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Dicarboxylic acid esters from the carbonylation of unsaturated esters under mild conditions
Inorganic Chemistry Communications 8 (2005) 878–881 www.elsevier.com/locate/inoche
Dicarboxylic acid esters from the carbonylation of unsaturated esters under mild conditions Cristina Jime´nez-Rodriguez a, Graham R. Eastham a b
b,1
, David J. Cole-Hamilton
a,*
EaStCHEM, School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, Scotland, United Kingdom Lucite International, Technology Centre, P.O. Box 90, Wilton, Redcar, Cleveland TS6 8JE, England, United Kingdom Received 13 May 2005; accepted 2 June 2005 Available online 10 August 2005
Abstract The methoxycarbonylation of unsaturated acids or esters catalysed by Pd complexes of bis(ditertiarybutyl-phosphinomethyl)benzene (DTBPMB) produces a,x-diesters with selectivities >95%, even if the double bond is deep in the chain or conjugated to the carbonyl group; unsymmetrical esters can also be produced with high selectivity. Ó 2005 Elsevier B.V. All rights reserved. Keywords: Palladium; Methoxycarbonylation; a,x-Diesters; Acrylic acids; Phosphine
a,x-Dicarboxylic acids and their esters are important industrial chemicals used in the synthesis of polyesters and polyamides such as nylon 6.6. They also find uses as lubricants or plasticers. They are often made by oxidation of cyclic alkanes or by carbonylation reactions, although the latter generally lead to mixtures of products with the added carboxylate group being distributed along the carbon chain [1]. Drent and coworker [2] has reported that 3-pentenenitrile can be methoxycarbonylated to methyl 5-cyanopentanoate with terminal selectivities as high as 93% (98% selectivity to cyano esters) using Pd complexes of a variety of diphosphines including bis(ditertiarybutylphosphinomethyl)benzene (DTBPMB) in the presence of methane sulphonic acid (MSA) and that the same system promotes the carbonylation of methyl 3-pentenoate to dimethyl 1,6-hexanedioate (96% selectivity) in methanol *
Corresponding author. Tel.: +44 0 1334 463805; fax: +44 0 1334 463808. E-mail addresses: [email protected] (G.R. Eastham), [email protected] (D.J. Cole-Hamilton). 1 Tel.: +44 0 1642 447109; fax: +44 0 1642 447119. 1387-7003/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2005.06.005
containing anisole at 60 bar and 100 °C [3]. We have recently reported that this system is also very active and selective for the methoxycarbonylation of terminal or internal alkenes to terminal esters under very mild conditions [4,5] and for the methoxycarbonylation of vinyl acetate to protected lactate esters [6,7]. We now report our studies on the use of the same catalytic system for the methoxycarbonylation of unsaturated acids and esters, in which we make a,x-diesters with very high selectivity from a range of starting materials with terminal or internal double bonds. The results are summarised in Table 1. Although no reaction was observed at 25 °C and 1 bar CO, the methoxycarbonylation of methyl propenoate proceeded efficiently in the presence of Pd/ DTBPMB and MSA at 20 bar and 40 °C to give dimethyl 1,4-butanedioate. The branched isomer was not detected, although 20% of the substrate was lost under the reaction conditions to the Michael addition product, methyl 3-methoxypropanoate. Using methyl methacrylate as the substrate, dimethyl 2-methylbutanedioate was produced selectively with no interference from Michael addition (Fig. 1).
C. Jime´nez-Rodriguez et al. / Inorganic Chemistry Communications 8 (2005) 878–881
879
Table 1 Methoxycarbonylation of unsaturated acids and esters to diesters of a,x-dicarboxylic acidsa Substrate
Amount of substrate/mmola
Conversion of substrate%
Selectivity to a,x-diester%
Methyl propenoate Methyl 2-methylpropenoate Methyl 3-pentenoatec 2-Pentenoic acidc,d 4-Pentenoic acidc,d 3-Hexenoic acidc Methyl oleatef Methyl linoleatef Methyl linolenate Butyl propenoatee Butyl 2-methylpropenoatec
22 19 21 9.9 9.1 17 6 6 6 14 13
100 100 100 100 100 17.3 100g 100i 100j 100 100
77b 100 99 97.3 96.3 100 >95%h 82%h 83%h 95k 93.4k,l
a
[Pd] = 0.008 mol dm 3, [DTBPMB] = 0.04 mol dm 3, [MSA] = 0.08 mol dm 3, substrate (2 cm3, the equivalent number of moles of substrate is shown in the table), methanol (10 cm3), Pco = 20 bar, 40 °C, 3 h. b 23% Methyl 3-methoxypropanoate. c 50 °C. d 4 h. e 1 bar, 25 °C. f 22 h. g 17% Isomerised monoester. h Di-methyl nonadecendioate. i 20% Unsaturated compounds. j 20% Unsaturated compounds. k Methyl butyl ester. l Dimethyl 2-methylbutanedioate (6.6%).
