THI CH~CMICAL LABORATORY OF THB UNIVERBITY OF MARYLAND ]
[CONTRIBUTION FROM
A NEW SYNTHESIS OF PICENE* NATHAN L. DRAKE
AND
WARREN C. McVEY
Received M a y 8, 1939
The occurrence of alkylated picenes among the products of dehydrogenation of many triterpenoids makes the synthesis of picene homologues of
/
I
CO(CH&COOH
I
* Taken in part from t h e Ph.D. Dissertation of Warren C. McVey. 464
A NEW SYNTHESIS OF PICENE
465
considerable interest. Certain polymethylated picenes have been synthesized by L. Ruzicka and co-workers' and 1,8-dimethylpicene haa also been synthesized in our own laboratoriesz. The work to be described was undertaken with the object of devising a new picene synthesis which might prove useful in the preparation of alkylated picenes, and the method which we planned to employ can be summarized by the preceding formulas. However, when I, dissolved in carbon disulfide, was treated with anhydrous aluminum chloride in an attempt to bring about cyclization, only a tarry product was obtained, and no picene could be isolated. The method of cyclization depicted above, involving a compound containing only aromatic rings is not the one most frequently employed, but such a method has been employed successfully in the synthesis of 1,8dimethylpicenel*2. The more common procedure in syntheses of this general nature is to effect ring closure involving the unsaturation of a hydroaromatic ring and the hydrogen of an aromatic ring in the fashion set forth by the formulas:3
In carrying out the synthesis formulated above, Cook and Hewett observed tlhe formation of a considerable quantity of a substance corresponding to the spirocyclopentane which they had earlier isolated during the synthesis of 1,%cyclopentanophenanthrene, and which they considered to be 7,8-dihydrophenalyl-7-spirocyclopentane(11), /
A
\
I1
I11
1 RUZICKA AND H ~ S L IHelv. , Chim. Acta, 17, 470, (1934); RUZICKA AND MORGELI, ibid., 19, 377, (1936); RUZICKA AND HOFMANN, ibid., 20, 1155, (1937);22, 126, (1939). e F.HOWARD, Thesis, University of Maryland, 1958. COOK AND HEWETT, J. Chem. S O C . , 146, 365 (1934).
466
NATHAN L. DRAKE AND WARREN C. MCVEY
a derivative of a substance to which Mayer and Seiglitz4had given the name “phenalene” (111). The presence of an alkyl group on the hydroaromatic ring where cyclization was expected to occur was shown by Cohen, Cook, Hewett, and Girard5 to repress spirane formation to such an extent that a 97 per cent. yield was obtained in the cyclization (IV-V) :
IV
V
whereas the cycIization of l-(@-l ‘-naphthylethy1)-A1-cycIopentene8 led to the formation of a mixture of products from which the pure picrate of 7,8-dihydrophenalylspirocyclopentanewas isolated in 28 per cent. yield. Inasmuch as we were unsuccessful in cyclizing I, we next turned to an examination of the behavior of 3,4-dihydro-l-phenethylphenanthrene when treated in carbon disulfide solution with aluminum chloride. Judging from the work of Cohen, Cook, Hewett, and Girard6one would expect considerable spirane formation in this reaction, and we found that the product was a viscous oil from which no pure substance could be isolated. However, from the products of dehydrogenation of the oil, picene could be obtained (yield 1 per cent.); the remainder of the oil was apparently not affected by the dehydrogenation (bath temperature 390-400”). When 3,4-dihydro-l-(/3-2’-tolylethyl)phenanthrene(VI)
VI was treated in carbon disulfide with aluminum chloride, and the resultant product was dehydrogenated, only picene could be isolated from the 6
MAYER AND SEIOLITZ, Ber., 66,1837 (1922). COHBN,COOK,HEWETT, AND GIRARD, J . Chem. SOC.,146,065 (1934).
