Method for preparing 2-phenylbenzotriazoles and 2-phenylbenzotriazole-N-oxides

This invention relates to a method for preparing a 2-phenylbenzotriazole of formula I, ##STR1## (wherein R.sub.1 represents hydrogen or chlorine atom, a lower alkyl group having a carbon number of 1 to 4, a lower alkoxyl group having a carbon number of 1 to 4, carboxyl group, or sulfonic acid group; R.sub.2 represents hydrogen or chlorine atom, a lower alkyl group having a carbon number of 1 to 4, or a lower alkoxyl group having a carbon number of 1 to 4; R.sub.3 represents hydrogen or chlorine atom, an alkyl group having a carbon number of 1 to 12, a lower alkoxyl group having a carbon number of 1 to 4, phenyl group, a phenyl group substituted with an alkyl group having a carbon number of 1 to 8, phenoxy group, or a phenylalkyl group, the alkyl part of which has a carbon number of 1 to 4; R.sub.4 represents hydrogen or chlorine atom, hydroxyl group, or a lower alkoxyl group having a carbon number of 1 to 4; and R.sub.5 represents hydrogen atom, an alkyl group having a carbon number of 1 to 12, or a phenylalkyl group, the alkyl part of which has a carbon number of 1 to 4), which comprises reducing an o-nitroazobenzene of formula III, ##STR2## (wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are as defined above) with an aldehyde reducing agent in the presence of an aromatic ketone catalyst and base. This invention further relates to a method for preparing a 2-phenylbenzotriazole of formula I as derfined above, which comprises reducing 1 mole 2-phenylbenzotriazole-N-oxide of formula II, ##STR3## (wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are as defined above) with 1 to 4 mole aldehyde in the presence of an aromatic ketone catalyst and base. This invention still further relates to a method for preparing a 2-phenylbenzotriazole-N-oxide of formula II as defined above, which comprises reducing 1 mole o-nitroazobenzene of formula III as defined above with 1 to 2 mole aldehyde in the presence of an aromatic ketone catalyst and base.

BACKGROUND OF THE INVENTION 
(a) Field of the Invention 
This invention relates to a method for preparing 2-phenylbenzotriazoles 
having the following general formula I, which are useful as an ultraviolet 
ray absorber. 
This invention further relates to a method for preparing 
2-phenylbenzotriazole-N-oxides having the following general formula II, 
which are a useful intermediate for said 2-phenylbenzotriazoles. 
(b) Description of the Prior Art 
2-phenylbenzotriazoles having the following general formula I, 
##STR4## 
(wherein R.sub.1 represents hydrogen or chlorine atom, a lower alkyl group 
having a carbon number of 1 to 4, a lower alkoxyl group having a carbon 
number of 1 to 4, carboxyl group, or sulfonic acid group; R.sub.2 
represents hydrogen or chlorine atom, a lower alkyl group having a carbon 
number of 1 to 4, or a lower alkoxyl group having a carbon number of 1 to 
4; R.sub.3 represents hydrogen or chlorine atom, an alkyl group having a 
carbon number of 1 to 12, a lower alkoxyl group having a carbon number of 
1 to 4, phenyl group, a phenyl group substituted with an alkyl group 
having a carbon number of 1 to 8, phenoxy group, or a phenylalkyl group, 
the alkyl part of which has a carbon number of 1 to 4; R.sub.4 represents 
hydrogen or chlorine atom, hydroxyl group, or a lower alkoxyl group having 
a carbon number of 1 to 4; and R.sub.5 represents hydrogen atom, an alkyl 
group having a carbon number of 1 to 12, or a phenylalkyl group, the alkyl 
part of which has a carbon number of 1 to 4) are known to be useful as an 
ultraviolet ray absorber to be added to plastics, paints, oils and the 
like. 
2-phenylbenzotriazole-N-oxides having the general formula II, 
##STR5## 
(wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are the same as 
defined above with regard to the general formula I) are known to be an 
important intermediate for said 2-phenylbenzotriazoles. 
Heretofore, these 2-phenylbenzotriazoles and 2-phenylbenzotriazole-N-oxides 
have been produced by chemically or electrolytically reducing 
o-nitroazobenzene derivatives having the general formula III, 
##STR6## 
(wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are the same as 
defined above with regard to the general formula I). However, these 
conventional methods respectively have merits and demerits, and are not 
always satisfactory. 
For example, Japanese Patent Publication No. 37-5934 and U.S. Pat. No. 
3,773,751 disclose a method for preparing 2-phenylbenzotriazoles or 
2-phenylbenzotriazole-N-oxides by chemically reducing o-nitroazobenzene 
derivatives in an alcoholic sodium hydroxide solution with zinc powder at 
a satisfactory yield. However, this sodium hydroxide-zinc system produces 
zinc sludge which results in waste water contamination problems. 
As disclosed in U.S. Pat. No. 2,362,988, ammonium sulfide, alkali-sulfide, 
zinc-ammonia system, hydrogen sulfide-sodium system and zinc-hydrochloric 
acid system are used as a chemical reducing agent for the above mentioned 
reduction reaction. However, this conventional method produces a large 
amount of sulfite or zinc salts which result in waste water contamination. 
The sulfite further generates sulfurous acid gas, and the used sulfide 
type reducing agent generates poisonous hydrogen sulfide, which results in 
environmental polution problems. 
Japanese Patent Laid Open Nos. 51-138679 and 51-138680 disclose a reduction 
method by the addition of pressurized hydrogen. Japanese Patent Laid Open 
No. 50-88072 discloses a reduction method by hydrazine. However, these 
methods are not satisfactory in view of yield and economy, and it is 
impossible to obtain the desired product of high purity because a side 
reaction is caused during the main reaction. Particularly, in the case of 
producing a chlorine-containing product, a side reaction such as 
dechlorination reaction is caused. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a novel method for 
preparing 2-phenylbenzotriazoles and 2-phenylbenzotriazole-N-oxides, which 
solves the above mentioned problems of the conventional methods. 
