US3766254A - Linear alkylphenol disulfonate phosphate free detergent actives - Google Patents

Abstract

HEAVY DUTY DETERGENT ACTIVE MATERIALS CAPABLE OF HEAVY DUTY WASHING PERFORMANCE IN THE ABSENCE OF PHOSPHATE BUILDERS ARE PROVIDED, THE MATERIALS COMPROSING RING POLYSULFONATED ALKYLPHENOLS IN WHICH THE ALKYL GROUPS ARE LINEAR OF 16-22 CARBON ATOMS AND NOT MORE THAN 25 MOL PERCENT OF THE ACTIVE MATERIALS HAVE THE ALKYL GROUP ATTACHING IN A POSITION PARA TO THE PHENOLIC HYDROXYL.

Description

United States Patent O 3,766,254 LINEAR ALKYLPHENOL DISULFONATE PHOS- PHATE-FREE DETERGENT ACTIVES Samuel H. Sharman, Kensington, and Mitchell Danzik,

Pinole, Calif, assignors to Chevron Research Eompany, San Francisco, Calif. No Drawing. Filed May 5, 1970, Ser. No. 34,886 Int. Cl. C(l7c 143/42 U.S. Cl. 260-512. R 6 Claims ABSTRACT OF THE DISCLOSURE Heavy duty detergent active materials capable of heavy duty washing performance in the absence of phosphate builders are provided, the materials comprising ring polysulfonated alkylphenols in which the alkyl groups are linear of 1622 carbon atoms and not more than 25 mol percent of the active materials have the alkyl group attaching in a position para to the phenolic hydroxyl.

BACKGROUND OF THE INVENTION This invention is concerned with certain alkylphenol disulfonates which are effective as heavy duty detergent actives.

Increased concern over water pollution has produced significant changes in household detergents. Initially, major emphasis has been placed on producing biodegradable surface-active components for detergents. The shift to linear surface-active materials, including linear alkylbenzene sulfonate (LAS) and alpha-olefin sulfonates, etc., has reduced pollution attributed to nonbiodegradability.

However, the above-mentioned surface-active materials are inadequate in terms of soil removal in the absence of phosphate builders. Increasing evidence appears to indicate that phosphates contribute to the growth of algae in the nations streams and lakes. This algae growth poses a serious pollution threat to the maintenance of clear, good domestic water supplies.

Consequently, there has developed a need for detergent active materials which will function successfully in the absence of phosphate builders. Recently, certain non-phosphate building materials have been proposed as replacements for the phosphates. Thus, materials such as the polysodium salts of nitrilotriacetic acid, ethylene diamine tetraacetic acid, copolymers of ethylene and maleic acid, and similar polycarboxylic materials have been proposed as builders. These materials, however, when employed with conventional detergent actives such as LAS, have, for one reason or another, not provide to be quite as eifective as phosphates in detergent formulations. For example, some of the materials have proven to be insufiiciently biodegradable to meet present and anticipated requirements.

It is therefore desirable to provide compounds which are effective as detergent active materials in the absence of phosphate builders and are also sufficiently biodegradable that their use results in contributing neither foam producers nor phosphates to the water supply.

In addition, in the past, with heavy duty detergents, it has been thought that to achieve good soil removal it was necessary to maintain a high pH in washing solutions. This concept, which began with the strongly alkaline laundry soaps, has continued to the present day LAS- phosphate combinations which are in widespread use in heavy duty detergent formulations. One apparent reason for this is that the alkylbenzene sulfonate detergents are not effective in heavy duty detergent formulations in the absence of a builder. The phosphate builders, for example, must be employed at a pH greater than 9 to be eifec tive, and even the newer builders such as sodium nitriloice acetate have a pH of about 9 in solution. The advantages to be gained with heavy duty detergents which may be employed at neutral pH are many. Deleterious effects from skin contact are lessened. Enzyme-type soil looseners may be more easily combined in neutral solutions. Injury to fabrics is minimized. It is, therefore, desirable to provide detergent active materials which, in addition to the previously mentioned non polluting characteristics, achieve their maximum detergency at or near neutral pH.

