Dimerization of lower .alpha.-olefins

A dimer of a lower .alpha.-olefin is prepared by dimerizing a lower .alpha.-olefin in the presence of a catalyst comprising PA0 (A) nickel chloride, PA0 (B) a trialkylaluminum PA0 (C) at least one phosphorus compound selected from the group consisting of compounds of the formulae: EQU PR.sup.1 R.sup.2 R.sup.3 (I) EQU P(NR.sup.1.sub.2).sub.3 (II) PA0 and EQU P(OR.sup.1).sub.3 (III) PA0 wherein R.sup.1, R.sup.2 and R.sup.3 are the same or different and each an alkyl group, a cycloalkyl group or a phenyl group and PA0 (D) 1,1,1,3,3,3-hexafluoroisopropanol, wherein the catalyst has improved activity because of the use of nickel chloride as a nickel component, so that the amounts of expensive trialkylaluminum and hexafluoroisopropanol can be decreased and the cost of the catalyst can be significantly reduced.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process for dimerization of a lower 
.alpha.-olefin. More particularly, the present invention relates to a 
process for dimerization of a lower .alpha.-olefin which uses a novel 
nickel-containing Ziegler catalyst. 
2. Description of the Related Art 
Dimers of lower .alpha.-olefins such as ethylene, propylene, butene, etc., 
are useful as basic compounds in the production of agricultural chemicals, 
perfumes and other chemicals or as monomers for the production of 
polymers. Some of the known processes for the preparation of the dimers of 
lower .alpha.-olefin comprise dimerization of the -olefin in the presence 
of a nickel-containing Ziegler catalyst. 
For example, Japanese Patent Kokai Publication No. 167932/1982 discloses a 
catalyst comprising a nickel salt, a trialkylaluminum, an organic 
phosphine, a halogenated phenol and water. When the .alpha.-olefin is 
dimerized in the presence of such a catalyst, in some cases, a small 
amount of precipitates may be formed in the reaction system, which results 
in reduction of cooling efficiency of a heat exchanger for cooling the 
reaction system. 
It was proposed to use a catalyst comprising a nickel salt of an organic 
acid, a trialkylaluminum, an organic phosphine and fluorinated isopropanol 
(cf. Japanese Patent Kokai Publication No. 158225/1987). 
SUMMARY OF THE INVENTION 
One object of the present invention is to provide a nickel-containing 
Ziegler catalyst which effectively catalyzes the dimerization the of lower 
.alpha.-olefins. 
Another object of the present invention is to provide a process for 
dimerization of the lower .alpha.-olefins. 
These and other objects of the present invention are accomplished by a 
novel nickel-containing Ziegler. catalyst comprising nickel chloride, a 
trialkylaluminum, a phosphorus compound and 
1,1,1,3,3,3-hexafluoroisopropanol. 
Accordingly, the present invention provides a process for preparing a dimer 
of a lower .alpha.-olefin comprising dimerizing the lower .alpha.-olefin 
in the presence of a catalyst comprising 
(A) nickel chloride, 
(B) a trialkylaluminum 
(C) at least one phosphorus compound selected from the group consisting of 
compounds of the formulae: 
EQU PR.sup.1 R.sup.2 R.sup.3 (I) 
EQU P(NR.sup.1.sub.2).sub.3 (II) 
and 
EQU P(OR.sup.1).sub.3 (III) 
wherein R.sup.1, R.sup.2 and R.sup.3 are the same or different and each an 
alkyl group, a cycloalkyl group or a phenyl group, 
(D) 1,1,1,3,3,3-hexafluoroisopropanol, 
and optionally (E) at least one active hydrogen-containing compound of the 
formula: 
EQU R--OH (IV) 
wherein R is a hydrogen atom, an alkyl group, an allyl group, an aryl group 
or an acyl group in an amount less than the equimolar amount to the 
trialkylaluminum.

