Selective water-based oxychlorination of phenol with hydrogen peroxide catalyzed by manganous sulfate

Abstract

An efficient method for the selective oxychlorination of phenol to 2,4-dichlorophenol catalyzed by manganous(II) sulfate is developed using hydrogen chloride as a chlorinating source, hydrogen peroxide as an oxidant and water as a solvent. The catalyst has high activity and selectivity under mild conditions. The products are automatically isolated from aqueous solution, which also contains the catalyst at the end of the reaction, and hence product separation and catalyst recycling are both simple in this system. The performance of manganous(II) sulfate with the oxidative chlorinating system HCl/H₂O₂ indicates that this is a promising synthetic method for the manufacture of various 2,4-dichlorophenol derivatives.

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Chlorination of phenols is a key synthetic method because chloro-substituted phenols are essential materials in the synthesis of herbicides, pharmaceuticals, insecticides, dyes, etc.^1,2 Among the various chloro-substituted phenols, main products include p-chlorophenol, o-chlorophenol, 2,4-dichlorophenol, 2,6-dichlorophenol and 2,4,6-trichlorophenol, which belong to a group named “light chlorophenols”.³ In this group, 2,4-dichlorophenol is the most important material since it is an intermediate for 2,4-dichlorophenoxyacetic acid, a herbicide that is widely used in crops, rice and other massive cultivations. Traditional methods for the synthesis of 2,4-dichlorophenol usually involve electrophilic aromatic chlorination of phenol with chlorine gas (Scheme 1).^3–5 However, the utilization of chlorine atoms in these processes is quite low, nearly half of the chlorine is released as waste gas, which results in a waste of material and environment hazards.^6,7

Scheme 1 Traditional methods for the synthesis of 2,4-dichlorophenol.

An alternative solution is oxidative chlorination, i.e. oxychlorination, which uses chloride anions as a chlorine source in the presence of an oxidant (Scheme 2).^7–12 In these systems, chloride anions are oxidized to chlorine by the oxidant and subsequently incorporated into the products. In general, chlorinating agents, such as sulfuryl chloride,^4,13 N-chlorosuccinimide,^11,12 copper chloride,^14–16 titanium tetrachloride¹⁷ and p-toluene sulfonyl chloride,¹⁸ are used as chlorine sources, and reagents like sulfuric acid,¹⁹ perchloric acid,^12,20 lithium diisopropylamide,¹⁸ dimethylsulfoxide,²¹ etc.²² are employed as oxidants. While the utilization of chlorine atoms in oxychlorination is remarkably increased compared to only half in traditional methods, further research is still required to use cheaper and environmentally friendly reagents.

Scheme 2 Oxychlorination for the synthesis of 2,4-dichlorophenol.

Compared with most studies focused on the synthesis of monochloro-substituted phenols,^4,23–28 the oxychlorination of phenols to 2,4-dichlorophenols is rather limited so far.^3,20,29 For example, Gusevskaya et al. reported a method for aerobic oxychlorination of phenols over a CuCl₂ catalyst, in which metal chlorides were used as chlorinating agents.^30,31 Feng et al. found a microwave method for aerobic oxychlorination of phenols catalyzed by CuCl₂ with hydrochloric acid as a chlorine source.²³ However, these methods are exploited for the synthesis of p-chlorophenols. Notably, Ratnasamy et al. developed a promising method for the oxychlorination/oxybromination of aromatics including phenols over copper phthalocyanines encapsulated in zeolites with HCl and alkali chlorides/bromides as halogen sources and dioxygen and hydrogen peroxide as oxidants,³² but the selectivity for 2,4-dichloroaromatics was low. Moreover, VOCs (volatile organic compounds) are usually present in these systems (Scheme 3).

Scheme 3 Oxychlorination for the synthesis of 2,4-dichlorophenol with environmentally friendly oxidants.

As for oxychlorination, we consider a desirable route for the chlorination of phenols with HCl using environmentally friendly oxidants, such as dioxygen or hydrogen peroxide,^23,32,33 in which chlorine anions are incorporated into the product via oxidation and water is the only by-product from the oxidants. On the other hand, the use of water as a solvent is particularly attractive because: (1) water is cheaper than VOC solvents; (2) the risk of explosions using a water-based system is much lower than that for systems containing VOCs; (3) 2,4-dichlorophenol is almost insoluble in water, and hence the product can be obtained by simple phase separation, which is convenient in application. However, this is a challenging topic, especially since catalytic methods for 2,4-dichlorophenol with high activity and selectivity have not been reported previously.

