The PROGRESS of ORGANIC SULFUR CHEMISTRY E. E. GILBERT* Yale University. New Haven, Connecticut
A general r m i m is presented of jundamendal dmelopments i n biological, medicind, and industfial organic sulfur chemistry for those who have completed one year of organic chemistry. Under "biological" are discussed the importance of sulfur i n proteins (in insulin, i n the process of denaturation, and i n producing elasticity), i n cell proliferation, and in vitamin Bx. Under "medicinal" are discussed the sulfonamides and the thiobarlvturates. Insecticides are included here.
I
NTRODUCTION of sulfur into the organic molecule has in the past led to compounds with specific properties extraordinarily useful to man. Most students of elementary organic chemistry are familiar with such widely known and striking instances as saccharine, mustard gas, the sulfonal group of hypnotics, and the antiseptic chloramine T. When such compounds are brought to mind, i t does not seem surprising that an element giving rise to such valuable products might yield others equally useful. The purpose of this review is to indicate, in general outline, some of the lesser known but perhaps equally interesting and useful compounds of sulfur, particularly in the light of biological and industrial developments within the past few years. No attempt a t complete coverage will be made; references to different fields will be cited in number sufficient to suggest that the organic chemistry of sulfur should be accorded the dignity of a separate category such as has already been attained, for instance, by the arsenicals. For a number of reasons the organic chemistry of sulfur has undergone a recent rebirth. Biological discoveries suggest that sulfur-containing compounds are essential to the development of evety living cell. Not only is sulfur present in the fleshy or protein portion of the body, but i t is an essential element of one of the vitamins. No form of life could exist without sulfur. An especially strong impetus to research on sulfur compounds has come from the petroleum refiners, who consider the large amounts of sulfur compounds present in their crudes to be undesirable impurities which must be removed to yield a salable product. The tons of highly reactive sulfur-containing com-
Under "industrial" are mentioned sulfur compounds in petroleum, sulfur dyes (thioindigaids, sulfonephthaleins, and sul&de type), detergents, syntans, sulfur plastics (Thiokol, polysulfones, thiourea types, and suljonamide types), and rubber accelerators. Formulas of the general types discussed are included. Emphasis is placed upon general properties due to presence of sulfur i n the molecule. Twenty-one references are cited to basic fiapers.
pounds so produced daily provide a tempting prospect for the industrial research chemist. A rapidly growing outlet for sulfur compounds of a type which may be produced easily and directly from these occurring in petroleum is found in the textile finishers and dyers, who are demanding increasing quantities of detergents and wetting agents which contain the sulfonic (-SOIH) grouping. From another quarter has come the discovery that sulfur compounds are useful drugs, and from still another that they yield useful plastics. In the following review the biological aspects will be taken up first; later the medicinal and more purely industrial aspects will be discussed. Before proceeding to the more specific results obtained from recent research, i t seems well to consider the properties of sulfur compounds as compared with their oxygen analogues. Nearly all organic textbooks point out that oxygen and sulfur form similar types of compounds. Parallels are indicated between the mercaptans and the alcohols, between the thioethers and the ethers, and between the thioacids and the oxygen acids. Such an analogy is exceedingly useful when comparing the structures of the simpler types of oxygen and sulfur compounds. However, sulfur differs from oxygen in that i t is capable of forming stable compounds in several higher valences, and it is upon this property that the usefulness of sulfur so largely depends. When we approach the realm of physical and physiological properties there seem to be few analogies. Almost none of the compounds considered here could be replaced by its oxygen analogue. A striking example is found in the contrast between dichlorodiethyl ether ((C1CH2CH2)z0)and its thio analogue. The former finds application in tremendous quantities as a solvent for refining in the petroleum industry, while the second * Present address: 808 Salem Avenue, Elizabeth, New Jersey. is the toxic and vesicant mustard gas. As researrh in 3:!3
the more applied branches of sulfur progresses, it becomes increasingly evident that oxygen and thio \ compounds should be classed separately. SULFUR IN BIOLOGY AND MEDICINE
