Patent GB-779873-A (GB)
Title: The manufacture of aluminium hydrocarbons
IPC: C01F7/54
Filed: 1953-07-28
Abstract: The invention comprises organo-aluminium fluorides of the general formul  RAlF2 and R2AlF, wherein R represents an alkyl or aryl radical, e.g. an alkyl radical containing up to 4 carbon atoms or the phenyl radical, and a process for the preparation of aluminium hydrocarbons of the general formula AlR3, wherein R represents an alkyl or aryl radical, by reacting at an elevated temperature on alkyl- or arylaluminium chloride, bromide or iodide with an alkali metal fluoride or with an alkali metal aluminium fluoride and an alkali metal fluride.  The above process is based on the following illustrative steps in which an organo-aluminium chloride and sodium fluoride are used as reactants:  (1) AlR2Cl + NaF --> AlR2F + NaCl (2) AlRCl2 + 2NaF --> AlRF2 + 2NaCl  (3) 3AlR2Cl + Na3AlF6 --> 3AlR2F + AlF3 + 3NaCl  wherein R represents an alkyl or aryl radical.  At this stage the alkyl- or aryl-aluminium fluorides may be recovered in pure form, e.g. by vacuum distillation.  These alkyl- and arylaluminiumfluorides disproportionate at elevated temperatures in the presence of suitable proportions of alkali metal fluoride into complex alkali metal aluminium florides such as cryolite or potassium cryolite, and aluminium trialkyls or triaryls as illustrated in the following equations:  (4) 3AlR2F + 3NaF --> 2AlR3 + Na3AlF6  (5) 3AlRF2 + 6NaF --> AlR3 + 2Na3AlF6  The corresponding potassium salts may be used in any of the reactions (1) to (5) illustrated above. The production of the aluminium trialkyls and triaryls can be coupled, therefore, with the production of cryolite (or potassium cryolite) or aluminium fluoride, or cryolite (or potassium cryolite) and aluminium fluoride.  Thus if an alkali metal fluoride is to be used as the sole reactant, it is possible to join together the steps illustrated by equations (1) and (2) on the one hand and by equations (4) and (5) respectively on the other hand in one operation without separating the aluminium alkyl (or aryl) fluoride in between.  In a second charge it is possible to use the complex alkali metal aluminium fluoride formed as illustrated in equation (4) or (5) in a reaction illustrated by equation (3). In this case, if aluminium fluoride itself is to be obtained as the by-product, it is necessary to separate the organo-aluminium fluoride at the end of this step, e.g. by solvent extraction with inert solvents and filtration or by distillation under vacuum. Step (4) or (5) then follows after the addition of alkali metal fluoride to form more complex alkali metal aluminium fluoride which may then be utilized in a reaction illustrated by equation (3).  If the complex alkali metal fluoride is to be the byproduct, the alkyl- or aryl-aluminium halide must be reacted with two mols. of alkali metal fluoride per gram atom of aluminium attached halogen in the combined reactions illustrated by equations (1) and (4) or by equations (2) and (5).  If an excess of aluminium fluoride is used a complex may be formed between the aluminium hydrocarbon product of the formula AlR3 and the aluminium fluoride, e.g. a complex of the formula NaAlR3F, and this complex may be decomposed by the addition of aluminium fluoride with the formation of the desired aluminium hydrocarbon and alkali metal aluminium fluoride.  The stage of the above process illustrated by equations (4) or (5) proceed by way of complex compounds of alkali metal fluoride and alkyl- or aryl-aluminium fluoride as illustrated in the following equations (for equation 4):  (6) 3AlR2F + 3NaF --> 3NaAlR2F2  (7) 3NaAlR2F2 --> 2AlR3 + Na3AlF6  and (for equation 5): (8) AlRF2 + NaF --> NaAlRF3  (9) 3NaAlRF2 + 3NaF --> AlR3 + 2Na3AlF6 The alkali metal aluminium organo-fluoride, e.g. as illustrated in equations (7) and (9) above, is preferably decomposed at a temperature of 150 DEG  to 200 DEG  C.  If alkyl- or aryl-aluminium sesquihalides (the halide being chlorine, bromine or iodine) are used for the preparation of the aluminium hydrocarbons, it is preferable to convert the sesquihalide into dialkyl- or diarylaluminium monohalide by reaction with trialkylor triaryl-aluminium which has been produced in a previous process. This reaction is illustrated in the following equation:  (10) AlC2H5Cl2 + Al(C2H5)2Cl + Al(C2H5)3 --> 3Al(C2H5)2Cl  The aluminium hydrocarbon resulting from the above processes may be separated by distillation or solvent extraction from the alkali metal aluminium fluoride and, if present, the alkali metal halide.  A solvent or suspension medium may be used to carry out the above processes, e.g. hexane, benzene, toluene, chlorobenzene, o - dichlorobenzene chlorinated diphenyl, hydrogenated diesel oil, or phenanthrene may be used.  If all stages are carried out in the presence of a solvent, the solvent chosen preferably has a boiling point which differs considerably, e.g. by 50-100 DEG C., from that of the trialkyl or triaryl aluminium compound to be formed.  