Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-02-01
2001-11-06
Solola, T. A. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S376000, C549S430000, C568S596000
Reexamination Certificate
active
06313322
ABSTRACT:
The present invention relates to a process for preparing acetals of the formula I
where
a) the Rs are, independently of one another, a C
1
-C
20
-alkyl or C
3
-C
20
-alkenyl radical or
b) the two R radicals together form the members of an unsubstituted or C
1
-C
10
-alkyl-substituted 5- to 7-membered cyclic acetal,
reacting 3-methyl-2-butenal in the presence of sulfamic acid, of a N-(C
1
-C
8
-alkyl)sulfamic acid or of a N,N-di(C
1
-C
8
-alkyl)sulfamic acid as catalyst with
in case (a)
a1) an alcohol of the formula IIa
R—OH (IIa)
where R has the meaning stated under (a),
a2) an orthoester of the formula (III)
HC—(OR)
3
(III)
where R has the meaning stated under (a) or
a3) a mixture of an alcohol of the formula (IIa) and an orthoester of the formula (III),
and in case (b)
b) with an alcohol of the formula IIb
HO—(CH
2
)
m
—OH (IIb)
where m is a number from 2 to 4, and a methylene group in the alcohol IIb may be substituted by a C
1
-C
10
-alkyl group.
The N-(C
1
-C
8
-alkyl)sulfamic acids and N,N-di(C
1
-C
8
-alkyl)sulfamic acids are called “alkylsulfamic acids” for short in the following text.
Known processes for preparing acetals of 3-methyl-2-butenal from 3-methyl-2-butenal and the corresponding alcohols use a variety of acidic catalysts. The following acids are normally employed as catalysts: phosphoric acid, ammonium nitrate, p-toluenesulfonic acid and potassium bisulfate.
Bull. Soc. Fr. 1965, 1007-1014 discloses the use of phosphoric acid. 3-Methyl-2-butenal is stirred with ethanol, triethyl orthoformate and phosphoric acid at room temperature for 40 hours. The reaction mixture is then taken up in ether, washed with 0.5 N aqueous ammonia and dried over sodium sulfate. Subsequent distillation affords 3-methyl-2-butenal diethyl acetal in a yield of 65%.
Liebigs Ann. Chem. 1986, 99-113 describes the reaction of 3-methyl-2-butenal with trimethyl or triethyl orthoformate and the corresponding alcohol using ammonium nitrate as catalyst. After reaction at room temperature for 8 hours, the undissolved catalyst is filtered off and, after addition of potassium carbonate, the reaction mixture is distilled. The dimethyl acetal is isolated in a yield of 63%, and the diethyl acetal is isolated in a yield of 51%.
The use of p-toluenesulfonic acid is described in J. Chem. Soc. (C) 1971, 811-816: 3-methyl-2-butenal, methanol and trimethyl orthoformate are stirred with p-toluenesulfonic acid at room temperature for 24 hours. The reaction mixture is then diluted with water and extracted with ether. The organic phase is washed with water and aqueous sodium bicarbonate solution, dried and distilled. The distillate still contains 10% 3-methyl-2-butenal. Nothing is stated about the yield.
Various acidic catalysts were tested in J. Org. Chem. 1995, 60, 1995, 3397-3400. Use of p-toluenesulfonic acid resulted in polymerization of the 3-methyl-2-butenal. Triethylammonium chloride, pyridinium p-toluenesulfonate, tetrabutylammonium bisulfate and ammonium bisulfate likewise gave unsatisfactory results. Potassium bisulfate proved to be more suitable. The reaction conditions are likewise described in the Patent Application EP 0629619. Triethyl orthoformate and 3-methyl-2-butenal are added to abs. ethanol at 4° C. The clear solution is cooled to 2° C., and potassium bisulfate is added. The heterogeneous reaction mixture warms to 10° C. owing to the exothermic reaction. The mixture is then allowed to warm to 21° C. over the course of 45 minutes and is then stirred at this temperature for 15 minutes. The catalyst is then filtered off and washed with ethanol. The filtrate is mixed with potassium carbonate and stirred at room temperature for one hour. The potassium carbonate is then likewise filtered off and washed with ethanol. Distillation affords 3-methyl-2-butenal dimethyl acetal in a yield of 85%. The disadvantages of this process are that elaborate temperature control is required and the alternating cooling and warming steps require increased energy consumption and elaborate apparatus.
