JP5484795B2 - 2-Benzyl-4- (3,4-dichlorophenyl) -5-methylimidazole compound - Google Patents

Description

  The present invention relates to a novel 2-benzyl-4- (3,4-dichlorophenyl) -5-methylimidazole compound.

  As an imidazole compound similar to the present invention, for example, Patent Document 1 discloses 2- (2,4-dichloro-benzyl) -5- (3,4-dichloro-phenyl) -1H-imidazole. However, this document does not disclose an imidazole compound in which a methyl group is bonded to the 4 (5) position of the imidazole ring.

Japanese translation of PCT publication No. 2003-500377 (7th page, 51st page)

  An object of the present invention is to provide a novel 2-benzyl-4- (3,4-dichlorophenyl) -5-methylimidazole compound.

  As a result of intensive studies in order to solve the above-mentioned problems, the present inventors have obtained a novel 2-benzyl-4- (3,4-dichlorophenyl) -5-methyl represented by the chemical formula (I) of Chemical Formula 1. Recognizing that an imidazole compound can be synthesized, the present invention has been completed.

（式中、Ｘ_１およびＸ_２は同一または異なって、水素原子、塩素原子もしくは臭素原子を表す。）

(In the formula, X ₁ and X ₂ are the same or different and each represents a hydrogen atom, a chlorine atom or a bromine atom.)

  The 2-benzyl-4- (3,4-dichlorophenyl) -5-methylimidazole compound of the present invention is an antioxidant on the surface of a metal, particularly copper (including a copper alloy), a curing agent or curing acceleration of an epoxy resin. It is also useful as an agent and as an intermediate material in the medical and agrochemical field.

Hereinafter, the present invention will be described in detail.
The 2-benzyl-4- (3,4-dichlorophenyl) -5-methylimidazole compound of the present invention is represented by the chemical formula (I) of Chemical Formula 2,
2-benzyl-4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (2-chlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (3-chlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (4-chlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (2,3-dichlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (2,4-dichlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (2,5-dichlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (2,6-dichlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (3,4-dichlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (3,5-dichlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (2-bromobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (3-bromobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (4-bromobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (2,3-dibromobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (2,4-dibromobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (2,5-dibromobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (2,6-dibromobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (3,4-dibromobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (3,5-dibromobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (3-bromo-2-chlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (4-bromo-2-chlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (5-bromo-2-chlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (2-bromo-6-chlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (2-bromo-3-chlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (4-bromo-3-chlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (5-bromo-3-chlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (2-bromo-5-chlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole,
2- (2-Bromo-4-chlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole and 2- (3-bromo-4-chlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole is mentioned.

（式中、Ｘ_１およびＸ_２は同一または異なって、水素原子、塩素原子もしくは臭素原子を表す。）

(In the formula, X ₁ and X ₂ are the same or different and each represents a hydrogen atom, a chlorine atom or a bromine atom.)

  The 2-benzyl-4- (3,4-dichlorophenyl) -5-methylimidazole compound of the present invention can be synthesized according to a known method. For example, as shown in the reaction formula of Chemical Formula 3, 2-position halogenated 3 ′, 4′-dichloropropiophenone compound and arylacetamidine compound are heated in an organic solvent in the presence of a dehydrohalogenating agent. It can be synthesized by reacting.

（但し、式中のＸ_１およびＸ_２は前記と同様であり、Ｘ_３は塩素原子、臭素原子またはヨウ素原子を表す。）

(However, X ₁ and X ₂ in the formula are the same as above, and X ₃ represents a chlorine atom, a bromine atom or an iodine atom.)

  In the above-mentioned reaction, the amount of the arylacetamidine compound used is preferably 0.8 to 1.5 times mol, more preferably 0. 0 to 1.5 times the 2-halogenated 3 ', 4'-dichloropropiophenone compound. What is necessary is just to set it as the ratio of 9-1.1 times mole. The amount of the dehydrohalogenating agent used is preferably a ratio of 1 to 10 times equivalent to the 2-position halogenated 3 ′, 4′-dichloropropiophenone compound.

  Examples of the 2-position halogenated 3 ′, 4′-dichloropropiophenone compound include 2-chloro-3 ′, 4′-dichloropropiophenone, 2-bromo-3 ′, 4′-dichloropropiophenone, 2-iodo-3 ', 4'-dichloropropiophenone is mentioned.