Herein, we present an efficient manganous(II) sulfate-catalyzed oxychlorination of phenol in water using the oxidative chlorinating system HCl/H₂O₂ (Scheme 4). Complete conversion of phenol and high selectivity for 2,4-dichlorophenol are both achieved under mild conditions. To the best of our knowledge, this is the first report on selective water-based oxychlorination of phenol into 2,4-dichlorophenol in the liquid phase under VOC-free conditions.

Scheme 4 Oxychlorination for the synthesis of 2,4-dichlorophenol with H₂O₂ in water.

In a typical reaction, phenol (1a) and a catalyst were added into water in a glass flask, and gaseous HCl was introduced to form a homogeneous solution. Then, 30% of an aqueous solution of H₂O₂ was added to start the reaction. In the initial study, the molar ratio of HCl : H₂O₂ : 1a at 7.1 : 1.9 : 1 was used to screen the catalysts, and the results are shown in Table 1. In the absence of H₂O₂, no reaction occurred even with a prolonged time (Table 1, run 1). When H₂O₂ was added in the absence of a catalyst, conversion of 1a reached 69% with a total yield of 67%, the products were composed of <1% of 2,4-dichlorophenol (1b), 45% of p-chlorophenol (p-) and 21% of o-chlorophenol (o-) (Table 1, run 2). In the presence of H₂O₂, metal salts showed different activities. Among the tested metal salts, NaCl, CaCl₂, MgCl₂, ZnCl₂, FeSO₄, FeCl₃, NiSO₄, Co(OAc)₂, Co(acac)₂, LiCl, Cu(NO₃)₂, Cu(OAc)₂ and CuBr₂ had a poor effect (Table 1, run 3–15), as both the conversions and total yields were lower than those using H₂O₂ alone. Notably, CuCl₂ and MnSO₄ indicated high activities; the product distribution showed a dependence on the catalysts. A conversion of 85% for 1a was obtained over CuCl₂, the total yield was 83%, containing <1% of 1b, 54% of p- and 29% of o- (Table 1, run 16). Conversion of 1a over MnSO₄ reached as high as 93% with a total yield of 91%, and the products were 16% of 1b, 49% of p-, 26% of o- and trace 2,6-dichlorophenol (1c) (Table 1, run 17). Obviously, MnSO₄ is more effective in the formation of 1b. Meanwhile, various manganese compounds were used, and the effect of anions on the reactions was tested (Table 1, run 18–20). Conversions and yields over MnCl₂ and Mn(NO₃)₂ were comparable with those of MnSO₄. Because the solubility of MnO₂ in the solution was not good and some solid precipitate was always observed during the reaction, its activity was poor. These results indicated that anions had no effect on the reactions, and Mn²⁺ was key in this system.

Table 1 Results for the oxychlorination of 1a over various catalysts calculated from GC data^a

Run	Catalyst	Conversion^b (%)	Total yield^c (%)	Yield^d (%)
				1b	p-	o-	1c
a Reaction conditions: 1a: 21.3 mmol, catalyst: 1 mol%, HCl: 151.3 mmol, H2O2 (30% aq. solution): 4.05 ml, 39.7 mmol, H2O: 9.8 ml, rt., 3 h.b Conversion (%) = [the converted 1a (mol)/initial 1a (mol)] × 100.c Total yield (%) = [all products (mol)/initial 1a (mol)] × 100.d Yield (%) = [target product (mol)/initial 1a (mol)] × 100.e No H2O2 was added.
1^e	—	<1	—	—	—	—	—
2	—	69	67	<1	45	21	—
3	NaCl	38	34	<1	22	12	—
4	CaCl2	45	41	<1	26	14	—
5	MgCl2	40	38	<1	22	16	—
6	ZnCl2	36	33	<1	19	14	—
7	FeSO4	54	51	<1	41	10	—
8	FeCl3	61	55	<1	33	22	—
9	NiSO4	56	40	<1	25	15	—
10	Co(OAc)2	21	20	<1	15	5	—
11	Co(acac)2	28	27	<1	19	8	—
12	LiCl	48	28	<1	18	10	—
13	Cu(NO3)2	18	16	<1	12	4	—
14	Cu(OAc)2	27	23	<1	16	7	—
15	CuBr2	56	51	<1	34	17	—
16	CuCl2	85	83	<1	54	29	—
17	MnSO4	93	91	16	49	26	Trace
18	MnCl2	91	89	14	47	28	Trace
19	Mn(NO3)2	94	90	19	45	26	Trace
20	MnO2	67	65	8	38	19	—

