Process for purifying vinylically unsaturated compounds prepared using a palladium-complex catalyst

A crude vinylically unsaturated product formed from a palladium-complex-catalyzed reaction of a reactant halide selected from the group consisting of aryl, allyl, vinyl, and benzyl halides, and a reactant olefin having a vinylic hydrogen, wherein the reaction is carried out in the presence of a hydrogen halide acceptor, is purified by first contacting the crude product with a base that is stronger than the hydrogen halide acceptor, then heating the stronger base-contacted product. The purified product shows a marked reduction in concentration bromine and palladium impurities. The product can then be further purified by such methods as chromatography, crystallization, or distillation to achieve a product that is more suitable for applications where very low levels of inorganic impurities are required.

BACKGROUND OF THE INVENTION 
This invention relates to an improved process of purifying a vinylically 
unsaturated compound prepared from the palladium-complex catalyzed 
reaction of an olefin containing a vinylic hydrogen and an aryl, allyl, 
vinyl, or benzyl halide. Specifically, the invention relates to an 
improved method of removing palladium and halide from the vinylically 
unsaturated compound. 
The palladium-complex catalyzed vinylation of organic halides is described 
by Heck in U.S. Pat. No. 3,922,299 and in Organic Reactions, vol. 27, p. 
345 (1982), both incorporated herein by reference. The reaction is 
represented by the following equation: 
##STR1## 
wherein R is aryl, allyl, vinyl, or benzyl, the Pd-complex is typically 
palladium bound to a trivalent organophosphorous or organoarsenic moiety, 
and an organic or halo moiety. Heck teaches that the reaction can be 
carried out with or without a solvent, with suggested solvents being 
acetonitrile, tetrahydrofuran, methanol, dimethylformamide (DMF), and 
N-methyl-pyrrolidinone. 
In U. S. Pat. No. 5,264,646, incorporated herein by reference, DeVries et 
al. discloses an improved process for the Heck-type vinylation reaction, 
wherein the reaction is carried out in a water-containing medium. 
The crude vinylically unsaturated compound prepared by the methods 
described by Heck and DeVries et al. is advantageously purified to remove 
inorganics, particularly palladium and halide, from the crude product. 
This purification is particularly crucial, for example, for high 
performance electronic applications, where it is often necessary to reduce 
inorganic impurity concentrations to low ppm levels. Present purification 
processes, such as distillation, crystallization, or chromatography, are 
necessary, yet often insufficient for reducing these inorganic impurities 
to the desired levels. Indeed, multiple purification steps may be required 
to achieve the desired reduction of impurities. Furthermore, these 
processes do not provide an easy means for recovering and recycling 
palladium. 
Because the recovery and recyclability of palladium is desirable, and 
multiple purification steps are undesirable, it would be an advantage to 
provide a simple means of reducing halide and palladium impurities in the 
crude vinylically unsaturated compound prior to a further purification 
step. 
SUMMARY OF THE INVENTION 
The present invention is an improved process of reducing the concentration 
of palladium and halide in a crude vinylically unsaturated product that 
has been extracted with water from a product mixture containing the crude 
vinylically unsaturated product, the product mixture being formed from a 
palladium-complex-catalyzed reaction of a reactant halide selected from 
the group consisting of aryl, allyl, vinyl, and benzyl halides, and a 
reactant olefin having a vinylic hydrogen; wherein the reaction is carried 
out in the presence of a hydrogen halide acceptor; the improvement 
comprising the steps of: 
a) contacting the crude vinylically unsaturated product with a base that is 
stronger than the hydrogen halide acceptor and phase-separable from the 
product; 
b) phase-separating the product in step (a) from the stronger base; then 
c) heating the separated product of step (b) under conditions such that the 
palladium can be isolated from the product by filtration or 
centrifugation; and 
d) removing the palladium from the product in step (c). 
In another aspect, the invention is an improved process of reducing the 
amount of palladium and bromide in a crude 
1,3-divinyl-1,1,3,3-tetramethyldisiloxanebisbenzocyclobutene product that 
has been extracted with water from a product mixture containing the crude 
product, the product mixture being formed by a palladium-complex-catalyzed 
reaction of a 4-bromobenzocyclobutene and 
1,3-divinyl-1,1,3,3-tetramethyl-disiloxane; wherein the reaction is 
carried out in an aqueous solution of 30-70 volume percent of 
dimethylformamide, and in the presence of potassium acetate or 
triethylamine, or a mixture thereof; the improvement comprising the steps 
of: 
a) contacting the crude product with aqueous sodium hydroxide; 
b) water-extracting the sodium hydroxide from the crude product; then 
c) heating the extracted crude product of step (b) under sufficient 
conditions to agglomerate the palladium; and 
d) removing the agglomerated palladium from the crude product in step (c). 