Even cyclic acetals, which ought to be obtained in far better yields because of their greater stability, are, according to DE U.S. Pat. No. 2,334,378, isolated only in yields comparable to those of the open-chain representatives (63-88%). According to this, 3-methyl-2-butenal and various 1,3-diols are heated with dichloromethane using a water trap. The catalyst used is p-toluenesulfonic acid. Excess 1,3-diol and p-toluenesulfonic acid are removed with water after the reaction is complete. The organic phase is fractionally distilled.
The disadvantages of previously disclosed processes using said acid are either moderate yields, long reaction times or elaborate workup methods, frequently as a consequence of the poor solubility of the acidic catalyst. It is common to all the processes that the acidic catalyst is removed from the reaction mixture either by a filtration step or by a wash with water and/or aqueous alkaline solutions.
It is an object of the present invention to provide a process which does not have the disadvantages of the prior art and, in particular, makes it possible to synthesize acetals of 3-methyl-2-butenal in high yields in an industrially straightforward manner.
We have found that this object is achieved by the process defined at the outset.
The novel process is, in the case of the preparation of compounds of type (a) of formula (I), particularly suitable for those formed from C
1
-C
20
-alkyl alcohols such as methanol, ethanol, propanol, isopropanol, butanol, sec-butanol and t-butanol, and C
3
-C
20
-alkenyl alcohols such as propenol, butenol, pentenol and 3-methyl-2-butenol, from the corresponding orthoesters of the formula (III) whose 3 alkoxy radicals are derived from the aforementioned alcohols, and/or from mixtures of the aforementioned alcohols and orthoesters.
If the alcohols of the formula (IIa) and the orthoesters of the formula (III) are used in the form of a mixture, the molar ratio thereof can vary within a wide range and is generally from 0.01:1 to 20:1, preferably 0.1:1 to 5:1.
In the case of the preparation of compounds of the formula (I) of type (b), suitable alcohols of the formula (IIb) are those which form with the carbonyl group of 3-methyl-2-butenal an unsubstituted or C
1
-C
10
-alkyl-substituted acetal, in particular C
1
-C
10
-alkyl-substituted C
2
-C
4
-diols such as 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2,4-pentanediol, 2-methyl-2,4-butanediol and 2,2-dimethyl-1,3-propanediol.
Sulfamic acid or alkylsulfamic acid is employed according to the invention as catalyst in this process in a concentration of from 0.001 to 10, preferably from 0.001 to 5, mol% based on 3-methyl-2-butenal.
In the novel process for preparing acetals of the formula (I) of type (a), 3-methyl-2-butenal, alcohols of the formula (IIa) or orthoesters of the formula (III) are employed preferably in a molar ratio (R1), formed from the amount of 3-methyl-2-butenal and the amount of units which are derived from these alcohols and orthoesters and are of the formula (IVa)
—OR (IVa)
where R has the same meaning as in formula (I), which is from 0.5:1 to 0.01:1, particularly preferably 0.4 to 0.05, taking only 2/3 of the amount of units of the formula (IVa) derived from orthoesters of the formula (III) into account.
To prepare acetals of type (b), 3-methyl-2-butenal and alcohols of the formula IIb are generally employed in a molar ratio (R2) of from 0.02:1 to 1:1.
The product of the formula (I) is generally required to be homogeneous, with the radical R always being the same hydrocarbon group, and correspondingly the alcohols of the formula (IIa) and the orthoesters of the formula (III), or the alcohols of the formula (IIb), are then chosen so that the radical R in the starting materials is also the same alkyl, alkenyl or alkanediyl group.
Since the acetalization of aldehydes with alcohols is an equilibrium reaction in which, in most cases, the equilibrium is not entirely on the acetal side, it is in many cases necessary, in
Ebel Klaus
Hieber Gisela
BASF - Aktiengesellschaft
Keil & Weinkauf
Solola T. A.
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