Organic compounds -- part of the class 532-570 series – Organic compounds – Nitriles
Reexamination Certificate
2001-02-26
2002-02-12
McKane, Joseph K. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitriles
C558S441000
Reexamination Certificate
active
06346640
ABSTRACT:
The present invention relates to a process for preparing cyanovaleric acid or esters by reacting 2-, 3- or 4-pentenenitrile or mixtures thereof with carbon monoxide and a hydroxyl compound in the presence of a catalyst system.
5-Cyanovaleric acid and its esters are useful starting materials for dyes, pesticides, fibers, especially polyamide fibers, and plastics. Hydrogenation to 6-aminocaproic acid or 6-aminocaproic esters and elimination of water or alcohol provides caprolactam.
The preparation of cyanovaleric acid and cyanovaleric esters by carbonylation of pentenenitriles in the presence of catalysts is known. Known syntheses involve a pentenenitrile being reacted with carbon monoxide in the presence of water or alcohol at elevated temperature and elevated pressure in the presence of a catalyst system. The catalyst systems used are predominantly cobalt compounds, such as Co
2
(CO)
8
or Co(OAc)
2
, together with nitrogen bases (see GB-1 497 046 and DE-2 541 640), specific solvents, such as sulfolane (see U.S. Pat. No. 4,508,660), cyclic amide or urea derivatives (see EP-373 579) or nitrites (see EP-377 838 and U.S. Pat. No. 4,933,483).
EP 0 450 577 describes an Rh/HI catalyst system for hydroxycarbonylating pentenenitrile to form cyanovaleric acid.
Nitrile compounds frequently form complexes with transition metals. Catalytically active catalyst complexes tend to become deactivated through nitrile coordination. This holds especially for palladium, since palladium very readily forms stable nitrile complexes, for example (PhCN)
2
PdCl
2
, (CH
3
CN)
2
PdCl
2
. The palladium-catalyzed carbonylation of olefins that contain nitrile groups therefore proceeds in general only at very low catalyst activity. For instance, U.S. Pat. No. 4,257,973 describes the carbonylation of 3-pentenenitrile using the catalyst system (Ph
3
P)
2
PdCl
2
/SnCl
2
. The reaction proceeds with unknown selectivity, the yield of unspecific cyanic esters being only 5% (see Example 108 of U.S. Pat. No. 4,257,973).
EP 0 495 547 describes a process for the monocarbonylation of optionally substituted olefinically unsaturated compounds in the presence of a catalyst system comprising palladium cations, a bidentate diphosphine ligand and an anion source. According to EP 0 495 547, the starting olefin can be substituted by cyano or nitrile groups, for example. When alkenoic acid derivatives, such as alkenonitriles, are used as starting materials, the alkenoic acid derivative shall preferably be a 2-alkenoic acid derivative. For the carbonylation of alkenoic acid derivatives, the catalyst system preferably comprises a promoter, for example quinones and nitro compounds. Example 59 of EP 0 495 547 carbonylates acrylonitrile with carbon monoxide and methanol in the presence of Pd(OAc)
2
, TBPD (1,3-bis(di-n-butylphosphino)propane), NiTFS (nickel di-trifluoromethylsulfonate) and 1,4-naphthoquinone. However, conversion to the monomethyl ester mononitrile of malonic acid was only 5%, based on the acrylonitrile used. From EP 0 495 547, a person skilled in the art would have expected even lower yields for the reaction of nitrile-substituted olefins other than acrylonitrile, by the process described therein.
We have now found that, surprisingly, the carbonylation of 2-, 3- or 4-pentenenitrile is possible in high yield and high selectivity using a catalyst system which is comparable to that of EP 0 495 547. We have also found novel catalyst systems and novel diphosphine ligands whereby the yield and selectivity can be increased even further.
The present invention accordingly provides the process for preparing cyanovaleric acid or esters by reacting 2-, 3- or 4-pentenenitrile or mixtures thereof with carbon monoxide and a hydroxyl compound in the presence of a catalyst system comprising (i) a palladium(II) compound, (ii) a bidentate diphosphine ligand, and (iii) an anion source.
