Production of alkyl 6-aminocaproate

Details Production of alkyl 6-aminocaproate Production of alkyl 6-aminocaproate

2000-11-16

2002-04-02

Geist, Gary (Department: 1623)

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

Organic compounds

Carboxylic acid esters

C560S208000

Reexamination Certificate

active

06365770

ABSTRACT:

FIELD OF THE INVENTION
The present invention concerns a process to produce alkyl 6-aminocaproate and/or caprolactam.
BACKGROUND OF THE INVENTION
Commercially, caprolactam is made by a process using cyclohexane as the starting material. Caprolactam is then polymerized to produce nylon-6. For cost reasons, it would be desirable to produce caprolactam with butadiene, a four carbon starting material, rather than the six carbon cyclohexane starting material currently used in commercial processes.
It is known that butadiene can be reacted with HCN to produce 3-pentenenitrile (3PN). One process for converting 3PN to caprolactam involves converting 3PN to adiponitrile (ADN). ADN is then partially hydrogenated to 6-aminocapronitrile, which is then converted to caprolactam by hydrolysis followed by cyclization. See for example, U.S. Pat. No. 6,069,246. The partial hydrogenation reaction produces a significant amount of hexamethylenediamine (HMD).
A second process for converting 3PN to caprolactam involves reductive amination of 5-formylvaleronitrile that is derived by hydroformylation of 3-pentenenitrile. The reductively aminated product is then subjected to hydrolysis and cyclized. U.S. Pat. No. 6,048,997 discloses a process in which a mixture containing 2-, 3-, and 4-pentenenitrile is reacted with carbon monoxide and hydrogen in the presence of a catalyst containing at least one Group VIII metal to produce a mixture comprising 3-, 4-, and 5-formylvaleronitrile. U.S. Pat. No. 5,986,126 teaches that 5-formylvaleronitrile is unstable and that the separation of 5-formylvaleronitrile from the branched 3- and 4-formylvaleronitriles is impractical because of yield losses that are suffered in distillation. To avoid this problem, U.S. Pat. No. 5,986,126 teaches that the separation of the linear product from the branched isomers is possible downstream after reductive amination of the formylvaleronitriles to produce aminonitriles (such as 6-aminocapronitrile) and diamines. In this second process, a significant amount of HMD is produced.
Both of the two 3PN-based processes described above produce significant amounts of HMD. It is not always desired to have HMD as a co-product in a commercial caprolactam operation. Thus, there is a need for a process that converts butadiene to caprolactam without the production of significant amounts of HMD. The present invention provides such a process.
BRIEF SUMMARY OF THE INVENTION
The present invention is a 3PN-based process for making alkyl 6-aminocaproate that does not produce significant amounts of HMD. The present invention accomplishes this by a process comprising:
(a) reacting 3-pentenenitrile with carbon monoxide and hydrogen in the presence of a hydroformylation catalyst comprising a Group VIII metal to produce a first reaction product which comprises 3-, 4-, and 5-formylvaleronitrile (FVN);
(b) isolating from the first reaction product a FVN mixture consists essentially of 3-, 4-, and 5-formylvaleronitrile;
(c) reacting the FVN mixture to produce a second reaction product which comprises alkyl 3-, 4-, and 5-cyanovalerate by either:
(i) contacting the FVN mixture with an alcohol, a molecular oxygen-containing gas, and a palladium-containing catalyst for a time sufficient to oxidize the FVN mixture to produce the second reaction product, or
(ii) oxidizing the FVN mixture in the presence of a molecular oxygen-containing gas for a time sufficient to oxidize the FVN mixture to produce an oxidation product comprising 3-, 4-, and 5-cyanovaleric acid, and reacting the oxidation product with an alcohol to produce the second reaction product;
(d) isolating the alkyl 5-cyanovalerate by distillation, and
(e) reacting alkyl 5-cyanovalerate with hydrogen in the presence of a hydrogenation catalyst to produce a third reaction product which comprises alkyl 6-aminocaproate, the alkyl group of which contains the same number of carbon atoms as the alcohol.
