Process for the telomerization of conjugated dienes and suitable catalyst therefor

Mono-alkadienyl alkyl ethers and di-alkadienyl alkyl ethers are prepared by telomerization of a conjugated diene, by causing said conjugated diene to react with an aliphatic alcohol or an aliphatic diol respectively, by operating in an aqueous/organic biphasic liquid system, in the presence of a catalytic system formed by: PA1 (a) a palladium salt or complex; PA1 (b) an alkyl-, alkylcycloalkyl-, or alkylarylphosphine ligand, bearing an acidic or neutral hydrophylic moiety, having the formula: ##STR1## wherein R.sub.1, R.sub.2, R.sub.3, x and y are as defined in the disclosure; and PA1 (c) an either inorganic or organic base.

The present invention relates to a process for preparing mono- and 
di-alkadienyl alkyl ethers by means of the telomerization of conjugated 
dienes and to a catalytic system suitable for that purpose, 
Alkadienyl alkyl ethers are well known compounds in the art, which find use 
in particular as solvents for paints, components in cosmetic formulations 
and crosslinking agents for organic polymers. The reaction of 
telomerization of conjugated dienes (for example, butadiene, isoprene, and 
so forth), with a compound bearing an active hydrogen atom (for example 
water, alcohol, carboxy acids, amines, ammonia, and so forth) is known to 
be catalyzed by transition metal compounds (in particular palladium 
compounds) and phosphines (J. Tsuji, Adv. Organomet. Chem. 17, 141-193, 
1979; R. F. Heck, "Palladium reagents in organic syntheses" 1990 Academic 
Press). 
A problem met these with telomerization reactions derives from the 
difficulty of separating and recovering the catalyst from the reaction 
products. 
On considering the high cost of the catalyst, it is evident that 
simplifying the recycle of said catalyst would lead to a more advantageous 
process from the financial view point. In this regard, one should observe 
that the catalyst is soluble in the reaction system and that, owing to the 
thermal instability thereof, not always the separation of the reaction 
products by distillation without decomposing the catalyst is possible. 
Therefore, the use of sulfonated aryl phosphines in the telomerization 
reactions was proposed in the art, as disclosed in the following patents: 
FR 2,366,237, DE 2,733,516, EP 296,550 and EP 436,226, which make it 
possible the catalyst to be separated from the reaction products by means 
of a simple phase separation. In fact, said phosphines endow the catalyst 
with a hydrophilic character, which catalyst is consequently selectively 
kept in the polar phase, whilst the reaction products remain in the a 
polar phase. 
The present Applicant found now, according to the present invention, that 
the use of particular alkyl, alkylcycloalkyl or alkylaryl phosphines 
bearing an acidic or neutral hydrophilic moiety in their molecule, as 
ligands for palladium, in a process of telomerization of conjugated 
dienes, makes it possible the catalyst activity and selectivity to the 
desired telomers to be unexpectedly improved, because the telomerization 
exclusively or substantially exclusively takes place at the conjugated 
function. 
The present Applicant found furthermore that the use of such ligands in an 
organic/aqueous two-phase liquid reaction vehicle, makes it possibile the 
catalyst and the reaction products to be easily separated at the end of 
the telomerization reaction. 
