Application of terephthalaldehyde_Kain Industrial Additive

Background^[1][2]

Terephthalaldehyde is an important fine chemical raw material downstream of paraxylene. Because there are two active aldehyde groups in its molecular structure, it can self-polymerize or copolymerize with other monomers to form polymer materials. It is mainly used Used in the synthesis of fluorescent materials, catalyst carriers and other high molecular polymer products. The traditional production method of terephthalaldehyde is through chlorination of p-xylene and subsequent hydrolysis under the action of nitric acid or metal oxides.

This production process requires a large amount of toxic chlorine, nitric acid and sodium hydroxide, and produces gases such as hydrogen chloride, NOx and chloroalkylbenzene, which can easily cause environmental pollution and equipment corrosion. Material leakage can also cause harm to the human body. . In addition to the traditional chlorination method, the synthesis methods of terephthalaldehyde also include terephthalic acid (ester) hydrogenation method, terephthaloyl chloride hydrogenation method and direct oxidation of paraxylene.

Structure

Apply^[1]

1. Fluorescent materials

Fluorescent whitening agents mainly include distyryl biphenyl (such as CBS, etc.) and bistriazine amino stilbene. ER-I is one of the representative varieties of distyryl biphenyl whitening agents. ER-I is synthesized in a pilot scale using triethyl phosphite, o-cyanobenzyl chloride and terephthalaldehyde as raw materials. First, phosphorous acid is used. Triethyl ester and o-cyanobenzyl chloride undergo Abuzov esterification to obtain an aromatic ring intermediate containing phosphorus and nitrogen, which is then reacted with terephthalaldehyde to form ER-I.

The research results show that when the molar ratio of phosphate ester and benzyl chloride is 1.1, the feeding temperature is controlled at 140°C, the reaction time is 9 h, and the total yield of the two-step reaction is 93%. The fluorescent whitening agent DX-EB is synthesized using (o-cyanobenzyl) dimethyl phosphonate, (p-cyanobenzyl) dimethyl phosphonate, terephthalaldehyde and sodium methoxide, when (p-cyanobenzyl) ) When the ratio of dimethyl phosphonate to (o-cyanobenzyl) dimethyl phosphonate is 1.5 and the reaction temperature is 40°C, the yield of 1-o-cyanostyryl-4-p-cyanostyrylbenzene The highest rate is 74.72%.

A new type of SBQ photosensitive monomer has been studied. Specifically, an organic base catalyst is used to replace the traditional weak acid and strong acid catalysts to synthesize a pyridine quaternary ammonium salt. The salt is added dropwise to a solution containing methanol, toluene and terephthalaldehyde. and other organic solvents in an organic alkaline solution, reflux for 5-8 hours to obtain a solution, and cool and crystallize to obtain a bright yellow SBQ monomer with a purity higher than 99%. In addition to being used as a fluorescent whitening agent, terephthalaldehyde can also be used to synthesize fluorescent materials for substance detection.

For example, using terephthalaldehyde and aminophenol as raw materials, a chemical fluorescence sensor with an aminophenol recognition unit and a terephthalaldehyde reporter unit with a metal complex function was synthesized. This fluorescence sensor can detect efficiently and selectively Cu2 + has been successfully used to detect the Cu2 + concentration in fresh L929 cells; Rhodamine and terephthalaldehyde are used to react with Schiff base to obtain photosensitive substances. When exposed to Hg2 +, the color changes from colorless to purple visible to the naked eye. Other alkali metals and transition metals only have slight interference on the spectrum. This photosensitive substance is grafted on the surface of SiO2 nanoparticles to ensure the repeatability of sensing and is expected to have further applications in optical sensors.

A semiconductor blue fluorescent thiazole dye compound was synthesized using terephthalaldehyde and dithiooxamide as substrates and sodium hydroxide as initiator. This compound can withstand temperatures up to 200°C. It not only absorbs at the wavelength of 264 nm in the ultraviolet region, but also has a strong absorption spectrum at 485 nm in the visible light region.

The valence band energy of this type of compound is 2.56 eV, and it is fluorescent at 467 nm and 497 nm. It may be used in electronics and optics in the future; using melamine and terephthalaldehyde as precursors, it can be used in dimethyl Polymers with fluorescent properties were obtained using three methods: solvothermal synthesis, normal reflux and microwave assistance in methyl sulfoxide. The results showed that the sample obtained by solvothermal synthesis at 180 ℃ has better detection ability of trinitrotoluene in soil. Performance, the lowest concentration of trinitrotoluene that can be detected is 1.8 nmol/L.

2. Catalysis and adsorption materials

Binary covalent porphyrin framework polymers were solvothermally synthesized using manganese tetrasubstituted hydrazide porphyrins and terephthalaldehyde. This type of polymer has good thermal stability below 350 ℃ and is used to catalyze benzene. Ethylene, cyclohexene, and ?-olefins can generate epoxy compounds with high selectivity. For example, when the reaction temperature is 80°C and tert-butanol peroxide is used as the oxygen source, the oxidation of cyclohexene is catalyzed. After 24 hours of reaction, the cyclohexene conversion rate is 99%. 1,2-epoxycyclohexane is selected. The efficiency is 99%; under the same conditions, the styrene conversion rate and the selectivity of styrene oxide are 99% and 68% respectively.

