United States Patent (19) (11) 4,219,498 Doi et al. - (45) Aug. 26, 1980 54 PROCESS FOR PREPARING HIGHLY : (56) References Cited PURE-2-ACRYLAMDO-2-METHYLPRO PUBLICATIONS PANESULFONCACID Vogel, "Practical Org. Chem,” 3rd Ed. (1962), pp. 122-125. (75) Inventors: Shunichi Doi; Masatake Kamogawa, both of Yokohama, Japan Primary Examiner-A. Siegel Attorney, Agent, or Firm-Cushman, Darby & Cushman 73) Assignees: Nitto Chemical industry Co., Ltd.; 57 ABSTRACT Mitsubishi Rayon Co., Ltd., both of This disclosure relates to a process for preparing highly Tokyo, Japan pure 2-acylamido-2-methylpropanesulfonic acid, which comprises the steps of adding acetic acid to a slurry 21 Appl. No.: 8,113 containing crystals of 2-acrylamido-2-methylpropane sulfonic acid obtained by the reaction of acrylonitrile, isobutene and either conc. sulfuric acid, fuming sulfuric (22 Filed: Jan. 31, 1979 acid or sulfuric anhydride plus water in a solvent, then distilling the resulting mixture to replace the reaction 30 Foreign Application Priority Data solvent with acetic acid, adding water or hydrous acetic Jun. 12, 1978 JP Japan .................................. 53/69928 acid to the resulting mixture, heating the mixture to dissolve said crystals, and subjecting the solution to 51) Int. Cl’............................................ CO7C 143/02 recrystallization. 52 U.S.C. ................................................ 260/513 N 58 Field of Search .................................... 260/513 N 7 Claims, No Drawings 4,219,498 1. 2 of AMPS used as a starting material. The larger the said PROCESS FOR PREPARNG HIGHLY values, the higher the molecular weight of the copoly PURE-2-ACRYLAMDO-2-METHYLPROPANE mer and the more favorable the effect on papermaking. SULFONCACD In purifying AMPS by recrystallization from a sol vent, the type of solvent-purification methods is limited BACKGROUND OF THE INVENTION because AMPS is soluble in only water, lower alcohols 1. Field of the Invention and dimethylformamide. Moreover, water tends to This invention relates to a process for the efficient cause polymerization and decomposition of AMPS at preparation of highly pure 2-acrylamido-2-methylpro temperatures of 50 C. or more, while dimethylformam panesulfonic acid. 10 ide is disadvantageous in that precipitation of crystals of 2. Description of the Prior Art 2-Acrylamido-2- AMPS is not easy and owing to its high boiling point methylpropanesulfonic acid (hereinafter referred to the drying of precipitated crystals requires a long per simply as AMPS) to be purified according to this inven iod of time. For these reasons, methanol seems to have tion is a known compound which is prepared by the been chiefly used as the solvent in conventional purifi methods described in U.S. Pat. Nos. 3,506,707 and 15 cation of AMPS by recrystallization, as described, for 3,544,597, British Pat. No. 1,090,779, West German example, in British Pat. No. 1,090,779 and Japanese Offenlegungsschrift No. 2,523,616, and Japanese Patent Patent Publication No. 30,059/75 in connection with Publication No. 30,059/75. compounds analogous to AMPS. In a preparative method typical of those described in The recrystallization method in which methanol is the above patent publications, isobutene and fuming 20 used as solvent, however, presents also the problems sulfuric acid are allowed to react in the presence of an that AMPS purified by the recrystallization method excess of acrylonitrile, which is also used as reaction yields polymers having not sufficient performance char medium, and the resulting AMPS is allowed to precipi acteristics and yield of recrystallization is unsatisfac tate directly from the reaction mixture. The crude crys tory. tals thus obtained are washed with acrylonitrile and, if 25 necessary, recrystallized from a solvent. w SUMMARY OF THE INVENTION Beside being used as an agent for improving the dye In order to solve the aforementioned problem, the ing property of acrylic or other fibers, AMPS and its present inventors have conducted research on the pro homologs can be polymerized to form useful homopoly duction of highly pure AMPS to find surprisingly that mers and copolymers. These polymers are useful as 30 the substitution of acetic acid for the reaction medium polyelectrolytes and are known to be usable as floccu lant, dispersant, adhesive and fluidity regulator, and after the completion of the synthetic reaction results in there are many patents in these fields. a highly pure AMPS crystals and that AMPS is stable in The crude AMPS crystals as obtained by washing hydrous acetic acid. with a solvent the crystals precipitated directly from 35 According to this invention, there is provided a pro the reaction mixture may be used in some of the above cess for the efficient preparation of highly pure AMPS, mentioned uses. However, in order to produce a poly which comprises adding acetic acid to a slurry contain mer having a considerably