In accordance therewith, the present invention relates to a process for 
preparing mono-alkadienyl alkyl ethers (IV) by means of the catalyzed 
reaction of a conjugated diene (I) with an aliphatic alcohol (II): 
##STR2## 
and for preparing di-alkadienyl alkyl ethers (V) by means of the catalyzed 
reaction of said conjugated diene (I) with an aliphatic diol (III): 
##STR3## 
wherein: R.sup.i represents a hydrogen atom or methyl radical, 
R.sup.ii represents a hydrogen atom, a C.sub.1 -C.sub.8 alkyl radical, or a 
phenyl radical, 
R.sup.iii represents a C.sub.1 -C.sub.8 alkyl radical, and 
R.sup.iv represents a C.sub.2 -C.sub.8 alkylene radical; 
characterized in that the reaction between the conjugated diene (I) and the 
alcohol (II) or diol (III) is carried out in an aqueous/organic two-phase 
liquid system, in the presence of a catalytic system formed by: 
(a) a palladium salt or complex; 
(b) an alkyl-, alkylcycloalkyl-, or alkylarylphosphine ligend, bearing an 
acidic or neutral hydrophylic moiety, having the formula (VI): 
##STR4## 
wherein: A represents a hydrophilic moiety of sulfate (--SO.sub.3 M), 
phosphate (--PO.sub.3 M.sub.2), hydroxy (--OH) or alkoxy (--OR.sub.4) 
character (in which M represents H, Li, Na, K and NH.sub.4 and R.sub.4 
represents a C.sub.1 -C.sub.5 alkyl moiety), 
R.sub.1 represents the hydrogen atom, a C.sub.1 -C.sub.5 alkyl moiety, a 
C.sub.5 -C.sub.6 cycloalkyl moiety, a C.sub.1 -C.sub.5 alkoxy moiety, an 
aryl (in particular, phenyl) radical or an aryloxy moiety, with said aryl 
moieties being optionally substituted with one or more halogen atoms or 
C.sub.1 -C.sub.5 alkyl moieties; 
R.sub.2 and R.sub.3 represent, each indipendently, a hydrogen atom or a 
methyl radical, 
x is a numeral comprised within the range of from 1 to 3, 
y ia a numeral comprised within the range of from 1 to 6; and 
(c) an either inorganic or organic base. 
The conjugated dienes (II) which are submitted to the process according to 
the present invention are advantageously selected from 1,3-butadiene, 
isoprene, piperylene, methylpentadiiene and phenylbutadiene. Preferably 
used is 1,3-butadiene. The conjugated dienes may be used either in pure, 
or substantially pure form, or as hydrocarbon streams containing one or 
more conjugated dienes, for example, a C.sub.4 fraction containing 
butadiene, or a C.sub.5 fraction containing isoprene and piperylene. 
The aliphatic alcohol (II) which is submitted to the process according to 
the present invention is preferably selected from methanol and ethanol. 
The aliphatic diol (II) which is submitted to the process according to the 
present invention is preferably selected from ethylene glycol and 
propylene glycol. 
The palladium salt or complex (a) of the catalytic system, used in the 
process according to the present invention, may be selected from palladium 
acetyl acetonate, .pi.-allylpalladium chloride, palladium chloride, 
palladium nitrate, palladium acetate, .pi.-allylpalladium acetate, 
palladium bis(benzylidene acetyl acetonate), palladium bis(cyclooctadiene) 
and bis (.pi.-allyl)palladium. The active palladium species in the 
telomerization reaction is thought to be zerovalent or univalent 
palladium. However, both palladium-(O) and palladium (II) compounds can be 
used, because the latter are easily reduced by the same conjugated diene, 
or by basic compounds present in the reaction environment. A particularly 
preferred palladium compound is bis(benzylidene acetyl acetonate). 
The preferred phosphinic ligands (b) for the catalytic system are those 
which are represented by formula (VI) in which R.sub.1 is selected from 
ethyl, cyclohexyl and phenyl radicals; R.sub.2 and R.sub.3 represent a 
hydrogen atom; A represents the sulfate moiety --SO.sub.3 M, with M 
standing for a sodium atom; and x is either 1 or 2. 
In particular, the use of sulfonated phosphines bearing their sulfonic 
group on their alkylic portion makes it possible the selectivity and 
stability of the catalytic system to be enhanced. 
Specific examples of such phosphines (b) are: 
Et.sub.2 PCH.sub.2 CH.sub.2 SO.sub.3 Na (Et=Ethyl); 
cyP(CH.sub.2 CH.sub.2 SO.sub.3 Na).sub.2, (cy=cyclohexyl); and 
PhP(CH.sub.2 CH.sub.2 SO.sub.3 Na).sub.2 (Ph=phenyl). 
The synthesis of the above specified phosphines, or of similar phosphines, 
is per se known and is reported, e.g., in U.S. Pat. No. 4,689,437, EP 
350,921 and in S. Ganguly, J. T. Mague, D. M. Roundhill, Inorg. Chem., 31, 
3500 (1992). 