DETAILED DESCRIPTION OF THE INVENTION 
The Ziegler catalyst of the present invention is characterized in the use 
of nickel chloride as a nickel-containing component. Nickel chloride to be 
contained in the Ziegler catalyst of the present invention may be in the 
form of an anhydrous salt or a hydrated salt. 
Specific examples of the trialkylaluminum (B) are trimethylaluminum, 
triethylaluminum, tri-n-propylaluminum, tri-isopropylaluminum, 
tri-n-butylaluminum, tri-isobutyl-aluminum, tri-n-pentylaluminum, 
tri-n-hexylaluminum, tri-cyclohexylaluminum, etc. 
The molar amount of the trialkylaluminum is usually 2 to 500 times, 
preferably 2 to 100 times, more preferably 2 to 10 times the amount of 
nickel chloride (A). 
Specific examples of the organic phosphine compound (I) which is one of the 
trivalent phosphorus compounds (C) are trimethylphosphine, 
triethylphosphine, tri-n-propylphosphine, tri-isopropylphosphine, 
tri-n-butylphosphine, tri-isobutylphosphine, tri-tert.-butylphosphine, 
tri-sec.butylphosphine, tricyclopropylphosphine, tricyclohexylphosphine, 
triphenylphosphine, tri-p-tolylphosphine, tri-p-methoxyphenylphosphine, 
tri-2,4,6-trimethylphenylphosphine, phenyl-di-isopropylphosphine, 
ethyl-di-isopropylphosphine, ethyl-di-tert.-butylphosphine, 
ethyl-dicyclohexylphosphine, methylpropylphenylphosphine, 
methylphenylbenzylphosphine, etc. 
Specific examples of the aminophosphine compound (II) are 
tris-dimethylaminophosphine, tris-diethylaminophosphine, 
tris-di-n-propylaminophosphine, tris-di-iso-propylaminophosphine, 
tris-di-n-butylaminophosphine, tris-di-isobutylaminophosphine, 
tris-di-tert.-butylaminophosphine, tris-dicyclohexylaminophosphine, etc. 
Specific examples of the phosphite (III) are tri-methylphosphite, 
triethylphosphite, tri-n-propylphosphite, tri-isopropylphosphite, 
tri-n-butylphosphite, tri-isobutylphosphite, tri-tert.-butylphosphite, 
tricyclohexylphosphite, triphenylphosphite, tri-p-tolylphosphite, 
tri-p-methoxyphenylphosphite, etc. 
Among the components (A) to (D) of the catalyst, the trivalent phosphorus 
compound (C) has the largest influence on the isomer distribution of the 
.alpha.-olefin dimers. For example, when 2,3-dimethylbutenes are to be 
prepared in high yields by dimerization of propylene, organic phosphines 
such as tri-isopropylphosphine, tricyclohexylphosphine, 
tri-sec.-butylphosphine, etc., are preferably used. 
The molar amount of the phosphorus compound (C) is usually 0.1 to 50 times, 
preferably 0.1 to 20 times, more preferably 0.1 to 2 times the amount of 
nickel chloride (A). 
1,1,1,3,3,3-Hexafluoroisopropanol (D) is one of the essential components of 
the Ziegler catalyst having the dimerization activity according to the 
present invention. Without 1,1,1,3,3,3-hexafluoroisopropanol, the catalyst 
has substantially no dimerization activity. Through variation of the 
amount of 1,1,1,3,3,3-hexafluoroisopropanol, the isomer distribution of 
the double bond in the olefin dimer can be controlled. For example, when 
the 2,3-dimethylbutenes are selectively prepared, 2,3-dimethylbutene-1 is 
obtained if the amount of 1,1,1,3,3,3-hexafluoroisopropanol is small, 
while 2,3-dimethylbutene-2 is obtained if the amount of 
1,1,1,3,3,3-hexafluoroisopropanol is increased. 
The molar amount of 1,1,1,3,3,3-hexafluoroisopropanol is 0.2 to 10 times, 
preferably 0.5 to 5 times, more preferably 1 to 4 times the amount of the 
trialkylaluminum (B). 
