γ-Valerolactone as an alternative biomass-derived medium for the Sonogashira reaction

Article abstract of DOI:10.1039/c4gc01728e

γ-Valerolactone (GVL) can be used as an efficient and practical alternative to the banned and commonly used dipolar aprotic solvents. In this contribution GVL has been used as a non-toxic, biodegradable, biomass-derived medium, for the definition of a sim

Full text of DOI:10.1039/c4gc01728e

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γꢀValerolactone as an alternative biomassꢀderived medium for the
Sonogashira reaction.
a
a
a
a
a
Giacomo Strappaveccia, Lorenzo Luciani, Elena Bartollini, Assunta Marrocchi, Ferdinando Pizzo,
Luigi Vaccaro *
a
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
γꢀValerolactone (GVL) can be used as an efficient and practical alternative to the banned and commonly used dipolar aprotic solvents. In
this contribution GVL has been used as a nonꢀtoxic, biodegradable, biomassꢀderived medium, for the definition of a simple and general
protocol for the Sonogashira crossꢀcoupling reaction. The chemical efficiency of GVL as medium is excellent and the best results have
been obtained using DABCO as base allowing to isolate products 3aꢀq in 60ꢀ96% yields. These results represent an example that proves
that biomassꢀderived safer solvents can be used efficiently in common transformations reaching higher greenness/sutainability as well as
high chemical efficiency.
1
0
all the type of solvents the dipolar aprotic media feature the major
Introduction
issues. This class of solvents is very useful to chemists, but
nowadays they are under strict environment, health and safety
regulations due to their toxicity and environmental impact. In
1
2
2
3
3
4
4
5
0
5
0
5
0
5
Although crude oil still remains a major feedstock for the
chemical industry, sustainability issues are directing attention
towards the definition of alternative materials deriving from
14
5
5
6
6
7
7
8
0
5
0
5
0
5
0
this context GVL may have an key role as a sustainable
substituent for this class of solvent. GVL has many excellent
1
renewable biomass resources to access fuels and new building
15,16
properties
that allow it to be an ideal choice of sustainable
blocks for the production of chemicals/materials . Indeed, the
replacement on a large scale of fossilꢀbased fuel/chemicals for
bioꢀbased compounds is a fundamental step to consolidate the
green chemistry principles in the frame of a modern and
competitive chemical production.
alternative to conventional polar aprotic solvents. For instance, its
15
polarity is very similar to that for the most common; indeed, the
dielectric constant of GVL at 25 °C is 36.47 whereas those
measured at the same temperature for CH CN, DMF, NMP and
3
DMA are 37.5, 36.7, 32.0 and 37.8, respectively. Moreover, it
features low melting (ꢀ31°C) and high boiling (207°C) points,
and a flash point (96°C) which is generally higher than those for
2ꢀ5
Notably, biomass, being the only renewable source of carbon,
is estimated to generate between 25ꢀ30% of the chemical
3
ꢀ5
commodities by 2030. In this context, a relevant research area
explored in recent years deals with the development of tools
which enable crude biomass deconstruction into valuable
multifunctional simpler compounds (platform chemicals) that
can be consequently converted into valueꢀadded chemicals, fuels
conventional dipolar aprotic solvents including CH CN (2°C),
3
DMF (58 °C ), NMP (61°C), and DMA (63°C). In addition, GVL
vapor pressure is 0.65 kPa at 25 ◦C, and, notably, it increases only
to 3.5 kPa at 80 ◦C. Finally, it is quite stable under neutral
conditions, and, particularly, it does not form measurable
amounts of peroxides in a glass flask under air within few weeks,
which makes it a safe material for use on a large scale.
6,7
and materials.
Among the building blocks, an ever increasing attention is
currently directed to γꢀvalerolactone (GVL), owing to its peculiar
chemicalꢀphysical properties which enable its use as a fuel
additive, solvent, as well as an ideal precursor for the production
To prove that GVL may be a valid replacement for common polar
aprotic solvents we developed an efficient protocol for the
palladium on activated charcoal (Pd/C) catalyzed Sonogashira
crossꢀcoupling reaction (Scheme 1), which is often performed in
8
of alkanes, alkenes, and valuable chemicals. GVL is
conventionally produced from lignocellulosic biomassꢀderived
9, 10
levulinic acid
and its esters via (catalytic) hydrogenation The
17
e.g. dimethylformamide (DMF).
use of GVL as solvent is particularly interesting since in many
wellꢀestablished chemical processes large amounts of organic
volatile compounds are used as reaction media and for separation,
which constitute, in addition, the largest percentage of all the
associated waste, thereby posing serious health/environmental
Although a number of reports on the use of GVL to replace
18
conventional polar aprotic solvents in chemical processes exist,
to the best of our knowledge this is the first case for Sonogashira
coupling.
