Selective reductive amination of nitriles

Details Selective reductive amination of nitriles Selective reductive amination of nitriles

2000-12-13

2002-06-04

Davis, Brian J. (Department: 1621)

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

Organic compounds

Amino nitrogen containing

C564S491000, C564S492000, C564S493000

Reexamination Certificate

active

06399830

ABSTRACT:

BACKGROUND OF THE INVENTION
Processes for the production of amines by the catalytic reductive coupling of a primary or secondary amine with a nitrile are known and widely used to produce a variety of secondary and tertiary amines. Di(fattyalkyl)alkylamines, and particularly di(fattyalkyl)methylamines, are representative of tertiary amines produced by reductive amination and are of particular value for the production of fabric softeners, hair conditioners, and antistatic agents.
Di(fattyalkyl)alkylamines can be converted to the fabric softeners, etc. via derivatization to the quaternary salt. Tertiary amine functionality is necessary for successful production of these derivatives. In contrast, intermediate mono(fattyalkyl)methylamines and byproduct secondary di(fattyalkyl)amines do not form the desired quaternary salts selectively, and therefore, are unsuited for processing to the desired end product. In addition, the intermediate and the byproduct amine lack the optimum balance of nonpolar (two long chain fattyalkyl groups) and polar (methylamino group) functionality to provide for the production of effective surfactants and antistats.
Representative patents which describe the reductive coupling of nitriles with amines are as follows:
U.S. Pat. No. 5,648,545 discloses the catalytic amination of a wide variety of nitriles by reacting a nitrogen compound such as ammonia, or a primary or secondary amine with the nitrile at temperatures of from about 80 to 250° C. and a hydrogen pressure of 1 to 400 bar. The catalytic amination is carried out in the presence of hydrogen and the catalyst is comprised of a reduced copper oxide/zirconium oxide. Alkali metal carbonate is added to the catalyst prior to reaction. An exemplary nitrile includes N-methylaminopropionitrile and representative amines reacted therewith includes mono and dimethylamine.
Canadian Patent 834,244 discloses a process for continuously producing high molecular weight secondary and tertiary amines by reacting high molecular aliphatic nitriles with volatile primary or secondary amines. The fatty acid nitriles have a carbon content from 8 to 22 carbon atoms and include lauryl and stearyl nitrile and the low boiling amines include dimethylamine, diethylamine, etc. The catalyst is an alkali-modified copper-chromium catalyst with the alkylation being conducted at a temperature of 120 to 180° C. and 180 to 210 atmospheres hydrogen pressure. Salts of alkali metals used in preparing the alkali-modified catalysts included those of potassium and sodium.
U.S. Pat. No. 5,869,653 discloses a process for the hydrogenation of nitriles to produce primary amines. In the catalytic hydrogenation of aliphatic nitriles, the nitrile is contacted with hydrogen in the presence of a sponge or Raney® cobalt catalyst employing lithium hydroxide as a promoter. A wide variety o f aliphatic nitriles (C
2−30
) are suggested as being suited for conversion to the primary amine by reaction with hydrogen.
U.S. Pat. No. 5,847,220 discloses a process for the catalytic hydrogenation of a cyanopropionaldehyde alkyl acetal in the presence of a nickel or cobalt catalyst promoted with alkali metal hydroxide to form aminobutyraldehyde alkyl acetals, i.e., the primary amine derivative of the cyanoalkyl acetals. The background in the patent discloses a variety of processes for the hydrogenation of nitriles, but these processes generally deal with the hydrogenation of the nitrile itself, rather than a reductive alkylation by the reaction of the nitrile with a primary or secondary amine.
