Paper
RSC Advances
catalytic species and prolong its lifetime. In all cases the indicated. The reaction was followed by GC analysis (as previ-
12
selectivity of the reaction was exceptional, leading only to the ously described ) using a Hewlett Packard HP4890-A GC with a
formation of DMS
remaining).
4
(with limonene starting material high performance capillary column HP-5 (crosslinked 5% PH
ME siloxane) (30 m  0.32 mm  0.25 mm), with He carrier gas
À1
Comparing the reaction prole data (Fig. 1) to that in Table 2, and a ow rate of 2 ml min . The injector was operated at
ꢀ ꢀ
2
inhibited the 250 C in split mode (ratio 1 : 20). The oven was heated to 50 C
where an increase in palladium catalyst Pd(OAc)
reaction (entry 10), an increase in the amount of catalyst and then increased at 1 C min to 80 C. Calibrations were
combined with more oxidant CuCl to oxidise the catalyst, performed for 1–6, with retention times of approximately
ꢀ
À1
ꢀ
2
clearly had a benecial effect. This highlights that the 1 16.9 min, 2 14.8 min, 3 22.7 min, 4 24.0 min, 5 20.3 min and
complexity of the reaction, which involves up to 12 steps, makes 6 14.2 min.
the outcome of changing one reagent very difficult to predict.
Nevertheless, reaction conditions have been identied to give a
method for the conversion of limonene selectively to DMS 4 in
Scaled up reaction
D-limonene (3.00 ml, 18.5 mmol) was added to a mixture of
PdOAc (10 mol%), CuCl (4 equiv.), 2,6-lutidine (9 equiv.) and
2 2
40% yield. The generation of a single dehydrogenated product
simplies signicantly the purication of the reaction. Indeed,
ꢀ
anhydrous DMF (45 ml). The reaction mixture was heated at
since 3 and 5 have boiling points within 1–4 C of DMS 4, the
ꢀ
1
(
20 C for 3 h, and DMS 4 isolated by vacuum distillation
production of a single dehydrogenation product is particularly
valuable. The dehydrogenation reaction was scaled-up (to 3 ml
D-limonene) using the reaction conditions in Table 2, entry 10,
ꢀ
30 mmHg, 80 C) in >99% purity (0.904 g, 37%).
(
Scheme 2, Fig. 1C) and the product DMS 4 readily separated by
Acknowledgements
vacuum distillation in 37% isolated yield and >99% purity (no
impurities detected). This method of generating DMS could be
used in a recirculatory ow reactor, which would recycle the
unconverted limonene.
The authors are grateful to the National Council of Science and
Technology of Mexico (CONACYT) for providing a stipend for S.
A. S.-V.
Notes and references
Conclusions
1
2
3
4
S. A. Sanchez-Vazquez, H. C. Hailes and J. R. G. Evans, Polym.
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P. A. Weyrich and W. F. Holderich, Appl. Catal., A, 1997, 158,
In summary, improved conditions have been developed for the
selective dehydrogenation of limonene to the monomer DMS 4
in a highly selective procedure. By performing the reaction at
ꢀ
120
C
with Pd(OAc)
2
catalyst, 2,6-lutidine as
a non-
coordinating base, and CuCl
2
as an oxidant approx. 40% of
DMS was formed. Notably, no products resulting from the
isomerization of the exocyclic double bond were observed under
these conditions.
145.
5
6
R. Neumann and M. Lissel, J. Org. Chem., 1989, 54, 4607.
M. A. Mart ´ı n-Luengo, M. Yates, M. J. Mart ´ı nez Domingo,
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Experimental
General experimental details
7
C. Fernandes, C. Catrinescu, P. Castilho, P. A. Russo,
M. R. Carrott and C. Breen, Appl. Catal., A, 2007, 318, 108.
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Downstream Derivatives, Marcel Dekker, New York, 2005.
Reagents were used as supplied: D-limonene (Aldrich, 97%);
palladium(II) triuroroacetate; palladium(II) acetate (Aldrich,
8
9
9
8%); palladium(II) chloride (Alfa Aesar, 47% of Pd); anhydrous
copper(II) chloride (Alfa Aesar, 98%); 2,6-di-tert-butylpyridine
Aldrich, >97%); N,N-diisopropylethylamine (Aldrich, >99%);
,2,6,6-tetramethylpiperidine (Aldrich, >99%); 2,4,6-collidine
(
2
1
1
1
1
0 R. B. Seymour, F. F. Harris and I. Branum, Ind. Eng. Chem.,
949, 41, 1509.
1 R. W. Lenz, J. E. Sutherland and L. C. Westfelt, Makromol.
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2 P. Horrillo-Mart ´ı nez, M. A. Virolleaud and C. Jaekel,
ChemCatChem, 2010, 2, 175.
3 B. M. Trost and P. J. Metzner, J. Am. Chem. Soc., 1980, 102,
1
(
Aldrich, 99%), except 2,6-lutidine (Aldrich, >99%) which was
ꢀ
dried with 4 A molecular sieves for 18 h prior to use. Solvents
were used as supplied: DMF (Acros, 99.8%); DMSO (Aldrich,
99.6%), and all other solvents (Aldrich, 99.9%).
Dehydrogenation of D-limonene 1 to DMS 4
3
572.
The following method was used, with the modications out- 14 J. E. Bercaw, N. Hazari and J. A. Labinger, J. Org. Chem., 2008,
lined above. D-limonene (1 equiv.) was added to a stirred solu- 73, 8654.
tion of PdX (catalyst, 5 mol%), CuCl (2 equiv.) and base (3 15 R. K. Henderson, C. Jimenez-Gonzalez, D. J. C. Constable,
2
2
equiv.), unless indicated otherwise, in anhydrous solvent. The
reaction was heated for the time and at the temperature
S. R. Alston, G. G. A. Inglis, G. Fisher, J. Sherwood,
S. P. Binks and A. D. Curzons, Green Chem., 2011, 13, 854.
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RSC Adv., 2014, 4, 61652–61655 | 61655