Activity of Halogens in Some Derivatives of Benzene Hydrocarbons with a Halogen in the Side Chain
Abstract Generated abstract
This study compares the reactivity of side chain halogens in several benzene derivatives, including benzyl chloride, benzal chloride, benzotrichloride, benzyl bromide, and halogenated benzyl cyanides. Equimolar reactions were followed in pyridine, in benzene solution, and with sodium methylate in methanol, with rates estimated from the formation of ionized halide precipitated as silver halide. The results indicate that bromides react far more rapidly than corresponding chlorides, that accumulation of chlorine atoms on the benzylic carbon tends to reduce halogen activity, and that a cyano group appears to increase bromine activity while decreasing chlorine activity. Sodium methylate was found, under the stated conditions, to be a much stronger reagent toward these halogen compounds than pyridine.
Full Text
B. V. Tronov and N. Kh. Sibgatullin
Activity of Halides in Certain Derivatives of Benzene Hydrocarbons with a Halide in the Side Chain
(Work carried out with funds from the Committee for Chemization and Osoaviakhim).
For testing the activity of the halide, the following were taken:
\[ \mathrm{C_6H_5 \cdot CH_2Cl,\quad C_6H_5 \cdot CHCl_2,\quad C_6H_5 \cdot CCl_3,\quad C_6H_5 \cdot CH_2Br,\quad C_6H_5 \cdot CHCl \cdot CN,} \]
\[ \mathrm{C_6H_5 \cdot CHBr \cdot CN.} \]
The last two compounds were obtained by chlorination and bromination of benzyl cyanide; their purity was checked by analysis for halide. The remaining substances were taken ready-made (Kahlbaum preparations, which were distilled before use).
The experiments were set up with pyridine in benzene solution and with sodium methylate in methyl alcohol. The reacting components were taken in equimolecular ratios and at a concentration of 1 gram-molecule per liter. Temperature: 18°–20°.
It was not possible to carry out the reaction with the alcoholate precisely with the most interesting compounds—benzyl cyanide halides. They can enter into interaction with \(\mathrm{CH_3ONa}\) not only by their halide, but also by the CN group, which would completely obscure the picture; even if an excess of methylate is taken, the result of the experiment still will not give an idea of the activity of the substance originally taken, since the halide will be split off already from the addition product.
The rate of reaction was measured by the usual method. After addition of water and removal with benzene of the unreacted halogen derivative, the ionized halide was precipitated with \(\mathrm{AgNO_3}\).
The results of the experiments are expressed in Tables 1 and 2. In polyhalogen compounds, the calculation of percentages was carried out per one halogen atom.
Table 1.
Experiments with pyridine.
| Halogen compound | 3 days | 7 days | 15 days | |
|---|---|---|---|---|
| \(\mathrm{C_6H_5 \cdot CH_2Cl}\) | Duration of exp. | 3 days | 7 days | 15 days |
| \(\mathrm{C_6H_5 \cdot CH_2Cl}\) | % | 0.7% | 1.4% | 8.2% |
| \(\mathrm{C_6H_5 \cdot CHCl_2}\) | Duration of exp. | 3 days | — | 15 days |
| \(\mathrm{C_6H_5 \cdot CHCl_2}\) | % | 1.4% | — | 2% |
| Compound | ||||||
|---|---|---|---|---|---|---|
| $C_6H_5\cdot CCl_3$ | Duration of exp. | — | 7 days | 15 days | ||
| % | — | 1.2% | 1.5% | |||
| $C_6H_5\cdot CH_2Br$ | Duration of exp. | 3 min. | 15 min. | 1 h. | 3 h. | 6 h. |
| % | 0.44% | 2% | 4.8% | 12.9 | 17.8 | |
| $C_6H_5\cdot CHCl\cdot CN$ | Duration of exp. | 1 day | 3 days | 7 days | ||
| % | 0.5% | 0.85 | 0.93 | |||
| $C_6H_5\cdot CHBr\cdot CN$ | Duration of exp. | 3 min. | 15 min. | 30 min. | ||
| % | 2% | 3.8 | 6.2 | |||
| Duration of exp. | 1 h. | 3 h. | 6 h. | |||
| % | 7.6% | 13.4 | 19.9 |
Table 2.
Experiments with $CH_3ONa$
| Compound | |||||
|---|---|---|---|---|---|
| $C_6H_5\cdot CH_2Cl$ | Duration of exp. | 1 h. | 6 h. | 24 h. | 72 h. |
| % | 7.3% | 23.9 | 52.6 | 73.1 | |
| $C_6H_5\cdot CHCl_2$ | Duration of exp. | 1 h. | — | 24 h. | 72 h. |
| % | 3.9% | — | 5.9 | 7.1 | |
| $C_6H_5\cdot CCl_3$ | Duration of exp. | 1 h. | — | 24 h. | 72 h. |
| % | 6.2% | — | 8.2 | 10.1 | |
| $C_6H_5\cdot CH_2Br$ | Duration of exp. | 0.5 min. | 3 min. | 15 min. | 1 h. |
| % | 16% | 23.5 | 45.4 | 72.1 |
The relative activity was calculated from the time in which one percent of the substance reacts. The numbers obtained are compared in Tables 3 and 4. The rate of reaction of benzyl bromide with pyridine is taken as unity. In the experiments with sodium methylate, a second unit was also taken (the numbers in parentheses)—the rate of interaction of $C_6H_5\cdot CH_2Cl$ with $CH_3ONa$.
