CA1154777A - Process for the production of 2-aryl-2h- benzotriazoles - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A process for the production of 2-aryl-2H-benzotriazoles comprises reducing and cyclizing the corresponding o-nitroazo-benzenes with hydrogen at a temperature in the range of about 20°C to about 100°C and at a pressure in the range of about l atmosphere to about 66 atmospheres in an alkaline aqueous organic, preferably an aqueous alkali/alkanol, medium at a pH
over 10 in the presence of a noble metal hydrogenation catalyst, preferably palladium. High yields of pure product are obtained with a concomitant reduction of undesired by-products and a reduction in effluent pollution problems.

Description

-This invention pertains to a process for the preparation of 2-aryl-2H-benzotriazoles and derivatives thereof. More particularly, the invention relates to a novel process for preparing 2~aryl-2H-benzotriazoles where-by high yields of the desired products are obtained and ef-fluent pollution problems occurring with present processes for making such products are essentially eliminated.

Heretofore, the conversion of an ortho-nitroazo-benzene to the corresponding 2-aryl-2H-benzotriazole has been accomplished by chemical and electrolytic reduction processes. For example, as seen in U.S. Patents 3,072,585 and 3,230,194, o-nitroazobenzene derivatives have been chemically reduced utilizing zinc in alcoholic sodium hy-droxide solutions to give good yields of the corresponding

2-aryl-2H-benzotriazoles. Ammonium sulfide, alkali sulfides, zinc with ammonia at 80-100C, sodium hydro-sulfide and zinc with hydrochloric acid have also been used as the chemical reducing agents for this transformation as disclosed in U.S. Patent 2,362,988. The use of ammonium sulfide was also reported by S.N. Chakrabarty et al, J.
Indian Chem. Soc., 5, 555, (1928); Chem. Abst., 23, 836, (1929) with mixed results depending on the presence or ab-. .
sence of substituent groups on the 2-aryl group. In some cases the desired 2-aryl-2H-benzotriazoles were not formed at all with the products of reduction being only the corresponding o-aminoazobenzenes.

'7 7~7 Electrolytic reduction of o-nitroazobenzenes was reported by H. Itomi, Mem.Coll.Sci. Kyoto Imp. Univ., 12~, No. 6, 343 (1929); Chem. Abst., 24, 2060 (1930) with the use of a copper cathode in dilute sodium hydroxide solution.
Yields varied from 25 to 60% depending on specific embodi-ments and conditions with a ma~or impurity being ~ormed, namely the corresponding o-aminoazobenzene.

The widely used zinc dust and sodium hydroxide chemical reducing system for transforming o-nitroazoben-zenes into the corresponding 2-aryl-2H-benzotriazoles was reported by K. Elbs, et al, J. Prakt. Chem.,108, 204 (1924);
Chem. Abst., 19, 514 ~1925). The yields of the desired 2-aryl-2H-benzotriazoles varied from 30 to 85% depending on the specific o-nitroazobenzene intermediate reduced.

The known chemical and electrolytic reduction processes for preparing 2-aryl-benzotriazoles are not practical or economically attractive in many cases. The widely used zinc dust and sodium hydroxide system produces effluent pollution problems in respect to waste disposal of zïnc sludge which is of increasing environmental concern.

The preparation in good yield of the isomeric, but chemically distinct lH-benzotriazoles by the catalytic reduction in alkaline medium of o-nitrophenylhydrazine and selected phenyl ring substituted alkyl and perfluoroalkyl 7 1~ 7 derivatives thereof was reported in Japanese patent publication, Sho 48-26012, August 3, 1973. The isomeric 2H-benzotriazoles of this invention cannot be prepared from phenylhydrazines.
It is therefore an object of this invention to provide a novel process for the preparation of 2-aryl-2H-benzotriazoles avoiding severe po~ution and environmantal problems.
A further object of this invention is to prepare 2-aryl-21-1-benzotriazoles by reducing and cyclizing the corresponding o-nitroazobenzene under certain conditions hereinafter set forth in greater detail whereby high yields of the products can be obtained in acceptable purity.
According to the present invention, there is provided a process for the production of 2-aryl-2H-benzotriazoles of the formula:

R3~ R ~ R4 (1) wherein Rl is hydrogen or chlorine; R2 is hydrogen, chlorine, lower alkyl of 1 to 4 carbon atoms, lower alkoxy of 1 to 4 carbon atoms or carboalkoxy of 2 to 9 carbon atoms, carboxy or -S03H; R3 is alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, phenyl, phenyl substituted wi~h alkyl groups, said alkyl groups having 1 to ~ carbon atoms, cycloalkyl or 5 to 6 carbon atoms, carboalkoxy of 2 to 9 carbon atoms, chlorine, carboxyethyl or aryl-alkyl of 7 to 9 carbon atoms; R4 is hydrogen, lower alkyl of 1 to 4 carbon atoms, lower alkoxy of 1 to 4 carbon atoms, chlorine or hydroxyl, and R5 is hydrogen, alkyl of 1 to 12 carbon atoms, chlorine, cycloalkyl of 5 to 6 carbon atoms or arylalkyl of 7 to 9 carbon atoms, which comprises ~' ' ~L~5~7 ~

reducing and cyclizing the corresponding o-nitroazobenzene with hydrogen at a temperature in the range of from about 20C to about 100C and at a pressure in the range of from about 1 atmosphere to about 66 atmospheres while mixed in a solvent system of an aqueous alkaline /water miscible organic medium having a pH greater than 10 in the presence of a hydrogenation catalyst selected from the group consisting of the noble metals of Group VIII
of the Periodic Table with the proviso that, when Rl, R2, R3, R4 or R5 is chlorine, the hydrogenation catalyst cannot be palladium, and recovering the desired 2-aryl-2H-benzotriazole.

