DE3731860A1 - Process for the preparation of 2-aryl-2H-benzotriazoles - Google Patents

Abstract

There is described a novel reduction process for the preparation of hydroxybenzotriazoles, which can be used as commercially available UV absorbers, from nitroazobenzenes, in which the starting material is reduced using sodium dithionite or its precursor, e.g. sulphur dioxide or its salts, in the presence of a formate. If desired, the benzotriazole-N-oxide intermediates can also be isolated and reduced to the desired product. A quinone can additionally be used as a reaction catalyst. Since only very few by-products are produced in the process described, if at all, it can be carried out in a particularly economical manner.

Description

The invention relates to an improved method of manufacture of 2-aryl-2H-benzotriazoles and their derivatives in high yield and high purity with - if at all - small amounts of waste, especially reduction processes for by coupling o- and / or p-alkyl-substituted Phenols obtained with a diazonium salt of o-nitroanilines o-nitroazophenols.

Hydroxyphenylbenzotriazoles are used to protect polymers, which are broken down by long exposure to light, e.g. B. of ABS resins and polyolefins, as UV absorption medium used. For this reason, the concerned Products pure and at most weakly colored, so they do not discolor the polymer to be protected. This the main reason is probably that there are already numerous Processes for their production there. Another reason for this, however, is in terms of economic considerations to seek a provision of clean procedures.

According to US Pat. Nos. 2,362,988 and 3,072,585, benzotriazoles can be used by oxidation of o-aminoazophenols.

In other, briefly dealt with in US-PS 41 41 903 and a process that has been extensively investigated leads to a reduction of o-nitroazophenols e.g. B. electrolytically catalytic path using hydrogen, carbon monoxide and Hydrazine or mainly zinc dust in alkaline Media (cf. US-PS 40 41 044).

In the case of others comparable with the method according to the invention The process is reduced by means of sulfur inorganic compounds. From US-PS 42 24 451 is, for example, an aqueous reduction process under Known use of sulfhydrate or a sulfide. At This process consists of the primary reduction product a benzotriazole N-oxide, which is then by means of zinc or tin is further reduced to the corresponding triazole. This shows that sulfides or sulfhydrates are not strong enough to the starting compounds to the benzotriazoles themselves to reduce. On the other hand, too, for the same purpose sodium dithionite has already been successfully used (cf. J. Rosevear and JFK. Wilshire in "Aust. J. Chem.", 1984, 37, 2489). A disadvantage of the latter method is that its implementation in basic media Decompose the dithionite as a by-product sulfur can. This makes this process tedious and sometimes leads to undesirable results.

Sodium dithionite has also been used for other reduction purposes,  e.g. B. to reduce vat dyes in dye factories and for the reduction of nitro groups in Laboratories (see J.G. de Vries and R.M. Kellogg in "J. Org. Chem." 1980, 45, 4126). Further it was already used to reduce heterocyclic N-oxides used (see M.J. Haddadin and employees in "Tetrahedron", 30, 659 (1974)). Because you go through dithionite Reduction of sulfites, bisulfites and sulfur dioxide with Sodium formate and other reducing agents (cf. US-PS 38 26 818), sulfur dioxide and its salts (sulfites) or can produce intermediate salts (bisulfites) this for the same purpose in the context of the method according to the invention tried successfully in the presence of a format. Without formates, sulfites alone cannot do o-nitroazophenols to reduce. In addition, instead of ethanol (cf. the specified Australian reference "Aust. J. Chem.") as solvent N, N-dimethylformamide and additionally Formate used, the required amount of dithionite can be cut in half and the process without education of colloidal sulfur more constant and far more successful carry out. When working in dimethylformamide solutions there is no need to add sodium hydroxide. To decrease the response time and quality improvement of the End products have proven beneficial, quinones and to use phase transfer catalysts.

According to the invention it is compared to the known Procedure provided a clean procedure in which Obtain lighter colored reaction products in higher yields will. That when performing the invention Process mixture obtained does not contain any discolouring Impurities and rubbery by-products. Required when carrying out the method according to the invention you don't have heavy metals like zinc. After all, that is Implementation of the method according to the invention also completely  harmless, because not with hydrogen, hydrazine and carbon monoxide must be worked.