OR
OR
OR +
O
Pd /DTBMPB/H + CO + MeOH
O
O OMe R'
R' R R' Me H Me Me Bu H Bu Me
77 100 95 93.4
O
+ MeO R' 23
Fig. 1. The formation of butanedioic esters from propenoic acids by methoxy carbonylation.
These reactions show that a double bond conjugated to a carbonyl group can be carbonylated using this system. Methyl 3-pentenoate is transformed selectively into dimethyl 1,6-hexanedioate. More remarkable, however, is the reaction of 2-pentenoic acid to give the same product with excellent selectivity. This reaction not only shows that unsaturated acids can be used as substrates, but also that a double bond can be isomerised out of conjugation and selectively carbonylated once it reaches the end of the chain. The same product is also obtained for methyl 4-pentenoic acid, so this system can transform a mixture of pentenoate esters or acids selectively into dimethyl adipate. These reactions are summarised in Fig. 2. We were interested in how deep the double bond could be within the chain but still allow the formation of a,xdiesters. We found that not only does methyl 3-hexenoic acid (Fig. 2) produce dimethyl 1,7-heptanedioate, but that even methyl oleate (methyl 9-octadecenoate) is transformed into dimethyl 1,19-nonadecanedioate (identified
by GCMS and 13C{1H} NMR spectroscopy) with very high conversion and selectivity (Table 1, and Fig. 3). This selectivity with methyl oleate is remarkable, since previous attempts at this reaction have usually provided products in which the new ester group is introduced onto any one of the chain C atoms in an unselective manner or, in the case of palladium based catalysts, selectively onto either end of the double bond without isomerisation [8]. Selective formation of the a,x-diacid or ester has previously been the province of metathesis (see below) or of enzyme chemistry as these products can be formed by over oxidation of long chain carboxylic acids when carrying out cytochrome p450 oxidations to x-hydroxycarboxylic acids [9]. There is considerable interest in these longer chain diesters, with the C18 diester being prepared from the self metathesis of methyl oleate [10]. That process, however, only proceeds to equilibrium (initial yield of ca. 25%) and only ca. 50% (based on C atoms) of the methyl oleate can be converted into dimethyl 1,18-octadecanedioate, the other 50% producing the other self
880
C. Jime´nez-Rodriguez et al. / Inorganic Chemistry Communications 8 (2005) 878–881
OR
OMe
+
Pd/DTBMPB/H n
O
O
m
R Me H H
OH
n n 0 1 1
O m
m 1 0 1
OMe
Pd/DTBMPB/H+ O
OMe
+ CO + MeOH
O
+ CO + MeOH O
OMe Fig. 2. The formation of a,x-diesters from methoxycarbonylation of esters or carboxylic acids containing double bonds at various positions in the chain.
O methyl oleate
methyl linoleate
OM e O Pd/BDTBMPB OM e o 30 bar, 80 C OM e O O
OM e O dimethyl 1,19-nonadecanedioate
methyl linolenate OM e Fig. 3. Formation of saturated a,x-diesters from oleochemicals.
metathesis product, 9-octadecene. Both methyl linoleate (methyl octadeca-9,12-dienoate) and methyl linolenate (methyl octadeca-9,12,15-trienoate) also give predominantly dimethyl 1,19-nonadecandioate under our methoxycarbonylation conditions, presumably by carbonylation followed by transfer hydrogenation of the remaining double bond(s). Interestingly small amounts of a product containing a terminal double bond are observed in the 13C NMR spectrum of the products obtained from methyl linolenate. These reactions are summarised in Fig. 3. Since the two ester groups are introduced into the product esters that we have synthesised in totally different ways (one is present in the starting material, the other is introduced by the methoxycarbonylation reaction), and since the reaction conditions are mild, we attempted to make unsymmetrical diesters by starting with an unsaturated butyl ester and carrying out the carbonylation reaction in methanol. Once again, these reactions were successful and we were able to produce butyl methyl 1,4-butanedioate in high yield and with good selectivity from methyl 3-propenoate, and butyl methyl 2-methylbutanoate from butyl 2-methylpropenoaote (Fig. 1). This simple synthesis of unsymmetrical esters makes them available for further study and allows for even further fine tuning of esters for use as plasticizers etc.