The formulation of liquid heavy duty detergent compositions achieves man desirable results. They are easy to package and measure, and their use opens the possibility of automatic dispensing in washing machines. However, in the past it has been impracticable to formulate heavy duty detergents in liquid form because of the insufficient solubility of the inorganic ingredients (phosphate builders, etc.) required for heavy duty applications and the high cost of organic substitutes for such inorganic ingredients. It is therefore highly desirable to provide detergent active materials having good water solubility and which, because of their excellent detergency without builders, can be formulated into effective, reasonably priced heavy duty liquid detergent formulations.

DESCRIPTION OF THE PRIOR ART U.S. Pat. No. 2,249,757 discloses as surface active agents a broad class of sulfonated, branched and linear, alkylphenols. The proposed sulfonated alkylphenols include both mono and disulfonates. The patent claims compounds of a general formula including alkylphenol disulfonates having from 12 to 18 carbon atoms in the alkyl group. By way of example, the alkylphenols are prepared by reacting phenol and olefins of 14 to 15 carbon atoms obtained by caustic soda treatment of monochlorinated petroleum distillate. The olefin and phenol are reacted in the presence of Zinc chloride. Such alkylphenols have a high content of para alkylphenol isomers, usually about 35 to 40%. The alkylphenol is then sulfonated with sulfuric acid, oleum, or chlorosulfonic acid. The disclosures of this patent precede both the nonbiodegradability problem and the more recent phosphate Water pollution problem.

SUMMARY OF THE INVENTION It has now been found that effective heavy-duty detergent compositions may be formulated without the necessity of phosphate builders by employing as the detergent active materials polysulfonated alkylphenols of the formula:

in which R is linear alkyl of 16 to 22 carbon atoms, X is H or a water-soluble salt-forming cation, n is 1.5 to 2, and not more than 25 mol percent of the sulfonated alkylphenols have R attached on the aromatic nucleus in a position para to -OX.

It has been discovered that the materials which degrade the detergent performance of the compounds in these phosphate-free formulations are those compounds in which the alkyl group R is substituted para to the hydroxyl group, these compounds possessing minimal detergent activity. The explanation of this phenomenon is unclear.

Thus the effective materials are primarily either ortho or meta alkyl substituted. Preferably, the major portion of the alkyl groups will be substituted -ortho to the phenolic hydroxyl group on the ring. The meta alkyl materials are effective as phosphate-free detergents; however, the

difficulty and consequent expense of making the high meta alkyl materials limits their use at this time in commercial formulations.

The compounds of this invention do not require the presence of a builder to achieve good detergency, and while they are effective over a broad pH range, reach their maximum effectiveness at a pH near neutral in detergent solutions. Thus washing at a pH of 6.5 to 8.0, preferably 6.5 to 7.5, will give maximum soil removal while securing the previously mentioned advantages which inhere in the use of neutral washing solutions. Further, the compounds may be easily compounded into. effective liquid heavy duty formulations because of the substantial solubility of the compounds in water and because. of the lack of need for adjunctive inorganic additives such as builders.

DESCRIPTION OF PREFERRED EMBODIMENTS NH (CH CH OH) 2 or HN+ (CH CH OH) The sulfonation of the alkylphenols to produce the com-' pounds of this invention may be accomplished by any suitable method. Thus, materials which may be reacted with the alkylphenol include chlorosulfonic acid, oleum,

or sulfuric acid. It is only'important that enough sulfonating agent be employed to incorporate an average of at least 1.5, preferably 1.6 atoms of sulfur (in the form of tion with oleum is preferred.

The alkali metal cations are preferred, and sodium ions are particularly preferred.

The alkyl groups representedby R are, as previously noted, linear, although the presence of a random methyl radical upon the linear chain, for example, may not adversely affectthe performance of the compound. Alkyl radicals representative of R include hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, and heneicosyl groups are preferred.

The compounds of the invention are preferably prepared by sulfonation of a suitable alkylphenol.

The alkylphenols which are suitable as precursors for the compounds of this invention are prepared by methods which provide low para-content isomer products. Such methods include thermal alkylation of phenol with an alpha olefin, thermal alkylation of phenol with an internal monoolefin, and those catalytic methods which result in production of a high ortho-content alkylphenol. Examples of alkylation catalysts which have been employed to produce high ortho-content alkylphenols include various metal phenoxides, particularly those of aluminum and magnesium; hydrogen fluoride-treated aluminum silicate; alkyl sulfonic acids; dimethyl sulfate; benzene sulfonic acid; naphthalene sulfonic acid; transitional alumina; and gallium and indium oxides.

