DE1248669B - Process for the preparation of 2 3-dihydrofurans - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

PATENT LETTERING

Int. Cl .:

Number:

File number:

Registration date:

Display day:

Issue date:

C07d

German class: Hq-IA

1248 669
B80007IVb / 12q
January 7, 1965
August 31, 1967

March 14, 1968

The patent specification corresponds to the patent specification

It is known that 2,5-dihydrofurans in the presence of alkali alcoholates or alkali hydroxides allowed to isomerize in alcohols to 2,3-dihydrofurans (German patent 817 921). A major disadvantage of this process is that large amounts of alkalis are used as catalysts required, their removal with regard to the official regulations for keeping the Waters cause great difficulties. The process also has the disadvantage that it is pressurized must be carried out, which makes expensive devices necessary. Furthermore, for the Carrying out the process Reaction times of up to 12 hours are required.

It has now been found that 2,3-dihydrofurans the general formula

Process for the production of
2,3-dihydrofurans

Patented for:

Aniline & Soda Factory in Baden
Aktiengesellschaft, Ludwigshafen / Rhein

Named as inventor:

Dr. Werner Hoffmann,

Dr. Heinrich Pasedach, Ludwigshafen / Rhine

in which R, R ₁ and R _{2 denote} a hydrogen atom or identical or different alkyl groups, by isomerizing 2,5-dihydrofurans of the general formula

H.

R.

■ BU

in which R, R ₁ and R _{2 have} the abovementioned meaning, iö advantageously obtained by the isomerization in the presence of a metal of Group VIII of the Periodic Table of the Elements, which is optionally applied to a support, as a catalyst and with at a temperature between 60 and 170 ^° C., optionally in the presence of an inert organic solvent.

The new method has the advantage that none waste materials that are difficult to remove arise, the reaction takes place in a much shorter time and can be done without applying pressure.

As starting materials are suitable in addition to the 2,5 ^ dihydrofuran the ones in the 2- and / or 5-step through Alkyl groups, preferably with 1 to 4 carbon atoms, substituted 2,5-dihydrofuran. The 2,5-dihydrofurans to be used can be prepared according to known Procedure, e.g. B. be prepared by dehydration of the corresponding alkene diols (1,4)

ao (cf. W. R e ρ ρ e and collaborators, annals of the Chemie, Vol. 596 [1955], p. 84).

As catalysts, for. B. palladium, platinum, cobalt, ruthenium or Raney nickel are used will. The metals can be supported on carriers such as activated carbon, silica gel, aluminum oxide, titanium dioxide, Asbestos or pumice stone. The amount of the active catalyst ingredient on the support can vary within wide limits. Usually it is between 0.1 and 50 percent by weight, based on weight on the supported catalyst. But it can also do more, e.g. B. up to 90 percent by weight. The reaction can be carried out in the liquid or gaseous phase, continuously or discontinuously.

You can work without or in the presence of inert organic solvents. As a solvent For example, benzene hydrocarbons such as benzene, toluene or xylene are suitable.

The reaction is preferably carried out at normal pressure

accomplished. The implementation can also take place under increased pressure, e.g. B. at pressures up to 50 ät, be made. It is expedient to work in an inert gas atmosphere. As an inert gas can e.g. B. nitrogen, carbon dioxide or noble gases be used,

The reaction temperatures are between 60 and 170 ⁰ C.

The 2,3-dihydrofurans obtained can be in the reaction product by acidic saponification to the corresponding open oxyketone or oxyaldehyde, conversion the same with HydröxylaminhydfochloridlösüHg and Titration of the released hydrochloric acid can be determined.

S69 514/367

The starting compounds do not give this reaction.

The process products can be purified by distillation. Contained in addition to the 2,3-dihydrofurans the forerunners still contain small amounts of furans. If the same contact is used repeatedly, the Furan formation almost, completely suppressed and the formation of 2,3-dihydrofuran is favored.

The products of the process are valuable intermediates for the manufacture of pharmaceuticals and Plastics.

The parts given in the following examples are parts by weight.

example 1

With 200 parts by Aluminiumoxydkugeln, which are loaded with 0.1 weight percent palladium, filled tube, 500 parts of 2,5-dihydrofuran are distilled under a weak stream of nitrogen at 170 ° to 150 ⁰ C. 495 parts of a reaction product are obtained which, on fractional distillation, give the following fractions: a first fraction (boiling point 32 to 36 ^° C.), which contains 25 parts of furan, a second fraction (boiling point 53 to 57 ^° C.), consisting of 315 parts 2,3-dihydrofuran (yield: 85% of theory, based on the converted 2,5-dihydrofuran), and a third fraction (boiling point 57 to 67 ^° C.) with 125 parts of 2,5-dihydrofuran.

