Method for preparing methylaniline by using vanadium as catalyst in the reaction of toluene and hydroxylamine salt

Abstract

The present invention is a method for using a vanadium element as a catalyst in the reaction of toluene and a hydroxylamine salt to produce toluidine. The method comprises the following steps: adding glacial acetic acid, deionized water, hydroxylamine hydrochloride, toluene, and a vanadium element to a reactor with a stirring and condensing reflux device, heating the reactor to 60-100° C., and stirring the reactor for 1-7 hours to obtain toluidine. The present invention does not require pre-treatment of the catalyst, and vanadium element powder is directly used as a catalyst in the reaction. The catalyst is simple and easy to obtain, low in price and stable, and catalyzes the reaction of toluene and a hydroxylamine salt under mild reaction conditions to produce toluidine in a single step with high selectivity and yield.

Description

Technical Field

[0001] The invention relates to the application of vanadium as a catalyst in the one-step reaction of preparing methylaniline by reacting toluene with hydroxylamine salt. Background Art

[0002] Aromatic amines, such as aniline and methylaniline, are an important class of organic compounds. They can be considered compounds in which the hydrogen atoms on the benzene ring of an aromatic hydrocarbon molecule are replaced by amino groups. They are important organic chemical raw materials and are widely used in industries such as pharmaceuticals, dyes, rubber, and polyurethanes. Methylaniline has three isomers: o-, p-, and m-methylaniline. At room temperature, o- and m-methylanilines are colorless to pale yellow liquids, while p-methylaniline is white flaky crystals. The amino group, methyl group, and benzene ring in the methylaniline molecule are all reactive, and further processing using methylaniline as a starting material can yield a range of derivatives. Therefore, methylaniline is widely used in industries such as pharmaceuticals, pesticides, and dyes. Annual domestic consumption exceeds 30,000 tons, making it a highly consumed and widely used organic intermediate.

[0003] Professor Hu Changwei of Sichuan University proposed a supported catalyst, using CeO₂ and γ-Al₂O₃ as supports, to produce V₂O₅ / γ-Al₂O₃, which increased the yield of methylaniline to 56% (Patent Publication No.: CN1706807A). However, the disadvantage of requiring a large amount of catalyst remained. In practice, the weight ratio of catalyst to the raw material hydroxylamine hydrochloride was still as high as 1:1.5, making it extremely uneconomical for industrial production.

[0004] To overcome the aforementioned shortcomings of low methylaniline yield and high economic costs, Gao Liya et al. prepared a supported CuO-V2O5 / Al2O3 catalyst, achieving a methylaniline yield of up to 60.3%. This method improves methylaniline yield, provides good catalyst reuse, and operates under mild reaction conditions. However, there is still room for improvement in increasing methylaniline yield. Summary of the Invention

[0005] The present invention aims to address the limitations of current technologies and to provide a method for producing methylaniline by using elemental vanadium as a catalyst in the reaction of toluene with a hydroxylamine salt. This method uses elemental vanadium as a catalyst, unlike previously used supported catalysts. The present invention eliminates the need for pre-treatment of the catalyst and directly uses vanadium powder as a catalyst in the reaction. Furthermore, the catalyst is readily available, inexpensive, and stable. It catalyzes the reaction of toluene with a hydroxylamine salt under mild reaction conditions to produce methylaniline in a single step with high selectivity and yield.

[0006] The technical solution of the present invention is:

[0007] A method for preparing methylaniline by using elemental vanadium as a catalyst in the reaction of toluene and hydroxylamine salt, the method comprising the following steps:

[0008] Add glacial acetic acid, deionized water, hydroxylamine hydrochloride, toluene, and vanadium into a reactor equipped with a stirring and condensing reflux device, raise the temperature to 60-100°C, and react for 1-7 hours under stirring to obtain methylaniline;

[0009] The volume ratio of acetic acid: water: toluene is 10-15: 1-5: 2, the molar ratio of toluene to hydroxylamine salt is 1: 1-5, and 0.08g-0.2g of vanadium is added to every 2ml of toluene;

[0010] The particle size of the vanadium element is 200-500 meshes.

[0011] The essential features of the present invention are:

[0012] The current preparation of aromatic compounds uses supported catalysts, which utilize an amino radical mechanism. First, amino radicals are generated by hydroxylamine and metal oxides in an acidic solvent. Toluene radicals are also generated by toluene and metal oxides in an acidic solvent. Then, the amino radicals react with toluene (or toluene radicals) to form methylaniline.