- 4a -A further embodiment of this invention is found in a process for the production of 2-(2-hydroxy-5-methyl-phenyl)-2H-benzotriazole which comprises treating 2-nitro-2'-hydroxy-5'-methylazobenzene with hydrogen at a tempera-ture in the range of from about 20C to about 100C and at a pressure in the range of about 1 atmosphere to about 66 atmospheres in an aqueous alkali/isopropanol medium in the presence of a hydrogenation catalyst comprising a noble metal of Group VIII of the Periodic Table, removing the noble metal catalyst by filtration, loweri:ng the pH of the system to a value less than 4 to precipitat.e the desired product, and recovering the desired 2-(2-hydroxy-5-methyl-phenyl)-2N-benzotriazole by conventional procedures.

A specific embodiment of the invention is exempli-fied in a process for the production of 2-~2-hydroxy-5-methylphenyl)-2H-benzotriazole, which comprises treating 2-nitro-2.'-hydroxy-5'-methylazobenzene with hydrogen at a temperature in the range of from about 20 to about 100C
and at a pressure in the range of from about 1 atmosphere to about 66 atmospheres in an aqueous alkali/isopropanol medium in the presence of a hydrogenation catalyst compris-ing palladium composited on charcoal, and recoverlng the desired 2-(2-hydroxy-5-methylphenyl)-2H-benzotriazole.

, ~ ~

~5~77~7 The process of this invention can be carried out at a temperature in the range of from about 20C to about 100C, preferably from about 30C to about 80C, and most preferably from about 40C to about 70C.

Other objects and embodiments will be found in the following, further detailed description of this invention.

The reduction of 2-nitro-2'-hydroxy-5'-methylazo-ben~ene was carried out in an aqueous alkali/alkanol solu-tion employing sufficient sodium hydroxide to convert the insoluble azobenzene intermediate into the corresponding soluble sodium phenolate salt. A hydrogenation catalyst comprising palladium composited on carbon was used and the reduction and cyclization effected at a hydrogen pressure of from about l to about 5.7 atmospheres at temperatures from about 20C to about 100C, with a recovery of pure product in yields in the order of up to 80~. However, higher pressures up to about 66 atmospheres may be also used with equivalent results.

The catalysts which are employed in the process of this invention for effecting the reduction of o-nitroazo-benzenes to form 2-aryl-2H-benzotriazoles comprise metals selected from the noble metals of Group VIII of the Period-ic Table, the preferred metal comprising palladium although it is contemplated within the scope of this invention that the other noble metals such as platinum,rhodium,ruthenium, '7 ~

osmium and iridium can also be used, although not neces-sarily with equivalent results. The metals may be used per se, as their oxides, or in a preferred embodiment of the invention, composited on a solid support such as carbon, silica or alumina. A particularly effective support com-prises charcoal. Very small quantities of catalyst are re-quired to effect the reductive cyclization of this inven-tion. Amounts of noble metal catalyst as low as about 0.001 to 0.0015 mol/mol of the o-nitroazobenzene to be re-duced are effective. More catalyst can be used, but using amounts over 0.005 mol/mol of the o-nitroazobenzene is gen-erally neither needed nor economically attractive.

The noble metal catalysts of this invention can be generally used interchangeably with one another in the in-stant process. However, as intimated above there are some differences between the individual metals. If the o-nitro-azobenzene starting material is substituted with a chlorine atom, the use of palladium catalysts cesults in the reduc-tive cycllzation to the 2-aryl-2H-benzotriazole, but the chlorine atom is also concomitantly cleaved off. However, substitution of palladium by rhodium the latter which ap-pears to be a milder, more selective catalyst results in the preparation o the 2-aryl-2H-benzotriazole still con-taining the chlorine atom. Accordingly, when th~ prepa-ration of a 2-aryl-2H-benzotriazole containin~ chlorine on either or both aromatic rings is - involved, a rhodium catalyst should bei used and the use of palladium catalysts should be avoided. A preferred catalyst for the reductive cyclization of a 2-nitroazobenzene inter-mediate substituted with chlorine to the corresponding chlorine substituted 2-aryl-2H-benzotriazole is rhodium composited on charcoal.

- As hereinbefore stated, the reduction is effected at reducing conditians including a temperature within the range of from about 20C to about 100C, a pressure ranging from about 15 to about looo pounds per square inch (about 1.05 to about 70 kg/cm2, about 1 to about 66 atmospheres) and with sufficient aqueous alkali/alkanol solution to con-vert the hydroxy-substituted o-nitroazobenzenes into their corresponding soluble alkaline phenolate salts. The soluble alkaline phenolate salts are prepared by adding the appro-priate hydroxy-substituted o-nitroazobenzene to an aqueous alkali/alkanol solution containing sodium hydroxide, potas-sium hydroxide, lithium hydroxide, sodium carbonate, potas-sium carbonate, ammonia or the like with an alcohol. Any water miscible alcohol can be used such as methanol, eth-anol, isopropanol, methyl cellosolve, n-butanol and the like. For reasons of economics, ease of operation and availability, isopropanol is preferred. The alkali/alkanol solution preferably comprise a mixture of sodium hydroxide/

~5~777 water/isopropanol in a ratio by weight of from about 30/
1000/30 to about 70/340/300 and preferably of from about 60/340/300 to about 60/440/200 for approximately each mole of the o-nitroazobenzene reduced. When using this aqueous alkali/alkanol solution, it is possible at the end of the reduction and cyclization reaction to remove the catalyst by filtration for further recycling if desired while leav-ing the desired 2-aryl-2H-benzotriazole product in solution as its alkaline salt.

Although the preferred solvent system for many of the 2-aryl-2H-benzotriazoles of this invention is aqueous alkali/isopropanol, other water miscible organic solvents can also be used advantageously in this process. Such water miscible organic solvents include ethers such as dioxane, tetrahydrofuran, 1,2-dimethoxyethane, 1,2-diethoxyethane and the like. Such solvents are particularly effective in aiding in dissolving the more difficultly soluble hydroxy-substituted o-nitroazobenzenes and their corresponding alkaline phenolate salts where the substituents R1, R2, R3, R4 and R5 tend to deter facile solubility in the alkaline aqueous organic media of this process.

