Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-12-05
2002-08-20
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
Reexamination Certificate
active
06437198
ABSTRACT:
The invention relates to a process for preparing alkali metal alkoxides, especially tertiary alkoxides such as sodium tert-butoxide.
The preparation of alkali metal alkoxides (also called alkali metal alcoholates) by reacting alkali metals with alcohols is common knowledge. In this reaction the chain length and the structure of the alcohol have a decisive influence on the reaction rate. The reaction rate decreases as the chain becomes longer and as the degree of branching in the alcohols goes up. Primary alcohols react very rapidly, whereas tertiary alcohols are extremely unreactive. The reaction of tertiary alcohols generally takes from several hours to several days.
A further factor is that, during the reaction, the saturation concentration of the respective alkoxide in the alcohol is frequently exceeded. The product precipitates and incrusts the alkali metal, so hindering it from further reaction. This is especially the case when the temperature is insufficient to melt the alkali metal and to allow its fine dispersion by stirring.
The low reaction rate causes problems in the implementation of the reaction. The achievable space-time yields are low, leading ultimately to high costs.
When the alkoxide is prepared, up to 3 mol of alcohol are bound as alcohol of crystallization per mole of alkoxide, depending on the preparation conditions. In some cases these alcohol-alkoxide complexes only crystallize out when the reaction is conducted in an inert solvent. As a result of the preparation-tied annexing of the alcohol of crystallization, the alkoxide becomes insoluble in numerous solvents. The alcohol of crystallization is difficult to eliminate from the alkoxides, and this may lead to unwanted side reactions in subsequent reaction steps. The aim is therefore to prepare alkoxides free from alcohol of crystallization within very short reaction times.
Various processes have been proposed for preparing alkali metal alkoxides, especially tertiary alkali metal alkoxides which are free from alcohol of crystallization, with a sufficient reaction rate.
DE-A 23 33 634 describes a process for preparing alkali metal and alkaline earth metal alkoxides which are free from alcohol of crystallization and are soluble in inert solvents by reacting alcohols such as iso alcohols, carbinols, secondary, tertiary and primary alcohols with alkali metals or alkaline earth metals in equimolar amount or in excess. The reaction takes place in an inert solvent under superatmospheric pressure and at temperatures at which, under atmospheric pressure, alcohol of crystallization would be eliminated. Since within this temperature/pressure range the alkali metal is in molten form it is easy to disperse, thereby achieving an increased reaction rate, and it can be added in fairly large pieces. Nevertheless, the reaction times are relatively long. The super-atmospheric pressure necessitates the use of pressure apparatus, which entails additional costs. The excess of metal employed with preference leads, after two or more reactions, to an accumulation of impurities, which may disrupt the reaction and which necessitate cleaning operations.
DE-C 26 12 642 diskloses a process for preparing alkali metal alkoxides which are free from alcohol of crystallization and are soluble in inert solvents by reacting tertiary alcohols such as tert-butyl alcohol and tert-amyl alcohol with stoichiometric amounts of alkali metal. The reaction is conducted in an inert solvent at a temperature above the melting point of the alkali metal and below the elimination temperature of the alcohol of crystallization. In order to increase the reaction rate the alkali metal is in dispersed form (particle size <100 &mgr;m). Here again, the reaction of tert-butanol, for example, must be conducted under superatmospheric pressure.
DD 298 502 describes a process for preparing alkali metal alkoxides which are free from alcohol of crystallization, by reacting alcohols, including tertiary alcohols, preferably in a slight excess, with alkali metals in an inert solvent. The reaction takes place at a temperature at which the alkali metal is in molten form and the alcohol is in vapor form. The alcohol is continuously recondensed and recycled to the reaction mixture.
JP-A 05 170680 (=DW93/252679) diskloses a process for preparing sodium tert-butoxide which is free from alcohol of crystallization by reacting tert-butyl alcohol with sodium, with the addition of from 5 to 15% by weight of an inert solvent, at a temperature of from 130 to 135° C. In this process the molten sodium is sprayed into the reaction mixture. Excess alcohol and solvent are removed by distillation. This process is highly complex. Moreover, the nozzles that are required are easily blocked, so that the process is susceptible to faults.
EP-A 0 749 947 diskloses a continuous process for preparing C
4
to C
8
sodium alkoxides. In this process a dispersion of sodium in an inert solvent is reacted at elevated temperature (from 100 to 140° C.) with from 0.4 to 0.6 times the molar amount of alcohol. From the resultant two-phase reaction mixture the upper phase, containing inert solvent and alkoxide, is decanted off and the lower phase, containing excess sodium, is admixed with fresh sodium and reacted again. A disadvantage of this process is that the reaction product has to be decanted off, which is awkward.
All of the abovementioned processes require additional high-boiling inert solvent. The removal of the solvent is generally laborious and, furthermore, is incomplete in the majority of cases. These additional impurities may be a disruption if the alkoxides are used, for example, in pharmaceutical syntheses. Furthermore, the use of an additional solvent gives rise to further costs for the purification of the solvent, for storage tanks and supply lines, etc. The alcohols obtained are normally used further directly as solutions in the corresponding inert solvents. To obtain solid alkoxides it is necessary to transfer the solutions to a drier, for example, and to free them from the solvent.
EP-A 0 192 608 describes a process for preparing alkali metal alkoxides of tertiary alcohols by reacting an alkali metal with a tertiary alcohol without adding inert solvents. In this case the hot alcohol is added with stirring to the molten alkali metal. The alcohol is employed in a 3-6-fold, preferably a 5-fold, molar excess. This process has the disadvantage that alcohols having boiling points below the melting point of the alkali metal that is employed cannot be reacted at a sufficient reaction rate, since the solid alkali metal cannot be dispersed adequately in the solvent. The alkali metal alkoxides obtained are used further directly in alcoholic solution.
It is an object of the present invention to provide a process for preparing alkali metal alkoxides which requires no additional high-boiling solvents and in which alcohols, especially slow-to-react alcohols with boiling points below the melting point of the alkali metal that is employed, such as tert-butanol, can be reacted completely with alkali metals. The reaction should take place very rapidly and under atmospheric pressure, and the alkali metal alkoxides should be obtained free from alcohol of crystallization. Moreover, it should be made possible to obtain the alkali metal alkoxides in solid form without great apparatus expenditure.
We have found that this object is achieved by a process for preparing alkali metal alkoxides by reacting alkali metals with alcohols in the presence of a catalyst.
The process of the invention allows rapid and complete reaction even of slow-to-react alcohols, such as tertiary alcohols, at below the melting point of the respective alkali metal under atmospheric pressure. The use of high-boiling solvents and expensive pressure apparatus is unnecessary. As a result, the process provided is cost-effective, economic, and simple to carry out.
The catalysts employed are generally solid catalysts, preferably in the form of their alcoholic solutions. It is preferred to employ transition metal salts.
Particularly suitable t
Bender Hans-Jürgen
Friedrich Holger
Guth Josef
Letzelter Thomas
Schweinzer Jürgen
BASF - Aktiengesellschaft
Keil & Weinkauf
Siegel Alan
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