4.d4 Z v O. f U - bs 2 XR 3 g6 7.7 g 952 3,677,952 United States Patent Office Patented July 18, 1972 2 linear or branched in its carbon backbone, and one to 3,677,952 two sulfonate groups per aromatic nucleus. Representa METHOD OF BLEACHING SULFONATE tive of this class are dodecylbenzenesulfonic acid, octa SURFACTANTS decylnaphthalenesulfonic acid, decyltoluenesulfonic acid, Lowell B. Lindy, Midland, Mich., assignor to The Dow decyldiphenyl ether disulfonic acid, dodecyldiphenyl ether Chemical Company, Midland, Mich. 5 disulfonic acid, dodecylchlorodiphenyl ether disulfonic No Drawing. Filed Oct. 2, 1970, Ser. No. 77,745 acid, and the sodium and potassium salts of these com Int, C. C11d 7/54 pounds. U.S. C. 252-94 7 Claims The process is particularly adapted to efficient de 10 colorizing of alkyldiphenyl ether disulfonates having an ABSTRACT OF THE DISCLOSURE average of about 1-1.3 alkyl groups of 8-18 carbon atoms and an average of about 1.6-2 sulfonate groups Alkylaryl sulfonate surfactants are bleached by react per diphenyl ether nucleus. ing their aqueous solutions with an inorganic hypohalite By the terms inorganic hypohalite and inorganic per and an inorganic permanganate, sequentially or in com manganate are meant hypochlorous acid, hypobromous bination. The process is particularly adaptable to de 5 acid, permanganic acid and the anhydrides and water colorizing higher alkyl diphenyl ether disulfonates using soluble inorganic salts of these, particularly the sodium sodium hypochlorite and potassium permanganate as the and potassium salts. In practice, sodium hypochlorite and bleaching agents. potassium permanganate are used since these are cheap 20 est and most readily available. Equivalents of potassium BACKGROUND OF THE INVENTON permanganate in this process include sodium permangan The present invention relates to a process whereby a ate, calcium permanganate, permanganic acid (in aqueous new combination of known bleaching agents is applied to solution), and manganese heptoxide. Hypohalite equival a crude sulfonate surfactant to obtain unexpectedly effec ents include sodium hypobromite, calcium hypochlorite, tive decolorization and it relates also to the bleached 25 hypobromous acid, potassium hypochlorite, and chlorine surfactant product. monoxide. Many of these can only be used in aqueous Many substances including textiles, paper pulp, vege solution. table oils, and others have been treated with inorganic The hypohalite bleaching step is preferably carried out bleaching agents such as hypochlorites, hypobromites, per with moderate heating, that is to say, at about 40-100 manganates, and peroxides to remove undesirable color. 30 C. and for a bleaching time of about 0.1-2 hours. The Bleaching agents such as these have also been applied to quantity of hypohalite can vary widely but it is most crude organic sulfonate surfactants. These surfactants advantageous to use about 1-5 percent by weight cal are often undesirably contaminated with color bodies or culated as sodium hypochlorite based on the weight of colored byproducts formed during the manufacturing surfactant. process which usually includes both alkylation and sul 35 The permanganate bleaching step is preferably done fonation reactions. For example, Sylvester, U.S. 2,738,- at about room temperature, for example, at about 15 365 describes the use of alkali hypochlorite to improve 30 C, although slight heating, say to about 50 C., may the color of alkyl aryl sulfonates and Wulff et al., U.S. be used. The preferred concentration of permanganate, 3,142,691 disclose the use separately of various bleach calculated as the potassium salt, is about 0.1-2.5 percent ing agents including hypochlorite, permanganate, and di 40 based on the weight of surfactant. With both hypohalite chromate to reduce the color of sulfonated fatty acids and permanganate, use of excessive bleaching agent pro and their derivatives. Some bleaching agents have been vides no advantage and may result in some loss of bleach used for the purpose in combination. Thus, Schurman, ing efficiency. Since bleaching with permanganate involves U.S. 2,804,466 shows the use of hypochlorite and per corresponding reduction of the permanganate to preci 45 pitate manganese dioxide, it is necessary to remove the oxide together to bleach sulfated and sulfonated anionic precipitated black oxide from the bleached surfactant surfactants. Solution. Any conventional means such as decantation or SUMMARY OF THE INVENTION centrifuging can be used but ordinarily a simple filtra It has now been found that color is removed with un tion is adequate. expected efficiency from alkyl aryl sulfonate surfactants 50 The bleaching process is carried out in aqueous solu when aqueous solutions of these substances are bleached tion and for practical reasons, a relatively concentrated by any combination of the steps: Solution is preferred. Surfactant solutions of 20-50 per cent concentration are illustrative. Similarly, the bleach (1) reacting by contacting an inorganic hypohalite with ing agents are