DE2013261A1 - Process for the production of furans - Google Patents

Description

670G Ludwigshafen, 18. March 1970 Process for the production of furans

The invention relates to a method for producing furans by condensation of 1,4-dicarbonyl compounds in the presence of hydrohalic acid.

It's from Ber. 85, 460 (1952) known that 1,4-dicarbonyl compounds in the presence of oxalic acid with elimination of water condense to derivatives of furan. On the other hand, teaches a work in Organic Synthesis, Vol. XVI, 26 [1,936] (John ' Wiley, N.T.) that ring opening of the furan can be achieved in the presence of dilute acetic acid and sulfuric acid.

In the processes known to date, the yields of the end product are unsatisfactory due to ring opening of the furan and the like Subsequent reactions, by-products and resinous residues are formed to a greater extent.

It has now been found that furans of the general formula I

R - c ^ C - R ₅

² I! !! ² i,

R ₁ -CCR ₁
1/1 ■

in which the individual radicals R ₁ and R _{2 can be} identical or different and each represent a hydrogen atom, an aliphatic, araliphatic or aromatic radical, advantageously obtained by condensation of 1,4-dicarbonyl compounds in the presence of an acid, if 1,4 -Dicarbonyl compounds of the general formula II

R. -G-OH- OH - C - R, II,

¹ Il Il '

0 0

in which R, and Rp have the aforementioned meaning in the present 657/69 _ 2 -

109841/1907

- 2 - O.Z. 26 667

of hydriodic acid, hydrobromic acid and / or hydrofluoric acid condensed as a catalyst.

The reaction can be carried out in the case of using ethyl acetate represented by the following formulas:

-H ₉ O

CH _x -CO-CH ₀ -CH-COOC ₀ Hc- ---> CH-C-

2 2, 25 ^ κ ti

CO-CH, CH, -C C-CH

^{9 D} ^^

H,

Compared to known processes, the process according to the invention provides furans in a simple way, in the best yield and purity. In view of the prior art, it was surprising ^Λ that the hydrohalic acids catalyze the inorganic acids, the condensation of the dicarbonyl compound, without that the yield is significantly worsened of end product by re-annular opening formed in the furan and subsequent lOlgereaktionen.

Preferred starting materials II and correspondingly preferred end products I are those in whose formulas the individual radicals RJ and R _{2 can be} identical or different and each have a hydrogen atom, an alkyl radical with 1 to 4 carbon atoms, an alkylcarbonyl radical with 2 to 4 carbon atoms, a carbalkoxy radical with 2 to 6 carbon atoms, an aralkyl radical having 7 to 10 carbon atoms or a phenyl radical. The radicals mentioned can also be substituted by groups which are inert under the reaction conditions, for example alkyl groups, alkoxy groups, carbalkoxy groups, alkylcarbonyl groups each having 1 or 2 to 4 carbon atoms.

The following 1,4-dicarbony compounds are used, for example, as starting materials II in question: 2,3-diacetylsuccinic acid propyl ester, 2-oxyglutaric acid dibutyl ester, acetonylacetoacetic acid ethyl ester and corresponding methyl, isopropyl, tert-butyl esters; Acetonylacetone, Succinic acid dialdehyde, 1-phenyl-2,5-dioxohejcan, 1,4-diphenylbutane-1,4-dione, 3-phenyl-2,5-hexanedione.

- 3 109841/1907

- 3 - ■ ■. ■ 0.Z.26 667 '

2013 267

The reaction is carried out in the presence of hydriodic acid, hydrobromic acid and / or hydrofluoric acid, in general in an amount from 0.01 to 10, preferably from 0.1 "to 1 percent by weight, based on starting material II carried out. The hydrohalic acid can be anhydrous, preferably im In the case of hydrofluoric acid, or in the form of an aqueous solution, preferably in the case of hydrobromic and hydroiodic acid, use or hydrohalic acid forming compounds, e.g., a bromide, iodide, fluoride and a hydrohalic acid add the acid liberating from it to the reaction. For example, sodium and potassium halides are used as halides and as acids sulfuric acid, phosphoric acids into consideration " A 50 to 100 percent strength by weight aqueous solution is preferred of hydrobromic or hydroiodic acid.

The reaction is carried out usually at a temperature between 50 and 200 ⁰ G, preferably between 80 and 140 ⁰ C, under atmospheric or superatmospheric pressure, continuously or discontinuously. It is expedient to use organic solvents which are inert under the reaction conditions, for example aromatic hydrocarbons such as benzene, toluene, xylenes; Chlorinated hydrocarbons such as ethylene chloride, trichloroethane, 1,2-dichloroethane, chlorobenzene; Nitro, methane, acetonitrile; Alkane monocarboxylic acid esters, such as methyl and ethyl acetate, propyl formate, methyl butyrate; or corresponding mixtures. In a preferred embodiment of the process, the water formed in the reaction is removed from the system during the reaction with organic solvents which, together with water, form an azeotropic mixture, for example with one of the aforementioned solvents. In this way, the condensation is generally carried out in a much shorter time.