In addition to the above essential components, the Ziegler catalyst of the 
present invention may comprise the active hydrogen-containing compound (E) 
of the formula (IV). Thereby, the isomer distribution of the olefin dimer 
can be varied. For example, in case of dimerization of propylene, the 
catalyst comprising the active hydrogen-containing compound (E) will 
increase the selectivity of 2,3-dimethyl-butene-1, 2,3-dimethylbutene-2 
and the like. 
Specific examples of the active hydrogen-containing compound (IV) are 
water, lower alkyl alcohols (e.g. methanol, ethanol, n-propanol, 
isopropanol, n-butanol, tert.-butanol, amyl alcohol, hexanol, heptanol, 
octanol, etc.), allyl alcohol, phenols (e.g. phenol, cresol, xylenol, 
etc.) and carboxylic acids, (e.g. acetic acid, propionic acid, etc.). 
Among them, water, methanol, ethanol, n-propanol, octanol, allyl alcohol, 
phenol, acetic acid and mixtures thereof are preferred. 
The molar amount of the compound (E) is less than equimolar to, preferably 
0.1 to 0.8 time, more preferably 0.2 to 0.6 time the amount of the 
trialkylaluminum (B). 
Although the catalyst system of the present invention can be stably used in 
the presence of the lower .alpha.-olefin to be dimerized during the 
preparation step, the catalyst is preferably prepared in the presence of a 
linear conjugated diolefin as a stabilizing aid. Examples of such 
conjugated diolefin are butadiene, isoprene and 1,3-pentadiene. The molar 
amount of the conjugated diolefin is not more than 200 times the amount of 
nickel chloride (A). Excessive use of the conjugated diolefin does not 
improve the stabilizing effect. 
The components (A) to (D) may be mixed in any order. Preferably, nickel 
chloride (A), the trivalent phosphorus compound (C), the trialkylaluminum 
(B) and 1,1,1,3,3,3-hexafluoroisopropanol (D) are added in this order 
[(A), (C), (B) and (D)]in the presence of a small amount of .alpha.-olefin 
or the conjugated diolefin as the stabilizing aid. When the optional 
component (E) is used, the components are added in the sequence of (A), 
(C), (B), (E) and (D). 
In general, the catalyst is prepared in an inert solvent. Examples of such 
solvent are aromatic hydrocarbons (e.g. benzene, toluene, xylene, etc.), 
aliphatic hydrocarbons (e.g. hexane, heptane, cyclohexane, etc.) and 
halogenated aromatic hydrocarbons (e.g. chlorobenzene, dichlorobenzene, 
etc.). Among them, the aromatic hydrocarbons and the halogenated aromatic 
hydrocarbons are preferred. 
The catalyst is prepared usually at a temperature of -80.degree. C. to 
+60.degree. C., preferably -20.degree. C. to +40.degree. C. 
In some cases, the catalyst may be prepared in the liquid or liquefied 
.alpha.olefin. 
The concentration of the catalyst during the dimerization is usually from 
10.sup.-5 to 10.sup.-1 mol/liter in terms of the concentration of the 
nickel component. The reaction temperature for dimerization is usually 
from -80.degree. C. to +60.degree. C., preferably from -21.degree. C. to 
+40.degree. C. The reaction pressure is from atmospheric pressure to 
autogenous equilibrium pressure at the reaction temperature. 
Examples of the lower .alpha.-olefin to be dimerized according to the 
present invention are those having at least 2, preferably 2 to 4 carbon 
atoms such as ethylene, propylene, 1-butene, etc. 
After the dimerization reaction, the reaction is stopped and the catalyst 
is separated from the reaction mixture by per se conventional manners. 
Then, the reaction mixture is rectified to obtain the desired dimer(s). 
The product can be analyzed and quantitatively determined by gas 
chromatography. 