Biologically sulfur is more commonly found in the form of an S S - or an S H group. Thioethers also occur widely. The researches of Dr. F. S. Hammett (I) over a period of years have led to the conclusion that the - S H or S S -group is essential in the important process of cell proliferation. When the concentration of the -SH group is increased artificially by exposing the living being to a compound containing this configuration, a marked increase in the velocity with which cells multiply is noted. Practical application has been made of this to accelerate the healing of wounds. Hammett feels that there may be some relationship between this function of sulfur and cancer, since the problem involved here is one of uncontrolled cell proliferation. He has carried out an extensive series of researches, the results of which strengthen his theory of the essential r81e of the S H and S S groups. However, his theory cannot as yet be considered established. It is interesting to note that the higher valences of sulfur (diphenyl sulfone (CeH&S02, was used) produce a retarding effect upon the velocity of cell proliferation. Many proteins contain small percentages of sulfur. When they are broken down by hydrolysis into their constituent amino acids, the sulfur is often found as NH*
1
of these proteins is their extraordinary elasticity. Silk is relatively non-elastic, and no sulfur is found in silk. The reason for this property is not yet known in full, but the results of recent X-ray studies suggest that the sulfur may in part explain it (3). 1nterGetation of the X-ray patterns shows that the protein molecules lie side by side like long chains; groups protruding from these chains connect them like the rungs of a ladder. I t may bethat when these connecting rungs are SSgroups, the property of elasticity is produced. Therefore i t seems possible that all muscular movements involve some change, as yet not completely characterized, in disnlfide linkages. Another important property of proteins is that of denaturation. This process has long baffled biochemists and i t has not yet been settled. In the case of wool it does seem clear that the process of denaturation, like that of stretching, involves a change in the -Slinking~( 4 ) . Their destruction by oxidation denatures the protein and destroys its elasticity. A common example of denaturation involving a change in sulfur bonds is found in a boiled (denatured) egg in which free hydrogen sulfide is always evident. One of the most interesting sulfur compounds to come to light recently is vitamin B1. Despite the involved structure of this essential substance, its nature has been fully elucidated, and now i t is being synthesized on a large commercial scale and placed on the market for general medical use. Complete physiological studies of this vitamin have not as yet been completed, but i t does seem certain that the presence of this N=C
- NHwHCI
CH.
cysteine (HSCH~~HCOOH), or as its oxidation prodNHI
I
uct cystine ((-SCHd2HCOOH)s).
Occurring less NHz I
I
widely are homocysteine (HSCHzCH&!HCOOH), and its S-methyl ether, methionine. Cysteine is an essential amino acid, and all cells contain a tripeptide called glutathione of which cysteine forms a part. Glutathione appears necessary for cell growth, and the cysteine portion of the molecule cannot successfully be replaced by any other amino acid. Insulin contains considerably more sulfur than most proteins. The exact structural nature of insulin still remains as problematical as that of other proteins, but this has not prevented its purification and profitable use in the treatment of diabetics. Recent researches (2) have shown that the activity of insulin is to a great extent dependent upon one or two 4% linkages in the large protein molecule. When these are reduced to -SH groups the activity of the insulin is decreased by one-half. An unsuccessful attempt was made to restore the activity of the insulin by oxidizing these S H groups back to -4%. The proteins, born, hair, wool, and muscle all contain sulfur as an essential ingredient. A common property
G-$H
C 'H-N'
I\cH+
I CH~OH
CI
interesting sulfur-containing compound is essential for the normal functioning of our nervous systems (5). Lack of vitamin B1 produces the disease known as beriberi. Medicinal Products.-Sulfur compounds have always stood high on the list of the physician's most useful tools largely because of the effectiveness of the sulfonds as hypnotics and the chlorsulfonamides as antiseptics. Tbe undoubted value of sulfur in therapeutics has in the past led to continual research on compounds containing it. 0ne.interesting fruit of this research was Intramine, which was claimed to be
effective in the treatment of syphilis (6). Intramine was evidently synthesized with the structure of salvarsan in mind.