Our findings demonstrated that GVL is a promising polar
medium to synthesize a number of acetyleneꢀcontaining systems
in high yields and in a more sustainable way. Further, we
demonstrated that GVL enable a far better control of palladium
1
1,12
concerns.
In this regard, the identification of green bioꢀbased solvents
13
deriving from renewable resources is therefore crucial. Among
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DOI: 10.1039/C4GC01728E
leaching into the final products compared to a number of more
9
1
1
1
1
1
1
1
1
K
2
CO
3
100
100
60
13
23
79
93
91
92
>99
95
94
conventional polar solvents, thereby enhancing the characteristics
of the recyclability of the catalyst system as well as limiting the
contamination of the products themselves with traces of heavy
metals.
We believe that this new utilization of GVL would importantly
allow it to broaden its scope to move forward in catalyzing the
switching process from an unsustainable oilꢀbased economy to a
more sustainable biomassꢀbased one.
0
1
2
3
4
5
6
7
KOH
5
Tetrabutylammonium
acetate
Tetrabutylammonium
acetate
100
60
DABCO
DABCO
DABCO
DABCO
DABCO
10
Results and discussion
100
60
To verify the applicability of GLV as reaction medium for the
Sonogashira crossꢀcoupling reaction, we employed first
iodobenzene (1a) and phenylacetylene (2a) as reference
substrates by testing several protocol conditions. Next, we
decided to broaden the substrate scope and apply the selected
conditions to a sterically hampered phenylacetylene and alkylꢀ
substituted alkynes (Scheme 1).
a
b
c
60
15
60
a
b
30
Performed with 0.5 mol% of Pd/C. Performed with 1 equiv of DABCO.
Performed with 1.2 equiv of phenylacetylene.
c
Thus, we investigated first the Sonogashira GVL protocol
optimization using iodobenzene (1a) and phenylacetylene (2a) as
reference substrates, by employing several type of amines,
commonly used for more conventional Sonogashira’s protocols,
e.g. triethylamine, piperidine, pirrolidine and diisopropylamine,
at different temperatures ranging from 60° to 100 °C (Table 1,
entries 1ꢀ8).
3
5
2
0
Scheme 1 Protocol for the Sonogashira crossꢀcoupling reaction
performed in GVL.
Notably, we focused on the cheap, ligandꢀfree Pd/C catalytic
40
We obtained unsatisfactory results, the best conversion being
19
system, avoiding any coꢀcatalyst, to render the protocol as
general as possible.
8
2% at 100 °C in the presence of piperidine (Table 1, entry 4).
25
Table 2. Screening of reaction media and data for palladium leaching in
the Sonogashira crossꢀcoupling between 1a and 2a.
Table 1. Screening of the bases in the Sonogashira reaction between 1a
and 2a.
Time Conversion
Pd leaching
(ppm)
Entry
Base
T
Conversion
Entry
Solvent
DMF
Yield (%)
70
(min)
(%)
b
(
°C)
(%)
1
2
3
4
5
6
7
8
5
100
617±5
144±2
384±4
424±4
19±0.2
n.p.
1
2
3
4
5
6
7
8
Triethylamine
Triethylamine
Piperidine
60
25
59
42
82
28
40
36
50
NMP
5
100
100
100
100
76
73
100
60
DMSO
10
69
CH
3
CN
30
72
Piperidine
100
60
GVL
240
240
240
240
70
Pirrolidine
H
2
O
n.p.
n.p.
n.p.
Pirrolidine
100
60
Toluene
THF
90
n.p.
Diisopropylamine
Diisopropylamine
70
n.p.
