METHOD OF PURIFYING 3-CHLORO-2-HYDROXYPROPYL TRIALKYLAMMONIUM CHLORIDE

Abstract: Method of purifying 3-chloro-2-hydroxypropyl trialkylammonium chloride. An aqueous slurry is prepared containing from 70 to 98 weight percent total solids including the chloride and impurities associated with the preparation thereof. To this slurry is then added a miscible alcohol having from 3 to 4 carbon atoms. A solid filtrate is collected and optionally washed with additional alcohol and dried. The solid filtrate is substantially more pure in the chloride than the starting material.

Description: METHOD OF PURIFYING 3-CHLORO-2-HYDROXYPROPYL TRIAL YLAMMONIUM CHLORIDE This invention relates to a method of purifying 3-chloro-2-hydroxypropyl trialkylammonium chloride which contains impurities typically formed during the reaction of epichlorohydrin with trialkylammonium hydrochloride. The reaction of epichlorohydrin with trimethylammonium hydrochloride in an aqueous medium to form 3-chloro-2-hydroxypropyl trimethylammonium chloride is well known. The resulting processed aqueous solution is commonly used to manufacture cationically active starch products. However, such an aqueous solution contains substantial quantities of by-products which are non-reactive in the starch manufacturing process, including, for example, l,3-bis(trimethylammonium chloride)-2-hydroxypropane, and 1,2-hydroxypropane- 3-trimethylammonium chloride. These non-reactive impurities are not easily removed and can pose serious disposal problems to the cationically active starch manufacturers. These impurities can also cause a higher level of FDA extractable quaternarys in paper manufactured with non-washed cationic starch. Another advantage to removing these impurities is the desire to transport more active 3-chloro-2-hydroxypropyl trialkylammonium chloride per unit weight of aqueous solution. Since the amount of total solids in the aqueous solution controls its freezing and crystallization point, the removal of these impurities allows a higher concentration of 3-chloro-2-hydroxypropyl trialkylammonium chloride per unit weight while effectively avoiding the freezing and crystallization point. As far as Applicant is aware, there has been no method heretofore devised for removing these non-reactive impurities. The only method of which Applicant is aware which can be employed to obtain 3-chloro-2-hydroxypropyl trimethylammonium chloride free of substantial non-reactive impurities is described in U.S. Patent 4,450,295. According to the method described in that patent, an aqueous trialkyla.τιmonium chloride solution was first prepared. To this solution was then added a solvent which formed an azeotrope with water, the azeotrope having a boiling point below that of the solvent alone. In addition, the solvent had to be immiscible with water and non-reactive with epichlorohydrin. The azeotrope of the solvent and the water was then distilled off leaving a dispersion of the trialkylammonium chloride in the organic solvent. Thereafter, the trialkylammonium chloride was reacted in the solvent with epichlorohydrin. Such a method was not generally desirable because of the great amount of energy required to distill the water-solvent azeotrope. In addition, existing facilities for manufacturing 3-chloro-2-hydroxypropyl trimethylammonium chloride were not easily retrofitted to employ the process. The invention is a method " of purifying 3-chloro-2-hydroxypropyl trialkylammonium chloride, comprising the steps of: (a) preparing an aqueous slurry of 3-chloro-2-hydroxypropyl trialkylammonium chloride containing impurities, said slurry having a total solids content from 70 to 98 percent by weight of said slurry; (b) mixing therewith a water-miscible alcohol having from 3 to 4 carbon atoms to form a water-alcohol slurry; and (c) collecting precipitated solids from said water-alcohol slurry. The precipitated solids obtained by the method contain a high purity product 3-chloro-2-hydroxypropyl trialkylammonium chloride which can have a purity in excess of 99 percent by weight. The success of the present method in solving the problem of purifying 3-chloro-2-hydroxypropyl trialkylammonium chloride lies in the surprising discovery that the impurities, such as l,3-bis(trialkylammonium chloride)-2-hydroxypropane and 1,2-hydroxypropane- 3-trialkylammonium chloride, remain substantially soluble in the water-alcohol mixture, whereas the desired product, 3-chloro-2-hydroxypropyl trialkylammonium chloride, has limited solubility therein. Thus, the traditional method of producing 3-chloro-2-hydroxypropyl trialkylammonium chloride by reacting epichlorohydrin with trialkylammonium hydrochloride