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(11) | EP 0 000 871 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
Method of preparing 2,2'-dithiodianiline Verfahren zur Herstellung von 2,2'-Dithiodianilin Procédé pour la préparation de 2,2'-dithiodianiline |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
TECHNICAL FIELD
[0001] This invention relates to a method of preparing 2,2'-dithiodianiline by reacting an alkali metal salt of o-aminothiodianiline with hydrogen peroxide.
[0002] The 2,2'-dithiodianiline is particularly useful for curing, crosslinking or extending isocyanate-terminated polyurethane prepolymers. It can be prepared by oxidizing the sodium salt of o-aminothiophenol. However, the 2,2'-dithiodianiline must be obtained in high purity form, without the attendant typical oxidation byproducts, for satisfactory use in the preparation of most cured polyurethanes.
BACKGROUND ART
[0003] Heretofore, 2,2'-dithiodianiline could be prepared by the steps of (A) oxidizing an aqueous solution of the sodium salt of o-aminothiophenol through the slow addition of hydrogen peroxide to form a water slurry of the water insoluble 2,2'-dithiodianiline, and solution of water soluble byproducts and (B) mixing toluene with the slurry to extract the 2,2'-dithiodianiline in the hydrocarbon phase.
[0005] However, such a method has particular disadvantages since the solid 2,2'-dithiodianiline product is directly subject to degradation by (A) rising to the top of the aqueous slurry during the reaction and being scorched, or oxidised, by contact with the hydrogen peroxide slowly being added, and (B) by being in direct contact with sodium hydroxide product in the aqueous phase. The 2,2'-dithiodianiline is simply subject to degradation by being in contact with both one of the reactants and by one of the products.
[0006] Therefore, it is an object of this invention to provide a method of preparing 2,2'-dithiodianiline through the oxidation of a salt of o-aminothiophenol and recovering the 2,2'-dithiodianiline in a relatively high purity form.
DISCLOSURE AND PRACTICE OF THE INVENTION
[0007] In accordance with this invention, a method of preparing 2,2'-dithiodianiline through the oxidation of a salt of o-aminothiophenol and recovering the 2,2'-dithiodianiline in a relatively high purity form is provided.
[0008] In accordance with this invention, a method of preparing 2,2'-dithiodianiiine by reacting an alkali metal salt or o-aminothiophenol with hydrogen peroxide is characterized by (A) agitating a mixture of a water solution of the sodium or potassium salt of o-aminothiophenol and an unstable dispersion therein of a liquid hydrocarbon selected from at least one of toluene, benzene, or xylene, (B) oxidizing said salt of o-aminothiophenol by slowly adding a water soluble peroxide to said agitated mixture, (C) discontinuing the agitation of the dispersion to allow the mixture to substantially immediately separate into a lower aqueous phase and upper hydrocarbon phase having a continuous, sharply defined innerface therebetween, (D) drawing off said lower aqueous phase and (E) distilling the remaining hydrocarbon phase to remove said hydrocarbon therefrom and recovering said 2,2'-dithiodianitine as a distilland.
[0009] It is important to appreciate that, in the oxidizing step (B) products are formed which comprise inorganic salts and sodium or potassium hydride as well as the defined 2,2'-dithiodianiline.
[0010] In the preferred practice of this invention, the method of preparing the 2,2'-dithiodianiline is characterized by (A) forming an agitated, unstable mixture comprised of (1) 100 parts by weight of an aqueous solution comprising 10 to 50 weight percent sodium or potasssium salt of o-aminothiophenol, and correspondingly, 90 to 50 weight percent water and (2) a dispersion therein of 10 to 50 parts by weight hydrocarbon selected from at least one of toluene, benzene or xylene, (B) oxidizing said salt of o-aminothiophenol by adding a water soluble peroxide to said agitated dispersion sufficiently slowly so that only a trace, if any, residual peroxide concentration is maintained in the dispersion, at a temperature in the range of 5°C. to 50°C., preferably 10°C. to 40°C., (C) discontinuing said agitation to essentially immediately yield a sharply defined lower aqueous phase and an upper hydrocarbon phase containing said 2,2'-dithiodianiline essentially exclusive of the remainder of said products contained in said aqueous phase, (D) drawing off said sharply defined aqueous phase and (E) distilling the remaining hydrocarbon phase to a pot temperature in the range of 130°C. to 150°C. under a reduced pressure in the range of 6666 Pa (50 mm Hg) to 26664 Pa (200 mm HG) to' remove said hydrocarbon solvent as a distillate and recover said 2,2'-dithiodianiline as a distilland.
