Some Results of Comparing the Effects of Different Catalysts in the Gustavson-Friedel-Crafts Reaction
Abstract Generated abstract
This study compares the behavior of aluminum chloride, ferric chloride, and antimony pentachloride as catalysts in selected Gustavson-Friedel-Crafts reactions of benzene with benzoyl chloride and ethyl nitrate, with additional experiments on benzene, butyl chloride, and antimony pentachloride. Product yields were measured at varying catalyst concentrations to distinguish stoichiometric from genuinely catalytic behavior and to assess when antimony pentachloride instead chlorinates benzene. The results indicate that ferric chloride and antimony pentachloride can act catalytically in acylation and related reactions, while aluminum chloride often gives less than one mole of product per mole of catalyst, and that chlorination by antimony pentachloride is suppressed when it is bound in complexes with the organic reagent. The authors interpret these observations in terms of two possible mechanisms, parallel and sequential activation of reactants by catalyst complexes.
Full Text
Some Results of Comparing the Effects of Various Catalysts in the Gustavson—Friedel—Crafts Reaction
B. V. Tronov, A. M. Petrova
For all processes united under the name of the Gustavson—Friedel—Crafts synthesis, the common feature is the use of a group of catalysts known as very active complex-forming agents of the electron-acceptor type. These include AlCl₃, FeCl₃, SnCl₄, SbCl₅, BF₃, HF, H₂SO₄, and others.
Most investigators see the reason for the action of these catalysts in their ability to give complex compounds either with benzene or with the reagent acting on benzene. However, on the question of exactly which complexes arise here and in what order the complex-formation reactions proceed, opinions differ.
The main reason for the disagreement should be considered to be the diversity of processes covered by a single name.
The principal aim of the present work is a more precise elucidation of the mechanism of some of the Gustavson—Friedel—Crafts synthesis reactions, with clarification of the order of formation of complexes.
To achieve this aim we took reagents with different directions of action, namely alkylating agents (butyl chloride) and acylating agents (benzoyl chloride and ethyl nitrate), as well as catalysts of different structure and properties. The reacting mixtures were heated in a water bath for 4 hours [1, 2].
The alkylating or acylating agent and benzene were taken in molecular ratios of 1 to 4.
The results of the experiments are summarized in the tables.
Table 1
| No. of experiments | Reagent | Moles of reagent per mole of C₆H₆ | Catalyst, moles per 1 mole of C₆H₆ | % yield (calculated on benzoyl chloride), AlCl₃ | % yield (calculated on benzoyl chloride), SbCl₅ | % yield (calculated on benzoyl chloride), FeCl₃ | % yield (calculated on catalyst), AlCl₃ | % yield (calculated on catalyst), SbCl₅ | % yield (calculated on catalyst), FeCl₃ |
|---|---|---|---|---|---|---|---|---|---|
| 1 | Benzoyl chloride | 0.250 | 0.250 | 92.5 | 78.9 | 92.1 | 92.5 | 78.9 | 92.1 |
| 2 | ″ ″ | 0.250 | 0.125 | 32.4 | 53.0 | 78.2 | 65.5 | 106.0 | 158.0 |
| 3 | ″ ″ | 0.250 | 0.06 | 21.7 | 70.9 | 38.7 | 87.6 | 288.7 | 156.0 |
| 4 | ″ ″ | 0.250 | 0.03 | 6.9 | 35.1 | 39.4 | 42.9 | 283.0 | 316.0 |
| 5 | ″ ″ | 0.250 | 0.015 | 3.5 | 9.6 | 19.4 | 56.3 | 157.0 | 311.0 |
Table 2
| Experiment Nos. | Reagent | Moles of reagent per 1 mole of \(C_6H_6\) | Catalyst, moles per 1 mole of \(C_6H_6\) | % yield (calculated on ethyl nitrate), \(AlCl_3\) | % yield (calculated on ethyl nitrate), \(SbCl_5\) | % yield (calculated on ethyl nitrate), \(FeCl_3\) | % yield (calculated on catalyst), \(AlCl_3\) | % yield (calculated on catalyst), \(SbCl_5\) | % yield (calculated on catalyst), \(FeCl_3\) |
|---|---|---|---|---|---|---|---|---|---|
| 1 | Ethyl nitrate | 0.250 | 0.250 | 96.7 | 92.2 | 90.9 | 96.7 | 92.2 | 90, [[unclear: final digit not visible]] |
| 2 | Ethyl nitrate | 0.250 | 0.125 | 81.0 | 77.2 | 57.0 | 161.8 | 154.5 | 114.0 |
| 3 | Ethyl nitrate | 0.250 | 0.06 | 29.2 | 42.2 | 23.6 | 118.0 | 171.0 | 94.8 |
| 4 | Ethyl nitrate | 0.250 | 0.03 | 13.7 | 25.9 | 24.6 | 110.0 | 205.0 | 196.0 |
| 5 | Ethyl nitrate | 0.250 | 0.015 | 6.04 | 13.0 | 10.7 | 105.0 | 200.0 | 183, |
It is known that antimony pentachloride vigorously chlorinates benzene, giving chlorobenzene and antimony trichloride [3]. If three components are taken, for example: benzene, \(SbCl_5\), and butyl chloride, benzoyl chloride, or ethyl nitrate, then chlorination is not observed. Evidently, some complexes are formed which bind the antimony pentachloride and do not allow it to chlorinate benzene. To verify at what ratios of the three components taken the chlorination process begins, we carried out the following experiments (Table 3).
