COOXIDATION OF THIOLACETIC ACIDAND INDENE
Sept. 20, 1964
94% ethanol (prepared by diluting 6% of water by volume with absolute ethanol t o the mark). The reaction mixture for the 50/, reaction was prepared by diluting 250 ml. of the solution with 250 ml. of 0.4 M sodium ethoxide in absolute ethanol; that for the 100yereaction was prepared by diluting 15 ml. of the solution with 15 ml. of 1 M sodium ethoxide in absolute ethanol. Solutions were equilibrated in the constant-temperature bath prior to mixing, and addition of base was done with the apparatus completely connected to prevent loss of any methyl sulfide. The system was maintained a t a pressure of ca. 100 mm., and the reaction bottle at 24" in the 5Ye reaction. After 5.5 min. the reaction was quenched with 110 ml. of 1 M aqueous HC1, and nitrogen passed through the mixture for another hour to expel products. The 100% reaction was run in a similar fashion for 1.5 hr. a t ca. 170-mm. pressure and 35". apparatus was the same as for 2 . The E l Reaction.-The the E2 reaction. Solutions were prepared in the same manner, except the 0.1 M solutions in 94% ethanol were diluted with equal values of absolute ethanol to give the final reaction mixtures. The 5% reaction was conducted at 40" for 3.8 hr. and a partial vacuum of 170 mm. The 100% reaction was conducted a t 75" for 3 hr. at atmospheric pressure. Purification of Dimethyl Sulfide Samples.-The collection trap was connected to a vacuum line and the sample distilled through a tube containing phosphorus pentoxide into a small sample tube. The material collected in this tube was transferred with a chilled hypodermic syringe t o a gas chromatograph ( Wilkins Aerograph Model A-90C) fitted with a 5-ft. column of 200/0 tri-o-cresyl phosphate on Chromosorb. At room temperature and a flow rate of 25 ml. per min. the retention time for isobutylene was 1.5 min. and for dimethyl sulfide 17 min. The latter peak was
[CONTRIBUTION FROM
THE
3791
collected in a trap immersed in liquid nitrogen. In the S N ~ - E ~ reactions another peak followed shortly after the dimethyl sulfide (probably t-butyl alcohol or I-butyl ethyl ether) but could be separated from it satisfactorily. The dimethyl sulfide was then distilled into the sample bulb and carefully degassed as described before. a Mass Spectrometry.-A Consolidated Model 21-620 instrument was used. The procedure was similar to that used before.' Sample pressure was normally 300 w. Some dependence of the apparent mass 62:mass 64 ratio on sample pressure was noted. A set of runs on the same pair of 100 and 5y0 samples over the range 150-300 p showed no significant variation in the isotope effect, provided the two samples of a pair were measured at the same pressure. This was accomplished by starting each series of runs a t the same scale deflection on the recorder, and carrying out the 20 consecutive scans on a rigidly timed schedule. The 1007, sample was run both before and after the 5y0 sample. The standard deviations from the mean of the averages of 20 scans usually were less than 0.2%. Kinetic Measurements.-Apparatus and sampling techniques were similar to those used by Williams.' Solvent: and solutions were prepared as described above (Preparation of Samples for Measurement of Mass Spectra). Temperature control was good to f0.05', and temperatures were checked against an N.B.S. thermometer. Chilled aliquots from the S N ~ - E Ireaction were titrated with standard base. Aliquots from the E2 reaction were quenched in 0.1 N hydrochloric acid and back titrated with standard base. No particular effort was made to attain maximum precision. Most of the rate constants are good to =k5oJ, or better, b u t those for the faster reactions may be as poor as +IO%.