DETAILED DESCRIPTION OF THE INVENTION
The present invention concerns a process for the production of alkyl 6-aminocaproate. Suitable alkyl groups are C
1
to C
12
linear or branched alkyl groups. Preferably the alkyl group is methyl or ethyl. More preferably, the alkyl group is methyl.
Production of 3-Pentenenitrile
3-Pentenenitrile (3PN) is produced commercially as an intermediate in the production of adiponitrile. The synthesis of 3PN is well known in the art. See for example, U.S. Pat. Nos. 3,496,215 and 5,821,378, the disclosures of which are incorporated herein by reference.
Hydroformylation of 3-Pentenenitrile
The hydroformylation of 3-pentenenitrile (i.e., the reaction of 3-pentenenitrile with carbon monoxide and hydrogen) to produce a reaction product which comprises 3-, 4-, and 5-formylvaleronitrile (FVN) is carried out in the presence of a catalyst comprising a Group VIII element. The hydroformylation reaction temperature can vary from room temperature to about 200° C., preferably between 50 and 150° C. The pressure is preferably between 0.15 and 10 MPa and more preferably 0.2 to 5 MPa.
Preferred catalysts are rhodium compounds. Examples of suitable compounds include Rh(CO) 2 (DPM), [DPM=t—C
4
H
9
—COCHCO—t—C
4
H
9
]; Rh(CO)
2
(acac), [acac=acetylacetonate]; Rh
2
O
3
; Rh
4
(CO)
12
; Rh
6
(CO)
16
; [Rh(OAc)
2
]
2
, [OAc=acetate]; and Rh(ethylhexanoate)
2
. Preferably, the catalyst is Rh(CO)
2
(acac), Rh(CO)
2
(DPM), or [Rh(OAc)
2
]
2
.
These catalysts can be used in combination with phosphorous-containing ligands such as monodentate or bidentate phosphine, phosphonites, phosphinites, or phosphite compounds. Examples of such ligands include triarylphosphites, such as triphenylphosphite; triarylphosphines, such as triphenylphosphine; and bis(diarylphosphino)alkanes, such as diphenylphosphinoethane. In addition, polydentate phosphite compounds may be used as ligands. An example of these includes compounds having a structural formula as follows:
where R
1
and R
2
are the same or different mono-valent aryl groups, X is an n-valent organic bridging group, and n is an integer between 2 and 6. R
1
and R
2
may be substituted. Such ligands are described, for example, in U.S. Pat. No. 5,710,344, the disclosure of which is incorporated herein by reference.
The mole ratio of 3-pentenenitrile to catalyst is generally 100:1 to 100,000:1, preferably 500:1 to 10,000:1. The mole ratio of ligand to rhodium is typically between 0.5:1 and 10:1.
The mole ratio of hydrogen to carbon monoxide for hydroformylation reactions is typically in the range of 100:1 to 1:10, preferably in the range of 4.0:1 to 0.5:1. Inert gases may also be present in the hydrogen and carbon monoxide feed stocks.
The hydroformylation reaction may be performed in the presence of a solvent. Suitable solvents include inert solvents or a solvent consisting of the hydroformylation products themselves. Suitable inert solvents include aromatic hydrocarbons, aliphatic hydrocarbons, nitriles, ethers, amides and urea derivatives, saturated hydrocarbons, and ketones. Some examples of suitable solvents include toluene, cyclohexane, benzene, xylene, Texanol® (2,2,4-trimethyl-1,3-pentanediol monoisobutyrate), diphenylether, tetrahydrofuran, cyclohexanone, benzonitrile, N-methylpyrrolidinone, and N,N-dimethylethylurea.
The hydroformylation reaction can be performed in a continuous or batch mode. The reaction can be performed in a variety of reactors, such as bubble column reactors, continuously stirred tank reactors, trickle bed reactors, and liquid-overflow reactors. Unreacted hydrogen, carbon monoxide, 3-pentenenitrile, and any solvent may be recovered and recycled to the hydroformylation reactor.
The hydroformylation reaction product comprises 3-, 4-, and 5-formylvaleronitriles, as well as unconverted 2-, 3-, and 4-pentenenitrile, catalyst, and high boilers. The separation of the FVN mixture from the catalyst and high boilers can be effected by utilizing thermally gentle evaporation techniques, known to those skilled in the art. Such techniques include the use of single stage flash evaporator

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