Process for the production of quaternary ammonium salts of fatty acid hydroxyalkanesulfonic acids

Quaternary ammonium salts of fatty acid hydroxyalkanesulfonic acids are made by reacting a hydroxyalkanesulfonic acid of the formula (I): EQU HO--(C.sub.n H.sub.2n)--SO.sub.3 H (I): wherein n=2 to 4 with a fatty acid having from 6 to 18 carbon atoms at a temperature range of from about 60.degree. C. to about 120.degree. C. and at a reduced pressure followed b reaction with an amine in an organic solvent.

BACKGROUND OF THE INVENTION 1. Field of the Invention 
This invention relates to a process for the production of quaternary 
ammonium salts of fatty acid hydroxyalkanesulfonic acids, in which a 
hydroxyalkanesulfonic acid is subjected to the condensation reaction with 
a C.sub.6-18 fatty acid at elevated temperature and reduced pressure, any 
water of solution present and the water of reaction formed are directly 
removed from the reaction mixture and the fatty acid hydroxyalkanesulfonic 
acid is reacted with a base to form the corresponding quaternary ammonium 
salt of the fatty acid hydroxyalkanesulfonic acid. 2. Description of the 
Related Art 
Fatty acid hydroxyalkanesulfonic acid salts, more particularly fatty acid 
isethionates in the C.sub.12-14 chain length range, are anionic 
surfactants with only minimal sensitivity to hardness, high foaming and 
wetting power and excellent compatibility with the skin. More 
particularly, they are distinguished by the fact that the skin can be 
cleansed without overly drying out. In addition, the soaps containing 
these compounds can even be used by people unable to tolerate typical high 
pH soaps. Accordingly, these compounds are used in cosmetic preparations 
and cleansing formulations 
Commercial fatty acid hydroxyalkanesulfonic acid salts are generally 
produced from the corresponding salt of hydroxyalkanesulfonic acid by 
reaction with the fatty acid in the presence of an esterification 
catalyst, for example ZnO, at temperatures of up to 250.degree. C. 
However, dark-colored products are obtained in the production of ammonium 
fatty acid hydroxysulfonic acid salts by this process. 
The fatty acid isethionates, particularly the sodium fatty acid 
isethionates frequently used, show only limited solubility in water which 
restricts their use to soaps, such as syndets and combination bars and 
opaque liquid formulations. 
Quaternary ammonium salts of fatty acid hydroxyalkanesulfonic acids, more 
particularly ammonium fatty acid isethionate, are highly soluble in water 
and may be used in clear liquid formulations. However, this possibility is 
impaired by the fact that the quaternary ammonium salts of fatty acid 
isethionic acid prepared by conventional methods are dark in color so 
that, in the absence of bleaching, the liquid formulations containing them 
are also dark in color. 
The problem addressed by the present invention was to provide a process for 
the production of quaternary ammonium salts of fatty acid 
hydroxyalkanesulfonic acids which would enable these compounds to be 
obtained in high yields and in light-colored highly concentrated form. 
SUMMARY OF THE INVENTION 
This invention relates to a process for making a quaternary ammonium salt 
of a fatty acid hydroxyalkanesulfonic acid comprising the steps of: (a) 
reacting a hydroxyalkanesulfonic acid of the formula (I): 
EQU HO--(C.sub.n H.sub.2n)--SO.sub.3 H (I) 
wherein n=2 to 4 with a fatty acid of the formula (II): 
EQU R.sup.2 COOH (II) 
wherein R.sup.2 CO is an aliphatic, linear or branched acyl radical having 
from 6 to 18 carbon atoms at a temperature range of from about 60.degree. 
C. to about 120.degree. C. and at a pressure sufficient to vaporize water 
at said temperature range to form a reaction mixture comprised of said 
fatty acid hydroxyalkanesulfonic acid while removing water from a reaction 
mixture; (b) dissolving said reaction mixture in an organic solvent; (c) 
forming a quaternary ammonium salt of said fatty acid 
hydroxyalkanesulfonic acid by reacting said reaction mixture with a base 
at a temperature of 18.degree. C. to 35.degree. C. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
It has surprisingly been found that it is possible by the process according 
to the invention to produce high yields of quaternary ammonium salts of 
fatty acid hydroxyalkanesulfonic acids which are light in color. The 
process according to the invention may be carried out at considerably 
lower temperatures than known processes and without a catalyst. 
In the process according to the invention, the hydroxyalkanesulfonic acid 
and the fatty acid are first subjected to the condensation reaction at 
temperatures of 60.degree. to 120.degree. C. and preferably at 
temperatures of 90.degree. to 110.degree. C. Any water of solution present 
and the water of reaction formed are directly distilled off. The molar 
ratio of fatty acid to hydroxyalkanesulfonic acid is in the range from 
1.5:1 to 1:1.5 and preferably in the range from 1:1 to 1:1.2. 
The condensation reaction is preferably carried out with no additional 
catalyst. The advantage of carrying out the reaction in this way is that 
there is no need for the removal of the catalyst from the reaction product 
otherwise necessary in condensation reactions and no catalyst residues are 
present in the reaction product. 
The hydroxyalkanesulfonic acid used is preferably used in water-free form. 
Water present in the starting substances is distilled off at the beginning 
of the reaction. The hydroxyalkanesulfonic acid may readily be produced 
from its salts. It is preferably obtained from the sodium salt via acidic 
ion exchangers. 
The fatty acid used as starting product corresponding to general formula 
(II) R.sup.2 COOH is selected from caproic acid, oenanthic acid, caprylic 
acid, pelargonic acid, capric acid, undecanoic acid, undecenoic acid, 
lauric acid, lauroleic acid, tridecanoic acid, myristic acid, myristoleic 
acid, pentadecanoic acid, palmitic acid, palmitoleic acid, heptadecanoic 
acid, stearic acid, petroselic acid, petroselaidic acid, oleic acid, 
elaidic acid, linoleic acid, linolaidic acid, linolenic acid, elaeostearic 
acid and technical mixtures thereof. Fatty acids on a vegetable or animal 
basis, which may be completely or partly hydrogenated, are preferred. 
Mixtures of coconut oil fatty acid are particularly preferred. 
The condensation reaction is carried out under a pressure under which water 
boils so that the water of reaction can readily be removed. A pressure in 
the range from about 2 to 100 mbar is preferred, water jet vacuum being 
particularly preferred. 
The reaction mixture of hydroxyalkanesulfonic acid and fatty acid is heated 
in vacuo. The mixture should be heated only slowly because the reaction 
mixture can foam in vacuo at the beginning of the reaction. The beginning 
and end of the reaction are reflected in the formation of water of 
reaction. On completion of the reaction, the reaction mixture is kept at 
elevated temperature for about another 20 minutes to 1 hour to remove any 
water present. Removal of the water can be accelerated by addition to the 
reaction mixture of an organic solvent which forms a low-boiling azeotrope 
with water and which removes the water as an azeotrope from the reaction 
mixture. 
The mixture is then dissolved in an inert organic solvent. Suitable 
solvents are any solvents with which the condensation product forms a 
homogeneous solution. Particularly suitable solvents are aliphatic and 
aromatic hydrocarbons, such as n-hexane, petroleum ether, isooctane; 
halogenated hydrocarbons, such as methylene chloride, chloroform or carbon 
tetrachloride; and alcohols, such as methanol, ethanol, n-propanol and 
i-propanol or mixtures thereof. Petroleum ether or a mixture of petroleum 
ether and i-propanol is preferably used. 
The dissolved condensation product is reacted with a base at a temperature 
of 18.degree. C. to 35.degree. C. and preferably at a temperature of 
20.degree. C. to 27.degree. C. The base may be used in the form of a pure 
substance or may be diluted with a corresponding solvent or inert gas. 
Suitable bases are, for example, ammonia, primary, secondary and tertiary 
(lower) alkylamines, in which lower alkyl is an alkyl containing 1 to 4 
carbon atoms, or aminoalcohols, in which the alcohol is a lower alcohol 
containing 1 to 4 carbon atoms, and glucamine. Examples of suitable alkyl 
amines are monomethyl amine, monoethyl amine, monopropyl amine, monobutyl 
amine, dimethyl amine, diethyl amine, dipropyl amine, dibutyl amine, 
trimethyl amine, triethyl amine, tripropyl amine, tributyl amine. Examples 
of suitable alkanolamines are, for example, trimethanolamine, 
triethanolamine, tripropyl amine and tributyl amine. 
The quaternary ammonium salt of the fatty acid hydroxyalkanesulfonic acid 
formed generally accumulates in the form of a white precipitate. On 
completion of the reaction, the reaction product is isolated in known 
manner. The solid product can normally be filtered off from the reaction 
mixture and subsequently washed with fresh solvent or solvent mixture 
several times, generally at least twice, and then dried in vacuo. If the 
product is soluble in the solvent, the solution obtained may be directly 
further processed or the product is obtained by distilling off the 
solvent. 
The reaction according to the invention gives a white powder in a high 
yield of generally more than 90%.

