Process for preparing carboxylic acids

Details Process for preparing carboxylic acids Process for preparing carboxylic acids

1999-09-14

2001-05-08

Vollano, Jean F. (Department: 1621)

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

Organic compounds

Carboxylic acids and salts thereof

C562S017000, C562S523000, C562S553000, C562S566000

Reexamination Certificate

active

06229045

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to the preparation of aliphatic carboxylic acids by the catalytic dehydrogenation of primary alcohols.
The preparation of carboxylic acids and salts of carboxylic acids using the corresponding primary alcohol as the starting material is often advantageous because the corresponding alcohols are often available and relatively inexpensive. The preparation of aliphatic carboxylic acids and their salts that possess oxygen, nitrogen and/or phosphorus heteroatoms, such as glycine, N-methylglycine, N-phosphonomethylglycine, iminodiacetic acid, N-phosphonomethyliminodiacetic acid, nitrilotriacetic acid, ethylenediaminetetraacetic acid, diglycolic acid, methoxyacetic acid, lactic acid, and the like, by such means is especially advantageous. These acids and their salts are valuable, for example, as intermediates for agricultural products and pharmaceuticals, as chelating agents, as animal feed additives, etc. Conversions of primary alcohols to their corresponding acids or to salts thereof have been carried out in the art by treatment of primary alcohols with a copper catalyst under conditions that lead to either dehydrogenation (U.S. Pat. Nos. 4,782,183, 5,220,054, 5,220,055, 5,292,936, 5,627,125, 5,689,000) or oxidation (U.S. Pat. No. 5,225,592). Hydrogen is produced as a by-product in the dehydrogenation processes and water is produced as a by-product in the oxidation processes. Raney copper has typically been used as the catalyst.
Catalysts comprising cobalt, copper, and a third metal selected from iron, zinc, and zirconium and mixtures thereof, which can be made by reducing mixtures the corresponding metal oxides with hydrogen, are known from U.S. Pat. No. 4,153,581. These catalysts were disclosed in the art to be useful for the conversion of alcohols, aldehydes, and ketones to amines.
The discovery of improved processes and catalysts for converting primary aliphatic alcohols to carboxylic acids or their salts would be highly desirable.
SUMMARY OF THE INVENTION
It has now been found that aliphatic primary alcohol compounds, including aliphatic primary alcohols possessing one or more oxygen, nitrogen or phosphorus heteroatoms, which heteroatoms may be viewed as atoms substituting for carbon atoms in the alkyl group or component atoms of substituents on the alkyl group, can be converted into salts of carboxylic acid compounds by contacting the primary alcohol with a catalyst comprising cobalt, copper, and at least one additional metal selected from cerium, iron, zinc, and zirconium in an alkaline aqueous medium.
The invention includes a process for preparing a salt of an aliphatic carboxylic acid compound that is unsubstituted or possesses one or more substituents that contain one or more oxygen, nitrogen and/or phosphorus atoms, which process comprises contacting a primary aliphatic alcohol compound that is unsubstituted or possesses one or more substituents that contain one or more oxygen, nitrogen and/or phosphorus atoms with a catalyst comprising, on a contained metals basis, about 10 to about 90 mole percent cobalt, about 8 to about 88 mole percent copper, and about 1 to about 16 mole percent of a third metal selected from cerium, iron, zinc, and zirconium, or mixtures thereof, in an alkaline aqueous medium, in the effective absence of oxygen, and at a temperature of about 120° C. to about 200° C.
The salts of aliphatic carboxylic acids obtained in the process can be converted to the corresponding aliphatic carboxylic acids by acidification with a strong acid using methods well established in the art.
