Continuous preparation of N-acylamino carboxylic acids and N-acy

Details Continuous preparation of N-acylamino carboxylic acids and N-acy Continuous preparation of N-acylamino carboxylic acids and N-acy

1998-04-30

1999-08-24

Barts, Samuel

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

Organic compounds

Fatty compounds having an acid moiety which contains the...

562575, C07C23100

Patent

active

059426357

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a process and an apparatus for the continuous preparation of N-acylamino carboxylic acids and N-acylamino sulfonic acids, and their alkali metal salts, from the alkali metal salts of amino carboxylic acids and amino sulfonic acids, respectively, and carbonyl halides in a reactor designed as circulating circuit.
Various synthetic routes are known for preparing long-chain acylamino acids from fatty acid derivatives and amino acids, and they differ essentially in the acylation component used. Although fatty acids (DE-A 20 04 099) and fatty acid methyl esters (EP-A O 033 392) are suitable in principle as acylation component, they have not to date been able to achieve industrial significance.
A process utilized industrially for preparing long-chain N-acylamino acids is condensation of fatty acid chlorides with amino acids, with elimination of hydrochloric acid, also known as the Schotten-Baumann reaction. This process has been known for a long time (DE-C 635 522) and is utilized commercially, for example to prepare oleoylsarcosine, also known under the name "Medialan acid", which is used in particular as corrosion inhibitor, fuel additive and in water repellants for leather.
The general principle for synthesizing Medialan acid, other acylsarcosinates and compounds of related structure (E. Jungermann et al., J. Amer. Chem. Soc. 78 (1956) 172 f; U.S. Pat. No. 3,544,606, FR-B 1 465 959, DD-C 85 757, DE-A 14 93 650, DE-A 16 18 097) comprises initially introducing the amino acid as Na salt in aqueous solution and in metering in, while stirring, the fatty acid chloride and NaOH sufficiently slowly to keep the temperature at below 35.degree. C. and the pH at 9-12.5. After the addition is complete, the pH of the reaction mixture is adjusted to <5 by adding H.sub.2 SO.sub.4. The acylamino acid obtained in this way is separated off as organic phase, where appropriate with the addition of an organic solvent to induce phase separation, which is subsequently removed again under reduced pressure. If the alkali metal salt of the acylamino acid is required, the acylamino acid is taken up in water and neutralized by adding NaOH. There have been numerous publications on the optimization of the individual process steps and reaction parameters, eg. the phase separation or the hydrolysis rate as a function of the pH and temperature.
The reaction of fatty acid halides with amino acid salts, which appears very straightforward at first sight, involves some critical points to which careful attention must be paid in order to be able to prepare acylamino acids in good yield and high purity. Since the reaction is very fast, when the two reactants are efficiently mixed the reaction is complete in <1 min. Thus, in the alkaline range (pH >8), the acylation reaction is distinctly faster (about 100 times) than the competing hydrolysis of the fatty acid chloride. The two reactions take place at approximately the same rate in an acidic medium. Raising the temperature increases the rate of hydrolysis more than that of condensation. Furthermore, the acylation reaction is highly exothermic, which means that the difference in the reaction rate can be utilized only if it is possible to remove the heat evolved in the reaction quickly enough. Since a dilute aqueous medium is used, the reaction mixture may be prone to foaming (surfactant).
Conventional stirred vessel technology carried out batchwise is in principle suitable for preparing acylamino acids, but has some disadvantages which eventually have adverse effects on the product quality. These disadvantages are: difficulty of controlling the temperature and removing the heat, furthermore relatively long holdup times per batch according to the quantity in the batch. As the reaction progresses, the properties of the reaction mixture, eg. concentration, volume, viscosity, change and thus so too do the variables determining the reaction rate.
It has therefore also been suggested to provide a remedy by a continuous synthesis. Thus, it is known (DE-A 14 93 660) for contin

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Chemical Abstracts, vol. 93, No. 16, Oct. 20, 1980, Kajl, Marian et al.
Chemical Abstracts, vol. 122, No. 5, Jan. 1995 is equivalent to JP 06 256 276.
J. Am Chem Soc. 78(1956), 1721, E. Jungermann et al.

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