Table 3
| No. | Reagents | In grams | Benzene, g | \(SbCl_5\), g | Molar ratios of reagents: benzene : catalyst | % yield of chlorobenzene |
|---|---|---|---|---|---|---|
| 1 | Butyl chloride | 30.84 | 59.6 | 94.7 | 1 : 2 : 0.95 | 1.77 |
| 2 | Butyl chloride | 46.26 | 89.5 | 194.41 | 1 : 2 : 1.3 | 31.2 |
| 3 | Ethyl nitrate | 22.76 | 44.75 | 71.02 | 1 : 2 : 0.95 | — |
| 4 | Ethyl nitrate | 18.21 | 35.8 | 77.2 | 1 : 2 : 1.3 | 43.4 |
| 5 | Benzoyl chloride | 35.1 | 44.7 | 71.02 | 1 : 2 : 0.95 | — |
| 6 | Benzoyl chloride | 28.11 | 35.8 | 77.2 | 1 : 2 : 1.3 | 29.4 |
Discussion of Results
The experiments we carried out with benzene and benzoyl chloride at different amounts of aluminum chloride, ferric chloride, and antimony pentachloride showed that with aluminum chloride the yield of ketone, calculated on the aluminum chloride taken, was always less than 100%, whereas with ferric chloride and antimony pentachloride the yield, by the same calculation, reached 316.0 and 283%, i.e., the process is truly catalytic. At the molar ratio \(0.5 : 2 : 0.125\), the activity of the catalysts is as follows:
\[ SbCl_5 > FeCl_3 > AlCl_3. \]
In the reaction with ethyl nitrate, antimony pentachloride also proved to be a good catalyst. At the same time, with aluminum chloride the yield of reaction products is sometimes more than 1 mole per mole of \( \mathrm{AlCl_3} \).
The reaction of benzene with benzoyl chloride and ethyl nitrate in the presence of ferric chloride also proved to be truly catalytic; i.e., the difference in the action of aluminum and antimony chlorides is explained not by the fact that aluminum chloride is dimeric and antimony pentachloride monomeric, but by another cause, most probably by the different strength of the complexes of these chlorides with the reaction products.
In experiments with butyl chloride, chlorination of benzene proceeded to a significant extent only when the amount of antimony pentachloride exceeded one molecule per molecule of \( \mathrm{C_4H_9Cl} \). This indicates the formation of a complex of composition \( \mathrm{C_4H_9Cl \cdot SbCl_5} \), i.e., probably one built analogously to complexes of aluminum halides. Such a complex may quite well dissociate into the ions \( (\mathrm{C_4H_9})^+(\mathrm{SbCl_6})^- \). Alkylation of benzene does not occur here, since the molecule of antimony pentachloride cannot activate the benzene ring owing to the rapidly occurring chlorination.
\[ \mathrm{C_6H_6 \cdot SbCl_5 \rightarrow C_6H_5Cl + HCl + SbCl_3.} \]
The observed regularities can be explained on the basis of the concept of activation by the catalyst of benzene and of the other reagent (a haloorganic compound, an acid halide, a simple or complex ester, etc.). This dual activation may be parallel or sequential. In the first case one molecule of catalyst adds to benzene, loosening the carbon–hydrogen bond; another molecule adds to the haloorganic compound, ester, etc., loosening in it the bond of the hydrocarbon radical with the halogen or oxygen; then replacement of hydrogen by alkyl occurs. In the second case the catalyst adds only to the acid halide, ester, etc., and the complex formed is then attracted to the carbon atom of benzene. In the resulting ternary compound the complex bond becomes a valence bond, with hydrogen being eliminated together with the halogen or the corresponding group of atoms of the ester, etc.
Conclusions
The reaction of benzene with benzoyl chloride and ethyl nitrate in the presence of chlorides of aluminum, iron, and antimony at different amounts of the catalysts has been studied. For comparison, the action of antimony pentachloride on a mixture of benzene with butyl chloride was also investigated.
- A conclusion has been drawn regarding two principal mechanisms of the Gustavson–Friedel–Crafts synthesis—with parallel activation of the reagents by the catalyst and with sequential activation. It has been shown that the type of activation can easily be determined with the aid of antimony pentachloride.
Literature
- Tronov B. V. and Petrova A. M. ZhOKh 23, 1019, 1953.
- Petrova A. M. ZhOKh 24, 491, 1954.
- A. Rosenheim. Berichte der Deutschen Chemischen Gesellschaft 34, 3383, 1901.