Process for the preparation of 2-(2',4'-dihydroxyphenyl)-4,6-diaryl-s-triazines

There is disclosed a process for the preparation of 2-(2', 4'-dihydroxyphenyl)-4,6-diaryl-s-triazines of formula ##STR1## which comprises reacting 2-hydroxy-4,6-diaryl-s-triazines of formula ##STR2## in the temperature range from 100.degree.-150.degree. C. with thionyl chloride in the presence of a catalytic amount of a polar solvent, and subsequently reacting the chloro-s-triazine intermediate with 1,3-dihydroxybenzene using a Lewis acid in the presence of an inert organic solvent, in which formulae (1) and (2) above the rings A may be further substituted by halogen, hydroxy, lower alkyl, lower alkoxy or lower alkoxycarbonyl. The process of the invention makes it possible to prepare in simple manner and in good yield 2-(2',4'-dihydroxphenyl)-4,6-diaryl-s-triazines which find utility as UV absorbers or as starting materials of the preparation of UV absorbers.

The present invention relates to a novel simplified process for the 
preparation of 2-(2',4'-dihydroxyphenyl)-4,6-diaryl-s-triazines from 
2-hydroxy-4,6-diaryl-s-triazines. 
The reaction of 2-hydroxy-4,6-diaryl-s-triazines with thionyl chloride to 
give 2-chloro-4,6-diaryl-s-triazines is disclosed, inter alia, in U.S. 
Pat. No. 2,691,018. 
It has now been found that 2-(2',4'-dihydroxyphenyl)-4,6-diaryl-s-triazines 
can be prepared in a single step by reacting 
2-hydroxy-4,6-diaryl-s-triazines with thionyl chloride and 
1,3-dihydroxybenzene without isolation of the chloro-s-triazine 
intermediate. 
Accordingly, the invention relates to a process for the preparation of 
2-(2',4'-dihydroxyphenyl)-4,6-diaryl-s-triazines of formula 
##STR3## 
which comprises reacting 2-hydroxy-4,6-diaryl-s-triazines of formula 
##STR4## 
in the temperature range from 100.degree.-150.degree. C. with thionyl 
chloride in the presence of a catalytic amount of a polar solvent, and 
subsequently reacting the chloro-s-triazine intermediate with 
1,3-dihydroxybenzene using a Lewis acid in the presence of an inert 
organic solvent, in which formulae (1) and (2) above the rings A may be 
further substituted by halogen, hydroxy, lower alkyl, lower alkoxy or 
lower alkoxycarbonyl. 
Lower alkyl and lower alkoxy in the definition of the substituents of the 
rings A of the compounds of formulae (1) and (2) denote those groups or 
moieties which contain 1 to 5, preferably 1 to 3, carbon atoms. Such 
groups are typically methyl, ethyl, n-propyl, isopropyl, n-butyl, 
sec-butyl, tert-butyl, amyl, isoamyl or tert-amyl and, respectively, 
methoxy, ethoxy, isopropoxy, isobutoxy or tert-butoxy. 
Halogen is fluoro, bromo and, preferably, chloro. 
Preferred compounds of formulae (1) and (2) are suitably those in which the 
rings A are not further substituted. 
Lewis acids are compounds having a deficiency in electrons or Broenstedt 
acids like HCl, HBr etc. 
To prepare the compounds of formula I it is preferred to use anhydrous 
aluminium chloride as Lewis acid. 
The reaction of the compound of formula (2) with thionyl chloride and 
1,3-dihydroxybenzene is carried out in organic medium. The organic medium 
is suitably selected from various solvents which must meet the sole 
condition that they are inert under the reaction conditions. Suitable 
solvents include: aromatic and aliphatic hydrocarbons and the alkylated, 
halogenated and nitrated derivatives thereof, typically nitrobenzene, 
chlorobenzene, o-dichlorobenzene, 1,2,3-trimethylbenzene, toluene, xylene, 
mixtures of xylene isomers, tetrahydronaphthalene, 
.alpha.-chloronaphthalene, acetylene tetrachloride, ethylene dichloride 
and the like. 
The preferred solvents for the reaction are toluene, xylene or mixtures of 
xylene isomers. 
In addition to the inert organic solvent, a polar organic solvent which has 
a boiling point in the range from 120.degree. to 150.degree. C. is also 
used in the first reaction step for the reaction with thionyl chloride. It 
is preferred to use dimethyl formamide as polar organic solvent, which has 
the advantage that only a minor excess of thionyl chloride of about 10-15% 
need be used for the reaction. If this polar solvent is dispersed with, 
then the reaction has to be carried out with a more than three-fold excess 
of thionyl chloride, as described in U.S. Pat. No. 2,691,018. 