The inorganic base used as the component (c) of the catalytic system can be 
selected from oxides, hydroxides, carbonates and alkoxides of alkali or 
alkaline-earth metals, or from organic bases, and preferably is sodium 
hydroxide. 
In the process according to the present invention, said component (a) of 
the catalytic system is present in the reaction vehicle at a level of from 
0.000001 to 1 molar, and preferably of from 0.00001 to 0.1 molar; said 
component (b) is present at a level of from 0.00001 to 10 molar, and 
preferably of from 0.0001 to 0.1 molar, and said component (c) is present 
at a Level of from 0.00001 to 10 molar, and preferably of from 0.0001 to 
0.1 molar. 
Furthermore, the process is carried out with a molar ratio of conjugated 
diene:Pd comprised within the range of from 10 to 100,000, and preferably 
of from 100 to 10,000, and with a molar ratio of aliphatic alcohol 
(II):conjugated diene comprised within the range of from 0.1 to 100, and 
preferably of from 1 to 50. 
In the process according to the present invention, the reaction system is 
an aqueous/organic two-phase liquid system. The organic phase can be 
constituted by a liquid hydrocarbon such as a paraffin, an olefin, a 
non-conjugated diene or an aromatic hydrocarbon, or by the same conjugated 
diene, used in an excess amount. 
The added water amount, which is used in order to favour the phase 
separation, should be large enough in order to secure the phase 
separation, but in the meanwhile it should not favour the competition of 
the alcohol in the nucleophilic attack of water in the telomerization 
reaction. 
In particular, it was found that good results are obtained when the process 
is carried out by operating with a weight ratio of aliphatic alcohol (II) 
or aliphatic diol (III) to H.sub.2 O comprised within the range of from 
100 to 0.001, and preferably of from 20 to 0.1. 
In particular, when as the reactant a water soluble aliphatic alcohol (II) 
or aliphatic diol (III) is used, the process is carried out with an 
aqueous-alcoholic phase of such an alcohol or diol. In this case, at 
reaction end, the organic phase containing the mono- or di-alkadienylalkyl 
ether is separated by an aqueous-alcoholic phase containing the catalytic 
system. Therefore, the mono- or di-alkadienil alkyl ether can be separated 
from the organic phase, and the catalyst can be separated from said 
aqueous-alcoholic phase. However, said aqueous-alcoholic phase containing 
the catalyst is preferably recycled without any preliminary-separation. 
When the aliphatic alcohol (II) or diol (III) is insoluble or sparingly 
soluble in water, at the end of the telomerization reaction aqueous 
catalyst phase and an organic phase will be obtained, with the latter, 
besides the mono- or di-alkadienyl alkyl ether, containing any unreacted 
alcohol (II) or diol (III). In that case, said alcohol or diol must be 
separated. 
In the process according to the present invention, the reaction is 
furthermore carried out at a temperature comprised within the range of 
from 20.degree. to 120.degree. C. and under a pressure comprised within 
the range of from 0.1 to 10 MPa and preferably under a pressure equal to 
the vapour pressure of the components of the reaction mixture. By 
operating under the above conditions, conversions of conjugated diene can 
be obtained which may reach values of 99% or even more, with initial 
reaction rates of approximately 10 s.sup.-1 (converted mols of conjugated 
diene per palladium mol per second) and very high selectivity values to 
alkadienyl-alkyl ethers (comprised within the range of from 80 to 100%). 
The resulting byproducts generally are either dimers of the conjugated 
diene, of higher telomers. 
The following experimental examples are reported in order to better 
illustrate the present invention.

EXAMPLE 1 
This example illustrates the use of the catalytic system according to the 
present invention in the reaction of telomerization of 1,3-butadiene with 
methanol at 80.degree. C. in a batch reactor. 
Inside an autoclave equipped with magnetic-driven stirring means, of 100 ml 
of volume, 0.095 mmol of Pd(dba).sub.2, (dba=dibenzylidene acetone), 0.57 
mmol of Et.sub.2 PCH.sub.2 CH.sub.2 SO.sub.3 Na, 0.76 mmol of NaOH, 185 
mmol of 1,3-butadiene, 285 mmol of methanol (about 11.5 ml), 1 ml of water 
and 24 ml of hexane are mixed with one another. The operation is carried 
out under a blanketing nitrogen atmosphere. 