(i) That is, an object of the present invention is to provide a method for 
preparing 2-phenylbenzotriazoles having the general formula I, 
##STR7## 
(wherein R.sub.1 represents hydrogen or chlorine atom, a lower alkyl group 
having a carbon number of 1 to 4, a lower alkoxyl group having a carbon 
number of 1 to 4, carboxyl group, or sulfonic acid group; R.sub.2 
represents hydrogen or chlorine atom, a lower alkyl group having a carbon 
number of 1 to 4, or a lower alkoxyl group having a carbon number of 1 to 
4; R.sub.3 represents hydrogen or chlorine atom, an alkyl group having a 
carbon number of 1 to 12, a lower alkoxyl group having a carbon number of 
1 to 4, phenyl group, a phenyl group substituted with an alkyl group 
having a carbon number of 1 to 8, phenoxy group, or a phenylalkyl group, 
the alkyl part of which has a carbon number of 1 to 4; R.sub.4 represents 
hydrogen or chlorine atom, hydroxyl group, or a lower alkoxyl group having 
a carbon number of 1 to 4; and R.sub.5 represents hydrogen atom, an alkyl 
group having a carbon number of 1 to 12, or a phenylalkyl group, the alkyl 
part of which has a carbon number of 1 to 4), characterized by reducing 
o-nitroazobenzenes having the general formula III, 
##STR8## 
(wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are the same as 
defined above) with an aldehyde catalyst in the presence of an aromatic 
ketone compound catalyst and base. 
(ii) Another object of the present invention is to provide a method for 
preparing 2-phenylbenzotriazoles having the general formula I, 
##STR9## 
(wherein R.sub.1 represents hydrogen or chlorine atom, a lower alkyl group 
having a carbon number of 1 to 4, a lower alkoxyl group having a carbon 
number of 1 to 4, carboxyl group, or sulfonic acid group; R.sub.2 
represents hydrogen or chlorine atom, a lower alkyl group having a carbon 
number of 1 to 4, or a lower alkoxyl group having a carbon number of 1 to 
4; R.sub.3 represents hydrogen or chlorine atom, an alkyl group having a 
carbon number of 1 to 12, a lower alkoxyl group having a carbon number of 
1 to 4, phenyl group, a phenyl group substituted with an alkyl group 
having a carbon number of 1 to 8, phenoxy group, or a phenylalkyl group, 
the alkyl part of which has a carbon number of 1 to 4; R.sub.4 represents 
hydrogen or chlorine atom, hydroxyl group, or a lower alkoxyl group having 
a carbon number of 1 to 4; and R.sub.5 represents hydrogen atom, an alkyl 
group having a carbon number of 1 to 12, or a phenylalkyl group, the alkyl 
part of which has a carbon number of 1 to 4), characterized by reducing 
2-phenylbenzotriazole-N-oxides having the general formula II, 
##STR10## 
(wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are the same as 
defined above) with an aldehyde reducing agentin an amount of 1 to 4 moles 
per mole of said 2-phenylbenzotriazole-N-oxides having the general formula 
II in the presence of an aromatic ketone compound catalyst and base. 
(iii) Still other object of the present invention is to provide a method 
for preparing 2-phenylbenzotriazole-N-oxides having the general formula 
II, 
##STR11## 
(wherein R.sub.1 represents hydrogen or chlorine atom, a lower alkyl group 
having a carbon number of 1 to 4, a lower alkoxyl group having a carbon 
number of 1 to 4, carboxyl group, or sulfonic acid group; R.sub.2 
represents hydrogen or chlorine atom, a lower alkyl group having a carbon 
number of 1 to 4, or a lower alkoxyl group having a carbon number of 1 to 
4; R.sub.3 represents hydrogen or chlorine atom, an alkyl group having a 
carbon number of 1 to 12, a lower alkoxyl group having a carbon number of 
1 to 4, phenyl group, a phenyl group substituted with an alkyl group 
having a carbon number of 1 to 8, phenoxy group, or a phenylalkyl group, 
the alkyl part of which has a carbon number of 1 to 4; R.sub.4 represents 
hydrogen or chlorine atom, hydroxyl group, or a lower alkoxyl group having 
a carbon number of 1 to 4; and R.sub.5 represents hydrogen atom, an alkyl 
group having a carbon number of 1 to 12, or a phenylalkyl group, the alkyl 
part of which has a carbon number of 1 to 4), characterized by reducing 
o-nitroazobenzenes having the general formula III, 
##STR12## 
(wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are the same as 
defined above) with an aldehyde reducing agent in an amount of 1 to 2 
moles per mole of said o-nitroazobenzenes having the general formula III 
in the presence of an aromatic ketone compound catalyst and base. 
