The present invention relates to a dialkyi zinc composition, a process for making dialkyi zinc, and specific uses of the dialkyi zinc composition.

In recent years, the demand for dialkyi zinc has grown because of its use as a catalyst or reagent in polymerization processes and pharmaceutics manufacturing and its use in the production of solar cells and semiconductor devices.

A problem observed in liquid dialkyi zinc and its compositions is the formation of solids of metallic zinc. These solids may cause plugging in equipment in which dialkyi zinc is used, resulting in production down times. The stability, in particular the thermal stability, of these compositions therefore needs improvement.

It has now been found that such improvement can be obtained by incorporating an alkene in such compositions. The present invention therefore relates to a thermally stable liquid composition comprising dialkyi zinc and 1 ppm to 20 wt% of an alkene, based on the weight of the entire composition. The liquid composition according to the present invention is thermally stable, which means that the liquid composition can be stored under nitrogen atmosphere (<2 ppm oxygen) and exclusion of light at 80°C for 20 hours without any significant change in its chemical or physical constitution, apart from the potential formation of some metallic zinc. Said metallic zinc formation should, however, be less than under the same conditions in the same composition not containing said alkene.

Any alkene can be used in the composition according to the invention. Preferably, the alkene contains 2-200 carbon atoms, more preferably 2-100, even more preferably 2-50, more preferably 5-20 carbon atoms, and most preferably 5-10 carbon atoms.

The term "alkenes" includes monoalkenes, conjugated or non-conjugated dienes, trienes, and tetraenes, cycloalkenes, cycloalkedienes, cyclotrienes, cyclotetraenes, and di-, tri- and tetra-substituted ethylene with alkyl-, alkenyl-, aryl- and/or heteroatom-containing substituents. Cycloalkenes, cyclodienes, cyclotrienes, and cyclotetraenes are the most preferred type of alkenes.

Specific examples of suitable monoalkenes are 1 -hexene, 1 -octene, 3-heptene (both cis- and trans-), 1 -octadecene, trans-4-octene, cis-4-octene, isobutene, and methylene cyclohexane.

Examples of suitable dienes are 1 ,7-octadiene, isoprene and trans,trans-1 ,4- diphenyl-1 ,3-butadiene.

Examples of suitable cycloalkenes, cycloalkadienes, -trienes, and -tetraenes are cyclopentene, cyclohexene, cycloheptene, cyclooctene, cyclopentadiene, dicyclopentadiene, 1 ,2,3,4,5-pentamethylcyclopentadiene, 1 ,4-cyclohexadiene, 1 ,5-dicyclooctadiene, 1 ,3,5,7-cyclooctatetraene, 1 ,6-diphenyl-1 ,3,5-hexatriene, and substituted versions thereof such as 1 -methyl-1 ,4-cyclohexadiene, 1 -methyl-1 - cyclohexene, and 4-methylcyclohexene. Of these, cyclopentene, cyclohexene, trans,trans-1 ,4-diphenyl-1 ,3-butadiene, 1 ,2,3,4,5-pentamethylcyclopentadiene, 1 ,4- cyclohexadiene, 1 -methyl-1 ,4-cyclohexadiene, 1 ,3,5,7-cyclooctatetraene, and 1 ,6- diphenyl-1 ,3,5-hexatriene are preferred. The most preferred are 1 ,4- cyclohexadiene and 1 -methyl-1 ,4-cyclohexadienes. Also suitable are bicyclic alkenes, such as bicyclo[5.3.0]decapentaene and 3- ethenyl(bicyclo[4.2.0]-octa-1 ,3,5-triene), tricyclic alkenes, such as tricyclo[3.3.2.0(2,8)]deca-3,6,9-triene, tricyclo[12.3.2.0(1 , 16)]nonadec-14(19)-ene, tricyclo[5.5.0.0(2,8)]dodeca-4,10-diene, 1 ,2, 3,4,5,6, 7, 8-octamethyl- tricyclo(4.2.0.0(2, 5))octa-3,7-diene, and 5-vinyl-tricyclo(8.2.2.2(4,7))hexadeca- 1 (13), 4(16), 5, 7(15), 10(14), 1 1 -hexaene, and tetracyclic alkenes such as tetracyclo[14.2.2.2(4,7).2(10, 13)]tetracosa-1 (18),2, 4,6, 8, 10,12, 14, 16,19,21 , 23- dodecaene.