The starting materials used for the carbonylation of the invention are 2-, 3- or 4-pentenenitrile or mixtures thereof. The use of 3- and/or 4-pentenenitrile or of mixtures comprising 3- and/or 4-pentenenitrile as main components is preferred. 3-Pentenenitrile or mixtures comprising 3-pentenenitrile as main component are most preferred. 3-Pentenenitrile is preparable for example by addition of hydrocyanic acid to butadiene, for example in the presence of nickel complexes or copper(I) chloride according to the procedures described in the German OPI documents 1 593 277, 2 344 767 and 2 009 470.
The process of the invention provides 5-cyanovaleric acid with high selectivity, regardless of whether 2-, 3- or 4-pentenenitrile or a mixture thereof is used. It is believed that 2-pentenenitrile and 3-pentenenitrile first isomerize into 4-pentenenitrile. The carbonylation of 4-pentenenitrile to form 5-cyanovaleric acid or ester by the process of the invention takes place substantially regioselectively with selectivities which are generally above 70%, preferably above 80%, based on cyanovaleric acid or ester formed.
The palladium(II) compound is preferably a palladium salt. Examples of suitable palladium salts include the salts of nitric acid, sulfuric acid, of sulfonic acids, for example chlorosulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, t-butylsulfonic acid, p-toluenesulfonic acid, or of a sulfonated ion exchange resin, or of a carboxylic acid, for example of an alkanoic acid, such as acetic acid or trifluoroacetic acid. It will be appreciated that when the palladium(II) compound is a palladium salt of a suitable acid, this compound may also function as the anion source to be used according to the invention. The palladium(II) compound, furthermore, may take the form of a palladium complex, for example of a complex with a bidentate diphosphine ligand. In this case, the palladium(II) compound will simultaneously contain the bidentate diphosphine ligand to be used according to the invention. The palladium(II) compound can also be formed in situ starting from the elemental state.
The amount of palladium(II) compound is not critical. The amount is preferably within the range from 10
−7
to 10
−1
mol of palladium per mole of pentenenitrile used, especially within the range from 10
−6
to 10
−2
.
The bidentate diphosphine ligand can be used as such or in the form of a complex with the palladium(II) compound. Preferably, the diphosphine ligand has the following general structural formula:
R
1
R
2
P—X—PR
3
R
4
where R
1
, R
2
, R
3
and R
4
are independently C
1
-C
20
-alkyl, C
3
-C
10
-cycloalkyl, aryl or hetaryl having up to 4 fused aromatic rings or C
7
-C
20
-aralkyl, which may each be substituted, or R
1
and R
2
and/or R
3
and R
4
are together C
2
-C
20
-alkylene, arylene or hetarylene having up to 4 aromatic rings or C
7
-C
20
-aralkylene, which may each be substituted, and X is a divalent bridging radical such that the flanking phosphorus atoms are separated by from 1 to 10 atoms.
In more preferred diphosphine ligands, R
1
, R
2
, R
3
and R
4
are each independently an unsubstituted, linear or branched, linear or cyclic alkyl radical having from 1 to 10 carbon atoms, or R
1
and R
2
and/or R
3
and R
4
are together a linear or branched, linear or cyclic alkylene radical having from 1 to 10 carbon atoms.
In particularly preferred embodiments, R
1
, R
2
, R
3
and R
4
are each selected from methyl, ethyl, propyl, isopropyl, n-butyl, s-butyl, t-butyl and/or cyclohexyl radicals, or R
1
and R
2
and/or R
3
and R
4
are together a pentamethylene, hexamethylene or cyclooctylene radical. Where it has been stated above that R
1
, R
2
, R
3
and R
4
may each be substituted, the substituents can be any substituents which do not impair the catalytic activity of the system. Suitable substituents include halogen atoms, alkoxy groups, haloalkyl groups, haloalkoxy groups, acyl radicals, acyloxy groups, amino groups, hydroxyl groups, nitrile groups, acylamino groups and aryl groups.
The diphosphine ligand to be used according to the invention is bidentate; that is, it must contain the two phosphine phosphorus atoms at an in
Schäfer Martin
Schulz Michael
Slany Michael
BASF - Aktiengesellschaft
Keil & Weinkauf
McKane Joseph K.
Murray Joseph
LandOfFree
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