DETAILED DESCRIPTION OF THE INVENTION 
In order to solve the above mentioned problems of the conventional methods, 
I have variously studied and found that the desired 2-phenylbenzotriazoles 
having the general formula I, 
##STR13## 
(wherein R.sub.1 represents hydrogen or chlorine atom, a lower alkyl group 
having a carbon number of 1 to 4, a lower alkoxyl group having a carbon 
number of 1 to 4, carboxyl group, or sulfonic acid group; R.sub.2 
represents hydrogen or chlorine atom, a lower alkyl group having a carbon 
number of 1 to 4, or a lower alkoxyl group having a carbon number of 1 to 
4; R.sub.3 represents hydrogen or chlorine atom, an alkyl group having a 
carbon number of 1 to 12, a lower alkoxyl group having a carbon number of 
1 to 4, phenyl group, a phenyl group substituted with an alkyl group 
having a carbon number of 1 to 8, phenoxy group, or a phenylalkyl group, 
the alkyl part of which has a carbon number of 1 to 4; R.sub.4 represents 
hydrogen or chlorine atom, hydroxyl group, or a lower alkoxyl group having 
a carbon number of 1 to 4; and R.sub.5 represents hydrogen atom, an alkyl 
group having a carbon number of 1 to 12, or a phenylalkyl group, the alkyl 
part of which has a carbon number of 1 to 4) can be produced with 
technically and economically satisfactory results without causing 
environmental polution, by reducing 
(i) o-nitroazobenzenes having the general formula III, 
##STR14## 
(wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are the same as 
defined above) or (ii) 2-phenylbenzotriazole-N-oxides having the general 
formula II, 
##STR15## 
(wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are the same as 
defined above) with an aldehyde reducing agent in the presence of an 
aromatic ketone compound catalyst and base. 
The desired product obtained by the method of the present invention has a 
higher purity, and accordingly has more favourable thermostability as 
compared with the product obtained by conventional method. 
The method (i) for preparing 2-phenylbenzotriazoles having the general 
formula I by reducing o-nitroazobenzenes having the general formula III in 
accordance with the present invention can be carried out by either one 
step or two steps depending on the conditions of temperature and the 
amount of aldehydes used as mentioned below. 
In the case of one step method: 
The suitable temperature condition for this process [Process (a)] is about 
20.degree. to 130.degree. C., preferably 40.degree. to 100.degree. C., 
and an aldehyde reducing agent is suitably used in an amount of about 2 to 
4 moles per mole of the starting material, i.e. o-nitroazobenzenes of the 
general formula III. The reaction is carried out in the following manner. 
##STR16## 
(wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are the same as 
defined above, and R represents hydrogen, alkyl group, phenyl group or 
substituted phenyl group). In the case of two step method: 
The suitable temperature condition is the same as in the above Process (a), 
i.e. about 20.degree. to 130.degree. C., preferably about 40.degree. to 
100.degree. C. The two step method is sometimes advantageous in view of 
the quality of product and the yield although it takes two steps. An 
aldehyde reducing agent is suitably used in an amount of 1 to 2 moles per 
mole of the starting material, i.e. o-nitroazobenzenes of the general 
formula III at the first step [Process (b)] to produce an intermediate 
product, and 1 to 4 moles, preferably 1 to 2 moles per mole of the 
intermediate, i.e. 2-phenylbenzotriazole-N-oxides of the general formula 
II at the second step [Process (c)]. 
The reaction is carried out in the following manner. 
##STR17## 
(wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R are the same as 
defined above). 
The method (ii) for preparing 2-phenylbenzotriazoles of the general formula 
I by reducing 2-phenylbenzotriazole-N-oxides of the general formula II is 
carried out in quite the same manner as in the above mentioned Process 
(c). 
In the method (ii), the desired 2-phenylbenzotriazole-N-oxides having the 
general formula II, 
##STR18## 
(wherein R.sub.1 represents hydrogen or chlorine atom, a lower alkyl group 
having a carbon number of 1 to 4, a lower alkoxyl group having a carbon 
number of 1 to 4, carboxyl group, or sulfonic acid group; R.sub.2 
represents hydrogen or chlorine atom, a lower alkyl group having a carbon 
number of 1 to 4, or a lower alkoxyl group having a carbon number of 1 to 
4; R.sub.3 represents hydrogen or chlorine atom, an alkyl group having a 
carbon number of 1 to 12, a lower alkoxyl group having a carbon number of 
1 to 4, phenyl group, a phenyl group substituted with an alkyl group 
having a carbon number of 1 to 8, phenoxy group, or a phenylalkyl group, 
the alkyl part of which has a carbon number of 1 to 4; R.sub.4 represents 
hydrogen or chlorine atom, hydroxyl group, or a lower alkoxyl group having 
a carbon number of 1 to 4; and R.sub.5 represents hydrogen atom, an alkyl 
group having a carbon number of 1 to 12, or a phenylalkyl group, the alkyl 
part of which has a carbon number of 1 to 4) can be produced with 
technically and economically satisfactory results without causing 
environmental polution, by reducing o-nitroazobenzenes having the general 
formula III, 
##STR19## 
(wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are the same as 
defined above) with an aldehyde reducing agent in the presence of an 
aromatic ketone compound catalyst and base. 
This reaction of the method (iii) is carried out in the following manner. 
##STR20## 
(wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R are the same as 
defined above). 
This reaction is quite the same as that of the above mentioned Process (b). 
The suitable temperature condition is about 20.degree. to 130.degree. C., 
preferably about 40.degree. to 100.degree. C., and an aldehyde reducing 
agent is suitably used in an amount of 1 to 2 moles per mole of the 
starting material, i.e. o-nitroazobenzenes of the general formula III. 
In order to smoothly carry out reaction, all the reactions of the above 
mentioned Process (a), Process (b) and Process (c) are carried out in an 
aqueous solution, or in an inert solvent such as alcohols, toluene, 
acetone, dimethylsulfoxide, acetonitrile and the like, or in a mixture of 
the above mentioned inert solvent with water. If necessary, a surface 
active agent, a phase-transfer catalyst, and the like may be added. 
