Preparation method of 1, 4-dimethylnaphthalene

Abstract

The invention relates to the technical field of organic synthesis, and discloses a preparation method of 1, 4-dimethylnaphthalene. The method comprises the step of carrying out acid catalysis reaction on a compound as shown in a formula (3) under an acidic condition. According to the method for preparing the 1, 4-dimethylnaphthalene, the used reagents are cheap and easy to obtain, the reaction conditions are mild, waste difficult to treat is not generated, and the yield and the purity of the 1, 4-dimethylnaphthalene are relatively high. # imgabs0 #

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, and in particular to a method for preparing 1,4-dimethylnaphthalene. Background Art

[0002] In the 1970s, the sprout inhibitory activity of 1,4-dimethylnaphthalene was first discovered. The compound was first registered in the United States in 1996. Due to its low toxicity, low risk and high sprout inhibitory activity, it is widely used as a sprout inhibitor during potato storage. As similar sprout inhibitors are banned, the market demand for 1,4-dimethylnaphthalene has been increasing year by year.

[0003] At present, the contents disclosed in some literature on the synthesis route of 1,4-dimethylnaphthalene are as follows:

[0004] (1) The literature Green Chem., 2018, 20, 1448-1454 reported the preparation of 1,4-dimethylnaphthalene according to the following reaction formula:

[0005]

[0006] In this method, the benzyne precursor is not easy to obtain, the synthesis is difficult and costly, the reaction conditions are harsh, and the synthesis route is long.

[0007] (2) The document Eur. J. Org. Chem, 2012, 552 reported the preparation of 1,4-dimethylnaphthalene according to the following reaction formula:

[0008]

[0009] The reduction reaction of this method requires an ultra-low temperature of -78°C, and the reaction conditions are harsh, making it difficult to achieve industrialization.

[0010] (3) Patent application CN115504848A reported the preparation of 1,4-dimethylnaphthalene according to the following reaction formula:

[0011]

[0012] The synthesis process reported in the patent application requires the use of expensive and dangerous Grignard reagents, which produce waste Mg salts that are difficult to handle. In addition, the methylation reagents (such as dimethyl sulfate) used for methylation are highly toxic and are not conducive to large-scale industrial production.

[0013] Therefore, it is urgent to develop a suitable preparation method for 1,4-dimethylnaphthalene to reduce its synthesis cost. Summary of the invention

[0014] The purpose of the present invention is to overcome the problem that the existing method for preparing 1,4-dimethylnaphthalene requires the use of expensive and highly toxic chemicals and has a high production cost, and to provide a new method for preparing 1,4-dimethylnaphthalene. The present invention uses common and inexpensive chemicals to replace expensive and highly toxic chemicals, provides a simple, safe, environmentally friendly and low-cost synthesis route, is suitable for large-scale industrial production, and greatly reduces the production cost of 1,4-dimethylnaphthalene.

[0015] In order to achieve the above object, the present invention provides a method for preparing 1,4-dimethylnaphthalene, which comprises: subjecting a compound represented by formula (3) to an acid-catalyzed reaction under acidic conditions,

[0016]

[0017] Preferably, the conditions of the acid-catalyzed reaction include: temperature of 60-120° C. and time of 1-20 h.

[0018] Preferably, the acid used in the reaction is at least one of sulfuric acid, phosphoric acid, p-toluenesulfonic acid and trifluoroacetic acid.

[0019] Preferably, the method further comprises preparing the compound represented by formula (3) according to the following steps:

[0020] In the presence of a catalyst, the compound represented by formula (2) is subjected to a hydrogenation reduction reaction.

[0021]

[0022] Preferably, the conditions for the hydrogenation reduction reaction include: temperature of 30-70° C. and time of 1-10 h.

[0023] Preferably, the catalyst is Raney nickel and / or palladium on carbon.

[0024] Preferably, the method further comprises preparing the compound represented by formula (2) according to the following steps:

[0025] In the presence of an organic solvent and a dehydrating agent, the compound represented by formula (1) is subjected to a ring-closing reaction.

