The present invention relates to a process for the production of dialkyl zinc and dialkylaluminium halide, a method of reducing the hydride content of trialkyl aluminium, and a trialkyl aluminium-containing formulation.

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

Dialkyl zinc is generally prepared by reacting zinc dihalide (e.g. ZnCI ₂ ) with trialkyl aluminium to form both dialkyl zinc and dialkyl aluminium halide. Dialkyl 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 other product, dialkyl aluminium halide, is also valuable and finds application as a co-catalyst in alkene polymerization. For these applications, dialkyl aluminium halide is desired to be as pure as possible.

Trialkyl aluminium is the product obtained from the reaction of aluminium with hydrogen and alkene, and as a result it generally contains hydrides such as R ₂ AIH, RAIH ₂ , and AIH ₃ as impurities; the main impurity being R ₂ AIH. The use of a trialkyl aluminium with a high hydride concentration for the reaction with zinc chloride leads to precipitation of metallic zinc, resulting in reactor fouling and a lower dialkyl zinc yield.

It is therefore desired to reduce the hydride concentration of trialkyl aluminium.

A method to achieve this has been disclosed in WO 2009/133929 and involves the reaction between trialkyl aluminium with a hydride content of 0.40-1.0 wt% and ethylene with a partial pressure of 0.1 -0.6 MPa, at a temperature of 65-95°C, and for a time period of 1 -10 hours.

It is an object of the present invention to provide a method for reducing the hydride concentration of trialkyi aluminium which is more convenient, can be performed at room temperature and atmospheric pressure, and/or results in even lower hydride concentrations.

It has now been found that this object can be met by reacting the trialkyi aluminium with an alkyne.

With this method, the hydride concentration of trialkyi aluminium can be reduced to less than 0.010 wt%, preferably less than 0.008 wt%, more preferably less than 0.005 wt%, and most preferably even less than 0.003 wt%.

The hydride concentration is expressed as wt% AIH ₃ . The hydride concentration is determined by introducing water into a sample - the water will hydrolyze any trialkyi aluminium and any aluminium hydrides - and analyzing any evolved gases (hydrogen, alkane) by gas chromatography. From the gas composition, one can calculate the amount of hydrides that must have been present in the sample. The alkyl groups of trialkyi aluminium is not limited in nature, but alkyl groups with

1 to 5 carbon atoms are generally preferred, 2-5 carbon carbon atoms are even more preferred. The most preferred trialkyi aluminium is triethyl aluminium.

Conventional commercial triethyl aluminium contains about 0.01 to 0.05 wt% hydride.

The term "alkyne" includes monoalkynes, dialkynes, etc. The alkyne preferably has

2 to 200, more preferably 3-200, even more preferably 4-100, even more preferably 4-50, and most preferably 4-18 carbon atoms. Examples of suitable alkynes are acetylene, 1 -propyne, 1 -butyne, 2-butyne, 1 - pentyne, 2-pentyne, 1 -hexyne, 2-hexyne, 3-hexyne, 1 -heptyne, 2-heptyne, 3- heptyne, 1 -octyne, 2-octyne, 3-octyne, 4-octyne, 1 -decyne, 5-decyne, 1 - tetradecyne, 1 ,6-heptadiyne, 1 ,7-octadiyne, 1 -octadecyne, phenylacetylene, diphenylacetylene, 4-ethynylbiphenyl. Terminal alkynes are preferred over nonterminal alkynes.

Also mixtures of alkynes may be used.

Alkynes reduce the hydride content significantly faster than alkenes. As a consequence, they are able to reduce the hydride content at lower temperatures and in a shorter time period.

The alkyne preferably has a boiling point of either significantly below the boiling point of the dialkyi zinc, or significantly above the boiling point of the dialkyi aluminium halide that will result from the process of the present invention. If the products resulting from the process are diethyl zinc and diethyl aluminium chloride, the boiling point of the alkyne preferably lies below 100°C (boiling point of diethyl zinc is 1 18°C) or above 230°C (boiling point of diethylaluminium chloride is 214°C), more preferably below 90°C or above 240°C. In this way, the alkyne can be easily removed by either distillation (if the boiling point is below that of the dialkyi zinc) or by remaining in the bottoms (if the boiling point is above that of dialkyi aluminium halide).

