US 2931820 A
Description (OCR text may contain errors)
PRODUCTION OF ALUMINIUM ALKYLS William Barclay and Peter Smith, Norton-on-Tees, England, assignors to Imperial Chemical Industries L mited, London, England, a corporation of Great Britain No Drawing. Application May 16, 1958 I Serial No. 735,684
This invention relates to the production of aluminium alkyls.
British patent specification No. 762,200 describes a process for the production of an aluminium alkyl which comprises a-first step of reacting aluminium with at least one primary alkyl halide in the presence of an inert solvent to form a sesquihalide and a second step of reacting the sesquihalide with an alkali metal in the presence'of an'in'ert solvent toform the desired aluminium alkyl.
In this process it is preferred that the first step is carried out at a temperature not exceeding 50 C. and that the second step is carried out at a temperature within the range 100 to 180 C.
The final reaction product of the above process consists of a Solution of an aluminium alkyl and insoluble material comprising finely divided aluminium and an alkali metal halide. The solution and the insoluble material are separated and the insoluble material may then be recycled to the first step of the process and the aluminium it contains reacted with further quantities of the primary alkyl halide. The alkali metal halide introduced in this way into the first step of the process may be separated from the sesquihalide solution by filtration.
Co-pending application U.S. Serial No. 714,948, filed February 13, 1958, describes a modification of the process of British patent specification No. 762,200 in which when the alkyl halide is an alkyl chloride, the reactio'n of the first step of the process is initiated by an alkyl bromide r iodide.
We have now found that the efiiciency of the above process can be considerably improved if the aluminium precipitated in the second step of the process is not separated from the solution of the aluminium alkyl and recycled to the first step of the process but is reacted in situ and in the absence of added aluminium, with a primary alkyl halide to form a sesquihalide which is then reacted with an alkali metal to give additional quantities of the aluminium alkyl.
In the absence of added aluminium the precipitated aluminium is converted into a sesquihalide rapidly and smoothly at temperatures of up to 250 C., no reaction initiator being necessary even when the primary alkyl halide is a primary alkyl chloride. As a result a high conversion of aluminium to aluminium alkyl can be achieved in a considerably less time than in the process of British patent specification No. 762,200. Further, since similar or the same temperatures can be used in the productio'n and dehalogenation of the sesquihalide much less cooling and reheating is required than in the recycle process of British patent specification 762,200. The filtration of alkali metal halide from the sesquihalide solution as described in British patent specification 762,200 is also eliminated.
According to the present invention there is provided a process for the production of an aluminium alkyl by reacting aluminium with a primary alkyl halide in the pres ence of an inert solvent and then reacting the solution of halide as hereinafter defined to form an alkyl aluminium sesquihalide and then reacting this alkyl aluminiums'es quihalide in situ with an alkali metal to give a second reaction product containing additional quantities of the aluminium alkyl.
It will .be appreciated that the second reaction product' will also contain aluminium formed in the dehalogenation of the sesquihalide. The process of the iIIVEHlIlOH thCIC fore, may be repeated a number of times to increase the conversion of aluminium into the aluminium alkyl. In; practice one repetition is sufiicient to give a high conver-' sion, for example about 87-88%, in a reasonable time.
After the completion of the process the solution of the aluminium alkyl in the inert solvent may be separated from insoluble matter by, for example, filtration. If de-' sired the aluminium alkyl may be' recovered by fractional distillation though this is often unnecessary."
Primary alkyl halides suitable for use in the process of the invention are defined as methyl chloride, bromide and iodide, ethyl chloride, bromide and iodide, propyl bromide and iodide, n-butyl bromide and iodide and isobutyl iodide.
The process is of particular value in the production of aluminium trimethyl and aluminium triethyl using methyl chloride or ethyl chloride respectively as the primary alkyl halide.
The temperature at which the process of the invention is conducted may be between 0 C. and 250 C. It is preferred that the temperature is within the range 50 C to 150 C. for example between 130 C. and 140 C.
Solvents suitable for use in the process are those which dissolve the organic reactants and organic products and which are inert under the reaction conditions employed. When the primary alkyl halide is gaseous at normal temperatures and pressures it is particularly desirable that it should be easily soluble in the solvent.
Preferably the solvent should be free from aromatic compounds especially in the formation of the sesquihalide. It is preferred that the solvent is a parafiinic or saturated alicyclic hydrocarbon.
Any alkali metal or alkali metal alloy may be used in the process of the invention. It is very convenient to use sodium or a sodium/ potassium alloy.
Air and moisture should be excluded from the apparatus in which the reaction is conducted.
Example 1.5 kg. ethyl bromide were added to a stirred suspension of 3.9 kg. aluminium powder in 15.8 kg. decalin contained in a closed reactor. After stirring for 1 hour the contents of the reactor were heated to C. and 13.8 kg. ethyl chloride added under pressure in 0.5 kg. portions at a rate sufficient to maintain the temperature at to C.
The reactor was then vented through a condenser and molten sodium equivalent to the halogen present (determined by analysis) added at a rate sufficient to maintain the temperature at 130 to 140 C. After the addition of the sodium was complete the temperature was maintained for a further 3 hours. This completed the first stage of the process. The reaction product comprised precipitated aluminium and sodium chloride and a solution of aluminium triethyl.
The reactor vent was then closed and 7.4 kg. ethyl chloride added under pressure at a rate suificient to main- Patented Apr. 5, 1 ,6
tain the temperature at 130 C. to 140 C. The reactor vent was then opened and molten sodium (50% of the weight previously used) added to the contents of the reactor at a rate sufficient to maintain the stated temperature which after the addition of sodium was completed, was maintained for a further 3 hours.
The procedure. described in the foregoing paragraph was then repeated using half the quantities of ethyl chloride and sodium stated in the said paragraph.
The reaction product was then cooled to 30 C. filtered and the filter cake washed three times with litres of decalin, the washings being added to the filtrate. This washing of the filter cake was repeated but the washings were now collected separately for use in the reaction of another batch of aluminium.
' The total reaction time of the process was 70 hours and the yield of aluminium triethyl was 12.5 kg. representing an overall yield of 90%. This yield was 75% greater than that obtained in the first stage of the process whereas the total reaction time was only 25% longer.
1. In a process for the production of an aluminium alk'yl by reacting aluminium with a primary alkyl halide in the presence of an inert solvent and then reacting the solution of the alkyl aluminium sesquihalide thus formed with an alkali metal to give a reaction product comprising aluminium and a solution of an aluminium alkyl the step of reacting at a temperature above C. the said reaction product in the absence of added aluminium with a primary alkyl halide selected from the group consisting of methyl chloride, methyl bromide, methyl iodide, ethyl chloride, ethyl bromide, ethyl iodide, pro'pyl bromide, propyl iodide, n-butyl bromide, n-butyl iodide, isobutyl io'dide, to form an alkyl aluminium'sesquihalide and then reacting this alkyl aluminium sesquihalide in situ with an alkali metal to give a second reaction product containing additional quantities of the aluminium alkyl.
2. A process as claimed in claim 1 in which the reaction product comprising aluminium is reacted to produce additional quantities of the aluminium alkyl at a temperature within the range 50 to C.
3. A process as claimed in claim 1 in which the alkali metal is sodium.
4. A process as claimed in claim 1 in which the inert solvent is a hydrocarbon selected from the group consisting of parafiinic and saturated alicyclic hydrocarbons.
France Apr. 23, 1956 Belgium July 22, 1955