[0026]

[0027] Preferably, the conditions for the ring-closure reaction include: temperature of 50-85° C. and time of 2-5 h.

[0028] Preferably, the organic solvent is selected from at least one of dichloroethane, dichloromethane, chloroform, cyclohexane and methyl isobutyl ketone, preferably dichloroethane.

[0029] Preferably, the dehydrating agent is selected from at least one of concentrated sulfuric acid, polyphosphoric acid, dicyclohexylcarbodiimide, phosphorus pentoxide and phosphorus oxychloride, preferably concentrated sulfuric acid and / or dicyclohexylcarbodiimide.

[0030] According to the technical solution of the present invention, the reagents used in the preparation process of 1,4-dimethylnaphthalene are cheap and easily available, the reaction conditions are mild, no waste that is difficult to treat is generated, and the yield and purity of 1,4-dimethylnaphthalene are high. DETAILED DESCRIPTION

[0031] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0032] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0033] The preparation method of 1,4-dimethylnaphthalene of the present invention comprises: subjecting the compound represented by formula (3) to an acid-catalyzed reaction under acidic conditions,

[0034]

[0035] In the method of the present invention, the conditions of the acid-catalyzed reaction may include: a temperature of 60-120° C., preferably 70-100° C.; and a time of 1-20 h, preferably 8-15 h.

[0036] In the method of the present invention, the molar ratio of the compound represented by formula (3) to the acid can be 1:1-2, preferably 1:1.2-1.8.

[0037] In the method of the present invention, the acid used in the process of preparing 1,4-dimethylnaphthalene by reacting the compound represented by formula (3) can be a conventional acid in the art. In a preferred case, in order to obtain a higher yield of the target product, the acid used is at least one of sulfuric acid, phosphoric acid, p-toluenesulfonic acid and trifluoroacetic acid, and sulfuric acid is most preferred.

[0038] In the present invention, when the acid used in the reaction process is sulfuric acid, preferably, the sulfuric acid is used in the form of concentrated sulfuric acid. Concentrated sulfuric acid refers to sulfuric acid with a concentration of 70wt.% or more. Preferably, the concentration of the concentrated sulfuric acid is 70-90wt.%.

[0039] In the method of the present invention, a solvent is generally required in the process of preparing 1,4-dimethylnaphthalene by reacting the compound represented by formula (3). The solvent may be a conventional organic solvent in the art, such as toluene, ethylene dichloride, chlorobenzene, etc.

[0040] In some embodiments, the process of preparing 1,4-dimethylnaphthalene by reacting the compound shown in formula (3) is as follows: under stirring, the compound shown in formula (3), a solvent and concentrated sulfuric acid are mixed, the temperature is raised to 60-120° C. and the reaction is carried out for 1-20 hours. After the reaction is completed, the temperature is lowered to 30-35° C., and the layers are allowed to stand and separate. After the solvent layer is separated, the solvent is removed under reduced pressure to obtain a crude 1,4-dimethylnaphthalene product, which is then distilled to obtain a 1,4-dimethylnaphthalene product.

[0041] In the present invention, the method for preparing 1,4-dimethylnaphthalene may further include preparing the compound represented by formula (3) according to the following steps:

[0042] In the presence of a catalyst, the compound represented by formula (2) is subjected to a hydrogenation reduction reaction.

[0043]

[0044] In the method described in the present invention, the conditions of the hydrogenation reduction reaction may include: temperature of 30-70°C, preferably 40-60°C; time of 1-10h, preferably 3-8h.

[0045] In the method of the present invention, the weight ratio of the compound represented by formula (2) to the catalyst can be 30-100:1, preferably 50-70:1.

[0046] In the method of the present invention, the catalyst is preferably Raney nickel and / or palladium on carbon.

[0047] In the method of the present invention, a solvent is generally required in the process of preparing the compound represented by formula (3) from the compound represented by formula (2). The solvent may be a conventional organic solvent in the art, such as methanol, ethylene dichloride, ethanol, etc.