CENTRAL BASICRESEARCH LABORATORY, Esso RESEARCH AND ENGINEERING COMPANY, LINDEN,N. J. ]
Organic Sulfur Compounds. XIV.' Oxidative Addition of Thiol Acids to Unsaturated Hydrocarbons. Cooxidation of Thiolacetic Acid and Indene by Molecular Oxygen BY ALEXISA. OSWALD,~ KARLGRIESBAUM, A N D WALTER NAEGELE RECEIVEDMARCH13, 1964 The mechanism of oxidative addition of thiol acids to unsaturated hydrocarbons was studied with thiolacetic acid and indene as niodel reactants. While the free-radical addition of thiolacetic acid to indene is a rather slow process, a rapid chain reaction occurs when solutions containing thiolacetic acid and indene are oxygenated at room temperature. In the cooxidation reaction, the 2-acetylmercaptoindanyl radical ( V ) resulting from addition of the acetylmercapto radical to indene combines with .02.to form a peroxy radical ( V I I ) . This hydroperoxide then abstracts hydrogen from thiolacetic acid to yield the unstable 2-acetylmercapto-1-indanyl (VIII), a new type of peroxide compound, as the primary cooxidation product. The hydroperoxide VI11 is slowly reduced by thiolacetic acid or thiols to the corresponding alcohol IX. Aliphatic amines catalyze this reduction The structures of the new addition and cooxidation products ( V I , VIII, and I X ) were established by n.m.r. and infrared spectroscopy. An analogous cooxidation mechanism seems applicable to the oxidative addition of thiolcarboxylic and thiophosphoric acids to olefinic hydrocarbons and anthracenes and opens a new synthetic route to 8-acylmercaptoalkanols.
Introduction The cooxidation of thiolacetic acid and hydrocarbons -anthracenes3, and fluorenes4-with molecular oxygen was first described by Mikhailov and Blokhina in 1951. Ten years later, Beckwith and Beng See5 reexamined the reaction of thiolacetic acid with anthracene and oxygen. On cooxidation with anthracene, Mikhailov and Blokhina3s4obtained diacetyl disulfide and' the two *isomeric 9,lO-dihydro-9,lO-bis(acetylmercapt0)anthracenes (IV) as the main products. Beckwith and Beng See found5 that S-acetylmercapto(1) Previmis paper of this series, J . A m . Chem. Sac., 86, 2877 (1964). (2) Central Basic Research Laboratory, Esso Research and Engineering Co., Esso Research Center, P . 0. Box 45, Linden, N . J. (3) B. M . Mikhailov and A. N. Blokhina, Dokl. A k a d . N a u k , S.S.S.R., SO, 373 (1951). (4) E. M . Mikhailov and A. N. Blokhina. Problemy Mckkonizma Org. Rcaklsii, A k a d . N a u k , U k r . S . S . R . ; Oldcl. Fie.-Mal. i K h i m . N a u k , 215 (1953);Chcm. Abstr., 60, 16,735f(1956). (5) A. L. J. Beckwith and Low Beng See, J. Chem. Sac., 1304 (1961).
anthracene (111) and some sulfur were also formed. Each group proposed a different reaction mechanism. We believe that the chain mechanism proposed by the second group is the more probable ace. This mech10-hyanism postulates 9, IO-dihydro-9-acetylmercaptodroperoxyanthracene (I) as the primary and 9,10dihydro-9-acetylmercapto- 10-hydroxyant hracene (II ) as the secondary unstable reaction products. This mechanism for thiolacetic acid cooxidation is analogous to the mechanism of cooxidation of simple thiols and CHFCR~
R' S . ___*
R'S-CH2-CRS' R' SH
R'S-CHZ-CRz-Oz.
___t
0%
R'S-CH2-CRz-OzH
(R'S.)
(6) A. A. Oswald. J. 078. Chem., SI, 443 (1959), 1 6 , 842 (1961); A. A . Oswald, B. E. Hudson. Jr., G. Rodgers, and F. Noel. ibid.. 1'7, 2439 (1962) (7) A. A. Oswald, F . Noel, and G. Fisk, ibid., 96, 842 (1961). (8) For a more detailed t r e a t m n t of this subject, see A. A . Oswald a n d T. J . Wallace, "Anionic Oxidation of Thiols and Co-oxidation of Thiols and Olefins by Molecular Oxygen," chapter in "Organic Sulfur Compounds," N . Kharasch, Ed., Pergamon Press, London, in press.
A. A. OSWALD,K. GRIESBAUM, AND W. NAECELE
3792
AcS
AcS
I
02
AcS
olefins that had been studied previously in our laboraIn the present paper we describe the results of our study of the cooxidation of thiolacetic acid and indene by molecular oxygen which support the above mechanism of thiolacetic acid-hydrocarbon cooxidations by the isolation of the initial hydroperoxide (VIII) and the subsequent alcohol (IX) cooxidation product. In conjunction with this cooxidation study, the closely related radical addition of thiolacetic acid to indene was also examined (Table I). A comparative nuclear magnetic resonance (n.m,r,) spectroscopic study of the new cooxidation and addition products obtained was also made (Fig. 1) to confirm their structures.