In another variation of this process, ~he inor-ganic alkali used to prepare the aqueous alkali solutions used in the alkaline aqueous organic media of this inven-tion may be replaced by water miscible organic amines.

. _ g _ ' .

~5~'777 Such amines not only provide the alkaline ambience needed for the reductive cyclization of the o-nitroazobenzenes to the corresponding 2-aryl-2H-benzotriazoles, but also aid in the dissolving of the more difficultly soluble members of said o-nitroazobenzenes and said 2-aryl-2H-benzotriazoles in the reaction media. Thus, the alkaline aqueous organic medium useful in this invention may comprise water con-taining a water miscible organic amine in the presence or absence of a water miscible amines may include primary, secondary or tertiary aliphatic alkanol or ether described previously. Such water miscible amines preferably with al-kyl groups of 1 to 4 carbon atomsl pyridine, morpholine, piperidine,piperazine, guanidine,-pyrrolidine, picoline and the like.

The alkaline aqueous organic media of this inven-tiOll may also comprise a ternary mixture of water, a water-miscible organic amine and a water-miscible alcohol or ether described earlier. An example of such a system would be water/isopropanol/diethylamine.

Isolation of a product in good yield and accept-able purity is another feature of this invention. The aque-ous alkali/alkanol solution of the desired hydroxy-substi-tuted 2-aryl-2H-benzotriazole salt, preferably the sodium salt, is acidified with aqueous mineral acid, preferably ~5~7~

sulfuric acid or hydrochloric acid to a pH of 4 below in order to precipitate the desired hydroxy-substituted 2-aryl-2H-benzotriazole as a crude product in yields in the range of 75 to 90~. The crude product may be further puri-fied by one of several procedures to give purified products of hight purity in yields in the range of 70 to 80~. A va-riety of trace by-products are formed during the reduction of o-nitroazobenzenes. These include the corresponding o-aminoazobenzenes, o-aminohydrazobenzenes, o-phenylenedi-aminel anilines, aminophenols and 1,2,3-benzotriazoles.
Most of these by-product impurities are removed by an acid, preferably sulfuric aeid, wash followed by an alcohol, preferably isopropanol, wash and finally a water wash of the erude 2H-benzotriazole produet. Alternatively, the erude produet may be dissolved in an organie solvent, such as toluene, and the impurities extracted by an aqueous acid solution, and the product isolated then from organic solution by conventional procedures.

The proeess of this invention may be efected in any suitable manner and may eomprise either a batch or continuous type of operation. For example, when a batch-type operation is used, a ~uantity of the hydroxy-substi-tuted o-nitroazobenzene, water, alkanol, such as iso-propanol, suffieient alkali, such as sodium hydroxide, to prepare the soluble alkaline phenolate salt along with the 7.

catalyst such as palladiumcomposited on charcoal, is placed in an appropriate apparatus such as a shaking or stirred autoclave. Hydrogen is pressurized in until the desired initial pressure is reached. The aut~clave and the contents thereof are then heated, if needed, to the desired reaction temperature and maintained thereat with agitation until the theoretical amount of hydrogen is absorbed whereupon no further hydrogen is taken up and the reduction reaction is complete. At the end of this time the excess pressure is vented, the aqueous alkali/alkanol solution, usually warm, is subjected to filtration , preferably under an inert atomosphere such as nitrogen or argon, to remove the cata-lyst. The solution is then brought to room temperature and acidified with mineral acid solution to precipitate the desired hydroxy-substituted 2-aryl-2H-benzotriazole crude product, which may be optionally further purified by treat-ment with aqueous acid and recrystallization from an organic solvent.

It is also contemplated within the scope of this invention that the preparation of the 2-aryl-2H-benzotria-zoles by the reduction and cyclization of o-nitroazoben-zenes may also be effected in a continuous manner, although not necessarily with equivalent resuits. For example, when a continous type operation is used, the hydroxy-substituted o-nitroazobenzene starting material is premixed with, and . ~

'' dissolved in an aqueous alkali/alkanol solution, said solu-tion fed continuouslyto a reaction zone which is maintained at the proper operating conditions of temperature and pres-sure and which contains the hydrogenation catalyst. Hydro-gen is pressurized into the reaction zone by a separate means. After a desired residence time, the reactor efflu-ent is continously discharged and the effluent solution is acidified to isolate the desired product. Due to the nature of the catalyst employed, a particularly effective contin-uoustype of operation comprlses a fixed bed of catalyst subjected to either an upward or downward flow of the reac-tion solution. If it is desirable to carry out the reduc-tion as a two-step process with a different operating tem-perature for each step, two reaction zones in series each operating at the preferred temperature range for the spe-cificreduction step involved may be used.

The reduction of o-nitroazobenzenes to the cor-responding 2-aryl-2H-benzotriazoles is a two-step process as outllned below.

7~

OH

R~ ~ Step 1 R2 ~702 \/~ R,~ ';

~H

R)~X\ / ~--\

Step 2 OH
R~ ~R~;
:R3 .
Step ~ - The reduction of the o~nitroazobenzene ~o the N-oxybenzotriazole derivative ~roceeds rapidly and exother mically even at low temperature under the process conditions o this i.nYention.

7~
St~p 2 The reà~c~ion OL t~le N-o~benæo~xiazole interm~dia~e to the correspo.~ding 2-aryl-2H~berlzotriazole product goes more slowlyO This reduction can be greatly expedited by addir.g more catalyst, raising the temperature, increasing the hydrogen pressure or by combination o these factors.