[0048] In the method described in the present invention, the process of preparing the compound represented by formula (3) from the compound represented by formula (2) can be carried out in a closed reactor, and the reaction process is carried out under a hydrogen environment.

[0049] In some embodiments, the process of preparing the compound represented by formula (3) from the compound represented by formula (2) is as follows: add the compound represented by formula (2), a catalyst and a solvent into a high-pressure reactor, seal it, and introduce hydrogen under pressure to 1-3 MPa, raise the temperature to 30-70°C while stirring, and react for 1-10 hours. After the reaction is completed, cool down, slowly release excess hydrogen, take out the reaction solution and filter it, and remove the solvent from the filtrate under reduced pressure to obtain the compound represented by formula (3).

[0050] In the present invention, the method for preparing 1,4-dimethylnaphthalene can also prepare the compound represented by formula (2) according to the following steps:

[0051] In the presence of an organic solvent and a dehydrating agent, the compound represented by formula (1) is subjected to a ring-closing reaction.

[0052]

[0053] In the method described in the present invention, the conditions of the ring-closing reaction may include: temperature of 50-85° C. and time of 2-5 h.

[0054] In the method of the present invention, relative to 100 parts by weight of the organic solvent, the amount of the compound represented by formula (1) is 10-100 parts by weight, preferably 30-60 parts by weight; the amount of the dehydrating agent is 1-20 parts by weight, preferably 3-10 parts by weight.

[0055] In the method of the present invention, the organic solvent can be a conventional organic solvent in the art. Preferably, in order to obtain a higher yield of the target product, the organic solvent is selected from at least one of dichloroethane, dichloromethane, chloroform, cyclohexane and methyl isobutyl ketone, and dichloroethane is most preferred.

[0056] In the method of the present invention, the dehydrating agent can be selected from at least one of concentrated sulfuric acid, polyphosphoric acid, dicyclohexylcarbodiimide, phosphorus pentoxide and phosphorus oxychloride, preferably concentrated sulfuric acid and / or dicyclohexylcarbodiimide. The concentration of the concentrated sulfuric acid is 70wt.% or more, preferably 70-90wt.%.

[0057] In some embodiments, the process of preparing the compound of formula (2) from the compound of formula (1) is as follows: under stirring, the compound of formula (1), an organic solvent and a dehydrating agent are mixed, the temperature is raised to 50-85° C. for reaction, after the reaction is completed, water is added and stirring is continued for 5-20 minutes, the mixture is allowed to stand for stratification, and then the solvent is removed under reduced pressure to obtain the compound of formula (2).

[0058] In the present invention, the compound represented by formula (1) can be directly purchased from the market, or can be prepared according to conventional methods in the art, such as reacting p-xylene with succinic anhydride under the action of aluminum chloride to prepare the compound represented by formula (1). The specific preparation process can refer to the content disclosed in patent application US20110160371A1.

[0059] In some embodiments, the preparation process of the compound represented by formula (1) may include: mixing succinic anhydride, aluminum chloride and a solvent under stirring, heating to 30-35°C, then dropping p-xylene into the mixture, and then keeping the mixture at 30-35°C for 1-10 hours, then quenching the aluminum chloride, standing and stratifying, and then decompressing and desolventizing to obtain the compound represented by formula (1). Here, the solvent used may be dichloroethane, chloroform, cyclohexane, etc.

[0060] In a more preferred embodiment, the preparation method of 1,4-dimethylnaphthalene comprises the following steps:

[0061] (1) p-xylene and succinic anhydride react under the action of aluminum chloride to obtain a compound represented by formula (1);

[0062] (2) subjecting the compound represented by formula (1) to a ring-closing reaction in the presence of an organic solvent and a dehydrating agent to obtain a compound represented by formula (2);

[0063] (3) subjecting the compound represented by formula (2) to a hydrogenation reduction reaction in the presence of a catalyst to obtain a compound represented by formula (3);

[0064] (4) Under acidic conditions, the compound represented by formula (3) is subjected to an acid-catalyzed reaction.