Melamine and terephthalaldehyde were polymerized at high temperature through Schiff base reaction under solvent-free conditions to form a polymer. The effects of different polymerization temperatures on the properties of the polymerized products were investigated. It was found that the sample obtained at the polymerization temperature of 250 °C had a wavelength of Under visible light irradiation of 420 nm, the photohydrolysis efficiency is 58.1 μmol h-1. This result is twice the photohydrolysis efficiency of the nitrogen-doped carbon sample C3N4. This type of material is expected to be used in the fields of catalysis, energy and environment. applied in.

Using phloroglucinol and terephthalaldehyde as raw materials, microporous organic framework polymers were synthesized by hydrothermal method. Under ultraviolet light irradiation, this type of, and the product needs to be separated from a large amount of pivalic acid system, which requires high energy consumption.

Under the conditions of reaction temperature of 350 ℃, hydrogen space velocity of 1250 h-1 and dimethyl terephthalate liquid space velocity of 0.22 kgl-1cat h-1, terephthalic acid on Cr-ZrO2 catalyst The conversion rate is 48.6%, the monoaldehyde selectivity is 68.2%, and the dialdehyde selectivity is 14.4%; under the same conditions, the conversion rate of catalytic hydrogenation of p-aldehyde methyl benzoate is 42.9%, and the dialdehyde selectivity is increased to 61.7 %, the selectivity of terephthalaldehyde on another Zn-ZrO2 (Zn/Zr material ratio is 1: 20) catalyst increased to 72.4%, but the conversion rate dropped to 28.2%.

3. Hydrogenation of terephthaloyl chloride

The hydrodechlorination of acid chloride compounds to aldehydes was an important reaction discovered by Rosenmand in the early twentieth century, so it was named Rosenmand reduction reaction. Pd/BaSO4 is usually used as the catalyst. In recent years, studies have found that Pd metal complexes can convert nearly 100% of benzoyl chloride into benzene within 1 hour at room temperature under the combined action of polymethylhydroxysilane, potassium fluoride, tris(2-furyl)phosphine, etc. Formaldehyde, this catalytic system can also efficiently catalyze other aromatic hydrocarbon acyl chloride compounds to produce aldehydes.

A Pd /SiO2 catalyst with a Pd loading of 3 wt% was prepared by the sol-gel method, using cyclohexane or toluene as the solvent to catalyze the hydrogenation of terephthaloyl chloride. When the reaction temperature was 180°C, the reaction was carried out for 25 hours. Afterwards, the conversion rate of terephthaloyl chloride was 99%, and the total selectivity of aldehyde products such as terephthalaldehyde and p-toluene was 76%. In addition to the Pd system catalyst, using Ru complex as the catalyst and dimethylphenol silane as the reducing agent, aldehydes can be obtained in high yields by catalyzing the hydrogenation of acid chloride in different solvents such as methylene chloride, acetone and acetonitrile.

4. Direct oxidation of p-xylene

With increasingly stringent environmental protection requirements at home and abroad, the one-step oxidation of paraxylene as raw material to produce terephthalaldehyde has attracted widespread attention from academia and industry at home and abroad. Foreign companies such as Eastman, Nippon, BASF and LG have carried out many years of research work on the oxidation of paraxylene to synthesize terephthalaldehyde. For example, Eastman Company introduced the oxidation of paraxylene to generate terephthalaldehyde through air oxidation. The catalyst selects a multi-component system of tungsten oxide or silicotungstic acid, aluminum oxide, and bismuth oxide. Under the reaction temperature of 550°C, the concentration of paraxylene The conversion rate and terephthalaldehyde yield can reach 41% and 54%.

Nippon Company uses alumina-supported antimony, iron and tungsten oxides as catalysts and oxidizes them with air. When the reaction temperature is 550°C, the conversion rate of paraxylene is 90.9%, and the production of terephthalaldehyde is The rate is 62.6%. Fe-Mo catalysts were prepared using chemical vapor deposition. These catalysts were characterized by XRD, TEM, XPS and other means, and their performance in the oxidation of paraxylene to terephthalaldehyde was investigated. In 2006, LG Chemical Company developed a direct oxidation process for the production of terephthalaldehyde (TPAL), which uses tungsten-containing metal composite oxides as catalysts in a multi-tube fixed-bed reactor with a shell-and-tube configuration. Under the conditions of 550-600 ℃ and normal pressure, the conversion rate of paraxylene is 70-78%, and the selectivity of terephthalaldehyde is 70-80%.

According to LG Chem, the use of new processes will greatly reduce production costs. Similar o-phthalaldehyde can also be produced by selective oxidation of o-xylene. There are few domestic studies on the direct oxidation of paraxylene to synthesize terephthalaldehyde, with only Guangxi University and Guangzhou University conducting research. Guangzhou University prepared a Fe-Mo-Ni metal oxide catalyst using a sol-gel method. The introduction of the additive Ni improved the catalytic activity of the Fe-Mo catalyst and increased the yield of terephthalaldehyde from 24.8 to 24.8 before modification. % increased to 38.3%, and the terephthalaldehyde selectivity was 47.7%.

Main reference materials

[1] Research progress on the synthesis and application of terephthalaldehyde

[2] Yang Yongmei, Xu Songhao. Research on the synthesis process of terephthalaldehyde [J]. Jiangsu Chemical Industry, 1999, 5, 21-22.