HUT61259A - Process for producing delta-1 enol ethers - Google Patents

Abstract

Method for producing compounds of formula (I), where R<1> stands for propyl or butyl and R<2> stands for (C1-C2) alkyl, characterized in that a compound of formula (II), where R<1> and R<2> have the meanings given above, is added in metered quantities at temperatures of 50 to 200 DEG C to the carboxylic acid of formula (III) R<3>-COOH, where R<3> stands for H, (C1-C6) alkyl, which can be halogenated, (C5-C6) cycloalkyl, phenyl, which can be substituted once or several times by (C1-C2) alkyl or halogen, or R<3> stands for carboxy (C1-C6) alkyl, and the reaction products of formula (I) and formula (IV) R<2>-OH, where R<2> has the meaning given above, are continuously distilled from the reaction mixture.

Description

The present invention relates to a process for the preparation of compounds of formula I

(I) wherein in the formula

R ¹ is propyl or butyl; r ² is C 1 or C 2 alkyl.

The alkyl enol ethers of formula (I) are valuable intermediates in the preparation of substances that effectively reduce the phytotoxic side effects of pesticides (U.S. Pat. No. 3,239,649.8).

It is known that the compounds of formula (I) can be prepared by laboratory methods, by reaction with acid-catalyzed alcohol at higher temperatures, from the corresponding ketals of formula (II) and subsequent distillation from the reaction mixture. Acid catalysts include p-toluenesulfonic acid, phosphoric acid, sulfuric acid, alkali hydrogen sulfate, boric acid and phosphoric acid pyridine or quinoline [Houben-Weyl, Methoden dérorganchen Chemie, Bánd 6/3 S. 97; Kunz, Lindig, Chem. Bér. 116: 220-229 (1983). These processes are limited to the vinyl ether described in the literature

It is provided in Λ% yield and after processing results in% distillation residue which must be partially destroyed by incineration [E. Taskinen: J. Chem. Thermodynamics 1973, 5, 783-791; E. Taskinen: J. Chem. Thermo. Dynamics 1974, 6, 345-353]. This results in heavy loads on an industrial scale, both ecologically and economically.

The unsatisfactory yield is mainly due to the reaction between the above-mentioned acids and the formed Δ en-enol ethers. Under the conditions of the cationic polymerization in question, significant amounts of oligomeric or polymeric products are formed [B. Vollmert: GrundriB derer macromolecular Chemie; Effenberger: Angew. Chemie 81 374 (1969)]. If the acid concentration is reduced to less than 1 mol% to reduce the formation of polymeric products, only a 20-30% yield of the desired product is achieved after a constant reaction time (see Comparative Examples 1 and 3).

In addition, acid-catalyzed processes known in the art generate large amounts (5-10%) of the corresponding h2-enol ethers as they are in thermodynamic equilibrium with the compounds of formula (I). Due to the small amount of acid and the high cleavage temperature of the ketals of Formula II, the amount of thermodynamically more stable 42-enol ethers is continuously increased during the reaction, thereby further decreasing the yield of the desired final product (see Comparative Example 1 and Taskinen, cited above).

• ·

Example

3-Methyl-2-methoxy-butene-1 system

CH ₃ /

\ ch ₃ och ₃

Al enol ether, (Ia) A2 enol ether, (V) [E. Taskinen, Acta Chem. Scand. B 28: 357-366 (1974)].

A further disadvantage of these processes is the long reaction time, since the catalytic action of acids has to be utilized to obtain the yields described in the literature. Thus, cleavage of 10 mol of 3,3-dimethoxy-2-methylbutane in the presence of catalytic amount (1 mol%) of p-toluenesulfonic acid required a reaction time of 10 hours to obtain 85% hl-enol ether (see Comparative Example 1). Increasing the amount of acid to mol% reduces the reaction time to 3 hours, but this results in a yield of less than 50% for 2cl-enol ether (see Comparative Example 2).

The present invention relates to a process for the preparation of compounds of formula I,

(I) wherein in the formula

R ¹ is propyl or butyl,

R ² is C 1 or C 2 alkyl.

The process involves the preparation of a compound of formula II

OR ² l

H ₃ C - C - R ¹ (II)

OR ²

- in the formula

R ¹ and R ² are added to a carboxylic acid of formula (III) above

R ³ - COOH (III)

- in the formula

R ³ is optionally halogenated C 1 -C 6 alkyl, C 5 -C 6 cycloalkyl, phenyl optionally mono- or polysubstituted with C 1 -C 2 alkyl or halo, or carboxy-C 1 -C 6 alkyl

50-200 ° C, and the reaction products I and IV are obtained

R ² - OH (IV)

- in the formula • ** 4 »♦. * · · · • ** * ·· · '·· «»

......... .. · · .. ·

-6R ² is continuously distilled off from the above reaction mixture.

By alkyl is meant both straight-chain and branched-chain alkyl. Preferably R ¹ is isopropyl. Halogenated alkyl means an alkyl group mono- or polysubstituted by fluorine, chlorine or bromine. Of particular interest are trifluoromethyl, trichloromethyl and tribromomethyl. Examples of compounds of formula (III) wherein R ³ is carboxy-C 1-6 -alkyl include malonic acid and diethyl malonic acid.

The compounds of formula II are known and may be prepared by methods known in the art [C. Ferri: Reaktionen dér org. Synthese 426-427, Georg Thieme Verlag Stuttgart 1978].

In contrast to prior art processes, the present invention provides the desired Δΐ-enol ethers in a yield of more than 97% of the theoretical yield, whereby the &lt; 2 &gt; enol ether and polymer residues are less than 1%. In addition, the continuous mode of operation makes the process of the invention particularly simple from an operational point of view.

