CHEMISTRY

Corresponding Member of the Academy of Sciences of the USSR N. I. SHUIKIN, B. L. LEBEDEV, and N. A. POZDNYAK

SYNTHESIS OF 6-ALKYLTETRALINS

In connection with our investigation of the reaction of catalytic alkylation of tetralin, it became necessary to synthesize certain standard 6-alkyltetralins required for the analysis of catalyzates by the method of infrared spectroscopy.

Fig. 1

Obtaining 6-alkyltetralins in pure form by the interaction of tetralin with alkyl bromides in the presence of AlCl₃ is practically impossible, since under these conditions, along with the β-isomer, up to 30% of the α-isomer is formed \((^{1})\), which is extremely difficult to separate. From the works of Schroeter \((^{2})\) and Levy \((^{3})\) it was known that, upon hydrogenation of 2-alkylnaphthalenes in the presence of a nickel catalyst, 6-alkyltetralins are formed predominantly. However, in a later study by Bailey and coauthors \((^{4})\) it was found that, upon hydrogenation of 2-alkylnaphthalenes, a mixture of 2-alkyl- and 6-alkyltetralins is formed in a ratio of 1 : 2.

Therefore it was decided to carry out the synthesis of 6-alkyltetralins according to the following schemes:

\[ \begin{aligned} \mathrm{I}\quad &\text{naphthalene} \xrightarrow[\left(\mathrm{AlCl_3}\right)]{\mathrm{RCOCl}} \text{acyl naphthalene }(\mathrm{COR}) \longrightarrow \text{naphthalene-}\mathrm{CH_2R} \quad(\text{\(n\)-alkyltetralins}) \\[6pt] \mathrm{II}\quad &\text{tetralin} \xrightarrow[\left(\mathrm{AlCl_3}\right)]{\mathrm{RCOCl}} \text{acyltetralin }(\mathrm{COR}) \xrightarrow{\mathrm{R'MgX}} \text{tertiary alcohol } \left(\mathrm{-C(OH)(R)(R')}\right) \xrightarrow[\mathrm{CuO{-}Cr_2O_3}]{\mathrm{H_2}} \text{tetralin-}\mathrm{CHR} \quad(\text{\(i\)-alkyltetralins}) \end{aligned} \]

The acylation of tetralin was carried out by the Friedel—Crafts method in nitrobenzene medium, since there are indications in the literature that, when tetralin is acylated in carbon disulfide medium, 2% of the α-isomer is obtained \((^{1})\), whereas in nitrobenzene medium substitution occurs only in the β-position \((^{5})\).

In the reaction of tetralin with the acid chlorides of the corresponding acids in nitrobenzene in the presence of \(\mathrm{AlCl_3}\) at \(0^\circ\), we obtained 1, 2, 3, 4-tetrahydro-6-naphthylbutyl, -\(n\)-amyl, -\(n\)-heptyl, and -\(n\)-nonyl ketones, whose properties are given in Table 1.

Table 1

Properties of the synthesized alkyl-6-tetralyl ketones

Tertiary alcohols were synthesized by the Grignard method. On treatment of 6-tetralylheptyl ketone with \(\mathrm{CH_3MgJ}\), 8-(6-tetralyl)nonanol-8 was obtained, with b.p. 180.5—182.5 (3 mm), \(n_D^{20}\) 1.5219 and \(d_4^{20}\) 0.9728.

Found, %: C 82.84; 82.88; H 10.71; 10.71
\(\mathrm{C_{19}H_{30}O}\). Calculated, %: C 83.14; H 11.02

Fig. 2

On treatment of 6-tetralyl-\(n\)-amyl ketone with \(n\)-\(\mathrm{C_3H_7Br}\), 6-(6-tetralyl)nonanol-6 was obtained, with b.p. 162—163°(1), \(n_D^{20}\) 1.5268 and \(d_4^{20}\) 0.9764.

Found, %: C 83.25; 83.05; H 10.50; 10.30
\(\mathrm{C_{19}H_{30}O}\). Calculated, %: C 83.14; H 11.02

Figures 1 and 2 show the IR spectra of the synthesized alcohols.* The tertiary alcohols were reduced with hydrogen in an autoclave in the presence of copper chromite \((^6)\) at 120 atm and \(240^\circ\). Under these conditions, their

* The IR spectra were recorded by E. D. Lubuzh, to whom the authors express their gratitude.

partial dehydration occurred; therefore the resulting hydrogenation product was subjected to additional hydrogenation in contact with Raney Ni at 50° and a hydrogen pressure of 70 atm. The properties of the resulting 6-(1-methyloctyl)tetralin and 6-(1-n-propylhexyl)tetralin are given in Table 2.

Table 2

Properties of 6-alkyltetralins

Normal 6-amyltetralin, 6-heptyltetralin, and 6-decyltetralin were obtained by reduction of the corresponding ketones by the modified Kishner—Wolff method ($^7$): decomposition of the hydrazones with sodium in diethylene glycol.

The properties of the synthesized hydrocarbons are given in Table 2. 6-(1-Methyloctyl)tetralin, 6-(1-n-propylhexyl)tetralin, 8-(6-tetralyl)-n-nonanol-8, and 6-(6-tetralyl)-n-nonanol-6 were obtained by us for the first time. The constants of the normal alkyltetralins agree well with the literature data ($^{8,9}$).

N. D. Zelinsky Institute of Organic Chemistry
Academy of Sciences of the USSR

Received
17 XII 1959

REFERENCES

$^1$ H. Luther, G. Wachter, Ber., 82, 161 (1941).
$^2$ G. Schroeter, Ber., 54, 2242 (1921).
$^3$ G. Levy, Ann. chim., 9, 5 (1938).
$^4$ A. S. Bailey, J. C. Smith, C. M. Staveley, J. Chem. Soc., 1956, 2731.
$^5$ A. Barbot, Bull. Soc. Chim. France (4), 47, 1314 (1930).
$^6$ R. Connor, K. Folkers, H. Adkins, J. Am. Chem. Soc., 53, 1091 (1932).
$^7$ K. Huang-Minlon, J. Am. Chem. Soc., 68, 2487 (1946).
$^8$ R. T. Hart, S. A. Robinson, J. Am. Chem. Soc., 70, 3731 (1948).
$^9$ R. T. Hart, S. A. Robinson, J. Am. Chem. Soc., 72, 1249 (1950).