A Synthesis of 6-Methoxytetralin - Journal of the American Chemical

James H. Hunter, and Alan H. Nathan. J. Am. Chem. Soc. , 1947, 69 (8), pp 2064–2064. DOI: 10.1021/ja01200a508. Publication Date: August 1947...
0 downloads 0 Views 139KB Size
NOTES

2064

aqueous thiocyanic acid. Ostwald's2 earlier conductivity experiments indicated that this acid is almost as strong as hydrochloric, but more recently Latimer3 estimated from thermodynamic calculatioas that it is a weak acid with an ionizaThe tion constant of approximately 1 X experiments summarized in Table I prove that thiocyanic acid is a strong acid. The third column gives the pH calculated from the relation, pH = -1 og (H+), where (H+) is the concentration of the hydrogen ion in moles per liter for complete dissociation of the acids. In a private communication Latimer has informed us that soon after he published his book he realized that thiocyanic acid is a strong acid. Experimental.-Solutions of thiocyanic acid were prepared by mixing equivalent amounts of perchloric acid and potassium thiocyanate solutions. The flH of each thiocyanic acid solution was measured with a commercial model, glass electrode at intervals over a period of thirty minutes. A:; a check, several solutions of pure perchloric acid having the same concentration as some of the thiocyanic acid jolutions were tested likewise. All readings were constant t o within 0.02-0.03pH unit. The temperature was 25 '.

TABLE I Concentration of acid, moles/liter HCNS HC10d

0 250.6 ,1244 ,04958 ,02513 .01256 ,00764 ,00509 ,00188

pH calcd.

0.60 0.1244 ,02513 ,01256

,00188

.91

1.30 1.60 1.90 2.12 2.29 2.72

HCNS

#H obs.

0.63 .94 1.33 1.63 1.92 2.15 2.32 2.72

HClOd p H obs.

0.93

ascertain whether partial aromatization could be applied to an a,P-unsaturated bicyclic ketone such as I. 0

I

I1

111

8-Keto-8,3,4,5,6,'7,8,10-octahydronaphthalene (I) was prepared from cyclohexanone through 2carbethoxycy~lohexanone~ according t o the procedure of Du Feu, McQuillin and R ~ b i n s o n . Ex~ tension of the classical method5 of bromination and subsequent dehydrobromination to the ketoperhydronaphthalene (I) was unpromising ; however, selective dehydrogenation with sulfur6 or palladinized charcoal' according to procedures which have been used for aromatization of monocyclic unsatured ketones yielded a phenolic prod uct. hlethylation of this crude product gave 6-methoxy-tetralin (IQ8 in approximately :30:& yield. Oxidation of I1 with chromic anhydride according to the method of Burnop, Elliot and LinsteadY yielded 6-methoxytetralone-1 (1111, identified by mixed melting point with an authentic specimen.' Experimental10

1.62 1.91

2.73

(2) W. Ostw;rld, J . p ~ k l Chem., . 82, 305 (1885). (3) W. Latimer, "Oxidation Potentials," Prentice-Hall, Inc., S e w York, N. Y , 1938, p. 128

DEPARTMENT OF CHEMISTRV OF SANFRANCISCO UNIVERSITY SAXFRANCISCO 17, CALIFORNIARECEIVED JUXE 10, 1947

A Synthesis of 6-Methoxytetralin BY JAMESH . HCXTER A N D ALANH. KATHAN

Concurrently with other studies which have resulted in a satisfactory method' for the production of 6-methoxytetralone-1 (111) in relatively large amounts, a synthesis of this compound from cyclohexanone was developed. I n the procedure of Thomas and Nathan,' the ultimate step involves the oxidation of B-methoxytetralin (LI) to the ketone (111). The new method described herein for the preparation of (11)was investigated a b ail alternative to that used,' but was abandoned in view of the unfavorable yields. Since aromatization of CY, $-cyclohexenones to phenols is an established but comparatively little used reaction,2 i t was of considerable interest t o (1) 1' homd.i hiid Ndthdn, in press ( 2 ) Homing, Chem Kut, , 33, 89 (194.3)

Vol. 69

6-Methoxytetra1in.-A mixture of 7.5 g. (0.05 mole) and 1 ,5 of 2-keto-2,3,4,5,6,7,8,10-octahydronaphthalene4 g. (0.05mole) of sublimed sulfur was heated under reflux for one hour a t a bath temperature up to 220"; during the early stages of heating brisk boiling occurred and hydrogen sulfide was evolved. The mixture mas cooled and transferred t o a small Claisen flask. Distillation gave 6.0 g. of yellowish oil, b. p . 130-160";it 1 1 m m . The distillate was dissolved in ether, extracted twice with dilute sodium hydroxide solution, and once with w;iter. Cnrbon dioxide was bubbled into the alkaline fr,ictioii until precipitation of the oily phenolic imterlal wCis complete, The oil was extracted with ether, dried ovcr magnesium sulfate and the'sohent removed: yield, 3.87 g. The crude phenol was dissolved in 33 nil. of IOc; sodium hydroxide solution, and 6 ml. of dimethyl su1f;cte added dropwise with mechanical stirring. AEi.er slirriiig for one and one-half hours, the product was extracted &th ether, the ethereal extract washed with \rater, dried over magnesium sulfate and the solvent removed. Di~tillation of the residue gave 2.69 g. ( 3 3 9 of ~i-inethoxytetralii~ boiling a t 127-129" a t 11 mm. .-1nuZ. Calcd. for CllHlrO: C, 81.11; H . 8.711, P'oti1111 : C, 81.04; H, 8.67. RESEARCH LABORATORIES THEUPJOHXCo. KALAMAZOO, MICHIGAN RECEIVED APRIL .5, 1917 (3) (4) (5) dnn., (6)

Kotz and hlichels, A?z?i., 360, 210 (1906). Du Feu, RlcQuilIin and Robinson, J . Chem. Knoevenagel, An%, 281, 98 (1854); b'uv., 26, I 9 5 1 f18!K

288, 339, 346 (1895). Horning, THISJOURNAL, 67, 1421 (1945) (7) Smith and Rouault, ibid., 65, 631 (1943) (8) Schroeter, An%, 426, 83 (1922). (9) Burnop, Elliot and Linstead, J . Chem. Soc., 797 (l'J4Ui. (10) Details for the preparation of 6-methoxytetralin ( I I j only are described since adequate directions for n i l other comlmundn i w volved are recorded in the literature.