100
45
Using inorganic bases such as potassium carbonate and potassium
2
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hydroxide (Table 1, entries 9 and 10) we had very low
conversions even at temperatures as high as 100 °C, likely owing
to their low solubility in the reaction media. Better results were
amount of leached palladium into the final products. Indeed,
when the reaction is performed in GVL, the metal product
contamination markedly decreases. (Table 2, entries 1ꢀ4 vs 5). It
obtained by employing tetrabutylammonium acetate, with a 50 is important to underline that the yields of the reaction performed
5
conversion of 93% at 100 °C (Table 1, entry 12). However, the
bestꢀperforming base was 1,4ꢀdiazabicyclo[2.2.2]octane
DABCO), with which we achieved a conversion of 91% at 60 °C
Table 1, entry 13). The higher reactivity of DABCO compared to
in these polar aprotic solvents remained similar, ranging from 69
to 73% (see Yield column in Table 2).
Furthermore, we demonstrated that by performing the reaction in
a number of not dipolar aprotic media, i.e. water, toluene or
(
(
other bases can be ascribed to its double double role as a base and 55 THF, which are also commonly used for the Sonogashira crossꢀ
1
1
2
2
3
3
0
5
0
5
0
5
as a ligand. It has been already reported that its use in the
couplings, the system showed lower reactivity (Table 3, entries
6ꢀ8). This data underlined that the use of a dipolar aprotic solvent
is preferable for Sonogashira reaction, and among them GVL
only can be identified as a green solvent.
2
0
Sonogashira reaction, led to an enhanced catalytic efficiency if
compared to other bases. Higher reaction temperatures (100 °C)
didn’t influence the reactivity of the system (Table 1, entry 14),
whereas by increasing the catalyst loading from 0.25 mol% to 0.5 60 Next, we applied the optimal reaction conditions to other
mol% (Table 1, entry 15) we reached the complete conversion of
a into product 3a. Moreover, we tried to further optimize the
reaction conditions by lowering the amount of the base used from
.2 to equivalent, or reducing the equivalents of
substrates (Table 3). Under these conditions we obtained good
reactivity for a wide range of aryliodide substrates, including both
activated substrates, such as 4ꢀnitroꢀiodobenzene (1b), 4’ꢀ
iodoacetophenone (1c) and 4ꢀiodobenzaldehyde (1d) (Table 3,
1
1
1
phenylacetylene substrate (Table 1, entries 16 and 17, 65 entries 2ꢀ4) and deactivated substrates such as 4ꢀiodotoluene (1e)
respectively), but in all cases the reactions didn’t reach
completeness.
or 4ꢀiodoanisole (1f) (Table 3, entries 5 and 6). Moreover, 2ꢀ
iodothiophene heterocycle (1g) reacted in good yield (Table 2,
entry 7) as well as bromoꢀderivatives 1hꢀi (Table 3, entries 8 and
9).
Next, we analyzed the behaviour of our system in different media
(Table 2 and Figure 1). We carried out the reaction in common
dipolar aprotic solvents such as DMF, NMP, DMSO and CH CN,
3
70
Table 3. Substrate scope of the Sonogashira reaction in GVL.
and we found that in these solvents the reactivity of the substrates
was higher than that in GVL. More in details, the reaction went to
completion after only 5 minutes when DMF and NMP were
employed (Table 2, entries 1ꢀ2), whereas it took 10 minutes to
occur by using DMSO (Table 2, entry 3) and half an hour in
Pd/C (0,5 mol%)
DABCO (1,5 equiv.)
R1
a-i
I
+
R2
2a-e
R1
R2
GVL (1M), 60 °C, N2
1
3a-q
1,5 equiv.
CH CN (Table 2, entry 4). On the other hand, the reaction in
3
Time
Yield
(%)
GVL went to completion after 4 hours (Table 2, entry 5). The
dielectric constant for all the employed media is quite similar,
therefore a polarity effect on the reaction, is likely rather limited.
This behavior may therefore be explained with a higher leaching
of palladium species in the reaction mixture when using
conventional polar solvents, due to the higher complexing ability
Entry
1
R
1
R
2
Product
(h)
4
3a
70
2
1
2
3
2
3b
3c
94
95
of these latter towards palladium, which may account for a
different catalytic activity.