in an aqueous medium can be employed to produce a slurry from which can be obtained substantially pure 3-chlαro-2-hydroxypropyl trialkylammonium chloride suitable for use in the manufacture of cationically active starch. According to the method of the present invention, there is first prepared an aqueous slurry having a total solids content of from 70 to 98 percent by weight of the slurry. In addition to the 3-chloro-2-hydroxypropyl trialkylammonium chloride, which for purposes of convenience is sometimes referred to herein as "the desired product", the slurry may contain substantial quantities of impurities which are typically formed during the reaction of epichlorohydrin with trialkylammonium hydrochloride in an aqueous medium. Thus, conventional methods and equipment known to those in the art can be used to prepare the 3-chloro-2-hydroxypropyl trialkylammonium chloride. The method is not, however, limited to purifying 3-chloro-2-hydroxypropyl trialkylammonium chloride prepared in an aqueous medium, and is useful in purifying the compound prepared in other media as well. When the impure 3-chloro-2-hydroxypropyl trialkylammonium chloride is obtained as a solid, the aqueous slurry is prepared by simply mixing the powdered or finely dividad solid with an appropriate aπount of water. When the 3-chloro-2-hydroxypropyl trialkylammonium chloride is prepared by reacting epichlorohydrin with trialkylammonium hydrochloride in an aqueous medium, an aqueous solution containing up to 70 percent solids by weight of the slurry is typically obtained. Water can be removed from this solution by evaporation or distillation to obtain a slurry with a total solids content of from 70 to 98 percent by weight of the slurry. As used herein, the term "total solids content" in reference to a slurry is used to indicate dissolved as well as precipitated solids. Regardless of its method of preparation, the total solids content of the slurry is preferably from 90 to 95 percent by weight of the slurry. Preferably, the water is removed from the aqueous medium reaction product by vacuum distillation at a temperature less than 50°C~ Although the distillation may be performed at a higher temperature, this will not normally be desirable because of the decomposition of the 3-chloro-2-hydroxypropyl trialkylammonium chloride into undesirable by-products. With the slurry is then mixed a water-miscible alcohol having from 3 to 4 carbon atoms to form a water-alcohol slurry. The particular alcohol used is not believed to be particularly critical as long as it is miscible with the water. Further, the alcohol mixed with the aqueous slurry does not need to be exceptionally pure and may contain substantial quantities of water and other impurities which are soluble in the resulting water-alcohol slurry. Preferably, however, the amount of such impurities present in the alcohol before mixing with the aqueous slurry is as small as possible. Specific representative examples of such alcohols include isopropanol, n-propanol and t-butanol, with isopropanol being preferred. In comparison with water alone, the 3-chloro-2-hydroxypropyl trimethylammonium chloride is less soluble, yet the impurities typically present remain substantially soluble in the water-alcohol mixture. The amount of alcohol which may be nixed with the aqueous slurry to exploit the preferential solubility of the impurities over that of the 3-chloro-2-hydroxypropyl trimethylammonium chloride in the resulting alcohol-water mixture ranges from 10 to 70 weight percent alcohol, based on the total weight of the resulting alcohol-water slurry, preferably from 25 to 50 weight percent the alcohol. The precipitated solids are then recovered by filtration, or by other means suitable for removing solids from liquid in which the solute is removed with the liquid. The solids so recovered are substantially more pure in the desired product, 3-chloro-2-hydroxypropyl trialklyammonium chloride, than the impure material in the aqueous slurry. The solid filtrate obtained may be used without additional processing, but if desired,' may optionally be washed with additional volumes of the alcohol or another non-solvent to remove additional impurities and/or dried to substantially remove any residual alcohol and water. The liquid water-alcohol filtrate may optionally be disposed of in one or more of several manners. Although it has a higher content of dissolved impurities relative to the desired product than the aqueous slurry, the liquid filtrate may be used as a low grade product, with or without removing the alcohol therefrom by azeotropic distillation. On a continuous commercial scale, however, it is