Example 2

B e i s ρ i e 1 3

100 parts of 2,5-dihydrofuran, and 0.5 part of palladium on asbestos (lOgewichtsprozentig), 5 hours at 150 ⁰ C in an autoclave and at a pressure of 10 atmospheres stirred. The 2,3-dihydrofuran content of the reaction product obtained in this way was then determined by stirring 1 g of the reaction product, 10 ecm of water and ίο 1 ecm of 1N hydrochloric acid for 15 minutes at room temperature, then 50 ml of 6.5 percent strength by weight aqueous hydroxylammonium chloride solution and add methyl orange as an indicator and stir for 1 hour. ImI 1N sodium hydroxide solution is then added and the hydrochloric acid liberated is then titrated with 1N sodium hydroxide solution. From the amount of caustic soda used, the. Calculate the 2,3-dihydrofuran content. This corresponds to a content of 36% 2,3-dihydrofuran.
ao

Example 4

100 parts of 2,5-dihydrofuran, and 1 part of platinum asbestos (lOgewichtsprozentig) are stirred for 5 hours at 150 ⁰ C in an autoclave at 10 atmospheres pressure. The 2,3-dihydrofuran content is determined as indicated in Example 3. It is 29% of theory.

30th

a) 100 parts of 2,5-dihydrofuran are carefully mixed with 50 parts of palladium on silica gel (0.5 percent by weight palladium). The temperature is kept ^{at 40 ° C. by cooling.} When the evolution of heat has ceased, the whole is slowly heated to 60 to 70 ° C., 600 parts of 2,5-dihydrofuran are added to the mixture over the course of 120 minutes and approximately the same amount of reaction product is distilled off at the same time. This is then fractionally distilled. 77 parts of furan, 287 parts of 2,3-dihydrofuran and 120 parts of starting material are obtained.

b) 100 parts of 2,5-dihydrofuran and the catalyst already used in batch a) are initially charged. When the catalyst is used for the second time, the exothermicity occurring under a) is no longer observed. Then the whole thereto in the course of 120 minutes, 600 parts is heated to 60 to 8O ⁰ C, was added 2,5-dihydrofuran, and simultaneously distilling off approximately the same amount of reaction mixture. Fractional distillation of the same gives 37 parts of furan, 359 parts of 2,3-dihydrofuran and 1.35 parts of starting material. , ...

c) 100 parts of 2,5-dihydrofuran and the catalyst consists of approach b) are initially introduced, and the whole is heated at 60 to 8O ⁰ C. Then add to the mixture in the course. 600 parts of 2,5-dihydrofuran are added over a period of 120 minutes, the reaction product formed being distilled off at the same time. This is then fractionally distilled. 22 parts of furan, 371 parts of 2,3-dihydrofuran and 125 parts of starting material are obtained.

The example shows that when the same catalyst is used several times, by-products are formed is pushed back and the yield of 2,3-dihydrofuran increases. ,,

Example5

100 parts of 2,5-dihydrofuran and 5 parts of Raney nickel are stirred for 5 hours at 150 ° C. in an autoclave at 10 atmospheric pressure, and then the reaction product is fractionally distilled. Here, 35 parts of 2,3-dihydrofuran, and at 57 to 67 ° C, 23 parts of the starting material proceed at 32 to 36 ° C, 3 parts of furan, at 53 to 57 ⁰ C above. The yield of 2,3-dihydrofuran is 45.5% of theory, based on converted 2,5-dihydrofuran.

Example6

100 parts of 2,2,5-trimethyl-2,5-dihydrofuran, and 1 part of palladium asbestos (30%) for 5 hours at 15O ⁰ C in an autoclave under a pressure of 10 atmospheres are stirred. The reaction product obtained is treated with 1N hydrochloric acid and hydroxylamine hydrochloride solution to determine the content of the corresponding 2,3-dihydrofuran, and the hydrochloric acid released is titrated. The amount of hydrochloric acid released corresponds to a content of 38% ^of 2,2,5-trimethyl-2,3-dihydrofuran. ,

■ '. Example 7

100 parts of 2,5-dimethyl-2,5-dihydrofuran and 1 part of palladium asbestos (30%) are stirred for 5 hours at 150 ° C. in an autoclave under a pressure of 10 atmospheres. The reaction mixture is then fractionally ■ distilled. This gives 38 parts of 2,5-Dimethy! -2,3-dihydrofuran of boiling point 88 to 90 ⁰ C and 56 parts of the starting material.

Example 8

Through a tube filled with 100 parts of alumina strands containing 0.1 percent by weight palladium

included, is filled, be-methyl-2,5-dihydrofuran 5 distilled at 170 ⁰ C within 60 minutes, 200 parts under a weak stream of nitrogen. To give 190 parts of a reaction product from which one by fractional distillation in addition to starting material, 105 parts (yield: 55% of theory) of 5-methyl-2,3-dihydrofuran receives from the boiling point of 82 ⁰ C.

Claims (1)

Claim: Process for the preparation of 2,3-dihydrofurans of the general formula in which R, R ₁ and R _{2 represent} a hydrogen atom or identical or different alkyl groups, ao by isomerization of 2,5-dihydrofurans of the general formula H. R ₁ OR ₂ in which R, R ₁ and R _{2 have} the abovementioned meaning, characterized in that the isomerization is carried out in the presence of a metal of Group VIII of the Periodic Table of the Elements, which is optionally applied to a support, as a catalyst and at a temperature between 60 and 170 ° C, optionally in the presence of an inert organic solvent, carried out. Considered publications:
German Patent No. 817 921;
Zeitschrift für Chemie, 3rd year (1963), pp. 222 to 226. 709 639/532 8.67 © Bundesdruckerei Berlin