As starting compounds in the preparation of the invention Compounds of the formula

in which mean:
R₁ is a hydrogen or chlorine atom and
R₂ and R₃, which may be the same or different, each represent a hydrogen atom, a short-chain alkyl radical having 1 to 5 carbon atoms or a phenylalkyl radical having 7 to 9 carbon atoms,
become azobenzenes of the formula:

wherein the radicals R₁, R₂ and R₃ have the meaning given own, used.

They can be used in a conventional manner, e.g. by the method known from US-PS 37 73 751, manufacture. You can directly in solution without insulation or Drying may be reduced, however most attempts have been made  with a view to a clear estimate of the yield with dry raw materials. The source material is in a suitable solvent, e.g. B. dimethylformamide, Benzene, toluene, xylene or white spirit or turpentine substitute (mineral spirit) or in one Mixed solvents such as dimethylformamide and chlorobenzene, solved. The reaction is preferably carried out under a nitrogen atmosphere. The solution obtained is, if necessary a base such as sodium hydroxide, sodium carbonate, Potassium hydroxide or potassium carbonate added. Farther 3-4.5 moles of sodium formate and 1.12-4 moles of solution Sodium dithionite in solid or dissolved form at once, added in equal amounts or continuously. After that the reaction mixture is preferably close to 80 ° C 100-104 ° C, heated. This forms in the reflux condenser some condensate. After a certain reaction time, for example 4 h, which depends on the reaction system used, the reaction is carried out by adding an appropriate one third solvent, such as isopropanol, to reduce the Solubility of the reaction product interrupted, whereupon inorganic mainly consisting of sodium sulfate insoluble salts at the highest possible in practice Temperature can be filtered off. Then the filtrate cooled to 5 ° C or less. The failed here light yellow solid product is separated off and dried. The Purity of products and progress in implementation can be easily determined by thin layer chromatography (Developer: n-hexane / ethyl acetate = 4/1). The Reaction products can be identified in terms of their identity and check quality by infrared spectral analysis. At the Recrystallization from isopropanol gives light yellow or almost white benzotriazoles of the formula I or their N-oxides of the formula:  

wherein the radicals R₁, R₂ and R₃ have the meaning given.

Obviously the N-oxides are the intermediates of Benzotriazoles. They represent the most undesirable discoloring Impurities represent the latter. You can if necessary isolate and according to known methods reduce (see US Pat. No. 4,224,451). Leave according to the invention however, they make themselves at will and then after further reduce the same procedure to the benzotriazoles.

To further improve the efficiency of the invention Quinones, such as sodium anthraquinone-2-sulfonate, or mixtures of quinones and phase transfer catalysts, such as 1,4-naphthoquinone and p-toluenesulfonic acid, can also be used. The implementation can within a wide pH range especially on the basic side. The system turns especially when using sodium dithionite by itself a. However, if salts of sulfur dioxide are used, the preferred pH range is 9.5-10. Occasionally must this pH of the reaction medium at the beginning and be set during the reaction.

In two-phase systems, the implementation is by cooling and removal of the aqueous phase interrupted. The organic Phase if necessary by distilling off concentrated by some solvent. To reduce the  Solubility of the reaction product becomes an appropriate one third solvent, e.g. B. isopropanol, followed by the whole is cooled to 5 ° C or below. The one here precipitated light yellow solid is separated off and dried. When recrystallized from isopropanol bright tan or almost white products.

When distilling the mother liquor from the crystallization Recovery of the solvents fall more light colored Product and consisting mainly of sodium sulfate inorganic salts. From this solid backlog If necessary, another product can be used Extraction and subsequent recrystallization Win isopropanol.

