Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1999-12-10
2001-02-20
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
Reexamination Certificate
active
06191319
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for preparing alkali metal alkoxides of higher alcohols from an alkali metal amalgam and the free alcohol.
2. Discussion of the Background
Alkali metal alkoxides are important intermediates for, inter alia, the pharmaceutical industry. They are also used as catalysts in the synthesis of many organic compounds. The alkoxides of sodium and potassium have achieved particular industrial importance. A number of methods are known for preparing alkali metal alkoxides (F. A. Dickes, Ber. Dtsch. Chem. Ges. 63, 2753 [1930]). Solutions of alkali metal hydroxides in an alcohol contain the corresponding alkali metal alkoxide in equilibrium. Removal of the water present in this equilibrium, e.g. by distillation, gives pure alkoxides. However, a large amount of energy is required for this method of shifting the equilibrium, particularly in the case of low-boiling alcohols.
Alkali metal alkoxides are obtained directly by “dissolving” an alkali metal in the corresponding alcohol. Here, sodium and potassium react violently with lower alcohols such as methanol and ethanol with evolution of hydrogen. The less reactive higher alcohols such as propanols and butanols are preferably reacted at above the melting point of the respective alkali metal, possibly under superatmospheric pressure while stirring.
However, alkali metals are expensive starting materials for the preparation of alkoxides. It is more economical to use the inexpensive, liquid alkali metal amalgams obtained in chloralkali electrolysis by the mercury process as alkali metal source. The use of catalysts for accelerating the reaction of alkali metal amalgam and alcohol is also known. Thus, the process described in EP-A-O 177 768 uses a bed of granular anthracite whose surface is coated with a heavy metal oxide or a mixture of heavy metal oxides. Alkali metal amalgam and alcohol are fed in continuously in a countercurrent manner and the alkali metal alkoxides are taken off continuously. A disadvantage of this process is that, in the preparation of alkali metal alkoxides of higher alcohols at acceptable reaction times, only from 60 to 80% of the alkali metal introduced in the form of the alkali metal amalgam can be reacted.
According to the proposal of German Patent Application 198 02 013.9, the alkali metal present in the alkali metal amalgam can be reacted to a greater extent even with higher alcohols at acceptable reaction times if the reaction is carried out in the presence of powder catalysts comprising transition metal carbides, nitrides or carbonitrides. Particularly suitable metals are molybdenum and tungsten and, of these, the carbides are particularly suitable. The powder catalysts are advantageously used at a mean particle diameter of from 1 to 10 &mgr;m. The reaction is therefore referred to as a microheterogeneously catalyzed reaction.
SUMMARY OF THE INVENTION
It has now surprisingly been found that the reaction rate and thus the spacetime yield in the preparation of alkali metal alkoxides of higher alcohols, i.e., alcohols having at least 3 carbon atoms, by reaction of an alkali metal amalgam with the free alcohol in the presence of a powder catalyst comprising a transition metal carbide, nitride or carbonitride is considerably increased if ultrasound is allowed to act on the reaction mixture during the reaction.
DETAILED DESCRIPTION OF THE INVENTION
The new process allows the preparation of alkali metal alkoxides at an up to 10 times higher reaction rate or space-time yield compared to a reaction carried out without ultrasound under otherwise identical conditions. This is surprising because slow reactions (with a reaction-controlled rate) cannot usually be accelerated appreciably by increasing the mixing (i.e. more rapid mass transfer to the catalyst surface). As a result of the higher reaction rate, a considerably greater quantity of alkali metal alkoxides can be prepared in existing equipment or new plants for a desired capacity can be made considerably smaller. This advantage is gained at a comparatively low additional equipment cost and energy consumption.
The process is particularly suitable for the reaction of alcohols having from 3 to 7 carbon atoms and a primary, secondary or tertiary carbinol group. Surprisingly, even the notoriously unreactive alcohols having a tertiary carbinol group can be reacted at a good reaction rate. Alcohols having more than seven carbon atoms can likewise be converted into their alkali metal alkoxides by the process of the invention, although the reaction rate decreases with increasing number of carbon atoms, even at elevated temperatures. The alcohols are preferably alkanols, but olefinic double bonds or one or two heteroatoms, for example ether oxygen atoms, may also be present in the carbon chain. Phenols and cresols are also considered to be higher alcohols for the purposes of the present invention. Examples of suitable higher alcohols are 1- and 2-propanol, 1- and 2-butanol, 2-methyl-1-propanol (isobutanol), 2-methyl-2-propanol (tert-butanol), 1-, 2- and 3-pentanol, 2-methyl-1-butanol, 2,2-dimethyl-1-propanol (neopentyl alcohol), 1-, 2- and 3-hexanol, 2-propen-1-ol (allyl alcohol), 2-buten-1-ol (butenol), 3-oxa-1-pentanol (ethyl glycol), phenol and o-, m- and p-cresol. The higher alcohol is advantageously used in an excess of up to 20 times, in particular from 5 to 15 times, the stoichiometric amount, based on the alkali metal, and, if desired, the excess higher alcohol is separated from the alkali metal alkoxide formed, e.g. by distillation.
Preferred alkali metal amalgams are liquid sodium and potassium amalgams having alkali metal contents of from 0.1 to 1 percent by weight, in particular from 0.3 to 0.6 percent by weight. Such alkali metal amalgams are available in industrial amounts from chloralkali electrolysis by the amalgam process.
The use of a transition metal carbide, nitride and/or carbonitride as described in German Patent Application 198 02 013.9 is an essential feature of the process of the present invention. Without the microheterogeneous catalyst, virtually no reaction of the alcohol with the alkali metal amalgam occurs even when using ultrasound. The preferred catalysts and particle sizes are as stated above. The mean particle diameter is preferably from 1 to 5 &mgr;m, in particular from 2 to 3 &mgr;m. The catalyst is preferably used in amounts of from 1 to 10 percent by weight, based on the higher alcohol.
The use of ultrasound for promoting the reaction is a further essential feature of the invention. A broad spectrum of frequencies is suitable for this purpose. Preference is given to using ultrasound at more than 16 kHz, in particular from 20 to 40 kHz. The specified frequencies include ranges which are still audible to the ears of young human beings. For the purposes of the present invention, these ranges are also counted as ultrasound. There is also a wide freedom of choice in respect of the amplitude (or the specific energy input). The amplitude is advantageously at least 0.1 W/cm
2
. Amplitudes of, for example, from 0.2 to 20 W/cm
2
have been found to be useful. Use is made of customary ultrasound generators such as ultrasonic probes for direct introduction of ultrasound or ultrasonic baths for indirect introduction.
The process of the invention can be carried out at room temperature (i.e. 20° C.) or at the temperature which is established as a result of the exothermic reaction. Particularly in the case of alcohols having 4 or more carbon atoms and a secondary or tertiary carbinol group, it can be desirable in the interests of an acceptable reaction rate to introduce additional heat indirectly. In general, the reaction is carried out at temperatures up to the boiling point of the respective alcohol and at atmospheric pressure.
The process of the invention is generally carried out without using an inert solvent or diluent. However, particularly in the case of alcohols having five or more carbon atoms which are relatively viscous at the reaction temperatures, t
Hamann Carl Heinz
Helling Jorg
Schmittinger Peter
Davis Brian J.
Degussa-Huels Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Richter Johann
LandOfFree
Process for preparing alkali metal alkoxides of higher alcohols does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for preparing alkali metal alkoxides of higher alcohols, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for preparing alkali metal alkoxides of higher alcohols will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2589488