[0065] In a further preferred embodiment, the preparation method of 1,4-dimethylnaphthalene comprises the following steps:

[0066] (1) Succinic anhydride, aluminum chloride and a solvent are mixed under stirring, and the temperature is raised to 30-35° C., and then p-xylene is added dropwise to the mixture, and then the mixture is kept at 30-35° C. for 1-10 hours, and then the aluminum chloride is quenched, the mixture is allowed to stand for stratification, and then the solvent is removed under reduced pressure to obtain a compound represented by formula (1);

[0067] (2) Mixing the compound represented by formula (1), an organic solvent and a dehydrating agent under stirring, heating to 50-85° C. for reaction, adding water after the reaction is completed, and continuing stirring for 5-20 minutes, standing to separate layers, and then desolventizing to obtain the compound represented by formula (2);

[0068] (3) Add the compound represented by formula (2), a catalyst and a solvent to a high-pressure reactor, seal it, and introduce hydrogen under pressure to 1-3 MPa. Raise the temperature to 30-70° C. under stirring, and react for 1-10 hours. After the reaction is completed, cool it down, slowly release the excess hydrogen, take out the reaction solution and filter it, and remove the solvent from the filtrate under reduced pressure to obtain the compound represented by formula (3);

[0069] (4) Under stirring, the compound represented by formula (3), a solvent and concentrated sulfuric acid are mixed, the temperature is raised to 60-120° C. and the reaction is carried out for 1-20 hours. After the reaction is completed, the temperature is lowered to 30-35° C., and the mixture is allowed to stand for stratification. After the solvent layer is separated, the solvent is removed under reduced pressure to obtain a crude 1,4-dimethylnaphthalene product, which is then distilled to obtain a 1,4-dimethylnaphthalene product.

[0070] The following examples further illustrate the preparation method of 1,4-dimethylnaphthalene of the present invention. The examples are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples.

[0071] The experimental methods in the following examples, unless otherwise specified, are all conventional methods in the art. The experimental materials used in the following examples, unless otherwise specified, are all commercially available.

[0072] Example 1

[0073] (1) In a 500 ml four-necked flask equipped with a mechanical stirrer, a thermometer, a condenser and a dropping funnel, 0.5 mol of succinic anhydride, 0.6 mol of aluminum chloride and 200 g of ethylene dichloride were added in sequence, the temperature was raised to 30° C., 0.5 mol of p-xylene was added dropwise, and the temperature was kept at 30° C. for 5 hours after the addition was completed. 130 g of ice water was added dropwise to quench the aluminum chloride, and the mixture was allowed to stand for stratification. After the ethylene dichloride layer was obtained, the ethylene dichloride was removed under reduced pressure to obtain the compound represented by formula (1), and its NMR characterization data are as follows: 1 H NMR (500MHz, CDCl3) δ7.50 (s, 1H), 7.20 (d, J = 7.5Hz, 1H), 7.13 (d, J = 7.5Hz, 1H), 3.22 (t, J = 6.5Hz, 2H), 2.79 (t, J = 6.5Hz, 2H), 2.45 (s, 3H), 2.37 (s, 3H).

[0074] After testing and calculation, the purity of the compound represented by formula (1) was 95.0%, the weight was 98.67 g, and the yield was 91.0%.

[0075] (2) In a 500 ml four-necked flask equipped with a mechanical stirrer, a thermometer and a condenser, 98.67 g (95%, 0.455 mol) of the compound represented by formula (1) obtained in step (1), 200 g of dichloroethane and 10 g of concentrated sulfuric acid (concentration: 70 wt.%) were added, and the mixture was heated to 50° C. with stirring and reacted for 3 hours. After the reaction was completed, 30 ml of water was added and stirred for 10 minutes. The mixture was allowed to stand for stratification to obtain a dichloroethane layer, and the solvent was removed under reduced pressure to obtain a compound represented by formula (2). Its NMR characterization data are as follows: 1 H NMR (500MHz, CDCl3) δ7.39 (s, 2H), 3.09 (s, 4H), 2.46 (s, 3H).