[0011] It is important to appreciate that it has been discovered that the practice of this invention especially enhances the stability and recovery of a relatively high purity 2,2'-dithiodianiline product by minimizing its contact with its degrading environment. The practice of this invention further enables larger batches to be produced in the same equipment utilized for the prior slurry process and, therefore, enables a general improvement in the overall process.
[0012] Indeed, the utilization of the unstable hydro- carbon/water solution dispers on effects both an effective insulation and clean separation of the 2,2'-dithiodianiline product in a relatively high purity form from the presence of degraded reactants and byproducts right at the point of reaction itself. As the reaction proceeds, the product is immediately both withdrawn from its reaction medium and insulated therefrom.
[0013] Generally, the 2,2'-dithiodianiline is uniquely of sufficiently high purity, without additional purification steps, to be satisfactorily used as a curative for some isocyanate-terminated polyurethane prepolymers although at least one water wash of the product is preferably for optimum results. It should readily be appreciated by those having skill in the polyurethane art that purity of reactants is of high priority in such polyurethane reaction systems.
[0014] For optimum purity of the 2,2'-dithiodianiline for use as a polyurethane curative, it is desired to water wash the hydrocarbon phase containing the 2,2--dithiodianiline (before the distillation step) with at least one, generally from 1 to 5, preferably 2 to 4, water washes. The primary purpose is to remove traces of sodium or potassium hydroxide which can typically adhere to surfaces of the physical reactor system itself and bleed into the product or hydrocarbon phase contained in the reactor.
[0015] In the conduct of the reaction, it is necessary to provide an agitated, unstable aqueous solution/hydrocarbon dispersion. The liquid hydrocarbon is chosen so that it is naturally immiscible with the aqueous solution. Therefore, the mixture requires agitation, preferably a very rapid or high degree of agitation, to provide and maintain the dispersion. When the agitation stops, the dispersion disappears within a few minutes, typically in a minute or less, yielding sharply defined aqueous and hydrocarbon phases. Such agitation can be provided by conventional means.
[0016] In the further conduct of this invention, it is desired to minimize the potential of excess of the peroxide reactant. On this basis, (1) the peroxide is only added slowly for this purpose and to keep the reaction exotherm down and (2) a test is made to determine if the reaction is essentially complete so that further peroxide addition is not necessary. For this test, the agitation is stopped, the phases automatically separated, and a sample of the aqueous phase withdrawn and tested for peroxide content. If the sample does not contain peroxide, the agitation and dispersion are re-established and peroxide addition resumed. If the sample contains peroxide, the reaction is considered complete.
[0017] For the practice of this invention, the o-aminothiophenol can conveniently be obtained from the reaction of benzothiazole with sodium hydroxide. Such a reaction is generally exothermic and can be conducted at a temperature in the range of about 130°C. to about 170°C. The product of such a reaction is upgraded to remove impurities by first steam stripping to remove volatiles, aniline and benzothiazole, following which water and hydrocarbon are added to adjust the concentration of the sodium salt of o-aminothiophenol in the water to about 3 to about 30 weight percent. The mixture can be, if desired, treated with activated carbon to remove trace impurities and filtered. The o-aminothiophenol salt, as an aqueous solution in the presence of the hydrocarbon is now ready for oxidation.
[0018] The practice of this invention is further illustrated by reference to the following example which is intended to be representative rather than restrictive of the scope of the invention. Unless otherwise indicated, all parts and percentages are by weight.
Example
[0019] To a suitable reactor was charged 1.2 parts of a 24 weight percent aqueous solution of the sodium salt of o-aminothiophenol and 1.5 parts toluene. The temperature of the mixture was adjusted to about 20°C. and rapidly agitated to form a dispersion which would be unstable if it were not for the agitation. To the rapidly stirred mixture and dispersion was then slowly added about 0.16 part by weight hydrogen peroxide as a 13.5 percent aqueous solution over a period of about 20 to 30 minutes. This amounted to about a 16 percent excess peroxide to insure complete oxidation. With stirring, the reaction system was maintained at a temperature in the range of about 20°C. to about 50°C., which was about a maximum allowable temperature, while the 2,2'-dithiodianiline product formed in the aqueous phase and immediately and exclusively withdrew and dissolved into the dispersed toluene phase.