Increased yields of aluminium hydrocarbons may be obtained by removing the resulting aluminium hydrocarbon as rapidly as possible from the reaction zone such as by combining the thermal decomposition which is illustrated by equation (7) and the separation of the aluminium hydrocarbon in a single process so that the aluminium hydrocarbon formed remains in the heated reaction zone for as short a time as is possible, e.g. by distilling off the aluminium hydrocarbon formed under reduced pressure during the thermal decomposition-preferably at a temperature between 200 DEG  and 300 DEG  C. under high vacuum. This particular modification may be carried out without the use of a vacuum or only a slight vacuum by passing a heated insert gas stream, e.g. heated to 200 DEG  to 300 DEG  C., preferably the superheated vapour of an inert liquid such as benzene, butane, pentane or hexane, through the reaction mixture as a heat transmitter and the resulting aluminium hydrocarbon is separated from the heat carrier e.g. by condensation.  A moving bed is useful for this modification particularly if the process is to be carried out in a continuous manner.  A further modification of the process for the preparation of the aluminium hydrocarbons is to carry out the process in two or more stages, the reaction being interrupted before it is complete and when the speed of the reaction has become too slow.  At this stage the organic aluminium compounds are separated from solid matter, e.g. by distillation or by solvent extraction, and reacted with a further quantity of alkali metal aluminium fluoride, and the solid residue is treated with fresh alkylor aryl-aluminium halide to complete the conversion to aluminium fluoride and alkali metal halide.  In the examples the following compounds are prepared: trimethyl-, triethyl, tributyl- and triphenyl-aluminium, diethylaluminium fluoride, ethylaluminium difluoride and the complex sodium aluminium dimethyl fluoride.  Specifications 767,400, 772,174 and 777,701 are referred to.ALSO:Alkali metal aluminium fluorides of the formula M3AlF6, wherein M represents an alkali metal, and aluminium fluoride, are obtained as by-products in a process for the preparation of aluminium hydrocarbons of the general formula AlR3, wherein R represents an alkyl or aryl radical by the reaction at an elevated temperature or alkyl- or aryl-aluminium chloride, bromide or iodide with an alkali metal fluoride or with an alkali metal aluminium fluoride and an alkali metal fluoride. The above process is based on the following illustrative steps in which an organo-aluminium chloride and sodium fluoride or sodium aluminium fluoride are used as reactants:-(1) AlR2Cl + NaF --> AlR2F + NaCl (2) AlRCl2 + 2NaF --> AlRF2 + 2NaCl (3) 3AlR2Cl + Na3AlF6 --> 3AlR2F + AlF3 + 3NaCl wherein R represents an alkyl or aryl radical.  The aluminium fluoride may be recovered at the completion of a reaction of the type illustrated in equation (3) e.g. by removing the organo-aluminium fluorides by vacuum distillation or solvent extraction.  The alkyl- or aryl-aluminium fluorides thus formed disproportionate at elevated temperatures in the presence of suitable proportions of alkali metal aluminium fluorides and the desired aluminium hydrocarbons as illustrated in the following equations:-(4) 3AlR2F + 3NaF --> 2AlR3 + Na3AlF6 (5) 3AlRF2 + 6NaF --> AlR3 + 2Na3AlF6 In the above equations the sodium fluoride may be replaced by any other alkali metal fluoride such as potassium fluoride.  Thus the production of aluminium hydrocarbons can be coupled with the production of cryolite (or potassium cryolite) or aluminium fluoride, or cryolite (or potassium cryolite) and aluminium fluoride.  If an alkali metal fluoride is used as the sole reactant, it is possible to join together the steps illustrated by equations (1) and (2) on the one hand and by equations (4) and (5) respectively on the other hand in one operation without separating the aluminium alkyl (or aryl) fluoride in between.  In a second charge it is possible to use the complex alkali metal aluminium fluoride formed as illustrated in equation (4) or (5) in a reaction illustrated by equation (3). Step (4) or (5) then follows after the addition of alkali metal fluoride to form more complex alkali metal aluminium fluoride, which may then be utilized in a reaction illustrated by equation (3).  If the complex alkali metal fluoride is to be the byproduct, the alkyl- or aryl-aluminium halide must be reacted with two mols of alkali metal fluoride per gram atom of aluminium attached halogen in the combined reactions illustrated by equations (1) and (4), or by equations (2) and (5).  If an excess of aluminium fluoride is used a complex may be formed between the aluminium hydrocarbon and the aluminium fluoride e.g. a complex of the formula NaAlR3F, wherein R has the above significance, and this complex may be decomposed by the addition of aluminium fluoride with the formation of aluminium hydrocarbon and alkali me