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Reactions over MnSO₄ were optimized, and the results are listed in Table 2. The effect of the catalyst was examined at a ratio of HCl : H₂O₂ : 1a = 7.1 : 1.9 : 1 (Table 2, run 1–3). As MnSO₄ was varied from 1 mol% to 10 mol%, 1a was completely converted at room temperature, the total yield decreased from 91% to 80%, the yield of 1b increased from 16% to 57%, but the yield for p-decreased from 49% to 15% and o- was from 26% to 8%. In these processes, trace 1c was found. Obviously, over 5 mol% of MnSO₄ resulted in lower total yields due to over-oxidation. When the amount of HCl was reduced and HCl : H₂O₂ : 1a was varied to 2.4 : 1.9 : 1, the conversion of 1a was 76% with a total yield of 74%, containing 9% of 1b, 39% of p-, 25% of o- and trace 1c (Table 2, run 4). A large excess amount of HCl promotes the formation of 1b. The effect of temperature was tested at a HCl : H₂O₂ : 1a ratio of 2.4 : 1.9 : 1 (Table 2, run 5–8). As the temperature was increased from 45 °C to 90 °C, 1a was completely converted at 80 °C and the total yield was 95%; the yield for 1b reached a maximum of 72% with 13% of p-, 9% of o- and 3% of 1c. Further increasing the temperature to 90 °C resulted in over-oxidation and the total yield decreased to 83%. Thus, 80 °C is desirable for the reactions.

Table 2 Results for the optimization of reaction conditions calculated from GC data^a

Run	MnSO4 (mol%)	T (°C)	HCl : H2O2 : 1a (molar ratio)	Conversion^b (%)	Total yield^c (%)	Yield^d (%)
						1b	p-	o-	1c
a Reaction conditions: 1a: 21.3 mmol, HCl: 151.3 mmol, H2O2 (30% aq. solution): 4.05 ml, 39.7 mmol, H2O: 9.8 ml, 3 h.b Conversion (%) = [the converted 1a (mol)/initial 1a (mol)] × 100.c Total yield (%) = [all products (mol)/initial 1a (mol)] × 100.d Yield (%) = [target product (mol)/initial 1a (mol)] × 100.e HCl: 50.4 mmol.f HCl: 50.4 mmol, H2O2 (30% aq. solution): 6.08 ml, 58.8 mmol.g HCl: 44.7 mmol, H2O2 (30% aq. solution): 6.08 ml, 58.8 mmol.h HCl: 42.6 mmol, H2O2 (30% aq. solution): 4.35 ml, 42.6 mmol.i Under Ar atmosphere.j HCl: 42.6 mmol, H2O2 (30% aq. solution): 6.08 ml, 58.8 mmol.k HCl: 44.7 mmol, H2O2 (30% aq. solution): 8.10 ml, 79.4 mmol.
1	1	25	7.1 : 1.9 : 1	93	91	16	49	26	Trace
2	5	25	7.1 : 1.9 : 1	100	82	55	16	9	Trace
3	10	25	7.1 : 1.9 : 1	100	80	57	15	8	Trace
4	1	25	2.4 : 1.9 : 1	76	74	9	39	25	Trace
5^e	1	45	2.4 : 1.9 : 1	89	86	25	38	22	1
6^e	1	60	2.4 : 1.9 : 1	94	92	41	31	18	Trace
7^e	1	80	2.4 : 1.9 : 1	100	95	72	13	9	3
8^e	1	90	2.4 : 1.9 : 1	100	83	65	11	5	2
9^f	1	80	2.4 : 2.8 : 1	100	97	93	1	Trace	3
10^g	1	80	2.1 : 2.8 : 1	100	95	91	1	Trace	3
11^g	—	80	2.1 : 2.8 : 1	100	96	34	39	23	Trace
12^h	—	80	2.0 : 2.0 : 1	94	91	31	35	25	Trace
13^h	1	80	2.0 : 2.0 : 1	85	83	58	15	10	1
14^g^,^i	1	80	2.1 : 2.8 : 1	100	93	89	2	Trace	2
15^j	1	80	2 : 2.8 : 1	96	92	85	3	2	2
16^k	1	80	2.1 : 3.7 : 1	100	88	73	4	2	9