Employing any of these alkylation techniques, it is, as previously'noted, important that thealkylphenol mixture must not have a para alkylphenol content of more than 25 and preferably not more than 20 mol. percent. This may be achieved by the noted thermal or catalytic methods with the direct product of the process having no more than the prescribed content or it may be'achieved by conventional acid catalyzed alkylation followed by distillation or by separation of the components by various extractive techniques such as water solubilization, etc. This separation may be accomplished either with the alkylphenol mixtures or with the sulfonated products.

The alkyl groups represented by R are generally derived from either alcohols, olefins, or haloparafiins. The position of the attachment of the aromatic nucleus on the alkyl chain may be at any point. With alpha olefins the predominant point of attachment of the alkylation product will be either at the 1 or 2 and principally at the 2 position of the chain. On the other hand, with an isomerized mixture of olefins or olefins derived from haloparaffins which have, in turn, been produced by halogenation of parafiins, the position of the double'bond will be generally completely random on the chain, and thus the corresponding alkyl chain-nucleus attachment will be random.

The sulfonation is usually accomplished with a ratio of at least 2 and preferably from 4 to 10 mols of availtion is allowed to proceed, maintaining the temperature of the reaction mixture within the desired limits. The time required for disulfonation will be dependent upon the reaction temperature, the sulfonating agent, the ratio of sulfonating agent to alkylphenol, and the total quantity of reactants present. The reaction is usually effected at a temperature in the range of 0 to 150 C., preferably 25. to 100 C.

After sulfonation, the product may be neutralized with a Water-soluble, salt-forming cationic neutralizing agent, usually a metal oxide or hydroxide, and preferably an alkaline earth metal or alkali metal hydroxide. The alkali metal hydroxides are preferred, and most preferred is sodium hydroxide.

The neutralized product, which will contain a substantial quantity of water, and from 1 to 4 parts of a normally inorganic sulfate from the neutralization of excess S0 (e.g. Na SO4), may be used, as is, in combination with conventional detergent additives to formulate liquid heavy duty detergents. Alternatively, water may be removed in any quantity to complete dryness by conventional concontration techniques such as evaporation, distillation,

drum drying, etc., to yield a concentrated solution, a slurry, or a dry particulate solid which may then be blended to'form a heavy duty detergent.

The solid product isolated as described above may be desalted by the usual procedures as used in an alkylbenzene sulfonate art. In this method the solid material is mixed with about a 70/30 alcohol/water solution. The insoluble inorganic sulfate is removed by filtration, and the organic surfactant maybe used as; such .or isolated by evaporation of the solvent. The liquid concentrates and slurries may be treated in similar fashion with allowance made for the quantity of water already present.

I These desalting procedures give a detergent product that is essentially free of inorganic salt.

The following examples describe the preparation of the compounds of this invention.

Example 1. Preparation of ortho heptadecy-l phenol disulfonate acid was added to the alkylphenol over a period of 15 minutes. The sulfonater was then heated to 75 C. in an oil bath, and stirring was continued for a period of 25 minutes. The product was then neutralized to pH 7 with 2.5 N NaOH in an ice bath. Analysis by Hyamine titration and dilute acid hydrolysis indicated that the product was'approximately a 50/50 mixture of heptadecylphenol' disulfonate and sodium sulfate. The yield was 91% based upon alkylphenol.

See method of House & Darrnh, Anal. Cl1cm., 26, 1492 (1054).

Example 2.-Preparation of heneicocylphenol disulfonate Following the general procedure of Example 1, 25.74 g. of 21.5% fuming sulfuric acid was reacted with 19.2 g. of heneicosylphenol (prepared by an acid-clay catalyzed alkylation of phenol with a mixture of heneicosenes and having a 62/38 ortho/para isomer distribution). The product was analyzed as in Example 1 and showed a 91% yield of heneicosylphenol disulfonate.

Following the general procedure of Example 1 a variety of materials were prepared employing as precursors alkylphenols in which the alkyl groups were linear and had aromatic nucleus attachment at all positions on the alkyl group and with varying proportions of ortho and para alkyl isomers. Mixtures of these materials were also prepared.