2,5
2,5
4
3d
90
5
6
7
8
4,5
5
3e
3f
80
75
65
75
GVL
CN
H
C
SO
DM
F
M
)
P
D
M
(
N
(a)
(b)
6
3g
3b
4
0
Figure 1. (a) Diagram illustrating the influence of the reaction medium on
the reaction time for Sonogashira crossꢀcoupling between 1a and 2a
12
(
100% conversion in 3a); (b) Conversion vs reaction time plot for
Sonogashira crossꢀcoupling between 1a and 2a in GVL
4
5
This was corroborated also by the Inductive Coupled Plasmaꢀ
Optical Emission Spectrometer (ICPꢀOES) measurements of the
9
12
3d
70
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DOI: 10.1039/C4GC01728E
2
2
3
3
0
5
0
5
Sonoshaghira reaction.
In this context, we found that the chemical efficiency of GVL as
medium is excellent and the best results have been obtained using
DABCO as base. The protocol has been extended to a wide range
of substrates and several products 3aꢀq have been isolated in
satisfactorily to very high yields, comparable to other known
1
1
1
1
1
1
1
0
1
2
3
4
5
6
4
2
3h
3i
74
91
96
70
65
60
77
1
9
procedures using toxic media.
Ths contribution is also aimed at demonstrating within chemistry
community that safer solvents can be used efficiently in common
transformations reaching higher greenness/sutainability as well as
high chemical efficiency. The use of GVL in strategic processes
may significantly reduce the environmental impact and energy
cost of the chemical industry.
Further investigations are ongoing to prove that GVL is a more
general and promising alternative for the critical replacement of
common toxic polar media.
2,5
4,5
5
3j
3k
3l
Experimental Section
6
3m
3i
Unless otherwise stated, all solvents and reagents were used as
obtained from SigmaꢀAldrich Co. without further purification.
Commercial Pd/C (10% wt) was not activated prior to use, and
O N
2
40 the value of palladium loading of the catalyst was taken from its
certificate of analysis available at http://www.sigmaaldrich.com.
commercial sources without any further purification. GLC
analyses were performed by using HewlettꢀPackard HP 5890A
equipped with a capillary column DBꢀ35MS (30 m, 0.53 mm), a
12
ha
1
b
b
b
b
1
1
1
2
7
8
9
0
4,5
4,5
4,5
6
3n
3o
3p
3q
94
96
87
61
4
5
5
6
5
0
5
0
FID detector and hydrogen as gas carrier. GCꢀEIMS analyses
were carried out by using a HewlettꢀPackard HP 6890N Network
GC system/5975 Mass Selective Detector equipped with an
electron impact ionizer at 70 eV.
NMR spectra were recorded on a Bruker DRXꢀADVANCE
200 MHz and a Bruker DRXꢀADVANCE 400 MHz ( 1 H at 400
MHz and 13 C at 100.6 MHz) in CDCl , and TMS was
3
employed as internal standard. Elemental analyses were
conducted on a FISONS instrument EA 1108 CHN. Melting
points are not corrected and they were measured on a Büchi 510.
An Inductive Coupled PlasmaꢀOptical Emission Spectrometer
a
b
The bromo derivative was used. 2 equiv of DABCO were used.
We also successfully extended the protocol to a sterically
hampered phenylacetylene, the 1ꢀethynylꢀ2ꢀ(
(ICPꢀOES 710 Agilent Technology) was used to determine the
amount of leached palladium into the reaction products.
trifluoromethyl)benzene (2b), obtaining results similar to those
for phenylacetylene 2a (Table 3, entries 10ꢀ16). Finally, to further
broaden the scope of the GVLꢀbased Sonogashira reaction, we
included as substrates two alkylꢀsubstituted alkynes, i.e. octꢀ1ꢀ
yne (2c) and hexꢀ1ꢀyne (2d) (Table 3, entries 17ꢀ19), and
ethynyltrimethylsilane (2e) (Table 3, entry 20). In all cases,
few percent amount of homoꢀcoupling products was detected
<4%), although conversion of (hetero)aryl iodides was complete.
5
1
1
1
2
1
1
3
4
4
4
5
4
Compounds 3a , 3b , 3c , 3d , 3e , 3f , 3g , 3h , 3i , 3j , 3k , 3l ,
5
6
6
6
7
3m , 3n , 3o , 3p , 3q are known compounds.
Experimental procedures for compounds 3aꢀq, characterization
data and copies of the H and CꢀNMR are reported in the
Electronic Supplementary Information (ESI).
