KR950006801B1 - Method for continuous production of 1-enol ethers - Google Patents

Abstract

No content.

Description

Continuous preparation of Δ1-enol ether

The present invention is to measure the compound of the general formula (II) below into a carboxylic acid of the general formula (III) to be introduced initially at a temperature of 50 ℃ to 200 ℃, the following general formula (I) and the following general formula ( A process for the preparation of the compound of formula (I) comprising the continuous distillation of the reaction product of IV) from the reaction mixture:

Wherein R ¹ is propyl or butyl, R ² is (C ₁ -C ₂ ) alkyl, R ³ is H, (C ₁ -C ₆ ) alkyl which may be halogenated, (C ₅ -C ₆ ) cyclo Phenyl, which may be mono- or polysubstituted with alkyl, (C ₁ -C ₂ ) alkyl or halogen, or carboxyl- (C ₁ -C ₆ ) alkyl.

Alkyl is not only straight chain but also branched alkyl. R ¹ is preferably isopropyl. Halogenated alkyl is especially alkyl mono- or polysubstituted with F, Cl or Br. Of these, trifluoromethyl, trichloromethyl and tribromomethyl radicals are particularly important. R ³ is a carboxy - (C ₁ -C ₆₎ alkyl is a suitable example of the general formula (III) compound is a malonic acid and diethyl malonate.

Compounds of formula (II) are known and can be prepared by conventional laboratory methods [C. Ferri, Reaktionen der org. Synthese (Reactions of Organic Synthesis), pages 426-427, Georg Thieme Verlag Stuttgart 1978.

Alkyl enol ethers of general formula (I) are useful intermediates for the preparation of substances which effectively reduce the phytotoxic side effects of plant-protective agents (detoxification agents: P3,923,649.8).

It is known that compounds of formula (I) can be prepared by conventional laboratory methods by acid-catalysing the alcohols from the corresponding ketals of formula (II) at elevated temperatures and then distilling from the reaction mixture. Examples of acid catalysts used are p-toluenesulfonic acid, phosphoric acid, sulfuric acid, hydrogen sulphate alkali metal salts, boric acid and hydrogen phosphate salts of pyridine or quinoline [Houben-Weyl, Methoden der Organischen Chemie (Methods of Organic Chemistry), volume 6 / 3 p. 97; Kunz, Linding, Chem. Ber. 116, 220-229 (1983). By this method, the vinyl ethers disclosed in the literature are obtained in a maximum yield of 85%, after which after distillation residues of about 15% remain, this residue has to be treated, for example by incineration [E, Taskinen, J. Chem. Thermodynamics 1973, 5, 783-791; E. Taskinen, J. Chem, Thermodynamics 1974, 6, 345-353]. This causes a big problem not only in ecology but also economically when implemented on an industrial scale.

This unsatisfactory yield is mainly due to the reaction of the aforementioned acid with the fished Δ1enol ether. Under the predominant cationic polymerization conditions, significant amounts of oligomeric or polymeric products are produced [B. Vollmert, Grundriss der makromolekularen Chemic (The Basics of Macromolecular Chemistry); Effenberger, Angew, Chemie 81, 374 (1969)]. However, if the acid concentration is reduced to less than 1 mole percent while maintaining the reaction time unchanged to inhibit the production of polymeric products, only 20-30% of the desired product yield is achieved (see Comparative Examples 1 and 3). .

In addition, in the acid-catalyst processes known in the literature, a large proportion of the corresponding Δ2 enol ethers (5 to 10%) are produced, since they are in thermodynamic equilibrium with the product (I). As a result of the separation of small amounts of acid and ketal (II) at high temperatures, the proportion of thermodynamically more stable Δ2 enol ethers continues to increase in the reaction, which also reduces the yield of the desired final product (Comparative Example 1 And the references cited in Taskinen cited).

[3-Methyl-2-methoxy-1-butene System]

Δ1 enol ether (I) Δ2 enol ether (II)

[E. Taskinen, Acta Chem. Scand. B 28 (1974) 357-3661]

Another disadvantage of this process is the long reaction time, since the acid must be used catalytically to achieve the yields disclosed in the literature. Thus, for example, separation of 10 moles of 3,3-dimethoxy-2-methylbutane using a catalytic amount of para-toluene sulfonic acid (1 mole%) yields about 85% of Δ1 enol ether. A reaction time of 10 hours is required (see Comparative Example 1). Increasing the amount of acid to, for example, 10 mole%, shortens the reaction time to about 3 hours, but results in less than 50% Δ1 enol ether yield (see Comparative Example 2).

In contrast, by the process according to the invention the desired Δ1 enol ether can be obtained in a yield of at least 97% of theory and the amount of Δ2 enol ether and polymeric residue is less than 1% each. In addition, the process according to the invention, due to its continuous process, is particularly easy to handle in terms of process engineering.

The process according to the invention comprises continuously metering the ketal of formula (II) to a heated carboxylic acid of formula (III) and the resulting Δ1 enol ether of formula (I) from the reaction mixture Distillation is continued with the alcohol of (IV). Separation of the final product (I) from alcohol (IV) is no problem and is carried out by distillation or extraction.

