1-Naphthaleneacetic Acid (NAA) is an important plant growth regulator that promotes plant growth. It is a compound widely used in plant growth regulators and fruit and vegetable ripening agents. Broad-spectrum plant growth regulator. It can promote cell division and expansion, induce the formation of adventitious roots, increase fruit setting, prevent fruit drop, and change the ratio of female and male flowers. Naphthaleneacetic acid can enter the plant body through the tender epidermis of leaves and branches, and seeds, and is transported to the action site along with the nutrient flow. It is usually used in wheat, rice, cotton, tea, mulberry, tomato, apple, melon, potato, forest trees, etc. It is a good plant growth stimulant. If it is used to prevent fruit drop, the concentration should not be too high, otherwise it will cause the opposite effect, because high concentration of naphthaleneacetic acid can promote the production of ethylene in plants. Among them, methyl aromatization synthesis method is one of the important methods for preparing NAA. Several common NAA synthesis methods are introduced below:
1. Methyl aromatization synthesis method:
This method starts from methylnaphthalene and prepares NAA through reactions such as oxidation, methylolation, and carboxylation. Specific steps are as follows:
Step 1: Preparation of Naphthalene:
First, styrene and toluene are mixed at a ratio of 5:1, and the cyclization reaction under the catalysis of tungstic acid is carried out at 100-120°C to prepare Naphthalene. The reaction needs to continue for 4-6 hours, and the quality of the product is determined by sampling to determine the end time of the reaction.
Step 2: Synthesis of 1-Naphthaleneacetonitrile:
Naphthalene and formaldehyde are mixed at a ratio of 1:1, and sodium sulfite and copper catalysts are added to allow thiourea addition reaction at 200°C to form 1-Naphthaleneacetonitrile. The reaction needs to last for 2-3 hours, and the quality of the reaction product is detected by spectrometry.
Step 3: Preparation of 1-Naphthaleneacetic Acid:
Mix 1-Naphthaleneacetonitrile with sodium hydroxide, water, and high-temperature ethanol for a reduction reaction to generate 1-Naphthaleneacetic Acid. By measuring the pH value and collecting the melting point of the product, the end time of the reaction and the yield were determined.
The methyl aromatization synthesis method can efficiently and stably prepare NAA, which provides important theoretical support for its industrial production. Among them, it is necessary to adjust the reaction conditions reasonably in the synthesis to ensure the quality of the product, and to control and recover the by-products produced during the reaction.
2. Acid chloride synthesis method:
This method uses naphthaleneacetic acid as raw material to prepare NAA through acylation, oxidation and other reactions. Acid chloride synthesis method and its specific steps.
as follows:
(1). Synthesis principle:
The synthesis methods of 1-Naphthalene acetic acid mainly include acylation method, acyl chloride method, ortho-nitrosylation method, etc. Among them, the acid chloride method is a relatively commonly used method. Its principle is to generate 1-Naphthaleneacetyl Chloride under the action of 1-Naphthaleneacetic Acid and Thionyl Chloride, and then hydrolyze it with sodium hydroxide to generate 1-Naphthaleneacetic Acid.
(2). Synthesis steps:
(2.1). Raw material preparation
1-Naphthalene acetic Acid and Thionyl Chloride are used as synthetic substances, and nitrobenzene, SOCl2, sodium hydroxide, ethanol, etc. are used as auxiliary reagents.
(2.2) Reaction process:
(2.2.1) Mix 1-Naphthaleneacetic Acid (10.0g) and Thionyl Chloride (10.0mL) in a 250mL round bottom flask, stir at room temperature for 30 minutes, and leave the mixed liquid at room temperature for 1 hour.
(2.2.2) Transfer the reaction solution to an ice-water washing room to cool for 30 minutes, filter the reaction product and wash with ethanol three times to remove impurities and obtain 1-Naphthaleneacetyl Chloride.
(2.2.3) Add 100mL of 1% NaOH solution dropwise to 1-Naphthaleneacetyl Chloride (5.0g). After the addition, the pH of the reaction solution is about 7. Continue stirring for 1 hour to hydrolyze it to generate 1-Naphthaleneacetic Acid.
(2.2.4) The reaction solution was adjusted to be acidic with concentrated hydrochloric acid, washed with ethanol three times, and the product was hanged and dried in a desiccator to finally obtain the target product 1-Naphthaleneacetic Acid.
(3) Reaction conditions:
Reaction temperature: room temperature;
Reaction time: 2 hours;
PH value: 7;
Solvent: absolute ethanol.
(4 Conclusion:
This article introduces the synthesis method of 1-Naphthaleneacetic Acid by acid chloride method and its specific steps. The method is relatively simple and efficient, and the product has high purity, which is suitable for industrial production. Attention should be paid to the control of reaction conditions so as not to affect the product yield.
3. Direct carboxylation method:
In this method, methylnaphthalene and carbon dioxide are used as raw materials, and NAA is obtained by direct carboxylation through a gas phase reaction. The specific steps of the method for the synthesis of 1-Naphthaleneacetic Acid by direct carboxylation are as follows:
(1.) Take 1mol of 1-naphthaleneacetic acid (Naphthaleneacetic Acid), 2mol of hydrogen peroxide (H2O2) and 3mol of acetic acid (CH3COOH) as raw materials.
(2.) Add a catalyst, the catalyst can be manganese acetate (Manganese Acetate), its role is to promote the reaction, the catalyst accounts for 0.1% of the total reaction system.
(3.) Mix the reaction materials and heat them to 70°C to generate a new product 1-Naphthaleneacetic Acid through the reaction.
(4.) Cool the reaction mixture and wash it several times with deionized water, then filter the sample with a vacuum filter.
(5.) Dry the filtered solid waste in a desiccator to a constant weight.
(6.) Finally, use laboratory instruments to characterize and analyze the newly synthesized 1-Naphthaleneacetic Acid, such as nuclear magnetic resonance (NMR), infrared spectroscopy (IR), etc.
The method has the advantages of simple operation, mild reaction conditions, high product purity and the like. The method for synthesizing 1-Naphthalene acetic Acid by direct carboxylation provides a new method for the field of organic synthesis and is expected to be applied to large-scale preparation.
The purity of the products produced by the three methods must be improved through crystal separation, crystallization purification and other treatment methods, and these treatment methods will not be described in this article. The above three methods have different advantages, disadvantages and scope of application. In specific applications, they need to be selected according to the actual situation in order to obtain the best production efficiency.