contemplated that a portion of the liquid water-alcohol filtrate is recycled by adding it to the aqueous slurry with make-up alcohol, and disposing of the remaining portion to avoid an excessive accumulation of water and other impurities in the system. Alternatively, the alcohol in the liquid filtrate is recovered by azeotropic distillation. Further, if the alcohol is used to wash the solid filtrate, the alcohol recovered from this step can also be used as make-up alcohol added to the aqυeous slurry. The method is illustrated by way of the following example : Example An aqueous solution containing about 61 weight percent solids was prepared by reacting epichlorohydrin with trimethylamine hydrochloride in water. The solids had the following analysis; Weight Percent Compound of Total Solids < « Analysis Method 3-chloro-2- hydroxypropy1 trimethylammonium chloride 84.0 0.5 Titration 1,3-Bis(trimethyl- ammonium chloride)- 2-hydrdxypro ane 9.0 8.0 HPIC 1,2-Hydroxypropane- 3-trimethylammonium chloride 7.0 5.0 HPLC 1,-3-Dichloropropane 0.0026 5.0 GC Epichlorohydrin <0.0001 - GC Trimethylamine hydrochloride 0.02 5.0 Titration Relative standard deviation in percent. The solution was reduced to a slurry having about 90 weight percent solids by vacuum distillation at 45°C. To this slurry was added isopropanol in an amount sufficient to obtain 27 weight percent isopropanol in the resulting alcohol-water slurry. The precipitated solids were then collected from the isopropanol-water slurry on a coarse glass frit and washed with two isopropanol aliquots, each of about the same amount used to obtain the alcohol-water slurry. The recovered solids were dried by first passing nitrogen gas through the filter cake, and then overnight in a vacuum oven at 50°C The product had the following analysis: Weight Compound Percent W" Analysis Method 3-chloro-2-hydroxypropyl trimethylammonium chloride 99.0 0.5 Titration 1,3-Bis(trimethylammonium chloride)-2-hydroxypropane <0.5 HPLC 1,2-hydroxypropane-3- trimethylammonium chloride <0.25 HPLC 1,3-Dichloropropanol <0.0001 GC Epichlorohydrin <0.0001 GC Trimethylamine hydrochloride <0.01 Titration 2. See note 1. As illustrated by the foregoing example, a product of only 84 percent purity is readily purified according to the method of the invention to have a purity of 99 percent. The foregoing disclosure and description of the invention are illustrative and explanatory thereof and various changes in the details may be made without departing'from the spirit of the invention.

Claims: CLAIMS 1. A method of purifying 3-chloro-2-hydroxypropyl trialkylammonium chloride, comprising the steps of: (a) preparing an aqueous slurry of 3-chloro-2-hydroxypropyl trialkylammonium chloride 5 containing impurities, said slurry having a total solids content of from 70 to 98 percent by weight of said slurry; (b) mixing therewith a water-miscible alcohol having from 3 to 4 carbon atoms to form a water-alcohol slurry; and 10 (c) collecting precipitated solids from said water-alcohol slurry. 2. The method of claim 1, wherein said solids content of said aqueous slurry is from 90 to 95 percent by weight of said slurry. 15 3. The method of claim 1, wherein said alcohol is present in said water-alcohol slurry in an amount of from 10 to 70 percent by weight of said water-alcohol slurry. 4. The method of claim 1, wherein said preparation of said aqueous slurry comprises: 20 (i) preparing an aqueous solution of 3-chloro-2-hydroxypropyl trialkylammonium chloride containing impurities formed during the reaction of epichlorohydrin with trialkylammonium hydrochloride; and 25 (ϋ) removing water from said solution to produce an aqueous slurry containing from 70 to 98 percent total solids by weight of said aqueous slurry. 5. The method of claim 4, wherein said removal of 30 said water is by vacuum distillation at a temperature less than 50°C. 6. The method of claim 1, wherein said 3-chloro-2-hydroxypropyl trialkylammonium chloride is 3-chloro-2-hydroxypropyl trimethylammonium chloride prepared by the reaction of epichlorohydrin with trimethylammonium hydrochloride. 7. The method of claim 6, wherein said reaction of epichlorohydrin with trimethylammonium hydrochloride is in an aqueous medium. 8. The method of claim 1, wherein said alcohol is isopropanol. 9. The method of claim 1, wherein said precipitated solids are collected by filtration. 10. The method of claim 1, further comprising the step of: (d) washing said collected solids with an additional amount of said alcohol.

Inventors: TASSET EMMETT L, TASSET, EMMETT, L.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1986
Main classification: C07C89
IPC codes: C07C213, C07C215