Phosphabenzene compounds and their use in hydroformylation

Details Phosphabenzene compounds and their use in hydroformylation Phosphabenzene compounds and their use in hydroformylation

2001-09-11

2003-01-21

Vollano, Jean F. (Department: 1621)

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

Organic compounds

Phosphorus containing

C568S451000, C568S454000

Reexamination Certificate

active

06509505

ABSTRACT:

This application is a 371 of PCT/EP00/02288 filed Mar. 15, 2000, now WO 00/55164.
The present invention relates to phosphabenzene compounds and their use in complexes of transition metals of transition group VIII of the Periodic Table of the Elements in the preparation of aldehydes by hydroformylation of olefins using CO/H
2
at up to 200° C. and pressures of up to 700 bar.
Hydroformylation is a known process utilized industrially for the preparation of aldehydes from olefins, carbon monoxide and hydrogen. As described in WO 97/46507, phosphabenzenes are active cocatalysts for the hydroformylation of olefins. This document describes a process for preparing aldehydes by hydroformylation of olefins using CO/H
2
in the presence of complexes containing phosphabenzene compounds as ligands.
However, the phosphabenzene compounds used, for example 2,4,6-triphenylphosphabenzene and 2,6-bis(2-naphthyl)-4-phenylphosphabenzene, but also phosphabenzenes such as 2,3,5,6-tetraphenylphosphabenzene or 2,3,4,5,6-pentaphenylphosphabenzene, have the disadvantage that they can be degraded under hydroformylation conditions by partial or complete hydrogenation of the phosphabenzene system and subsequent addition reactions (see Examples 11-14). This forms, inter alia, secondary and tertiary phosphines which greatly inhibit the hydroformylation activity of the catalyst system.
Similar phosphabenzene compounds are described in DE-A-19 621 967 and DE-A-16 68 416.
It is an object of the present invention to provide phosphabenzene ligands which avoid the disadvantages of the known ligands.
We have found that this object is achieved by phosphabenzene compounds of the formula (I)
where the radicals R
1
to R
13
are, independently of one another, hydrogen, COOM, SO
3
M, NR
3
X, NR
2
, OR, COOR or SR (where M=hydrogen, NH
4
or alkali metal, X=anion, R=hydrogen or C
1
-C
6
-alkyl), or C
1
-C
12
-alkyl, C
6
-C
12
-aryl, C
7
-C
12
-aralkyl, C
7
-C
12
-alkaryl or C
3
-C
6
-heteroaromatics, where the alkyl, aryl, alkaryl and aralkyl radicals may bear the abovementioned radicals as substituents and two or more of the radicals may be joined to form aliphatic or fused-on rings, where at least one of the radicals R
4
and R
8
and at least one of the radicals R
9
and R
13
is not hydrogen.
Preferably, at least one of the radicals R
4
and R
8
and at least one of the radicals R
9
and R
13
are, independently of one another, C
1
-C
12
-alkyl, C
6
-C
12
-aryl, C
7
-C
12
-aralkyl or C
7
-C
12
-alkaryl, or R
4
and R
3
and/or R
13
and R
1
form a C
2
-C
4
-alkylene radical.
Particularly preferably, at least one of the radicals R
4
and R
8
and at least one of the radicals R
9
and R
13
are C
1
-C
6
-alkyl, or (R
4
and R
3
) and (R
13
and R
1
) in each case form a C
2
-C
3
-alkylene radical.
R
2
is preferably a phenyl radical which may be substituted by from 1 to 5, preferably from 1 to 3, in particular 1 or 2, C
1
-C
6
-alkyl radicals.
Particularly preferably, the radicals R
1
and R
3
are hydrogen and in each case at most three of the radicals R
4
to R
8
and R
9
to R
13
are not hydrogen. The radicals R
4
to R
8
and R
9
to R
13
in each case particularly preferably have a maximum of 6, in particular a maximum of 3, carbon atoms. In particular, the phosphobenzene compounds of the formula (I) have no atoms apart from the one phosphorus atom which are not carbon or hydrogen.
The compounds of the formula (I) preferably contain, in addition to the phosphobenzene ring, from 3 to 5, in particular 3, further aromatic rings. The number of alkyl radicals in the compounds of the formula (I) is preferably 0 in the case of purely cyclic structures, otherwise preferably from 2 to 7, in particular from 2 to 6. The alkyl radicals can be linear or branched. Preferably, only linear alkyl radicals are present. The same applies analogously to bridging alkylene groups.