It was not until recently that the true value of the thiobarbiturates was discovered. It was found (7) that in general those barbiturates which had desirable properties also worked well when the oxygen was replaced by sulfur. The thiobarbiturates are less stable than the barbiturates and are consequently broken down faster in the body, with the result that their action is quite brief compared with the oxygen compounds. Their action seems as intense during the period of shorter duration. This slight alteration of properties resulting from the replacement of oxygen by sulfur was deemed highly desirable from a medical standpoint, and upon announcement of this discovery there was an immediate flurry of research by a number of leading drug houses. Insecticides.-By placing sulfur in molecules of proved as effective as the more complicated dyes in different configurations from those active in healing, spite of its much simpler structure and complete lack i t is possible to produce compounds highly toxic to of dyeing properties. (The germicidal action of some compounds is thought to be linked with tinctorial certain fdrms of life. According to a recent survey (S), properties.) It is interesting to note that Prontylin the organic sulfur compounds are demanding increashad actually been synthesized as long ago as 1908 ing interest as insecticides. The insecticide molecule during an investigation to determine the effectiveness should possess a high degree of specificity, since it is of certain groups in making dyes cling to textile fibers. desired to poison the parasite without damaging the Not until twenty-seven years later were its remarkable host. Phenthiazine, germicidal properties discovered. Although it may still be too early to generalize upon the effectivenessof the sulfonamides as a class, enough data has already accumulated to suggest that they may be specific for many types of infection caused by streptococcus (small bacteria). A great many serious cheaply and directly made from diphenyl amine and diseases may be included under the category of strepto- sulfur, even shows promise of replacing lead arsenate coccus infections, among them childbed fever, septic for some insecticidal purposes. Many sulfur comangina, and erysipelas. If such does prove to be the pounds have been found to equal or to surpass nicotine case, the discovery of the therapeutic value of the in effectiveness; nicotine and lead arsenate have both sulfonamides may prove to be one of the far-reaching found steady use as standard insecticides over a long pharmacological discoveries. The success of Prontylin period of years. Among the types of sulfur compounds has led to a flood of patents on compounds containing which have been investigated are the thiocyanates sulfur with a view toward obtaining even more active (RSCN), and the mustard oils (RNCS). The thioand less toxic drugs. (Prontylin has recently been cyanates in particular are attracting industrial attention since they are easily and directly made from merfound to attack the white blood corpuscles.) captans found in petroleum by the following reaction: One of the most interesting recent advances is the ClCN + RSCN HCl discovery of the hypnotic action of the thiobarbiturates. RSH Ever since the barbiturates were first introduced into SULFUR IN INDUSTRY medical use (1903) a strong feeling has existed that the corresponding thiobarbiturates were lethal and comAn especially strong impetus in the development of pletely unsuited for medical use. This prejudice may organic sulfur chemistry has come from the petroleum have arisen from the brief statement by Fischer and refiners. The sulfur content of crude oils varies from Mering that a dog died as a result of a single injection. 0.2 per cent. to 5 per cent. (9). The sulfur is present That the thiobarbiturates should not have been more in many varying forms-as elementary sulfur, hydrogen thoroughly tested seems all the more strange when it sulfide, or carbon disulfide-or organically combined is considered that the corresponding thio compounds in the form of mercaptans and their derivatives such as are often prepared as intermediates in the synthesis thioethers and disulfides. Small amounts of more of the barbiturates. Thiourea is condensed with a complex organic sulfur compounds also occur in crude malonic ester by the usual reaction, and the resulting oils. It has been estimated (10) that one hundred thiobarbiturate is desulfurized to a barbiturate: fifty to two hundred tons per day of mercaptans alone could be obtained as a by-product of refining. The NH-CO NH-40 sulfur compounds of petroleum not only can be isolated S=C -they must be removed to render the product attracI I R I I R tive to the customer. I t does not seem strange that the NH-CO NH-CO Activity in medicinal sulfur research was never really intense until the report in 1935 by Dr. Domagk, the chemotherapist of the German Dye Trust, that certain dyes containing sulfonamide groupings proved effective against many types of streptococcus without damaging the host. A number of related sulfonamides were synthesized by Dr. Horlein of the Trust's synthetic department, and one compound called Prontylin
