Sept. 20, 1960
,IUD
DISSOCIATION CONSTAKTS
1-Cyclopropylethyl S-Methyl Xanthate.--& general procedure for xanthate preparation" was employed. From 16.2 g. (0.495 mole) of 1-cyclopropylethanol, n Z 5 D 1.4292, there was obtained 1-cyclopropylethyl S-methyl xanthate boiling a t 70' (0.2 mm.), 45.7 g., 52.3%, n 2 5 ~1.5454, dZ54 1.0878, C-H absorptions a t 3005 and 3082 cm.-I, additional absorptions a t 1225 and 1050(s) cm.-'. Ami. Calcd. for C7H120S?: C, 47.69; H, 6.86. Found: C , 47.84; H, 7.02. Pyrolysis of 1-Cyclopropylethyl S-Methyl Xanthate.1-Cyclopropylethyl S-methyl xanthate was pyrolyzed1u*12 as previously described for 1-cyclopropylethyl acetate. From 21 g. (0.119 mole) of 1-cyclopropplethyl S-methyl xanthate, 1.5454, and a t 200-245', 3.7 g., 46Yc, of material boiling a t 25-40' (755 mm.) was obtained. The latter material was washed with 50 ml. of cold 5yc aqueous sodiuni bicarbonate, dried over calcium hydride and distilled from sodium metal to yield 1.1 g. of a 3-component olefin mixture. Alternatively, 1-cyclopropylethyl S-methyl xanthate (116.8 g., 0.66 mole) was boiled in a small distillation assembly. Ebullition commenced a t a pot temperature of 130" and the temperature slowly rose to a steady 230' value a t which it was maintained for an additional 2 hr. The distillate was treated as above to yield 20 g., 44.5Tc, of :HI olefin mixture consisting of vinylcyclopropane, 95%, 1,4-pentadiene, trace amount, and an unidentified olefin, trace amount. Rectification through a 90 theoretical plate concentric tube column yielded vinylcyclopropane boiling a t 40.E40.8' (755 mm.), n Z 61.4104, ~ dZ3*0.7157, C-H absorptions a t 3005, 3019, 3083, 1645(s), 1020(s), and 905(s) em.-' [lit.' b.p. 40.19" (760 mm.), ~ * O D 1.4138, Po,0.72105, 547, from 1-cyclopropylethanol by dehydration over alumina]. Anal. Calcd. for C 6 H ~ C, : 88.16; H , 11.84; XD,23.34. Found: C , 88.03; H , 12.02; r l l ~ , 2 3 . 6 0 . 1-Cyclopropylethyl Methyl Dithio1carbonate.-The pot residue, S-methyl xanthate, above, was a two-component mixture as evidenced by G.P.C. Pyrolysis a t 360' failed to cleave this material. Distillation of 61.8 g. of this material through a 7" Vigreux column followed by rectification through a 14" packed column yielded a yellow oil hoiling a t 236-237' (759 mm.), 25.2 g., n Z 51.5358, ~ dZ54 1.0908, which was pure in G.P.C. i\bsorptions a t 3002 and 3082 ern.-' indicated that the cyclopropyl group had remained intact, and additional absorptions a t 1645(s) and 868(s) cm. were noted for I-cyclopropylethyl methyl dithiolcarbonate.
OF
Anal. Calcd. for C;HI~OS2: C , 17.69;H, 6.86; Found: C , 47.54; H, 7.00; S , 36.20.
4899
S,36.37.
1-Cyclopropylethanethio1.-1-Cyclopropylethql methyl dithiolcarbonate (14 g., 0.079 mole), n Z 51.5334, ~ was saponified essentially according to the procedure of Shriner, et el.30 The mixture was acidified with acetic acid since mineral acids could open the cyclopropyl group. The aqueous phase was estracted with ether and the organic phase, after washing with 5yo aqueous sodium bicarbonate and drJ-ing, was distilled to yield 1-cyclopropylethanethiol boiling a t llb115.5' (758 mm.), 2 . 5 g., 31Yc, n 2 j ~1.4626, d 2 j l 0.8836, C-H absorptions a t 3001 and 3079 cm.-'. Anal. Calcd. for CjHluS: C, 58.76; H, 9.86; S,31.37; d / ~ ,31.50. Found: c, 58.83; H , 9.50; s, 31.78; 110, 31.83. 1-Cqclopropplethanethid was treated with 2,4-dinitrtifluorobenzene essentially according to the procedurc of Bnst, et nl.,26 and an orange-yellolv crystalline sulfide inelting a t 74.5-75' was obtained.
Acknowledgment.-The assistance given hy hliss 31. Caldera, Blr. S. Abramowitz and Dr. R . Bauman in obtaining and interpreting infrared data was deeply appreciated. This research was supported by the United States Air Force under Contract No. AF 33(616)-5253, monitored by the llaterials Laboratory, n'right Air Development Center, Wright-Patterson Air Force Base, Ohio. Summary.-( 1) 1-Cyclopropylethyl acetate was prepared and pyrolysis of this material yielded cyclopentene and smaller amounts of vinylcyclopropane and 1,4-pentadiene. (2) 1-Cyclopropylethano1 yielded vinylcyclopropane, 2-methyltetrahydrofuran and small amouuts of both 1,4-pentadiene and cyclopentene when subjected to sulfuric acidcatalyzed dehydration. (3) 1-Cyclopropylethyl S-methyl xanthate was prepared and pyrolysis of this material yielded vinylcyclopropane and I cyclopropylethyl methyl dithiolcarbonate. (30) R. T,. Shriner, R . C. Fusun and 1 ) . Y . C u r t i n , " T h e Systematic Identification of Organic Compounds." John Wiley and Sons. Inc., K e w Y o r k , N. Y . ,F o u r t h Ed., 19.56, p. 2;jI).