Examples of o-nitroazobenzenes expressed by the general formula III used as 
a starting material in the methods (i) and (iii) include: 
2-nitro-2'-hydroxy-5'-methylazobenzene, 
2-nitro-2'-hydroxy-5'-t-octylazobenzene, 
2-nitro-2'-hydroxy-5'-t-butylazobenzene, 
2-nitro-2',4'-dihydroxyazobenzene, 
2-nitro-4-chloro-2',4'-dihydroxyazobenzene, 
2-nitro-2'-hydroxy-4'-methoxyazobenzene, 
2-nitro-2'-hydroxy-5'-t-amylazobenzene, 
2-nitro-4'-chloro-2'-hydroxy-5'-t-amylazobenzene, 
2-nitro-2'-hydroxy-5'-n-dodecylazobenzene, 
2-nitro-4-chloro-2'-hydroxy-5'-n-dodecylazobenzene, 
2-nitro-4-chloro-2'-hydroxy-5'-t-octylazobenzene, 
2-nitro-4-methyl-2'-hydroxy-5'-methylazobenzene, 
2-nitro-4,6-dichloro-2'-hydroxy-5'-t-butylazobenzene, and 
2-nitro-4-carboxy-2'-hydroxy-5-methylazobenzene. 
Examples of 2-phenylbenzotriazole-N-oxides of the general formula II used 
in the method (ii) of the present invention include: 
2-(2-hydroxy-5-methylphenyl)benzotriazole-N-oxide, 
2-(2-hydroxy-5-t-butylphenyl)benzotriazole-N-oxide, 
2-(2-hydroxy-5-t-octylphenyl)benzotriazole-N-oxide, 
2-(2,4-dihydroxyphenyl)benzotriazole-N-oxide, 
2-(2,4'-dihydroxyphenyl)-5-chlorobenzotriazole-N-oxide, 
2-(2-hydroxy-4'-methoxyphenyl)benzotriazole-N-oxide, 
2-(2-hydroxy-5-t-amylphenyl)benzotriazole-N-oxide, 
2-(2-hydroxy-5-n-dodecylphenyl)benzotriazole-N-oxide, 
2-(2-hydroxy-5-n-dodecylphenyl)-5-chlorobenzotriazole-N-oxide, 
2-(2-hydroxy-5-t-octylphenyl)-5-chlorobenzotriazole-N-oxide, 
2-(2-hydroxy-5-methylphenyl)-5-methylbenzotriazole-N-oxide, 
2-(2-hydroxy-5-methylphenyl)-5-carboxybenzotriazole-N-oxide, 
2-(2-hydroxy-3-t-butyl-5-methylphenyl)-5-chlorobenzotriazole-N-oxide, 
2-(2-hydroxy-3,5-di-t-butylphenyl)-5-chlorobenzotriazole-N-oxide, 
2-(2-hydroxy-3,5-di-t-amylphenyl)benzotriazole-N-oxide, 
2-(2-hydroxy-3,5'-di-t-butylphenyl)benzotriazole-N-oxide, 
2-(2-hydroxy-3-t-butyl-5-methylphenyl)benzotriazole-N-oxide, 
2-(2-hydroxy-3,5'-di-t-octylphenyl)benzotriazole-N-oxide, 
2-(2-hydroxy-3,5'-di-t-octylphenyl)-5-chlorobenzotriazole-N-oxide, 
2-(2-hydroxy-3-t-butyl-5-methylphenyl)-5-methylbenzotriazole-N-oxide, 
2-(2-hydroxy-3,5'-di-t-butylphenyl)-5-n-butylbenzotriazole-N-oxide, 
2-(2-hydroxy-3-sec-butyl-5-t-butylphenyl)-5-n-butylbenzotriazole-N-oxide, 
2-(2-hydroxy-3-sec-butyl-5-t-butylphenyl)-5-t-butylbenzotriazole-N-oxide, 
2-(2-hydroxy-3,5-di-t-butylphenyl)-5,7-dichlorobenzotriazole-N-oxide, 
2-(2-hydroxy-3,5-di-t-amylphenyl)-5-chlorobenzotriazole-N-oxide, 
2-[2-hydroxy-3,5-di-(.alpha.,.alpha.-dimethylbenzyl)phenyl]benzotriazole-N- 
oxide, 
2-[2-hydroxy-3,5-di-(.alpha.,.alpha.-dimethylbenzyl)phenyl]-5-chlorobenzotr 
iazole-N-oxide, 
2-(2-hydroxy-3-.alpha.-methylbenzyl-5-metylphenyl)benzotriazole-N-oxide, 
and 
2-(2-hydroxy-3-.alpha.-methylbenzyl-5-metylphenyl)-5-chlorobenzotriazole-N- 
oxide. 
The starting material, i.e. o-nitroazobenzenes of the general formula III 
used in the present invention can be easily prepared by diazotizing 
o-nitroanilines expressed by the following general formula IV, 
##STR21## 
(wherein R.sub.1 and R.sub.2 are the same as defined above) by the usual 
method and by subjecting the resultant product to coupling reaction with 
phenols expressed by the general formula V, 
##STR22## 
(wherein R.sub.3, R.sub.4 and R.sub.5 are the same as defined above). 
It is preferable to prepare these 2-phenyltriazole-N-oxides of the general 
formula II by reducing o-nitroazobenzenes of the general formula III as a 
starting material in accordance with the above mentioned Process (b), but 
these materials can also be prepared by other known methods. 
Examples of aldehydes used as a reducing agent include formaldehyde, 
paraformaldehyde, acetoaldehyde, benzaldehyde, anisaldehyde, and the like. 
Among them, formaldehyde and paraformaldehyde are most preferable. 
These aldehyde reducing agents are used in an amount of 2 to 4 moles per 
mole of o-nitroazobenzenes of the general formula III when 
2-phenylbenzotriazoles of the general formula I are prepared from said 
o-nitroazobenzenes by one step as shown in the above mentioned Process (a) 
[Method (i)]. 
