Abstract Generated abstract
This paper describes the preparation of pure 6-alkyltetralins needed as standards for infrared spectroscopic analysis of tetralin alkylation products, addressing the difficulty of separating isomeric mixtures formed by direct Friedel-Crafts alkylation. The authors synthesized normal 6-amyltetralin, 6-heptyltetralin, and 6-decyltetralin through Friedel-Crafts acylation of tetralin in nitrobenzene followed by modified Kishner-Wolff reduction, and prepared branched 6-alkyltetralins via Grignard addition to 6-tetralyl ketones and subsequent catalytic hydrogenation. Physical constants, elemental analyses, and infrared spectra are reported for the intermediates and products. The work provides new syntheses of 6-(1-methyloctyl)tetralin, 6-(1-n-propylhexyl)tetralin, and two corresponding tertiary alcohol intermediates, while the constants of the normal homologs agree with published data.
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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
| Ketones | b.p., °C/mm | \(d_4^{20}\) | \(n_D^{20}\) | C, % calculated | C, % found | H, % calculated | H, % found | Yield, % |
|---|---|---|---|---|---|---|---|---|
| tetralyl—\(\mathrm{COC_4H_9}\) | 201/15 | 1.0090 | 1.5406 | 83.28 | 83.01 82.89 |
9.32 | 9.24 9.28 |
60.6 |
| tetralyl—\(\mathrm{COC_5H_{11}}\) | 167—168/2 | 0.9986 | 1.5358 | 83.42 | 83.28 83.20 |
9.61 | 9.77 9.91 |
66.0 |
| tetralyl—\(\mathrm{COC_6H_{13}}\) | 183—185/4 | 0.9844 | 1.5319 | 83.55 | 83.15 83.20 |
9.90 | 9.82 9.97 |
61.6 |
| tetralyl—\(\mathrm{COC_7H_{15}}\) | 191—192/4 | 0.9789 | 1.5282 | 83.66 | 83.63 83.61 |
10.14 | 10.18 10.36 |
81.6 |
| tetralyl—\(\mathrm{COC_9H_{19}}\) | 199—200.5/3 | 0.9655 | 1.5218 | 83.86 | 83.45 83.40 |
10.56 | 10.70 10.43 |
60.7 |
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
| Alkyltetralins | B.p., °C/mm | $n_D^{20}$ | $d_4^{20}$ | $MR_D$, calc. | $MR_D$, found | C, %, calc. | C, %, found | H, %, calc. | H, %, found |
|---|---|---|---|---|---|---|---|---|---|
| 6-$\mathrm{C_5H_{11}}$-tetralin | 124—125.5/3 | 1.5184 | 0.9236 | 65.67 | 66.42 | 89.02 | 88.63; 88.70 | 10.98 | 10.87; 10.97 |
| 6-$\mathrm{C_7H_{15}}$-tetralin | 162—163/4 | 1.5128 | 0.9142 | 74.91 | 75.74 | 88.62 | 87.97; 87.91 | 11.38 | 11.75; 11.89 |
| 6-$\mathrm{C_{10}H_{21}}$-tetralin | 185.5—186.5/4 | 1.5060 | 0.9045 | 88.76 | 89.21 | 88.15 | 88.36; 88.20 | 11.85 | 11.47; 11.40 |
| 6-$\mathrm{CH(CH_3)C_7H_{15}}$-tetralin | 157/4 | 1.5079 | 0.9077 | 84.14 | 84.80 | 88.29 | 88.30 | 11.71 | 11.71 |
| 6-$\mathrm{CH(C_3H_7)C_5H_{11}}$-tetralin | 145—145.5/4 | 1.5110 | 0.9112 | 84.14 | 84.87 | 88.29 | 88.40 | 11.71 | 11.51 |
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
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