The following examples are intended to illustrate the invention vivid.

example 1 5-chloro-2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) -2H- benzotriazole

A 100 ml, with a stirrer, a reflux condenser and a three-neck flask equipped with a nitrogen inlet is mixed with 12 ml of dimethylformamide, 3.89 g (10 mmol) 2-nitro-4-chloro-2′-hydroxy-3 ′, 5′-di-tert-butylazobenzene, 2.53 g (37.2 mmol) sodium formate and 2 g (11.5 mmol) Sodium dithionite charged, whereupon the reaction mixture with stirring and under a nitrogen atmosphere to weak Reflux is heated. After heating for 1 hour The reaction mixture becomes reflux temperature (100-105 ° C) with another gram of sodium dithionite (5.7 mmol), whereupon heating continues for a further 1.5 hours at gentle reflux becomes. After adding 40 ml of isopropanol  Reaction mixture heated to 80-85 ° C for 20 minutes. In the end the reaction mixture is filtered hot. The one separated here solid residue from mainly sodium sulfate is discarded. The filtrate is cooled to below 5 ° C. The light tan product which has precipitated is separated off, washed with a very small amount of isopropanol and dried in vacuo to give 2.10 g of benzotriazole will. Further benzotriazole is obtained by evaporation the mother liquor in a rotary evaporator and recrystallization the evaporation residue with 10 ml isopropanol. The overall yield is 3.0 g (84%) of the reaction product mp 153.5-155.5 ° C.

Example 2 2- (2'-Hydroxy-5'-methylphenyl) -2H-benzotriazole

A 100 ml, with a stirrer, a reflux condenser and a three-neck flask equipped with a nitrogen inlet is mixed with 10 ml of dimethylformamide, 2.57 g (10 mmol) of 2-nitro 2'-hydroxy-5'-methylazobenzene, 3.00 g (44 mmol) sodium formate and 3.57 g (34 mmol) of sodium bisulfite, whereupon the reaction mixture with stirring and under a nitrogen atmosphere For 1 h under gentle reflux 100-105 ° C is heated. After adding 20 ml of isopropanol the reaction mixture is described in Example 1 Worked up way, with a total yield of 1.67 g (74.2%) reaction product, mp 129-130 ° C is obtained.

Example 3 2- (2'-Hydroxy-3 ', 5'-di-tert-amylphenyl) -2H-benzotriazole

A 100 ml, with a stirrer, a reflux condenser and a three-neck flask equipped with a nitrogen inlet  is mixed with 10 ml of dimethylformamide, 3.83 g (10 mmol) of 2-nitro- 2′-hydroxy-3 ′, 5′-di-tert-amylazobenzene 2.53 g (37 mmol) Sodium formate and 3.24 g (31 mmol) sodium bisulfite, whereupon the reaction mixture with stirring and under a nitrogen atmosphere for 1 hour under gentle reflux is heated to 100-105 ° C. After adding 35 ml Isopropanol is the reaction mixture in the example 1 worked up described, whereby a total of 2.84 g (80.9%) reaction product of mp 80-81 ° C obtained will.

Example 4 2- [2′-hydroxy-3 ′, 5′-di- (1 ′ ′, 1 ′ ′ - dimethylbenzyl)] - 2H- benzotriazole

A 100 ml, with a stirrer, a reflux condenser and a three-neck flask equipped with a nitrogen inlet is mixed with 5 ml of dimethylformamide, 2.4 g (5 mmol) 2-nitro-2- [2′-hydroxy-3 ′, 5′-di- (1 ′ ′, 1 ′ ′ - dimethylbenzyl)] - azobenzene, 1.5 g (22 mmol) sodium formate and 1.5 g (14 mmol) sodium bisulfite was added, followed by the reaction mixture with stirring and under a nitrogen atmosphere Heated to 100-105 ° C for 1 h under gentle reflux becomes. After adding 20 ml of isopropanol, the reaction mixture worked up in the manner described in Example 1, with a total of 1.24 g (55.4%) reaction product an mp of 138-138.5 ° C can be obtained.

Example 5 5-chloro-2- (2′Hydroxy-3 ′, 5′-di-tert-butylphenyl) -2H- bezotriazole

A 100 ml, with a stirrer, a reflux condenser and a three-neck flask equipped with a nitrogen inlet  is mixed with 6 ml of dimethylformamide, 4 ml of chlorobenzene, 3.89 g (10 mmol) of 2-nitro-4-chloro-2'-hydroxy-3 ', 5'-di-tert-butylazobenzene, 3.0 g (44 mmol) sodium formate and 3.5 g (33.7 mmol) sodium bisulfite was added, followed by the reaction mixture with stirring and under a nitrogen atmosphere is heated to weak reflux. After 1.5 hours Heating to reflux temperature (100-105 ° C) become 50 ml Isopropanol added, whereupon the reaction mixture in the is worked up in the manner described in Example 1. Here a total of 2.68 g (75.1%) of reaction product is obtained.