Results Addition.-In the absence of oxygen, thiolacetic acid was found to add slowly to indene to yield quantitatively 2-acetylmercaptoindane , (VI), a colorless
Vol. 86
ceeds by a radical mechanism through a 2-mercaptoindanyl radical (V) intermediate. Cooxidation.-Oxygenation of solutions containing thiolacetic acid and indene, each about 0.3 mole/l. concentration, resulted in a rapid, exothermic cooxidation. In an aliphatic hydrocarbon solvent, such as heptane, the reaction was practically complete after 3-hr. oxygenation a t room temperature with most of the cooxidation product precipitated as a colorless solid. Ultraviolet light was an effective catalyst for the cooxidation, indicating a radical type reaction with a chain mechanism. The structure of the isolated cooxidation products depended upon the reaction temperature. When the oxygenated reaction mixture was irradiated with ultraviolet light at -15' for 6 hr., a small amount of a solid melting at 48-50' precipitated as the only product from the cooxidation mixture. The solid gave a positive hydrdperoxide test by the iodide method. Quantitative hydroperoxide group analysis by the thiol method,' infrared absorption spectroscopy, and elemental analyses indicated that it is the monohydrate of the expected primary cooxidation product 2-acetylmercapto-1-indanyl hydroperoxide (VIII). The hydroperoxide VI11 after isolation turned into a brown solid on standing a t room temperature. In chloroform solution, however, i t was fairly stable. D
S
A
C
4.
V
The hydroperoxide could be reduced by the thiol m e t h ~ d ' - ~with ~ ' ~ 2-naphthalenethiol in the presence of an aliphatic amine catalyst to yield the corresponding alcohol, 2-acetylmercapto- 1-indanol (IX) i- 2 2-ClOH,SH
v
VI
solid which could be distilled in vacuo without decomposition. t-Butyl hydroperoxide and ultraviolet light catalyze the reaction (Table I), indicating that i t pro-
dlH
vm
TABLE I
OH
CATALYSIS OF THIOLACETIC ACIDADDITIONTO INDENE" Catalyst
Thiolacetic acid reacted, %b
None 45 &Butyl hydroperoxide" 79 Ultraviolet lightd 95 89 Oxygene a n-Heptane solutions containing thiolacetic acid and indene, both in 0 4 mole/l. concentration, were stored for 17 hr. a t room temperature. * Determined by subtracting the thiolacetic acid left after 3 hr. from the original amounts. c 0.075 mole/l. d From 5-cm. distance through cooling water by a Hanau laboratory immersion lamp #3!3. 6 On oxygenation solid Z-acetylmercapto-1-indanyl hydroperoxide cooxidation product precipitated from the solution.
M
This alcohol is more stable than the hydroperoxide. It melts without decomposition at 119.5-120.5'. When the cooxidation reaction was carried out a t a higher temperature, 5 O , the precipitate consisted of the 2-acetylmercapto-1-indanylalcohol (IX) and the hydroperoxide VI11 with some adsorbed diacetyl disulfide. Product analysis made it apparent that a t 5' (9) A . A. Oswald, F . Noel, and A . J . Stephenson, J . 0 7 8 . Chem , 16, R9ti9 (1961). (IO) A . A . Oswald, K. Grieshaum, and B. E. Hudson, J r . , i b i d . , 118, 2351, 2355 (1963).
Sept. 20, 1964
COOXIDATION OF THIOLACETIC ACIDAND INDENE
3793
TABLE I1 PARAMETERS OF NUCLEAR MAGNETIC RESONANCE SPECTRA OF THIOLACETIC ACID-INDENE ADDITION A N D COOXIDATION PRODUCTS
-
2
Chemical shifts for the various protons in deuteriochloroform solution (about 10%) downfield from tetramethysilane internal reference, p.p.m.: s, singlet; d , doublet; q, quartet; m, multiplet; b , broad peak H' H4 H' HZ HL Hi6 H 4 7
q 3 . 45b,d.' q 3 ,45*.d,' q 2 .88b,C.d m 4.24"*'" 0 q 2 . s8"C.d d 5.38' 2,83i,l.m q 3,57'"." m 4.4@.','." 2" b 5.63 q 3.44"O'P d 5.13h q 2.79i",p m 3 . 9Oh