These aldehyde reducing agents are used in an amount of 1 to 4 moles, 
preferably 1 to 2 moles per mole of 2-phenylbenzotriazole-N-oxides of the 
general formula II when 2-phenylbenzotriazoles of the general formula I 
are prepared from said 2-phenylbenzotriazole-N-oxides as shown in the 
above mentioned Process (c) [Method (ii)]. 
These aldehyde reducing agents are used in an amount of 1 to 2 moles per 
mole of o-nitroazobenzenes of the general formula III when 
2-phenylbenzotriazole-N-oxides of the general formula II are prepared from 
said o-nitroazobenzenes as shown in the above mentioned Process (b) 
[Method (iii)]. 
Examples of an aromatic ketone compound catalyst include benzophenone; 
benzophenone substituted with alkyl group, alkoxyl group, halogen atom, or 
hydroxyl group; benzanthrone; anthrone; 9-fluorenone; 9-xanthenone; and 
the like. Among them, preferable examples include 9-fluorenone, anthrone 
and benzanthrone. 
These aromatic ketone catalysts may be used alone or in a mixture of two or 
more. It is sometimes more preferable to use them in a mixture of two or 
more. 
In any case of the above mentioned Processes (a), (b) and (c), an aromatic 
ketone catalyst is used generally in an amount of 0.2 to 30%, preferably 2 
to 20% on the basis of the weight of the starting material, i.e. 
o-nitroazobenzenes or 2-phenylbenzotriazole-N-oxides. 
Examples of the base used in the present invention include sodium 
hydroxide, potassium hydroxide and the like. The base is used in an amount 
of 1 to 12 moles, preferably 2 to 8 moles per one mole of the starting 
material, i.e. o-nitroazobenzenes or 2-phenylbenzotriazole-N-oxides.

The present invention is further illustrated by the following Examples, but 
is not limited thereto. 
EXAMPLE 1 
2-nitro-2'-hydroxy-5'-methylazobenzene 12.9 g was added to a mixture of 
methanol 60 ml, water 30 ml and 97% sodium hydroxide 12.4 g, and the 
resultant mixure was stirred while raising temperature to 65.degree. C. 
Thereafter, the mixture was cooled to 40.degree. C., and 9-fluorenone 0.8 
g and then 80% paraformaldehyde 2.1 g were added to the mixture for 1 
hour. The resultant mixture was then heated to the boiling point 
(75.degree. C.), and was stirred at the boiling point for 6 hours, thus 
almost all of the azobenzene having disappeared to produce 
2-(2-hydroxy-5-methylphenyl)benzotriazole-N-oxide. 
Thereafter, water 50 ml was added to the reaction liquor, and the reaction 
liquor was neutralized to pH 8 with 62% sulfuric acid 16 g to precipitate 
a crystal. The crystal thus obtained was filtered by suction, and the 
separated crystal was then dried, thus producing 10.7 g of 
2-(2-hydroxy-5-methylphenyl)benzotriazole-N-oxide having a melting point 
of 138.degree. to 140.degree. C. at the yield of 89.0%. 
EXAMPLE 2 
The same procedure as in Example 1 was repeated, except that 
2-nitro-2'-hydroxy-5'-methylazobenzene 12.9 g was replaced respectively by 
(a) 2-nitro-2'-hydroxy-5'-butylazobenzene 14.9 g, (b) 
2-nitro-2'-hydroxy-5'-t-octylazobenzene 17.8 g, and (c) 
2-nitro-2',4'-dihydroxyazobenzene 14.9 g. 
The products thus obtained and their properties are as follows: 
(a) 2-(2-hydroxy-5-t-butylphenyl)benzotriazole-N-oxide: Yield: 12.7 g 
(90.0%), Melting Point: 73.degree. to 78.degree. C. 
(b) 2-(2-hydroxy-5-t-octylphenyl)benzotriazole-N-oxide: Yield: 14.2 g 
(84.0%), Melting Point: 106.degree. to 111.degree. C. 
(c) 2-(2,4'-dihydroxyphenyl)benzotriazole-N-oxide: Yield: 9.7 g (80.0%), 
Melting Point: 246.degree. to 248.degree. C. 
EXAMPLE 3 
95% potassium hydroxide 17.7 g was added and dissolved in a mixture of 
ethyl alcohol 80 ml and water 10 ml. 
2-nitro-2'-hydroxy-5'-methylazobenzene 12.9 g was then added to the 
resultant solution at 50.degree. to 60.degree. C. for 30 minutes while 
stirring, and thereafter 9-fluorenone 0.6 g and 35% formalin 5.6 g were 
added to the solution in 30 minutes. The resultant mixture was stirred for 
1 hour at 65.degree. to 70.degree. C., and was further reacted at the 
boiling point (85.degree. C.) for 4 hours, thus almost all of the 
azobenzene having disappeared to produce 
2-(2-hydroxy-5-methylphenyl)benzotriazole-N-oxide. 
Thereafter, water 50 ml was added to the reaction liquor, and the reaction 
liquor was neutralized to pH 8 with 62% sulfuric acid to precipitate a 
crystal. The crystal thus obtained was filtered by suction to separate the 
crystal, and the separated crystal was fully washed with water and further 
with ethyl alcohol. The washed crystal was then dried, thus producing 10.6 
g of 2-(2-hydroxy-5-methylphenyl)benzotriazole-N-oxide having a melting 
point of 138.degree. to 140.degree. C. at the yield of 88.0%. 
EXAMPLE 4 
Methanol 60 ml, water 30 ml, 97% sodium hydroxide 12.4 g, and 
2-nitro-2'-hydroxy-5'-methylazobenzene 12.9 g were mixed and stirred. 