A NEW SYNTHESIS OF PICENE
467
reaction products, but the yield was about four and a half times as great as that obtainable from 3 ,4-dihydro-1-phenethylphenanthrene. It should be noted that the cyclization of VI is a different sort of process from that studied by Cook et a15 when they noted the improvement of yield caused by :3 methyl group in the hydroaromatic ring at the point where a new bond was to be established. In our case cyclization might have been expected to take place at 6' with the formation of a product which would yield 10-methylpiceneon dehydrogenation. However, the picene obtained showed no depression of melting point when mixed with the substance prepared from unmethylated intermediate, and Ruzicka6 has shown that, in those cases which he investigated, methylated picenes, if they are unlike, do show a depression in the mixture melting point determination. The loss of an alkyl group from an aromatic hydrocarbon in the presence of aluminum chloride is a well-known process, but that this loss should be attended by cyclization at the point vacated by the alkyl is extremely interesting and worthy of further study. Attempts to produce 8-methylpicene by dehydrogenating the product obtained from the treatment of 3 ,4-dihydro-l-(@-4'-tolylethyl)phenanthrene with aluminum chloride in carbon disulfide failed. We have not yet examined the behavior of 3 ,4-dihydro-l-(@-3'-tolylethyl)phenanthrene, but it seems reasonable that this substance should cyclize smoothly, and that 9-methylpicene could be made from it. EXPERIMENTAL
B-i-Naphthoylpropionic acid.-The method used in this synthesis was a modification of the one described by Fieser and Peters.7 The modifications which we have introduced were concerned principally with the separation of the 1-, and 2-isomers; consequently that part of the preparation starting with the crude mixture of B-1- and @-2-naphthoylpropionic acids, produced by the reaction of succinic anhydride on naphthalene in nitrobenzene solution in the presence of aluminum chloride, alone will be described. Sixty-eight grams of finely pulverized crude acids was suspended in 1500 ml. of warm water, and 50 ml. of 2N sodium hydroxide was added (1/3 the amount necessary for complete neutralization). The mixture was held at 50-60" for several hours, preferably overnight, with occasional shaking, and was then cooled to room temperature and filtered. The filtrate was acidified, and the resulting B-l-naphthoylpropionic acid was filtered and recrystallized several times from 20% acetic acid. The product melted a t 132-3". The residue of undissolved acids was returned to the flask, treated with another 50-ml. portion of 2N sodium hydroxide, filtered, and the filtrate was acidified as before. The product so obtained was a mixture of both isomers, free from tarry material, and was added to the next batch of crude acid. The residue undissolved by the two treatments with alkali consisted almost exclusively of p-2-naphthoylpropionic acid contaminated with tarry material. 6
7
RUZICKA AND HOFMANN, Helv. Chim. Acta, 22, 127 (1939). FIEBER AND PETERS, J . Am. Chem. SOC., 64,4350 (1932).
468
NATHAN L. DRAKE AND WARREN C. MCVEY
y-1-Naphthylbutyric acid.-This acid was prepared by use of the modified Clemmensen procedure described by Martins. The product melted at 107.5-108.5". 1-Keto-l ,b,S,4-tetrahydrophenanthrene.-Fifty grams of y-I-naphthylbutyric acid was suspended in 500 ml. of dry benzene in a three-necked flask provided with a mercury-sealed stirrer, a reflux condenser, and a t r a p for hydrogen chloride. Phosphorus pentachloride (50 9 . ) was added, and stirring was commenced. The acid dissolved within a few minutes, whereupon the mixture was heated under reflux for a n hour and a half. The solution was next cooled to 0-5" by means of a n ice bath, and maintained at this temperature during the addition of 34 g. of pulverized anhydrous aluminum chloride over a period of about 30 minutes. The mixture was then allowed t o warm t o room temperature, and was kept a t this temperature overnight without stirring. The mixture was then heated under reflux for two and one-half hours, and, after cooling, was poured upon ice and hydrochloric acid. The precipitated I-keto1,2,3,4-tetrahydrophenanthrenewas extracted with benzene, washed carefully with sodium carbonate and water, and finally distilled in vacuum. The yield of product distilling at 145-150"at 1mm. was 37 g. (81%). After crystallization from methanol the product melted at 95-6". Anal. Calc'd for C I ~ H I ~ O C,: 85.67; H, 6.17. Found: C, 85.49; H, 6.13. The 2,4-dinitrophenylhydrazoneof the ketone, prepared in the usual manner, and recrystallized from pyridine, melted a t 283-5" with decomposition. N, 14.89. Found: N, 14.80,14.62. Anal. Calc'dforC2611sN~O~: 9-(8-HydrozyethyZ)toluene.