Carbonylation of allylic ethers to esters

A method is disclosed for the production of esters by reaction of an allylic ether with carbon monoxide in the presence of a catalytically effective amount of a Group VIII noble metal catalyst and a halide compound to obtain esters. The halide compound is present in an amount sufficient to prevent the catalyst from being converted into a Group VIII metal during the reaction. When the reaction is conducted in the presence of a quaternary ammonium salt the ester may be extracted by solvent extraction to minimize catalyst decomposition caused when extractive distillation is used to separate the ester.

TECHNICAL FIELD 
The present invention generally relates to the production of esters by the 
reaction of allylic ethers with carbon monoxide in the presence of a metal 
compound as a catalyst. 
PRIOR ART 
Palladium chloride has been employed as a catalyst for the carbonylation of 
alkoxyoctadienes to alkyl nonadienoate esters however only low yields 
(less than 10%) of the ester were produced. Compounds of the 
palladium-type metals (i.e. the Group VIII noble metals) therefore did not 
appear to be good candidates for catalyzing reactions of this type even 
though some catalytic activity was noted with palladium chloride. The 
production of esters in this type of reaction on an industrial scale would 
require higher yields than the 10% initially observed. 
Scheben, U.S. Pat. No. 3,626,005 discloses a process for the preparation of 
unsaturated acyl halides by carbonylating vinylic halides in the presence 
of a Group VIII noble metal catalyst such as palladium metal, the catalyst 
composition optionally containing metals such as gold, silver, copper and 
the like. Additionally, Jenner, et al., U.S. Pat. No. 2,876,254 also 
disclose a process for the preparation of esters from olefins, carbon 
monoxide and alcohols in the presence of a catalyst system comprising a 
Group VIII noble metal such as palladium and an alcohol-soluble salt of 
tin or germanium. 
Various other U.S. Patents similarly teach the production of esters such as 
Knifton, U.S. Pat. No. 4,172,087 in which a process for the preparation of 
unsaturated aliphatic esters from aliphatic dienes such as butadiene is 
disclosed by reacting such unsaturated components with carbon monoxide and 
an alcohol in the presence of a palladium catalyst and an amine base. 
Group VIII metal catalysts are also disclosed for the preparation of 
esters in a similar manner by Zachry, et al., U.S. Pat. No. 3,161,672; 
Tsuji, et al., U.S. Pat. No. 3,427,344; Fenton, U.S. Pat. No. 3,652,655; 
Biale, U.S. Pat. No. 3,530,168 and Brewbaker, U.S. Pat. No. 3,367,961. 
Tsuji, et al. J.A.C.S. 86, pp. 4350-4353 (1964) discloses the carbonylation 
of allyl ethyl ether in ethanol as a solvent to ethyl 2-butenoate in the 
presence of palladium chloride as a catalyst, whereas Chan, XXIII 
International Conference on Coordination Chemistry, July 29August 3, 1984, 
Univ. of Colorado (Abstract of Poster Presentation TH p. 51-6) describes 
the affects of solvents, catalyst promoters and inhibitors on the 
palladium catalyst dicarbonylation of 1,4-difunctionalized-2-butenes. 
None of the above references addresses the problem of overcoming the low 
selectivities obtained when employing a palladium halide catalyst for the 
production of esters by the reaction of allylic ethers with carbon 
monoxide. 
Additionally, in the manufacture of alkyl acyclic esters using expensive 
Group VIII noble metal catalyst, it is necessary that the catalyst be 
recycled if it is to be employed on an industrial scale. 
The ester product of the reaction may be separated from the reaction 
mixture by means of distillation, or vacuum distillation; however, both 
distillation processes require energy input which could also add to the 
cost of the process. Although solvent extraction processes are known in 
the art these known methods are not totally satisfactory for the 
separation of the ester from the catalyst either because of the cost of 
the solvents or the fact that some of the palladium catalyst is carried 
over into the ester that the catalyst is to be separated from. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to overcome these and 
other difficulties encountered in the prior art. 