U.S. Pat. No. 5,557,011 discloses a process for producing diamines by reductive coupling of secondary amine with an aliphatic nitrile. In the background of the art, palladium/carbon catalysts were used as the primary reductive coupling catalyst. The improvement in the process wherein palladium is used as a catalyst resided in utilizing an oxidic support, such as a gamma alumina, silica, titania, zirconia, etc. which may be modified by inclusion of up to 15 wt % metal oxides of subgroups IB-VIIB, or Group VIII of the periodic table. Preparation of di-tert-amines from the corresponding dinitriles and secondary amines with palladium supported on an oxide (specifically, on an oxide selected from the group consisting of &ggr;-alumina, silica, titania, or zirconia) or on an oxide treated with an alkali metal/alkaline earth oxide is shown.
U.S. Pat. No. 5,894,074 discloses a process for the preparation of tertiary amines from nitriles and secondary amines utilizing a palladium catalyst. The improvement in the process utilizing palladium as a catalyst or catalysts incorporating small amounts of calcium oxide, alumina, magnesium oxide, etc., resided in the inclusion of a small amount at least one further metal selected from the group of 1B and Group VIII, as well as cerium and lanthanum on a support. Examples of the latter class of catalysts include 0.5 wt % palladium/alumina with 20% calcium oxide and 1.0 wt % palladium/alumina with 20% magnesium oxide.
BRIEF SUMMARY OF THE INVENTION
This invention pertains to an improvement in a process for the formation of di(fattyalkyl)alkylamines, and particularly, di(fattyalkyl)methylamines, wherein a fatty nitrile is reacted with a primary alkylamine in the presence of a heterogenous metal reductive amination catalyst and hydrogen. The improvement resides in effecting the reaction in the presence of an effective amount of an acidic promoter, preferably a solid acidic promoter having a pK of less than or equal to about 2.
There are numerous advantages associated with the improved process and these include:
an ability to produce di(fattyalkyl)alkylamines in high selectivity and at high production rates;
an ability to produce di(fattyalkyl)alkylamines in a single step;
an ability to produce a reaction product having a minor portion of byproduct mono(fattyalkyl)alkylamine thereby facilitating separation of the product di(fattyalkyl)alkylamine, from the mono(fattyalkyl)alkylamine;
an ability to effect reductive coupling of two equivalents of a fatty nitrile with a primary amine to produce the corresponding mixed tertiary amine and minimize or avoid coproduction of the corresponding fatty di/trialkylamines;
an ability to reductively aminate a wide range of nitriles; and,
an ability to use the catalyst over an extended time.
DETAILED DESCRIPTION OF THE INVENTION
This invention pertains to a selective single step process for the reductive amination of nitriles to produce tertiary amines, especially fatty (≦C8) nitriles, by reaction of the corresponding nitrile with a primary amine. This process chemistry comprises reacting two moles of a fatty nitrile with a primary amine through the intermediacy of the mono(fattyalkyl)methylamine followed by in situ reductive coupling with another mole of fatty nitrile to produce the di(fattyalkyl)methylamine.
The single step catalytic reductive amination is described in Equation 1.
Selectivity problems can occur in the above reaction. It is believed that selectivity to the di(fattyalkyl)alkylamines often suffers because of (a) failure to effect a second reductive coupling with the reductively coupled methylamine or (b) generation of an alternate byproduct. The alternate byproduct is believed to be formed owing to a competing reaction pathway: (a) reduction of the nitrile to the corresponding primary amine, and (b) subsequent coupling of that amine with a second equivalent of nitrile to generate a secondary di(alkyl)amine. The perceived pathway to this alternate byproduct is described by Equation 2.
The objective is to minimize alternate byproduct formation set forth by equation 2.
In the practice of the process, a wide variety of nitriles may be used in the reductive amination process, and these nitriles include C
2+30
aliphatic and aromatic nitriles. Specific examples of nitriles include:
aliphatic nitriles such as acetonitrile, propionitrile, butyronitrile and valeronitrile; ether nitriles such as ethoxypropionitrile, methoxypropionitrile, isopropoxynitrile, biscyanoethylether, bis-(2-cyanoethyl)ethylen

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