Table 3.
Relative reaction rates with pyridine.
| Halogen compound | Relative reaction rate at: 1% | 2% | 3% | 4% | 5% | 10% | 15% | 20% |
|---|---|---|---|---|---|---|---|---|
| $C_6H_5\cdot CH_2Cl$ | $1.5\cdot 10^{-3}$ | $1.7\cdot 10^{-3}$ | $2.4\cdot 10^{-3}$ | $2.8\cdot 10^{-3}$ | $3.3\cdot 10^{-3}$ | $5.1\cdot 10^{-3}$ | — | — |
| $C_6H_5\cdot CHCl_2$ | $2.9\cdot 10^{-3}$ | $0.8\cdot 10^{-3}$ | — | — | — | — | — | — |
| $C_6H_5\cdot CCl_3$ | $9.8\cdot 10^{-4}$ | $5.8\cdot 10^{-4}$ | — | — | — | — | — | — |
| $C_6H_5\cdot CH_2Br$ | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| $C_6H_5\cdot CHCl\cdot CN$ | $8\cdot 10^{-4}$ | — | — | — | — | — | — | — |
| $C_6H_5\cdot CHBr\cdot CN$ | — | 3.5 | 2.8 | 2.4 | 2.2 | 1.5 | 1.2 | 17 |
Table 4.
Relative reaction rate with \(CH_3ONa\)
| Halogen compound | Relative reaction rate at 4% | 5% | 10% | 15% | 20% | 30% | 40% | 50% |
|---|---|---|---|---|---|---|---|---|
| \(C_6H_5 \cdot CH_2Cl\) | 2.2 | 2.1 | 2.05 | 29 | — | — | — | |
| (1) | (1) | (1) | (1) | (1) | (1) | (1) | ||
| \(C_6H_5 \cdot CHCl_2\) | 0.58 | 0.23 | 0.015 | — | — | — | — | — |
| — | (0.1) | (0.007) | — | — | — | — | — | |
| \(C_6H_5 \cdot CCl_3\) | — | 1.15 | 0.03 | — | — | — | — | — |
| — | (0.5) | (0.014) | — | — | — | — | — | |
| \(C_6H_5CH_2Br\) | — | — | — | 524 | — | — | — | — |
| — | — | — | (256) | (139) | (76) | (68) | (67) |
Table 5.
CONCLUSIONS.
1) Influence of the nature of the halide.
| Halogen compound | Relative activity 0–5% | 5–20% | 15% | 20% | 30% | 40% | 50% |
|---|---|---|---|---|---|---|---|
| \(C_6H_5 \cdot CH_2Br : C_6H_5 \cdot CH_2Cl\) (with pyridine) |
435 | 235 | — | — | — | — | — |
| \(C_6H_5 \cdot CHBrCN : C_6H_5CHClCN\) (with pyridine) |
1000 | — | — | — | — | — | — |
| \(C_6H_5 \cdot CH_2Br : C_6H_5 \cdot CH_2Cl\) (with \(CH_3ONa\)) |
— | — | 256 | 139 | 76 | 68 | 67 |
2) Influence of the accumulation of halide atoms.
Here too few experiments have so far been carried out, and their results fluctuate. In general, comparing \(C_6H_5 \cdot CH_2Cl\), \(C_6H_5 \cdot CHCl_2\), and \(C_6H_5 \cdot CCl_3\), it may be said that the accumulation of chlorine atoms in one unit adjacent to the benzene ring decreases the activity both with respect to amines and with respect to alcoholates.
Table 6.
3) Effect of the CN group.
| Halogen compound | Relative activity in pyridine: 1% | Relative activity in pyridine: up to 5% | Relative activity in pyridine: 5–10% | Relative activity in pyridine: 10–15% |
|---|---|---|---|---|
| \( \mathrm{C_6H_5 \cdot CHCl \cdot CN : C_6H_5 \cdot CH_2Cl} \) | 0.5 | — | — | — |
| \( \mathrm{C_6H_5 \cdot CHBr \cdot CN : C_6H_5 \cdot CH_2Br} \) | — | 2.7 | 1.85 | 1.35 |
The CN group exerts a directly opposite effect on different halides. The activity of bromine increases noticeably, while the activity of chlorine decreases.
4) Effect of the nature of the reagent acting on the halogen compound.
Under the conditions of our experiments, i.e., in solutions of concentration 1 N (with \( \mathrm{C_5H_5N} \) in benzene and \( \mathrm{CH_3ONa} \) in methyl alcohol), sodium methylate proves to be a many times stronger reagent. It is still difficult to derive quantitative ratios, since entirely different percentage ranges are involved.