-This alcohol was prepared from o-bromotoluene and ethylene oxide by the Grignard reaction. The method employed was similar to one earlier described for the preparation of n-hexyl alcohol.9 The yield of product distilling at 99-105" under 1mm. pressure was 62%; d z 1.0195; n: 1.5349. Anal. Calc'd for COH120: C, 79.37; H, 8.88. Found: C, 79.14, 79.20; H, 8.95, 8.77. p-9'-TolyZethylJ, 6-dinitrobenzoate.-Prepared from 3,5-dinitrobenzoyl chloride in the usual manner, and recrystallized from ethanol, this ester melted at 126-128". Anal. Calc'd for ClaH1dN20a: C, 58.18; H, 4.27. Found: C, 58.38, 58.41; H, 4.34, 4.18. 4-(p-HydrozyethyZ)toluene.-This substance was prepared from p-bromotoluene by a method similar to that used for 2-(fl-hydroxyethyl)toluene, described above. The yield was 53% based on the aryl halide. The product distilled a t 100-106" under 1mm. pressure, and a t 235" at atmospheric pressure; dg 1.0008; n: 1.5282. Anal. Calc'd for CoH120: C, 79.37; H, 8.88. Found: C, 79.29; H, 9.02. @-/t'-TolyethylS,6-dinitrobenzoate.-Prepared in the usual way, and recrystallized from ethanol, this ester formed yellowish needles which melted at 147-9". Anal. Calc'd for C1sHldN206: C, 58.18; H, 4.27. Found: C, 58.32, 58.28; H, 4.31, 4.25. d-(p-ChZoroethyl)toluene.-2-(~-Hydroxyethyl)toluene (34 g.) was mixed with dry dimethylaniline (61 g.). The mixture was cooled in a n ice and salt bath, and 60 g. of thionyl chloride was added. The resultant black, viscous solution was allowed t o stand overnight at room temperature and was then heated on the steam bath for an 8
9
MARTIN,J . Am. Chem. Soe., 68, 1438 (1936). Organic Syntheses, John Wiley and Sons, Inc., New York, Vol. 6, page 54 (1926).
A NEW SYNTHESIS OF PICENE
469
hour. The mixture was then poured into water, the halide was extracted with ether, washed with 5% sodium carbonate solution, and with water, and finally dried and distilled in vacuum. The 2-(j3-chloroethyl)toluene boiled at 80-84" under 1 mm. pressure, and at 223" at atmospheric pressure; d: 1.0553; n: 1.5313. The yield was 85%A n d . Calc'd for CoH11Cl: C1, 22.93. Found: C1, 22.73, 23.07. ~-(~-ChZoroethyZ)toZuene.-This halide was prepared as described directly above; yield 85%. The substance boiled at 81-85' under 1 mm. pressure, and at 222" at atmospheric pressure; d i 1.0370; n: 1.5251. A n d . Calc'd for CsHllCl: C1,22.93. Found: C1,22.96,22.85. 3,4-Dihydro-l-phenethylphenanthrene.-To a cooled, stirred ethereal solution of the Grignard reagent prepared from 6.0 g. of magnesium and 37 g. of phenethyl bromide wasadded slowly32.Og. of l-keto-l,2,3,4-tetrahydrophenanthrenedissolved in 200 ml. of a solvent consisting of one part of anhydrous ether and one part of anhydrous benzene. After the addition of the solution of ketone was complete, the cooling bath (ice water) was removed, and the mixture was refluxed for one hour. Ether was then distilled until the temperature of the soZution reached 75", whereupon refluxing was continued for five hours longer. The addition complex was then decomposed with ice and hydrochloric acid, and the product was extracted, dried, and distilled in vacuum; during this treatment the tertiary alcohol originally produced underwent dehydration. The yield of 3,4-dihydro-l-phenethyIphenanthrene, boiling a t 185-187" under 0.5-1 mm. pressure, was 24.0 g. Some unchanged ketone was recovered from the fore-run, so that the yield, based on the ketonenot recovered was 69%. The product was difficult to crystallize; best results were obtained by the use of 95% ethanol, from which the product formed colorless hexagonal plates which melted at 62-3". A n d . Calc'd for C*rHlo: C, 92.91; H, 7.09. Found: C, 93.01, 92.60; H, 6.97, 7.24. The trinitrobenzenate of this hydrocarbon, prepared from equimolar quantities of s-trinitrobenzene and the phenanthrene dissolved in a small quantity of hot 95% alcohol, separated in orange needles which melted a t 91-2". Anal. Calc'd for CzsHzsNaOs: C, 67.60; H, 4.66. Found: C, 67.81; H, 4.71. S,4-Dihydro-l-(~-W'-toZyZethyZ)phenanthrene.