best employed as dry solids or in relative the solution, and (2) reacting by contacting an inorganic permanganate 55 ly concentrated Solution depending upon the particular with the solution and separating the resultant preci compound involved. pitated manganese oxide. EXAMPLES Unexpectedly, the two bleaching agents in combination provide significantly better bleaching than any quantity 60 In the following examples, 100 gram samples of 45% of either bleaching agent alone. Also, the order in which aqueous alkylated and sulfonated diphenyl ether were the steps are carried out makes little difference in the treated with aqueous sodium hypochloride, with po results obtained, and in fact, substantially the same results tassium permanganate, and with combinations of the are also obtained when the two bleaching compounds are two sequentially or essentially simultaneously, each in added more or less simultaneously. 65 various proportions as shown. Potassium permanganate was added as the powdered solid at about room tem DETAILED DESCRIPTION perature and the treated solution was filtered with a The process is applicable to any of the well known filter aid, usually diatomaceous earth, to remove pre class of alkyl aryl sulfonate surfactants. This class is char cipitated manganese oxide. Sodium hypochlorite was acterized by the presence of at least one higher alkyl sub 70 added as a 15% aqueous solution and the mixture was stituent on the aromatic nucleus, higher alkyl being de then heated on a steam bath for about one hour. Color fined as defining a radical of 8-18 carbon atoms, either of the treated solutions was determined by comparison 3,677,952 3 4. with a standard Gardner varnish color scale numbered Evidently, differences in the quantity of KMnO, used with increasing color to a maximum value of 18. initially had no significant effect on the final result. The alkylated diphenyl ether sulfonates had been Use of more than 5% of NaOCl appeared to be some prepared according to known methods by alkylating di what harmful. phenyl ether in the presence of a Friedel–Crafts catalyst EXAMPLE 5 such as AlCls with a suitable olefin, tetrapropylene and To a sample of 45% aqueous disodium dodecyldi 1-decene being those actually used, in proportions such phenyl ether disulfonate (from tetrapropylene alkylate) that the diphenyl ether nucleus contained an average having Gardner color 12 there was added simultaneous of 1-1.3 alkyl groups, and then sulfonating the product ly 0.44% by weight of KMnO4 (solid) and 3.33% of with SO3 to contain an average of 1.6-2 sulfonate 0. NaOCl (as a 15% aqueous solution). The mixture was groups per molecule. heated on a steam bath for an hour, then it was cooled EXAMPLES 1-2 and filtered. The filtrate had a color of 4.5 on the Samples of two different alkyldiphenyl ether disul Gardner scale. fonates, each in 45% aqueous solution, were bleached In contrast to the results presented above, another by addition of 3.33% by weight of NaOCl (as 15% 5 Sample of the same disulfonate solution used in Exam aqueous solution) based on the dry weight of disulfonate ple 5 was treated with 3.33% of NaOCl as above and and heated as described above. The cooled solutions 0.2% of hydrogen peroxide (30% aq.) (equivalent to were then bleached additionally by addition of 2.2% 0.9% KMnO) was added to the cooled solution. The of KMnO. Sample A was essentially disodium n-decyl bleached solution had a Gardner color of 6.5. diphenyl ether disulfonate prepared from 1-decene al 20 Using the procedure described in any of the above kylate and Sample B was essentially the corresponding examples, other crude or undesirably colored alkylaryl sulfonates as previously defined are effectively bleached branched dodecyl disulfonate prepared from tetrapro to obtain light colored products. In this way, sodium pylene alkylate. Gardner colors of the treated and un dodecylbenzenesulfonate, potassium nonylnaphthalene treated solutions are listed below. 25 Sulfonate, hexadecyltoluenesulfonic acid, and similar sul fonates are obtained as desirable white or off-white ma Gardner color terials after bleaching with hypohalite and permanganate After After Sample Initial NaOCl. KMnO as shown. I claim: A------------ 3 0 4. 30 1. A process for bleaching an aqueous solution of an B------------- 12 9 5 alkyl aryl sulfonate surfactant which comprises any com bination of the steps: EXAMPLE 3 (1) reacting by contacting an inorganic hypohalite Samples of 45% aqueous disodium dodecyldiphenyl with said solution, and ether disulfonate (from tetrapropylene alkylate) were (2) reacting by contacting an inorganic permanganate treated with different amounts of 15% aqueous NaOCl with said solution and separating the resultant pre as described above and the treated solutions were then cipitated manganese oxide therefrom. treated further with KMnO as indicated. The untreated 2. The process of claim 1 wherein the surfactant is disulfonate solution was dark in color, having a Gardner an alkyldiphenyl ether sulfonate having an average of color of 12.