Distillation: processes – separatory – Distilling to separate or remove only water – From organic compound
Reexamination Certificate
1997-04-25
2001-04-10
Manoharan, Virginia (Department: 1764)
Distillation: processes, separatory
Distilling to separate or remove only water
From organic compound
C203S029000, C203S057000, C203S075000, C203S076000, C203S077000, C203S092000, C203S093000, C203S098000, C203SDIG001, C203S097000, C203S094000, C568S699000
Reexamination Certificate
active
06214172
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for the preparation of methylglyoxal dimethyl acetal (1,1-dimethoxy-2-propanone) by reacting methylglyoxal (2-oxopropanal) with methanol in the presence of an acidic catalyst, in particular of an acidic ion exchanger.
In the previously described preparations of methylglyoxal dimethyl acetal (MGDA) from methylglyoxal (MG) and methanol, it was frequently attempted to remove the water, which can originate both from the starting methylglyoxal solution and from the reaction itself, from the mixture by means of entraining agents during the reaction (eg. Braude et al., J. Chem. Soc. 3328 (1955); Hoechst AG, DE 29 47 383). This requires the use of readily volatile, generally toxic assistants, for example benzene, which may contaminate the product. Moreover, the yields described are only 67% at the most. 1,2,2,2-Tetramethoxypropane is described as a waste product.
Furthermore, a Japanese Patent Application (JP 59199651A) describes the acetalation of methylglyoxal with methanol over ion exchangers in suspensions, working up being effected by means of extraction with methylene chloride as the solvent. Since methylglyoxal dimethyl acetal is largely used for the preparation of pharmaceutical products, the use of this toxic assistant appears unacceptable. No information is given with regard to the whereabouts of the ion exchanger and the distillation residues. In addition, our own experiments (cf. Comparative Example) show that the yields stated in JP 59199651A cannot be repeated with the methylglyoxal available in industry (about 40% strength aqueous solution). The methanol excess of 1:23 used in the Examples in this publication and the long reaction times of 16 hours are moreover disadvantageous for an industrial methylglyoxal dimethyl acetal synthesis.
It is an object of the present invention to remedy the abovementioned disadvantages in the preparation of methylglyoxal dimethyl acetal from methylglyoxal and methanol.
SUMMARY OF THE INVENTION
We have found that this object is achieved by the novel and improved process for the preparation of methylglyoxal dimethyl acetal in which, after the reaction of methylglyoxal and methanol in the presence of a catalyst, the product methylglyoxal dimethyl acetal is obtained by azeotropic distillation with water.
The process can be carried out continuously or, preferably, batchwise. For carrying out the further process, methylglyoxal, which contains more than 40% by weight of water, is preferably concentrated is to a water content of less than 40% by weight by distilling off water under reduced pressure. Further preferred embodiments are described in the subclaims.
DETAILED DISCLOSURE
The methylglyoxal used in the present invention is as a rule industrial methylglyoxal which contains about 60% by weight of water. This aqueous methylglyoxal solution is preferably concentrated with respect to methylglyoxal to water contents of less than 40, particularly preferably less than 20, % by weight by distilling off water at 20-1013, particularly preferably 50-150, mbar, and, where the water contents are reduced to less than 5%, sparingly volatile solvents, for example relatively high-boiling alcohols (eg. decanol or diethylene glycol) or relatively high-boiling ethers (eg. diethylene glycol butyl ether) or similarly high-boiling solvents may be added to improve the stirability.
The actual reaction of methylglyoxal with methanol preferably takes place at a molar methylglyoxal: methanol ratio of from 1:2 to 1:50, preferably from 1:8 to 1:15.
The catalysis of the reaction is carried out, for example, in a conventional manner, for example at strongly acidic pH. Acidic ion exchangers in the form of fixed beds or as a suspension, as S commercially obtainable (for example BayKat 2611, Amberlyst 15, etc.), are preferably used as such acidic catalysts. The temperatures during the reaction over the catalysts are preferably from 20 to 120° C., particularly preferably from 50 to 90° C. The reaction need not necessarily lead to 100% conversion, and accordingly the duration of the reaction over the ion exchangers may vary.
A preferred reaction time is from 4 to 7, in particular from 5 to 6, hours and preferred reaction temperatures are from 50 to 100° C., in particular from 60 to 80° C.
In order to obtain the product, water is added to the reacted mixture; fractional distillation is then carried out, methylglyoxal dimethyl acetal surprisingly not being hydrolyzed by the added water although the pH of the reactor discharge is acidic (pH for example 2.0); furthermore, 1,1,2,2-tetramethoxypropane which is also formed and is an undesirable by-product is hydrolyzed to the desired product methylglyoxal dimethyl acetal. In the fractional distillation of the reaction product, after the low boilers and the excess methanol have been separated off, a single-phase mixture of MGDA-H
2
O-methanol is advantageously initially taken up until methanol has been very substantially separated off from the reacted mixture. The azeotropic mixture of methylglyoxal dimethyl acetal and water (which may still contain a little methanol) which then passes over separates at the top into two phases, with the result that crude methylglyoxal dimethyl acetal can be obtained in a simple manner.
As stated above, the reaction can be carried out continuously or, preferably, batchwise. During the procedure, all substances involved in the process which still contain methylglyoxal dimethyl acetal, methylglyoxal or products convertible into methylglyoxal are continuously recycled to the process until, after a plurality of process steps, for example 12 process steps, a yield of, typically, over 80% of crude methylglyoxal dimethyl acetal is finally reached.
REFERENCES:
patent: 2421559 (1947-06-01), Guest et al.
patent: 3478060 (1969-11-01), Maschke et al.
patent: 3956074 (1976-05-01), Bittler
patent: 4158019 (1979-06-01), Meyer
patent: 4383893 (1983-05-01), Kaibel et al.
patent: 4385965 (1983-05-01), Müller et al.
patent: 4473444 (1984-09-01), Feldman et al.
patent: 4607126 (1986-08-01), Sajtos
patent: 5137605 (1992-08-01), Greiner et al.
patent: 5362918 (1994-11-01), Aizawa et al.
patent: 1252193 (1967-10-01), None
patent: 2947383 (1981-06-01), None
patent: 1473782 (1977-05-01), None
patent: 59-199651 (1983-04-01), None
Braude et al, J. Chem. Soc., p. 3328 (1955).
Dietz Rainer
Ebel Klaus
Fritz Gerhard
Groning Carsten
Kaibel Gerd
BASF - Aktiengesellschaft
Manoharan Virginia
Shurtleff John H.
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