The reaction temperature (= ketal separation temperature) is 50 ° C to 200 ° C, preferably 60 ° C to 150 ° C.

Ketal of formula (II) is fed through a distillation column or metered directly to a distillation boiling device at 5/1. The advantage of this continuous process is that ketal (II) is always added to excess carboxylic acid (III), resulting in a very high proportion of ketal separation. The acid (III) is not consumed in the reaction, nor is it removed by distillation from the reaction vessel (of the reaction mixture) due to the difference in boiling points for the reaction products (I) and (IV). Thus, as the reaction proceeds (ketal treatment), only the amount of initially introduced carboxylic acid (III) is shown as catalytic amount in the mass balance of the reaction.

The process according to the invention should be considered more surprising since the carboxylic acid of formula (III), which is present in very excess during the actual reaction period, does not cause any reaction with the resulting Δ1 enol ether. Therefore, in the present invention, the polymerization product produced by the known method is not obtained.

Further, it is known that vinyl ether (enol ether) easily reacts with carboxylic acids, for example acetic acid, to produce vinyl acetate or hemiacylal, possibly resulting in reduced yield of product (W). Reppe A, 601 (1956) 81-138; D.F. Schorstakowski and N.A. Gerstein, J. allg. Chem. 21, 1452 (1951); Chem. Zb1. 1952, 5395].

Such unwanted side reactions are also not observed in the process according to the invention.

The following examples are presented to illustrate the invention.

Example 1

[3-methyl-2-methoxy-1-butene]

677 g of 2,2-dimethoxy-3-methylbutane (97.5% purity) was continuously metered for 4 hours in a distillation boiling device containing 50 g of pyrionic acid at 110 ° C., and the reaction product was separated into a 150 cm separator column. Distillate through. 652 g of distillate consisting of 489 g of 3-methyl-2-methoxy-1-butene and 163 g of methanol are obtained at a column head temperature of 50 to 80 ° C., corresponding to a theoretical yield of 97.8%. Δ2 enol ether is not detected at all.

Example 2

[3-methyl-2-methoxy-1-butene]

10,155 g of 2,2-dimethoxy-3-methylbutane (97.5% purity) was continuously weighed for 35 hours in a distillation boiling device containing 150 g of isovalroic acid at 110 ° C, and the reaction product was separated from 150 cm. Distillate through a tube distillation column. 9767 g of distillate consisting of 7314 g of 3-methyl-2-methoxy-1-butene and 2453 g of methanol are obtained at a column head temperature of 50 to 80 ° C., corresponding to 97.5% yield of theory. Δ2 enol ether is not detected at all.

Comparative Example 1

677 g of 2,2-dimethoxy-3-methylbutane (97.5% purity) were heated to reflux with 8.7 g of para-toluenesulfonic acid and distilled for 10 hours through a 150 cm separator column. 596 g of distillate consisting of 420 g Δ1 enol ether, 30 g of Δ2 enol ether and 146 g of methanol are obtained, corresponding to 84% yield of theory.

Comparative Example 2

677 g of 2,2-dimethoxy-3-methylbutane (97.5% purity) are heated to reflux with 8.7 g of para-toluenesulfonic acid and distilled for 3 hours through a 150 cm separator column. 383 g of distillate consisting of 420 g Δ1 enol ether, 50 g of Δ2 enol ether and 93 g of methanol are obtained, corresponding to a 48% yield of theory. In addition, 294 g of tough polymeric distillation residue is obtained.

Comparative Example 3

677 g of 2,2-dimethoxy-3-methylbutane (97.5% purity) are heated to reflux with 0.8 g of para-toluenesulfonic acid and distilled for 10 hours through a 150 cm separator column. 177 g of distillate consisting of 120 g Δ1 enol ether, 11 g of Δ2 enol ether and 46 g of methanol are obtained, corresponding to a 24% yield of theory.

After further distillation for 25 hours, a total of 569 g of distillate consisting of 375 g of Δ1 enol ether, 55 g of Δ2 enol ether and 139 g of methanol is obtained, corresponding to a 75% yield of theory.

Claims (3)

At a temperature of 50 ° C. to 200 ° C., the compound of the following general formula (II) was initially weighed into the carboxylic acid of the following general formula (III), and the reaction of the following general formula (I) with the following general formula (IV) A process for the preparation of the compound of formula (I), comprising distilling the product continuously from the reaction mixture: Wherein R ¹ is propyl or butyl, R ² is (C ₁ -C ₂ ) alkyl, R ³ is H, (C ₁ -C ₆ ) alkyl which may be halogenated, (C ₅ -C ₆ ) cyclo Phenyl, which may be mono- or polysubstituted with alkyl, (C ₁ -C ₂ ) alkyl or halogen, or carboxyl- (C ₁ -C ₆ ) alkyl. The method of claim 1, wherein R ¹ is isopropyl. The process according to claim 1 or 2, wherein the reaction temperature is 60 to 150 ° C.