The present invention addresses a need in the art by providing effective 
post-reaction treatments which reduce palladium and halide impurities in a 
vinylically unsaturated product prepared by Heck-type chemistry. 
DETAILED DESCRIPTION OF THE INVENTION 
The post-reaction processes of the present invention are suitable for 
vinylically unsaturated products derived from reactant aryl, allyl, vinyl, 
benzyl halides, and reactant olefins such as those described in DeVries et 
al., U.S. Pat. No. 5,243,068, supra. Preferred reactant halides are 
substituted or unsubstituted aryl halides. Representative examples include 
halogenated benzenes and naphthalenes, such as C.sub.1 -C.sub.6 
alkylbromobenzene, C.sub.1 -C.sub.6 alkylbromonaphthalenes, and 
bromobenzocyclobutenes (Br-BCBs). Br-BCBs can be prepared by the method 
described by Liu in U.S. Pat. No. 4,822,930, incorporated herein by 
reference. The most preferred aryl halide used in the process of the 
present invention is 4-bromobenzocyclobutene (4-Br-BCB). 
Representative reactant olefins include vinyl, allyl, and methallyl 
hydrocarbons, such as ethylene, propylene, 1-butene, 2-butene, 
2-methyl-l-propene, 1,3-butadiene, 1,4-pentadiene, 1,5-hexadiene, 
3-methyl-1-butene, styrene, substituted styrenes, divinylbenzenes, 
vinylnaphthalenes, stilbene, and allyl cyclohexane; vinyl, allyl, and 
methallyl compounds containing a heteroatom, such as acrylate and 
methacrylate esters, acrylonitrile, and methacrylonitrile; vinyl or allyl 
organosilicon compounds, such as tri-C.sub.1 -C.sub.6 -alkylvinylsilanes; 
and siloxanes represented by the formula: 
##STR2## 
wherein each R is independently C.sub.1 -C.sub.6 -alkyl, cycloalkyl, 
aralkyl, or aryl; R.sub.1 is independently vinyl, allyl, or methallyl; and 
n is an integer from 1 to 4500. 
More preferably R1 is vinyl, each R is methyl, ethyl, or phenyl; and n is 
an integer from 2 to 10. An especially preferred siloxane is 
1,3-divinyl-1,1,3,3tetrametyhyldisiloxane. 
The most preferred vinylically unsaturated products are prepared from 
4-Br-BCB and a mixture of m- and p-vinyltoluene; 4-Br-BCB and 
divinylbenzene; ethylene and o-bromotoluene; 4-Br-BCB and ethylene; 
4-Br-BCB and styrene; and 4-Br-BCB and 
1,3-divinyl-1,1,3,3-tetramethyldisiloxane. 
The molar ratio of reactant halide to reactant olefin can be determined by 
routine experimentation. Generally, molar ratios of 0.5:1 to 1.5:1 are 
preferred for the synthesis of monoadducts, with higher ratios of reactant 
halide to reactant olefin being preferred for higher adducts. 
The reaction is carried out in the presence of a palladium-complex 
catalyst. The palladium-complex catalyst suitable for the preparation of 
the vinylically unsaturated product is generally described in U.S. Pat. 
No. 3,922,299, supra. Preferably, the catalyst is formed from palladium 
(II) acetate and a triaryl phosphine, such as triphenylphosphine, or 
tris-(o-tolyl)phosphine. 
The reaction requires a hydrogen halide acceptor, which is sufficiently 
strong to form a salt with a hydrogen halide, especially hydrogen bromide 
or hydrogen iodide, yet sufficiently weak so as not to deactivate the 
catalyst or undesirably decompose the reactants or product. Preferred 
hydrogen halide acceptors include trialkylamines and salts of weak acids 
and strong bases, such as alkali metal or alkaline earth metal acetates 
and bicarbonates. More preferred hydrogen halide acceptors for the 
practice of the present invention are potassium acetate, and 
triethylamine, with potassium acetate being especially preferred. 
The reaction may be carried out with or without a solvent, and is 
preferably carried out with a solvent. Representative solvents include 
nitriles, such as acetonitrile; alcohols, such as methanol or ethanol; 
N,N-dialkylformamides, such as dimethylformamide; N-alkyl pyrrolidinones, 
such as N-methylpyrrolidinone; glycol ethers, dioxane, tetrahydrofuran, 
and water. 