After adding benzanthrone 1.2 g to the resultant mixture at 65.degree. to 
70.degree. C., 80% paraformaldehyde 2.3 g was added to the mixture for 2 
hours, and then the reaction liquor was further stirred at the boiling 
point (75.degree. C.) for 5 hours, thus o-nitroazobenzene having 
disappeared to product 2-2-hydroxy-5-methylphenyl)benzotriazole-N-oxide. 
Thereafter, water 50 ml was added to the reaction liquor, and the reaction 
liquor was neutralized to pH 8 with 62% sulfuric acid 16 g to precipitate 
a crystal. The crystal thus obtained was filtered by suction to separate 
the crystal, and the separated crystal was fully washed with water and 
further with methanol. The washed crystal was then dried, thus producing 
10.1 g of 2-(2-hydroxy-5-methylphenyl)benzotriazole-N-oxide having a 
melting point of 138.degree. to 140.degree. C. at the yield of 83.5%. 
EXAMPLE 5 
2-nitro-2'-hydroxy-5'-methylazobenzene 12.9 g was added to a mixture of 
methanol 60 ml, water 30 ml and 97% sodium hydroxide 12.4 g, and the 
resultant mixture was stirred while raising temperature to 65.degree. C. 
9-fluorenone 1.2 g and then 90% acetoaldehyde 3.2 g were added to the 
mixture for 1 hour. The resultant mixture was then heated to the boiling 
point (75.degree. C.), and was stirred at the boiling point (75.degree. 
C.) for 6 hours, thus almost all of the azobenzenes having disappeared to 
produce 2-(2-hydroxy-5-methylphenyl)benzotriazole-N-oxide. 
Thereafter, water 50 ml was added to the reaction liquor, and the reaction 
liquor was neutralized to pH 8 with 62% sulfuric acid 16 g to precipitate 
a crystal. The crystal thus obtained was filtered by suction, and the 
separated crystal was fully washed with water and further with methanol. 
The washed crystal was then dried, thus producing 10.5 g of 
2-(2-hydroxy-5-methylphenyl)benzotriazole-N-oxide having a melting point 
of 138.degree. to 140.degree. C. at the yield of 87.0%. 
EXAMPLE 6 
2-nitro-2'-hydroxy-5'-methylazobenzene 12.9 g was added to a mixture of 
methanol 60 ml, water 30 ml and 97% sodium hydroxide 12.4 g, and the 
resultant mixure was stirred while raising temperature to 65.degree. C. 
Thereafter, the mixture was cooled to 40.degree. C., and 9-fluorenone 0.8 
g and then 80% paraformaldehyde 2.1 g were added to the mixture for 1 
hour. The resultant mixture was then heated to the boiling point 
(75.degree. C.), and was stirred at the boiling point for 6 hours, thus 
almost all of the azobenzene having disappeared to produce 
2-(2-hydroxy-5-methylphenyl)benzotriazole-N-oxide (Process (b) having 
completed). 
In order to conduct Process (c), the reaction liquor was then cooled to 
70.degree. C., 9-fluorenone 0.2 g and then 80% paraformaldehyde 2.5 g were 
added to the reaction liquor for 30 minutes. Thereafter, the reaction 
liquor was heated to the boiling point (75.degree. C.), and was stirred 
for futher 4 hours, thus the N-oxide having disappeared to complete 
Process (c). 
Thereafter, water 50 ml was added to the reaction liquor, and the reaction 
liquor was neutralized to pH 8 with 62% sulfuric acid 16 g to precipitate 
a crystal. The crystal thus obtained was filtered by suction to separate 
the crystal, and the appeared crystal was fully washed with water and 
further with methanol. The washed crystal was then dried, thus producing 
9.2 g of 2-(2-hydroxy-5-methylphenyl)benzotriazole having a melting point 
of 128.degree. to 130.degree. C. at the yield of 81.8%. 
EXAMPLE 7 
The same procedure as in Example 6 was repeated, except that 
2-nitro-2'-hydroxy-5'-methylazobenzene 12.9 g was replaced respectively by 
(a) 2-nitro-2'-hydroxy-5'-butylazobenzene 14.9 g, (b) 
2-nitro-2'-hydroxy-5'-t-octylazobenzene 17.8 g, and (c) 
2-nitro-2',4'-dihydroxyazobenzene 14.9 g. 
The products thus obtained and their properties are as follows: 
(a) 2-(2-hydroxy-5-t-butylphenyl)benzotriazole: Yield: 11.0 g (84.0%), 
Melting Point: 96.5.degree. to 98.0.degree. C. 
(b) 2-(2-hydroxy-5-t-octylphenyl)benzotriazole: Yield: 12.8 g (79.0%), 
Melting Point: 103.degree. to 105.degree. C. 
(c) 2-(2,4-dihydroxyphenyl)benzotriazole: Yield: 9.2 g (70.5%), Melting 
Point: 187.degree. to 189.degree. C. 
EXAMPLE 8 
95% potassium hydroxide 17.7 g was added and dissolved in a mixture of 
ethyl alcohol 80 ml and water 10 ml. 
2-nitro-2'-hydroxy-5'-methylazobenzene 12.9 g was then added to the 
resultant solution at 50.degree. to 60.degree. C. for 30 minutes while 
stirring, and thereafter 9-fluorenone 0.6 g and 35% formalin 5.6 g were 
added to the solution in 30 minutes. The resultant mixture was stirred for 
1 hour at 65.degree. to 70.degree. C., and was further reacted at the 
boiling point (85.degree. C.) for 4 hours, thus almost all of the 
azobenzene having disappeared to complete the reaction of Process (b). 