Example 3.Preparation of a mixture of octadecyl-, nonadecyl-, and eicosylphenol disulfonates A mixture of about equal amounts of octadecenes, nonadecenes, and eicosenes was prepared by isomerization of the corresponding mixture of l-isomers. This mixture was employed to alkylate the phenol. The crude alkylphenol was distilled, and the fraction having a boiling range of 444 to 472 F. at 5 mm./Hg was taken as the product. Analysis of this product showed it to contain over 96% ortho alkyl isomers.

A 360 g. portion of the distilled alkylphenol mixture was charged to an 800 ml. sulfonater equipped with a thermometer, dropping funnel, reflux condenser, and mechanical stirrer. While the material was being strongly agitated, 514 g. of 21.5 fuming sulfuric acid was added through the dropping funnel over a period of 36 minutes while the temperature was maintained at from 5 to C. The temperature was then raised to 75 C. for 30 minutes. The reaction was then quenched by dropping the product onto ice, cooling it to a temperature of 0-5 C. The product was then neutralized with 490 ml. of 50% NaOH. The final volume was adjusted to 2700 ml. Analysis by the previously described method showed a 95 yield of alkylphenol disulfonate.

Example 4.--Drying of alkylphenol disulfonate A 500 ml. portion of the product of Example 3 was dried in a conventional small-scale drum drier in which the drums were operated under a pressure of 30 p.s.i. of steam. In this manner there was recovered about 150 g. of dry particulate solid which analyzed 52.5% of the mixture alkylphenol disulfonate, 44.0% sodium sulfate, with the balance being water.

The compounds of this invention are useful as heavy duty detergent actives. In the past, heavy duty detergent formulations useful for removing soil from textiles have comprised an organic surfactant (detergent) and an inorganic phosphate builder; the phosphate being present by weight, in an amount of from one to four times that of the detergent. The compounds of the present invention are excellent soil removers without the aid of any phosphate builder. That is, the compounds of this invention satisfy all need for both organic surfactant and builder in the final heavy duty detergent formulation. One way that this may be accomplished is by preparing a mixture of the disulfonate materials of the instant invention and an inert material, e.g. water, sodium sulfate, sodium carbonate, etc. Such mixtures may contain any amount of disulfonate in excess of about 10%, preferably or more. One useful composition comprises from 30 to 50% disulfonate and the remainder, sodium sulfate. Many other combinations make useful formulations and may be either liquid solutions or particulate solids.

-As heavy duty detergents, it is contemplated that the disulfonate compounds will be used in wash water at concentrations of about 0.01% to about 0.10%. This is within the same range of concentrations as are employed with the present day commercial detergents. In other words, the soil removal properties of the present compounds are essentially equivalent to the soil removal properties of an equal amount of the current commercial surfactant combined with at least an equal amount of phosphate.

Detergency of the compounds of the present invention is measured by their ability to remove natural sebum soil from cotton cloth. By this method, small swatches of cloth, soiled by rubbing over face and neck, are washed with test solutions of detergents in a miniature laboratory washer. The quantity of soil removed by this washing procedure is determined by measuring the refiectances of the new cloth, the soiled cloth, and the washed cloth, the results being expressed as percent soil removal. Because of variations in degree and type of soiling, in water and in cloth, and other unknown variables, the absolute value of percent soil removal is not an accurate measure of detergent effectiveness and cannot be used to compare various detergents. Therefore, the art has developed the method of using relative detergency ratings for comparing detergent effectiveness.

The relative detergency ratings are obtained by comparing and correlating the percent soil removal results from solutions containing the detergents being tested with the results from two defined standard solutions. The two standard solutions are selected to represent a detergent system exhibiting relatively high detersive characteristics and a system exhibiting relatively low detersive characteristics. The systems are assigned detergency ratings of 6.3 and 2.1, respectively.

By washing portions of each soiled cloth with the standardized solutions, as well as with two test solutions, the results can be accurately correlated. The two standard solutions are identical in formulation but are employed at different hardnesses.

(Control B) is prepared by dissolving the above formulation (1.0 g.) in one liter of 50 p.p.m. hard water (calculated as /3 calcium carbonate and /3 magnesium carbonate). The low detersive standard (Control A) contained the formulation (1.0 g.) dissolved in one liter of 180 ppm. water (same basis).