The invention is illustrated by the following Example. 
Example 
About 57.9 g of isethionic acid (93%, 0.427 mole) and 85.53 g lauric acid 
(0.427 mole) were combined under nitrogen and heated in a water jet 
vacuum. The reaction actually began below 100.degree. C. and was 
accompanied by gentle foaming. The main reaction was terminated after 1 h. 
The reaction mixture was kept at a maximum temperature of 120.degree. C. 
for another 30 minutes. 
11.8 g water and small quantities of lauric acid distilled over 
(theoretical: 11.6 g water). The resulting reaction mixture (131.6 g) was 
dissolved in 1.4 liters petroleum ether and ammonia was passed through 
with stirring at 25.degree. C. The quaternary ammonium salt precipitating 
was washed three times with fresh petroleum ether and dried in a water jet 
vacuum. 135 g of a white powder were obtained. The product had the 
following composition: 
approximately 91 to 93% of lauroyl isethionate NH.sub.4 salt (determined by 
Epton titration of the anionic surfactant content) 
approximately 2 to 3% of lauric acid NH.sub.4 salt (determined by HPLC) and 
approximately 5 to 7% of ammonium isethionate (determined by HPLC). 
After filtration and washing with the solvent, the product had a Klett 
color value of 49 (1 cm cuvette, 30% solution) whereas a commercial 
product had a Klett color value of 69 (1 cm cuvette, 30% solution).