Alkylaluminium

Unfortunately, investigations with ionic liquids containing high amounts of AlEtCl2 showed several limitations, including the reductive effect of the alkylaluminium affecting the temperature stability of the nickel catalyst. At very high alkylaluminium concentrations, precipitation of black metallic nickel was observed even at room temperature. 

For this specific task, ionic liquids containing allcylaluminiums proved unsuitable, due to their strong isomerization activity [102]. Since, mechanistically, only the linkage of two 1-butene molecules can give rise to the formation of linear octenes, isomerization activity in the solvent inhibits the formation of the desired product. Therefore, slightly acidic chloroaluminate melts that would enable selective nickel catalysis without the addition of alkylaluminiums were developed [104]. It was found that an acidic chloroaluminate ionic liquid buffered with small amounts of weak organic bases provided a solvent that allowed a selective, biphasic reaction with [(H-COD)Ni(hfacac)]. 

The reaction takes place at low temperature (40-60 °C), without any solvent, in two (or more, up to four) well-mixed reactors in series. The pressure is sufficient to maintain the reactants in the liquid phase (no gas phase). Mixing and heat removal are ensured by an external circulation loop. The two components of the catalytic system are injected separately into this reaction loop with precise flow control. The residence time could be between 5 and 10 hours. At the output of the reaction section, the effluent containing the catalyst is chemically neutralized and the catalyst residue is separated from the products by aqueous washing. The catalyst components are not recycled. Unconverted olefin and inert hydrocarbons are separated from the octenes by distillation columns. The catalytic system is sensitive to impurities that can coordinate strongly to the nickel metal center or can react with the alkylaluminium derivative (polyunsaturated hydrocarbons and polar compounds such as water). 

A similar catalytic dimerization system has been investigated [40] in a continuous flow loop reactor in order to study the stability of the ionic liquid solution. The catalyst used is the organometallic nickel(II) complex (Hcod)Ni(hfacac) (Hcod = cyclooct-4-ene-l-yl and hfacac = l,l,l,5,5,5-hexafluoro-2,4-pentanedionato-0,0 ), and the ionic liquid is an acidic chloroaluminate based on the acidic mixture of 1-butyl-4-methylpyridinium chloride and aluminium chloride. No alkylaluminium is added, but an organic Lewis base is added to buffer the acidity of the medium. The ionic catalyst solution is introduced into the reactor loop at the beginning of the reaction and the loop is filled with the reactants (total volume 160 mL). The feed enters continuously into the loop and the products are continuously separated in a settler. The overall activity is 18,000 (TON). The selectivity to dimers is in the 98 % range and the selectivity to linear octenes is 52 %. 

Chloroaluminate laboratory preparations proved to be easily extrapolated to large scale. These chloroaluminate salts are corrosive liquids in the presence of protons. When exposed to moisture, they produce hydrochloric acid, similarly to aluminium chloride. However, this can be avoided by the addition of some proton scavenger such as alkylaluminium derivatives. In Difasol technology, for example, carbon-steel reactors can be used with no corrosion problem. 

Kennedy, J. P. and Gillham, J. K. Cationic Polymerization of Olefins with Alkylaluminium Initators. Vol. 10, pp. 1-33. 

Cationic Olefin Polymerization Using Alkyl Halide Alkylaluminium Initiator Systems... 

The particle size depends on the chain length of the aluminium-alkyl group and the concentration of the tri-alkylaluminium compound applied. If mixtures of, e.g., Fe- and Co-carbonyl compounds are used, Fe/Co alloy particles are formed. When the magnetic particles... 

Often a suitable potentiometric indication for Lewis titrations is not available, whereas a conductometric indication can still be applied a well known example is the Bonitz titration29 of triethylaluminium (Et3Al) with an azine, such as isoquinoline, for determination of active alkylaluminium in the precatalysts of the Ziegler synthesis of polyethene or polypropene beyond the titration parameter A of the 1 1 complex, the conductivity suddenly decreases,... 

See Nitromethane Alkylmetal halides See Other ALKYLALUMINIUM HALIDES... 

Accidental use of methanol in place of hexane to rinse out a hypodermic syringe used for a dilute alkylaluminium solution caused a violent reaction which blew the plunger out of the barrel. 

Ethylaluminium diiodide [2938-73-0] EtAlI2 491M, 1975, 153 It ignites in air. See Other ALKYLALUMINIUM HALIDES c2h5aii2... 

Dipropylaluminium hydride [2036-15-9] Pr2AlH HCS 1980, 444 See entry ALKYLALUMINIUM ALKOXIDES AND HYDRIDES C6H15A1... 

See related alkylaluminium alkoxides and hydrides, metal halides... 

Ethoxydiisobutylaluminium [15769-72-9] EtOAl(CH2CHMe2)2 May ignite in air. See entry ALKYLALUMINIUM ALKOXIDES AND HYDRIDES c10h23aio... 

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