Process for preparing betaines

Details Process for preparing betaines Process for preparing betaines

2002-05-02

2003-09-23

Shippen, Michael L. (Department: 1621)

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

Organic compounds

Carboxylic acids and salts thereof

C562S526000

Reexamination Certificate

active

06624327

ABSTRACT:

This application is a national phase filing of PCT International Patent Application No. PCT/EP00/06452, filed on Jul. 6, 2000, which claims priority from European Patent Application No. 99202584.1, filed on Aug. 6, 1999.
The invention relates to a process for preparing betaines.
Betaines are surfactants which are of value in personal care products, e.g., as a skin cleanser, and as an animal feed.
Several processes for preparing betaines are known in the art including alkylation and oxidation procedures.
U.S. Pat. No. 5,895,823 discloses a process for preparing aqueous solutions of betaines by reacting an aqueous solution of a choline salt, particularly choline hydroxide, with oxygen in the presence of a supported noble metal catalyst at a temperature of 20 to 100° C. The best results in terms of choline conversion and betaine selectivity are obtained by sparging oxygen through an aqueous solution of choline hydroxide at 78° C. for 5.5 h using 5% Pd/C as the catalyst, i.e. Example 5 of U.S. Pat. No. 5,895,823.
Disadvantages of the process of U.S. Pat. No. 5,895,823 are that the choline conversion and the betaine selectivity are both relatively low and the reaction is carried out for a prolonged period of time at a relatively high temperature, leading to a low space-time yield. Furthermore, a relatively high amount of catalyst is used. All in all, the process of U.S. Pat. No. 5,895,823 is unattractive for carrying out on a technical scale in an economical way.
An important parameter for a process employing a noble metal catalyst which is to be carried out on an industrial scale is the stability of the catalyst, i.e., the loss of precious noble metal leading to a decrease in catalytic activity, and related to that the recyclability of the catalyst. It was found that the 5% Pt/C catalyst exemplified in Examples 1 and 2 of U.S. Pat. No. 5,895,823 has poor stability/recyclability.
Hence, for all of the above-mentioned reasons there is a need in the art for an improved process for preparing betaines.
Surprisingly, we have found a process which does not suffer from the aforementioned disadvantages and in which the noble metal catalyst can be reused many times without showing a significant loss of noble metal.
The process of the present invention is a process for preparing betaines of formula I:
wherein R
1
represents a C
1
-C
24
hydrocarbon group, and R
2
and R
3
independently represent a C
1
-C
3
hydrocarbon group, comprising reacting an aqueous solution of an ethoxylated quaternary ammonium compound of formula II:
wherein R
1
, R
2
, and R
3
have the same meaning as described above and X
−
represents a suitable anion, with oxygen or an oxygen-containing gas under alkaline conditions in the presence of a supported and promoted Pt catalyst at a temperature ranging from room temperature to 70° C.
R
1
may be a linear or branched, saturated or unsaturated C
1
-C
24
hydrocarbon group. R
2
and R
3
independently may be a linear or branched C
1
-C
3
hydrocarbon group. Preferably, R
1
is a C
1
-C
22
, more preferably C
1
-C
18
, most preferably C
1
-C
3
hydrocarbon group. R
2
and R
3
preferably are methyl or ethyl, most preferably methyl groups. Typical examples of R
1
groups include methyl, ethyl, hexyl, octyl, decyl, dodecyl, oleyl, coco, and tallow groups.
Preferred compounds of formula II are compounds in which R
1
represents a C
1
-C
24
hydrocarbon group and R
2
and R
3
represent methyl groups. Particularly preferred compounds of formula II are the so-called choline salts, in which R
1
-R
3
represent methyl groups.
The X
−
group may be any anion and it typically results from the method that is chosen to prepare the ethoxylated quaternary ammonium compound of formula II. For example, it may result from the quaternization of the corresponding tertiary amine with a hydrocarbyl halide such as methyl chloride, methyl iodide, allyl chloride, and 2-chloroethanol, or a dihydrocarbyl sulfate such as dimethyl sulfate and diethyl sulfate. For example, choline chloride can be obtained by the reaction of trimethylamine with 2-chloroethanol. However, choline chloride can also be obtained by the reaction of trimethylamine hydrochloric acid salt with ethylene oxide. Alternatively, the anion may result from an anion-exchange reaction, e.g., by converting choline chloride into choline hydroxide.
Suitable ethoxylated tertiary amines and quaternization procedures leading to the starting materials of the process of the present invention as well as the exchange reactions mentioned above are well-known to one of ordinary skill in the art.
Preferably, the anion is a halide ion, most preferably a chloride ion.
Typical examples of compounds of formula II include choline salts such as choline chloride, choline dihydrogen citrate, tricholine citrate, choline bitartrate, choline acetate, choline phosphate, choline sulfate, choline carbonate, choline bicarbonate, and choline hydroxide, N-coco N,N-dimethyl N-(2-hydroxyethyl) ammonium chloride, N-tallow N,N-dimethyl N-(2-hydroxyethyl) ammonium chloride, N-dodecyl N,N-dimethyl N-(2-hydroxyethyl) ammonium chloride, and N-oleyl N,N-dimethyl N-(2-hydroxyethyl) ammonium chloride.
A particularly preferred starting material is choline chloride, which is, e.g., commercially available in the solid form (99% and p.a.) and in the form of a 75 wt % aqueous solution.
The process in accordance with the present invention is carried out using means and equipment known to a person of ordinary skill in the art. It can be carried out either batchwise or in a continuous reactor operation. Preferably, a reactor equipped with a turbo stirrer is used.
The oxidation reaction is started after the introduction of oxygen into a reaction mixture containing a compound of formula II and a catalyst, typically by starting the stirrer of the reactor (see below).
The concentration of the starting material, i.e. the ethoxylated quaternary ammonium compound of formula II, in the reaction mixture before commencing the oxidation reaction according to the present invention can vary within a wide range, typically from 5 to 75 wt %, based on the total weight of the reaction mixture. In the case of choline chloride a starting concentration in the range of 10 to 45 wt % is preferred.
The oxidation process according to the present invention must be carried out under alkaline conditions, i.e. at a pH greater than 7. This typically is achieved by adding an (earth) alkali metal hydroxide or an aqueous solution thereof to the reaction mixture, although other bases like triethylamine, trimethylamine, and sodium carbonate may be used as well. The use of an alkali metal hydroxide such as sodium hydroxide is preferred, and the invention will be described further with respect to the use of this base. As a result of using an alkali metal hydroxide and a salt of formula II an alkali metal salt, e.g., sodium chloride, is obtained as a by-product in the invention process.
When the anion is a hydroxide ion or the anion of a weak acid such as acetate or bicarbonate, no additional base is necessary, although additional base may enhance the reaction rate. In this case no alkali metal salt is generated.
It was found that when choline hydroxide was used as the starting material, the product solution coloured and the catalyst degraded more and more after each reaction cycle. Furthermore, choline hydroxide, which has to be prepared from choline chloride via an anion-exchange reaction, is not stable in highly concentrated form. The use of choline bicarbonate also resulted in deactivation of the catalyst.
Typically, about an equimolar amount or up to 5 mole % excess of alkali metal hydroxide, based on the amount of ethoxylated quaternary ammonium compound of formula II, is used in the invention process. However, depending on the type of anion as explained above or on the application in which the product of the process of the invention is to be used, it may be desirable to use a less than equimolar amount of base.
In the case of choline chloride being used as the starting material, the use of less

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