It is a further object of the present invention to provide a catalyst for 
the reaction of an allylic ether with carbon monoxide for the production 
of an ester. 
It is a further object of the invention to provide such a catalyst based on 
a Group VIII metal and especially a Group VIII metal halide. 
It is an additional object of the present invention to provide a catalyst 
based on a Group VIII noble metal halide which is stable during the 
reaction of an allylic ether with carbon monoxide for the formation of an 
ester. 
It is a further object of the present invention to provide a method for 
separating an ester from a catalyst comprising a Group VIII noble metal 
halide by means of a solvent extraction process. 
These and other objects have been achieved according to the present 
invention which comprises a method for the production of esters comprising 
reacting an allylic ether with carbon monoxide in the presence of a 
catalytically effective amount of a catalyst to produce an ester, the 
catalyst comprising a Group VIII noble metal halide and mixtures thereof 
and a halide compound selected from the group of hydrogen halides, 
carbonyl halides, acyl halides and mixtures thereof. The halides in this 
respect comprise the chlorides, bromides and iodides. 
The reaction is conducted by dissolving the catalyst in a solvent 
comprising a quaternary ammonium salt or phosphonium compound or mixtures 
thereof which are liquid at the reaction temperature and from which the 
alkyl acyclic ester produced is separated from the catalyst by solvent 
extraction with a non-polar organic solvent. 
DETAILED DESCRIPTION 
In the production of esters by the reaction of an allylic ether with carbon 
monoxide in the presence of a Group VIII noble metal catalyst (i.e. 
ruthenium, rhodium, palladium, osmium, iridium and platinum and mixtures 
thereof) such as a palladium chloride catalyst it was observed that 
although the palladium chloride did in fact catalyze the reaction to the 
ester, the yields of the ester obtained were less than 10%. In trying to 
determine the cause for these low yields which are unacceptable for 
industrial scale reactions it was noted that during the course of the 
reaction the palladium chloride catalyst was unstable in that the catalyst 
was being converted into palladium metal. Although the prior art would 
indicate that palladium metal would catalyze the reaction of carbon 
monoxide with an allylic ether actual experience established that the 
formation of palladium metal during the carbonylation reaction detracted 
from the activity of the catalyst. 
Means were sought to prevent the catalyst from being converted into the 
metal during the course of the reaction whereupon it was discovered that 
by employing a halide compound selected from the group of hydrogen 
halides, carbonyl halides, acyl halides and mixtures thereof the 
instability of the Group VIII noble metal halides was overcome. The 
halides in this respect comprise the chlorides, bromides and iodides. 
Accordingly, the reaction is conducted in the presence of the Group VIII 
noble metal halide catalyst as described herein along with the halide 
compound which is present in an amount sufficient to prevent the catalyst 
from being converted into a Group VIII metal during the reaction. 
The allylic ethers that may be reacted according to the method of the 
present invention comprise any acyclic or cyclic allylic ether having up 
to about 20 carbon atoms and especially those having from about 4 to about 
20 carbon atoms. In addition, the aforesaid ethers may contain up to about 
4 olefinically unsaturated positions and especially up to about 2 
olefinically unsaturated positions along an acyclic hydrocarbon chain. The 
esters produced have up to about 21 carbon atoms and especially from 5 to 
about 21 carbon atoms and similarly may be acyclic or may comprise an 
acyclic ester group attached to a cyclic group such as a cyclic 
hydrocarbon and have up to about 4 olefinically unsaturated positions 
along the acyclic hydrocarbon chain and especially up to about 2 of such 
olefinically unsaturated positions. The acyclic hydrocarbon group of the 
ether or ester may be straight chain or a branched chain and has from 1 to 
about 6 and especially from 1 to about 4 carbon atoms. 