Generally, the reaction ceases when the ~-oxy in-ter~edi~t~ is completely reduced to the corresponding ~-aryl~
2H-benzotriazole making for facile control of this catalytic h~drogenation process. However, with some highly substituted benzotriazoles, reduction should be s~opped when the appropri-ate amount of hydrogell has been absorbed and reacted to prevent further reductive cleavage oE the desired 2-aryl-2H-benzotria-~oles prepared.

Specifically, the instant invention provldes an improved process for production o~ compounds having the formula I

OH R

R2 ~ N ~ R

~ 3 wherein Rl is hydrogen or chlorine, R2 i5 hydrogen, chlorine, lo~er al]~yl oE 1 to 4 .

7~

carbon atoms, lower alkoxy of l to 4 carbon atoms, carbo-alkoxy of 2 to 9 carbon atoms, carboxy or -S03H, R3 is alkyl of l to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, phenyl, phenyl substituted with alkyl groups, said alkyl groups having 1 to 8 carbon atoms, cy-cloalkyl of 5 to 6 carbon atoms, carboalkoxy of ~ to 9 car-bon atoms, chlorine, carboxyethyl or arylalkyl of 7 to 9 carbon atoms, R4 is hydrogen, lower alkyl of 1 to 4 carbon àtoms,lower alkoxy of l to 4 carbon atoms, chlorine or hydroxyl, and R5 is hydrogen, alkyl of 1 to 12 carbon atoms, chlorine, cycloalkyl of 5 to 6 carbon atoms or arylalkyl of 7 to 9 carbon atoms.

R2 can be lower alkyl of 1 to 4 carbon atoms such as methyl, ethyl or n-butyl. R2 can also be lower alkoxy of 1 to 4 carbon atoms such as methoxy, ethoxy or n-butoxy.
R2 can also be carboalkoxy of 2 to 9 carbon atoms such as carbomethoxy, carboethoxy, or carbo-n-octoxy.

R3 can be alkyl of l to 12 carbon atoms such as methyl, ethyl, sec-butyl, tert-butyl, amyl, tert-octyl or n-dodecyl. R3 can also be alkoxy of l to 4 carbon atoms such as methoxy, ethoxy or n-butoxy. R3 is also phenyl substituted with alkyl groups, said alkyl groups having . ' ~ .

- :1. 3L r:3~77~

1 to 8 carbon atoms such as methyl, tert-butyl, tert-amyl or tert-octyl. R3 can also be cycloalkyl of 5 to 6 carbon atoms such as cyclopentyl or cyclohexyl. R3 is also carbo-alkoxy of 2 to 9 carbon atoms such as carbomethoxy, carbo-ethoxy, carbo-n-butoxy or carbo-n-octoxy. R3 is also aryl-alkyl of 7 to 9 carbon atoms such as benzyl, a-methyl-benzyl or a,a-dimethylbenzyl.

R4 can be lower alkyl of l to 4 carbon atoms sueh as methyl, ethyl or n-butyl.

R4 can also be lower alkoxy of l to 4 carbon atoms such as methoxy, ethoxy or n-butyloxy.

R5 can be lower alkyl of l to 8 carbon atoms such as methyl, sec-butyl, tert-butyl, tert-amyl or tert-octyl.

R5 ean also be cycloalkyl of 5 to 6 carbon atoms sueh as cyclopentyl or cyclohexyl. R5 is also arylalkyl of 7 to 9 carbon atoms sueh as benzyl, a-methylbenzyl or a,a-dimethylbenzyl.

Preferably Rl is hydrogen Preferably R2 is hydrogen, chlorine, lower alkyl of l to 2 carbon atoms, methoxy or carboxy.

.. . . .
Preferably R3 is alkyl of 1 to 8 carbon atoms cyclohexyl, phenyl, chlorine, a-methylbenzyl or carboxy-ethyl.

177~

Preferably R4 is hydrogen, hydroxyl or methyl.

Preferably R5 is hydrogen, chlorine, alkyl of 1 to 8 carbon atoms, cyclohexyl, benzyl or a-methylbenzyl.

Most preferably R2 is hydrogen or chlorine.

Most preferably R3 is methyl, tert-butyl, tert-amyl, tert-octyl, sec-butyl, cyclohexyl, chlorine or carboxyethyl.

Most preferably R4 is hydrogen.

Most preferably R5 is hydrogen, chlorine, methyl, sec-butyl, tert-butyl, tert-amyl, tert-octyl or a-methyl-benzyl.

The process involved the reduction of an o-nitro-azobenzene intermedlate of the formula II

OH

1 ~ N ~ ~ ~ R5 II

wherein Rl, R2, R3, R4 and R5 are as described previously.

The starting o-nitroazobenzene intermldiates are prepared by couplin~ the appropriate o-nitrobenzenedi-azonillm compounds of formula III

0 / ~ III

~ 2 N02 wherein Rl and R2 are as described previously and X is chlo-ride, sulfa.e, or other anionic species, but preferably chloride, with phenols of formula IV
O~I

~ R5 IV
`"`~/\ ' : - ~3 which coupl~ in the ortho position to the hvdroxy group.

The o nitrobenzenediazonium compounds are in turn prepared by standard diazotization procedures using sodium nitrite in acid solution with the correspondin~ o-nitro anilines of formula ~

~1~,\, ~H2 V, ~2 ~ l9 .

~ . ~

;

~ o~ illustration purposes some ~pecific examples o~ compounds of formul~s IV and V are listed. These items are generally available as items of commerce.

