Catalytic preparation of alkali metal alkoxides

Details Catalytic preparation of alkali metal alkoxides Catalytic preparation of alkali metal alkoxides

2001-09-28

2003-12-02

Richter, Johann (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C423S180000, C423S192000

Reexamination Certificate

active

06657091

ABSTRACT:

The present invention relates to a process for the catalytic preparation of alkali metal alkoxides by reacting alkali metal amalgam with an alcohol in the presence of a catalyst.
Alkali metal alkoxides (systematic name: “alkali metal alkanolates”) are well known reagents in organic chemistry. They are used where strong bases are required as reactants, and are employed as catalysts in certain reactions. Alkali metal alkoxides produced and used in relatively large amounts are virtually exclusively aliphatic alkoxides of lithium, sodium and potassium having from 1 to 4 carbon atoms in the alkyl radical of the alcohol, in particular lithium, sodium and potassium methoxide, ethoxide, n-propoxide, isopropoxide, n-butoxide and tert-butoxide. A number of methods of preparing alkali metal alkoxides are known. The most widespread are the reaction of the alkali metal with the alcohol so as to liberate hydrogen and the reaction of the alkali metal hydroxide with the alcohol and removal of the water formed as by-product. A process specifically employed for preparing higher alkali metal alkoxides is the reaction of an alkali metal methoxide or ethoxide with a higher alcohol and removal of methanol or ethanol. This latter process and the reaction of alkali metal hydroxide with alcohol and removal of the by-product water are frequently inferior to the direct reaction of alkali metal with alcohol from an economic point of view, since they are comparatively energy-intensive.
The direct reaction of an alkali metal with an alcohol is the simplest method of preparing alkali metal alkoxides. The reactivity of the alkali metals increases in the order lithium, sodium, potassium, rubidium and cesium, and the reactivity of the alcohols decreases with increasing molecular weight of the alcohol and increasing degree of branching of the alkyl radical. The reaction is advantageously carried out using a dispersion of the alkali metal in an inert solvent or using alkali metal amalgam. A general overview of aliphatic alkali metal alkoxides, their preparation and use is given, for example, in Ullmann's Encyclopedia of Industrial Chemistry, Fifth Edition, Volume A
1
, Weinheim 1985, as item 3 under the keyword “Alcohols, Aliphatic”. An overview of the industrial production of alkali metal alkoxides from alkali amalgam and reaction apparatuses used for this purpose is given, for example, in; R. B. MacMullin “By-products of Amalgam-type Chlorine Cell”, Chemical Engineering Progress September 1950, pp. 440-455 , 448.
In the preparation of higher alkali metal alkoxides (which for the purposes of the present invention are alkoxides having at least 3 carbon atoms in the organic radical), the method described by MacMullin, loc. cit., can be employed but is frequently economically unsatisfactory because of low reaction rates. Processes which make a higher space-time yield possible by use of a catalyst have therefore been developed.
Such catalytic methods have been known for a long time. Thus, U.S. Pat. No. 2,069,403 teaches a process for preparing alkali metal alkoxides by reacting alkali metal amalgam with alcohols having up to 4 carbon atoms, in which the reaction is carried out in the presence of a catalyst comprising graphite or iron-chromium alloys which may, if desired, further comprise alloying constituents such as nickel, molybdenum, tungsten or manganese. A specific embodiment of this process and a typical reactor are described in U.S. Pat. No. 2,336,045. Here, the amalgam and the alcohol are passed in countercurrent through the reactor in which the catalyst is present in the form of packing. In these documents, the catalyst is referred to as “electrode”.
In the process of U.S. Pat. No. 2,761,880, the alkali metal amalgam is fed in in the form of a dispersion in countercurrent to the alcohol, with electrode graphite, activated carbon and/or iron turnings additionally being used as catalyst. A preferred catalyst is a mixture of activated carbon with 10-20 of iron turnings. DE-A-973 323 discloses a catalyst comprising 0.1-10% by weight of a metal of the iron group, in particular iron or nickel, on a graphite support. EP-A-177 768 proposes a catalyst comprising heavy metal oxide or oxides, in particular a mixture of nickel oxide and molybdenum oxide, applied to the surface of a particulate anthracite support for preparing alkali metal alkoxides. U.S. Pat. No. 5,262,133 teaches the use of tungsten carbide, iron on carbon supports, iridium, ruthenium or mixtures thereof as catalyst. EP-A-810 193 discloses catalysts comprising carbides and nitrides of chromium, molybdenum or tungsten and also catalysts comprising titanium carbide. In the process of DE-A-198 02 013, the catalysts used comprise transition metal carbides, nitrides or carbonitrides, in particular molybdenum carbide or tungsten carbide, in powder form, and in the process of EP-A-1 018 499 this powder catalyst is suspended by action of ultrasound.
However, the space-time yield is still unsatisfactory in many known processes and the known processes giving a relatively high space-time yield require catalysts which are comparatively expensive because of their short operating life or high price. It is an object of the present invention to find a simpler, more economically satisfactory process which makes possible a very high space-time yield and makes do with an inexpensive catalyst.
We have found that this object is achieved by a process for preparing alkali metal alkoxides by reacting alkali metal amalgam with alcohol in the presence of a catalyst comprising iron having a carbon content of at least 0.3% by weight.
The catalyst used in the process of the present invention is inexpensive, has a high operating life and makes it possible to achieve high space-time yields. A particular advantage of the process of the present invention is that it can be carried out without problems in existing reactors so that no conversion of existing plants is necessary.
In the process of the present invention, lithium, sodium, potassium, rubidium or cesium is used as alkali metal. Preference is given to using sodium or potassium. The alkali metal amalgam in which the alkali metal used is present can be produced by any known process for preparing alkali metal amalgam, for example by mixing alkali metal and mercury, but is usually prepared in a known manner by electrolysis of a solution of an appropriate salt, for example a halide, in general the alkali metal chloride, in an electrolysis cell. A type of electrolysis cell which is particularly suitable for this purpose is that in which the known amalgam process for preparing chlorine and sodium hydroxide is usually carried out. The amalgam generally contains at least 0.05% by weight of alkali metal, preferably at least 0.1% by weight and particularly preferably at least 0.2% by weight. It generally contains not more than 1% by weight of alkali metal, preferably not more than 0.7% by weight and particularly preferably not more than 0.5% by weight.
As alcohol, it is in principle possible to use any compound having a hydroxy group attached to a carbon-containing radical. Use is generally made of aliphatic alcohols, in particular those having a straight-chain or branched alkyl radical having from 1 to 8 carbon atoms. Preference is given to using primary, secondary or tertiary alcohols having from one to five carbon atoms, particularly preferably from one to four carbon atoms. Examples of alcohols used in the process of the present invention are methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol (sec-butanol), 2-methyl-1-propanol (isobutanol), 2-methyl-2-propanol (tert-butanol), 1-, 2- or 3-pentanol, neopentanol, tert-pentanol, hexanol, heptanol or octanol.
The most economically important and therefore preferred products of the process of the present invention are sodium and potassium methoxide, ethoxide and tert-butoxide. Preference is therefore given to using methanol, ethanol or tert-butanol.
It is likewised possible to use alcohols having more than one hydroxy group, for example glycol.
After the alkali metal a

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