-This substance was prepared by a method quite similar to that described for the preparation of 3,4-dihydro-l-phenethylphenanthrene. The yield was 79% on the basis of the ketone consumed. The product distilled at 190-195' under 0.5-1 mm. pressure, and crystallized readily from 95% ethanol, from which i t formed colorless well-defined plates which melted at 57-8". Anal. Calc'd for C2sHZ2:C, 92.57; H, 7.43. Found: C, 92.83, 92.58; H, 7.43, 7.34. The trinitrobenzenate of this hydrocarbon, prepared in the usual way, formed orange laths from ethanol, and melted at 101.5-1025". This compound shows slightly oblique extinction. Anal. Calc'd for CioHzsNsOs: C, 68.09; H, 4.93. Found: C, 68.29; H, 4.85. 3,4-Dihydro-l-(~-4'-toZyZethyZ)phenanthrene.-A method of preparation similar t o that described above for 3,4-dihydro-l-phenethylphenanthrenegave a yield of 63% of the phenanthrene based on ketone consumed. The product distilled at 200-205" under 0.5-1.0 mm. pressure, and formed a viscous liquid which solidified on standing,
470
NATHAN L. DRAKE AND WARREN C. MCVEY
and after several recrystallizations from ethanol, from which i t forms quadrilateral plates which show symmetrical extinction, melted at 79.5-81'. Anal. Calc'd for CZ8H22:C, 92.57;H, 7.43. Found: C, 92.66,92.59;H, 7.29,7.46. The picrate was prepared by dissolving the reactants in a small volume of hot 95% ethanol. After several recrystallizations from ethanol, the picrate melted at 101102";i t forms brick-red laths from ethanol. Anal. Calc'd for C Z Q H Z I N ~C, H, 4.78. O ~66.02; : Found: C, 66.08;H, 4.98. I-Phenethy1phenanthrene.-Thirteen grams of 3,4-dihydro-l-phenethylphenanthrene was intimately mixed with 5 g. of palladium-charcoal catalyst,loand heated in a flask connected to a vertical section of large-bore glass tubing about 2 feet in length, provided with a bubble counter at the top. During the dehydrogenation the temperature of the bath was raised slowly from 270" at the beginning to 300" by the end of the first hour, and to 320" by the end of the second hour. After cooling, the contents of the flask were extracted with successive portions of boiling ethanol. Upon concentrating the combined filtrates, crude yellow I-phenethylphenanthrene separated. The crude material was dissolved in petroleum ether, and the solution was passed through a 9-inch column packed with ground alumina ("Hydralo" ground to 100-200 mesh and activated by heating i t a t 250" in vacuo). The column was washed with successive portions of hot petroleum ether until a portion of the filtrate, on evaporation, showed no residue. Almost all of the yellow impurity remained in the first few centimeters of the alumina a t the top of the column. After several recrystallizations from methanol, from which i t separates in the form of colorless plates, the product melted a t 86.5-89.5". The yield of purified material was 9.2g. from 10.8 g. of crude dehydrogenation product. Anal. Calc'd for CZ2H18:C, 93.57;H, 6.43. Found: C, 93.38,93.34;H, 6.50,6.49. I-Phenethylphenanthrene forms a sparingly soluble trinitrobenzenate which contains two moles of nitro compound, and separates from ethanol in narrow yellow laths which melt a t 149-151'. Anal. Calc'dfor C S ~ H ~ ~ C, N 57.63; ~ O ~H, ~ 3.41. : Found: C,57.67,57.96,57.83,57.79;H,3.66,3.57,3.58,3.62. All attempts to cyclize 1-phenethylphenanthrene by treatment in carbon disulfide with aluminum chloride under reflux and at lower temperatures, yielded tarry material from which no picene could be obtained by high-vacuum sublimation. Cyclization and dehydrogenation of 3,i-Dihydro-1-phenethy1phenanthrene.-A solution of 3.7 g. of 3,4-dihydro-l-phenethylphenanthrenein 37 ml. of carbon disulfide was cooled to 0" by means of an ice and salt bath, and 3.7 g. of pulverized anhydrous aluminum chloride was added in small portions, with shaking, over a period of 30 minutes. The mixture was allowed to stand overnight a t 5", and was then poured on ice and hydrochloric acid. When the carbon disulfide had been removed by steam distillation, the viscous red oil which remained was taken up in ether, washed first with concentrated hydrochloric acid, then with sodium hydroxide solution (20%), and finally with water. After the ethereal solution had been dried, the ether was removed by distillation, and the residual oil was distilled in vacuum. The distillate (2.99.) was an extremely viscous oil which distilled a t 205-215" under 0.5-1.0 mm. pressure. After several weeks of standing the substance became opaque, lo
DIELSAND GHDKE,Be?-.,68,1232(1925).