1
13
a
10
(
6
5
Representative experimental procedure for the Sonogashira
protocol. Synthesis of compound 3a.
Good to high reaction yields were achieved.
Conclusions
In a screw capped vial equipped with a magnetic stirrer Pd/C
1
0% wt. (5.3 mg, 0.5 mmol%), GVL (1 mL), DABCO (139 mg,
In conclusion, we have reported the use of GVL as a nonꢀtoxic,
biodegradable, biomassꢀderived medium. We have demonstrated
that GVL can be used as an efficient and practical alternative to
the banned and commonly used dipolar aprotic solvents. In
particular, our attention has been devoted to strategic carbonꢀ
70
1.2 mmol, 99% purity), iodobenzene (1a) (208 mg, 0.114 mL, 1
mmol, 98% purity), and ethynylbenzene (2a) (156 mg, 0.168 ml,
1
resulting mixture was purged with nitrogen and left under stirring
at 60 °C. After reaction completion, petroleum ether was added
15
.5 mmol, 98% purity) were consecutively added and the
carbon coupling reaction widely used in organic synthesis such as 75 and the reaction mixture was filtered over a small pad of celite,
washed with neutral water and, subsequently, with acidic water
4
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(
1 M HCl). The organic layer was dried over sodium sulphate and
9
A. M. Raspolli Galletti, C. Antonetti, V. De Luise, M. Martinelli,
Green Chem., 2012, 14, 688ꢀ694.
S.W. Fitzpatrick, World Patent: WO 96/40609.
P. G. Jessop, Green Chem., 2011, 13, 1391ꢀ1398.
the solvent was removed under vacuum. The crude oil was
purified by column chromatography on silica gel (petroleum
ether) to obtain 1,2ꢀdiphenylethyne (3a) as a white solid (124 mg,
70% yield).
1
1
0
1
6
7
7
5
0
5
12 C. Capello, U. Fischer, K. Hungerbühler, Green Chem., 2007, 9,
27–934.
I. T. Horváth, Green Chem., 2008, 10, 1024–1028.
5
9
1
3
Acknowledgements
14 R. K. Henderson, C. JiménezꢀGonzález, D. J. C. Constable, S. R.
Alston, G. G. A. Inglis, G. Fisher, J. Sherwood, S. P. Binks, A. D.
Curzons, Green Chem., 2011, 13, 854–862
15 Dielectric constant of GVL at 25 °C is 36.47, S. Aparicio R. Alcalde,
Phys. Chem. Chem. Phys., 2009, 11, 6455–6467, Dielectric constant
for other polar aprotic solvents (25 °C): Acetonitrile= 37.5, DMF=
We greatfully acknowledge the Università degli Studi di Perugia,
and the Ministero dell’Istruzione, dell’Università e della Ricerca
(MIUR) within the program “FirbꢀFuturo in Ricerca“ ref. N.
1
0
RBFR08JKHI for financial support. We also thank the reserch
project “BIT3G“ – National Green Chemistry Cluster for
financial support.
3
6.7, NMP= 32.0, DMA= 37.8; Vogel’s Textbook of Practical
Organic Chemistry, Longman, 4th edition.
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a
Dr. G. Strappaveccia, Dr. L. Luciani, Dr. E. Bartollini, Dr. A.
80
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Marrocchi, Prof. F. Pizzo, Prof. L. Vaccaro, Laboratory of Green
Synthetic Organic Chemistry, CEMIN – Dipartimento di Chimica,
Biologia e Biotecnologie, Università di Perugia Via Elce di Sotto 8,
0
6123 Perugia, Italia. Fax: +39 075 5855560; Tel: +39 075 5855541; E-
.
mail: luigi.vaccaro@unipg.it
†
1
Supplementary information.
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18 For recent representative examples see: (a) G. Strappaveccia, E.
Ismalaj, C. Petrucci, G. Lanari, A. Marrocchi, M. Drees, A. Facchetti,
L. Vaccaro, Green Chem. 2014, doi: 10.1039/C4GC01677G; (b) M.
A: Mellmer, D. M. Alonso, J. S. Lutherbacher, J. M. R. Gallo, J. A.
Dumesic, Green Chem. 2014, doi: 10.1039/C4GC01768D; (c) E.
Ismalaj, G. Strappaveccia, E. Ballerini, F. Elisei, O. Piermatti, D.
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