[0020] The final oxidation product contained 2,2'-dithiodianiline in high purity form in the dispersed toluene phase while the water phase selectively contained reaction byproducts which included inorganic salt, sodium hydroxide as well as the original water.
[0021] Agitation was stopped and the mixture automatically and quickly separated into a sharply defined upper toluene phase and a lower aqueous phase in a few seconds to a few minutes. The lower aqueous phase was simply drawn off and separated from the toluene phase. The organic toluene phase was washed three times with about 8.3 parts by weight of water, with the water phase being drawn off after each wash. The parts by weight was based on one part by weight final 2,2'-dithiodianiline.
[0022] It is important to appreciate that the 2,2'-dithiodianiline product can be degraded by the sodium hydroxide. Therefore, the immediate extraction of the 2,2'-dithiodianiline product into the toluene phase during the actual reaction step has a very special value.
[0023] The toluene from the toluene phase was simply removed by flash distillation from the top of the reactor through a condenser into a receiver at a reduced pressure of about 1333 Pa (100 mm Hg) and a pot temperature of about 150°C. The remaining molten distilland product was removed from the reactor by pressurizing with about 34474 Pa (5 psig) from the reactor at about 130°C. and packaged in containers in which it solidified when cooled below about 90°C. The overall yield was above 90 percent of 2,2'-dithiodianiline of a total amine content (purity of about 98.1 percent).
(A) en ce qu'on agite un mélange d'une solution aqueuse d'un sel de sodium ou de potassium du o-aminothiophénol et d'une dispersion instable de toluène, de benzène, de xylène, ou d'au moins un de ces trois hydrocarbures liquides,
(B) en ce qu'on fait oxyder ce sel du o-amino-. thiophénol en ajoutant lentement au mélange agité un peroxyde soluble dans l'eau
(C) en ce qu'on termine l'agitation de la dispersion pour permettre au mélange de se séparer pratiquement immédiatement dans une phase inférieure aqueuse et dans une phase supérieure d'hydrocarbure ayant entre elles une interface continue bien définie
(D) en ce qu'on soutire cette phase inférieure aqueuse et
(E) en ce qu'on distille la phase restante d'hydrocarbure pour en éliminer l'hydrocarbure et obtenir la 2,2'-dithiodianiline comme résidu de distillation.
(A) en ce qu'on forme un mélange agité instable, comprenant (1) 100 parts en poids d'une solution aqueuse composée de 10 à 50% (en poids) d'un sel. de sodium et de potassium de l'o-aminothiophénol et respectivement de 90 à 50% (en poids) d'eau et (2) en ce qu'on forme dans ce mélange une dispersion qui comprend 10 à 50 parts en poids de toluène, de benzène, de xylène, ou au moins 10 à 50 parts d'un de ces trois hydrocarbures
(B) en ce qu'on fait oxyder le sel de l'o-aminothiophénol en ajoutant suffisamment lentement un peroxyde soluble dans l'eau à cette dispersion agitée, de façon à ce que seulement une trace de concentration de peroxyde résiduel, si trace il y a, est retenue dans la dispersion, la température étant comprise entre 5°C et 50°C.
(C) en ce qu'on termine l'agitation pour avoir pratiquement immédiatement une phase inférieure bien définie et une phase supérieure d'hydrocarbure contenant la 2,2'-dithiodianiline, le reste des produits contenus dans la phase aqueuse étant pratiquement absent de cette phase.
(D) en ce qu'on soutire la phase aqueuse bien définie et
(E) en ce qu'on distille la phase restante d'hydrocarbure à une température de récipient comprise entre 130°C et 150°C, à une pression réduite comprise entre 6666 Pa (50 mm Hg) et 26664 Pa (200 mm Hg) pour éliminer le solvant d'hydrocarbure comme distillat et de récupérer la 2,2'-dithiodianiline comme résidu de distillation.