We conclude that palladium complexes of DTBMPB in the presence of MSA catalyse the production of a,xdiesters from unsaturated esters containing terminal or internal double bonds with yields and selectivities close to 100% in many cases. The reactions can be carried out under mild conditions (20 bar, 40 °C) and full conversion has been observed after 3 h with substrate:catalyst ratios from 60 to 230. Diesters of different alcohols are available by this route.
Acknowledgement We thank Lucite International for a studentship (C.J.-R.).
References [1] M. Beller, A.M. Tafesh, Other carbonylations, in: B. Cornils, W.A. Herrmann (Eds.), Applied Homogeneous Catalysis with Organometallic Compounds, vol. 1, VCH, Weinheim, 1996, p. 187. [2] W. Jager, E. Drent, US Patent, 2004, 6743911. [3] E. Drent, and W. Jager, US Patent, 2001, 0044556. [4] C.J. Rodriguez, D.F. Foster, G.R. Eastham, D.J. Cole-Hamilton, Chem. Commun. (2004) 1720. [5] G. Eastham, C. Jimenez, D.J. Cole-Hamilton, WO (2004) 014834.
C. Jime´nez-Rodriguez et al. / Inorganic Chemistry Communications 8 (2005) 878–881 [6] A.J. Rucklidge, G.E. Morris, D.J. Cole-Hamilton, Chem. Commun. (2004) 1176. [7] G. Eastham, A.J. Rucklidge, D.J. Cole-Hamilton, WO (2004) 050599.
881
[8] E.N. Frankel, F.L. Thomas, J. Am. Oil Chem. Soc. (50) (1973) 39. [9] U. Scheller, T. Zimmer, D. Becher, F. Schauer, W.H. Schunck, J. Biol. Chem. (273) (1998) 32528. [10] J.C. Mol, Top. Catal. (27) (2004) 97.
Dicarboxylic acid esters from the carbonylation of unsaturated esters under mild conditions Cristina Jime´nez-Rodriguez a, Graham R. Eastham a b
b,1
, David J. Cole-Hamilton
a,*
EaStCHEM, School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, Scotland, United Kingdom Lucite International, Technology Centre, P.O. Box 90, Wilton, Redcar, Cleveland TS6 8JE, England, United Kingdom Received 13 May 2005; accepted 2 June 2005 Available online 10 August 2005
Abstract The methoxycarbonylation of unsaturated acids or esters catalysed by Pd complexes of bis(ditertiarybutyl-phosphinomethyl)benzene (DTBPMB) produces a,x-diesters with selectivities >95%, even if the double bond is deep in the chain or conjugated to the carbonyl group; unsymmetrical esters can also be produced with high selectivity. Ó 2005 Elsevier B.V. All rights reserved. Keywords: Palladium; Methoxycarbonylation; a,x-Diesters; Acrylic acids; Phosphine
a,x-Dicarboxylic acids and their esters are important industrial chemicals used in the synthesis of polyesters and polyamides such as nylon 6.6. They also find uses as lubricants or plasticers. They are often made by oxidation of cyclic alkanes or by carbonylation reactions, although the latter generally lead to mixtures of products with the added carboxylate group being distributed along the carbon chain [1]. Drent and coworker [2] has reported that 3-pentenenitrile can be methoxycarbonylated to methyl 5-cyanopentanoate with terminal selectivities as high as 93% (98% selectivity to cyano esters) using Pd complexes of a variety of diphosphines including bis(ditertiarybutylphosphinomethyl)benzene (DTBPMB) in the presence of methane sulphonic acid (MSA) and that the same system promotes the carbonylation of methyl 3-pentenoate to dimethyl 1,6-hexanedioate (96% selectivity) in methanol *
Corresponding author. Tel.: +44 0 1334 463805; fax: +44 0 1334 463808. E-mail addresses: [email protected] (G.R. Eastham), [email protected] (D.J. Cole-Hamilton). 1 Tel.: +44 0 1642 447109; fax: +44 0 1642 447119. 1387-7003/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2005.06.005
containing anisole at 60 bar and 100 °C [3]. We have recently reported that this system is also very active and selective for the methoxycarbonylation of terminal or internal alkenes to terminal esters under very mild conditions [4,5] and for the methoxycarbonylation of vinyl acetate to protected lactate esters [6,7]. We now report our studies on the use of the same catalytic system for the methoxycarbonylation of unsaturated acids and esters, in which we make a,x-diesters with very high selectivity from a range of starting materials with terminal or internal double bonds. The results are summarised in Table 1. Although no reaction was observed at 25 °C and 1 bar CO, the methoxycarbonylation of methyl propenoate proceeded efficiently in the presence of Pd/ DTBPMB and MSA at 20 bar and 40 °C to give dimethyl 1,4-butanedioate. The branched isomer was not detected, although 20% of the substrate was lost under the reaction conditions to the Michael addition product, methyl 3-methoxypropanoate. Using methyl methacrylate as the substrate, dimethyl 2-methylbutanedioate was produced selectively with no interference from Michael addition (Fig. 1).
