Method for producing phosphabenzene compounds

Details Method for producing phosphabenzene compounds Method for producing phosphabenzene compounds

2000-03-30

2001-07-03

Vollano, Jean F. (Department: 1621)

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

Organic compounds

Phosphorus containing

C562S030000, C564S016000, C560S008000

Reexamination Certificate

active

06255532

ABSTRACT:

This is the national phase of PCT/EP 98/06216, filed Sep. 30, 1998, now WO 99/16774.
Phosphabenzene compounds can be used as ligands in transition-metal complexes used in the hydroformylation of olefins. In DE-A 196 21 967, having the title “Hydroformylation process, and catalysts containing phosphorus compounds as ligands which are suitable therefor”, which has an earlier priority date, but was not published before the priority date of the present application, corresponding complexes and processes for their preparation are described. According to one process variant, bis-3,3′-(2,4,6-triphenyl-3-phosphabenzene)-1,1′-biphenyl can be prepared by reacting the corresponding pyrilium salt with phosphine.
DE-A 1 618 668 describes a process for the preparation of substituted phosphabenzenes in which pyrilium salts are reacted with trishydroxymethylphosphine, trishydroxymethylphosphine chloride or tetrahydroxymethylphosphine hydroxide. The phosphine compounds are difficult to prepare, and the process is uneconomical.
F. Lieb, “Synthesen und Reaktionen von Phosphorinen, Untersuchungen zur Darstellung von Systemen mit Arsen-Kohlenstoff-Doppelbindungen” [Syntheses and Reactions of Phosphorins, Studies on the Preparation of Systems Containing Arsenic-Carbon Double Bonds], inaugural dissertation, Wiirzburg, 1969, pages 106 and 107, describes a process for the preparation of 2,4,6-triphenylphosphorin (2,4,6-triphenylphosphabenzene), in which 2,4,6-triphenylpyrilium tetrailoroborate in n-butanol is reacted at −78° C. with PH
3
, which dissolves in the diluent. After the reaction vessel has been sealed, the reaction proceeds for 41 hours at 110° C. under autogenous pressure.
Carrying out the reaction under autogenous pressure has the disadvantage that the concentration of the reactants changes constantly and long reaction times are necessary. The introduction of PH
3
at −78° C. requires the use of corresponding cooling equipment. The process in a sealed reaction vessel is difficult or impossible to control.
It is an object of the present invention to provide a process for the preparation of phosphabenzene compounds which is economical and avoids the disadvantages of the known processes.
We have found that this object is achieved by a process for the preparation of phosphabenzene compounds of the formulae I and II
where R
1
to R
6
, independently of one another, are hydrogen, COOM, SO
3
M, NR
3
X, NR
2
, OR, COOR or SR, C
1
-C
12
-alkyl, C
6
-C
12
-aryl, C
7
-C
12
-aralkyl, or C
3-6
-heterocycloalkyl having 1 to 3 heteroatoms, and wherein C
1
-C
12
-alkyl, C
6
-C
12
-aryl, C
7
-C
12
-aralkyl, or C
3-6
-heterocycloalkyl are optionally substituted by COOM, S03M, NR
3
X, NR
2
, OR, COOR or SR where M is hydrogen, NH
4
or an alkali metal, X is an anion, R is hydrogen, C
1-6
-alkyl, or C
1-12
-alkyl, C
6-12
-aryl, C
7-12
-aralkyl or C
3-6
-heterocycloalkyl having 1 to 3 heteroatoms which may be substituted by the above radicals or linked to form fused rings, and
W is a bridge comprising a covalent bond, an oxo group, a sulfur group, an amino group, a di-C
1-6
-alkylsilicon group or a C
1-16
-radical, which may be part of one or more linked cyclic or aromatic rings and may be interrupted by 1 to 3 heteroatoms, where the phosphabenzene ring o- or m-position not bonded to the bridge may carry one of the radicals R
1
to R
6
,
with the exception of bis-3,3′-(2,4,6-triphenyl-3-phosphaphenyl)-
1,1′-biphenyl,
by reacting corresponding pyrilium salts with PH
3
in the presence of a catalytic amount of acid and in the presence or absence of a solvent or diluent. In the novel process, pyriliwn salts are mixed with PH3 at above 0° C. and reacted at from 0° C. to 200° C. and at a pressure greater than 1 bar.
It has been found in accordance with the invention that phosphabenzene compounds of the above formulae are obtainable by reacting the corresponding pyrilium salts, i.e. compounds in which phosphorus in the formulae I and II has been replaced by O
+
with a corresponding counterion, with PH
3
if certain process conditions are observed. The pyrilium salts are commercially available or can easily be prepared. 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 in the range from 5 to 35 bar, in particular in the range from 20 to 30 bar. The overall pressure in the system depends on the particular solvent. The overall pressure can be increased by injecting PH
3
or an inert gas.
In a preferred procedure, PH
3
is 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 fast reaction to give the desired phosphabenzene compounds. High product purities and conversions are achieved. The novel process can be employed reliably for a multiplicity of products. It can be carried out continuously or batchwise, preferably batchwise.
In a particularly advantageous process variant, the pyrilium salts are mixed with PH
3
at ambient temperature, and the resultant mixture is heated to a temperature in the range from 110 to 130° C. for the reaction.
The temperature during the reaction is particularly preferably from 115 to 125° C. The reaction is preferably carried out in an autoclave. Besides PH
3
, it is also possible tadditionally to use an inert gas to set the desired overall pressure. However, it is preferred to use PH
3
alone.
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 is preferably carried out in the presence of an acidic catalyst. Suitable acidic catalysts are mineral acids, such as HI, HCl or HBr. In particular, hydrogen bromide in acetic acid or acetic anhydride is used as the acidic catalyst.
After the reaction, the reaction mixture is preferably decompressed and, if desired, flushed with an inert gas. In order to remove unreacted PH
3
in liquid form, the gases leaving the reaction mixture are cooled and passed through a separator, and the PH
3
removed is fed back into the reaction.
A particularly economical and ecologically acceptable process is therefore one in which PH
3
is passed into a reactor, the reaction is carried out, and the gas stream is passed, via a further line, through a condenser of any desired design, in which the PH
3
is condensed out. In a downstream separator of any desired design, the PH
3
is then separated off and fed back into the reaction, for example with the aid of a pump. In order to obtain an offgas which is particularly low in PH
3
, it is advantageous to use a second downstream condenser and separator. In order completely to free the reactor gas space and the apparatuses employed from PH
3
, which is advantageous owing to the toxicity of PH
3
, a flushing line for flushing with an inert gas, such as nitrogen, should be provided. The flushing gas should be passed through the combination of condenser and separator.
The time needed for the reaction depends on the nature of the pyrilium salt. Depending on the pyrilium salt, the reaction is preferably carried out for a period of from 1 to 4 hours. The proportion of solvent, based on the pyrilium salts employed, is preferably from 5 to 50% by weight, particularly preferably from 15 to 35% by weight. The amount of acidic catalyst employed is, based on the pyrilium salts, preferably from 0.01 to 1%, particularly preferably from 0.03 to 0.1%. In the case of reaction using a solvent, the concentration of PH
3
in the solvent depends on the PH
3
partial pressure and the nature of the solvent; in particular in the case of a continuous reaction procedure, a high concentration of PH
3
in the solvent shoul

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