When the hydrogen halide acceptor is a salt of a weak acid and a strong 
base, water or a water-containing solvent is advantageously employed; 
preferably an aqueous solution consisting of about 10 to 0 about 90 volume 
percent of an organic solvent selected from the group consisting of 
nitriles, alcohols, N,N-dialkylformamides, N-alkylpyrrolidinones, glycol 
ethers, dioxane, and tetrahydrofuran; more preferably an aqueous solution 
of about 30 to about 70 volume percent of dimethylformamide or 
N-methylpyrrolidinone. 
The temperatures suitable for formation of the vinylically unsaturated 
product vary from about room temperature up to a temperature below which 
the product or starting materials decompose or polymerize. Reaction 
temperatures in the range of about 80.degree. C. to about 120.degree. C. 
are preferred. When the reaction is complete, water is added to the 
reaction mixture, which comprises the crude vinylically unsaturated 
product, solvent, and salts, and the aqueous phase is removed. The crude 
vinylically unsaturated product is ready for post-treatment. 
Treatment of Crude Vinylically Unsaturated Product 
The term "crude" is used herein to refer to the vinylically unsaturated 
product prior to purification by chromatography, crystallization, or 
distillation. The crude vinylically unsaturated product prepared in the 
manner described by Heck or DeVries et al. is first contacted with a base 
that is stronger than the hydrogen halide acceptor. The stronger base is 
water-extractable from the vinylically unsaturated product, and may be 
added to the product in an aqueous or non-aqueous form. If the hydrogen 
halide acceptor is an alkali metal or alkaline earth metal acetate, 
preferred stronger bases include alkali metal or alkaline earth metal 
hydroxides, such as lithium hydroxide, sodium hydroxide, potassium 
hydroxide, calcium hydroxide, or magnesium hydroxide; trialkylamines, such 
as triethylamine, trimethylamine, or tri-n-butylamine; an alkali metal 
ethylenediamine tetramine (EDTA), such as tetrasodium EDTA; a carbonate, 
such as potassium carbonate or sodium carbonate; or an alkoxide, such as 
sodium methoxide and sodium ethoxide. 5 Aqueous sodium hydroxide, 
preferably about 0.02, more preferably from about 0.05, and most 
preferably from about 0.1 weight percent, to about 10, more preferably to 
about 5, and most preferably to about 2 weight percent aqueous sodium 
hydroxide, is an especially preferred stronger aqueous base for alkali 
metal or alkaline earth metal acetates or bicarbonates, as well as 
trialkylamines. 
The stronger base is contacted with the product in such a manner and in 
sufficient quantity to transfer halide from the product to the stronger 
base. Preferably, the stronger base is added to the crude product with 
stirring at a temperature in the range from about 25.degree. C., more 
preferably from 40.degree. C., and most preferably from about 50.degree. 
C., to preferably about 90.degree. C., more preferably to about 75.degree. 
C., and most preferably to about 60.degree. C. When an aqueous base is 
used, the pH of the aqueous phase is preferably in range of about 10, more 
preferably from about 11, to about 14, more preferably to about 13. 
Though not bound by theory, it is believed that the stronger base 
dehydrohalogenates hydrohalogenated impurities in the product, thereby 
converting at least a portion of such impurities to useful product; 
concomitantly, the dehydrohalogenation process serves to reduce the amount 
of halide in the crude product mixture. The following reaction scheme 
illustrates this point: 
##STR3## 
It is also possible that the stronger base may dehalogenate the 
post-reacted palladium-complex catalyst, thereby reducing the stability of 
the complex and allowing the palladium metal to be more readily 
recoverable in a subsequent heat treatment step. 
It has been discovered that certain strong bases, such as alkali metal 
hydroxides and alkoxides, when used as hydrogen halide acceptors, 
undesirably deactivate the palladium-complex catalyst. Therefore, these 
catalyst-deactivating strong bases are not useful as hydrogen halide 
acceptors, even though they would be expected to suppress the formation of 
hydrohalogenated byproducts. However, the combination of a 
non-catalyst-deactivating weaker base used in the reaction medium, 
followed by post-reaction treatment with a stronger base that is capable 
of removing halide from the product, provides improved purification 
without significant yield loss. 
A solvent which is miscible with the product, but immiscible with water is 
advantageously added to the crude product to promote the separation of the 
stronger base from the product. Preferred solvents include hydrocarbon 
solvents, such as xylene, mesitylene, toluene, and petroleum ethers, such 
as Isopar G. 
The product and optionally a solvent for the product are phase-separated 
from the stronger base by extracting the stronger base with water. The 
isolated product, or the product and solvent, is then heated under 
conditions such that the palladium can be recovered from the product by 
filtration or centrifugation without decomposing or polymerizing the 
product. At a sufficiently high temperature, preferably in the range from 
about 100.degree. C., more preferably from about 120.degree. C., to about 
180.degree. C., more preferably to about 150.degree. C., palladium 
agglomerates out of the aqueous base treated product. This agglomerated 
palladium is preferably recovered by filtration through a filter having a 
pore size of less than 2 microns, more preferably less than 0.5 micron, 
and most preferably less than 0.2 micron. 