[0013] In the present invention, vanadium is directly used as a catalyst, and hydroxylamine, toluene and metallic vanadium are used to generate amino free radicals and toluene free radicals in an acidic solvent to generate methylaniline.

[0014] The catalyst used in the present invention is a simple metal element powder. Only by adding vanadium element powder, toluene and hydroxylamine salt can react under mild conditions to generate methylaniline.

[0015] The effects and benefits of the present invention are:

[0016] The catalyst of the present invention exhibits high selectivity and reactivity in the one-step reaction of toluene with hydroxylamine salt to produce methylaniline, achieving a selectivity of 96.86% and a yield of 74.98%. Compared to the traditional impregnation method for preparing supported catalysts with superior catalytic performance reported in the literature, the catalyst of the present invention is simple, readily available, low-cost, and environmentally friendly, offering promising prospects for application and industrialization. DETAILED DESCRIPTION

[0017] Example 1

[0018] To a 100ml three-necked flask equipped with a stirring and reflux system were added 5ml of deionized water, 10ml of glacial acetic acid, 0.1g of catalyst (powdered vanadium, 300 mesh), and 2.63g of hydroxylamine hydrochloride (37.86mmol). The mixture was stirred at 30°C for 10 minutes until the hydroxylamine hydrochloride was completely dissolved. Then, 2ml of toluene (18.93mmol, toluene:hydroxylamine molar ratio of 1:2) was added to the flask, and the temperature was raised to 75°C for 5 hours. After cooling to room temperature, the reaction system was neutralized with 30% by weight NaOH solution in an ice-water bath to a pH of 7-8. The organic phase was then extracted with 10ml of ethyl acetate, and the sample was analyzed qualitatively and quantitatively by gas chromatography. The experimental results are shown in Table I.

[0019] Examples 2 to 5

[0020] The other operating steps and reaction conditions were the same as in Example 1, except that the amounts of hydroxylamine hydrochloride added were different: 1.315 g, 3.945 g, 5.26 g, and 6.575 g, respectively (based on the molar ratio of toluene to hydroxylamine, 1:1, 1:3, 1:4, and 1:5, respectively). The experimental results are shown in Table 1.

[0021] Table I Effect of the amount of hydroxylamine hydrochloride added on the reaction of toluene with hydroxylamine hydrochloride to produce methylaniline

[0022]

[0023] Examples 6 to 10

[0024] The other operating steps and reaction conditions were the same as those in Example 1, except that the reaction temperatures were 60° C., 70° C., 80° C., 90° C., and 100° C. The experimental results are shown in Table II.

[0025] Table II Effect of reaction temperature on the reaction of toluene with hydroxylamine hydrochloride to produce methylaniline

[0026]

[0027] Examples 11 to 16

[0028] The other operating steps and reaction conditions were the same as those in Example 1, except that the amounts of catalyst used were 0.08 g, 0.12 g, 0.14 g, 0.16 g, 0.18 g, and 0.2 g, respectively. The experimental results are shown in Table III.

[0029] Table III Effect of catalyst dosage on the reaction of toluene with hydroxylamine hydrochloride to produce methylaniline

[0030]

[0031] Examples 17 to 22

[0032] The other operating steps and reaction conditions were the same as those in Example 1, except that the amount of catalyst used was 0.14 g and the reaction times were 1 h, 2 h, 3 h, 4 h, 6 h, and 7 h, respectively. The experimental results are shown in Table IV.

[0033] Table IV Effect of reaction time on the reaction of toluene with hydroxylamine hydrochloride to prepare methylaniline

[0034]

[0035] As shown in Tables I to IV, under the appropriate reaction conditions: a toluene to hydroxylamine hydrochloride molar ratio of 1:2, a reaction temperature of 75°C, a catalyst dosage of 0.14 g, and a reaction time of 5 h, the toluene conversion rate was 77.41%, and the methylaniline yield was 74.98%.

[0036] Matters not covered by the present invention are known technologies.

Claims

1. A method for preparing methylaniline by using vanadium as a catalyst in the reaction of toluene with a hydroxylamine salt, characterized in that the method comprises the following steps: Add glacial acetic acid, deionized water, hydroxylamine hydrochloride, toluene, and vanadium into a reactor equipped with a stirring and condensing reflux device, raise the temperature to 75°C, and react for 1-7 hours under stirring to obtain methylaniline; The volume ratio of acetic acid: water: toluene is 10-15: 1-5: 2, the molar ratio of toluene to hydroxylamine salt is 1: 2, and 0.14 g of vanadium is added to every 2 ml of toluene. The particle size of the vanadium element is 200-500 meshes.

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