+
+
oil companies should encourage the pursuit of mercaptan research. If the rehers are anxious to dispose of an undesirable product, the textile manufacturers are equally anxious to purchase sulfur compounds of a different nature. Some of the best dyes are made with the help of sulfur, and sulfur-containing detergents and penetrating agents are employed in enormous quantities in many textile operations. It is interesting to note that the latter class may be produced from the type of sulfur compound which the refiners are a t present throwing away as undesirable. Dyes.-Although indigo has led the field continuously over a long period of years as the dyestuff used in largest tonnage, the less widely publicized sulfur black has maintained a consistently close second. In the year 1936, no less than 14,600,000 pounds of sulfur black were produced (11); yet the chemical.constitutiou of this valuable product is so complicated that it has never been elucidated. It is produced very cheaply by fusing sodium polysnlfide with dinitrochlorobenzene or related compounds. Exactly what occurs in this reaction is unknown, but by a complex series of oxidation-reductions and condensations, a compound containing both nitrogen and sulfur is finally obtained. The sulfur dye is dissolved in sodium sulfide solution in which the cloth to be dyed is then immersed. Upon exposure to the air oxidation occurs and the color is precipitated fast upon the fibers. In spite of their problematical structure i t has been possible to develop a uniform type of product, and for years the sulfur dyes as a class have seen wide use a t a cheap cost of manufachue. They offer a great variety of colors for the dyeing of cotton-yellow, green, tan, blue, orange, and black. This wide range of color seems quite remarkable; from analogy with other types of dyes it might be expected that the members of this same family of sulfur dyes might possess differing shades of the same color. Another class of sulfur dyes known for their unusual properties is the thioindigoids. They are of known and fairly simple constitution; they possess a sulfur group present in indigo and its instead of the -NHderivatives. The placing of substituents in the indigo
molecule has the effect in most instances of deepening the color already present in the parent molecule. However, the thioindigoids offer a case similar to that of the sulfur dyes of unknown constitution. Instead of deepening of shade a complete color change may be produced. For example, by merely altering the position of ethoxyl groups in the thioiudigo molecule the color may be shifted from bright orange to dark violet. The profound influence of the sulfur atom in producing color is shown by the interesting observation that similar mole-
cules containing oxygen instead of sulfur are not dyestuffs a t all. A third type of sulfur-containing dye is 6nding increasing use as indicators where accurate determination of pH is necessary. Although many of the older standard indicators are still completely satisfactory for many purposes, a great advance was made with the introduction of the sulfonephthaleins (12). The sulfonephthaleins are similar in structure to the familiar phenolphthalein~,except that a SO2 group is substituted for a CO group :
A number of hromo-, chloro-, and iodosulfonephthaleins are on the market as indicators. Detergents and Wetting Agents.-The only practical method of conferring the properties of a strong acid upon an organic molecule is by introduction of the S O s H or the -0SOaH group. (The -COOH group is by comparison weakly acidic.) The presence of the sulfonic group tends to produce easy solubility in water; the larger the organic group the less the solubility in water. By varying the organic portion of the sulfonic acid or sulfate, i t is therefore possible to produce any degree of solubility. It is easy to see why the sulfonic group is so often introduced into the molecules of dyes. Not only does it tend to render the large dyestnff molecule more soluble, but the addition of such a highly reactive point makes i t easy for the dye to cling to the textile fibers. The textile industry has for many years employed empirical methods of producing wetting agents, or substances which allow moisture to penetrate the fibers and cling to them. A standard wetting azent, known as ~ u r k Red e ~ Oil, is produced by treating castor oil (a triglyceride of a long-chain fatty acid) with strong sulfuric acid. Sulfonic groups were introduced into the castor oil molecule by this procedure. Considering the tons of Turkey Red Oil employed annually, it seems strange that no serious effort was made until fairly recently to elucidate the exact structure of the sulfonated oils (13). Another series of wetting agents has come as a byproduct of petroleum refmimg. During the process of refining it has been a common practice to treat the petroleum with strong sulfuric acid. By this process the hydrocarbon constituents to some extent were sulfonated, producing a mixture of sulfonic acids which, although unknown in composition, proved useful in the textile industry.
