Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-07-25
2002-06-11
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S861000, C568S866000, C568S867000
Reexamination Certificate
active
06403845
ABSTRACT:
The present invention relates to a process for preparing 1,5-pentanediols by single-stage reaction of alkoxydihydropyrans with water and hydrogen in the presence of a catalyst and also to the use of the catalyst in this process.
1,5-pentanediol is an important intermediate for the production of polyesters, polyurethanes and heterocyclic compounds such as 1-methylpiperidine which are used as intermediates in the production of drugs and crop protection agents.
Pentanediol is produced industrially on a large scale, as described in Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Vol. Al, p. 307, by catalytic hydrogenation of glutaric acid, which is obtained industrially as a coproduct in the production of adipic acid, or its esters. In the catalytic hydrogenation of adipic acid/glutaric acid mixtures, pentanediol is obtained in a proportion of only about 10 mol%. Furthermore, the isolation of very pure pentanediol from this mixture is difficult because of the very similar boiling points of pentanediol and hexanediol.
A further process for preparing pentanediol starts from glutaraldehyde which is obtained by acid hydrolysis of alkoxydihydropyrans. Processes for the hydrogenation of dialdehydes are described in DE-A 4 414 274; in these processes, it is also possible to use the hemiacetals or acetals of the dialdehydes. As catalyst, use is made of a monolithic catalyst comprising a noble metal on a metal support coated with aluminum/silicon oxide. A disadvantage of these processes is that a two-stage reaction starting from alkoxydihydropyrans, namely acid hydrolysis and subsequent hydrogenation, is necessary.
There have therefore been attempts to convert alkoxydihydropyran directly into pentanediol in a single-stage process. DE-A 1 003 704 and U.S. Pat. No. 2,546,019 describe processes in which pentanediol is obtained by single-stage reaction of alkoxydihydropyran with water and hydrogen in the presence of a catalyst. Hydrogenation catalysts which are said to be able to be used are metals such as Pt, Pd, Au, Ag, Zn, V, W, Co, Ni, Ru, Rh, Mn, Cr, Mo, Ir, Os, Pb, their alloys and also their oxides and sulfides. As preferred hydrogenation catalysts, mention is made of pyrophoric metal hydrogenation catalysts comprising nickel, cobalt and iron. These hydrogenation catalysts, which are known as Raney catalysts, can be dispersed as finely divided powders in the reaction solution or can also be used as fixed-bed catalysts in the form of relatively large particles. A further possibility mentioned is to apply the metal catalyst to a support material such as pumice or kieselguhr. Disadvantages of the finely divided Raney catalysts are their pyrophoric properties, which mean that the powders have to be handled under inert gas, and also their toxicity. Reactions using finely divided Raney catalysts are predominantly carried out batchwise, and the suspension has to be filtered after the reaction. Carrying out these reactions continuously is relatively difficult, since continuously the reaction mixture has to be filtered and the catalyst retained on the filter has to be returned to the reactor. Furthermore, the production of Raney catalysts, which are suitable as fixed-bed catalysts, is technically complicated.
It is an object of the present invention to provide a single-stage process for preparing pentanediols from alkoxydihydropyrans, which makes do without the use of Raney catalysts.
We have found that this object is achieved by a process for preparing 1,5-pentanediols of the formula (I)
by single-stage reaction of alkoxydihydropyrans of the formula (II)
where, in the formulae (I) and (II),
R, R′, R″, R′″ can be identical or different and are each hydrogen or a linear or branched saturated hydrocarbon radical having from 1 to 20 carbon atoms in which the hydrocarbon chain may contain O, S and N as heteroatoms and which may be monosubstituted or polysubstituted by hydroxy, thiol or amino groups or halogens,
with water and hydrogen in the presence of a catalyst comprising oxides of nickel, zirconium and copper.
The catalyst used according to the present invention comprises oxides of nickel, zirconium and copper. The catalyst may further comprise molybdenum oxide. The catalyst used according to the present invention preferably comprises from 20 to 75% by weight, particularly preferably from 30 to 70% by weight, very particularly preferably from 40 to 60% by weight and especially from 35 to 55% by weight, of nickel oxide, preferably from 10 to 75% by weight, particularly preferably from 10 to 60% by weight, very particularly preferably from 15 to 50% by weight and especially from 25 to 45% by weight, of zirconium dioxide and preferably from 5 to 50% by weight, particularly preferably from 5 to 40% by weight, very particularly preferably from 10 to 35% by weight and especially from 10 to 20% by weight, of copper oxide. The catalyst may further comprise up to 5% by weight, for example from 0.1 to 5% by weight, of molybdenum oxide. The proportions by weight indicated are in each case based on the oxidic, unreduced catalyst and add up to 100% by weight.
In one embodiment, the catalyst used according to the present invention comprises nickel oxide, zirconium dioxide and copper oxide and no molybdenum oxide. In a further embodiment, the catalyst used according to the present invention further comprises 0.1-5% by weight of molybdenum oxide. The catalysts according to the present invention preferably comprise only the metals nickel, zirconium, copper and, if desired, molybdenum and any further metals only in traces, for example in amounts of <1 mol %, preferably <0.1 mol %, based on the total metal content. Preference is thus given to catalysts which consist essentially of the abovementioned metal oxides in the amounts specified above.
In general, the catalysts used according to the present invention are used in the form of unsupported catalysts. For the purposes of the present invention, the term “unsupported catalyst” refers to a catalyst which, in contrast to a supported catalyst, consists only of catalytically active composition. Unsupported catalysts can be used by introducing the catalytically active composition milled to a powder into the reaction vessel or by converting the catalytically active composition into shaped catalyst bodies, for example spheres, cylinders, rings or spirals, by milling, mixing with shaping aids, shaping and heat treatment and installing these in the reactor.
In general, precipitation methods are employed for preparing the catalysts used according to the present invention. Thus, for example, they can be obtained by coprecipitation of the nickel and copper components from an aqueous salt solution containing these elements by means of mineral bases in the presence of a slurry of a sparingly soluble, oxygen-containing zirconium compound and subsequent washing, drying and calcination of the precipitate obtained. Sparingly soluble, oxygen-containing zirconium compounds which can be used are, for example, zirconium dioxide and hydrated zirconium oxide. Molybdenum can be added before drying as ammonium heptamolybdate.
The catalysts used according to the present invention can be obtained by coprecipitation of the nickel and copper components by adding an aqueous mineral base, in particular an alkali metal base such as sodium carbonate, sodium hydroxide, potassium carbonate or potassium hydroxide, while stirring to a hot aqueous salt solution containing copper and nickel until precipitation is complete. The precipitates obtained in these precipitation reactions are generally chemically nonuniform and comprise, inter alia, mixtures of oxides, hydrated oxides, hydroxides, carbonates and insoluble basic salts of the metals used. It may be found to be advantageous to age the precipitates to improve their filterability.
The catalyst used according to the present invention is preferably prepared by precipitating salts of the metals nickel, copper and zirconium in aqueous solution at from 30 to 90° C. and a pH of from 5 to 9, filtering the
Eller Karsten
Höhn Arthur
Hunger Jürgen
Nouwen Jan
Pfeffinger Joachim
Padmanabhan Sreeni
Price Elvis O.
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