Preferred reactions are those in which the solvent is xylene or a mixture 
of xylene isomers and dimethyl formamide. 
A preferred embodiment of the process of this intention comprises reaction 
2-hydroxy-4,6-diphenyl-s-triazine with thionyl chloride in the presence of 
a catalytic amount of dimethyl formamide, and subsequently reacting the 
chloro-s-triazine intermediate with 1,3-dihydroxybenzene using aluminium 
chloride in the presence of toluene, xylene or a mixture of xylene 
isomers. 
The inventive process affords the further possibility of discontinuing the 
reaction after the reaction of the starting command of formula (2) with 
thionyl chloride, and isolating the intermediate without much effort. In 
this case, compounds of formula 
##STR5## 
wherein A is as defined in formulae (1) and (2), are obtained in good 
yield. 
The invention further relates to the preparation of the starting compounds 
of formula (2). 
The process for the preparation of 2-hydroxy-4,6-diaryl-s-triazines of 
formula (2) comprises reacting an aqueous alkaline solution of a 
benzamidine hydrohalide in the temperatures range from 0.degree. to 
80.degree. C. with an alkyl formate to an alkyl benzimidoylcarbamate, 
adding an inert organic solvent to the resultant emulsion, and reacting 
the organic phase containing the alkyl benzimidoylcarbamate to give the 
2-hydroxy-4,6-diaryl-s-triazine according to the reaction scheme 
##STR6## 
wherein Hal.sub.1 and Hal.sub.2 are halogen and R is C.sub.1 -C.sub.4 
alkyl, and A is as previously defined. 
R as C.sub.1 -C.sub.4 alkyl is methyl, ethyl, propyl, isopropyl, butyl, 
sec-butyl or tert-butyl. The preferred meaning is ethyl. 
The ring closure to give the 2-hydroxy-4,6-diphenyl-s-triazine is also 
conveniently carried out under a reduced pressure of 150-200 mbar for 
rapid removal of the alcohol and urethane. 
The benzamidine hydrohalide is suitably benzamidine hydrobromide and, 
preferably, benzamidine hydrochloride. 
Preferred alkyl formates are ethyl bromoformate and, more particularly, 
ethyl chloroformate. 
The aqueous alkaline benzamidine hydrohalide solution is preferably an 
alkali metal hydroxide solution, most preferably a sodium hydroxide 
solution. 
The reaction of the ethyl benzimidoylcarbamate to the compound of formula 
(2) is carried out in an inert organic solvent having a boiling point of 
160.degree.-250.degree. C. Suitable solvents are: o-dichlorobenzene, 
nitrobenzene, 1,2,3-trimethylbenzene, a mixture of 26.5% of diphenyl and 
73.5% of diphenyl ether (.RTM.Dowtherm) or anisole. Preferred solvents are 
suitably o-dichlorobenzene and 1,2,3-trimethylbenzene .RTM.Dowtherm. 
The reaction to give the compounds of formula (2) may be carried out under 
phase transfer conditions and using a phase transfer catalyst such as 
tetrabutylammonium bromide, butyltriethylammonium bromide or chloride, 
butyltributylammonium bromide or chloride. 
The hydroxy triazines of formula (2) are known, for example from A. Pinner, 
Chem. Ber. 23, 1919 (1890). 
Compared with the process described therein, the compounds of formula (2) 
are obtained by the process of this invention in a one-step process 
without isolation of the alkyl benzimidoylcarbamate. Moreover, the 
hydroxyphenyl-s-triazine of formula (2) is obtained in such good purity 
that it may conveniently be further processed, without isolation, to a 
2-(2',4'-dihydroxyphenyl)-4,6-diaryl-s-triazine of formula (1). These 
compounds can thus also be prepared in simple manner and in good yield by 
a one pot process. 
The invention accordingly also relates to a process for the preparation of 
2-(2',4'-dihydroxyphenyl)-4,6-diaryl-s-triazines of formula (1), which 
comprises reacting a benzamidine hydrohalide with an alkyl formate to 
2-hydroxy-4,6-diaryl-s-triazine of formula (2) under a reduced pressure of 
150-200 mbar as described above, and reacting this intermediate, without 
isolation, in the temperature range from 100.degree.-150.degree. C. with 
thionyl chloride in the presence of a catalytic amount of a polar solvent, 
and subsequently reacting the chloro-s-triazine intermediate with 
1,3-dihydroxybenzene, using a Lewis acid in the presence of an inert 
organic solvent, to give the compound of formula (1). 