The following table shows the yield of the end product when using various acids as catalysts compared to hydriodic acid according to the process of the invention. You illustrated the technical progress achieved with hydrogen halide. *

109841/1907

- 4 - O.Z. 26th

2013761

Tabel

1 mole of ethyl acetonylacetoacetate is converted into ethyl 2,5-dimethyl-3-furancarboxylate with 2 moles of toluene condensed. The end product is isolated by distillation under reduced pressure.

Acid catalyst ($ 0.5 mole) per mole of yield of final

Aet of hydrogen in the (in grams) theory

concentrated hydrochloric acid 4.6 21

conc. Sulfuric acid 4.2 20

p-toluenesulfonic acid 5.5 26

Oxalic acid 8.0 40

o-phosphoric acid 7.4 48

o-boric acid 8.0 45

Hydroiodic acid 18.0 91

The reaction can be carried out as follows: A mixture of starting material II hydrochloric acid and optionally Water, expediently together with solvent, is kept at the reaction temperature for 1 to 10 hours. The water formed is advantageously removed by means of azeotropic distillation during the entire reaction time. Afterward the end product is isolated from the mixture in a known manner, e.g. by fractional distillation.

The compounds which can be prepared by the process of the invention are bactericides, hardeners and valuable starting materials for the production of dyes, pesticides, solvents, auxiliaries in the paint and fragrance industry. With regard to the use, reference is made to Ullmanns Encyklopadie der technischen Chemie, Volume 7, pages 707 ff.

1O98A1 / 1907

- 5 ■ - O.Z. 26 667

The parts listed in the following examples mean " Parts by weight.

Example 1 - . ■ ";

In a stirred tank, 186 parts of ethyl acetate are dissolved in 184 parts of toluene and condensed in the presence of one part of an aqueous 57% hydroiodic acid for 4 hours at a temperature of 85 to 125 ^° C. The water formed is removed from the reaction mixture by azeotropic distillation removed, After 18 parts of water have been distilled off, the toluene is removed and the end product is isolated

by fractional distillation in vacuo. At 93

92 to 93 ⁰ C 153 parts of 2,5-dimethyl-3-furancarboxylic acid

ethyl ester (n ^ = 1.4686) (91 $ of theory). .

Example 2

114 parts Aeetonylaceton are condensed in the presence of a portion of an aqueous solution of hydriodic acid at 90 57 $ ⁰ C analogously to Example. 1 91 parts (95 liters of theory) of 2,5-dimethylfurari with a boiling point of 93 to 94 ^° C. are obtained.

Example 3 '

, As described in Example 1. In a stirred vessel, 186 parts * Acetonylacetessigsäureäthylester dissolved in 184 parts of toluene and condensed in the presence of a portion of a 48 $ aqueous hydrobromic acid at a temperature of 100 to 120 ⁰ C. In otherwise the same manner, 155 parts of 2,5-dimethyl-3-furancarbonsäureäthylester (nj = 1.4686;. Kp.g = 92-93 ⁰ C). ·

- 6 10 98-1 / 190 7

- 6 - O.Z. 26 667

Example 4

In a steel pressure vessel, 186 parts of ethyl acetonylacetoacetate are dissolved in 100 parts of toluene at room temperature and 50 parts of anhydrous hydrofluoric acid are added. The mixture is heated to 80 ^° C. for one hour and, after cooling to room temperature, the hydrogen fluoride is removed in vacuo. The residue is extracted by shaking with water and the organic phase formed is distilled. Obtained in Kp, / -. = 92-93 ⁰ G 156 parts of 2,5-dimethyl-3-furancarbonsäureäthylester (n ^ = 1.4686).

- 7 - 109841/1907

Claims (1)

- 7 - 0.Z, 26 667 Claim. Process for the preparation of furan of the general formula I. R ₉ -CCR ^R 1 - in which the individual radicals R ^. and Rp can be identical or different and each represent a hydrogen atom, an aliphatic, araliphatic or aromatic radical, by condensation of 1,4-dicarbonyl compounds in the presence of an acid, characterized in that 1,4-dicarbonyl compounds of the general formula II R ₁ -C-CH-CH-CR. II, o o in which R. and Rp have the aforementioned meaning in the present of hydriodic acid, hydrobromic acid and / or hydrofluoric acid condensed as a catalyst. Badische Anilin- & Soda-Fabrik AG. . 109841/1907