Process for preparing tetrahydrofuran from dialkoxybutenes

Details Process for preparing tetrahydrofuran from dialkoxybutenes Process for preparing tetrahydrofuran from dialkoxybutenes

1998-11-12

2001-01-02

Rotman, Alan L. (Department: 1612)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C549S509000

Utility Patent

active

06169189

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a process for preparing tetrahydrofuran by reacting dialkoxybutenes with water and hydrogen in the presence of catalysts or catalyst combinations which are both capable of hydrogenation and have acidic or basic centers.
BACKGROUND ART
Tetrahydrofuran is obtained industrially on a large scale by cyclization of 1,4-butanediol (Weissermel, Arpe Industrielle Organische Chem., 4th Edition, VCH Verlagsgesellschaft Weinheim, 1994, page 111). Another possibility for preparing it comprises hydrogenation of dihydrofuran (EP-A 524 216).
The starting materials for the precursors in these cases are acetylene, propylene or propylene oxide, maleic anhydride or butadiene. Because butadiene is very readily available, there is now a preferential search for novel processes starting from butadiene and allowing tetrahydrofuran to be prepared in a simpler manner and at lower cost, the intention being in particular to reduce the number of reaction stages.
Intermediates based on the starting material butadiene are dialkoxybutenes which may be in the form of 1,4-dialkoxy-2-butenes (in cis and trans forms) and of 1,4-dialkoxy-1-butenes.
They can be described by the general formulae
RO—CH
2
—CH═CH—CH
2
—OR  I
and
RO—CH
2
—CH
2
—CH═CH—OR  II,
where R is identical or different C
1
-C
15
-alkyl or cycloalkyl, C
6
-C
12
-aryl or C
7
-C
15
-aralkyl radicals.
The 1,4-butenediol diethers of the formulae I and II can be prepared in various ways, e.g. by reacting dibromobutene with two equivalents of alcohols, by oxidative additions of alcohols onto butadiene (SU-A 1 046 238 or EP-A 462 031) or by addition of alcohols onto vinyloxirane (WO-A 8 902 883).
Another method, to which this invention likewise relates, comprises addition of alcohols onto butadiene to form monoalkoxybutenes as disclosed in WO 95/19334 and metathesis thereof to dialkoxy-2-butenes and 2-butene.
DISCLOSURE OF THE INVENTION
We have found that tetrahydrofuran can be prepared in good yield in a few stages starting from butadiene when 1,4-butenediol diethers of the formulae I and/or II
RO—CH
2
—CH═CH—CH
2
—OR  I
RO—CH
2
—CH
2
—CH═CH—OR  II,
where the R radicals can be identical or different and are C
1
-C
15
-alkyl or cycloalkyl radicals, C
6
-C
12
-aryl radicals or C
7
-C
15
-aralkyl radicals, are reacted with water and hydrogen at from 20 to 300° 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.
It is assumed that the reaction according to the invention takes place by the individual steps depicted in the following scheme:
it being possible to return the eliminated alcohol to the preparation of the starting compounds I and II.
The following information is available in the literature on the individual steps assumed for this:
Isomerization of dialkoxy-2-butenes to the corresponding di-alkoxy-1-butenes has not been described. However, the isomerization of bistrimethylsilyl 2-butene ether to bistrimethylsilyl 1-butene ether (C. Malanga et al. Tetrahedron Lett. 36 (1995) 1133-1136) with nickel hydrides is to be regarded as similar.
Nor is the hydrolytic cleavage of dialkoxy-1-butenes to the corresponding alcohol and aldehyde ether known, the literature containing only examples of the acid-catalyzed hydrolysis of simple enol ethers (e.g. T. Okuyama et al., J. Am. Chem. Soc. 89 (1967) 5826-5831).
Hydrogenation of aldehyde ethers with Raney nickel as catalyst (compounds alkylated in the alpha position are exclusively used as alkoxy radical) to the corresponding 4-alkoxybutanols is described, as is the subsequent cyclization to THF on acidic catalysts, in EP 18 164 B1. However, in this case the ether component is eliminated not only as alcohol but also as the corresponding dehydrated product, i.e. as olefin, which can be reused only with difficulty in a cyclic process which is preferred for economic reasons. If the olefin is produced, in addition THF is not the primary product, but 1,4-butanediol is and forms THF only after elimination of water.