Compounds of Formula IV

p-cresol 2 r 4 -di-tert-butylphenol 2,4-di-tert-amylphenol 2,4-di-tert~octylphenol 2-~ert-buty]-4-methylphenol 4~cyclohexylphenol 4-tert-butylphenol 4 tert-amylphenol 4-tert-octylphenol 2,4-dimethylphenol

3,4-dimethylphenol

4-chlorophenol 2,4-dichlorophenol 3,4-dichlorophenol 4-phenylphenol 4-phenoxyphenol 4-o-tolylphenol 4-t4'-tert-octyl)phenylphenol ethyl 4-hydroxyben~.oate n-octyl 4-hydroxyben20ate .:

`

4-methoxyphenol 4-n-octylphenol 4-dodecylphenol resorcinol 4-(a-methylben~yl)phenol 2-(-methylbenzyl)-4-methylphenol 2-cyclohexyl-4-methylphenol 4-sec-butylphenol 2-sec-butyl-4-tert-butylphenol 2-tert-butyl-4-sec-butylphenol 4-carboxyethylphenol 2-methyl-4-carboxysthylphenol Preferably compounds of formula IV useful in this invention are p-cresol 2,4-di-tert-butylphenol 2,4-di-tert-amylphenol 2,4-di-tert-octylphenol 2-tert-butyl-4-methylphenol 4-tert-octylphenol 4-n-octylphenol 4-n-dodecylphenol ;' resorcinol ''' ~ ' ~ . . ~

:, 7~;~7 2-sec-butyl-4-tert-butylphenol 2-(a-methylbenzyl)-4-methylpheno Compounds of Formula V

o-nitroaniline 4-chloro-2-nitroaniline 4,5-dichloro-2-nitroaniline 4-methoxy-2-nitroaniline 4-methyl-2-nitroaniline 4-ethyl-2-nitroaniline n-butyl 3-nitro-4-aminobenzoate n-octyl 3-nitro-4-aminobenzoate 4-n-butoxy-2-nitroaniline 3-nitro-4-aminobenzoic acid 3-nitro-4-aminobenzenesulfonic acid Preferably compounds of Formula V useful in this invention are o-nitroaniline 4-chloro-2-nitroaniline The o-nitroazobenzene intermediates of Formula II
where Rl is chlorine; R2 is chlorine, lower alkyl of 1 to : - 4 carbon atoms, lower alkoxy of 1 to 4 carbon atoms, carbo-alkoxy of 2 to 9 carbon atoms; R3 is phenyl, phenyl sub-stituted with alkyl groups said al]cyl groups have 1 to 8 , carbon atoms, carboalkoxy of 7 to 9 carbon atoms, arylalkyl of 7 to 9 carbon atoms, alkyl of 9 to 12 carbon atoms, R4 is alkyl of 1 to 4 carbon atoms, alkoxy of 1 to 4 carbon atoms, chlorine; and R5 is alkyl of 1 to 12 carbon atoms, chlorine, cyeloalkyl of 5 to 6 earbon atoms or arylalkyl of 7 to 9 carbon atoms generally exhibit somewhat limited sol-ubility in aqueous alkaline organic media. With such inter-mediates the use of increased amounts of water-miseible organie solvents described previously is generally neees-sary in the proeess of this invention.

The 2-aryl-2H-benzotriazoles have found wide use as dyestuff intermediates, optical brightner blue fluo-reseent agents and seleetive ultraviolet light absorbing stabilizers affording valuable proteetion for fibers, films and a variety of polymerie structures subjeet to deterioration by ultraviolet radiation. These materials have beeome important items of eommerce.

The 2-aryl-2H-benzQtriazoles are eomplex organie moleeules whieh ~-equire eareful synthetie proeedures for their produetion in good yield and aeceptable purity.

The present invention is concerned with an im-proved process to prepare ultraviolet stabilizers whieh are substituted 2-aryl-2H-benzotriazoles. These are dis-tinguished by a very slight absorption in visible light ~s~

and very high fastness to light in various substrates.
Particularly valuable members of these stabilizers are compounds having a free hydroxyl group in the 2-position of the aryl group linked to the 2-nitrogen of the benzo-.
triazole and which are further substituted in the 3- and

5- or in the 4- and 5-positions by lower alkyl groups and may be substituted by a chlorine in the 5-position of the benzotriazole nucleus.

The description, preparation and uses o~ these valuable substituted 2-aryl-2H-benzotriazoles are further taught in the U.S. Patent Numbers 3,004,896, 3,055,896, 3.072,585, 3,074,910, 3,189,615 and 3,230,194.

The following e~amples are given to illustrate the process of the present invention, but are not intended to limit the scope of the present invention in any manner whatsoever.

- 24 ~

~47 '~

Example 1 2-(2-Hydrox~-5-meth~lphenyl)-2H-benzotriazole To a l-liter, low pressure hydrogenation reactor were charged under nitrogen at room temperature 52.5 grams of 2-nitro-2'-hydroxy-5'-methylazobenzene (98~ pure) dis-solved in a solution of 9 grams of sodium hydroxide in 30 grams of water and 45 grams of isopropanol and 1.5 grams of 5~ palladium on charcoal hydrogenation catalyst slurried in 21 grams of water. The amount of catalyst is about 3% based on the abzobenzene intermediate. The reactor was flushed several times with hydrogen and then pressurized with hydrogen to 3.7-4 atmospheres. The contents of the reactor were hydrogenated at 35-40C for approximately 40-45 min-utes. There was a mild exotherm observed during this period requiring some external cooling of the reactor to maintain temperature at this desired range. One mole equiv-alent of hydrogen was absorbed based on the azobenzene intermediate indicating that the first step of the cyclic reduction had occurred.

The temperature of the reactor was then increased to 50-55C and hydrogenation continued until the uptake of hydrogen ceased. This required another 40-45 minutes. No noticeable exother~ was observed d~ring this second step of the reduction during which another mole equivalent of ~5~777 hydrogen was absorbed. The hydrogen remaining in the reac-tor was now vented and a nitrogen atmosphere was reimposed on the reactor conten~s.

The reactor contents were the filtered under nitrogen to remove the palladium on charcoal catalyst dis-persed therein. The recovered catalyst was washed on the filter with a solution of 15 grams of 10% aqueous sodium hydroxide. This catalyst was then suitable for reuse in another hydrogenation reaction after further washing.