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When we increased the amount of H₂O₂, i.e. the ratio of HCl : H₂O₂ : 1a was varied from 2.4 : 1.9 : 1 to 2.4 : 2.8 : 1, the yield of 1b reached as high as 93% with 1% of p-, trace o- and 3% of 1c (Table 2, run 9). If HCl was further decreased and HCl : H₂O₂ : 1a was tuned to 2.1 : 2.8 : 1, the total yield was 95%, and the yield for 1b was 91% with 1% of p-, trace o- and 3% of 1c (Table 2, run 10). In the absence of MnSO₄, the full conversion of 1a with a total yield of 96% was achieved, and the yield for 1b was 34% with 39% of p-, 23% of o- and trace 1c (Table 2, run 11). When the reaction was carried out based on the theoretical equation (Scheme 4), i.e. HCl : H₂O₂ : 1a was 2.0 : 2.0 : 1, 85% of 1a was converted with a total yield of 83%, and the products were 58% of 1b, 15% of p-, 10% of o- and 1% of 1c (Table 2, run 13). In the absence of MnSO₄, 94% of 1a was converted with a total yield of 91%, containing 31% of 1b, 35% of p-, 25% of o- and trace 1c (Table 2, run 12). Obviously, the presence of MnSO₄ significantly increased the yield of 1b, and hence MnSO₄ is key for the selective chlorination of 1a to 1b. When the reaction was performed under an Ar atmosphere (Table 2, run 14), the results were comparable with those in air (Table 2, run 10), so oxygen has no effect on the reactions. If 1a was chlorinated based on a ratio of HCl : 1a at 2.0 : 1, the yield of 1b was 85% with 3% of p-, 2% of o- and 2% of 1c (Table 2, run 15). As a large excess amount of H₂O₂ was used (HCl : H₂O₂ : 1a = 2.1 : 3.7 : 1), over-oxidation occurred and the total yield decreased to 88% (Table 2, run 16). Because the decomposition of H₂O₂ is inevitable, the used amount of H₂O₂ in the reaction is higher than the theoretical value. The utilization of H₂O₂ and HCl based on the optimized conditions (Table 2, run 10) is 66% and 87%, respectively.

When HCl : H₂O₂ : 1a was 3.1 : 4.2 : 1, full conversion of 1a was achieved at 80 °C for 3 h and the total yield was 91%, the yield for 2,4,6-trichlorophenol was 73% with 11% of 1b, 7% of 1c and trace p- and o-. If HCl : H₂O₂ : 1a was increased to 3.5 : 4.2 : 1, full conversion of 1a with a total yield of 94% was obtained, and 80% of 2,4,6-trichlorophenol with 6% of 1b and 8% of 1c were found as the products. Thus, while the performance of MnSO₄ is better in the synthesis of 1b, it is also active in the synthesis of 2,4,6-trichlorophenol.

In our experiments, we found that the reagents formed a homogeneous solution before reaction, and two discrete phases were observed at the end of the reaction. The top phase is an aqueous solution containing the catalyst, and the lower is an organic phase mainly composed of 1b, p-, o- and 1c. This means that the products automatically come out from the aqueous solution. This property is really convenient for product collection via phase separation. Moreover, since MnSO₄ remains in the aqueous solution, recycling of the catalyst is simple.

In fact, commercial hydrochloric acid can be directly used rather than gaseous HCl in the reactions, as similar results were also obtained under the optimized conditions. However, we think that the use of gaseous HCl is more economical, particularly for large scale production. If hydrochloric acid is used, the products can be obtained by phase separation, but the collection of the catalyst requires the removal the whole aqueous solution via evaporation. Then, the collected catalyst, 1a and hydrochloric acid are mixed for the next run. As gaseous HCl is used, the products were isolated by phase separation, the remaining aqueous solution was concentrated by removing excess water from the solution of H₂O₂ under reduced pressure, and gaseous HCl was introduced into the concentrated solution. Then, 1a is added for the next run. Compared with gaseous HCl, it is clear that more water needs to be evaporated when using hydrochloric acid.

Based on the optimized conditions, the recycle test results of the catalyst are shown in Table 3. After each run, the same procedure was performed until the catalyst was used 6 times. These results indicate that the catalyst was recyclable, and no significant decrease in activity was observed even after 6 runs.