The manufacture of these compounds has always been empirical, and the need was felt for better and cheaper wetting agents of definite composition. At the same time the launderers and textile finisherswere demanding a cleaner (or detergent) superior to soap. Soap cannot be used in hard water, since the calcium and magnesium salts of the soap fatty acids are insoluble. Besides, soap is not as efficient a cleanser as might be desired. A study of the problem revealed that the only practical solution to both these problems lay in blocking the -COOH of the soap acid molecule a t the same time introducing an -OSOaH group. (The sodium salt was actually used.) A number of methods were employed to accomplish this. Perhaps the most interesting is the one involving reduction of the -COOH group of the fatty acids, made by saponifying cocoanut oil, to the corresponding -CH20H group. This alcohol was then reacted with strong sulfuric acid to give -CH2OSOsH, which as its sodium salt is the active constituent of "Dreft" and the shampoo, "Drene." The first step involving the reduction of the -COOH group caused the most difficulty; finally it was worked out by operating in the presence of a catalyst under high pressures of hydrogen. In this way alcohols were obtained using naturally occurring oils such as cocoanut, sperm, or tallow for starting materials. The alcohols used to make detergents and wetting agents usually contain from eight to nineteen carbon atoms. The higher members are good wetting agents but poor detergents, and the opposite is true of the lower members. Recent research (14) has shown that if the -OH group to which the sulfate is attached is placed toward the middle of the long hydrocarbon chain rather than a t the end (as in the previous case), wetting agents are produced which are far superior to any yet known. Apparently almost any type of colloidal or surface properties may be produced by varying the type of carbon compound employed. The calcium and magnesium salts of these alkyl sulfates are soluble a t laundering temperatures even in sea water; the sodium salts are much better cleansers than ordinary soap, and they do not injure the most delicate fabrics. Another series of sulfonic acids with pronounced colloidal properties are the so-called "syntans," which came into use in Germany and England as early as 1912 (15). They are made by condensing a phenol sulfonic acid (cresol and naphthol sulfonic acids are also used) with formaldehyde in the presence of an acid catalyst, or condensing agent. Derivatives of diphenylmethane are thus produced:
They are widely used in conjunction with natural tanning extracts, the advantage lying in a marked shorten-
ing of the tanning time. The syntans are employed with great success where a light shade is required. Resins and Plastics.-One of the most characteristic properties of sulfur in its low valences is high unsaturation. The formation of sulfonic acids is one aspect of the relieving of this unsaturation. A more unusual aspect is the formation of a resin. Even elementary sulfur, if heated slightly above 17Z°C., forms a highly viscous, resinous, orange-colored substance (16). Upon cooling or upon heating much above this temperature the resinous properties disappear. Although sulfur probably could not be used as a practical resin, it is interesting to note that it is formed by the same type of reaction as Bakelite and other common synthetic plastics. Even when sulfur possesses a valence of four it remains strongly unsaturated. This fact was beautifully illustrated by the observation that sulfur dioxide and olefins can react to yield polymers which are saturated, the sulfur rising to a valence of six in the process. For example, from propylene and sulfur dioxide i t was possible to produce a polysulfone with no carbon-carbon double bonds (17). These polymers dissolve in organic solvents; if the solution is poured on a surface and the solvent is allowed to evaporate, a tough transparent film is produced. Since the raw materials are cheap, i t seems possible that these polysulfones may find wide application. No review of sulfur plastics would be complete without mention of a new type of rubber substitute termed Thiokol. By reacting ethylene dichloride (or any other aliphatic dichloride) with sodium polysulfide, a tough rubbery mass is obtained which for many purposes is superior to natural rubber, especially for contact with petroleum products which dissolve natural rubber (18). The Thiokols are tetrasulfides of the type (-CH2CHe-S-S-). By varying the type of dihalide em-