A miniature laboratory washer is so constructed that four different solutions can be used to wash different parts of the same swatch. This arrangement ensures that all four solutions are working on identical soil (natural facial soil). Relative detergency ratings (RDRs) are calculated from soil removals (SRs) according to the equation:

Percent SR ,.Percent SR A Percent SR c 3 PeI'OeDl'iSR n- A A further refinement in the determination of relative detergency ratings was developed. In this method, instead of employing two standard formulations, one of the formulations used in preparing the four test solutions had a known relative detergency rating (RDR) which had been determined by the above formula. Relative detergency ratings of the other three formulations were then determined by comparing the percent soil removal (SR) of these formulations with that of the known formulation.

Table I presents the detergency data on a group of representative alkylphenol disulfonates, all having at least ortho alkyl attachment. For comparison, the detergency rating is given for a linear alkylbenzene sulfonate (LAS) (having from 11 to 14 carbon atoms straight chain alkyl groups) both with and without a phosphate builder.

RDR=2.2+4.1

Each formulation tested of the test material (active) alongwith 1% carboxy- V methylcellulose, 7% sodium silicate, 8% Water, and. suf-- ficient sodium, sulfate to total 10.0%. v The LAS comparison formulations were prepared in the same way except comprised25 weight percent 'fonatehas little, if any, detergencyrl n mixtures: with the highly effective ortho-alkylphenol disulfonate, the para' that one formulation contained an additional 40% by a weight of sodium triphosphate and'in each formulation Effect of molecular weight on the detergency of alkylphenol disultonates Relative detergency rating (at 0.15% concentration) ing effect of the para isomer was also observed in .ter, but to a somewhat lesser degree.

The above tests show that the para-alkylphenol disulisomer compound depresses the soil removal properties to such an extent that a 70% ortho-30% para mixture is only about as good as linear alkylbenzene sulfonate with:

out phosphate (see Table I, test 1). This is unsatisfactory performance and is not acceptable for a heavy duty phosphate-free detergent. I a

Alkylphenol monosulfonates are known detergents and V constitute the main by-product occurring in the prepara-' tion of alkyphenol disulfonates. The amount of monosulfonate in the product is determined by analyzing for the average number of surface active groups incorporated (AG1) into the alkylphenol molecule. Table III presents the detergency of several mixtures of monoand di-sul- Test 50 ppm. 180 ppm. 7 .Compoundtested Water Water fonated alkylphenols prepared froma blend of approxi- Linear alkylbenzenc 5111mm ants) 3.2 1.4 20 matelyequalamountsof Octadecyh,mnadecyh'and ewes- LAS (20%) sodium triphosphite (40%)- 5. 7 3.7 ylph nols. Tctradecylphenol disulfonate 3.6 Hexadeoylphenol disultonate 5.9 4. 4 T B 111 5 Hcptadecylphenol disulfonat 5.7 4.7 6 Octadecylphenol d1su1f0nate 5,4 4,2 Effect of alkylphenol monosulfonate content on the detergency of 7 Eicosylphenol disulfonate 6. 3 4. 7 V alkylphenol lsulfonates 8 A blend of approximately equal 6. 0 4.3 2r

amounts of octadecyL, nonadecyl-, 0 Relative de e g and eicosylphenol disulionates. s lfonate content, rati g at('0,15% 9- A blend qfl approximately dequal 51 4.5 'Dercenli O Q' amountso iexa ecyl-,hcpta ecyl-, octadecyb, nonadecyland eicosyl- TBSt number I AGI Mono- D1- 50 ppm. 180 [LP-1T1. phenol disull'onates.

1. 87 13 87 5. 6 4. 1. 59 a 41 59 4.8 2. All'of the above compounds were prepared by dISUI-g'" 17 0;98--- 100 0 3.1 1.

' fonating' an alkylphenolin'which thearomatic nucleus is attached predominately to the number two carbon of the alkyl group (end chain attachment). Essentially the same detergency results are obtained fromalkylphenol disulfonates in which the aromatic nucleus is not attached predominately to any one carbon atom of the alkyl group, but is at all possible positions (random attachment). For

example, a blend of approximately equal amounts of octadecyl-, nonadecyl and eicosylphenol disulfonates having random attachment, gave relative detergency ratings of 5,6 and 4.2 in '50 p.p.m. and 180 p'.p .m. water,.respe'ctive- 1y compare with test 8 above).

'These examples show that the alkylphenol disulfonates having an alkyl group chain length in excess of 14 carbon atoms are extremely efficient detergents. The alkylphenol other 40%. These two blends werethen further combined to give a series of blends inwhich the'paraisomer content varied between these two values. Table II shows the detergency efiectiveness of these various blends. e

disulfonates of this invention remove soil as'eifectively TABLE II Effect of para isomer content on the detergency of alkylphenol.