  These 2-position halogenated 3 ', 4'-dichloropropiophenone compounds are obtained by halogenating the 2-position of 3', 4'-dichloropropiophenone. As the halogenation, chlorination or iodination can be performed, but the bromination reaction in which 1 mol of bromine is reacted with 1 mol of 3 ′, 4′-dichloropropiophenone is the simplest.

  As 3 ′, 4′-dichloropropiophenone, a commercially available reagent can be used.

  The arylacetamidine compound can be obtained by reacting arylacetamidine hydrochloride and an alkaline agent to remove hydrochloric acid. In the synthesis reaction of the imidazole compound, the arylacetamidine compound is replaced with arylacetamidine compound. Amidine hydrochloride and a salt of an arylacetamidine compound and a conventionally known inorganic acid or organic acid can also be used.

  Arylacetamidine hydrochloride can be synthesized according to a known method. For example, as shown in the reaction formula of Chemical Formula 4, a benzylcyanide compound is reacted with a lower alcohol such as hydrogen chloride gas and ethanol, converted to arylacetimidate hydrochloride, and further reacted with ammonia to form an aryl. Acetamidine hydrochloride can be synthesized.

（但し、式中のＸ_１およびＸ_２は前記と同様である。）

(However, X ₁ and X ₂ in the formula are the same as above.)

As the hydrochloride of the arylacetamidine compound obtained by such a reaction,
Phenylacetamidine hydrochloride,
(2-chlorophenyl) acetamidine hydrochloride,
(3-chlorophenyl) acetamidine hydrochloride,
(4-chlorophenyl) acetamidine hydrochloride,
(2,3-dichlorophenyl) acetamidine hydrochloride,
(2,4-dichlorophenyl) acetamidine hydrochloride,
(2,5-dichlorophenyl) acetamidine hydrochloride,
(2,6-dichlorophenyl) acetamidine hydrochloride,
(3,4-dichlorophenyl) acetamidine hydrochloride,
(3,5-dichlorophenyl) acetamidine hydrochloride,
(2-bromophenyl) acetamidine hydrochloride,
(3-bromophenyl) acetamidine hydrochloride,
(4-bromophenyl) acetamidine hydrochloride,
(2,3-dibromophenyl) acetamidine hydrochloride,
(2,4-dibromophenyl) acetamidine hydrochloride,
(2,5-dibromophenyl) acetamidine hydrochloride,
(2,6-dibromophenyl) acetamidine hydrochloride,
(3,4-dibromophenyl) acetamidine hydrochloride,
(3,5-dibromophenyl) acetamidine hydrochloride,
(3-bromo-2-chlorophenyl) acetamidine hydrochloride,
(4-bromo-2-chlorophenyl) acetamidine hydrochloride,
(5-bromo-2-chlorophenyl) acetamidine hydrochloride,
(2-bromo-6-chlorophenyl) acetamidine hydrochloride,
(2-bromo-3-chlorophenyl) acetamidine hydrochloride,
(4-bromo-3-chlorophenyl) acetamidine hydrochloride,
(5-bromo-3-chlorophenyl) acetamidine hydrochloride,
(2-bromo-5-chlorophenyl) acetamidine hydrochloride,
(2-bromo-4-chlorophenyl) acetamidine hydrochloride and
(3-Bromo-4-chlorophenyl) acetamidine hydrochloride.

  Any known dehydrohalogenating agent can be used without limitation. Examples of such a dehydrohalogenating agent include inorganic alkalis such as sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, triethylamine, 1,8 -Organic bases such as diazabicyclo [5,4,0] -7-undecene (DBU), metal alkoxide compounds such as sodium methoxide, potassium tert-butoxide, and the like.

  Any known solvent can be used without limitation as long as it can dissolve the 2-position halogenated 3 ′, 4′-dichloropropiophenone compound and the arylacetamidine compound and does not participate in the reaction. . Examples of such solvents include alcohols such as isopropyl alcohol and tert-butanol, hydrocarbons such as hexane and toluene, halogenated hydrocarbons such as chloroform and chlorobenzene, esters such as ethyl acetate, and nitriles such as acetonitrile. , Ethers such as tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, amides such as N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), and the like. A combination of solvents may be used.

  The reaction temperature is preferably room temperature to reflux temperature, and the reaction time is preferably 1 to 10 hours. The reaction may be usually performed under atmospheric pressure.

