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.
