Journal of Molecular Catalysis, 37 (1986) 339 - 347 339

REACTIONS OF TETRALIN INDUCED BY METAL SALTS AND COMPLEXES PART I. SELECTIVITY IN TETRALIN REACTIONS CATALYZED BY MODIFIED AXI,

ANNA KORDA and STANISLAW K. TYRLIK

Labomtory of Homogeneous Catalysis, Institute of Organic Chemistry PAN, ul. Kaeprzaka 44,00-224 Warsaw (Poland)

(Received November 12,1985; accepted April 29,1986)

Reaction of tetralin in the presence of AlCls and its modifications has been reinvestigated and the products identified. 5- and 6-(1-phenylbutyl) tetralins are the primary products, which subsequently form partly hydro- genated tricyclic aromatic compounds and benzene. Further reactions produce ethylbenzene, n-butylbenzene, ethyltetralins and n-butyltetralins.

A catalytic system containing AlCl, and hydrated salts (CHsCOONa* 3H20 and FeC1,*2H,O) has been found to convert tetralin to 5- and 6-(l- phenylbutyl)tetralins with high selectivity.

Introduction

The Lewis acid-catalyzed chemistry of aromatic hydrocarbons is a subject of constant interest [ 1,2]. The reaction of benzene in the presence of AlCls has very low selectivity and gives rise to many hydrocarbons, such as al- kylated benzenes, diphenyl, diphenyhnethane, tetralin, different condensed ring hydrocarbons etc. AlCl,-inducedreactions of tetralin were first reported in 1924 [ 31. In this reaction benzene, phenylbutyltetralin, perhydroanthracene, octanthrene (octahydrophenanthrene) and octhracene (octahydroanthracene) are formed [4]. Recently Stobart and Zaworodko observed formation of phenanthrene and anthracene skeletons from tetralin in the presence of AlCls [ 2 - 51. Thermal reactions of tetralin at 400 - 500 “C also produce many different products: butylbenzene, methylindane, styrene, n-propyl- benzene and ethyltoluenes [ 61. Radical mechanisms for these reactions have been suggested [6,7]. One of the most important unsolved problems in metal salt-induced reactions of aromatic hydrocarbons is their low selectivity. Knowledge of the mechanism of these processes is in a very preliminary stage - especially concerning the fate of the metal compound.

Reactions of tetralin and other partially hydrogenated condensed aromatic hydrocarbons could be a source of aliphatic chemicals, Thus we have undertaken the study of the reactions of tetralin induced by metal salts and complexes.

0304-5102/86/$3.50 0 Elsevier Sequoia/Printed in The Netherlands

340

Experimental

Chemicals Tetralin used was a commercial product distilled from Na under purified

argon, AIC13 was used as received and_ EtsAl$& was manufactured by Blachownia Chemical Works Poland. FeC12*2Hz0 was prepared by dehydra- tion of FeC12*4H,0 at 90 “C under vacuum. NaH, NaBHa, Mg, Na, CaO and MgO were commercial products used as received.

General procedure: reactions with AlC13 and AlC13 + reducing agents or oxides

The reactions were carried out under purified argon in a 100 ml three- necked flask equipped with a magnetic stirrer, condenser, septum and a thermometer. In a typical experiment 5 mmol (0.66 g) of AlCls was intro- duced into a vessel and 50 mm01 (6.7 ml) of tetralin was injected. The reaction was stirred at the desired temperature for the desired period of time. Then reducing agents or oxides were used; 5 mmol of these reactants and 5 mmol of AlCls were introduced together into the flask. Tetralin was injected into the mixture of solid reactants.

Reactions with hydrolyzed aluminium chloride 2.5 mmol (0.33 g) of AlCls and 2.5 mmol (0.4 g) of FeC1,*2H,O (or

1.7 mmol of CH,COONa*3H,O) with 50 mmol of tetralin were stirred at room temperature during - 10 h. The solution was then filtered and heated to 200 ‘C for -3 h.

Chromatographic analysis and mass spectra 0.2 ml samples were withdrawn from the reaction vessel with a hypo-

dermic syringe, quenched by diethyl ether and analyzed by means of gas chromatography; a Chrom 5 gas chromatograph was used with FID and a column of 1 m silicone OV-17 5% on Chromosorb W, temperature programme: (1) 100 “C! for !O min; (2) temp. rise 100 - 220 “C during 10 min; (3) 220 “C for 10 min. Benzene, ethyl- and n-butylbenzenes were identified by their retention times. The other products were identified by means of mass spectral analysis performed with an LKB 9000 GC-MS apparatus.

