262 O’BRIEN
The Journal of Organic Chemistry
The Kinetics of the Reaction of 1-Phenyl-lH-tetrazole-5-thiolSodium Salt with Substituted 1,4-Naphthoquinone 2,3-Epoxides D. F. O’BRIEN Research Laboratories, Eastman Kodak Company, Rochesler, New York 14660
Received June 6, 1967 The kinetics of the reaction of 1-phenyl-1H-tetrazole-5-thiolsodium salt with ZJ3-epoxides of Diels-Alder adducts of 1,4benzoquinone were examined. The reaction was followed by determining the amount of unreacted mercaptide. Potentiometric titration with silver nitrate was utilized to analyze for mercaptan. The buffered reaction is first order in epoxide and first order in mercaptan. The reaction rates and activation parameters are discussed.
The reactions of 2,&epoxides of 1,4-benzoquinone cyclopentadiene Diels-Alder adducts (1) with 1phenyl-5-mercaptotetraxole (HPMT) give 2-thioether enediones (2). When vigorous conditions are employed, the products are the isomeric Zthioether hydroquinones (3). (See eq 1.) The configurations of the starting epoxide 1 and the enedione 2 are as shown.2 The reaction proceeds smoothly in ethanol
4
5
Experimental Section 4- HS-C,
P-7 N-N
-
I
C8HS R 1
0V
P 2
R
M
T
OH R 3
and somewhat slower in benzene.’ The use of equimolar amounts of base accelerates the reaction and yields only 3.‘ The reaction of la with the triethylamine salt of HPMT in ethanol gave a 94% yield of 3a.l There are few studies of reactions of mercaptans with epoxides of conjugated 1,4 ketones.’ No quantitative data are available. The kinetics of the reaction were examined to assist in understanding the mechanism and the effect of the carbonyls on the ring-opening reaction. For the study, seven epoxides, la-e, 4, and 5, were examined. Epoxide 4 was obtained from l a by catalytic hydrogenation.2 The ex0 adduct 5 resulted from the thermal isomerization of la.’ (1) H. 9. Wilgus, 111, E. Frauenglass, P. P. Chieaa, G. H. Nawn. F. J . Evans, and J. W. Gates, Jr., Can. J . Chem., 44, 603 (1966). (2) D. F. O’Brien and J. W. Gates, Jr., J. O w . Chem., 80, 2593
(1965).
Epoxides.-The epoxides utilized in this study were prepared by the method reported previously.* I-Phenyl-1H-tetrazole-5-thiol Sodium Salt (NaPMT).-The mercaptide, Eastman Grade, was oven dried to a constant weight and stored in a desiccator. A solution of the mercaptide in 90% ethanol (theoretical, 0.0215 N ; found, 0.0212 N (standardized by iodine titration)) was stable for several months. Buffer Solution.LLutidine, Eastman Grade, and lutidinium perchlorate, mp 110-111’, were dissolved in 90% ethanol t o give a solution of 0.204 and 0.205 N , respectively. Silver Nitrate Solution.-A standardized solution of silver nitrate in water (0.100s =k 0.0002 N ) was diluted to give 0.01002 N silver nitrate. Basic Conversion of 5,8-Methano-l-( 1‘-phenyl-S’-tetrazolylthio)-4a,5,8,8a-tetrahydro-l,4-naphthoquinone (Pa) into 5,s Methano-1-( 1’-phenyl-5’-tetrazolylthio)-5,&dihydro-l ,I-naphthohydroquinone (3a).-A solution of 2a (3.50 g, 0.01 mole) and 30 ml of ethanol was warmed to reflux, triethylamine (1.0 g, 0.01 mole) was added, and the mixture refluxed for 15 min. The initial yellow color changed t o dark red-brown. After reflux, charcoal was added, and the mixture was warmed and then filtered into 300 mi of ice and water, which was acidified with 5 ml of acetic acid. The precipitate was collected, dried, and crystallized from acetic acid-water to give 1.7 g of 3a, 48% yield. Similar results were obtained with 2,6-lutidine as the base. Reaction of Cyclohexene Oxide with NaPMT.-A solution of NaPMT (10.0 g, 0.080 mole, 0.23 N ) in 220 ml of ethanol was outgassed with nitrogen. The solution was treated with cyclohexene oxide (5.0g, 0.053 mole, 0.24 N). The mixture was stirred at room temperature under nitrogen for 17 hr. The white precipitate was collected and dried. Concentration of the filtrate t o 100 ml gave more of the same solid. The white solid was acidified in solution, reisolated, and crystallized from ethanol to give 3.35 g (45% yield) with mp 187-188.5’. The infrared spectrum w8s the same as that of 1-phenyl-5-hydroxytetrazole.Treatment of the alcohol with base gave the original white solid. Further concentration of filtrate gave a crude product, whose infrared spectrum showed hydroxyl absorption, and its odor indicated it was a mercaptan, possibly 2-mercaptocyclohexanol. Kinetic Procedure.-Temperature variation was no more than 10.03’. Temperatures were checked with thermometers calibrated by the National Bureau of Standards. The solutions were prepared with an ethanol-water solvent (90% by volume at 15.56’). Reactant solutions, epoxide, mercaptide, buffer, and neutral salt, of appropriate concentrations, were prepared. The required volumes of these solutions were combined by means of automatic delivery pipets calibrated with the ethanol-water solvent. The reaction mixture was kept at Dry Ice-isopropyl alcohol temperatures and outgassed with nitrogen. The cold, deoxygenated solution was distributed among
(3) M. J. Youngquiat, D. F. OBrien, and J. W. G a t e , Jr., J. A m . Chem. Soe., 00, 4960 (1966).
(4) J.
0.Pritchard and F. A. Long, ibid., T Q , 2365 (1957).
I’d.33, N O . 1, JanUUr?/ 1968
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