. disulfonates Isorner distribution of the Relative detergency alkylphenol disulfonate test rating (at 0.15% compound 1 concentration),

180 ppm. Test number 7 Percent ortho 'Percent para water In addition to the above, essentially'100% para ojcta These data show that the mono sulfonated alkylphenol (Test; 17) is about equivalent to linear alkylbenzene sulfonate without phosphate in both hard and soft water (see Table I, test 1). For satisfactory phosphate-free detergent performance, it is necessary that the amount of mono sultfonated alkylphenol be less than i.e., the A61 must be greater than 1.5.

It will be understood that groups vary in their carbon chain length between 16 and 24. Thus, in most instances, a single molecular weight species will not be as practical commercially as the mixtures, and generally most'eifective compositions will comprise mixtures wherein at least 10 and preferably at least 15% by weight of at least two species of the sulfonated alkylphenols are present in which R is an alkyl radical of V ;l6, 17, 18, 19, 20, 21 or 22 carbon atoms.The preferred range of carbon atoms will be from about 17 to 21 and most preferably from about 18 to 20, carbon atoms.

The alkylphenoldisulfonates may be employed in combination withother detergent active materials. They, are, 1,.

particularly elfective with other dianionic materials, examples of which include linear alkyl and alkenyl disulfates and disulfonates. A particularly useful class 'of materials foruse in detergent active combinations is that of linear ally incorporated to'enhance the detergent properties. 7 I Suchmaterials mayinclude but are not limited to anticorrosion, antiredeposition, bleaching and sequestering agents, and certain organic and inorganic alkali. metal. and alkaline earth metal salts such as inorganic sulfates, carbonates or borates', Also nonphosphate builders may be included in the composition. Examples of these builders are the sodium salts of nitrilotriacetic acid, ethylene didecylphenol disulfonates were'synthesized and found to a have no soil removal properties. The detergency depressamine 'tetraacetic acid, and ethylene maleic acid copolymers, etc. Also small quantities of phosphate builders may soft wa- V the effective compositions of 7 this invention include those materials which comprise a mixture of the sulfonated alkylphenols in which the alkyl be included although, of course, they are not necessary for efiective detergency.

While the character of this invention has ben described in detail with numerous examples, this has been done by way of illustration only and without limitation of the invention. It will be apparent to those skilled in the art that modifications and variations of the illustrative examples may be made in the practice of the invention within the scope of the following claims.

We claim:

1. Detergent active polysulfonated alkylphenols produced by reacting a sulfonating agent selected from the group consisting of sulfuric acid, chlorosulfonic acid, and oleum with a mixture of monoalkylphenols in which the alkyl groups are substantially linear and of 1622 carbon atoms and wherein the ratio of the sulfonating agent to the alkylphenol is suflicient to provide at least two mols of available S per mol of alkylphenol, the reaction being carried out at a temperature of from 0 to 150 C. for a period of time sufiicient to incorporate an average of 1.5 to 2 sulfonic acid groups per molecule into the alkylphenol, said alkylphenols being characterized in that not more than 25 mol percent of the molecules have the alkyl group attached in a position para to the phenolic hydroxyl group.

2. The polysulfonated alkylphenol of claim 1 in which 10 the sulfonating agent is employed in an amount sufficient to provide from 4 to 10 mols of available S0 per mol of alkylphenol.

3. The polysulfonated alkylphenol of claim 1 in which the sulfonating agent is oleum.

4. Detergent active material prepared by neutralizing the product of claim 1 with an equivalent amount of a base selected from the group consisting of alkali metal or alkaline earth metal hydroxides or oxides.

5. The polysulfonated alkylphenol of claim 1 in which the al-kyl group contains from 17 to 21 carbon atoms.

6. The polysulfonated alkylphenol of claim 1 in which the product contains 1.6 to 2 sulfonic acid groups per molecule.

References Cited UNITED STATES PATENTS 2,205,948 6/1940 Flett 260-512 2,283,199 5/1942 Flett 260512 2,271,635 2/1942 Flett 260512 2,267,725 12/1941 Flett 260-512 DANIEL D. HORWITZ, Primary Examiner US. Cl. X.R.