Anthrone 0.4 g and 35% formalin 6.4 g were then added to the reaction 
liquor by dropwise for 30 minutes, and the reaction liquor was further 
reacted for 8 hours while stirring, thus the intermediate product of 
Process (b) having disappeared to complete the reaction of Process (c). 
Thereafter, water 50 ml was added to the reaction liquor, and the reaction 
liquor was neutralized to pH 8 with 62% sulfuric acid 16 g to precipitate 
a crystal. The crystal thus obtained was filtered by suction to separate 
the crystal, and the separated crystal was fully washed with water and 
further with ethyl alcohol. The washed crystal was then dried, thus 
producing 8.7 g of 2-(2-hydroxy-5-methylphenyl)benzotriazole-N-oxide 
having a melting point of 138.degree. to 140.degree. C. at the yield of 
77.3%. 
EXAMPLE 9 
Methanol 60 ml, water 30 ml, 97% sodium hydroxide 12.4 g, and 
2-nitro-2'-hydroxy-5'-methylazobenzene 12.9 g were mixed and stirred. 
After adding benzanthrone 1.2 g to the resultant mixture at 65.degree. to 
70.degree. C., 80% paraformaldehyde 4.6 g was added to the mixture for 2 
hours, and then the reaction liquor was further stirred at the boiling 
point (75.degree. C.) for 5 hours, thus o-nitroazobenzene having 
disappeared to produce 2-(2-hydroxy-5-methylphenyl)benzotriazole-N-oxide 
(Process (b) having completed). In order to conduct Process (c), the 
reaction liquor was further stirred for 6 hours, thus the N-oxide having 
disappeared to complete Process (c). 
Thereafter, water 50 ml was added to the reaction liquor, and the reaction 
liquor was neutralized to pH 8 with 62% sulfuric acid 16 g to precipitate 
a crystal. The crystal thus obtained was filtered by suction to separate 
the crystal, and the separated crystal was fully washed with water and 
further with methanol. The washed crystal was then dried, thus producing 
8.4 g of 2-(2-hydroxy-5-methylphenyl)benzotriazole having a melting point 
of 128.degree. to 130.degree. C. at the yield of 74.7%. 
EXAMPLE 10 
2-nitro-2'-hydroxy-5'-methylazobenzene 12.9 g was added to a mixture of 
methanol 60 ml, water 30 ml and 97% sodium hydroxide 12.4 g, and the 
resultant mixture was stirred while raising temperature to 65.degree. C. 
9-fluorenone 1.2 g and then 90% acetoaldehyde 6.5 g were added to the 
mixture for 1 hour. The resultant mixture was then stirred at the boiling 
point (75.degree. C.) for 6 hours, thus almost all of the azobenzene 
having disappeared to produce 
2-(2-hydroxy-5-methylphenyl)benzotriazole-N-oxide (Process (b) having 
completed). In order to conduct Process (c), the reaction liquor was 
further stirred at the boiling point for 5 hours, thus the N-oxide having 
disappeared to complete Process (c). 
Thereafter, water 50 ml was added to the reaction liquor, and the reaction 
liquor was neutralized to pH 8 with 62% sulfuric acid 16 g to precipitate 
a crystal. The crystal thus obtained was filtered by suction to separate 
the crystal, and the separated crystal was fully washed with water and 
further with methanol. The washed crystal was then dried, thus producing 
9.1 g of 2-(2-hydroxy-5-methylphenyl)benzotriazole having a melting point 
of 128.degree. to 130.degree. C. at the yield of 80.9%. 
EXAMPLE 11 
Methanol 110 ml, water 20 ml, 97% sodium hydroxide 12.4 g, and 
2-nitro-2'-hydroxy-5'-t-octylazobenzene 17.8 g were mixed and stirred. 
After adding 9-fluorenone 2.4 g to the resultant mixture at 65.degree. to 
70.degree. C., 80% paraformaldehyde 6 g was added to the mixture for 4 
hours, and then the reaction liquor was further stirred at the boiling 
point (73.degree. C.) for 6 hours, thus the reduction reaction having 
completed. 
Thereafter, water 50 ml was added to the reaction liquor, and the reaction 
liquor was neutralized to pH 8 with 62% sulfuric acid 16 g to precipitate 
a crystal. The crystal thus obtained was filtered by suction to separate 
the crystal, and the separated crystal was fully washed with water and 
further with methanol. The washed crystal was then dried, thus producing 
13.1 g of 2-(2-hydroxy-5-t-octylphenyl)benzotriazole having a melting 
point of 103.degree. to 105.degree. C. at the yield of 81.0%. 
EXAMPLE 12 
2-(2-hydroxy-3-t-butyl-5-methylphenyl)-5-chlorobenzotriazole-N-oxide 16.6 g 
was added to a mixture of methanol 72 ml, water 20 ml and 97% sodium 
hydroxide 12.4 g, and the resultant mixture was stirred at 70.degree. C. 
for 30 minutes, then having been cooled to 65.degree. C. After adding 
9-fluorenone 0.8 g to the resultant mixture, 80% paraformaldehyde 2.5 g 
was added to the mixture for 30 minutes, and the resultant mixture was 
stirred at 60.degree. to 70.degree. C. for 1 hour, and further at the 
boiling point (73.degree. C.) for 4 hours, thus 
2-(2-hydroxy-3-t-butyl-5-methylphenyl)-5-chlorobenzotriazole-N-oxide 
having disappeared to complete the reduction reaction. 
Thereafter, water 50 ml was added to the reaction liquor by dropwise at 
65.degree. to 70.degree. C., and then reaction liquor was neutralized with 
62.5% sulfuric acid 12 g to precipitate a crystal. The crystal thus 
obtained was filtered by suction to separate the crystal, and the 
separated crystal was fully washed with water and further with methanol. 