The combined, highly alkaline filtrates containing the desired product were acidified with approximately 25 grams of 50~ aqueous sulfuric acid with vigorous agitation under a nitrogen atmosphere to a pH value of 2.5 to 3.0 as measured by narrow range pHydrion indicator paper. The mix-ture was stirred for one hour and the pH value of 2.5-3.0 checked again. The yellow precipitate which formed was collected by flltration and washed with 500 ml portions of warm water until all inorganic sulfate salts were com-pletely removed. The yellow, crude product was dried at 70-80C under 15 mm pressure to a constant weight of 38.3 grams (85~ of theory).

The crude product could be further purified by washing a toluene solution of the crude product with warm '~

7`~7 sulfuric acid solution followed by recrystallization from toluene and isopropanol to give 36.0 grams (80~ of theory) of pure material.

Example 2 2-(2-Hydroxy-S-methylphenyl?-2H-benzotriazole When using the procedure of Example 1, the hydrogen pressure employed was in the range of 3.3-2 atmo-spheres instead of 4-3.7 atmospheres and the reaction tem-peratures washeld at 58-60C rather than at 35-40C for the first step and 50-55C ~or the second step, the reaction time was 140 minutes rather than 80-90 minutes for complete absorption of hydrogen. The yield of crude product was essentially the same, namely 81% of theory.

When in Example 2, the hydrogen pressllre employed was atmospheric, the reaction time was extended to 280 minutes, but the yield of crude product was the same (81%
of theory).

When 5~ palladium on charcoal was used at the 1.5% concentration level based on azobenzene intermediate with atmospheric hydrogen pressure, the reaction time was 500 minutes and the yield of crude product was 85%.

- . .

.
`

7~

Exam~le 3 2-(2-Hydroxy-5-methylphenyl)-2H-benzotriazole If in Example 2, the 5% palladium on charcoal catalyst was replaced by an equivalent amount of 5~ plati-num on charcoal, the reaction time for all hydrogen to be absorbed was extended to 400 minutes and yield of crude product was 31.5 grams (70% of theory).

Platinum is an operative catalyst for this hydro-genation, but is somewhat less effective than palladium.

Example 4 2-(2-Hydroxy-5-methylphenyl)-2H-benzotriazole If in Example 2, the 5% palladium on charcoal catalyst was replaced by an equivalent amount of 5% rhodium on charcoal, the reaction time for all hydrogen to be ab-sorbed was extended to 240 minutes and the yield of crude product was 28.4 grams (63% of theory).

Rhodium is also an operative catalyst for this hydrogenation process, but appears to be somewhat less ef-fective than palladium, but more effective than platinum in the preparation of 2-(2-hydroxy-5-methylphenyl)-2H-benzotriazole.

fi~

Example 5 2-(2-Hydroxy-5-methylphenyl)-2H-benzotriazole When using the procedure of Example 1, the sodium hydroxide was replaced by a molar equivalent amount of diethylamine, the cyclic reduction reaction occurred in a sluggish manner giving the above noted product in a yield of 30%.

Example 6 2-(2-Hydroxy-3 ! 5-di-tert-amylphenyl)-2~-benzotriazole When using the procedure of Example 1 an e~uiva-lent amount of 2-nitro-2'-hydroxy-3',~'-d.i~-tert-amylazo-benzene was substituted for 2-nitro-2'-hydroxy-5'-methyl--azobenzene, the above noted product was obtained in a 30 to 50~ yield. The corresponding`N-oxy compound was also found as a by-product.

Example 7 .
2-(2-Hydroxy-5-tert-octylphenyl)-2H-benzotriazole When using the procedure of Example 1 an equiva-lent amount o 2-nitro-2'-hydroxy-5'-tert-octylazobenzene is s.ubstituted for 2-nitro-2'-hydroxy-5'.-methylazobenzene, . , . . . i . .
the above noted product is obtained.

. .

Example 8 5-Chloro-2-(2-hydroxy-3,5-di-tert-butylphenyl)-2H-benzotriazole __ _ When in Example 1, the 2-nitro-2'-hydroxy-5'-methylazobenzene is replaced by an equivalent amoun-t of 2-nitro-5-chloro-2'-hydroxy-3',5'-di-tert-butylazobenzene and the 5% palladium on charcoal catalyst is replaced by an equivalent amount of 5~ rhodium on charcoal catalyst, the above noted product is obtained.

If the 5% palladium on charcoal catalyst is used, the resulting product is the deschloro compound 2-(2-hydroxy-3,5-di-tert-butylphenyi~-2H-benzotriazole.

, ~
Exam~ 9 5-Chloro-2-t2-hydroxy-3-tert-butyl-5-methylphenyl)-2H-benzotriazole When in Example 1, the 2-nitro-2'-hydroxy-5' methylazobenzene is replaced by an equivalent amount of 2-nitro-5-chloro-2'-hydroxy-3'-tert-butyl-5'-methylazobenzene and the 5~ palladium on charcoal catalyst is replaced by a like amount of 5% rhodium on charcoal catalyst, the above noted product is obtained. . , :~ , ,,, ~
.