[0076] After testing and calculation, the purity of the compound represented by formula (2) was 94.5%, the weight was 84.45 g, and the yield was 93.3%.

[0077] (3) In a 500 ml autoclave, 60.6 g of the compound represented by formula (2) obtained in step (2) (94.5%, 0.3 mol), 1 g of Raney nickel and 150 g of methanol were added in sequence. After sealing, hydrogen was introduced under pressure to 3 MPa. The mixture was stirred and heated to 50° C. for reaction for 6 hours. After the reaction was completed, the temperature was lowered and excess hydrogen was slowly released. The reaction liquid was taken out and filtered. The Raney nickel of the filter cake was recovered and reused. The filtrate was decompressed to remove methanol to obtain the compound represented by formula (3). Its NMR characterization data are as follows: 1 H NMR (500MHz, CDCl3) δ7.22(s,2H),4.84-4.80(m,2H),2.45(s,6H),2.34-2.28(m,2H),1.86-1.80(m,2H),1.55(br,2H).

[0078] After testing and calculation, the purity of the compound represented by formula (3) was 95.5%, the weight was 57.3 g, and the yield was 95.0%.

[0079] (4) In a 250 ml four-necked flask equipped with a mechanical stirrer, a thermometer, and a condenser, 0.2 mol of the compound represented by formula (3) obtained in step (3), 100 g of toluene, and 0.3 mol of concentrated sulfuric acid (concentration of 70 wt.%) were added in sequence, and the temperature was raised to 100° C. for reaction for 10 hours. After the reaction was completed, the temperature was lowered to 30° C. and allowed to stand for stratification. The toluene layer was separated and toluene was removed under reduced pressure to obtain a crude 1,4-dimethylnaphthalene product. The crude product was subjected to rectification to obtain a 1,4-dimethylnaphthalene product, and its NMR characterization data are as follows: 1 H NMR (500MHz, CDCl3) δ8.08-7.98(m,2H),7.59-7.50(m,2H),7.21(s,2H),2.66(s,6H).

[0080] After testing and calculation, the purity of the 1,4-dimethylnaphthalene product was 99.5%, the weight was 44.87 g, and the yield was 95.4%.

[0081] Example 2

[0082] (1) According to step (1) of Example 1, the compound represented by formula (1) was prepared.

[0083] (2) The compound represented by formula (2) was prepared according to step (2) in Example 1, except that the reaction temperature was 60° C. As a result, the purity of the compound represented by formula (2) was 95.5% and the yield was 94.5%.

[0084] (3) The compound represented by formula (3) was prepared according to step (3) in Example 1, except that 1 g of palladium carbon was used as the catalyst. As a result, the purity of the compound represented by formula (3) was 95.6% and the yield was 95.4%.

[0085] (4) The 1,4-dimethylnaphthalene product was prepared according to step (4) in Example 1, except that the reaction temperature was 60° C. As a result, the purity of the 1,4-dimethylnaphthalene product was 98.6% and the yield was 93.2%.

[0086] Example 3

[0087] (1) According to step (1) of Example 1, the compound represented by formula (1) was prepared.

[0088] (2) The compound represented by formula (2) was prepared according to step (2) in Example 1, except that the reaction temperature was 70° C. As a result, the purity of the compound represented by formula (2) was 95.7% and the yield was 94.8%.

[0089] (3) The compound represented by formula (3) was prepared according to step (3) in Example 1, except that the reaction temperature was 30° C. As a result, the purity of the compound represented by formula (3) was 94.3% and the yield was 93.5%.

[0090] (4) The 1,4-dimethylnaphthalene product was prepared according to step (4) in Example 1, except that the reaction temperature was 70° C. As a result, the purity of the 1,4-dimethylnaphthalene product was 98.9% and the yield was 94.2%.