Example 6 5-chloro-2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) -2H- bezotriazole

A 100 ml, with a stirrer, a reflux condenser and a three-neck flask equipped with a nitrogen inlet with 6 ml of dimethylformamide, 4 ml of toluene, 3.89 g (10 mmol) 2-nitro-4-chloro-2'-hydroxy-3 ', 5'-di-tert-butylazobenzene, 3.0 g (44 mmol) sodium formate and 3.5 g (33.7 mmol) sodium bisulfite was added, followed by the reaction mixture with stirring and under a nitrogen atmosphere is heated to weak reflux. After 1.5 hours Heating to reflux temperature (100-105 ° C) become 50 ml Isopropanol added. Then the reaction mixture worked up in the manner described in Example 1, a total of 2.68 g (75.1%) of reaction product is obtained will.

Example 7 2- (2'-hydroxy-5'-methylphenyl) -2H-benzotriazole-N-oxide

A 250 ml, with a stirrer, a reflux condenser and a three-neck flask equipped with a nitrogen inlet  with 100 ml of water, 1.5 g of sodium hydroxide, 2.57 g (10 mmol) 2-nitro-2'-hydroxy-5'-methylazobenzene and 3.0 g (44 mmol) sodium formate was added, followed by the reaction mixture with stirring and under a nitrogen atmosphere 70-75 ° C is heated. Now in portions 2.2 g (12.6 mmol) of sodium dithionite in 20 ml of water were added, that the dithionite concentration is maintained remains, but there is no excess dithionite (which is caused by a light blue color due to a previously added Drop of 1,1'-dimethyl-4,4'-bipyridylium dichloride Solution is displayed). Usually needed one for the addition 3.5 h. After that, the implementation is still Continued for 30 min. After filtering the reaction mixture at 50 ° C the filtrate is concentrated with 5 ml HCl acidified. The pale yellow precipitate that occurred we collected and recrystallized from 13 ml of isopropanol. After drying, 1.8 g (74.7%) of light yellow are obtained Benzotriazole-N-oxide, mp 138-139 ° C.

Example 8 2- (2'-Hydroxy-5'-methylphenyl) -2H-benzotriazole

A 250 ml, with a stirrer, a reflux condenser and a three-neck flask equipped with a nitrogen inlet with 100 ml of water, 1.5 g of sodium hydroxide, 2.57 g (10 mmol) 2-nitro-2'-hydroxy-5'-methylazobenzene and 3.00 g (44 mmol) of sodium formate, whereupon the Reaction mixture with stirring and under a nitrogen atmosphere is heated to 70-75 ° C. Now be accordingly Example 7 6.68 g (38 mmol) of sodium dithionite in portions in 60 ml of water such that the dithionite concentration is maintained, but no dithionite surplus arises. Usually you need for this Addition 11 h. The reaction is then continued for 1 hour.  After cooling the reaction mixture to room temperature the reaction by-products are filtered off. The clarified solution is washed three times with 10 ml of chloroform extracted. After removing the solvent in one Rotary evaporator will evaporate the residue 12 ml of isopropanol recrystallized and dried, whereby 1.6 g (71.1%) of light tan benzotriazole can be obtained.

Example 9 5-chloro-2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) -2H- benzotriazole N-oxide

A 100 ml, with a stirrer, a reflux condenser and a three-neck flask equipped with a nitrogen inlet is mixed with 30 ml water, 3.0 g sodium hydroxide, 20 ml chlorobenzene, 3.89 g (10 mmol) of 2-nitro-4-chloro-2′-hydroxy-3 ′, 5′- di-tert-butylazobenzene, 3.0 g sodium p-toluenesulfonate, 0.2 g of 1,4-naphthoquinone and 2.04 g (30 mmol) of sodium formate charged, whereupon the reaction mixture with stirring and heated to weak reflux under a nitrogen atmosphere (95-100 ° C). Then in portions inside 3.6 g (21 mmol) of sodium dithionite in 20 ml of water for 4 h admitted. The reaction is then continued for 30 min continued at 100-105 ° C for a long time. After cooling the Reaction mixture to room temperature separate layers from each other. The upper layer of chlorobenzene is added twice Washed 30 ml of water. After removing the solvent in a rotary evaporator the evaporation residue recrystallized from 40 ml isopropanol and dried, 3.55 g (95.2%) of light yellow benzotriazole N-oxide are obtained will.  