The 2-benzyl-4- (3,4-dichlorophenyl) -5-methylimidazole compound produced under the above reaction conditions can be isolated by ordinary post-treatment.
For example, the reaction mixture after completion of the reaction is distributed into an aqueous layer and an organic solvent layer, the organic solvent layer is washed with water, and the organic solvent is distilled off to obtain a crude compound, and further, a recrystallization operation, etc. Can be purified.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. Reference examples 1 and 2 show synthesis examples of phenylacetamidine hydrochloride and 2-bromo-3 ', 4'-dichloropropiophenone, respectively.

[Reference Example 1]
<Synthesis of phenylacetamidine hydrochloride>
Hydrogen chloride gas 44.6 g (1.22 mol) was blown into a solution composed of 117.8 g (1.006 mol) of phenylacetonitrile and 55.8 g (1.21 mol) of dehydrated ethanol at 5 to 10 ° C. over 4 hours. It is. When the reaction solution was returned to room temperature for 1 day at 4 ° C. and allowed to stand for 2 days, a white solid ethyl phenylacetimidate hydrochloride was precipitated.
The solution of 35.6 g (2.09 mol) of ammonia and 246 g of dehydrated ethanol was added little by little while pulverizing the ethyl phenylacetimidate hydrochloride collected by filtration and shaking under ice cooling. Then, the mixture was stirred for 2 hours under ice-cooling and further returned to room temperature and stirred overnight. After filtering off the insoluble matter as a white solid, the filtrate was evaporated to dryness under reduced pressure to give pale yellow candy-like phenylacetamidine hydrochloride 172. 0.5 g (1.011 mol, yield 100.5%) was obtained.

[Reference Example 2]
<Synthesis of 2-bromo-3 ', 4'-dichloropropiophenone>
To a solution consisting of 45.8 g (0.226 mol) of 3 ′, 4′-dichloropropiophenone and 46 g of methanol, 36 g (0.2253 mol) of bromine was added dropwise over 50 minutes at 62 to 65 ° C. After cooling the reaction solution, it was distributed to 75 g of toluene and 91 g of water. The toluene layer was washed with water and dried over magnesium sulfate, and then the solvent was distilled off under reduced pressure to give 2-bromo-3 ′, 4 ′ as a pale yellowish green oil. -64.3 g (0.228 mol, yield 101.1%) of dichloropropiophenone was obtained.

[Example 1]
<Synthesis of 2-benzyl-4- (3,4-dichlorophenyl) -5-methylimidazole>
A suspension of 28.7 g (0.168 mol) of phenylacetamidine hydrochloride, 59 g (0.427 mol) of potassium carbonate and 210 ml of N, N-dimethylformamide was stirred at 50 ° C. for 30 minutes, and at the same temperature, 4-Bromo-3 ', 4'-dichloropropiophenone (48.8 g, 0.173 mol) was added little by little, and the mixture was further stirred at the same temperature for 4 hours. Next, the reaction suspension was cooled and then partitioned into 800 ml of water and 300 ml of chloroform. After the chloroform layer was washed twice with water, chloroform was distilled off under reduced pressure, and 150 ml of toluene was added to the candy-like concentrate. Crystals precipitated by heating and stirring. The precipitated crystals were collected by filtration, washed with toluene and dried to obtain a cream powder. The powder was recrystallized from acetonitrile to obtain 18.8 g (0.059 mol, yield 35.3%) of milky white powdery crystals.

The melting point of the obtained crystal, the Rf value of thin layer chromatography, ¹ H-NMR and mass spectral data were as follows.
・ Mp.158-161 ℃
・ TLC (silica gel, acetone): Rf = 0.70
・¹ H-NMR (CDCl ₃ ) δ: 2.28 (s,
3H), 3.94 (s, 2H), 7.12-7.66 (m, 7H)
・ MS m / z (%): 316 (M ⁺ , 100), 301 (3), 281 (3), 239 (4),
198 (2), 171 (4), 144 (3), 122 (9), 103 (6), 91 (8), 77 (4).
From these spectral data, the obtained compound was identified as 2-benzyl-4- (3,4-dichlorophenyl) -5-methylimidazole represented by the chemical formula of Chemical Formula 5.

[Example 2]
<Synthesis of 2- (2-chlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole>
First, (2-chlorophenyl) acetamidine hydrochloride was synthesized according to the method of Reference Example 1 by replacing phenylacetonitrile of Reference Example 1 with (2-chlorophenyl) acetonitrile.
Subsequently, a synthetic test was performed in accordance with the method of Example 1 by replacing the phenylacetamidine hydrochloride of Example 1 with (2-chlorophenyl) acetamidine hydrochloride to obtain milky white powdery crystals.