The term "boiling point" in this specification refers to the boiling point at atmospheric pressure.

The trialkyi aluminium is pre-treated with the alkyne under inert atmosphere in a weight ratio trialkyi aluminium : alkyne of at least 50:50, preferably at least 80:20, even more preferably at least 90:10, and most preferably at least 99.7:0.3. A solvent can be present during this pre-treatement. Suitable solvents include aromatic and saturated aliphatic hydrocarbons. Specific examples of suitable solvents are n-hexane, cyclcohexane, 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, and THF.

Pre-treatment of trialkyl aluminum with an alkyne is preferably performed at a temperature in the range 0-130°C, more preferably 10-100°C, and most preferably 20-50°C and for a preferred period of 0.1 -1000 hours, more preferably 1 -100 hours, and most preferably 5-40 hours.

The present invention therefore also relates to a method of reducing the hydride content of trialkyl aluminium by contacting the trialkyl aluminium with an alkyne for a period of 0.1 -1000 hrs at a temperature in the range 0-130°C.

The present invention also relates to a storage stable formulation comprising trialkyl aluminium and an alkyne, more preferably a formulation comprising 5-99.7 wt% of trialkyl aluminium, 0.3-50 wt% of an alkyne with 3-200 carbon atoms, and 0- 94.7 wt% of a solvent.

"Storage stable formulation" is defined in this specification as a formulation which can be stored at 20°C under nitrogen atmosphere (<2 ppm oxygen) for 5 days without any significant change in its chemical or physical constitution, except for the reduction in hydride content. Dialkyi zinc is generally prepared by reacting zinc dihalide (preferably ZnCI ₂ ) with trialkyl aluminium to form both dialkyi zinc and dialkyi aluminium halide. This reaction is preferably performed in a dry, i.e. non-aqueous, inert gas atmosphere. An organic solvent may be present during the reaction. The reaction is preferably performed at a temperature in the range 20 to 100°C, more preferably 30 to 70°C. The amount of trialkyl aluminum is preferably 1 .6 to 2.4 moles, more preferably 1.8 to 2.2 moles per 1 mole of the zinc halide. The reaction is complete when the zinc halide has dissolved in the reaction mixture. This may take about 5 minutes to 15 hours, depending on the reaction conditions. After completion of the reaction, the formed dialkylzinc is distilled from the reaction mixture. Before said distillation, it is preferred to separate and remove any precipitates contained in the reaction product by, e.g., filtration. To prevent thermal decomposition of the dialkyi zinc or dialkyi aluminum halide, it is preferred to perform the distillation under reduced pressure.

After having distilled the dialkyi zinc from the reaction mixture, the residue might be distilled again, also at reduced pressure, in order to remove and purify the dialkyi aluminium halide. Dialkyi zinc has the formula R ₂ Zn, in which R denotes an alkyl group. This alkyl group preferably has 1 -5 carbon atoms, and most preferably is ethyl.

EXAMPLES Comparative Example 1

A vial was filled with 0.46 g 1 -octene and 43.78 g triethyl aluminium with a hydride content of 0.022 wt% under nitrogen atmosphere in a glove box. The vial was kept for 10 days at room temperature, followed by 64 hours at 60°C, and samples were taken at regular time intervals. These samples were analyzed for their hydride content by gas chromatography according to the method described in the specification.

The results are displayed in Table 1. Table 1

Example 2

Vials were filled with different amounts of 1 -decyne and triethyl aluminium (TEAL) with a hydride content of 0.0178 wt% hydride under nitrogen atmosphere in a glove box. These vials were kept for 9 days at room temperature, and samples were taken at regular time intervals. These samples were analyzed for their hydride content as described in Example 1.

The results are displayed in Table 2.

Table 2

Example 3

Vials were filled - under nitrogen atmosphere in a glove box - with 20 g triethyl aluminium (TEAL) with a hydride content of 0.0335 wt% and an amount of aliphatic unsaturated hydrocarbon corresponding to a diethylaluminium hydride/unsaturation mole ratio of 2: 1 . These vials were kept for 9 days at room temperature, and samples were taken at regular time intervals. These samples were analyzed for their hydride content as described in Example 1.

The results are displayed in Table 3.

Table 3

The results in the Table show that alkynes have a higher activity than alkenes and that terminal alkynes perform the best.