The washed crystal was then dried, thus producing 14.7 g of 
2-(2-hydroxy-3-t-butyl-5-methylphenyl)-5-chlorobenzotriazole having a 
melting point of 138.degree. to 140.degree. C. at the yield of 93.0%. 
EXAMPLE 13 
The same procedure as in Example 12 was repeated, excepted that 
2-(2-hydroxy-3-t-butyl-5-methylphenyl)-5-chlorobenzotriazole-N-oxide 16.6 
g was replaced respectively by (a) 
2-(2-hydroxy-3,5-di-t-butylphenyl)-5-chlorobenzotriazole-N-oxide 19.5 g, 
(b) 2-(2-hydroxy-3,5-di-t-butylphenyl)benzotriazole-N-oxide 17.8 g, and 
(c) 2-(2-hydroxy-3,5-di-t-amylphenyl)benzotriazole-N-oxide 19.2 g. 
The products thus obtained and their properties are as follows: 
(a) 2-(2-hydroxy-3,5-di-t-butylphenyl)-5-chlorobenzotriazole: Yield: 16.1 g 
(90.0%), Melting Point: 154.degree. to 155.5.degree. C. 
(b) 2-(2-hydroxy-3,5-di-t-butylphenyl)benzotriazole: Yield: 14.8 g (91.5%), 
Melting Point: 150.degree. to 152.degree. C. 
(c) 2-(2-hydroxy-3,5-di-t-amylphenyl)benzotriazole: Yield: 15.4 g (88.0%), 
Melting Point: 77.degree. to 79.degree. C. 
EXAMPLE 14 
2-(2-hydroxy-3-t-butyl-5-methylphenyl)-5-chlorobenzotriazole-N-oxide 16.6 g 
was added to a mixture of ethyl alcohol 80 ml, water 10 ml and 95% 
potassium hydroxide 17.7 g, and the resultant mixture was stirred at 
80.degree. C. for 30 minutes, then having been cooled to 65.degree. C. 
After adding anthrone 1.4 g to the resultant mixture, 35% formalin 6.5 g 
was added to the mixture by dropwise for 30 minutes, and the resultant 
mixture was stirred at 65.degree. to 70.degree. C. for 1 hour, and further 
at the boiling point (87.degree. C.) for 10 hours, thus 
2-(2-hydroxy-3-t-butyl-5-methylphenyl)-5-chlorobenotriazole-N-oxide having 
disappeared to complete the reduction reaction. 
Thereafter, water 50 ml was slowly added to the reaction liquor, and the 
reaction liquor was neutralized with 62.5% sulfuric acid 12 g to 
precipitate a crystal. The crystal thus obtained was filtered by suction 
to separate the crystal, and the separated crystal was fully washed with 
water and further with ethyl alcohol. The washed crystal was then dried, 
thus producing 14.5 g of 
2-(2-hydroxy-3-t-butyl-5-methylphenyl)-5-chlorobenzotriazole having a 
melting point of 138.degree. to 140.degree. C. at the yield of 92.0%. 
EXAMPLE 15 
2-(2-hydroxy-3,5-di-t-butylphenyl)-5-chlorobenzotriazole-N-oxide 18.7 g was 
added to a mixture of methanol 80 ml, water 30 ml and 97% sodium hydroxide 
12.4 g, and the resultant mixture was stirred at 70.degree. C. for 30 
minutes, then having been cooled to 60.degree. C. After adding 
benzanthrone 1.2 g to the resultant mixture, 90% acetoaldehyde 3.2 g was 
added to the mixture by dropwise for 30 minutes, and the resultant mixture 
was stirred at 60.degree. to 70.degree. C. for 30 minutes, and further at 
the boiling point (74.degree. C.) for 4 hours, thus 
2-(2-hydroxy-3,5-di-t-butylphenyl)-5-chlorobenzotriazole-N-oxide having 
disappeared to complete the reduction reaction. 
Thereafter, water 50 ml was added to the reaction liquor by dropwise at 
65.degree. to 70.degree. C., and the reaction liquor was neutralized with 
62.5% sulfuric acid 12 g to precipitate a crystal. The crystal thus 
obtained was filtered by suction to separate the crystal, and the 
separated crystal was fully washed with water and further with methanol. 
The washed crystal was then dried, thus producing 15.9 g of 
2-(2-hydroxy-3,5-di-t-butylphenyl)-5-chlorobenzotriazole having a melting 
point of 154.degree. to 155.5.degree. C. at the yield of 89.0%. 
EXAMPLE 16 
2-(2-hydroxy-5-methylphenyl)benzotriazole-N-oxide 10.7 g was added to a 
mixture of methanol 60 ml, water 30 ml and 97% sodium hydroxide 12.4 g, 
and the resultant mixture was heated to 70.degree. C. After adding 
9-fluorenone 1.0 g to the resultant mixture, 80% paraformaldehyde 2.5 g 
was added to the mixture for 30 minutes, and the resultant mixture was 
heated to the boiling point (75.degree. C.). The resultant mixture was 
further stirred at the boiling point for 4 hours, thus 
2-(2-hydroxy-5-methylphenyl)benzotriazole-N-oxide having disappeared to 
complete the reduction reaction. 
Thereafter, water 50 ml was added to the reaction liquor, and the reaction 
liquor was neutralized with 62% sulfuric acid 16 g to precipitate a 
crystal. The crystal thus obtained was filtered by suction to separate the 
crystal, and the separated crystal was fully washed with water and further 
with methanol. The washed crystal was then dried, thus producing 9.2 g of 
2-(2-hydroxy-5-methylphenyl)benzotriazole having a melting point of 
129.degree. to 130.degree. C. at the yield of 92.1%.