Table 3 Recycle test results of the catalyst^a

Run time	Conversion^b (%)	Total yield^c (%)	Yield^d (%)
			1b	p-	o-	1c
a Reaction conditions: 1a: 21.3 mmol, MnSO4: 1 mol%, HCl: 44.7 mmol, H2O2 (30% aq. solution): 6.08 ml, 58.8 mmol, H2O: 9.8 ml, 80 °C, 3 h.b Conversion (%) = [the converted 1a (mol)/initial 1a (mol)] × 100.c Total yield (%) = [all products (mol)/initial 1a (mol)] × 100.d Yield (%) = [target product (mol)/initial 1a (mol)] × 100.
1	100	95	91	1	Trace	3
3	100	94	90	1	Trace	2
6	98	92	88	2	Trace	1

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Since 2,4-dichloro-substituted phenol derivatives present a series of valuable materials for fine chemicals, this method was further used in the chlorination of various phenol derivatives (see ESI, Table 1S†). Although monochloro-substituted phenols, such as p- and o-, are undesirable products in our reactions, these compounds can be efficiently converted into 1b in our method. Complete conversion of p- was obtained in a high yield of 96% for 1b, and the yield of 1b was 94% for the total conversion of o-. Thus, monochloro-substituted phenols can be effectively utilized, and the by-product that remains in our system is only 1c. As for bromo- or iodo-substituted phenols, side-reactions of debromination/deiodination occurred and resulted in a complex mixture. This method is effective for alkylphenols, which were successfully chlorinated as various 2,4-dichlorophenols. A yield of 75% was achieved for 3b from o-cresol (3a), and an 81% yield for 4b was obtained from 2-tert-butylphenol (4a). Complete conversion of 5a (3,5-dimethylphenol) was achieved, and the yield for 5b was 86%. The chlorination of ethers of phenol can also be easily performed under similar conditions. Complete conversion of anisole (6a) led to a yield of 82% for 6b, and a high yield of 81% for 7b was achieved from 3,5-dimethylanisole (7a). Thus, we consider that our study offers a versatile synthetic method in the manufacture of various 2,4-dichlorophenol derivatives (Scheme 5).

Scheme 5 Oxychlorination for the synthesis of 2,4-dichloro-substituted phenol derivatives with H₂O₂ under VOC-free conditions.

The molar ratio of H₂O₂ : 1a was 2 : 1 according to the theoretical equation (Scheme 4), but it was 2.8 : 1 under the optimized conditions (Table 2, run 10). The used amount of H₂O₂ is higher than the theoretical value. It is well known that the catalytic decomposition of H₂O₂ over metal ions is inevitable, and the interactions of Mn²⁺ with H₂O₂ lead to numerous reactive species, such as oxygen atoms, active oxygen species or OH˙/OOH˙ radicals, which are possible active species for reactions. In our experiments, when a free radical scavenger, 2,6-di-tert-butyl-4-methyl phenol, was added into the reactions, the yield of 1b significantly decreased to 30%. Although this result indicates that a free radical pathway is possibly involved in the reactions, our attempts to find out the free radicals or active species failed because of the complexity of this system. In controlled experiments, we found that the addition of H₂O₂ into an aqueous solution of HCl immediately resulted in light yellow gas, which was Cl₂ based on GC-MS analysis. Thus, while the exact free radicals or active species are not yet clear, the main pathway can be presented as shown in Scheme 6: HCl is oxidized by H₂O₂ to Cl₂; the generated Cl₂ reacts with 1a to form 1b with the release of HCl, which is re-oxidized and re-used until 1a is exhausted. Details of the reaction mechanism are under investigation, and we will report the results in future.

Scheme 6 A reaction pathway of the oxychlorination of phenol over an Mn²⁺ catalyst.

Conclusions

In summary, we have developed a simple, mild and efficient method for oxychlorination of phenol to 2,4-dichlorophenol catalyzed by manganous(II) sulfate in the liquid phase. In this system, hydrogen chloride was used as a chlorinating agent, hydrogen peroxide as an oxidant and water as a solvent. We envisage that our method will be effective in the manufacture of various 2,4-dichlorophenol derivatives based on the following reasons: (1) high activity and selectivity; (2) VOC free; (3) simple product separation and recyclable catalyst.