[0091] Example 4

[0092] (1) According to step (1) of Example 1, the compound represented by formula (1) was prepared.

[0093] (2) The compound represented by formula (2) was prepared according to step (2) in Example 1, except that the reaction temperature was 80° C. As a result, the purity of the compound represented by formula (2) was 96.1% and the yield was 95.1%.

[0094] (3) The compound represented by formula (3) was prepared according to step (3) of Example 1, except that the reaction temperature was 40° C. As a result, the purity of the compound represented by formula (3) was 94.6% and the yield was 94.1%.

[0095] (4) The 1,4-dimethylnaphthalene product was prepared according to step (4) in Example 1, except that the reaction temperature was 80° C. As a result, the purity of the 1,4-dimethylnaphthalene product was 99.16% and the yield was 94.6%.

[0096] Example 5

[0097] (1) According to step (1) of Example 1, the compound represented by formula (1) was prepared.

[0098] (2) The compound represented by formula (2) was prepared according to step (2) in Example 1, except that the reaction temperature was 85° C. As a result, the purity of the compound represented by formula (2) was 96.2% and the yield was 95.2%.

[0099] (3) The compound represented by formula (3) was prepared according to step (3) of Example 1, except that the reaction temperature was 60° C. As a result, the purity of the compound represented by formula (3) was 95.7% and the yield was 94.9%.

[0100] (4) The 1,4-dimethylnaphthalene product was prepared according to step (4) in Example 1, except that the reaction temperature was 90° C. As a result, the purity of the 1,4-dimethylnaphthalene product was 99.45% and the yield was 95.3%.

[0101] Example 6

[0102] (1) According to step (1) of Example 1, the compound represented by formula (1) was prepared.

[0103] (2) The compound represented by formula (2) was prepared according to step (2) in Example 1, except that 10 g of polyphosphoric acid was used as the dehydrating agent. As a result, the purity of the compound represented by formula (2) was 93.2% and the yield was 93.4%.

[0104] (3) The compound represented by formula (3) was prepared according to step (3) in Example 1, except that the reaction temperature was 70° C. As a result, the purity of the compound represented by formula (3) was 95.8% and the yield was 95.2%.

[0105] (4) The 1,4-dimethylnaphthalene product was prepared according to step (4) in Example 1, except that the reaction temperature was 110° C. As a result, the purity of the 1,4-dimethylnaphthalene product was 99.23% and the yield was 93.6%.

[0106] Example 7

[0107] (1) According to step (1) of Example 1, the compound represented by formula (1) was prepared.

[0108] (2) The compound represented by formula (2) was prepared according to step (2) in Example 1, except that 10 g of dicyclohexylcarbodiimide was used as the dehydrating agent. As a result, the purity of the compound represented by formula (2) was 93.1% and the yield was 93.2%.

[0109] (3) According to step (3) in Example 1, the compound represented by formula (3) was prepared.

[0110] (4) The 1,4-dimethylnaphthalene product was prepared according to step (4) in Example 1, except that the reaction temperature was 120° C. As a result, the purity of the 1,4-dimethylnaphthalene product was 98.89% and the yield was 93.1%.

[0111] Example 8

[0112] (1) According to step (1) of Example 1, the compound represented by formula (1) was prepared.

[0113] (2) The compound represented by formula (2) was prepared according to step (2) in Example 1, except that 10 g of phosphorus pentoxide was used as the dehydrating agent. As a result, the purity of the compound represented by formula (2) was 93.9% and the yield was 93.8%.

[0114] (3) According to step (3) in Example 1, the compound represented by formula (3) was prepared.

[0115] (4) The 1,4-dimethylnaphthalene product was prepared according to step (4) in Example 1, except that the acid used was phosphoric acid. As a result, the purity of the 1,4-dimethylnaphthalene product was 99.0% and the yield was 94.3%.

[0116] Example 9

[0117] (1) According to step (1) of Example 1, the compound represented by formula (1) was prepared.

