Distillation: processes – separatory – With disparate physical separation – Utilizing liquid-liquid extracting of distillation product
Patent
1995-06-19
1998-04-28
Bhat, Nina
Distillation: processes, separatory
With disparate physical separation
Utilizing liquid-liquid extracting of distillation product
203 46, 203 98, 203DIG16, 202202, 202204, 544 2, 549355, 549397, 549463, B01D 1100, C07D29100
Patent
active
057440107
DESCRIPTION:
BRIEF SUMMARY
6-Methyl-3,4-dihydro-1,2,3-oxathiazin-4-one 2,2-dioxide (hereafter acesulfam-H) has been used for some time in the form of its potassium salt (hereafter acesulfam-K) ##STR1## because of its intensive sweet taste as a sweetener in the food sector.
A series of different processes are known for the preparation of acesulfam-K (see inter alia Angewandte Chemie, 22(1973), pages 965 to 973). Of particular current interest is a process in which, in a solvent, preferably methylene chloride, amidosulfonic acid, but preferably a soluble salt of amidosulfonic acid, is first reacted with diketene to form the acetoacetamido compound. The salts of amidosulfonic acid used are generally alkaline metal salts or ammonium salts, preferably trialkylammonium salts. In the reaction with diketene, the salt of acetoacetamidosulfonic acid (I) is formed in accordance with the reaction equation ##STR2## (M=base cation, in particular HN(alkyl C.sub.1 -C.sub.6).sub.3). The acetoacetamido compound (I) preferably dissolved in methylene chloride is then reacted under defined reaction conditions with a solution of SO.sub.3, preferably in methylene chloride, and thus cyclized; the SO.sub.3 is preferably used in excess (see for this EP-A 155,634, EP-A 159,516, EP-A 217,076 and EP-A 218,076). A cyclization product is formed in this manner, from which by reaction with water (hydrolysis) in a hydrolysis vessel, acesulfam-H, the so-called "sweetener acid" (II), is formed: ##STR3##
Both the cyclization and the hydrolysis are rapid, highly exothermic reactions.
The reaction mixture separates into an organic phase, preferably a methylene chloride phase, and an aqueous sulfuric acid phase. The majority (about 4/5) of the sweetener acid (II) is situated in the organic phase, about 1/5 is dissolved in the sulfuric acid phase. The sulfuric acid phase contains almost the entire amount of the alkali metal or ammonium, preferably trialkylammonium, as sulfate, preferably trialkylammonium hydrogen sulfate. The sulfuric acid phase, after stripping off any solvent still present, preferably methylene chloride, can be further utilized in another place. The isolation of the sweetener acid in the form of the desired salt (III) is expediently carried out by the method described in the abovementioned EP-A 218,076. In this, the sweetener acid contained in the sulfuric acid phase is first extracted therefrom in an extraction vessel using a solvent, preferably methylene chloride. The solvent used here is combined with the normal solvent phase which contains the majority of the sweetener acid. The small amount of sulfate dissolved in the solvent phase is then extracted from the combined solvent phases using only a little water in an extraction vessel and returned with the extraction water to react the cyclization product with water in the hydrolysis vessel to form sweetener acid. The sweetener acid is extracted from the remaining, substantially sulfate-free solution of the sweetener acid in the solvent, in the form of the desired salt, preferably the potassium salt, using aqueous alkali metal hydroxide solution, preferably potassium hydroxide solution. The aqueous solution of the sweetener (III) can be worked up by conventional methods, for example by evaporation or precipitation using external solvents, to give the pure crystalline sweetener (III).
The remaining solvent is water-saturated and contains a large part of the by-product formed in the reaction, such as acetone, trialkylamine and trialkylammonium salt of the sweetener acid when the trialkylamnonium salt of amidosulfonic acid was used, undefined high boilers and dissolved resins.
The solvent thus contaminated cannot be reused in this form. Thus in the mixing of the SO.sub.3 in the cyclization stage with the contaminants, dark-colored solid insoluble compounds are formed which lead to blockages in the piping. In addition, with acetone, colored secondary products occur which pass through to the sweetener solution. A colorless sweetener can no longer be isolated from such solutions. Neither can this contaminated
REFERENCES:
patent: 3689485 (1972-09-01), Clauss
patent: 3969348 (1976-07-01), Pietsch et al.
patent: 4263102 (1981-04-01), Schorr et al.
patent: 4289586 (1981-09-01), Sabatka
patent: 4804755 (1989-02-01), Reuschling et al.
Engelmann Axel
Kaufmann Wolf-Dietmar
Laugwitz Bernd
Litterer Heinz
Roscher Gunter
Bhat Nina
Hoechst Aktiengesellschaft
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