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Green Chemistry
Page 4 of 5
COMMUNICATION
Journal Name
DOI: 10.1039/C6GC01900E
Table 5. Calculated green metrics
Entry
Yield (%)
80
91
> 99
AE
E-kernel
0.391
0.350
E-excess
E-aux
12.363
> 24.543
389.536
E-total
PMI
This procedure
Nishiguchi procedure5a
Taya procedure4b
0.89
0.81
0.85
0
23.690
0
12.753
> 48.581
389.711
13.753
> 49.581
390.711
0.175
We next examined the reaction profile through time, which was used as catalyst, methanol was utilized as esterifying
revealed to have a great influence on the process (Figure 4). agent and the reaction was carried out at room temperature.
The conversion of adipic acid increases fairly linearly up to 89% Different aluminas were tested and their activities were
after 48 hours, the threshold beyond which further progress is correlated to their different proprieties and acidity; the
no longer observed; the yield of the monoester reaches the selectivity of the process has been ascribed to a balanced
value of 80% after this period, resulting in a selectivity towards acidity/basicity of the bifunctional alumina catalyst that
2
of 90%; It should be emphasized that it remains always above prevents the esterification of a COOH functionaly likely thanks
90% throughout the first 48 hours. Afterwards, it shrinks and to the formation of a carboxylate anion by reaction with basic
the amount of diester start to increase significantly. sites, favouring the esterification of the second COOH group
It was finally evaluated the applicability of the reaction to through interaction with acid sites instead.
3
various linear and aromatic dicarboxylic acids (Table 4).
The reaction has been extended to various linear dicarboxylic
Slightly lower yields were obtained using dicarboxylic acids acids obtaining good yields, high selectivity and green metrics
with longer chains, whereas monoester selectivity remained significantly improved over existing methods.
around 90%. The lower reactivity of long chain dicarboxylic
acids can be ascribed to their reduced solubility in methanol.
Phthalic acids, which are completely insoluble, were indeed
Notes and references
recovered unchanged. On the other hand, other alcohols could
be used but likely require a dedicated optimisation of reaction
conditions. Under standard conditions, no diester was
observed using ethanol, propanol and isopropanol, although
‡
We thank MIUR for funding. Support from SIR Grant
RBSI14NKFL is similarly acknowledged.
1
2
3
4
M. Minami, S. Kai, JP 04,182,452 (1992) (Chem. Abstr., 1993
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(a) H. Ogawa, Y. Ichimura, T. Chihara, S. Teratani, K. Taya,
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Chihara, K. Taya, J. Am. Chem. Soc. 1985, 107, 1365-1369; T.
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conversion of
1 did not exceed 10% upon 24 hours at room
temperature in these cases (details in ESI).
In order to carefully evaluate both efficiency and cleanness of
the process, the protocol was performed on a 250 mmol scale
of adipic acid in 500 mL of methanol; after 48 h, the catalyst
was completely recovered by filtration (1.23 g, 98%), the
reaction mixture was concentrated (300 mL of methanol were
recovered) and then left at 4 °C to promote the precipitation
of the unreacted adipic acid. After 12 hours the suspension
was filtered and dried obtaining the desired product in 93%
purity. The final product is not contaminated by aluminium,
which was not detected by ICP analysis. Furthermore, the
same analysis on a crude mixture gave a negligible value (4.5
ppm). This result together with its successful reuse also
suggests the high potential durability of the catalytic system.
On the base of these results, some green metrics parameters12
such as overall percent yield, overall atom economy (AE),13
overall E-factor14 and intensity (PMI)15 were calculated and
compared to those obtained by using other reported
procedures (Table 5). These data confirm the higher efficiency
of our method, which enables to minimise formation of wastes
compared to existing procedures. Values of AE, E-total and
PMI clearly confirm the sustainable character of our approach.
5
6
7
B
2007, 72, 149-156.
8
9
F. Lónyi, J. Valyon, Micropor. Mesopor. Mater. 2001, 47, 293-
301.
H.Hattori, Y.Ono, Solid Acid Catalysis. From Fundamentals to
Appications, CRC press, Boca Raton, 2015.
10 V. Sima Kumar, B. M. Nagaraja, V. Shashikala, P.
Seetharamulu, A. H. Padmasri, B. David Raju, K. S. Rama Rao,
J. Mol. Catal. A: Chem. 2004, 223 (1-2), 283-288.
11 H. Ogawa, J. Phys. Org. Chem. 1991, 4, 346-352.
12 A.P. Dicks and A. Hent, Green Chemistry Metrics, Springer
Briefs in Green Chemistry for Sustainability, 2015, 17-43.
13 B. M. Trost, Science 1991, 254, 1471-1477.
14 (a) R. A. Sheldon, Chemtech 1994, 24, 38-47; (b) R. A.
Sheldon, Chem. Ind. 1997, 12-15; (c) R. A. Sheldon, Chem.
Commun. 2008, 3352-3365; (d) J. Augè, Green Chem. 2008
10, 225-231.
15 C. Jimenez-Gonzalez, C. S. Ponder, Q. B. Broxterman, J. B.
Manley, Org. Process Res. Dev. 2011, 15, 912-917.
Conclusions
,
The selective protection of dicarboxylic acids was examined
using adipic acid as a model reagent and following an
environmentally friendly approach: a solid acid (acid alumina)
4 | J. Name., 2012, 00, 1-3
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