The process of the invention is often preferably used to convert aliphatic primary alcohol compounds possessing substituents containing one or more oxygen, nitrogen and/or phosphorus heteroatoms to the corresponding carboxylic acid compounds or their salts. The conversion of optionally N-substituted 2-aminoethanol and 2-aminopropanol compounds and optionally mono-O-substituted 1,2-ethanediol (ethylene glycol) and 1,2-propanediol (propylene glycol) compounds (substituents on the 2-hydroxyl in the latter) is often preferred. The conversion of diethanolamine to iminodiacetic acid or an alkali metal salt of iminodiacetic acid, of ethanolamine to glycine or an alkali metal salt of glycine, of N-methylethanolamine to sarcosine or an alkali metal salt of sarcosine, of N-phosphonomethylethanolamine to N-phosphonomethylglycine or an alkali metal salt of N-phosphonomethylglycine, and of N-phosphonomethyldiethanolamine to N-phosphonomethyliminodiacetic acid or an alkali metal salt of N-phosphonomethyliminodiacetic acid are often, independently, of special interest.
Catalysts containing about 30 to about 50 mole percent cobalt, about 45 to about 65 mole percent copper, and about 3 to about 10 mole percent of the third metal, on the basis of the total metal content, are generally most preferred. Zirconium is often a preferred third metal.
It is often preferred to carry out the process at about 140° C. to about 200° C.
It is usually preferred to carry out the reaction in an aqueous medium containing an alkali metal hydroxide compound in the amount of at least about one mole to about 2 moles per mole of primary alcohol moiety undergoing conversion to carboxylic acid group. Sodium hydroxide is often preferred as the alkali metal hydroxide compound.
DETAILED DESCRIPTION OF THE INVENTION
The process of the present invention involves the catalytic dehydrogenation of aliphatic primary alcohol compounds, including aliphatic primary alcohol compounds possessing oxygen, nitrogen and/or phosphorus heteroatoms, to obtain salts of carboxylic acids. This dehydrogenation reaction can be illustrated by the following equation:
Z—CH
2
OH+OH
−
→Z—CO
2
−
+2H
2
wherein Z is an alkyl group that optionally possesses one or more oxygen, nitrogen and/or phosphorus containing substituents.
The salts of carboxylic acids obtained in the dehydrogenation reaction can be converted to the corresponding acids by acidification with a strong acid according to the equation:
Z—CO
2
−
+H
+
→Z—CO
2
H
Suitable acids include mineral acids such as hydrochloric acid, hydrobromic acid, sulfuric acid, and phosphoric acid and other strong acids such as trifluoroacetic acid, benzenesulfonic acid, and the like. Suitable acids generally have a pK
a
of about 5 or less. Acidification of the reaction mixture produced in the dehydrogenation to obtain the corresponding carboxylic acids is an optional second step in the process. Thus, the process of the invention can be used to prepare either aliphatic carboxylic acids or their salts.
The salts and acids prepared in the process of the invention can be recovered by conventional means, if desired.
A broad variety of aliphatic primary alcohol compounds are suitable starting materials in the process. Importantly, these alcohol compounds may possess oxygen, nitrogen and/or phosphorus heteroatoms. Primary aliphatic alcohols possessing one or more oxygen or nitrogen containing substituents are often preferred. The process works best when applied to aliphatic primary alcohols that are essentially soluble in the alkaline aqueous medium used under the reaction conditions employed.
The process of the invention is especially useful for the preparation of aliphatic carboxylic acids of Formula II or salts thereof from aliphatic primary alcohols of Formula I:
X—CH(R)CH
2
OH I→X—CH(R)CO
2
H II
wherein
X represents H, CH
3
, OH, O(C
1
-C
4
)alkyl, OCH(R)CH(R)OH, OCH(R)CO
2
H, OCH(R)CH(R)NH
2
, OCH(R)CH(R)—NH(C
1
-C
4
)alkyl, OCH(R)CH(R)N((C
1
-C
4
)alkyl)
2
, OCH(R)CH(R)—N(CH(R)CH
2
OH)
2
, OCH(R)CH(R)N(CH(R)CO
2
H)
2
, NH
2
, NH(C
1
-C
4
)alkyl, NHCH
2
P(O)(OH)
2
, N((C
1
-C
4
)alkyl)
2
, NHCH(R)CH(R)OH, N(CH(R)CH(R)OH)
2
, NHCH(R)CO
2
H, N(CH(R)CO
2
H)
2
, N(C
1
-C
4
)alkyl) (CH(R)CH(R)OH), N(CH(R)CH(R)OH)(CH
2
P(O)(OH)
2
), N(CH(R)CO
2
H)(CH
2
P(O)(OH)
2
), N(C
1
-C
4
)alkyl) (CH(R)CO
2
H), N(CH(R)CH(R)OH)(CH(R)CO
2
H), N(CH
2
CH
2
OH)CH
2
CH
2
N(CH
2
CH
2
OH)
2
, or N(CH
2
CH
2
OH)CH
2
CH
2
N(CH
2
CH
2

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