The melting point of the obtained crystal, the Rf value of thin layer chromatography, ¹ H-NMR and mass spectral data were as follows.
・ Mp. 150-152 ℃
・ TLC (silica gel, ethyl acetate): Rf = 0.58
¹ H-NMR (d ₆ -DMSO) δ: 2.38 (s,
3H), 4.09 (s, 2H), 7.27-7.80 (m, 7H)
・ MS m / z (%): 350 (M ⁺ , 23), 315 (100), 280 (3), 171 (2),
137 (3), 122 (10), 102 (4), 89 (3).
From these spectral data, the obtained compound was identified as 2- (2-chlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole represented by the chemical formula of Formula 6.

Example 3
<Synthesis of 2- (4-chlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole>
First, (4-chlorophenyl) acetamidine hydrochloride was synthesized according to the method of Reference Example 1 by replacing phenylacetonitrile of Reference Example 1 with (4-chlorophenyl) acetonitrile.
Subsequently, a synthetic test was performed in accordance with the method of Example 1 by replacing the phenylacetamidine hydrochloride of Example 1 with (4-chlorophenyl) acetamidine hydrochloride to obtain yellowish white powdery crystals.

The melting point of the obtained crystal, the Rf value of thin layer chromatography, ¹ H-NMR and mass spectral data were as follows.
・ Mp. 180-181 ℃
・ TLC (silica gel, acetone): Rf = 0.72
・¹ H-NMR (d ₆ -DMSO) δ: 2.36 (s,
3H), 3.96 (s, 2H), 7.29-7.80 (m, 7H)
MS m / z (%): 350 (M ⁺ , 100), 335 (1), 315 (14), 279 (3),
190 (3), 175 (4), 164 (4), 137 (7), 125 (10), 122 (15), 102 (8), 89 (4), 75 (3).
From these spectral data, the obtained compound was identified as 2- (4-chlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole represented by the chemical formula of formula 7.

Example 4
<Synthesis of 2- (2,4-dichlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole>
First, (2,4-dichlorophenyl) acetamidine hydrochloride was synthesized according to the method of Reference Example 1 by replacing the phenylacetonitrile of Reference Example 1 with (2,4-dichlorophenyl) acetonitrile.
Subsequently, the phenylacetamidine hydrochloride of Example 1 was replaced with (2,4-dichlorophenyl) acetamidine hydrochloride, and a synthetic test was performed according to the method of Example 1 to obtain white powdery crystals. .

The melting point of the obtained crystal, the Rf value of thin layer chromatography, ¹ H-NMR and mass spectral data were as follows.
・ Mp. 117-119 ℃
・ TLC (silica gel, acetone): Rf = 0.74
・¹ H-NMR (d ₆ -DMSO) δ: 2.36 (s,
3H), 4.07 (s, 2H), 7.33-7.77 (m, 7H)
・ MS m / z (%): 386 (M + 2, 100), 384 (M ⁺ , 31), 349 (100), 299 (3),
279 (3), 193 (4), 171 (7), 159 (9), 139 (10), 121 (6), 102 (5).
From these spectral data, the obtained compound was identified to be 2- (2,4-dichlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole represented by the chemical formula (8). .

Example 5
<Synthesis of 2- (3,4-dichlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole>
First, (3,4-dichlorophenyl) acetamidine hydrochloride was synthesized according to the method of Reference Example 1 by replacing the phenylacetonitrile of Reference Example 1 with (3,4-dichlorophenyl) acetonitrile.
Subsequently, the phenylacetamidine hydrochloride of Example 1 was replaced with (3,4-dichlorophenyl) acetamidine hydrochloride, and a synthetic test was performed according to the method of Example 1 to obtain milky white powdery crystals. .

The melting point of the obtained crystal, the Rf value of thin layer chromatography, ¹ H-NMR and mass spectral data were as follows.
・ Mp. 194-195 ℃
・ TLC (silica gel, acetone): Rf = 0.67
・¹ H-NMR (d ₆ -DMSO) δ: 2.33 (s,
3H), 3.96 (s, 2H), 7.25-7.77 (m, 6H)
・ MS m / z (%): 386 (M + 2, 100), 384 (M ⁺ , 78), 371 (1), 349 (7),
314 (9), 239 (7), 212 (3), 198 (3),
171 (7), 159 (9), 139 (10), 122 (7), 102 (4), 89 (2).
From these spectral data, the obtained compound was identified as 2- (3,4-dichlorobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole represented by the chemical formula of formula 9. .

