reaction),
enhancing the rate with increasing pressure as expected.35
The amount of promoter DBU amidine and the presence of
an alkylating agent were found to be of great importance for
carbonates conversion, supporting the proposed mechanism
(Scheme 1). In addition, the results show that the successful
1 h of reaction time, under clean conditions. Peak 1 (ꢃ11 min)
is associated to the remaining isopentyl alcohol and peak 2
(ꢃ23 min) corresponds to the formation of butyl-isopentyl
carbonate (2), which can be conrmed by its MS spectra, as
shown in Fig. 1b.
Fig. 2a shows the chromatogram of butyl-isobutyl carbonate
synthesized under the optimal reaction conditions. The pres-
ence of remaining isobutyl alcohol represented by peak 3 (ꢃ7
min) can be seen. Fig. 2b corresponds to the mass spectra of
peak 4 (ꢃ18 min) associated to the formation of butyl-isobutyl
carbonate.
Butyl-isopentyl and butyl-isobutyl carbonates synthesized
under the optimal experimental conditions, 40 ꢀC and 80 bar of
CO2 for 1 h of reaction time were quantied using a calibration
curve. The results showed that from 10 mmol of alcohols, used
in both reactions, 7 mmol of butyl-isopentyl carbonate (70%)
and 7.3 mmols of butyl-isobutyl carbonate (73%) were obtained.
Table 4 shows the linear regression coefficient (R) of the curve,
the values obtained for the converted quantities (mmol) of
carbonates and the standard deviation (S) calculated consid-
ering the average concentration as the results were obtained in
triplicate. The retention indexes for the compound were 23 min
for butyl-isopentyl carbonate and 18 min for butyl-isobutyl
carbonate.
Table 3 Chromatographic yield (%) of butyl-isopentyl and butyl-iso-
butyl obtained under different experimental conditions (alcohols ¼ 10
mmol, 1 h, 40 ꢀC were fixed in all the experiments)
Butyl-isopentyl Butyl-isobutyl
Table 1 Chromatographic yields (%) of butyl-isopentyl and butyl- mmol of DBU mmol of BuBr P (bar) carbonate
carbonate
isobutyl carbonates at different reaction times (40 ꢀC, 80 bar)
—
1
5
10
10
10
10
15
15
15
—
15
15
15
80
80
80
80
10
—
80
—
—
80
—
ꢃ6
—
94
—
—
74
—
ꢃ2
—
96
Reaction time (h) Butyl-isopentyl carbonate Butyl-isobutyl carbonate
1
2
3
6
93%
94%
97%
96%
94%
96%
96%
95%
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Table 4 The data obtained from the calibration curves of butyl-iso-
pentyl and butyl-isobutyl carbonates (0.2, 0.4, 0.6 and 1.0 mol Lꢂ1). R:
linear coefficient and S: standard deviation
Converted carbonates
Quantied reaction
R
(mmol)
S
Butyl-isopentyl carbonate
Butyl-isobutyl carbonate
0.9992
0.9993
9.97
9.86
0.69%
0.44%
is relative to the carbonates formed in the reaction. For
comparison, the chromatogram of crude fusel alcohols has
been shown, which shows the presence of ethyl alcohol (3%),
propyl alcohol (1%), butyl alcohol (2%), isobutyl alcohol (5%)
and isopentyl alcohol (89%). The chromatogram of crude fusel
alcohol can be found in the ESI.†
The syntheses of both carbonates were also carried out using
the strong bases DBN and TBD as nucleophilic activators of the
starting alcohols. The results showed that butyl-isopentyl and
butyl-isobutyl carbonates were obtained in 86% and 89% of
chromatographic conversion, respectively, when DBN was used
Fig. 1 (a) The chromatogram obtained from the synthesis of butyl-
isopentyl carbonate at 40 ꢀC and 80 bar for 1 h and (b) the mass
spectrum of the carbonate eluted at ꢃ23 min (peak 2).
¨
in the reaction. This might be due to the lower Bronsted base
character of the amidine DBN (when compared with DBU),32
and consequently its lower deprotonating activity. In addition,
when the reactions were performed with TBD, butyl-isopentyl
and butyl-isobutyl carbonates were obtained in 49% and 45%
of chromatographic conversion, respectively. The resulting low
yield of carbonates might be due to the fact that DBN28 and
TBD29,36 can also form a carbamic adduct with CO2 and this
could compete with the formation of the ionic carbonate
intermediate. The chromatograms and the mass spectra of the
carbonates are shown in the ESI (S7 to S17†).
