Organic compounds -- part of the class 532-570 series – Organic compounds – Sulfur containing
Reexamination Certificate
1998-02-13
2001-05-22
Vollano, Jean F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Sulfur containing
C568S021000
Reexamination Certificate
active
06235941
ABSTRACT:
TECHNICAL FIELD
This invention relates to an improved process by which organic disulfides, especially lower alkyl disulfides, can be produced in high yield and with high efficiency.
BACKGROUND
U.S. Pat. No. 5,659,086 describes a process for producing organic disulfides comprising the steps of (1) contacting a base and a mercaptan to form a brine phase comprising the base and a basic salt of a mercaptan; (2) contacting the brine phase with a mercaptan and hydrogen peroxide to form an aqueous phase and an organic phase; (3) separating the aqueous phase form the organic phase; (4) recovering the organic phase; and optionally, (5) removing a portion of water from the aqueous phase and thereafter repeating the steps of (2) to (5). The separation of step (3) is conducted by decantation, centrifugation, solvent extraction, chromatographic separation, or a combination of any two or more thereof, with decantation being preferred.
SUMMARY OF THE INVENTION
This invention provides a novel, highly efficient process enabling production of organic disulfides in high yield and purity. Not only is the process very easy and simple to carry out, but in addition the process (i) eliminates the need for forming an organic phase of liquid organic disulfide product and conducting a separation between such product and the total aqueous phase used in the reaction, (ii) enables efficient control of a highly exothermic reaction, and (iii) minimizes alkanesulfonic acid salt formation during the reaction.
In accordance with one of the embodiments of this invention there is provided a process for production of organic disulfide wherein an aqueous solution of basic mercaptide salt and water-soluble peroxide are contacted or mixed in a reaction zone under conditions effective to produce a vapor phase comprising organic disulfide, while concurrently recovering vapor phase from the reaction zone. Contact between the peroxide and the aqueous solution of basic mercaptide salt results in an exothermic reaction taking place. By maintaining a suitably low pressure in the reaction zone, a vapor phase comprising organic disulfide product is formed and concurrently removed or withdrawn from the reaction zone. This vaporization consumes a portion of the heat of reaction produced. At the same time by operating under suitable reaction temperature and pressure conditions, a portion of the water can be caused concurrently to vaporize from the aqueous solution in the reaction zone thereby further consuming the exothermic heat of reaction produced. Consequently, the temperature in the reaction zone is more readily controlled and maintained. Thus in the preferred modes of operation a vapor phase is formed comprising the organic disulfide being produced and water resulting from vaporization of a portion of aqueous reaction medium, and this vapor phase is removed (withdrawn or recovered) from the reaction zone concurrently with its formation, e.g., substantially as soon as it is formed.
It will be seen, therefore, that in conducting the process it is desirable to feed or introduce at a uniform or substantially uniform rate one of the reactants (i.e., the peroxide or the aqueous solution of basic mercaptide salt) into the reaction zone containing the other such reactant. Such feed rate preferably results, under the reaction conditions being used, in formation of vapor phase at a rate corresponding or substantially corresponding to the rate at which the vapor phase is being withdrawn from the reaction zone, thus providing and maintaining steady state conditions in the reaction zone. The feed itself can be intermittent or continuous. Preferably, the peroxide is fed into the aqueous solution of basic mercaptide salt, and preferably such feed is continuous during at least a major portion (more than 50%) of the reaction period. Most preferably, the continuous feed of peroxide is maintained during substantially the entire reaction period. Another way of conducting this reaction is to feed both reactants into the reaction zone at rates that result in formation of vapor phase at a rate corresponding or substantially corresponding to the rate at which the vapor phase is being withdrawn from the reaction zone, thereby providing and maintaining steady state conditions in the reaction zone.
Thus this invention provides, inter alia, a process for production of organic disulfide, which process comprises reacting mercaptide and peroxide in an aqueous reaction medium under conditions such that organic disulfide is formed and is vaporized, and concurrently recovering vapor phase comprising at least vaporized organic disulfide formed in the reaction, and preferably a vapor phase further comprising water vaporized from the aqueous reaction medium.
Another embodiment of this invention is a process for production of organic disulfide, which process comprises:
a) reacting a mercaptan with a base in an aqueous medium to form an aqueous solution of basic mercaptide salt;
b) contacting aqueous solution of basic mercaptide salt formed in a) and peroxide in a reaction zone under reaction conditions effective to produce a liquid aqueous reaction mixture and a vapor phase comprising organic disulfide; and
c) concurrently withdrawing vapor phase from the reaction zone of b).
The withdrawn vapor phase is condensed and can be dried and purified in any suitable manner, but preferably is distilled. As noted above, preferably the withdrawn vapor phase comprises both vaporized organic disulfide product and vaporized water, and in such case the vapors are condensed to form a two-phase mixture of a predominately organic phase of organic disulfide and an aqueous phase of predominately water; and most preferably, these phases are separated from each other by gravity separation. The separated organic phase can then be further purified to achieve whatever final product purity is desired. A portion of the separated aqueous phase can be, and preferably is, recycled in amounts sufficient to maintain material and energy balance.
In each of the above embodiments, it is particularly preferred to utilize reaction conditions in the reaction between peroxide and mercaptide that cause or result in vaporization of liquid water from the reaction medium at a rate sufficient to consume in the range of about 50-100% of the exothermic heat of reaction resulting from the exothermic reaction that is occurring in that reaction zone. Also, additional heat above the heat of reaction can be put into the reactor, e.g., by means of a heating jacket, to effect even greater stripping of organic disulfide from the reactor. This minimizes the amount of dissolved disulfide in the aqueous phase which otherwise can react to form sulfonic acid with attendant losses of the desired product and of the inorganic base being used.
In conducting the process the amount of water present in the reaction mixture in b) should be at least sufficient to keep the reactants and reaction products in solution, but without use of an excessive amount of water above such amount. Thus it is desirable to proportion the feeds such that at the outset of the reaction between peroxide and mercaptide, the aqueous base solution contains about 15 wt % of the base such as sodium or potassium hydroxide, and to control the feeds such that the aqueous reaction solution contains no more than about 35 wt % of dissolved salts, and preferably in the range of about 20 to about 30 wt % of dissolved salts. Thus water can be fed to the reaction mixture in b) periodically as needed to maintain the reaction mixture in solution, and at least a portion of the water can be introduced as a peroxide solution, preferably as a solution of hydrogen peroxide.
Usually, the peroxide is introduced to the reaction mixture in the form of a solution, and typically as an aqueous solution which generally is in the range of a 1 to about 70% peroxide solution. In order to maintain a highly desirable material and energy balance in the reaction system of b), it is preferred to use a highly concentrated aqueous hydrogen peroxide solution, e.g., in the range of about
Cheng Chi Hung
Sulzer Gerald M.
Albemarle Corporation
Pippenger Philip M.
Vollano Jean F.
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