According to the present invention, since the Ziegler catalyst contains 
nickel chloride as the nickel component, the catalytic activity can be 
greatly increased. For example, the amounts of the expensive 
trialkylaluminum and hexafluoroisopropanol can be decreased, so that the 
cost of catalyst can be considerably reduced. 
In addition, by the use of the active hydrogen-containing compound, the 
isomer distribution in the produced olefin dimers can be advantageously 
controlled. 
PREFERRED EMBODIMENTS OF THE INVENTION 
Practically and presently preferred embodiments of the present invention 
will be illustrated by the following Examples. 
EXAMPLE 1 
In a stainless steel 100 ml autoclave which had been evacuated, dried and 
filled with nitrogen, chlorobenzene containing 0.05 mmol of anhydrous 
nickel chloride (5 ml), chlorobenzene containing 0.05 mmol of 
tricyclohexylphosphine (0.5 ml) and isoprene (4 mmol, 0.4 ml) were added 
in this order and mixed. Then, chlorobenzene containing 0.25 mmol of 
triethylaluminum (0.25 ml) was added and the mixture was stirred while 
cooling with ice. To the ice-cooled mixture, chlorobenzene containing 0.75 
mmol of 1,1,1,3,3,3-hexafluoroisopropanol (hereinafter referred to as 
"HFIP") (0.75 ml) was added while stirring, followed by stirring for 10 
minutes. To the catalyst solution, absolute chlorobenzene (4.6 ml) was 
added and then propylene was injected in the autoclave to a pressure of 4 
kg/cm.sup.2 followed by stirring at 20.degree. C. for 30 minutes. 
After the reaction was completed, the reaction mixture was sampled under 
pressure and subjected to gas chromatography with using n-pentane as the 
internal standard. The results are shown in Table 1. 
The reaction mixture after purging unreacted propylene was clear, and no 
deposit was found on the inner wall of the autoclave. 
EXAMPLE 2 
In the same manner as in Example 1 except that after the addition of the 
triethylaluminum solution, chlorobenzene containing 0.1 mmol of methanol 
(0.2 ml) was added and the mixture was stirred, and then the HFIP solution 
was added followed by stirring, the catalyst was prepared and the 
dimerization was carried out. The results are shown in Table 1. 
The reaction mixture was clear, and no deposit was found on the inner wall 
of the autoclave. 
EXAMPLES 3-6 
In the same manner as in Example 1 but using the organic 
phosphorus-containing compound (0.05 mmol) shown in Table 2 in place of 
tricyclohexylphosphine, the catalyst was prepared and the dimerization was 
carried out. 
The results are shown in Table 2. 
TABLE 1 
__________________________________________________________________________ 
Effi- Selec- 
Selec- 
Distribution of dimers (%) Isomeri- 
Exam- 
ciency*.sup.1 
tivity*.sup.2 
tivity*.sup.3 
2,3-di- 
2,3-di- zation 
ple of of dimers 
of DMBS 
methyl- 
methyl- 
4-methyl- 
2-methyl- ratio*.sup.4 
No. catalyst 
(%) (%) 1-butene 
2-butene 
2-pentene 
1-pentene 
2-pentene 
2-hexene 
(%) 
__________________________________________________________________________ 
1 23.1 .times. 10.sup.3 
69.2 77.7 5.1 72.6 6.5 1.8 14 0 93.4 
2 17.4 .times. 10.sup.3 
60.2 84.8 4.8 80 3.2 0.8 11.2 0 94.4 
__________________________________________________________________________ 
Note: 
*.sup.1 Efficiency of the catalyst based on the converted propylene 
(C.sub.3 '). (Mole of converted propylene C.sub.3 ')/(gatom of Ni .times. 
time (hrs)) 
*.sup.2 A percentage (by mole) of the dimers based on converted propylene 
*.sup.3 A percentage (by mole) of 2,3dimethylbutenes (DMBS) in the dimers 
*.sup.4 (2,3-dimethyl-2-butene/2,3-dimethylbutenes) .times. 100. 