Claims (17)

WHAT IS CLAIMED IS:

1. A process for the production of 2-aryl-2H-benzotriazoles of the formula I

(I) wherein Rl is hydrogen or chlorine R2 is hydrogen, chlorine, lower alky1 of 1 to 4 carbon atoms, lower alkoxy of 1 to 4 carbon atoms or carbo-alkoxy of 2 to 9 carbon atoms, carboxy or -S03H, R3 is alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, phenyl, phenyl substituted with alkyl groups, said alkyl groups having 1 to 8 carbon atoms, cycloalkyl of 5 to 6 carbon atoms, carboalkoxy of 2 to 9 carbon atoms, chlorine, carboxyethyl or arylalkyl of 7 to 9 carbon atoms, R4 is hydrogen, lower alkyl of 1 to 4 carbon atoms, lower alkoxy of 1 to 4 carbon atoms, chlorine or hydroxyl, and R5 is hydrogen, alkyl of 1 to 12 carbon atoms, chlorine, cycloalkyl of 5 to 6 carbon atoms or arylalkyl of 7 to 9 carbon atoms, which comprises reducing and cyclizing the corresponding o-nitro-azobenzene with hydrogen at a temperature in the range of from about 20°C to about 100°C and at a pressure in the range of from about 1 atmosphere to about 66 atmospheres while mixed in an aqueous alkaline/organic medium having a pH greater than 10 in the presence of a hydrogenation cata-lyst selected from the group consisting of the noble metals of Group VIII of the Periodic Table with the proviso that, when Rl, R2, R3, R4 or R5 is chlorine, the hydrogenation catalyst cannot be palladium, and recovering the desired 2-aryl-2H-benzotriazole.

2. A process according to Claim 1 which further comprises removing the noble metal catalyst by filtration, and lowering the pH of the aqueous alkaline/organic medium to a value less than 4 to precipitate the desired product.

3. A process according to Claim 1 wherein the hydrogenation catalyst is selected from the group consisting of palladium, platinum and rhodium.

4. A process according to Claim 1 wherein the hydrogenation catalyst is palladium.

5. A process according to Claim 4 characterized in that said palladium is composited on charcoal.

6. A process according to Claim 4 wherein the alkaline organic medium is an aqueous alkali/alkanol solution.

7. A process according to Claim 4 for the pro duction of a compound of formula I wherein R1 is hydrogen, R2 is hydrogen, lower alkyl of 1 to 2 carbon atoms, methoxy or carboxy, R3 is alkyl of 1 to 8 carbon atoms, cyclohexyl, phenyl,.alpha.-methylbenzyl or carboxyethyl, R4 is hydrogen, hydroxyl or methyl, and R5 is hydrogen, alkyl of 1 to 8 carbon atoms, cyclohexyl, benzyl or .alpha.-methylbenzyl.

8. The process according to claim 4 for production of a compound of formula I wherein Rl is hydrogen, R2 is hydrogen or chlorine R3 is methyl, sec-butyl, tert-butyl, tert-amyl, tert-octyl, methoxy, cyclohexyl, or carboxyethyl, R4 is hydrogen, and R5 is hydrogen, methyl, tert-butyl, sec-butyl, tert-amyl, tert-octyl or .alpha.-methylbenzyl.

9. A process for the production of 2-(2-hydroxy-5-methylphenyl)-2H-benzotriazole which comprises reducing and cyclizing 2-nitro-2'-hydroxy-5'-methylazobenzene with hydrogen at a temperature in the range of about 35° to 60°C and at a pressure in the range of from about 1 atmosphere to about 40 atmospheres while mixed in a solvent system of an aqueous sodium hydroxide/isopropanol medium having a pH greater than 10 in the presence of palladium and recovering the product.

10. A process for the production of 2-(2-hydroxy-5-tert-octylphenyl)-2H-benzotriazole which comprises reducing and cyclizing 2-nitro-2'-hydroxy-5'-tert-octylazobenzene with hydrogen at a temperature in the range of about 35° - 55°C and at a pressure in the range of from about 3.7 to about 4.0 atmospheres while mixed in a solvent system of an aqueous sodium hydroxide/
isopropanol medium having a pH greater than 10 in the presence of palladium and recovering the product.

11. A process for the production of 2-(2-hydroxy-3,5-di-tert-amylphenyl-2H-benzotriazole which comprises reducing and cyclizing 2-nitro-2'-hydroxy-3',5'-di-tert-amylazobenzene with hydrogen at a temperature in the range of about 35° - 55°C and at a pressure in the range of from about 3.7 to about 4.0 atmospheres while mixed in a solvent system of an aqueous sodium hydroxide/isopropanol medium having a pH greater than 10 in the presence of palladium and recovering the product.

12. A process according to claim 4 wherein the hydrogenation catalyst is rhodium.

13. A process according to claim 12 characterized in that said rhodium is composited on charcoal.

14. A process according to Claim 12 for the production of a compound of formula I wherein Rl is hydrogen, R2 is hydrogen, chlorine, lower alkyl of 1 to 2 carbon atoms, methoxy or carboxy, R3 is alkyl of l to 8 carbon atoms, cyclohexyl, phenyl, chlorine, .alpha.-methylbenzyl or carboxyethyl, R4 is hydrogen, hydroxyl or methyl, and R5 is hydrogen, alkyl of 1 to 8 carbon atoms, chlorine, cyclohexyl, benzyl or .alpha.-methylbenzyl.

15. A process according to Claim 12 for the pro duction of a compound of formula I wherein Rl is hydrogen, R2 is hydrogen or chlorine, R3 is methyl, sec-butyl, tert-butyl, tert-amyl, tert-octyl, methoxy, cyclohexyl, chlorine or carboxyethyl, R4 is hydrogen, and R5 is hydrogen, chlorine, methyl, tert butyl, sec-butyl, tert-amyl, tert-octyl or .alpha.-methylbenzyl.

16. A process for the production of 5-chloro-2-(2-hydroxy-3,5-di-tert-butylphenyl)-2H-benzotriazole which comprises reducing and cyclizing 2-nitro-5-chloro-2'-hydroxy-3',5'-di-tert-butylazoobenzene with hydrogen at a temperature in the range of about 35°-55°C and at a pressure in the range of from about 3.7 to about 4.0 atmospheres while mixed in a solvent system of an aqueous sodium hydroxide/isopropanol medium having a pH greater than 10 in the presence of rhodium and recovering the product.