Di-, tri- and tetra-substituted ethylene with alkyl-, alkenyl- aryl- and/or heteroatom- containing substituents can also be used as alkenes in the process of the present invention, just like mono-substituted ethylenes, phenylethylene (styrene), alpha- methylphenylethylene, cyanoethylene (acrylonitrile), vinylpyridines, chloroethylene, fluoroethylene, chloroprene, vinyl acetate, allyl acetate, allyl chloride, allylfluoride, allyl cyanide, allyl alcohol, diallyl ether, allylethyl ether, vinyl ethers and vinyl esters, vinyl amines and vinyl amides, vinyl sulfides, vinylsilanes, divinyl zinc, trivinylaluminium, divinylmagnesium, trivinylboron, acrylic acid, its esters and amides, and methacrylic acid, its esters and amides; di-substituted ethylenes, e.g. 1 ,2- and 1 ,1 -diphenylethylene, 1 ,2- and 1 , 1 -dichloroethylene; tri-substituted ethylenes, e.g. triphenylethylene, trichloroethylene, trifluoroethylene.; and tetra- substituted ethylenes, e.g. tetraphenylethylene, tetracyanoethylene, tetrachloroethylene, tetrafluoroethylene.

The alkene is present in the composition in an amount of at least 1 ppm, preferably at least 0.001 wt%, more preferably at least 0.0025 wt%, even more preferably at least 0.005 wt%, even more preferably at least 0.01 wt%. even more preferably at least 0.2 wt%, even more preferably at least 0.3 wt%, and most preferably at least 0.5 wt%.

The alkene is present in the composition in an amount of not more than 20 wt%, preferably not more than 10 wt%, more preferably not more than 5 wt%, and most preferably not more than 1 wt%.

These weight percentages are all based on the weight of the entire composition. Dialkyi zinc has the formula R ₂ Zn, in which R denotes an alkyl group. This alkyl group preferably has 1 -50 carbon atoms, more preferably 1 -10 carbon atoms, and most preferably is ethyl. Other compounds that can be present in the composition according to the present invention include other organometallic compounds and solvents.

Examples of suitable organometallic compounds are diethylaluminium chloride, triethylaluminium, and other aluminium organics.

Examples of suitable solvents are aromatic and aliphatic hydrocarbons, ethers, and amines. Specific examples of suitable solvents are n-hexane, cyclohexane, n- heptane, n-octane, n-decane, n-dodecane, n-tetradecane, 2-methylhexane, 3- methylhexane, 2,2-dimethylpentane, 2,2,3-trimethylbutane, 3-ethylpentane, decahydronaphthalene, benzene, toluene, xylene, methylnaphthalene, diethylether, THF, dioxane, and triethylamine.

The composition according to the present invention is prepared by adding the alkene to liquid dialkyi zinc or a solution of dialkyi zinc, or vice versa, in the absence of air. Alkenes can be used in the production of dialkyi zinc to reduce fouling during its production process by suppressing thermal decomposition of the dialkyi zinc during distillation.

Dialkyi zinc is generally prepared by reacting zinc dihalide (e.g. ZnCI ₂ ) with trialkyl aluminium to form both dialkyi zinc and dialkyi aluminium halide. Dialkyi zinc can be removed from the resulting reaction mixture by distillation. This process has been disclosed in various documents, e.g. US 3,124,604 and EP 2 223 024. The reaction is generally performed at temperatures of 20-100°C, preferably 20-70°C. In the process according to the present invention, the alkene is added either (i) to the reaction mixture comprising zinc halide and/or dialkyi zinc, either before or after completion of the formation of the dialkyi zinc, or (ii) to dialkyi zinc prior to or during the distillation.

Various alkenes can be used in this process. In one embodiment, the alkene has a boiling point within about 5°C of the boiling point of the dialkyi zinc. Such alkenes prevent dialkyi zinc decomposition in vapours as well as in the bottoms. The boiling points of dialkyi zincs are generally in the range 40-150°C. For instance, the boiling point of diethyl zinc is 1 18 °C. It should be noted that the term "boiling point" in this specification refers to the boiling point at atmospheric pressure.

In another embodiment, if the presence of the alkene in the final dialkyi zinc product is undesired, the use of an alkene with a significantly higher (at least 5°C higher) or significantly lower (at least 5°C lower) boiling point is desired.

The use of alkenes with such lower boiling points also prevents dialkyi zinc decomposition in vapours; whereas the use of alkenes with such higher boiling points reduces decomposition of dialkyi zinc in the bottoms.