Examples of various allylic ethers that may be reacted according to the 
method of the present invention comprises: 
methyl allyl ether 
8-methoxy-1,6-octadiene 
methyl 2-butenyl ether 
3-methoxy-1-phenylpropene 
4-methoxy-1-phenyl-2-butene 
methyl 4-methoxycrotonate 
1-methoxy-2-penten-4-one 
1,4-dimethoxy-2-butene 
ethyl allyl ether 
isopropyl allyl ether 
8-isopropoxy-1,6-octadiene 
1-ethoxy-2-hexene 
3-ethoxy-1-phenylpropene 
1-methoxy-2-hexene 
1-isopropoxy-2-pentene 
8-phenoxy-1,6-octadiene 
phenyl allyl ether 
benzyl allyl ether 
1-phenoxy-2-butene 
1-phenoxy-2-hexene 
1-phenoxy-2-penten-4-one 
1-phenoxy-2-pentene 
benzyl 2-butenyl ether 
The catalyst employed for the carbonylation reaction of the present 
invention comprises the Group VIII noble metal halides, i.e., the halides 
of ruthenium, rhodium, palladium, osmium, iridium, platinum and mixtures 
thereof, ruthenium, rhodium, palladium and platinum being preferred and 
palladium being especially preferred. The halides are selected from 
chloride, bromide and iodide and mixtures thereof, the chloride being 
preferred. 
The halide compounds that are employed in an amount sufficient to prevent 
the catalyst from being converted into a Group VIII metal during the 
reaction comprise hydrogen chloride, hydrogen bromide, hydrogen iodide, 
phosgene, acyl chlorides, acyl bromides, acyl iodides, and the like. 
Mixtures of these halide compounds may also be used. The acyl halides have 
from 1 to about 8 and especially 1 to about 5 carbon atoms and one or two 
halogen atoms such as acetyl chloride; acetyl bromide; acetyl iodide; 
proponyl chloride; butyryl chloride, malonyl chloride and the like. A 
lower alkanol (i.e. one having from 1 to about 6 carbon atoms) preferably 
is used with the carbonyl halide or acyl halide. 
The catalyst is employed in the carbonylation reaction in an amount 
anywhere from about 0.005 mole % to about 1.0 mole % and especially from 
about 0.05 mole % to about 0.2 mole % based on the ether employed in the 
reaction, this amount comprising a catalytically effective amount. 
The amount of the halide compound employed in the reaction may be anywhere 
from about 5 to about 50 molar excess and especially from about 10 to 
about 30 molar excess based on the Group VIII metal, this amount 
comprising an amount sufficient to prevent said catalyst from being 
converted into said Group VIII metal during the carbonylation reaction. 
Any other amount of catalyst or halide compound may be employed and is 
readily determined by a person having ordinary skill in the art knowing 
that the catalyst as described herein will promote the carbonylation 
reaction noted above and that the halide compound will prevent the Group 
VIII metal of the catalyst from being formed during the carbonylation 
reaction. 
The carbonylation reaction may be conducted at temperatures from about 
50.degree. C. to about 200.degree. C. and at pressures from about 1,000 
psig to about 5,000 psig. Other temperatures and pressures may also be 
employed and may be readily determined by a person having ordinary skill 
in the art having the within disclosure of the catalyzed carbonylation 
reaction. 