In the mass spectra of 1-phenyl-n-butyltetralins, the most abundant ion is m/e 145, which is the expected tetralin -CH2[C,JIIICH2] fragment formed by the loss of C&H&H&Hz (M 119). Other fragments are: m/e 131 51.2% C1,,H1i; m/e 91 44.8% tropylium ion: m/e 117 20.9% C&Ig; m/e 115 16.1% C&I,. Fragmentation of ethyltetralins Ci2Hi6 (M 160) gives as the most abundant ion m/e 131 (CJI,,) which is formed by loss of the ethyl fragment from the parent molecule. Other fragments (m/e 160 27.5% parent ion; m/e 91 21.4% tropylium ion; m/e 132 19.9% Cl&Ilz tetralin ion; m/e 145 18.8% &His M-CHs; m/e 117 18.1% C&I,) show typical fragmentation for this class of molecules [8].

341

Similarly, fragmentation of n-butyltralins Ci4H2a (M 188) consists of subsequent loss of the fragments of the alkyl group: m/e 159 100% Ci2Hi5; M-C2HS; m/e 173 57.0% Ci3H1, M-CH,; m/e 145 54.2% C,iHi3 M-&I&; m/e 131 47.6% ClOHll M-C4H9. Other ions are as expected m/e 91 17.8% tropylium ion and m/e 117 15.1% CgHg [8]. The most abundant ion of the partially saturated tricyclic compound Ci4H1s is the parent ion m/e 186. Its fragmentation consists of the loss of CzH4 (M 28) giving m/e 158 77.2% Ci2Hi4. Other ions are m/e 129 41.2% C,J&,; m/e 128 39.5% Ci,,H,; m/e 145 39.3% C1lH,,; m/e 143 CllHll 34.7%; m/e 115 23.3% C&H,. These ions seem typical for this type of molecule [ 81.

Results

Reactions of tetralin induced by AlC13 A1C13 dissolves in tetralin (10 X molar excess of tetralin) at room

temperature. The fresh solution is orange and produces two layers after several hours: the top layer remains orange, the bottom layer is brown. The two layers differ in composition. As long as the reacting mixture is kept at room temperature, no black coloration is developed. At 110 “C the two layers disappear and a black colour develops within several minutes. The com- position of the reaction mixture at different temperatures is given in Table 1. Probably the very first products of the reaction are the two isomers 5- and 6- (l-phenylbutyl)tetralin IA and IB (Scheme 1). Further reaction of the two isomers gives three-ring compounds octanthrene (IIA) and octhracene (IIB), respectively, and benzene. Tetralin conversion increases with temperature, and after 10 h at 200 “C reaches -60%. However, the selectivity under these conditions is low. Other reactions of IA and IB proceed giving a mixture of at least eight principal products (Table 1). A fair amount of black tar also appears at the bottom of the flask. There are minor amounts, (up to 3%) of some other products, e.g. methyltetralin, n-propyltetralin, 1,4diphenyl- butane. There are no significant amounts of methylindan and olefins, e.g. styrene, which were observed by other authors [ 61.

Reactions of tetralin induced by hydrolyzed AlCl, A solution of anhydrous aluminium chloride in tetralin was modified

by water ( AlC13:H20 = 1: 1.5) and by hydrated salts CH&OONa* 3Hz0 and FeC12*2HZ0. Results are given in Table 2. Addition of water deactivates the system (conversion of tetralin = -8%) without improving its selectivity. However, hydrolysis of A1C13 by hydrated salts produces active soluble alu: minium species which are very selective catalysts. In these systems tetralin is converted mainly to 1-phenylbutyltetralins, all subsequent reactions being strongly inhibited. This result can only be accomplished if, after some preliminary mixing of tetralin + AI& + hydrated salts, the reaction mixture is filtered from the solids. With both hydrated salts used (CH,COONa*3H,O and FeC12*2Hz0) the conversion of tetralin is -30% with 86% and 90%

TA

BL

E

1 : K

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(mol

%)

of t

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tion

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m

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Org

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com

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Roo

m

tem

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ture

11

0 “C

20

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top

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ttom

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top

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la

yer

ben

zen

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ben

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tetr

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tetr

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s n

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s oc

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66.4

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7.2

trac

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9 8.