The liquid composition according to the present invention finds use in various industries, including the polymerization industry, nuclear industry, electronics industry, and for the manufacture of solar cells, semiconductor devices, and pharmaceuticals. The alkene not only stabilizes the liquid compositions according to the present invention, but also reduces zinc formation during processes in which this composition is used as DEZ source.

EXAMPLES

Examples 1 -21

Thermal stability tests were conducted as follows. In a glove box under nitrogen atmosphere (<2 ppm oxygen), a 10 ml vial was filled with 3 ml diethyl zinc (DEZ; 3 ml) and optionally alkene and the vial was closed with a cap with a Teflon coated membrane. The vials were covered by aluminium foil in order to prevent light- induced decomposition. The vials were heated in an oil bath at 80°C for 24 hours. After cooling down to room temperature, the samples were examined visually for solids formation.

The results are presented in the Table below.

Experiment alkene Alkene Appearance after ^≥ 20h content at 80°C

1 (comp.) Lumps of solids (5 mm diameter) and Zn mirror on the vial wall

2 cyclopentene 0.5 wt% Transparent liquid with a very small amount of solids

3 cyclopentene 0.6 wt% Transparent liquid with a very small amount of solids

4 cyclohexene 0.5 wt% Transparent liquid with a very small amount of solids

5 cyclohexene 0.6 wt% Transparent liquid with a very small amount of solids

6 1 ,5-cyclooctadiene 0.6 wt% Lower amount of solids than in DEZ alone 1 -hexene 0.6 wt% Lower amount of solids than in DEZ alone

3-heptene 0.6 wt% Lower amount of solids than in DEZ alone trans-4-octene 0.5 wt% Lower amount of solids than in DEZ alone

1 -octadecene 0.5 wt% Lower amount of solids than in DEZ alone trans,trans-1 ,4-diphenyl-1 ,3- 0.5 wt% Transparent liquid with a butadiene very small amount of solids

1 ,7-octadiene 0.5 wt% Lower amount of solids than in DEZ alone

1 ,2,3,4,5- 0.5 wt% Transparent liquid with a pentamethylcyclopentadiene very small amount of solids

1 ,4-cyclohexadiene 0.5 wt% Transparent liquid without solids isoprene 0.5 wt% Transparent liquid with a very small amount of solids

1 ,6-diphenyl-1 ,3,5- 0.5 wt% Transparent liquid without hexatriene solids 17 cyclooctatetraene 0.5 wt% Transparent liquid without solids

18 1 -methyl- 1 ,4 0.5 wt% Transparent liquid without cyclohexadiene solids

19 1 -methyl-1 ,4 0.01 wt% Transparent liquid without cyclohexadiene solids

20 2,5-norbornadiene 0.5 wt% Lower amount of solids than in DEZ alone

21 cycloheptene 0.5 wt% Lower amount of solids than in DEZ alone

The tests were repeated using different concentrations of cyclohexene: 0.05, 0.1 , 0.5, 1 , and 2 wt%. The samples with 0.5, 1 , and 2 wt% cyclohexene remained clear after heating at 80°C for 24 hours, while the samples with 0.1 wt% or lower showed some solid formation, although less than in neat DEZ. Similar results were obtained with cyclopentene.

Different concentrations of 1 -methyl-1 ,4 cyclohexadiene - 0.001 , 0.01 , 0.05, 0.1 , 0.5 wt% - were tested for longer time. The sample with 0.5 wt% 1 -methyl-1 ,4 cyclohexadiene remained transparent after 2.5 weeks at 80°C. After 3 days at 80°C the sample with 0.001 wt% had less solids than neat DEZ.

Examples 22-24

Solids were filtered off from crude DEZ with a fine fritted filter flask. The clear crude DEZ solution was kept in a bottle wrapped with aluminium foil to block out the light. A 250 ml 3-neck round bottom flask equipped with a thermocouple and a magnetic stirring bar was used for the experiments. The typical charges for the experiments were 100 g filtered crude DEZ solution and 5 g alkene for each run. The reaction mixtures were heated at 1 10°C for 24 hours. During the entire experiment, the 250 ml reaction flask was wrapped with purple rags to block out the light. After this heating, the reaction mixtures were cooled down to room temperature and carefully decanted. The gray solids that had been formed were washed three times with heptanes and dried overnight in the glovebox.

The Table below lists the amount of solids formed during the experiments. It is clear that the addition of an alkene, more preferably a cycoalkene, results in reduced solids formation.