II II
s
S ployed it has been found possible to produce compounds with different desirable properties. The Thiokol obtained from dichlor diethyl ether is remarkable in that it has the liveness, elasticity, and strength of ordinary rubber, and in that it may be vulcanized. When the two "side" sulfurs are removed leaving a disulfide linkage, all elastic and rubbery qualities are lost, but these may be replaced by heating the disulfide with sulfur to restore the tetrasulfide structure. It thus becomes possible to create and destroy elasticity a t will and with compounds of known structure merely by taking advantage of the polyvalence of sulfur. (See earlier remarks on the stretching of muscle.) A closer study of this interesting change may lead to a more fundamental understanding of the whole problem of elasticity. Thiokol is being produced on a large scale today. However, in common with many other sulfur compounds, i t possesses an objectionable odor, and only when this problem is overcome may Thiokol become a household article. The previously mentioned resins all owe their proper-
harden more quickly such will no longer be the case. Rubber Chemicals.-Almost one hundred years ago Goodyear discovered the process of vulcanization by heating rubber with sulfur. The mushroom growth of the rubber industry since then has been based on sulfur and sulfur compounds. It might, therefore, be expected that sulfur chemistry would have received a tremendous impetus in an attempt to find better sulfur compounds for the treatment of rubber. But such was not the case until the fairly recent period of organized research in the rubber laboratories. A salable product was produced by the empirical process, and for years no attempt was made to improve upon it. In the vulcanization of natural rubber with sulfur it was observed that this process occurred most easily and auicklv in the uresence of an "accelerator." The !%st resear& on ac&lerators was hit or miss, but now it is known that they function as catalysts in that they unite with free sulfur to form an unstable compound and then pass it on to the rubber molecule in a more reactive form, the accelerator molecule being regenerated and re-used (20). The whole process of vulcanization thus depends upon the inherent unsaturation of low-valent sulfur. Organic compounds containing large percentages of sulfur have always proved the most efficient accelerators, and every year sees the preparation of an increasing number of possible useful products. One substance, called mercaptobenzothiazole, has been found particularly useful as an accelerator.
ties to the polyvalence of sulfur. In a type known as the sulfonamide class such is apparently not the case. In the manufacture of saccharine large amounts of fitoluenesulfonyl chloride
are inevitably obtained as an undesirable by-product together with the ortho compound
desired for making the sweetening agent. As is usually the case in industry, an attempt was made to find a use for the large amounts of unused para product. It was found that by reacting the para sulfonamide (obtained by reacting the sulfonyl chloride with ammonia) with formaldehyde, a synthetic resin was obtained with two properties highly desirable in a resin-solubility and fusibility. Further research with different kinds of sulfonamides was then undertaken (19) in an attempt to find other types which might yield useful resins with formaldehyde. As a result of this investigation, it is now possible to obtain sulfonamide resins of almost any degree of hardness and adapted to a wide variety of uses. Resins obtained by condensing urea with formaldehyde have attained wide usage. Many everyday objects are made from this plastic--radio cabinets, clocks, buttons, dishes, and so forth. Even prior to the discovery of urea plastics it was found possible to obtain a resin from formaldehyde and thiourea. Resins of useful properties could be so obtained, but their adoption has proved slow in the face of the cheaper and equally satisfactory urea plastics. Perhaps when a method is discovered to make the thiourea-formaldehyde resins
..