The reaction mixture is heated up to the temperature of 80.degree. C. By 
operating in that way, after a three-hour reaction, a conversion of 
1,3-butadiene of 98% was obtained, with a selectivity to alkadienylmethyl 
ethers of 95% and consequently a yield of the latter of 93%. 
EXAMPLE 2 
This example displays that the conversion and selectivity values remain 
good even when the catalytic system is recycled. 
The catalytic system from Example 1 dissolved in the MeOH-H.sub.2 O phase 
after separating the hydrocarbon phase is used. After make-up of reacted 
methanol, 24 ml of hexane and 139 mmol of butadiene are added; the 
reaction is carried out under the same conditions as of Example 1. 
After a 3-hour reaction, a conversion of 1,3-butadiene of 90% was obtained 
with a selectivity to telomers of 96%, with the yield of the latter being 
hence of 86%. 
EXAMPLE 3 
This example demonstrates that a high performance of the catalytic system 
also obtained with other sulfonated phosphines. 
The process is carried out under the same conditions as of Example 1, with 
the catalytic system being however constituted by 0.095 mmol of 
Pd(dba).sub.2, 0.12 mmol of cyP(CH.sub.2 CH.sub.2 SO.sub.3 Na).sub.2, 
(cy=cyclohexyl), 0.76 mmol of NaOH, 185 mmol of 1,3-butadiene, 285 mmol of 
methanol, 1 ml of water and 24 ml of hexane. The operation is carried out 
under a blanketing nitrogen atmosphere. 
The reaction mixture is heated at a temperature of 80.degree. C. By 
operating in that way, after a three-hour reaction a conversion of 
1,3-butadiene of 69% was obtained with a selectivity to alkadienyl-methyl 
ethers of 94%, with the yield of the latter being therefore of 65%. 
Also in this case, the products are easily separated from the catalyst. 
EXAMPLE 4 (COMISON EXAMPLE) 
This example shows that the absence of the base causes a decrease in 
catalytic system performance. 
The process is carried out under the same conditions as of Example 1, but 
without the base. 
After a three-hour reaction, a conversion of 72% is obtained with a 
selectivity to telomers of 96%, with the telomer yield being of 69%. 
EXAMPLE 5 (COMISON EXAMPLE) 
This example shows that according to the present invention, the yields to 
desired products are maximized, with the other experimental conditions 
being the same, as compared to the prior art. 
The process is carried out in the same way and according to the same 
experimental modalities as disclosed in Example 1. 
The catalytic system is prepared as disclosed in DE 2,733,516 and is 
constituted by 55 mg of Pd(dba).sub.2, 0.38 mmol of PhP(PhSO.sub.3 
Na).sub.2, 172 mmol of 1,3-butadiene, 285 mmol of methanol (about 11.5 
ml), 1 ml of water and 24 ml of hexane. The whole operation is carried out 
under a blanketing nitrogen atmosphere. 
The reaction mixture is heated up to the temperature of 80.degree. C. By 
operating in that way, after a three-hour reaction a conversion of 
1,3-butadiene of 66% was obtained with a selectivity to alkadienyl-methyl 
ethers of 92%, corresponding to a yield of the latter of 61%. 
Furthermore, at the end of the reaction, the presence may be observed of 
metal palladium and when the aqueous phase is recycled (as in Example 2), 
a further reaction does not occur. 
EXAMPLE 7 
In this example, ethanol is used as the aliphatic alcohol. 
The process is carried out under the sane operating conditions as of 
Example 1, with the same catalytic systems and with 104 mmol of 
1,3-butadiene, 285 mmol of ethanol (about 16.6 ml), 1 ml of water and 24 
ml of hexane: the operation is carried out under e blanketing nitrogen 
atmosphere. 
The reaction mixture is heated up to the temperature of 80.degree. C. By 
operating in that way, after a three-hour reaction a conversion of 
1,3-butadiene of 97% was obtained with a selectivity to alkadienyl-ethyl 
ethers of 84%, and a yield of the latter of 82%.