17. A process for the production of 5-chloro-2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-2H-benzotriazole which comprises reducing and cyclizing 2-nitro-5-chloro-2'-hydroxy-3'-tert-butyl-5'-methyylazobenzene with hydrogen at a temperature in the range of about 35°-55°C and at a pressure in the range of from about 3.7 to about 4.0 atmospheres while mixed in a solvent system of an aqueous sodium hydroxide/isopropanol medium having a pH greater than 10 in the presence of rhodium and recovering the product.

(18) A process for the production of 2-aryl-2H-benzotriazoles of the Formula I

Rl is hydrogen or chlorine;
R2 is hydrogen, chlorine and lower alkyl of 1 to 4 carbon atoms;
R3 is alkyl of 1 to 8 carbon atoms and chlorine;
R4 is hydrogen, lower alkyl of 1 to 4 carbon atoms and chlorine;
R5 is hydrogen, alkyl of 1 to 8 carbon atoms and chlorine;
comprising reducing and cyclizing the corresponding o-nitroazo-benzene of the Formula II

with hydrogen at a temperature in the range of 20°C to about 100°C
and at a pressure of 1 to 66 atmospheres while dissolved in a solvent system of an aqueous water miscible organic alkaline medium containing an alkali metal hydroxide as base and having a pH greater than 10 in the presence of a hydrogenation catalyst selected from platinum, palladium, nickel, cobalt, rhodium or molybdenum with the proviso that when Rl, R2, R3, R4 and R5 is chlorine, the hydrogenation catalyst cannot be palladium, and recovering the desired 2-aryl-2H-benzotriazole.

(19) A process as in claim 18 in which the o-nitrophenylazo-hydroxyphenyl starting compound of Formula II is 2-(2'-nitrophenyl-azo)p-cresol and the resulting benzotriazole compound of Formula I is 2-(2'-benzotriazolyl)p-cresol.

(20) A process as in claim 18 in which the o-nitrophenylazo-hydroxyphenyl starting compound of Formula II is 2-nitro-2'-hydroxy-5'-tert.octylazobenzene and the resulting benzotriazole compound of Formula I is2-(2-hydroxy-5-tert.octylphenyl)-2H-benzotriazole.

(21) A process as in claim 18 in which the o-nitrophenylazo-hydroxyphenyl starting compound of Formula II is 2-nitro-2'-hydroxy-3',5'-di-tert.amylazobenzene and the resulting benzotriazole compound of Formula I is 2-(2-hydroxy-3',5',-di-tert.amylphenyl)-2H-benzo-triazole.

(22) A process as in claim 18 in which the o-nitrophenylazo-hydroxyphenyl starting compound of Formula II is 2-nitro-5-chloro-2'-hydroxy-3'-tert.butyl-5'methylazobenzene and the resulting benzotriazole compound of Formula I is 5-chloro-2-(2-hydroxy-3-tert.-butyl-5-methylphenyl)-2H-benzotriazole.

(23) A process as in claim 18 in which the o-nitrophenylazo-hydroxyphenyl starting compound of Formula II is 2-nitro-5-chloro-2'-hydroxy-3',5',di-tert.butylazobenzene and the resulting benzo-triazole compound of Formula I is 5-chloro-2-(2-hydroxy-3',5',di-tert.butylphenyl)-2H-benzotriazole.

(24) A process for the production of 2-aryl-2H-benzotriazoles of the Formula I

wherein:
Rl is hydrogen or chlorine;
R2 is hydrogen chlorine and lower alkyl of 1 to 4 carbon atoms;
R3 is alkyl of 1 to 8 carbon atoms and chlorine;
R4 is hydrogen, lower alkyl of 1 to 4 carbon atoms and chlorine;
R5 is hydrogen, alkyl of 1 to 8 carbon atoms and chlorine;
comprising reducing and cyclizing the corresponding o-nitroaza-benzene of the Formula II

with hydrogen at a temperature in the range of 20°C to about 100°C
and at a pressure of 1 to 66 atmospheres while dissolved in a solvent system of an aqueous alkaline/water miscible organic medium having a pH greater than 10 in the presence of a hydrogenation catalyst selected from platinum, palladium, nickel, cobalt, rhodium or molybdenum with the proviso that when Rl, R2, R3, R4 and R5 is chlorine, the hydrogenation catalyst cannot be palladium, and recovering the desired 2-aryl-2H-benzotriazole.

(25) A process as in claim 24 in which the o-nitrophenylazo-hydroxyphenyl starting compound of Formula II is 2-(2'-nitrophenyl-azo)p-cresol and the resulting benzotriazole compound of Formula I
2-(2'-benzotriazolyl)p-cresol.

(26) A process as in claim 24 in which the o-nitrophenylazo-hydroxyphenyl starting compound of Formula II is 2-nitro-2'-hydroxy-5'-tert.octylazobenzene and the resulting benzotriazole compound of Formula I is2-(2-hydroxy-5-tert.-octylphenyl)-2H-benzotriazolee.

(27) A process as in claim 24 in which the o-nitrophenylazo-hydroxyphenyl starting compound of Formula II is 2-nitro-2'-hydroxy-3',5'-di-tert.amylazobenzene and the resulting benzotriazole compound of Formula I is 2-(2-hydroxy-3',5'-di-tert.amylphenyl)-2H-benzo-triazole.

(28) A process as in claim 24 in which the o-nitrophenylazo-hydroxyphenyl starting compound of Formula II is 2-nitro-5-chloro-2'-hydroxy-3'-tert.butyl-5'-methylazobenzene and the resulting benzotriazole compound of Formula I is 5-chloro-2-(2-hydroxy-3-tert.
butyl-5-methylphenyl)-2H-benzotriazole.

(29) A process as in claim 24 in which the o-nitrophenylazo-hydroxyphenyl starting compound of Formula II is 2-nitro-5-chloro-2'-hydroxy-3',5',di-tert.butylazobenzene and the resulting benzo-triazole compound of Formula I is 5-chloro-2-(2-hydroxy-3',5', di-tert.butylphenyl)-2H-benzotriazole.