Experimental section

Typical procedure for oxychlorination of phenol

Phenol and a catalyst were added to water in a three-neck flask equipped with a gas inlet, a liquid inlet and a reflux condenser (open to air). Gaseous HCl was introduced and dissolved as an aqueous solution. The flask was immersed in a preheated oil bath and vigorously stirred with a magnetic stirrer. Then, H₂O₂ (30% aq. solution) was added dropwise by a channel pump during the reaction. At the end of the reaction, the mixtures were left to stand for 1.5 h, and an isolated organic phase from the aqueous solution formed at the bottom. The organic phase was collected and diluted with acetonitrile to prepare the sample for quantitative analysis. The conversions and yields were determined by gas chromatography. Each experiment was reproduced at least three times. The experimental error in the determination of the conversions and yields normally did not exceed 4%. Pure products were obtained by column chromatography using silica gel (petroleum ether) and confirmed by GC-MS, ¹H and ¹³C NMR.

¹H NMR and ¹³C NMR analytical data of products

2,4-Dichlorophenol. ¹H NMR (600 MHz, CDCl₃) δ: 7.32 (d, J = 2.4 Hz, 1H), 7.15 (dd, J = 2.4, 9.6 Hz, 1H), 6.95 (d, J = 9.0 Hz, 1H), 5.51 (s, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 150.2, 128.6, 128.56, 125.6, 120.4, 117.1.

4-Chlorophenol. ¹H NMR (600 MHz, CDCl₃) δ: 7.19 (d, J = 9.0 Hz, 2H), 6.76 (d, J = 8.4 Hz, 2H), 4.90 (s, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 154.1, 129.6, 125.7, 116.7.

2-Chlorophenol. ¹H NMR (600 MHz, CDCl₃) δ: 7.29 (m, 1H), 7.16 (m, 1H), 7.01 (m, 1H), 6.85 (m, 1H), 5.62 (s, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 151.4, 129.1, 128.5, 121.4, 119.9, 116.3.

2,6-Dichlorophenol. ¹H NMR (600 MHz, CDCl₃) δ: 7.26 (d, J = 7.8 Hz, 2H), 6.82 (t, J = 8.4 Hz, 1H), 5.85 (s, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 147.9, 128.3, 121.2, 121.1.

2,4,6-Trichlorophenol. ¹H NMR (600 MHz, CDCl₃) δ: 7.28 (s, 2H), 5.81 (s, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 146.9, 128.1, 125.4, 121.6.

2,4-Dichloro-6-methylphenol. ¹H-NMR (600 MHz, CDCl₃) δ: 7.16 (d, J = 2.4 Hz, 1H), 7.02 (d, J = 2.4 Hz, 1H), 5.24 (s, 1H), 2.26 (s, 3H); ¹³C NMR (150 MHz, CDCl₃) δ: 148.4, 129.6, 127.3, 125.8, 124.7, 119.8, 16.3.

2,4-Dichloro-6-t-butylphenol. ¹H-NMR (600 MHz, CDCl₃) δ: 7.20 (d, J = 2.4 Hz, 1H), 7.15 (d, J = 2.4 Hz, 1H), 5.80 (s, 1H), 1.38 (s, 9H); ¹³C NMR (150 MHz, CDCl₃) δ: 148.5, 138.9, 126.2, 125.9, 124.7, 121.1, 35.5, 29.1.

2,4-Dichloro-3,5-dimethylphenol. ¹H-NMR (600 MHz, CDCl₃) δ: 6.80 (s, 1H), 5.48 (s, 1H), 2.46 (s, 3H), 2.32 (s, 3H); ¹³C NMR (150 MHz, CDCl₃) δ: 149.5, 136.0, 134.2, 126.5, 118.5, 115.1, 20.8, 18.3.

2,4-Dichloroanisole. ¹H NMR (600 MHz, CDCl₃) δ: 7.34 (d, J = 2.4 Hz, 1H), 7.19 (dd, J = 2.4, 9.0 Hz, 1H), 6.82 (d, J = 9.0 Hz, 1H), 3.86 (s, 3H); ¹³C NMR (150 MHz, CDCl₃) δ: 153.9, 129.9, 127.9, 125.6, 123.2, 112.8, 56.3.

2,4-Dichloro-3,5-dimethylanisole. ¹H NMR (600 MHz, CDCl₃) δ: 6.67 (s, 1H), 3.86 (s, 3H), 2.47 (s, 3H), 2.36 (s, 3H); ¹³C NMR (150 MHz, CDCl₃) δ: 153.2, 136.3, 134.9, 126.8, 120.9, 111.4, 59.3, 21.2, 18.2.

Acknowledgements

We are thankful for the funding support from the Innovative Research Team in College and Universities of Liaoning Province (No. LT2014007).

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c7ra00319f

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