[COVTRIBUTION FROM THE SCHOOL O F CHEMISTRY OF THE UNIVERSITY O F
BY ~ ~
LIERCAPTANS
MINNESOTA, M I V N E A P O L I 5 14, hII\h ]
Inductive Effects on the Acid Dissociation Constants of Mercaptans' U R I C11. E KREEVOY, EDWINT.HARPER,RICHARD E. DUVALL, HERBERT s. I ~ I L G U 111, S AND , LEROYT. DITSCH
RECEIVED M A R C H 24, 1960 The acid dissociation constants of a number of mercaptans have been measured by a varietv of methods. These constants, along with some taken from the literature, have been correlated with the Taft u*-parameters. The correlation holrls for eleven mercaptans hut fails for thiophenol and hydrogen sulfide. The former is attributed tn a resonance effert, ~ I I C latter t o a steric effect on solvation.
A knowledge of the acid dissociation constants of sitiiplt mercaptans is fundamental to an under-
standing of the chemistry of these compounds for two reasons. First, many important reactions of mercaptans may proceed through the mercaptide ions, and secondly the acid dissociation constants can give important information about the ( 1 ) This research was supported, i n p a r t , b y t h e U. S . Army hledicrll Research a n d Development C o m m a n d through contract DA-4W
193-MD-2027 and i n p a r t b y t h e hTational Science Fnundation through u n n t KO. N . S . F . - ( > S R t . Reproductinn i n whole or i n part is perm i t t e d fcvr nny p i i r p < ~ w o i t h e IJnited States Gnvernmenl.
distribution of electrotis it1 iiiercal)taiis.' 111 spitc. of this, there semi to be only a small iiumher OF such constants available,'-'" and most of these arc. ( 2 ) M. Calvin in S. Colowick, rt ul., "Glutathi-.I
-d.,.
i lr acid solution. n'ave lengths for dissociatiiiti ciinstant determinations were chosen so as to approximately niaximizc the ratio of the extinction coefficients of the ion and the neutral molecule. I n all determinations measurements were inade a t a t least two wave lengths. At the wave lengths used the mercaptide extinction coefficient was about ten times t h a t for the neutral mercaptan. In all the basic solutions there was a noticeable change in optical density on standing, due t o the air oxidation of the mercaptan, so ciptical densities were measured as rapidly as possible after the solutions were niade up. In determining the acid dissociation constants, basic buffers were needed. These were made up t o approximately the rcquired pH using the components recommended by Bates.31 The pH of these solutions was determined potentior r ~ e t r i c a l l y ,using ~ ~ a hydrogen electrode and a k e d s and S m t h r u p student potentiometer, before the addition of the mercaptan. Gas Solubility Measurements.--Gas solubility nieasurements were made in a straightforward manner using the Lipparatus shown in Fig. 2 . T h e mercaptan was placed in flask -1,the water or aqueous buffer was placed in flask D, :ind hoth were cooled with Dry Ice-acetone. The whole s\-steni was then pumped down t o a pressure of -13.1 nun.. : t i read on the hIcLeod gauge, E. The system showed no leakage a t this pressure over a period of several days. Thc :iqurous solution was then permitted to warm up til 2.i" ;tiid the vapor pressure over i t was read on the manometer, C . U'.ater vapor was also admitted t o the reservoir, R . I Liquid and vapor temperatures were controlled by keeping thc whole apparatus in a large, electrically heated, icccooled air thermostat ,) Mercaptan vapor then was admitted t o the reservoir, B, and its vapor pressure measured. The mercaptan vapcr now was admitted t o D, which was stirred magnetically, and its solubility in the aqueous solution was determined from the drop in pressure and the known volumes of the various parts of the system. The preparation and standardization of the buffer siilutions is described under spectrophotometric determinations. Material~.~~-Thiophennlwas Mathieson, reagent grade, arid T V ~ Sredistilled before use (b.p. 55-56" (10 m r n . ) ) . Ethyl inercaptoacetate was Eastman Kodak Co., practical grade, and was redistilled (b.p. 68-69" (32 m m . ) ) . Mercaptoacetone was prepared by the method of Hromatka 2-Ethoxyethanethiol was aiid Engel35 (1n.p. 95-100'). prepared by thc method of Swallen and B ~ o r (b.1). d ~ ~1'77'). 2-Mercaptoethanol was nbtained from Union Carbidc Chemicals Co. arid redistilled under water-pump vacuum. I t had ~ z 1.4975. ~ ~ D Bennett3' reports n s o1.4996. ~ Monothioglycerol was obtained from Evans Chemetics Inc. a s :I 46(7 solution in water and was used without further purification. Benzyl mercaptan was a gift from Evans Chernctics Inc. It had an assay of 95.5% and was used without further purification. Allyl mercaptan was obtained from Xldrich Chemical Co. and ethanethiol from Eastm Kodak Co. Both were of the best grade supplied by t h firms and were used without purification, except that th were distilled into the gas solubility apparatus.
Acknowledgment.-The authors are grateful to the U. S. Army Medical Research and Development Command and to the National Science Foundation for support of this work and to Evans Chemetics, Inc., for the gift of chemicals. (33) Reference 16, p. 238. (34) All holling points are uncurrected; xll melting points arc cor rrcterl (3.i) C). Hrotnatka and I . ICngeI, dfoirrilch., 78, 3 2 ( l ! l l X ) (36) I, C Swallen and E. u ~ ~ n r'rEiis d, J C ~ U R S A I , ,62, fi,;: ( i ! i . i o ) . (87) G.hf. Bennett, J . Cizcin. S M 213!l ( l ' j 2 2 )