Examples of phosphobenzenes which may be mentioned are:
It has been found that, in particular, the introduction of 2-alkylaryl substituents in the 2 and 6 positions of the phosphobenzene system gives a significantly increased stability of the cocatalyst under hydroformylation conditions an d the catalyst systems display comparable activities to those of corresponding unsubstituted systems.
The degradation of phosphobenzene compounds having 2-alkylaryl substituents in the 2 and 6 positions of the phosphobenzene system under hydroformylation conditions is significantly reduced compared to analogous systems bearing unsubstituted aryl substituents.
The principle of the preparation of the phosphobenzenes is known. General synthetic methods may be found in G. Märkl in Multiple Bonds and Low Coordination in Phosphorus Chemistry (Editors M. Regitz, O. J. Scherer), Thieme, Stuttgart, 1990, pp. 220 to 257 (and the references cited therein). Processes for preparing phosphobenzene compounds from pyrylium salts by reaction with phosphine are described in WO 97/46507, DE-A-196 21 967 and the earlier-priority DE-A-197 43 197 which is not a prior publication.
The preparation is preferably carried out by reacting corresponding pyrylium salts with PH
3
in the presence or absence of a catalytic amount of acid or base and in the presence or absence of a solvent or diluent. The pyrylium salts are preferably brought into contact with PH
3
at above 0° C. and reacted at from 0° C. to 200° C. and a pressure above 1 bar.
It has been found, according to the present invention, that phosphobenzene compounds of the formula above are obtainable by reaction of the corresponding pyrylium salts, i.e. compounds in which the phosphorus in the formula is replaced by O
+
together with a corresponding counterion, with PH
3
if particular process conditions are adhered to. The pyrylium salts are commercially available or can be prepared by simple means. PH
3
is commercially available.
The reaction is preferably carried out at a PH
3
partial pressure in the range from 0.1 to 100 bar, particularly preferably from 5 to 35 bar, in particular from 20 to 30 bar. The total pressure in the system depends on the solvent employed. The total pressure can be increased by injection of PH
3
or inert gas.
PH
3
is preferably passed into the reaction mixture during the reaction in order to keep the PH
3
partial pressure essentially constant. This procedure allows a particularly economical and rapid reaction to form the desired phosphobenzene compounds. High product purities and conversions are achieved. The process of the present invention can be used reliably for many products. It can be carried out continuously or batchwise, preferably batchwise. In a particularly advantageous process variant, the pyrylium salts are combined with PH
3
at ambient temperature, and the mixture obtained in this way is heated to from 60 to 140° C., preferably from 80 to 130° C., in order to bring about the reaction.
The reaction temperature is particularly preferably in the range from 100 to 120° C. The reaction is preferably carried out in an autoclave. In addition to PH
3
, it is possible to make additional use of an inert gas by means of which the desired total pressure is set. However, preference is given to using only PH
3
.
The reaction can be carried out in the presence or absence of a solvent or diluent. It is preferably carried out in the presence of a solvent or diluent. Suitable solvents or diluents are, for example, lower aliphatic alcohols such as methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, tert-butanol or pentanol isomers, preferably ethanol, propanol or butanols, in particular n-butanol.
The reaction can be carried out in the presence of an acid catalyst. Suitable acid catalysts are mineral acids such as HI, HCl, HBr. In particular, hydrogen bromide in acetic acid or acetic anhydride is used as acid catalyst. Preference is given to carrying out the reaction without an acid catalyst.
After the reaction, the reaction mixture is preferably depressurized and, if desired, purged with an inert gas. The gases given off from the reaction mixture are cooled to separate

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