The process according to the invention is conveniently carried out by continuously adding the ketals of formula II to the heated carboxylic acids of formula III and continuously distilling off the resulting 1-enol ether of formula I with the alcohol of formula IV formed. from the reaction mixture. General picture (I) • ·

The separation of the final products from the alcohols of the formula (IV) is not difficult, and is carried out by distillation or extraction.

The reaction temperature (= ketal cleavage temperature) is between 50 ° C and 200 ° C, preferably between 60 ° C and 150 ° C.

The ketal of formula (II) is either fed through the distillation column or added directly to the distillation flask. The advantage of this continuous mode is that the ketals (II) are always added to the excess carboxylic acids of the formula (III), thus providing a very high cleavage rate of the ketal. The acid of formula (III) is not consumed during the reaction and, due to the difference in boiling point of the reaction products (I) and (IV), is not removed from the reaction vessel (reaction mixture) by distillation. As a result, the amount of carboxylic acid (III) used in the reaction mass balance appears to be only catalytic in the amount of the (ketal) material to be converted into the reaction.

The process according to the invention is to be considered as more surprising since the carboxylic acid (III), which is present in a large excess at the time of the actual reaction, does not undergo any reaction with the Z 1-enol ethers formed. Therefore, the polymerization products of the known processes are not formed here.

It is also known that vinyl ethers (enol ethers) readily react with carboxylic acids, such as acetic acid, to form vinyl acetate or semi-acyl, and thus form a compound of formula (I)

-8 product yields may decrease [W. Reppe: A, 601 (1956) 81-138; D. F. Schorstakowski and N. A. Gerstein, J.: Barely. Chem., 21, 1452 (1951); Chem. 1952, 5395].

These undesirable side reactions are not observed in the process of the invention.

The following examples illustrate the invention.

Example 1

3-Methyl-2-buten-l

2,2-Dimethoxy-3-methylbutane (677 g, 97.5%) was continuously added over 4 hours to a distillation flask containing 50 g of propionic acid at 110 ° C and the reaction products were distilled through a 150 cm split-tube distillation column. . At 50-80 ° C, 652 g of distillate are obtained, consisting of 489 g of 3-methyl-2-methoxybuten-1 and 163 g of methanol, corresponding to a yield of 97.8%. & 2-enol ether cannot be detected.

Example 2

3-Methyl-2-buten-l

10 -155 g (97.5%) of 2,2-dimethoxy-3-methylbutane are continuously added over 35 hours to a distillation flask containing 150 g of isovaleric acid at 110 ° C and the reaction products are distilled through a 150 cm split-tube distillation column. . At a head temperature of 50-80 ° C, 9767 g of distillate is obtained, consisting of 7314 g of 3-methyl-2-methoxybuten-1 and 2453 g of methanol, corresponding to a 97.5% yield.

Δ2-enol ether cannot be detected.

Comparative Example 1

2,27-Dimethoxy-3-methylbutane (677 g, 97.5%) 8.7 g of p · ·

The reaction mixture was maintained at reflux with -9-toluenesulfonic acid and distilled over a 150 cm split-tube distillation column over 10 hours. 596 g of distillate are obtained, consisting of 420 g of &lt; 1 &gt; enol ether, 30 g &lt; 2 &gt; enol ether and 146 g of methanol, corresponding to 84% yield.

Comparative Example 2

2,2-Dimethoxy-3-methylbutane (677 g, 97.5%) was heated to reflux with 87 g of p-toluenesulfonic acid and distilled over a 150 cm split-tube distillation column over 3 hours. 383 g of distillate are obtained, consisting of 240 g of Δΐ-enol ether, 50 g of Δ2-enol ether and 93 g of methanol, corresponding to a yield of 48%.

Further, 294 g of a polymeric viscous distillation residue were obtained.

Comparative Example 3

2,2-Dimethoxy-3-methylbutane (677 g, 97.5%) was heated to reflux with 0.8 g of p-toluenesulfonic acid and distilled over a 150 cm split-tube distillation column over 10 hours. 177 g of distillate are obtained, consisting of 120 g of L1 enol ether, 11 g of A2 enol ether and 46 g of methanol, corresponding to a 24% yield.

After another 25 hours of distillation in total

569 g of distillate are obtained, consisting of 375 g of Al-enol ether, 55 g of Δ 2-enol ether and 139 g of methanol, corresponding to 75% yield.

Claims (3)

1. Process for the preparation of compounds of formula (I) - in the formula R ¹ is propyl or butyl, R ² is C 1 or C 2 alkyl, characterized in that it is a compound of formula II OR ² I H ₃ C - C - R ¹ (II) OR ² - in the formula ^R1 and ^R2 are as defined above for formula (III) is added to carboxylic acid of formula R ³ - COOH (III) - in the formula R ³ is optionally halogenated C 1-6 alkyl, C 5-6 cycloalkyl, In the case of C 1 -C 2 alkyl or halogen, mono- or polysubstituted phenyl or carboxy- (in the case of C 1 -C 2 alkyl or halogen); (C 1 -C 6) alkyl 50-200 ° C, and the resulting reaction products of formulas I and IV R ² - OH (IV) - in the formula ^R2 as defined above is continuously distilled off from the reaction mixture. 2. A process according to claim 1 for the preparation of compounds of formula I wherein R ¹ is isopropyl, wherein the appropriately substituted starting compounds are used. Process according to claim 1 or 2, characterized in that it is carried out at a temperature. the reaction temperature is 60-150 ° C The agent shall: