Process for the continuous preparation of alkyl...

Details Process for the continuous preparation of alkyl... Process for the continuous preparation of alkyl...

1999-05-04

2001-08-14

Geist, Gary (Department: 1623)

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

Organic compounds

Oxygen containing

C568S054000, C568S449000, C568S451000

Reexamination Certificate

active

06274773

ABSTRACT:

The invention relates to a process for the continuous preparation of an alkyl 5-formylvalerate by reacting an alkyl 3-pentenoate with carbon monoxide and hydrogen by hydroformylation using a catalyst system comprising rhodium or iridium and a multidentate organic phosphite ligand according to the general formula:
in which n is 2-6, X is an n-valent organic bridging group and in which the end groups R
1
-R
2
are monovalent aryl groups.
Such a process is described in WO-A-9518089. This patent application describes a process in which methyl-5-formylvalerate is prepared with a selectivity of 80% starting from methyl 3-pentenoate using a catalyst system consisting of rhodium and a tetravalent organic phosphite, in which R
1
and R
2
are phenyl groups substituted on the ortho and para position with a tert-butyl group and X is a group according to C—(CH
2
—)
4
.
A disadvantage of this process is that the catalyst is not stable over a prolonged period of time. For example after some days of continuous operation the reaction rate will continuously drop due to deactivation of the catalyst. Deactivation of the catalyst is not desired when performing a continuous hydroformylation process especially in a large scale process.
The object of this invention is a process with a reduced catalyst deactivation.
This object is achieved in that the process is carried out in the presence of an acid compound having a pKa between 1 and 12 when measured in water of 18° C.
It has been found that the catalyst activity can be stabilized over a prolonged period of time when such an acid is present. Moreover in spite of the addition of an acid no significant amount of 5-formylvaleric acid is formed due to acid catalyzed hydrolysis of the ester group of the alkyl 5-formylvalerate.
The addition of an acid, such as aromatic compounds substituted with carboxylic or hydroxy groups, to a rhodium-organophosphite complex catalyzed hydroformylation process is known from EP-A-590613. The organophosphite ligands described in this application however differ from the ligand according to formula (1) in that the end groups of the bisphosphite ligands are connected to each other, forming a cyclic structure. The cyclic structure is present when two of the organic groups (groups like R
1
and R
2
) are connected with each other. According to EP-A-590613 the catalyst deactivation is caused by the presence of this unique cyclic end group structure. The degradation product of the ligand described in EP-A-590613 is referred to as “the poisoning phosphite” having the corresponding cyclic structure. Such a poisoning phosphite however cannot be formed when a phosphite according to formula (1) is used.
The acid is preferably present in an amount of 0.05 to 20 wt % during the hydroformylation reaction. More preferably between 0.1 and 1 wt %.
The acid can be any acid with a pKa between 1 and 12 and preferably between 2.5 to 10, measured in water of 18° C. Examples of suitable acids are aromatic carboxylic acids, for example optionally substituted benzoic acid, p-chloro-benzoic acid, phthalic acid, aliphatic carboxylic acids, for example dicarboxylic acids having between 2-20 carbon atoms, for example adipic acid, glutaric acid and fumaric acid, mono carboxylic acids, for example valeric acid, butynic acid, decanoic acid, mono methyl adipate, mono methyl glutarate, phenols, for example phenol, cresol, p-methylphenol, bisphenols, bis-&bgr;-naphthol, dihydroxy naphthalene. Preferably the acid has a normal boiling point higher than 200° C.
R
1
and R
2
in formula (1) are preferably the same or different monovalent aryl groups with 6 to 20 carbon atoms. It is to be understood that the various R
1
and R
2
groups can be different from each other. Preferably all R
1
and R
2
groups are the same because the resulting ligands are more readily available. Preferably R
1
and R
2
are monovalent aryl groups, for example phenyl, containing at least one group, R
3
, other than hydrogen in an ortho position relative to the oxygen atom, where R
3
is a C
1
to C
20
alkyl or C
6
-C
20
aryl group and preferably a C
1
-C
6
alkyl group. Other preferred monovalent aryl groups for R
1
and R
2
are monovalent fused aromatic ring systems with 2 or more rings having 10-20 carbon atoms. R
1
and R
2
can optionally be further substituted with for example C1-C10 alkyl, C
6
-C
20
aryl, C
1
-C
10
alkoxy, C
6
-C
20
aryloxy groups, triarylsilyl, trialkylsilyl, carboalkoxy, carboaryloxy, alkylcarbonyl, arylcarbonyl, oxazole, amide, amine or a nitrile or halogen groups, for example F, Cl or Br.
When the aryl groups R
1
and R
2
are substituted with at least one R
3
-group in the ortho-position relative to the phenolic oxygen atom, higher linear selectivity is observed using these ligands in a hydroformylation process. Examples of these R
3
groups are methyl, ethyl, propyl, isopropyl, isobutyl, tert-butyl or n-butyl. R
3
is preferably only one bulky group, having a steric hinderance of isopropyl or greater. When less bulky substituents are used preferably both ortho positions are substituted with these groups. Preferably R
1
and R
2
are 2-isopropylphenyl or 2-tert-butylphenyl groups.
Another preferred class of aryl groups for R
1
and R
2
are fused aromatic ring systems with 2 or more rings having 10 to 20 carbon atoms which do not necessarily have to be substituted at the ortho position (on the carbon atom adjacent to the carbon atom which is bonded to the oxygen atom in formula (1)) with groups other than hydrogen. It has been found that when R
1
and/or R
2
is such an unsubstituted aromatic ring system, high catalyst activity, a high selectivity to terminal aldehyde and a high linearity can be achieved. Examples of such fused aromatic ring systems are phenanthryl, anthryl and naphthyl groups. Preferably 9-phenanthryl or 1-naphthyl groups are used.
X is preferably an organic group having between 1 and 40 carbon atoms, and more preferably between 4 and 40 carbon atoms. Bidentate ligands, having a bivalent bridging group (n=2), are most mentioned in the patent literature. Examples of bridging groups X can be found in U.S. Pat. No. 4,748,261, EP-A-556681 and EP-A-518241. Preferably the bridging group X is such that the multidentate phosphite ligand can form a chelate-type complex with the metal employed (rhodium or iridium) during the reaction conditions. By a chelate type complex is meant that (substantially) at least two phosphorus atoms of a ligand molecule form a coordinated bond with one rhodium or iridium atom/ion. By a non-chelate-type complex is meant that only one phosphorus P atom of a ligand molecule forms a coordinated bond with one rhodium or iridium atom/ion. The choice of bridging group X of the ligand will determine whether a chelate-type complex can be formed in the reaction zone. Examples of bridging groups which result in a ligand which can form a chelate-type bridging group are for example described in WO-A-9518089. Preferably bridging group X has a structure according to formula (2) or (3):
in which Q is —O—, —S— or a —CR
4
R
5
— divalent group and m is 0 or 1 and R
4
and R
5
is hydrogen or a methyl group and Y and Z hydrogen or organic groups containing at least one carbon atom, and more preferably containing 1-20 carbon atoms. Preferably m=0.
Preferably Y and Z are individually selected from the, group of alkyl, aryl, triarylsilyl, trialkylsilyl, carboalkoxy, carboaryloxy, aryloxy, alkoxy, alkylcarbonyl, arylcarbonyl, oxazole, amide, amine or a nitrile.
For Y and Z, the alkyl group is preferably a C
1
-C
10
alkyl group, for example methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, isobutyl, pentyl or hexyl. An example of a suitable triarylsilyl group is triphenylsilyl and examples of a suitable trialkylsilyl group are trimethylsilyl and triethylsilyl. Preferred aryl groups have 6 to 20 carbon atoms, for example phenyl, benzyl, tolyl, naphthyl, anthranyl or phenanthryl. Preferred aryloxy groups have 6 to 12 carbon atoms, for example phenoxy. Preferred alkoxy groups have 1 to 20 carbon atoms, for example met

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