Example 10 5-chloro-2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) -2H- benzotriazole N-oxide

A 100 ml, with a stirrer, a reflux condenser and a three-neck flask equipped with a nitrogen inlet is mixed with 30 ml of water, 5.1 g of sodium hydroxide, 20 ml chlorobenzene, 3.89 g (10 mmol) 2-nitro-4-chloro-2'- hydroxy-3 ′, 5′-di-tert-butylazobenzene, 2.04 g (30 mmol) Sodium formate and 0.02 g sodium anthraquinone-2-sulfonate charged, whereupon the reaction mixture with stirring and heated to weak reflux under a nitrogen atmosphere (95-100 ° C). Now in portions within 4 h 3.6 g (21 mmol) of sodium dithionite in 20 ml of water were added. The reaction is then continued for a further 30 minutes 100-105 ° C continued. After cooling the reaction mixture layers separate from one another at room temperature. The top layer of chlorobenzene is added twice Washed 30 ml of water. After removing the solvent the evaporation residue is removed using a rotary evaporator recrystallized from 40 ml isopropanol and dried, where 3.6 g (96.5% light yellow benzotriazole N-oxide be preserved.

Example 11 5-chloro-2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) -2H- benzotriazole

A 100 ml, with a stirrer, a reflux condenser and a three-neck flask equipped with a nitrogen inlet is mixed with 6 ml of dimethylformamide, 4 ml of chlorobenzene, 2.39 g (6.4 mmol) 5-chloro-2- (2'-hydroxy-3 ', 5'-di-tert.- butyl) -2H-benzotriazole-N-oxide, 5.5 g sodium carbonate, 2.10 g (31 mmol) sodium formate and 2.03 g (20 mmol)  Sodium bisulfite is fed, whereupon the reaction mixture with stirring and under a nitrogen atmosphere to weak Reflux is heated. After heating for 1.5 hours The reflux temperature (100-105 ° C) are 50 ml of isopropanol added, whereupon the reaction mixture in the in Example 1 described way is worked up, Here a total of 1.49 g (65.1%) of reaction product is obtained.

Claims (7)

1. Process for the preparation of 2-aryl-2H-benzotriazoles of the formula: in which mean:
R₁ is a hydrogen or chlorine atom;
R₂ is a hydrogen atom, a short-chain alkyl radical with 1 to 5 carbon atoms or a phenylalkyl radical with 7 to 9 carbon atoms and
R₃ is a hydrogen atom, a short-chain alkyl radical with 1 to 5 carbon atoms or a phenylalkyl radical with 7 to 9 carbon atoms,
characterized in that an o-nitroazophenol of the formula: wherein R₁, R₂ and R₃ have the meaning given, reduced in N, N-dimethylformamide in the presence of sodium formate at about 80-110 ° C with sodium dithionite. 2. The method according to claim 1, characterized in that the sodium dithionite by sodium bisulfite or replaced sodium sulfite. 3. The method according to claims 1 or 2, characterized in that that a mixture of solvents N, N-dimethylformamide and an aromatic solvent or a water-immiscible white spirit or white spirit (mineral spirit). 4. The method according to claims 1 or 2, characterized in that water is used as the solvent. 5. The method according to claims 1 to 4, characterized in that you have a quinone and a phase transfer catalyst also used. 6. Process according to Claims 2 to 5, characterized in that the end product is benzotriazole N-oxide of the formula: wherein R₁, R₂ and R₃ have the meaning given, produces. 7. The method according to any one of claims 1 to 5, characterized in that a benzo as the starting material triazole-N-oxide of formula III used.