C. Jime´nez-Rodriguez et al. / Inorganic Chemistry Communications 8 (2005) 878–881
879
Table 1 Methoxycarbonylation of unsaturated acids and esters to diesters of a,x-dicarboxylic acidsa Substrate
Amount of substrate/mmola
Conversion of substrate%
Selectivity to a,x-diester%
Methyl propenoate Methyl 2-methylpropenoate Methyl 3-pentenoatec 2-Pentenoic acidc,d 4-Pentenoic acidc,d 3-Hexenoic acidc Methyl oleatef Methyl linoleatef Methyl linolenate Butyl propenoatee Butyl 2-methylpropenoatec
22 19 21 9.9 9.1 17 6 6 6 14 13
100 100 100 100 100 17.3 100g 100i 100j 100 100
77b 100 99 97.3 96.3 100 >95%h 82%h 83%h 95k 93.4k,l
a
[Pd] = 0.008 mol dm 3, [DTBPMB] = 0.04 mol dm 3, [MSA] = 0.08 mol dm 3, substrate (2 cm3, the equivalent number of moles of substrate is shown in the table), methanol (10 cm3), Pco = 20 bar, 40 °C, 3 h. b 23% Methyl 3-methoxypropanoate. c 50 °C. d 4 h. e 1 bar, 25 °C. f 22 h. g 17% Isomerised monoester. h Di-methyl nonadecendioate. i 20% Unsaturated compounds. j 20% Unsaturated compounds. k Methyl butyl ester. l Dimethyl 2-methylbutanedioate (6.6%).
OR
OR
OR +
O
Pd /DTBMPB/H + CO + MeOH
O
O OMe R'
R' R R' Me H Me Me Bu H Bu Me
77 100 95 93.4
O
+ MeO R' 23
Fig. 1. The formation of butanedioic esters from propenoic acids by methoxy carbonylation.
These reactions show that a double bond conjugated to a carbonyl group can be carbonylated using this system. Methyl 3-pentenoate is transformed selectively into dimethyl 1,6-hexanedioate. More remarkable, however, is the reaction of 2-pentenoic acid to give the same product with excellent selectivity. This reaction not only shows that unsaturated acids can be used as substrates, but also that a double bond can be isomerised out of conjugation and selectively carbonylated once it reaches the end of the chain. The same product is also obtained for methyl 4-pentenoic acid, so this system can transform a mixture of pentenoate esters or acids selectively into dimethyl adipate. These reactions are summarised in Fig. 2. We were interested in how deep the double bond could be within the chain but still allow the formation of a,xdiesters. We found that not only does methyl 3-hexenoic acid (Fig. 2) produce dimethyl 1,7-heptanedioate, but that even methyl oleate (methyl 9-octadecenoate) is transformed into dimethyl 1,19-nonadecanedioate (identified
by GCMS and 13C{1H} NMR spectroscopy) with very high conversion and selectivity (Table 1, and Fig. 3). This selectivity with methyl oleate is remarkable, since previous attempts at this reaction have usually provided products in which the new ester group is introduced onto any one of the chain C atoms in an unselective manner or, in the case of palladium based catalysts, selectively onto either end of the double bond without isomerisation [8]. Selective formation of the a,x-diacid or ester has previously been the province of metathesis (see below) or of enzyme chemistry as these products can be formed by over oxidation of long chain carboxylic acids when carrying out cytochrome p450 oxidations to x-hydroxycarboxylic acids [9]. There is considerable interest in these longer chain diesters, with the C18 diester being prepared from the self metathesis of methyl oleate [10]. That process, however, only proceeds to equilibrium (initial yield of ca. 25%) and only ca. 50% (based on C atoms) of the methyl oleate can be converted into dimethyl 1,18-octadecanedioate, the other 50% producing the other self
880
C. Jime´nez-Rodriguez et al. / Inorganic Chemistry Communications 8 (2005) 878–881
OR
OMe
+
Pd/DTBMPB/H n
O
O
m
R Me H H
OH
n n 0 1 1
O m
m 1 0 1
OMe
Pd/DTBMPB/H+ O
OMe
+ CO + MeOH
O
+ CO + MeOH O
OMe Fig. 2. The formation of a,x-diesters from methoxycarbonylation of esters or carboxylic acids containing double bonds at various positions in the chain.