The combination of aqueous base treatment followed by heat treatment 
results in a vinylically unsaturated product that contains a significant 
reduction in halide and palladium impurities. If the palladium-complex 
catalyst used to prepared the vinylically unsaturated product contains 
phosphorous, the crude product that has been subjected to treatment with a 
stronger base, and prior to heat treatment, is advantageously treated with 
a peroxide, such as aqueous hydrogen peroxide or t-butyl hydroperoxide to 
oxidize phosphine residues to corresponding phosphine oxides. These 
phosphine oxides can then be removed, for example, by passing the crude 
product through a phosphine oxide adsorbing medium, such as a silica gel 
column. The treated crude product can also be purified further by means 
such as crystallization, distillation, or chromatography. The 
post-reaction processes described herein have the advantage of isolating 
impurities in a single location, thereby making recovery and reuse of 
palladium easier.

The following example is provided to illustrate the process of present 
invention but is not intended to limit the scope thereof. 
EXAMPLE 
Synthesis and Purification of 
-1,3-divinyl-1,1,3,3-tetramethyldisiloxanebisbenzocyclobutene (DVS-bisBCB) 
Potassium acetate (870 g) and deionized water (420 mL) are charged into a 5 
L thermowell three-neck flask, equipped with an overhead electric agitator 
with a teflon stirshaft, a thermocouple-controlled heating mantle with a 
timer and a high-temperature shutoff, a nitrogen inlet atop a condenser 
leading to an oil bubbler, and a glass funnel. The reactor is purged with 
nitrogen, warmed to 40.degree. C. and stirred. When the potassium acetate 
is dissolved, 4-BrBCB (560 g) and 
1,3-divinyl-l,l,3,3-tetramethyldisiloxane (280 g) are added to the reactor 
with DMF rinsing. Palladium (II) acetate (0.84 g) and 
tris-(o-tolyl)phosphine (4.56 g) are dissolved with about 100 g of DMF, 
and the dissolved catalyst mix is added to the reactor with DMF rinses. 
The total amount of DMF used is 840 mL. The reactor is sparged with 
nitrogen for 25 minutes using the condenser as the outlet. The reaction 
temperature is raised to 94.degree. C. The reaction is complete at 24 
hours, as determined by GC-analyzed disappearance of Br-BCB. 
Deionized water (1.2 L) is added with stirring and the temperature is 
adjusted to 60.degree. C. The aqueous phase is separated from the organic 
phase. An aliquot of the organic phase is mixed with Isopar G, and washed 
3 times with deionized water. The Isopar G is removed and the aliquot is 
found to contain 182 ppm bromine and 606 ppm palladium by neutron 
activation analysis. Aqueous sodium hydroxide (0.5 weight percent NaOH, 
1.2 L) is added to the reaction mixture with stirring for 4 hours at 
60.degree. C. Isopar G (600 g) is then added to the mixture, the aqueous 
phase is removed, and the organic layer is extracted with three 1.6-L 
portions of water, whereupon the pH of the last aqueous layer is reduced 
to 8. An aliquot of the sodium hydroxide-washed, water-washed organic 
phase is found to contain 15 ppm Br and 602 ppm palladium after removal of 
the Isopar G. 
t-Butyl hydroperoxide (2.3 g) is added to the organic phase, which is then 
heated to 60.degree. C. for 6 hours. An aliquot of the 
hydroperoxide-treated organic phase is filtered through a 0.2 micron 
filter, and the filtrate is found to contain 15 ppm Br and 608 ppm 
palladium after removal of the Isopar G. 
The product mixture is then heated to 120.degree. C. for 6 hours, whereupon 
the mixture turns black from agglomerated palladium. The mixture is then 
cooled to room temperature and passed through a 0.2 micron filter, where 
the agglomerated palladium is recovered. An aliquot of the filtrate, which 
is a clear yellow color, is found to contain 10 ppm Br and 9 ppm palladium 
after removal of Isopar G. 
The reaction product is then passed through a column containing 220 g of 
silica gel and 22 g of MgSO.sub.4. The column is rinsed with two 400-g 
portions of Isopar G. The Isopar G is distilled from the the combined 
effluents, and the product is distilled through a short-path molecular 
distillation unit. The chromatographed and distilled product is found to 
contain 1.5 ppm Br and less than 0.5 ppm palladium as determined by 
neutron activation analysis.