TABLE 2 
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Distribution of dimers (%) 
Organic Efficiency 
Selectivity 
2,3-di- 
2,3-di- 
Example 
P-cont. of of dimers 
methyl- 
methyl- 
4-methyl- 
2-methyl- 
2-methyl- 
No. compound catalyst 
(%) 1-butene 
2-butene 
2-pentene 
1-pentene 
2-pentene 
2-hexane 
__________________________________________________________________________ 
3 P(i-Pr).sub.3 
20.8 .times. 10.sup.3 
82.0 10.7 61.4 11.1 2.1 14.7 0 
4 P(n-Pr).sub.3 
31.2 .times. 10.sup.3 
85.6 2.7 38.2 11.9 5.1 42.2 0 
##STR1## 9.9 .times. 10.sup.3 
89.6 1.5 21.2 12.4 0 64.9 0 
6 
##STR2## 28 .times. 10.sup.3 
90.9 3.4 32.7 15.3 6.4 42.1 0 
__________________________________________________________________________ 
EXAMPLES 7-13 
In the same manner as in Example 2 but using the active hydrogen-containing 
compound (0.1 mmol) shown in Table 3 in place of methanol, the catalyst 
was prepared and the dimerization was carried out. 
The results are shown in Table 3. 
TABLE 3 
______________________________________ 
Ex- Yield of 
Selectivity 
am- Active H- Effi- dimethyl- 
of dimethyl- 
ple containing ciency of butenes 
butenes 
No. compound catalyst (%) (%) 
______________________________________ 
7 H.sub.2 O 24 .times. 10.sup.3 
48.3 80.6 
8 C.sub.2 H.sub.5 OH 
22.8 .times. 10.sup.3 
53.4 81.2 
9 n-C.sub.3 H.sub.7 OH 
16.1 .times. 10.sup.3 
48.8 79.9 
10 n-C.sub.8 H.sub.17 OH 
18.7 .times. 10.sup.3 
44.9 80.4 
11 CH.sub.2CHCH.sub.2 OH 
21.5 .times. 10.sup.3 
49.7 80.5 
12 
##STR3## 23.4 .times. 10.sup.3 
48.2 80.5 
13 CH.sub.3 COOH 15.5 .times. 10.sup.3 
46.1 80.9 
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COMATIVE EXAMPLE 1 
In the same manner as in Example 1 but using nickel naphthenate (0.05 mmol) 
in place of nickel chloride, 0.5 mmol of triethylaluminum and 1.5 mmol of 
HFIP, the catalyst was prepared and the dimerization was carried out. 
The results are shown in Table 4. 
COMATIVE EXAMPLE 2 
In the same manner as in Example 1 except that, after the addition of 
isoprene, water (0.25 mmol, 4.5 .mu.l ) was added, then chlorobenzene 
containing 0.5 mmol of triethylaluminum (0.5 ml) and chlorobenzene 
containing 1.75 mmol of 2,4,6-trichlorophenol (1.75 ml) were added in this 
sequence followed by stirring for 15 minutes and the chlorobenzene (3.35 
ml) was added, the catalyst was prepared and the dimerization was carried 
out. 
The results are shown in Table 4. 
COMATIVE EXAMPLE 3 
In the same manner as in Comparative Example 2 but using 0.125 mmol of 
water, 0.25 mmol of triethylaluminum and 0.875 mmol of 
2,4,6-trichlorophenol, the catalyst was prepared and the dimerization was 
carried out. 
The results are shown in Table 4. 
TABLE 4 
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Compa- Yield of Selectivity 
rative dimethyl- 
of dimethyl- 
Example Efficiency butenes butenes 
No. of catalyst (%) (%) 
______________________________________ 
1 18.7 .times. 10.sup.3 
39.7 87.4 
2 13 .times. 10.sup.3 
42.6 70.1 
3 3.1 .times. 10.sup.3 
27.5 71.2 
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