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13

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Sel

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Scheme 1. Reactions of tetralin in the presence of AlC13 and AlCl’s-derived systems.

selectivity of 1-phenyltetralins respectively. The remaining solid, when con- tacted with a fresh amount of tetralin, is much less selective than the soluble species (gives - 15% conversion with 51% selectivity).

Reactions of tetralin induced by reaction products (A1C13 + reducing agents or oxides}

Results of this series of experiments are shown in Table 3. Reducing agents make the system less active (conversions of tetrahn vary from - 5% to -25%). This is probably due to the decreased Lewis acidity of A1C13 reduction products. The conversion of tetralin is low; only l-phenylbutyltetralins, three- ring compounds and benzene are produced. Alkylated benzenes and tetralins are not formed. In the presence of calcium and magnesium oxides, the system has the same selectivity and activity as with AlC13 alone.

TA

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2 w

Com

posi

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(m

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th

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Com

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(m

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te

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50 m

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AlC

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5 m

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red

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agen

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(5

mm

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Org

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top

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Sel

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56

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, 6

h.

346

Reactions of tetralin induced by sesquiuluminium chloride The initial products of this reaction are ethyltetralins, formed probably

by alkylation of tetralin with the ethyl groups of organoaluminium com- pound (Table 4). The mechanism of this reaction remains ambiguous and requires further study. After a longer reaction time, I-phenylbutyltetralins are formed and their subsequent reactions take place. After 10 h the com- position of the reaction mixture resembles that obtained with AN&, except for higher content of ethyltetralins.

TABLE 4

Composition of reaction mixture (mol%) tetralin (50 mmol) and Et&12C!13 (0.5 mmol), 200 “C

Organic compound 3h IO h

benzene ethylbenzene n-butylbenzene tetralin ethyltetralins n-butyltetralins octanthrene + octhracene l-phenyl-n-butyltetralins

Selectivity (%a) of 1 -phenyl-n- butyltetralins

trace 9.1 trace 4.0 - 4.3 32.2 40.7 12.0 12.2 - 1.5 trace 9.5 trace 15.5

0 26

Discussion

The general reaction scheme is shown in Scheme 1. In the first stage of the reaction the C&~-&J bond of tetralin is cleaved, probably by the elec- trophilic attack of the Lewis acid or Lewis acid-derived catalyst. The carboca- tion thus formed attacks another molecule of tetralin, producing the two primary products 5- and 6-(l-phenyl-n-butyl)tetralins LA and IB in approxi- mately equal amounts. The subsequent reaction involves another splitting of a C-C bond. It is preferably another &2sgP3 bond of IA and IB. This process, after cyclization, leads to benzene and three-ring compounds IIA and IIB in approximately equal amounts.

For preparation of light aliphatic or subsituted aromatic hydrocarbons, cyclization is an undesirable process. It is strongly inhibited in the presence of the catalyst prepared by gentle hydrolysis of AlC13 with hydrated salts, which is specific enough to promote only reaction (1). Reaction (3) proceeds also through C&.,2+&,3 bond cleavage and leads to the products III, whereas reaction (4) proceeds through C&3+&, 3 bond cleavage and gives products IV. In contrast to reactions (1) and (2), these processes demand an additional source of hydrogen. The products III and IV are formed in the most drastic conditions (prolonged heating at 200 “C).

347

Acknowledgement

Mrs. B. Baranowska is gratefully acknowledged for performing mass spectral measurements.

References

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Amsterdam, p. 67. 5 S. R. Stobart and M. J. Zaworotko, J. Chem. Sot., Chem. Commun., (1984) 1700. 6 J. M. C. Penninger and U. W. Slotboom, Red. Trau. Chim. Pays-Bas, 92 (1973) 513,

1089. 7 J. A. Franz and D. M. Camaioni, J. Org. Chem., 45 (1980) 5247. 8 E. Stenhagen, S. A. Abrahamson and F. W. McLafferty, Registry of Mass Spectral

Data, Wiley, New York, 1974, Vols. 1, 2.