O methyl oleate
methyl linoleate
OM e O Pd/BDTBMPB OM e o 30 bar, 80 C OM e O O
OM e O dimethyl 1,19-nonadecanedioate
methyl linolenate OM e Fig. 3. Formation of saturated a,x-diesters from oleochemicals.
metathesis product, 9-octadecene. Both methyl linoleate (methyl octadeca-9,12-dienoate) and methyl linolenate (methyl octadeca-9,12,15-trienoate) also give predominantly dimethyl 1,19-nonadecandioate under our methoxycarbonylation conditions, presumably by carbonylation followed by transfer hydrogenation of the remaining double bond(s). Interestingly small amounts of a product containing a terminal double bond are observed in the 13C NMR spectrum of the products obtained from methyl linolenate. These reactions are summarised in Fig. 3. Since the two ester groups are introduced into the product esters that we have synthesised in totally different ways (one is present in the starting material, the other is introduced by the methoxycarbonylation reaction), and since the reaction conditions are mild, we attempted to make unsymmetrical diesters by starting with an unsaturated butyl ester and carrying out the carbonylation reaction in methanol. Once again, these reactions were successful and we were able to produce butyl methyl 1,4-butanedioate in high yield and with good selectivity from methyl 3-propenoate, and butyl methyl 2-methylbutanoate from butyl 2-methylpropenoaote (Fig. 1). This simple synthesis of unsymmetrical esters makes them available for further study and allows for even further fine tuning of esters for use as plasticizers etc.
We conclude that palladium complexes of DTBMPB in the presence of MSA catalyse the production of a,xdiesters from unsaturated esters containing terminal or internal double bonds with yields and selectivities close to 100% in many cases. The reactions can be carried out under mild conditions (20 bar, 40 °C) and full conversion has been observed after 3 h with substrate:catalyst ratios from 60 to 230. Diesters of different alcohols are available by this route.
Acknowledgement We thank Lucite International for a studentship (C.J.-R.).
References [1] M. Beller, A.M. Tafesh, Other carbonylations, in: B. Cornils, W.A. Herrmann (Eds.), Applied Homogeneous Catalysis with Organometallic Compounds, vol. 1, VCH, Weinheim, 1996, p. 187. [2] W. Jager, E. Drent, US Patent, 2004, 6743911. [3] E. Drent, and W. Jager, US Patent, 2001, 0044556. [4] C.J. Rodriguez, D.F. Foster, G.R. Eastham, D.J. Cole-Hamilton, Chem. Commun. (2004) 1720. [5] G. Eastham, C. Jimenez, D.J. Cole-Hamilton, WO (2004) 014834.
C. Jime´nez-Rodriguez et al. / Inorganic Chemistry Communications 8 (2005) 878–881 [6] A.J. Rucklidge, G.E. Morris, D.J. Cole-Hamilton, Chem. Commun. (2004) 1176. [7] G. Eastham, A.J. Rucklidge, D.J. Cole-Hamilton, WO (2004) 050599.
881
[8] E.N. Frankel, F.L. Thomas, J. Am. Oil Chem. Soc. (50) (1973) 39. [9] U. Scheller, T. Zimmer, D. Becher, F. Schauer, W.H. Schunck, J. Biol. Chem. (273) (1998) 32528. [10] J.C. Mol, Top. Catal. (27) (2004) 97.