In another aspect of the invention, it has been discovered that the esters 
produced according to the invention may be separated from the catalyst by 
solvent extraction when the carbonylation reaction is conducted in the 
presence of a solvent comprising quaternary ammonium or phosphonium 
compounds such as the quaternary ammonium salts or mixtures thereof, and 
more particularly, the quaternary ammonium halides. Those quaternary 
ammonium salts that are liquid at the temperature of the carbonylation 
reaction are employed in this respect and generally comprise the 
tetra-alkyl ammonium halides especially the chlorides. Tetrabutyl ammonium 
chloride is especially suitable in this regard although other quaternary 
ammonium salts may be employed and include: 
Tetrabutylammonium bromide 
Tetra(decyl)ammonium bromide 
Tetradodecylammonium bromide 
Benzyldimethyltetradecylammonium chloride 
Benzylhexadecyldimethylammonium chloride 
Benzyldimethyldodecylammonium bromide 
Benzyldimethyldodecylammonium chloride 
Tetrahexylammonium chloride 
Benzyltributylammonium chloride 
Tetra(decyl)ammonium chloride 
Phosphonium compounds that may be employed comprise: 
Tetrapentylphosphonium chloride 
Tetrahexylphosphonium chloride 
Tetrabutylphosphonium chloride 
Tetrabutylphosphonium bromide 
Tetrabutylphosphonium iodide 
Tetrahexylphosphonium bromide 
Benzyltributylphosphonium chloride 
When the carbonylation reaction is conducted in the presence of a 
quaternary ammonium salt or phosphonium compound the ester obtained may be 
separated from the reaction mixture by means of solvent extraction whereby 
the ester is dissolved in a non-polar organic solvent such as a petroleum 
ether or the acyclic hydrocarbons and especially the aliphatic 
hydrocarbons having from about 4 to about 10 carbon atoms and especially 
those having from about 5 to about 8 carbon atoms. Either linear or 
branched chain acyclic hydrocarbon compounds may be employed in this 
respect although the linear ones are preferred. Examples of these 
hydrocarbons comprise pentane, hexane, heptane, octane, nonane and the 
like. Other solvents that may be employed comprise: 
2-methyl pentane 
2-methyl hexane 
3-methyl hexane 
2-methyl pentane 
30-60 petroleum ether

The following examples are illustrative. 
EXAMPLE 1 
Several reactions were conducted in 71 ml glass lined Parr-shaker bombs at 
100.degree. C., for six hours. In each of the four reactions, 5 ml (28.6 
mmoles) of 8-methoxy-1,6-octadiene was charged to the Parr bomb followed 
by purging four times with CO after which the bomb was pressured to 2,000 
psig with CO. The catalysts used in each instance comprise 0.005 g 
PdCl.sub.2. 
In the first bomb, 0.477 g CuCl.sub.2.2H.sub.2 O was charged; in the second 
bomb, 0.477 g CuCl.sub.2. 2H.sub.2 O, 0.25 ml 12.5% phosgene solution in 
toluene was charged; in the third bomb, 0.477 g CuCl.sub.2 H.sub.2 O along 
with 17.9 ml acetyl chloride (0.5 mmole) was charged; and in the fourth 
bomb, 0.25 ml, 12.5% phosgene solution in toluene was also charged. 
All reaction mixtures had small amounts of precipitate. The reaction 
products from each of the bombs was analyzed by GLC means employing a 
Silar 10 CP column and the conversion of 8-methoxy-1,6-octadiene and 
selectivity to methyl-3,8-nonadienoate was measured. The results obtained 
are listed below. 
______________________________________ 
8-Methoxy-1,6-octadiene 
Methyl-3,8-nonadienoate 
Percent Percent 
Conver- Selec- 
Bomb No. 
Mmoles sion Mmole tivity 
______________________________________ 
1 1.3 95.9 22.6 82.8 
2 0.6 97.9 25.8 92.1 
3 0.8 97.2 24.4 88.1 
4 18.8 34.2 9.0 91.8 
______________________________________ 
EXAMPLE 2 
Four reactions were carried out in 71 ml glass lined Parr bombs. Each bomb 
was charged with 2.0 g tetrabutylammonium chloride solution in water (23% 
water) and 0.005 g PdCl.sub.2. The bombs were dried at 90.degree. C. in a 
vacuum oven (0.01 mm Hg) for four hours and let cool under vacuum 
overnight. 