(A) en ce qu'on forme un mélange agité de (1) 100 parts en poids d'une solution aqueuse comprenant 15 à 30% en poids de sel de sodium du o-aminothiophénol et repective- ment 85 à 70% en poids d'eau et (2) en ce qu'on forme une dispersion de 15 à 25 parts (en poids) de toluène, à une température comprise entre 100C et 40°C,
(B) en ce qu'on fait oxyder le sel de sodium en ajoutant lentement de l'eau oxygénée au mélange,
(C) en ce qu'on termine l'agitation pour former la phase inférieure aqueuse bien définie et la phase supérieure d'hydrocarbure,
(D) en ce qu'on soutire la phase aqueuse et
(E) en ce qu'on distille la phase d'hydrocarbure pour obtenir la 2,2'-dithiodianiline comme résidu de distillation.
(A) dass man die Mischung einer wässerigen Lösung von Natrium- oder Kaliumsalz von o-Aminothiophenol und einer unstabilen Dispersion von Toluol, Benzol oder Xylol, wenigstens aber einem der drei vorhergenannten flüssigen Kohlenwasserstoffen rührt,
(B) dass man das o-Aminothiophenolsalz oxydiert, indem langsam ein wasserlösliches Peroxyd zur gerührten Mischung zugegeben wird,
(C) dass man die Rührung der Dispersion beendet um der Mischung zu erlauben sich praktisch sofort in eine untere wässerige Phase und eine obere Kohlenwasserstoffphase aufzuteilen, wobei eine kotinuierliche scharfe Phasengrenzfläche auftritt,
(D) dass man die untere wässerige Phase abzieht und
(E) dass man die restliche Kohlenwasserstoffphase destilliert, um den Kohlenwasserstoff davon zu entfernen und das 2,2'-Dithiodianalin als Destillationsrückstand zu erhalten.
(A) dass man eine aufgerührte, unstabile Mischung bildet, die aus (1) 100 Gewichtsteilen einer wässerigen Lösung besteht, wobei die wässerige Lösung 10 bis 50 Gewichtsprozente Natrium- oder Kaliumsalz von o-Aminothiophenol, und in entsprechendem Masse 90 bis 50 Gewichtsprozente Wasser enthält, und (2) dass man eine Dispersion in jener aufgerührten unstabilen Mischung bildet, die aus 10 bis 50 Gewichtsteilen Toluol, Benzol, Xylol oder aus 10 bis 50 Gewichtsteilen wenigstens einer der drei vorher genannten Kohlenwasserstoffe besteht,
(B) dass man jenes o-Aminothiophenolsalz oxydiert indem man ein wasserlösliches Peroxyd zur aufgerührten Dispersion genügend langsam hinzugibt, so dass bei einem Temperaturbereich von 5°C bis 50°C nur eine Spur, wenn überhaupt der restlichen Peroxyd-konzentration in der Dispersion zurückbleibt,
(C) dass man die Rührung beendet um praktisch sofort eine scharf abgegrenzte untere wässerige Phase und eine obere Kohlenwasserstoffphase zu erhalten, die das 2,2'-Dithiodianalin im wesentlichen ausschliesslich der restlichen Produkte der wässerigen Phase enthält,
(D) dass man jene scharf abgegrenzte wässerige Phase abzieht,
(E) dass man die restliche Kohlenwasserstoffphase bei einer Gefässtemperatur im Bereich von 130°C bis 150°C und einem reduzierten Druck im Bereich von 6666 Pa (50 mm Hg) bis 26664 Pa (200 mm Hg) destilliert um das Kohlenwasserstofflösungsmittel als Destillat zu entfernen und das 2,2'-Dithiodianalin als Destillationsrückstand zu erhalten.
(A) dass man eine aufgerührte Mischung von (1) 100 Gewichtsteilen einer wässerigen Lösung bildet die 15 bis 30 Gewichtsteile Natriumsalz von o-Aminothiophenol und, in entsprechendem Masse, 85. bis 70 Gewichtsprozente Wasser enthält, und (2) dass man eine Dispersion in: der aufgerührten Mischung bildet, die 15 bis 25 Gewichtstejle Toluol bei einem Temperaturbereich von 10°C bis 40°C bildet,
(B) dass man das Natriumsalz oxydiert indem man zu jener aufgerührten Dispersion langsam Wasserstoffperoxyd hinzufügt,
(C) dass man die Rührung beendet um die scharf abgegrenzte untere wässerige Phase und die obere Kohlenwasserstoffphase zu erhalten,
(D) dass man die wässerige Phase abzieht und
(E) dass man die Kohlenwasserstoffphase destilliert um 2,2'-Dithiodianilin als Destillationsrückstand zu erhalten.