Verfahren zur Herstellung von Tetraalkylblei

摘要

Lead alkyl compounds are made using a lead anode and an electrolyte containing a Grignard reagent, e.g. EtMgCl, alkyl chloride, and an ether of higher boiling point than the lead alkyl, e.g. the dibutyl or hexyl ethyl ether of diethylene glycol. The electrolytic product is treated with HCl forming two layers, the copper containing the lead alkyl, high boiling ether, and any other solvent, and the lower one containing MgCl2 solution and some solvent. These are then separated, and distilled to recover the product and individual solvents. Alternatively the product may be freed from light solvent components when separate layers are formed, and the lead alkyl layer after some extraction and concentration of the lead compound, recycled to the electrolysis stage. Tetrahydrofuran or benzene may be used as extracting solvents, which are of lower boiling point than lead tetraalkyl. As a further modification these extraction solvents may be added to the electrolyte, and lower boiling members removed from the electrolyte product by "flashing off" at low pressure. Grignard reagent is formed in a vessel 11 by adding Mg metal, methyl or ethyl chloride, benzene or tetrahydrofuran, and the diethylene glycol ether. The mixture passes to the electrolyte cell 19, and additional methyl chloride is charged during electrolysis. The cell contains lead anodes and stainless steel cathodes, and the electrolyte is cycled externally through a cooler 31. Reaction is effected at 41 DEG C. and 3.1 p.s.i.g. After 11 hours 95% of the Grignard metal is connected to the lead alkyl. The product passes to a cooler 33 and then to a separating vessel 36 to which dilute HCl is added, mixture being effected in a turbine mixer, e.g. in the line 34. The lower aqueous layer containing some solvent is drawn off and solvent recovered in an azeotroping tower 41. The upper phase is distilled in a vacuum tower 43, the overhead stream containing tetrahydorfuran, some benzene, and traces of other products, and is returned as a reflux to the vacuum tower 43. This is connected to a drying tower 55 and other units to recover and separate the components as necessary. The bottoms containing some benzene, all the glycol ether and lead alkyl, passes to a steam distillation tower 83, from which the lead alkyl and benzene comes off the top, and the glycol ether forms the main constituent of the bottom. These two fractions are further treated in distillation and drying towers to separate the constituents. The progress of the electrolyte stage may be estimated by conductivity, tests details of which are given.