Example 6
<Synthesis of 2- (4-bromobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole>
First, (4-bromophenyl) acetamidine hydrochloride was synthesized according to the method of Reference Example 1 by replacing phenylacetonitrile of Reference Example 1 with (4-bromophenyl) acetonitrile.
Next, the phenylacetamidine hydrochloride of Example 1 was replaced with (4-bromophenyl) acetamidine hydrochloride, and a synthetic test was performed according to the method of Example 1 to obtain white powder crystals.

The melting point of the obtained crystal, the Rf value of thin layer chromatography, ¹ H-NMR and mass spectral data were as follows.
・ Mp.207-208 ℃
・ TLC (silica gel, hexane: ethyl acetate = 1: 1): Rf = 0.43
・¹ H-NMR (d ₆ -DMSO) δ: 2.07 (s,
3H), 3.92 (s, 2H), 7.21-7.78 (m, 7H)
・ MS m / z (%): 398 (M + 4, 46), 396 (M + 2, 100), 394 (M ⁺ , 62),
361 (2), 315 (11), 299 (3), 279 (3), 239 (4),
198 (5), 183 (3), 171 (10), 140 (8), 122 (20), 102 (14), 89 (6), 75 (3).
From these spectral data, the obtained compound was identified as 2- (4-bromobenzyl) -4- (3,4-dichlorophenyl) -5-methylimidazole represented by the chemical formula of Formula 10.

Example 7
A surface treatment solution containing 2-phenylimidazole as an active ingredient separately from the imidazole compounds synthesized in Examples 1 to 6, respectively, was prepared, and a chemical film was formed on the copper surface by bringing the treatment solution into contact with copper. The anti-oxidation performance on the copper surface on which the imidazole compound acts was evaluated by measuring the wet time of the molten solder with respect to copper. In this case, it is determined that the shorter the wetting time, the better the antioxidant performance of the imidazole compound.
The details of the evaluation test are as follows.
(1) Preparation of surface treatment solution After dissolving an imidazole compound, an acid, a metal salt, and a halogen compound in ion-exchanged water so as to have the composition shown in Table 1, the pH is adjusted with ammonia water to prepare a surface treatment solution. Prepared.
(2) Surface treatment method A test piece (5 mm x 50 mm x 0.3 mm copper plate) made of metallic copper is degreased, then soft-etched, and immersed in a surface treatment solution at a predetermined temperature for a predetermined time to obtain a copper surface. After the chemical conversion film was formed on, it was washed with water and dried.
(3) Wetting time measurement The surface-treated test piece was immersed in a post-flux [trade name “JS-64MSS” manufactured by Hiroki Co., Ltd.] and solder wettability tester (SAT-2000, Inc.). Solder wetting time (seconds) was measured using Resca. The solder used was tin-lead eutectic solder (trade name: H63A, manufactured by Senju Metal Industry), and the measurement conditions were a solder temperature of 240 ° C., an immersion depth of 2 mm, and an immersion speed of 16 mm / second.
In addition, the test piece which measured the solder wetting time includes (A) a sample immediately after the surface treatment, (B) a sample left in a constant temperature and humidity chamber at a temperature of 40 ° C. and a humidity of 90% RH for 96 hours, and (C ) Further heated at 200 ° C. for 10 minutes.
The test results obtained were as shown in Table 1.

  According to the test results shown in Table 1, the surface treatment liquid containing the 2-benzyl-4- (3,4-dichlorophenyl) -5-methylimidazole compound of the present invention as an active ingredient is resistant to moisture on the surface of copper. In addition, since a chemical conversion film having excellent heat resistance can be formed, it is useful for preventing oxidation of the copper surface.

According to the present invention, 2-benzyl- useful as an antioxidant on the surface of metals, particularly copper (including copper alloys), as a curing agent or curing accelerator for epoxy resins, and as an intermediate material in the field of medicine and agrochemicals. A 4- (3,4-dichlorophenyl) -5-methylimidazole compound can be provided.

Claims (1)

A 2-benzyl-4- (3,4-dichlorophenyl) -5-methylimidazole compound represented by the chemical formula (I) of Chemical Formula 1.

(In the formula, X ₁ and X ₂ are the same or different and each represents a hydrogen atom, a chlorine atom or a bromine atom.)