2,4-Dichlorobenzyl chloride, an intermediate of Diclorbu-
trazol and Miconazole fungicides, was also studied as an alky-
lating agent. 2,4-Dichlorobenzyl chloride is the precursor for
potential fungicides with resistance to sun irradiation or high
temperatures and does not injure the host plant when applied
to destroy fungi. However, its synthesis requires long reaction
times, high temperatures and the products are obtained in low
yields.37 Thus, other materials can be prepared using this
precursor and their fungicidal properties can be further inves-
tigated. The syntheses were performed using fusel isopentyl and
isobutyl alcohols and the promoter base DBU, because it shows
better effectiveness in the reactions. The corresponding
carbonates were obtained in excellent yields of 99% and 97%,
In an exploratory experiment, a crude fusel alcohol sample
was used as the raw material for the synthesis of NPOCs by
direct reaction with CO2. The reaction was carried out without
any solvent and the temperature was 40 ꢀC. The corresponding
chromatogram is shown in Fig. 3. The remaining isopentyl
alcohol (1-residual) can be observed; however, no isobutyl
alcohol is seen. Peaks 4 and 2 correspond to butyl-isobutyl
carbonate (7%) and butyl-isopentyl carbonate (71%), respec-
tively. Peaks 6 and 7 are attributed to butyl-ethyl (12%) and
butyl–butyl (9%) carbonates, respectively. These carbonates are
also formed due to the presence of the corresponding alcohols
in the crude fusel alcohol. The chromatographic conversion (%)
Fig. 2 (a) The chromatogram obtained from the synthesis of butyl-
isobutyl carbonate at 40 ꢀC and 80 bar for 1 h and (b) the mass Fig. 3 Chromatogram obtained from the synthesis of NPOCs from
spectrum of the carbonate eluted at ꢃ18 min (peak 4).
fusel oil at 40 ꢀC and 80 bar for 1 h.
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respectively. The chromatogram and the mass spectra of both higher for carbonates than for alcohols, supporting the alkyl
carbonates are shown in the electronic ESI (S-18 to S-21†).
carbonate formation. The band at 1638 cmꢂ1 n(C]O) observed
The unreacted 2,4-dichlorobenzyl chloride obtained from in the spectra is due to the esters (methyl benzoate and methyl
the synthesis of 2,4-dichlorobenzyl-isopentyl and 2,4- acetate) and aldehydes (acetaldehyde), which are low boiling
dichlorobenzyl-isobutyl carbonates was quantied using a point compounds present in the crude fusel oil and might co-
calibration curve. The results showed that from 10 mmol of distillate with the isobutyl and isopentyl alcohols. The forma-
alkylating agent, used in both reactions, only 0.028 and 0.14 tion of the carbonates from fusel oil is conrmed by the pres-
mmol remained unreacted. For the reactions carried out with ence of the band at 1750 cmꢂ1 n(C]O), which is not observed in
butyl bromide, we did not built a calibration curve because it the fusel oil spectra. The main bands and attributions observed
was all consumed in the reactions. Table 5 shows the linear in Fig. 4 are summarized in Table 6. The FT-IR spectra of the
regression coefficient (R) of the curve, the values obtained of crude fusel alcohol and its corresponding NPOCs, 2,4-
unreacted and converted quantities (mmol) of alkylating agent dichlorobenzyl-isopentyl
and
2,4-dichlorobenzyl-isobutyl
and the standard deviation (S) calculated considering the carbonates are shown in the ESI (S35 and S36†).
average concentration as the results were obtained in tripli-
cates. The retention index for this compound was 16 min.
Butyl-isononyl carbonate was synthesized in this study to
investigate if the methodology is also suitable for long-chain
In the 1H-NMR spectra of the butyl-isobutyl and butyl- alcohols. Long-chain alcohols have been used for the
isopentyl carbonates, due to the withdrawing nature of synthesis of urethane upon their reaction with urea using metal
oxygen, the H3 and H4 signals are observed in the deshielding salts such as zinc acetate and lead acetate as catalysts. The
region at 3.90 and 4.18 ppm. H1, H2, H5 and H6 resonate from addition of triphenylphosphine as
a co-catalyst yielded
0.94 to 1.98 ppm. In the 13C-NMR spectra of such compounds, carbonates.39 Isononyl alcohol is used to produce plasticizers of
the chemical shi of carbon (OCOO) from the carbonyl group is low cost with several applications.40 It is also used as a fragrance
centered at 155 ppm, which is in agreement with the literature38 ingredient in cosmetics, shampoos, household cleaners, among
and conrms the formation of the expected products.
others.41 Therefore, the formation of carbonates from isononyl
1
In the H-NMR spectra of 2,4-dichlorobenzyl-isopentyl and
2,4-dichlorobenzyl-isobutyl carbonates, the hydrogen signals of
the aliphatic region are observed in the range between 0.94 and
5.22 ppm. The formation of these carbonates can also be
conrmed by the presence of aromatic hydrogens in the region
between 7.24 and 7.40 ppm. For these compounds, a new signal
appears at ꢃ4.65 ppm in both spectra. This is attributed to the
methylene hydrogen of the remaining alkylating agent that
could not be removed during the purication process. The 13C-
NMR spectra show the chemical shis of the aromatic ring
carbons in the range of 127–134 ppm, and the carbonate carbon
resonates at ꢃ155 ppm. In addition, the methylene carbon
signal of the remaining alkylating agent is observed at 42 ppm.