During 1936 four million dollars worth of this compound was sold to rubber manufacturers in this country (11). Other types of compounds used as accelerators are: dithiocarbamates (RNHCSSR'), dithio acids (RCSSH). and trithiocarbonates (R2CSa) (21). Some of these compounds are so active that they produce rapid vulcanization even a t room temperature.
LITERATURE CITED
HAXXETT,F. S., "Chromosome and aster dimensions of dividing cells in regenerating tissues of clymenella torqnata exposed t o sulfhydryl and sulfoxide," Profoplalasma, 22, 1 7 3 4 (Oct., 1934). W m m , A. AND K. G. STERN."Studies on the constitution of insulin. 11. Further experiments on reduced insulin preparations," J.B i d . C h m . . 119,215-22 (June, 1937). Asrsrmu. W. T. AND R. L o m x . "An X-rav studv of the hvdration and denaturation of rotei ins."^^. him. Soc... 137, 851 (1935). J. B., "Reactivity of the sulfur linkages in SPEAKMAN, wool," Nature, 132,930 (Dec. 16. 1933). Wrmrms. R. R.. "The beriberi vitamin." Ind. E m . Chem.. MA< P., "The-chemistry of synthetic drugs," Longmans, Green & Co., London, 1931, p. 237. "Sulfur-containing TABERN,D. L. AND E. H. VOLWILER, barbiturate hypnotics," I. Am. Chen. Soc., 57, 1961-3 m,+ ,".L.,
,a**\ A""w,.
WEST,C. J., editor, "Annual survey of American chemistry," Reinhold Publishing Corp., New York City, Vol. X, 1935, p. 263.
.
(9) ELLIS, C.. "Prospects of a petroleum chemical industry," Ind. Eng. Chem., 26,833 (Aug., 1934). (10) MALISOW,W. M., E. M. MARKS,AND F. G. HESS, "A study of mercaptan chemistry," Chem. ReYims, 7,493-547 (Dec., 1930). (11) United States Tariff Commission Reports: "Production and sales of coal-tar crudes and of dyes and other synthetic organic chemicals," Washington, D. C.. 1936. (12) . . COHEN,B., "Synthesis and indicator properties of some new sulfonephthaleins," Pub. Health Repts., 41, 3051-74 (1926); through Chem. Abstr.. 21, 1111 (1927). (13) HART, R., "Fractionation and composition of sulfonated oils," Ind. Eng. Chem., Anal. Ed., 9, 177-81 (Apr., 1937). W ~ K E SB., F. AND J. N. WICKERT,"Synthetic aliphatic ' penetrants," ibid.. 29,1234-9 (Nov., 1937). (15) United States Tariff Commission Reports, Second Series, Washington, D. C., 1930! p. 50. (16) MEYER, K. H., "Inorganic substances with rubber-like properties," Trans. Feraday Soc., 32,149 (Jan., 1936). C. S. AND M. HUNT,"The reaction between sul(17) MARVEL. fur dioxide and olefins. 11. Propylene," I. Am. Chem. Soc.. 57, 1691-6 (Sept.. 1935).
(18) Parnrc~.J. C., "The formation of high polymers by condensation between metallic polysulfides and dihalogenated hydrocarbons and ethers," Trans. F a r o d q Soc., 32, 347-57 (Jan., 1936). (19) WALTER, G., "Conditions under which insoluble and infusible resins are produced, especially those formed by
aryl-sulfonamide and formaldehyde," iGd., 32, 402-12 (Jan,, 1936). LEwrs, W.K's L' SQmEss AND R. D. NmmG, "Mechamsmof rubber vulcanization withsulfur,"Ind. Eng. Chem., 29, 113&44 (Oct., 1937). (21) m e u , w. F., " ~ ~ ~ ~ ~ ~can. i ~~h~.t Met., 21, 179 (May, 1937).
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