In the light of the abovementioned prior art, it was surprising that it is possible to obtain THF from dialkoxybutenes of the formulae I and II in one or a maximum of two stages and, at the same time, to obtain the alcohol component (hence with the possibility of recycling and design of a cyclic process) with high selectivity.
The reaction can take place in one or two stages.
In the one-stage variant, the compounds of the formulae I and/or II are reacted in the gas or liquid phase in the presence of water and hydrogen, and of a catalyst which is capable of hydrogenation and which has either Brönsted and/or Lewis acid or base centers, or to which an appropriate catalyst which is a Brönsted and/or Lewis acid or base has been added, to give THF and alcohol.
The R radicals in the precursor and intermediates may be different but are preferably the same. The radicals preferably used are those which afford a primary alcohol after elimination.
In the two-stage variant, compounds of the formulae I and/or II are reacted in the presence of water and hydrogen and of a hydrogenation catalyst to give 1,4-butanediol monoether which is then, with or without intermediate purification, converted on an acidic or basic catalyst into THF and alcohol.
The one- or two-stage process can be carried out batchwise or, preferably, continuously.
The description of the following features of the process applies both to the one-stage procedure and to the first stage of the two-stage variant:
The molar ratio of water to 1,4-butenediol diethers of the formulae I and/or II is 100:1, preferably 50:1, particularly preferably 10:1.
The reaction pressure, which is essentially determined by hydrogen, is from 1 to 300 bar, preferably 1 to 200 bar, particularly preferably 1 to 100 bar, and the reaction temperatures are in the range from 20 to 300° C., preferably 40 to 270° C., particularly preferably 80 to 200° C.
Catalysts particularly used according to the invention are those capable of catalytic hydrogenation of ketones or aldehydes with hydrogen to alcohols. As a rule, they contain one or more elements of subgroup I, II, VI-VIII or main group III-V of the periodic table of the elements or compounds thereof. The catalysts may be in the form of homogeneous solutions (examples in H. Kropf, Methoden der organischen Chemie (Houben-weyl), Volume IV/1c, Georg Thieme Verlag Stuttgart, 1980, pages 45-67) or heterogeneous.
Examples of preferred homogeneous catalysts are complexes of rhodium, ruthenium, iridium, palladium, platinum and cobalts with phosphine or phosphite ligands, whose preparation is described, for example, in CA-A 7 276 41, H. Brunner in Hartley: The chemistry of the metal-carbon bond; Vol. 5, pages 110-124, John Wiley & Sons, New York 1989 and T6th et al., Inorg. Chim. Acta 42, (1980) 153 and in the literature cited therein. Suitable metal complexes are furthermore described in WO 95-19 334.
Ru complexes are particularly preferred. Examples which may be mentioned are HRuCl(CO) (TPP)
3
and H
2
Ru(CO) (TPP)
3
(TPP=triphenylphosphine).
The heterogeneous catalysts may be employed either in a fixed arrangement, or else mobile, e.g. in a fluidized bed reactor, or in suspension. Examples thereof are described, for example, in Houben-Weyl, Methoden der organischen Chemie, Volume IV/1c, pages 16 to 26.
Preferred among these hydrogenation catalysts are those containing one or more elements of group Ib, IIb, VIb, VIIb and VIII, in particular copper, chromium, rhenium, cobalt, rhodium, nickel, palladium, ruthenium, iron and platinum or compounds thereof.
The catalysts employed in the process according to the invention may be, for example, what are called precipitated catalysts. Catalysts of this type can be prepared by precipitating their catalytically active components from solutions of their salts, in particular from solutions of their nitrates and/or acetates, for example by adding solutions of alkali m

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