Electrophilic substitution in the aromatic series. The iodination reaction
Abstract Generated abstract
This paper examines direct electrophilic iodination of aromatic compounds using elemental iodine in a mixed sulfuric and nitric acid system. The method was tested on hydrocarbons, ketones, ethers, carboxylic acids, and keto acids, with reaction conditions, yields, and melting points reported for mono and diiodinated products. Fluorene, fluorenone, fluorene and fluorenone carboxylic acids, phenanthrenequinone, phenylacetic acid, anisole, diphenyl ether, and benzophenone underwent iodination under controlled conditions, while acetophenone derivatives reacted at the acetyl side chain rather than the aromatic ring. Several iodinated fluorene and fluorenone carboxylic acid derivatives not previously described were characterized by UV and IR spectroscopy, chemical transformations, and comparison with independently synthesized compounds.
Full Text
ELECTROPHILIC SUBSTITUTION IN THE AROMATIC SERIES.
IODINATION REACTION
V. T. Slyusarchuk, A. N. Novikov
(Presented by the Scientific Seminar of the Organic Departments of the Chemical-Technological Faculty)
The method previously developed by us for the electrophilic substitution of a hydrogen atom by iodine in the presence of a mixed sulfuric–nitric acid system (1–5) has been tested in the present work on a large number of compounds of the aromatic series belonging to hydrocarbons, ketones, ethers, carboxylic acids, and keto acids. The fluorene, fluorenone, fluorene-5-carboxylic acid, fluorenone-5-carboxylic acid, phenanthrenequinone, phenylacetic acid, anisole, and benzophenone chosen for study are readily iodinated under mild conditions by elemental iodine in the presence of the nitrating mixture to give the corresponding monoiodo and diiodo derivatives. Acetophenone and 4-acetyldiphenyl, under analogous conditions, are not converted into products of substitution by iodine in the benzene ring. The acetyl radical is attacked by iodine, with formation of a compound containing iodine in the side chain, which under the conditions of iodination is oxidized and gives a carboxylic acid.
Some of the iodinated derivatives obtained by us have not been described in the literature; the known ones were synthesized by the classical method through the Sandmeyer reaction [6–9] from amino compounds or by direct iodination in the presence of fuming nitric or iodic acid.
The structures of the substances obtained for the first time were determined from spectroscopic data, chemical transformations into described compounds, and mixed syntheses.
Experimental part
The starting compound, finely ground iodine, glacial acetic acid, and carbon tetrachloride were introduced into a round-bottom flask equipped with a reflux condenser, dropping funnel, and stirrer (in cases where the reaction proceeded above 40°C).
The flask was placed in a bath heated to the specified temperature, and then, with vigorous mechanical stirring, a mixture consisting of nitric acid, \(d\ 1.4\), and sulfuric acid, \(d\ 1.83\text{–}1.84\), was added dropwise.
After completion of the reaction, the mixture was cooled, diluted with water, and the precipitate was filtered off, washed, and recrystallized from the appropriate solvent until its melting point remained constant. Under strictly controlled conditions, oxidation and nitration products are not formed.
Table 1
| Starting substance: name | Starting substance: quantity, g | Iodine, g | Acetic acid, ml | Nitric acid, ml | Sulfuric acid, ml | Reaction temperature, °C | Reaction time, h | Product: name | Yield, % | m.p., °C |
|---|---|---|---|---|---|---|---|---|---|---|
| Fluorene | 4,2 | 3,15 | 125 | 0,5 | 2 | 20—25 | 1 | 2-Iodofluorene | 45 | 126—127 |
| Fluorene | 4,2 | 6,34 | 100 | 0,8 | 4 | 40—45 | 0,5 | 2,7-Diiodofluorene | 50 | 213,5 |
| Fluorenone | 2,25 | 1,6 | 25 | 0,5 | 2,5 | 45—50 | 1 | 2-Iodofluorenone | 60 | 150—151 |
| Fluorenone | 4,5 | 6,34 | 50 | 2 | 10 | 100 | 1 | 2,7-Diiodofluorenone | 75 | 199—200 |
| Fluorenonecarboxylic acid-5 | 5,6 | 3,15 | 150 | 4 | 15 | 100 | 3 | 2-Iodofluorenonecarboxylic acid-5 | 60 | 237 |
| 2-Iodofluorenonecarboxylic acid-5 | 7 | 2,54 | 250 | 8 | 17 | 120 | 3 | 2,7-Diiodofluorenonecarboxylic acid-5 | 50 | 320—321 |
| Fluorenecarboxylic acid-5 | 4,2 | 5,08 | 100 | 1 | 4 | 35—40 | 0,5 | 2-Iodofluorenecarboxylic acid-5 | 40—45 | 251—252 |
| Phenanthrenequinone | 4 | 2,54 | 50 | 2 | 5 | 85—90 | 4 | 2-Iodophenanthrenequinone | 25 | 220—221 |
| Phenanthrenequinone | 4 | 5 | 150 | 6 | 18 | 113 | 12 | 2,7-Diiodophenanthrenequinone | 50 | 310 |
| Anisole | 5,4 | 6,35 | 50 | 1 | 2 | 10 | 2 | 4-Iodoanisole | 20—25 | 51 |
| Anisole | 5,4 | 12,7 | 50 | 3 | 12 | 20 | 2 | 2,4-Diiodoanisole | 45 | 68—69 |
| Diphenyloxide | 34 | 25,4 | 60 | 4 | 10 | 20 | 0,5 | 4-Iododiphenyloxide | 25 | 43—44 |
| Diphenyloxide | 17 | 25,4 | 50 | 5 | 11 | 25 | 1 | 4,4′-Diiododiphenyloxide | 65 | 140—141 |
| Phenylacetic acid | 34 | 32 | 80 | 7,5 | 28 | 50 | 2 | 4-Iodophenylacetic acid | 30—35 | 134—135 |
| Benzophenone | 4,5 | 3,17 | 30 | 3 | 10 | 90—100 | 1 | 3,3-Diiodobenzophenone | 40—45 | 123—124 |
The conditions under which the reactions were carried out, the products, their yields, and melting points are given in Table 1.
