MERCAPTANS IN COSMETICS* By EVE•tETT G. McDo•oucH, PH.D. l/ice-President, Evans Chemetics, Inc., Nbw York, N.Y. AT mRST glance the title of this paper strikes one as a paradox, because the word cosmetics connotes a pleasant-smelling preparation, while the unpleasant odor of mer- captans is proverbial. In fact, they have been described by such terms as evil, provoking, ferocious, revolting, unbearable, and nauseating. The odor of mercaptans is most persistent even in extreme dilution. Emil Fischer(I) commented on the fact that ethyl mercaptan can be de- tected by smell in amounts as small as 2 X 10 -•2 of one gram. Note that this is less than 1/200 of the smallest amount of sodium that can be detected with the spectroscope. The revolting odor of the defensive secretion of the skunk is due to butyl mercaptan(2). Them•lodorof•eces (3) and urine (4) after asparagus has been eaten is at least in part due to the presence of methyl mercaptan. Meaning literally seizing mer- cury-the name mercaptan is derived from the Latin mercurium captans, and it originated in the fact that mercaptans react very readily with mercuric oxide to form crystalline compounds. Although the first synthesis of a mercaptan was re- * Presented at the December 6, 1946, Meeting, New York City. ported as early as 1834 by Zeise(5), the mercaptans as a group of com- pounds have been so little explored that no standard nomenclature has been adopted for them. There are 'at least five systems of nomenclature for mercaptan compounds and the need for systematizing the nomen- clature was the subject of a recent article(6). Undoubtedly mercaptans have been used in the synthesis of many other compounds, but these uses have never been publicized. In general their presence is not desired. In the petroleum industry alone, millions of dollars have been spent on research for methods of removing' mercaptans from petroleum. Dur- ing the first world war, n-butyl mer- captan was under consideration as a camouflage gas and a small plant did produce some. The second world war brought forth two uses ß lauryl mercaptan as a modifier in the manufacture of Buna S synthetic rubber and dithiog/ycero/ as an antidote or protective agent against Lewisite gas. The name "Bal" for British Anti-Lewisite is commonly applied to this latter compound since it was developed by the British. This compound is finding peace-time use as an antidote for 27

28 JOURNAl. OF THE SOCIETY OF COSMETIC CHEMISTS arsenic and mercury poisoning. It has always appealed to me that the cosmetic industry has been the first user of many materials. Here again, 'the cosmetic industry can truthfully boast that it was first to commercialize for peace-time use a material from a new group of com- pounds-the mercaptans. Of the two discoveries which have led to the use of mercaptans in cos- metics, one has revived a dying market the other has revived a field which had already been pro- nounced dead, and this mercaptan cosmetic has grown to be the single biggest income-producer in our entire industry. The former refer- ence is to the cosmetic product, the cream depilatory the latter, to a product, the cold waving lotion, and the new methods of cold waving growing from it. MERCAPTANS IN DEPILATORIES Cosmetic depilatories containing sulfides have been known and used for centuries. The •trabian Nights and many other ancient records mention them, yet the same prob- lems which were so picturesquely described by Koeune(7) in 1937 have existed unsolved for centuries. In Koeune's own words The use of sulphides in depila- tories brings in its t3ain a number of vexed problems which have, and probably can be, only par- tially solved. For example, we have, first and forel•ost, the problem of minimising and dis- guising the distinctly insalubrious odour. Then, of scarcely less im- portance, we have to consider the serious caustic action ()n the skin. And in case by some mysterious alchemy we should dissipate the smell of the sulphide, a malign fate draws across the track some very red herrings in the form of drying out of the depilatory in the tube, deterioraticm of the active ingredients, discoloration of.the paste, while the good perfume which one has reluctantly sacri- ficed to the God of Sulphide turns in its grave and rises up in horrible forms which stink of the very pit itself. Like so many problems crying for solution, "the mysterious alchemy" called for by Koeune was forthcom- ing independently and almost at the same time from two research groups. In Holland a Dutchman, Karel Bohemen, found that thi,•)glycolic acid and other mercapto-carboxylic acids could be used in certain alka- line media. His discovery resulted in the issuance of patents in cer- tain foreign countries to him o• his agent--Fletcher. In America, Evans and McDonough discovered that mercaptans could be used in cosmeti.c cream depilatories, and after a priority contest with Bohe- men, a U.S. Patent was issued only to them. In foreign countries be- cause the conflict with Bohemen patents was governed by different laws, the patents issued to Evans and McDonough cover the use of mercaptans other than mercapto- carboxylic acid in depilatories. Briefly summarized, Evans and McDonough found that: 1. All merdaptans in an alka- line solution, preferably at a pH greater than 9.0 and less than 12.5