The marked influence of the position of a substituent in determining the therapeutic properties of quinoline derivatives gives significance to all information on the reactivity of quinoline isomers. The differing an timalarial specificity of plasmochin and SN 7618l and the absence of antimalarial action in the position isomers of hydrocinchonine2 are facts awaiting explanation.The present study expands the general knowledge of quinolyl derivatives possessing simple functional groups; it also presents certain properties of the mercapto-quinolines which might make a more extensive series of 6and 7-substituted quinolylniercaptans of iralue in considering energy relationships of isOmeric structures. The preparation of the mercaptans and symmetrical sulfides is based on the reaction of halides with thiourea to. form isothiouronium salts and subsequently mercaptans. NH2CSNH2 ."Rosenhauer and' associates4 synthesized quinolyl-, lepidyl-and quinaldyl-mercaptans by the interaction of thiourea with chloroquinolines. However, they encountered varying amounts of diquinolyl sulfides in replacing the chlorine of 4chloroquinolines. Surrey and Lindwall,5 also, found that certain reaction conditions favor the formation of his-(A-1iitro-2-pyridyl) monosulfide.In the experience of this Laboratory, 2-chloro-7methylquinoline and 2,7-dichloro-4-methylquinoline were converted to the corresponding isothiouronium salts, and subsequently to mercaptans, in good yield. In the titration of the three iso--thiouronium salts, which we were able to separate and identify analytically, it was observed that the aqueous solution was faintly alkaline to litmus, or became alkaline with a very small portion of 0.1 N sodium hydroxide; as was expected, titration to an end-point with phenolphthalein required the calculated amount of 0.1 fi sodium hydroxide.The 2-mercaptans were yellow, crystalline products of low solubility in alcohol, aqueousalcoholic alkali, and chloroform; complete oxiclation to the disulfides was rather slow. Symmetrical 2,2'-quinolyl sulfides were obtained only by ( 1 ) T h e Board for Co-ordination of Malarial Studies, Science, 105, 8 19413). S S = s u r r e y number, a n identifying number for ccrmpounds which will appear in a forthcoming monograph entitled, "A . direct synthesis. In contrast, 4,4'-quinolyl sulfides were invariably encountered among the reaction products from treatment of 4-chloroquinolines with thiourea.With the use of thiourea to introduce the sulfur linkage in the 4-position, only one pure isothiouronium salt was isolated : 7-methyl-4-quinoly1isothiouronium chloride was obtained in a 45% yield. However, even in this case the hydrochloride of bis-(7-methyl-4-quinolyl) sulfide also was obtained. In two other examples, analyses indicated that the crystalline reaction product was mainly the hydrochloride of bis-( i-chloro-2methyl-4-quinolyl) sulfide and of bis-(6-methoxy-2-methyl-4-quinolyl) sulfide, respectively. During titration the hydrochlorides of the sulfides remained acid to litmus until nearly all the cal...