In the production process of triazine UV absorbers, the production of intermediates is the key part, which determines the production capacity of the corresponding products. The specific process is as follows.

1. The synthesis process of UV-1164, UV-400 and UV-405.

The synthesis process of UV-1164, UV-400 and UV-405 is shown in Figure 1.

Synthesis routes of UV-400, 405 and 1164.
Figure 1. Synthesis routes of UV-400, 405 and 1164.

The synthesis of intermediate 1 consists of two steps.

The first step is the Friedel-Crafts reaction of cyanuric chloride with m-xylene in chlorobenzene or o-dichlorobenzene with aluminum trichloride as a catalyst and concentrated hydrochloric acid as co-catalyst. The reaction selectivity of m-xylene with cyanuric chloride is good, and the number of m-xylene substituents on the triazine ring can be controlled by the molar ratio of the two raw materials. The yield of the reaction in this step is relatively high. It can reach 80%-90%.

The second step is the Friedel-Crafts reaction of the intermediate from the first step with resorcinol. The solvent and catalyst are again chlorobenzene or o-dichlorobenzene and AlCl3.

At present, the synthesis of intermediate 1, the two-step reaction is generally used in the “one-pot method”. In other words, after the first step of the reaction, no post-treatment is carried out and resorcinol is added directly to the reaction solution for the second step of the reaction. The target product is obtained at the end of the reaction.

The advantage of this “one-pot method” is that there is no post-treatment in the first step of the reaction. The process of washing, distillation, centrifugation, drying and refining of the reaction solution can be eliminated.

Intermediate 1 and n-octyl chloride were used as raw materials, DMF/DMAc (N,N-dimethylformamide/N,N-dimethylacetamide) as solvent and K2CO3, Na2CO3 or NaOH as catalyst for the Williamson reaction. The target product UV-1164 was obtained in 80%-90% yield after refinement.

Intermediate 1, C12-C13 alkyl glycidyl ether/isooctyl glycidyl ether as raw material, toluene/xylene/homo-trimethylbenzene as solvent, tetrabutylammonium bromide, dodecyltrimethylammonium bromide, ethyltriphenylphosphonium iodide or ethyltriphenylphosphonium bromide as the catalyst, was used in the addition reaction to obtain UV-400/UV-405. this step of the addition reaction has few side reactions and does not remove small molecules (HCl /H2O). So the yield of this step is very high, generally more than 95%.

For the quality of the target product, the quality of Intermediate 1 itself is crucial. To get high quality UV-400 or UV-405, the content, transmittance and chromaticity of intermediate 1 need to reach a high level.

Synthetic route of glycidyl ethers.
Figure 2. Synthetic route of glycidyl ethers.

The main production process of alkyl glycidyl ethers required for UV-400 and UV-405 is as follows.

Isotridecanol/isooctanol, epichlorohydrin as raw material, NaOH and tetrabutylammonium bromide/dodecyl trimethylammonium bromide as a catalyst, 60-70℃ reaction. After the reaction, water washing and distillation were carried out to obtain the corresponding glycidyl ethers.

Since epichlorohydrin itself is easily hydrolyzed into mono- or di-alcohols, and the hydrolyzed alcohol reacts with the epoxy group. In addition, the raw alcohol and the product glycidyl ether likewise react in the presence of a phase transfer catalyst. Therefore, the synthesis process of glycidyl ethers is accompanied by complex side reactions.

2. Synthesis process of UV-1577 and UV-425.

The synthetic routes of UV-1577 and UV-425 are shown in Figure 3.

Synthetic route of UV-425 and 1577.
Figure 3. Synthetic route of UV-425 and 1577.

The synthesis process of intermediate 2 is exactly the same as that of intermediate 1. Only it is more difficult to use “one pot method”. It needs to be separated and purified during the process.

Unlike Intermediate 1, the substituents at the 2 and 4 positions on the triazine ring are benzene rings, and the Friedel-Crafts reaction between benzene and melamine is poorly selected, so it is difficult to achieve a controlled reaction of the number of benzene rings on the triazine ring by the method of raw material proportioning.

Intermediate 2 was subjected to Williamson reaction with n-hexyl chloride or n-octyl chloride to obtain UV-425 and UV-1164. this step of the reaction is exactly the same as the principle and process of Intermediate 1 and n-octyl chloride. The subsequent treatment process is also similar.

3. The synthesis process of UV-1600 and UV-479.

The intermediate of UV-1600 and UV-479, the synthesis process of intermediate 3. The more used method in the literature is the Grignard reagent method. That is, 4-bromobiphenyl is used as raw material and it is prepared as Grignard’s reagent biphenyl-based magnesium bromide. The latter is reacted with cyanuric chloride to obtain the corresponding intermediate. This intermediate is reacted with resorcinol for Friedel-Crafts reaction to get intermediate 3.

The biggest advantage of the Grignard reagent method is the good selectivity of the reaction. The amount of biphenyl on the triazine ring can be effectively controlled. The disadvantage is that the solvent tetrahydrofuran (THF) used for the preparation of Grignard’s reagent requires a low water content (generally less than 100 PPM). The loss of THF during subsequent treatment is high. The effluent contains more THF. and the recovered THF is difficult to use again.

In addition, Grignard reagent biphenyl-based magnesium bromide is very active and can react with both water and CO2. Therefore, it is difficult to store the actual Grignard, and try to use it now. The process route for the preparation of Intermediate 3 by the Grignard reagent method is shown in Figure 4.

Process route for the synthesis of intermediate 3 by Grignard reagent method
Figure 7. Process route for the synthesis of intermediate 3 by Grignard reagent method.

In addition, there is a palladium-catalyzed Suzuki reaction in the literature to prepare Intermediate 3. The Suzuki reaction also has good selectivity. However, the catalyst used for the reaction, tetrakis(triphenylphosphine)palladium (Pd(PPh3)4), is relatively expensive and difficult to apply. Moreover, the raw material biphenylboronic acid needs to be made in-house. Its preparation also requires the use of expensive palladium catalysts. Therefore, the Suzuki reaction catalyzed by palladium to produce Intermediate 3 is not as feasible as the Grignard reagent method.

The Suzuki reaction route is shown in Figure 5.

Figure 5. Palladium-catalyzed Suzuki reaction synthesis.

Currently, there is little literature related to the synthesis of Intermediate 3. There are even fewer reports of synthetic processes that are compatible with industrial production. Therefore, the synthesis process of intermediate 3 is still of high scientific value.

As for Intermediate 3 and brominated alkanes for the Williamson reaction to obtain UV-1600/479, the reaction principle and process are exactly the same as those of UV-1164 and UV-1577, and will not be repeated. Among them, the brominated reagent 2-bromopropionic acid isooctyl ester used in UV-479 can be obtained by esterification of 2-bromopropionic acid with isooctanol. It can also be obtained by the esterification of methyl 2-bromopropionate with isooctanol.

4. Synthesis process of UV-460, UV-5, and UV-477.

Intermediate of UV-460/5/477, Intermediate 4. Although there is only one step Friedel-Crafts reaction (see Figure 6).

Synthesis process route of intermediate 4.
Figure 6. Synthesis process route of intermediate 4.

However, this reaction is sensitive to the activity of reaction solvent and catalyst. And the subsequent treatment process is more tedious. The control of the conditions is more demanding and the amount of delicate solvent is larger for refinement. The reaction of the last step is also Williamson etherification reaction. The reaction conditions are not significantly different from the last step of UV-1577, UV-1164 and UV-1600 reactions.