Each of the bombs was charged with 1 ml p-xylene (internal standard) 0.5 ml 
phosgene solution (12.5% in toluene) 5 ml 8-methoxy-1,6-octadiene (28.6 
mmoles). Each of the bombs was charged with the following amounts of 
methanol: bomb 1; 0.030 ml methanol (0.74mmoles); bomb 2;0.060 ml methanol 
(1.5 mmoles); bomb 3; 0.119ml methanol (3.0 mmoles); bomb 4; 0.239 ml 
methanol (5.9 mmoles). The bombs were then purged four times with CO and 
pressured to 2,000 psig with CO and placed in a shaker oven at 100.degree. 
C. for three hours. 
When the reaction was complete, GLC analyses of the contents of each of the 
bombs was conducted to determine the conversion of the 
8-methoxy-1,6-octadiene and the selectivity to methyl-3,8-nonadienoate. 
The results obtained are tabulated below. 
______________________________________ 
8-methoxy-1,6-octadiene 
Methyl,3-8,nonadienoate 
Percent Percent 
Conver- Selec- 
Bomb No. 
Mmoles sion Mmoles tivity 
______________________________________ 
1 14.7 48.6 12.9 92.8 
2 6.9 75.9 19.1 88.0 
3 3.8 86.7 20.8 83.4 
4 0.2 99.3 25.3 89 
______________________________________ 
The foregoing examples show that phosgene and a protic solvent such as a 
lower alkanol having 1 to 6 carbon atoms, e.g. methanol can be used to 
generate hydrogen chloride in bench-scale reactions. Conversion is 
dependent on the alkanol (e.g. methanol) charge even above the 
stoichiometric amount required to react with phosgene; selectivity is not 
significantly affected. Octadienyl chloride is formed in this reaction, 
its concentration increasing slowly to reach constant value. 
Selectivities are not as high as expected in some runs. Therefore, the 
dependence of selectivity on ether conversion was determined. Selectivity 
increased with conversion to a maximum of 99% at 60% conversion, and 
decreased at higher conversions. This decrease resulted from further 
reaction of methyl nonadienoate to form ten-carbon dibasic esters. 
The affect of phosgene concentration (in the range 0.02-0.08M) on reaction 
rate and ether selectivity was also explored. Rate, though not very 
sensitive to phosgene concentration in this range, was highest at about 
0.05M phosgene. Maximum selectivities are also observed at this level (95% 
selectivity at 79% conversion; 99% selectivity at 44% conversion). 
The affect of pressure in the range 500-3500 psig was also investigated. 
Maximum rate was observed at 2500 psig. Selectivity decreased from 97% to 
less than 90% above 3000 psig. 
The foregoing data also indicate that in the carbonylation of 
8-methoxy-1,6-octadiene to methyl-3,8-nonadienoate with palladium chloride 
as a catalyst the addition of a halide compound to the reaction solution 
stabilizes the palladium catalyst so that palladium does not precipitate 
out as a metal and high 8-methoxy-1,6-octadiene conversions may be 
realized. 
The use of a quaternary ammonium salt as a solvent with the catalyst system 
allows removal of product ester (methyl-3,8-nonadieneate) by extraction 
with a non-polar organic solvent such as petroleum ether, pentane, hexane 
and the like. The soluble palladium catalyst, as illustrated in the 
examples may then be recycled without being exposed to a distillation 
step. 
The esters obtained according to the method of the invention may be 
hydrogenated and used as lubricants, plasticizers or functional fluids or 
may be hydrolyzed to form an acid having unsaturated groups. The acid 
obtained may be incorporated into polyesters manufactured from phthalic 
anhydride, glycols, and maleic anhydride and which are subsequently 
cross-linked with styrene all of which is known in the art. The 
unsaturated acid obtained provides a site along the polyester chain for 
cross-linking with styrene or equivalent monomers. 
Although the invention has been described by reference to some embodiments, 
it is not intended that the novel method for the production of esters by 
carbonylation of an alkyl acyclic ether in the presence of a catalyst be 
limited thereby but that modifications thereof are intended to be included 
as falling within the broad scope and spirit of the foregoing disclosure 
and the following claims.