All the 1H-NMR and 13C-NMR spectra can be found in the ESI.†
Fig. 4 shows the FT-IR spectra of isopentyl alcohol (A), butyl-
isopentyl carbonate (B), isobutyl alcohol (C) and butyl-isobutyl
carbonate (D). The formation of both carbonates is conrmed
by the presence of the characteristic bands at 1256 n(C–O) and
1750 cmꢂ1 n(C]O). Other absorption bands that are present in
the alcohols spectra are also observed for both carbonates such
as at 1459, 2870 and 2956 cmꢂ1 n(C–H). The bands associated to
the presence of –CH2– groups at 2870 and 2956 cmꢂ1 were
Fig. 4 The FT-IR spectra of (a) isopentyl alcohol (A) and butyl-iso-
pentyl carbonate (B) and (b) butyl alcohol (C) and butyl-isobutyl
carbonate (D).
Table 6 Main bands (cmꢂ1) observed in the FT-IR spectra of butyl-
isopentyl and butyl-isobutyl carbonates
n(C–O)
Compounds
n(O–H) n(C–H) n(C]O) primary alcohols
Isopentyl alcohol
Butyl-isopentyl carbonate
Isobutyl alcohol
3417
—
2959
2872
2959
2872
2965
2878
—
1059
1059a
1036
1036a
1054
1054a
1750
—
Table
5 The data obtained from the calibration curve of 2,4-
dichlorobenzyl chloride (0.2, 0.4, 0.6 and 1.0 mol Lꢂ1). 2,4-DCBC: 2,4-
3417
dichlorobenzyl chloride; R: linear coefficient; and S: standard deviation
Butyl-isobutyl carbonate
Fusel alcohols
3417a 2965
2878
3441
1750
—
Quantied
Unreacted
Converted
reaction
R
2,4-CDBC (mmol) 2,4-CDBC (mmol) S
2956
2870
2870
2,4-DCB-isopentyl 0.9992 0.028
carbonate
2,4-DCB-isobutyl 0.9992 0.14
carbonate
9.97
9.86
0.69%
0.44%
NPOCs from fusel
alcohols
3441
1750
a
Comparatively lower intensity.
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alcohol might be of great interest for their use as materials for carbonates in excellent yields under clean conditions, without
industrial applications. the use of solvents, at low temperatures and with short reaction
The synthesis of butyl-isononyl carbonate was carried out time. Exploratory experiments show the conversion of crude
using the nucleophilic activator DBU and BuBr under the same fusel alcohol to NPOCs. DBU amidine used as the nucleophilic
previously determined experimental conditions. The reaction activator or promoter showed higher effectiveness in the
was also carried out without any solvent. The results show that reactions.
the carbonate was obtained in 93% of chromatographic
conversion, which conrms that the proposed methodology can
be employed to convert long chain alcohols to carbonates. The
chromatograms and the mass spectra of isononyl alcohol and
Acknowledgements
˜
the corresponding carbonate can be found in the ESI (S30 to The authors are thankful to Fundaçao de Apoio a Pesquisa do
˜
Estado de Sao Paulo (FAPESP) for research funds (2013/21668-
S33†).
Cholesteryl group can be considered a promising functional 0 and 2013/24487-6), a PhD fellowship (2012/13901-3), under-
group present in molecules, which could be applied to optical graduation research fellowships (2011/23438-6, 2012/24330-7,
lters for high-power laser systems,42 rewritable memories and 2012/24661-3 and 2014/00289-3) and to Programa de Pos-grad-
´
also recording media.43 Thus, the crystal structures of uaçao em Ciencia e Tecnologia de Materiais (POSMAT). Authors
˜
ˆ
´
cholesteryl-butyl carbonate and cholesteryl-oleyl carbonate are are also grateful to Professor Dr Gil Valdo Jose da Silva e Dr
˜
being investigated for liquid crystals applications. Furthermore, Vinicius Palaretti from Universidade de Sao Paulo (USP) for the
a series of esters and carbonates of cholesterol have been NMR measurements. This work is a special dedicatory from
studied to understand these substances in biological systems.44 Eduardo R. Perez Gonzalez addressed to Prof. Douglas Wagner
Moreover, cholesteryl carbonates are generally prepared Franco by introducing me in the study of the Chemistry of
using cholesteryl chloroformate as a precursor.45,46 However, the Carbon Dioxide and Fusel Alcohols.
synthesis of this precursor is limited to using toxic phosgene as
´
´
a raw material.47 Therefore, in our study, we also explored an
efficient and non-phosgene route to cholesteryl carbonate
synthesis using the nucleophilic activators DBU and TEAB,
Notes and references
´
BuBr and pressurized CO2 under the previously described
experimental conditions. The results showed that cholesteryl-
butyl carbonate was successfully obtained using the proposed
methodology. The mass spectrum of the carbonate can be
found in the ESI (S34†).
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