A NEW SYNTHESIS O F PICENE
471
and finally solidified t o a pasty mass. Repeated attempts t o recrystallize the product were unsuccessful, as were also attempts to prepare a picrate or a trinitrobensenate. The viscous yellow oil (2.4g.) was mixed with 1.2 g. of palladium-charcoal catalyst and heated in the apparatus described above; the bath temperature was maintained a t 390-400" for two hours. When the mixture had cooled, i t was leached with ether until no more colored material was extracted, then placed in a Soxhlet extractor and extracted with chloroform for 20 hrs. The chloroform solution was evaporated t o dryness, and the residue was again leached with ether. The brown ether-insoluble residue was then heated in a sublimer in high vacuum at 270-290'. The sublimate was dissolved in hot chloroform, in which i t was but slightly soluble; upon cooling picene separated in glistening white plates. The yield was 29.5mg., m.p. 367-368.5'. Ana!. Calc'd for C2*H14: C, 94.93; H, 5.07. Found: C, 94.72, 94.74;H, 5.08,5.29. Cyclization of 3, 4-dihydro-l-(j3-dt-toly1ethyl)phenanthreneand dehydrogenation of the cyclized product.-This cyclization was carried out by a procedure like t h a t described for 3,4-dihydro-l-phenethylphenanthrene. The product was a viscous yellow oil which boiled at 205-1O0under0.5-1 mm. pressure (7.5g. from 9.7 g. starting material), and which did not show any evidence of crystallization after standing for several months. The oil formed no picrate or trinitrobenzenate; d: 1.097;n: 1.6440. A mixture of 5.4g. of this oil and 2.7 g. of palladium-charcoal catalyst was heated in the dehydrogenation apparatus for two hours (bath temperature, 380-400"), and then worked u p as described above. The yield of sublimed and recrystallized picene from 5.4 g. of cyclized product was 230 mg.; the product melted at 367-369'. Anal. Calc'd for C22H14: C, 94.93;H, 5.07. Found: C, 94.76,94.93;H, 5.25, 5.24. This product and that obtained from 3,4-dihydro-l-phenethylphenathreneshowed no depression of melting point when mixed. Attempts to cyclize 8,4-dihydro-I-(~-4'-tolylethyl)phenanthrene,and to dehydrogenate the product.-Under conditions similar to those described above 3,4-dihydro-1(8-4'-to1ylethyl)phenanthrene yielded an exceedingly viscous oil (b. p. 210-2'20" under 0.5-1.0 mm. pressure) when treated in carbon disulfide with anhydrous aluminum chloride. The product solidified slowly to a pasty mass from which i t proved impossible to separate any pure compounds. Dehydrogenation of this product by the method previously described yielded no picene. SUMMARY
1. Picene has been synthesized from 3,4-dihydro-l-phenethyIphenanthrene and from 3,4-dihydr0-1-(~-2~-tolylethyl)phenanthrene. 2. No picene or methylpicene was obtained from 3,4-dihydr0-1-(@-4~tolylethyl)phenanthrene. 3. Attempts to cyclize 1-phenethylphenanthrene failed.