high molecular weight, the ing crystals of AMPS obtained by the reaction of acry crude crystals must be completely dissolved in a solvent lonitrile (hereinafter referred to as AN), isobutene, and and recrystallized therefrom. either conc. sulfuric acid, fuming sulfuric acid or sulfu For instance, the copolymer of AMPS and acrylam ric anhydride plus water (preferably fuming sulfuric ide for use as a mucilaginous material for papermaking acid) in a solvent, then distilling the resulting mixture to and a flocculant must have a high molecular weight, replace the reaction solvent with acetic acid, adding and in order to produce such a high molecular weight water or hydrous acetic acid to the mixture, heating the copolymer, AMPS must have such a high purity as to 45 mixture to dissolve said crystals, and subjecting the be obtained by repeated recrystallization, otherwise no solution to recrystallization. satisfactory result can be obtained. In conventional methods for purifying AMPS, crude The use of a copolymer of AMPS and acrylamide as AMPS crystals directly precipitated out of the reaction a mucilaginous material for papermaking has been de mixture are first taken out of the reaction system, and scribed in U.S. Pat. No. 3,772,142 and Japanese Pat. 50 then recrystallized from a solvent, whereas the process Application Kokai (Laid-Open) Nos. 59,507/75 and of this invention is characterized in that both the reac 27,808/77. tion and the purification are carried out in the same Regarding the function of a mucilaginous material for vessel and the separation, washing and drying of crys papermaking, Japanese Patent Application Kokai tals are carried out in one series, resulting in a great (Laid-Open) No. 27,808/77 states that "this function is 55 reduction in equipment cost, labor cost, and materials to enable fibers of a pulp and the like to be dispersed in cost as well as improvement in workability and produc water, and the most important point'is whether or not tivity. Further, since the recrystallization is effected the mucilaginous material added only in a small amount after crude AMPS crystals are dissolved in hydrous to a fiber slurry in sheet formation can sufficiently con acetic acid, the crystals thus obtained are so sufficiently trol the rate of drainage; the practical usefulness of a 60 pure that the crystals can be used to produce a copoly mucilaginous material in controlling the rate of drain mer with acrylamide for a mucilaginous material for age is evaluated in terms of anti-freeness which corre papermaking. When an excess of AN is used to serve as sponds to the spinnability of an aqueous solution of said reaction medium, it follows that the AN is recovered by mucilaginous material, said spinnability corresponding distillation in the presence of acetic acid after comple also to the amount of mucilaginous material used per 65 tion of the reaction. Owing to the polymerizing ten unit weight of pulp in practical papermaking'. The dency of AN, the recovery of AN has hitherto had to be values of both spinnability and anti-freeness, which are carried out by distillation under reduced pressure or defined hereinafter, increase with an increase in purity under reflux of AN containing a polymerization inhibi 4,219,498 3 4. tor, however the AN can be efficiently recovered at points lower than that of acetic acid and, hence, are atmospheric pressure without polymerization of AN replaceable similarly to AN. according to the process of this invention. This is one of The replacement of the reaction medium with acetic the characteristic features of this invention. acid can be effected by the removal of the former by 5 atmospheric distillation, because AMPS has a quite high DETAILED DESCRIPTION OF THE thermal stability in the presence of acetic acid. INVENTION After the solvent replacement, water is added to the As for the solvents in which to dissolve crude AMPS system and the mixture is heated preferably at 60' to crystals in the reaction system and from which to re 110 C., more preferably at 80 to 90° C., to dissolve crystallize AMPS, it may be conceivable from the view 10 AMPS crystals. After completion of the dissolution, the point of dissolving AMPS to employ water, lower alco solution is cooled to precipitate crystals. Beside the hols including methanol as representative, and dimeth customary way of crystallization in which the change in ylformamide. However, methanol is unsuitable for the solubility with a change in temperature is utilized, it is solvent replacement, because it has a boiling point possible to improve the yield of recrystallization by lower than that of AN; ethanol and higher alcohols are 15 decreasing the water content of acetic acid by distilla unsuitable, because a large amount thereof is necessary tion or by the addition of glacial acetic acid or acetic owing to low solubility of AMPS in these solvents or it anhydride. The mixture is cooled to about 20° C.