[0118] (2) The compound represented by formula (2) was prepared according to step (2) in Example 1, except that 10 g of phosphorus oxychloride was used as the dehydrating agent. As a result, the purity of the compound represented by formula (2) was 93.7% and the yield was 93.6%.

[0119] (3) According to step (3) in Example 1, the compound represented by formula (3) was prepared.

[0120] (4) The 1,4-dimethylnaphthalene product was prepared according to step (4) in Example 1, except that the acid used was p-toluenesulfonic acid. As a result, the purity of the 1,4-dimethylnaphthalene product was 99.2% and the yield was 94.8%.

[0121] Example 10

[0122] The 1,4-dimethylnaphthalene product was prepared according to the method of Example 1, except that in step (4), the acid used was trifluoroacetic acid. As a result, the purity of the 1,4-dimethylnaphthalene product was 99.3% and the yield was 94.7%.

[0123] Comparative Example 1

[0124] This comparative example is to prepare 1,4-dimethylnaphthalene according to the method of patent application CN115504848A.

[0125] Take 20g of 4-bromomethylnaphthalene, add 20mL of tetrahydrofuran, 20mL of toluene and 2.5g of bis(triphenylphosphine)nickel dichloride in sequence, stir and heat to 60°C, slowly drop 90ml of 6M methylmagnesium chloride tetrahydrofuran solution, keep warm and react for 12h, then drop the reaction solution into 5wt.% dilute hydrochloric acid water to quench, separate the phases, desolventize the organic phase, and distill out 1,4-dimethylnaphthalene product at 100Pa and 100°C with a purity of 92.1% and a yield of 91.79%.

[0126] Furthermore, it can be seen from the process that the synthesis process requires the use of expensive and dangerous Grignard reagents, which produce waste Mg salts that are difficult to handle, so the process is not easy to produce in an environmentally friendly manner.

[0127] It can be seen from the above examples and comparative examples that 1,4-dimethylnaphthalene is prepared according to the method described in the present invention, the reagents used are cheap and readily available, the reaction conditions are mild, no waste that is difficult to treat is generated, and the yield and purity of 1,4-dimethylnaphthalene are high.

[0128] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing 1,4-dimethylnaphthalene, characterized in that: The method comprises: subjecting the compound represented by formula (3) to an acid-catalyzed reaction under acidic conditions, 2. The method according to claim 1, characterized in that The conditions of the acid-catalyzed reaction include: temperature of 60-120° C. and time of 1-20 h.

3. The method according to claim 1 or 2, characterized in that: The acid used in the reaction process is at least one of sulfuric acid, phosphoric acid, p-toluenesulfonic acid and trifluoroacetic acid.

4. The method according to any one of claims 1 to 3, characterized in that: The method further comprises preparing the compound represented by formula (3) according to the following steps: In the presence of a catalyst, the compound represented by formula (2) is subjected to a hydrogenation reduction reaction.

5. The method according to claim 4, characterized in that The conditions of the hydrogenation reduction reaction include: temperature of 30-70° C. and time of 1-10 h.

6. The method according to claim 4, characterized in that The catalyst is Raney nickel and / or palladium on carbon.

7. The method according to any one of claims 4 to 6, characterized in that: The method further comprises preparing the compound represented by formula (2) according to the following steps: In the presence of an organic solvent and a dehydrating agent, the compound represented by formula (1) is subjected to a ring-closing reaction.

8. The method according to claim 7, characterized in that The conditions of the ring-closing reaction include: temperature of 50-85° C. and time of 2-5 h.

9. The method according to claim 7, characterized in that: The organic solvent is selected from at least one of dichloroethane, dichloromethane, chloroform, cyclohexane and methyl isobutyl ketone, preferably dichloroethane.

10. The method according to claim 7, characterized in that The dehydrating agent is selected from at least one of concentrated sulfuric acid, polyphosphoric acid, dicyclohexylcarbodiimide, phosphorus pentoxide and phosphorus oxychloride, preferably concentrated sulfuric acid and / or dicyclohexylcarbodiimide.

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