Process for preparing tetrahydrofuran from dialkoxybutenes

A process for preparing tetrahydrofuran, which comprises reacting 1,4-butenediol diethers of the formulae I and/or II RO--CH.sub.2 --CH.dbd.CH--CH.sub.2 --OR I RO--CH.sub.2 --CH.sub.2.dbd.CH--CH.sub.2 --OR II, where the R radicals can be identical or different and are C.sub.1 -C.sub.15 -alkyl or cycloalkyl radicals, C.sub.6 -C.sub.12 -aryl radicals or C.sub.7 -C.sub.15 -aralkyl radicals, with water and hydrogen at from 20 to 300.degree. C. under from 1 to 300 bar in the presence of catalysts or catalyst combinations which comprise components which are both capable of hydrogenation and have acidic or basic centers and a novel process for preparing 1,4-butanediol diethers of the formula I by metathesis are described.

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We claim:

1. A process for preparing tetrahydrofuran, which comprises reacting 1,4-butenediol diethers of the formulae I and/or II

where the R radicals can be identical or different and are C.sub.1 -C.sub.15 -alkyl or cycloalkyl radicals, C.sub.6 -C.sub.12 -aryl radicals or C.sub.7 -C.sub.15 -aralkyl radicals, with water and hydrogen at from 20 to 300.degree. C. and from 1to 300 bar in the presence of catalysts or catalyst combinations which comprise components which are both capable of hydrogenation and have acidic or basic centers.

2. The process defined in claim 1, wherein the catalysts or catalyst combinations comprise one or more elements of subgroup I, II or VI-VIII or of main group III-V of the periodic table of the elements, or their compounds in the hydrogenationcomponent.

3. The process defined in claim 1, wherein the catalysts or catalyst combinations comprise one or more of the elements rhenium, copper or ruthenium or their compounds in the hydrogenation component.

4. The process defined in claim 1, which is carried out in two stages by

a) first reacting the butenediol diethers of the formulae I and/or II with water and hydrogen in the presence of a hydrogenation catalyst to give the corresponding 1,4-butanediol monoethers of the formula III

and

b) subsequently cyclizing the 1,4-butanediol monoethers in the presence of acidic or basic catalysts at 40 to 280.degree. C. to give tetrahydrofuran.

5. A process for preparing tetrahydrofuran which comprises reacting 2-butanol ethers of the formula IV

where the R radicals can be identical or different and are C.sub.1 -C.sub.15 -alkyl or cycloalkyl radicals, C.sub.6 -C.sub.12 -aryl radicals or C.sub.7 -C.sub.15 -aralkyl radicals, in the presence of a metathesis catalyst to give butene and the1,4-butenediol diethers of the formula I

and subsequently reacting the 1,4-butenediol diethers alone or in combination with 1,4-butenediol diethers of the formula II

with water and hydrogen at from 20 to 300.degree. C. and from 1 to 300 bar in the presence of catalysts or catalyst combinations which comprise components which are both capable of hydrogenation and have acidic or basic centers.

6. The process defined in claim 5, wherein the metathesis catalysts comprise ruthenium or ruthenium compounds.

7. The process defined in claim 6, wherein the ruthenium compounds are of the formula RuCl.sub.2 (.dbd.CHR)(PR'.sub.3).sub.2 where R is hydrogen, alkyl or aryl and R' is alkyl.

8. The process defined in claim 6, wherein the ruthenium compounds are of the formula [RuX.sub.2 (.eta..sup.6 -p-cymene)PCy.sub.3 ]/N.sub.2 CHR' where X is halogen, Cy is cyclohexyl and R' is hydrogen, alkyl, aryl or trimethylsilyl.

9. The process defined in claim 5, wherein the compound of the formula IV is 1-butoxy-2-butene.

10. The process defined in claim 4, wherein the butenediol diesters of the formulae I and/or II are converted to the 1,4-butanediol monoethers of the formula III at from 20 to 300.degree. C. and from 1 to 300 bar.

11. The process defined in claim 1, which is carried out in the gas phase or the liquid phase.

12. The process defined in claim 1, which is carried out continuously.

13. The process defined in claim 1, wherein water is present in an amount of 100 mol, per mol of the 1,4-butenediol diesters of the formula I and/or II, or less.

14. The process defined in claim 1, wherein the catalysts or catalyst combinations are employed in the form of homogeneous solutions.

15. The process defined in claim 1, wherein the catalysts or catalyst combinations comprise one or more of the following elements or compounds thereof: copper, chromium, rhenium, cobalt, rhodium, nickel, palladium, ruthenium, iron and platinum.

16. The process defined in claim 1, wherein the catalysts or catalyst combinations are employed in the form of catalysts supported by a carrier material, wherein the catalytically active components are applied to the carrier material by way ofprecipitation, impregnation, by vapor deposition or by flame spraying.

17. The process defined in claim 16, wherein the catalysts or catalyst combinations comprise one or more of the following: platinum on active carbon, palladium on active carbon, palladium on aluminum oxide, cobalt on active carbon, cobalt onsilicon dioxide, cobalt on aluminium oxide, iron on active carbon, manganese on active carbon, rhenium on active carbon, rhenium on silicon dioxide, rhenium/tin on active carbon, rhenium/palladium on active carbon, copper on active carbon, copper onsilicon dioxide, copper on aluminium oxide, copper chromite and barium copper chromite.

18. The process defined in claim 1, wherein the acidic or basic centers of the catalysts or catalyst combinations consist of one or more Lewis acid or base, or Bronsted acid or base.