Preparation of phosphabenzene compounds

Details Preparation of phosphabenzene compounds Preparation of phosphabenzene compounds

2000-03-14

2001-06-26

Vollano, Jean F. (Department: 1621)

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

Organic compounds

Phosphorus containing

C562S030000, C560S008000, C564S016000

Reexamination Certificate

active

06252117

ABSTRACT:

Phosphabenzene compounds can be used as ligands in transition metal complexes which are used in the hydroformylation of olefins.
DE-A 196 21 967 describes such complexes and processes for preparing them. In one process variant, 3,3′-bis(2,4,6-triphenylphosphabenzene)-1,1′-biphenyl can be prepared by reaction of the corresponding pyrylium salt with phosphine.
DE-A-16 18 668 describes a process for preparing substituted phosphabenzenes in which pyrylium salts are reacted with trishydroxymethylphosphine, tetrahydroxymethylphosphine chloride or tetrahydroxymethylphosphine hydroxide. The phosphine compounds are difficult to prepare and the process is not economical.
F. Lieb “Synthesen und Reaktionen von Phosphorinen, Untersuchungen zur Darstellung von Systemen mit Arsen-Kohlenstoff-Doppelbindungen”, Inaugural Thesis, Würzburg, 1969, pages 106 and 107, describes a process for preparing 2,4,6-triphenylpyrylium tetrafluoroborate in n-butanol at −78° C., in which the reaction is carried out using PH
3
in the presence of a catalytic amount of acid (acetic anhydride/HBr) or of CaCO
3
which dissolves in the diluent, as base. After closing the reaction vessel, the reaction is carried out for 41 hours at 110° C. under autogenous pressure. The use of bases leads to formation of salts which necessitates further separation steps.
DE-A-16 68 416 describes phosphabenzenes and processes for preparing them by reaction of substituted pyrylium salts with phosphine. The reaction takes place in a glass autoclave in which phosphine is formed from phosphonium iodide only after closing the autoclave. Alternatively, phosphine is condensed in the reactor, which requires a temperature below the boiling point of phosphine, viz. −87° C. The reaction is then again carried out in an autoclave.
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 appropriate cooling equipment. The process in a closed reaction vessel is difficult or impossible to control.
In DE-A-197 43 197, which has an earlier priority date but was not published before the priority date of the present application, some of the disadvantages described are avoided by a process in which pyrylium salts are reacted with phosphine in the presence of a catalytic amount of acid and in the presence or absence of a solvent or diluent. Here, the pyrylium salts are combined with phosphine at above 0° C. and reacted at from ≧0° C. to 200° C. and a pressure above 1 bar. The pyrylium salts are preferably combined with phosphine at ambient temperature and the resulting mixture is heated to a temperature in the range from 110 to 130° C. for the reaction. In the process described, catalytic amounts of acid are used. As acid catalysts, use is made of mineral acids such as HCl, HBr or HI. However, such free mineral acids can cause corrosion damage to metal autoclaves, pressure vessels or other reaction vessels. Furthermore, there is the risk of the desired product being contaminated with halide ions. When phosphabenzenes are used as cocatalysts, even traces of such contaminants can have an adverse effect on the catalyst properties.
It is an object of the present invention to provide a process for preparing phosphabenzene compounds which can be carried out economically and avoids the disadvantages of the known processes.
We have found that this object is achieved by a process for preparing phosphabenzene compounds of the formulae I and II
where R
1
to R
6
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=an anion, R=hydrogen or C
1-6
-alkyl) or C
1-12
-alkyl, C
6-12
-aryl, C
7-12
-aralkyl, C
7-12
-alkaryl or C
3-6
-heterocycloalkyl having from 1 to 3 heteroatoms which may be substituted by the above radicals, where two or more of the radicals may also be joined to form aliphatic or fused-on rings,
and
W is a bridge comprising a covalent bond, an oxo group, a sulfur group, an ammo group, a di-C
1-6
-alkylsilicon group or a C
1-16
-radical which may be a constituent of one or more linked cyclic or aromatic rings and may be interrupted by from 1 to 3 heteroatoms, where the o or m position of the phosphabenzene ring which is not bound to the bridge may in each case bear one of the radicals R
1
to R
6
, by reacting corresponding pyrylium salts with PH
3
in the presence or absence of a solvent or diluent. In the process of the invention, the pyrylium salts are combined with PH
3
at above 0° C. and are reacted at a temperature in the range from 0° C. to 200° C. and a pressure above 1 bar without addition of an acid catalyst or a base. Not adding an acid catalyst or a base enables the process to be simplified and made more economical.
In one embodiment, 3,3′-bis(2,4,6-triphenylphosphabenzene)-1,1′-biphenyl is excepted.
It has surprisingly been found that phosphabenzene compounds of the above formulae can be obtained by reacting the corresponding pyrylium salts, i.e. compounds in which the phosphorus in the formulae I and II is replaced by O
+
and an appropriate counterion is present, with PH
3
if certain process conditions are adhered to. The pyrylium salts are readily available industrially or can be prepared by simple means. PH
3
is available industrially.
Even when the addition of an acid catalyst, in particular a mineral acid, is omitted, the process can be carried out in yields which are as high as before or even higher.
The free acid corresponding to the anion of the pyrylium salt can be separated from the product mixture obtained after the reaction by aqueous extraction and returned to the preparation of the pyrylium salt. The aqueous solution of, for example, tetrafluoroboric acid obtained in the extraction with water can, if desired, be isolated prior to recycling. The aqueous solution contains no mineral acid contamination.
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.
During the reaction, PH
3
is preferably passed into the reaction mixture in order to keep the PH
3
partial pressure essentially constant. This procedure allows a particularly economical and rapid reaction to form the desired phosphabenzene 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 resulting mixture is reacted by heating to a temperature in the range from 60 to 140° C., preferably from 80 to 130° C.
The temperature of the reaction is particularly preferably from 100 to 120° C. The reaction is preferably carried out in an autoclave. In addition to PH
3
, it is possible to use 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 and diluents are, for example, lower aliphatic alcohols such as methanol, ethanol, n-propanol, n-butanol, i-butanol, tert-butanol or pentanol isomers, preferably ethanol, propanol or butanols, in particular n-butanol.
After the reaction, the reaction mixture is preferably depressurized and, if desired, purged with an inert gas. The gases carried from the reaction mixture are cooled and passed through a separator to separate off unreacted PH
3
in liquid form and the PH
3
separated off is returned to the reaction.
A particularly economically and ecologically acc

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