Determination of the structure of compounds not previously described. 2,7-Diiodofluorenone was obtained from fluorenone via the 2,7-dinitro, diamino, and diazonium compounds. The melting point of a mixed sample
Fig. 1. IR spectra in Vaseline oil. Bands of NaCl. 1—2-iodofluorene, 2—2,7-diiodofluorene, 3—2-iodofluorenone, 4—2,7-diiodofluorenone, 5—2-iodofluorenonecarboxylic acid-5,6—2,7-diiodofluorenonecarboxylic acid-5, 7—2-iodofluorenecarboxylic acid-5, 8—2,7-diiodophenanthrenequinone, 9—2-iodophenanthrenequinone.
with diiodofluorenone synthesized by direct iodination showed no depression.
2,7-Diiodofluorene was converted by oxidation with sodium dichromate into 2,7-diiodofluorenone, identical in mixed-sample melting point with the diiodofluorenone obtained by direct iodination.
To determine the structure of diiodofluorenonecarboxylic-5-acid, the latter was obtained by counter synthesis from phenanthrenequinone according to the reaction:
\[ \text{[[chemical scheme: phenanthrenequinone + I_2 \rightarrow iodinated phenanthrenequinone; oxidation with CrO_3 to a diiododicarboxylic acid; cyclization in H_2SO_4 to diiodofluorenonecarboxylic-5-acid]]} \]
Both acids are identical. The UV and IR spectra of the compounds obtained are presented.
Fig. 2. UV spectra in heptane. 1—2-iodofluorene, 2—2,7-diiodofluorene, 3—2-iodofluorenone, 4—2,7-diiodofluorenone, 5—2-iodofluorenonecarboxylic-5 acid, 6—2,7-diiodofluorenonecarboxylic-5 acid.
Conclusions
- By direct iodination in the presence of a sulfuric–nitric acid mixture, the following were obtained: 4-iodophenylacetic acid, 4-iododiphenyl ether, 4,4′-diiododiphenyl ether, 4-iodoanisole, 2,4-diiodoanisole, 3,3′-diiodobenzophenone, 2-iodofluorene, 2,7-diiodofluorene, 2-iodofluorenone, 2,7-diiodophenanthrenequinone, 2-iodophenanthrenequinone, 2,7-diiodofluorenone, 2-iodofluorenecarboxylic-5 acid, 2-iodofluorenonecarboxylic-5 acid, and 2,7-diiodofluorenonecarboxylic-5 acid. The last five compounds have not been described in the literature.
- UV and IR spectra of the compounds obtained were recorded.
REFERENCES
- B. V. Tronov, A. N. Novikov. ZhOKh, 23, 1124 (1953).
- A. N. Novikov, ZhOKh, 24, 655 (1954).
- B. V. Tronov, A. N. Novikov. Izv. VSh, Chemistry and Chemical Technology, 3, 872 (1960).
- A. N. Novikov, T. A. Khalimova. ZhVKhO named after D. I. Mendeleev, 7, 234 (1962).
- A. N. Novikov, T. A. Khalimova. USSR Author’s Certificate No. 162518; Bull. Inventions, No. 10 (1964).
- Beilst., 11 Erd., 5, 535 (1943).
- Ch. Abstr., 4971⁵ (1938).
- Beilst., 11 Erd., 7, 409 (1948).
- R. D. Desei, R. H. Kundel. Ch. Abstr., 9849ᵃ (1952).