The process of this invention makes it possible to prepare 
2-(2',4'-dihydroxyphenyl)-4,6-diaryl-s-triazines and also the starting 
compounds in simple manner and in good yield. 
The compounds obtained by the process of this invention find utility as UV 
absorbers or as starting materials for the preparation of UV absorbers. 
The invention is illustrated by the following Examples.

PREATION OF THE STARTING MATERIALS 
Example 1 
47 g of benzamidine hydrochloride are dissolved in 250 ml of water and to 
the solution was added 80 g of a 30% solution of sodium hydroxide. With 
rapid stirring and gentle cooling, the 32.6 g of ethyl chloroformate are 
slowly run into the reaction mixture over c. 5 minutes, the temperature 
rising to 40.degree.14 45.degree. C. The reaction mixture is stirred for 
11/2 hours at 45.degree.-50.degree. C. to bring the reaction to 
completion. Then 150 ml of o-dichlorobenzene are run into the resultant 
emulsion. After stirring briefly, the o-dichlorobenzene phase is separated 
from the aqueous phase, heated to the boil in a flask with distillation 
head, and kept for 11/2 hours at the boil (175.degree.-180.degree. C.). 
After cooling to room temperature, the precipitated product is isolated by 
filtration, washed twice with methanol and dried at 80.degree. C. under 
vacuum. For purification, the product is heated for 15 minutes to the boil 
in 250 ml of a solution of methanol/water in the ratio 8:2 and then 
isolated by filtration, giving the compound of formula 
##STR7## 
The yield of crude product after drying is 30.5 g (=81.6% of theory). The 
melting point after one recrystallisation is 296.degree.-298.degree. C. 
EXAMPLE 2 
412.2 g of a 38% solution of benzamidine hydrochloride in methanol are 
mixed with 500 ml of 1,2,3-trimethylbenzene. Then 300 ml of methanol are 
distilled from the mixture at 40.degree.-50.degree. C. under a weak 
vacuum. After addition of 100 ml of water and 80 g of a 50% aqueous 
solution of sodium hydroxide, the mixture is stirred for a further 30 
minutes at 20.degree.-30.degree. C. To the reaction mixture are added 150 
ml of water, 80 g of a 50% aqueous solution of sodium hydroxide and 1 g of 
tetrabutylammonium bromide. With rapid stirring (500 rpm) and cooling, 
112.9 g of ethyl chloroformate are then added dropwise at 
15.degree.-20.degree. C. over 1 hour, while keeping the pH at 8-8.5 by 
addition of 50% aqueous sodium hydroxide. The reaction mixture is stirred 
for 1 hour, then heated to 70.degree. C. and the water is removed from the 
organic phase. As described in Example 1, the organic phase is heated for 
2 hours to 170.degree.-175.degree. C., while simultaneously removing 
ethanol by distillation. After cooling, the precipitated product is 
purified with methanol/water, giving 105 g (=84.3% of theory) of the crude 
compound of formula (101) with a melting point of 295.degree.-297.degree. 
C. (after recrystallisation). 
Example 3 
157.6 g of benzamidine hydrochloride (purity: 99.4%) are stirred for 30 
minutes at room temperature with 250 ml of water and 80 g of a 50% 
solution of sodium hydroxide. After addition of a further 30 g of sodium 
hydroxide solution, 112.9 g of ethyl chloroformate are added dropwise, 
with rapid stirring (500 rpm) and cooling, over 1 hour at 
15.degree.-20.degree. C. The resultant crystal slurry is stirred for a 
further hour at room temperature. After addition of 100 ml of 
1,2,3-trimethylbenzene, the slurry is heated to 85.degree. C. and the 
crystalline product dissolves. The aqueous phase is separated and the 
organic phase is run into 400 ml of 1,2,3-trimethylbenzene at 
170.degree.-175.degree. over 1 hour, while simultaneously distilling 
alcohol from the mixture. After stirring for 1 hour at 
170.degree.-175.degree. C. and then cooling to room temperature, the 
precipitated product is isolated by filtration and purified as described 
in Example 1, giving 105.5 g of the compound of formula (101). The melting 
point is in the range 296.degree.-297.degree. C. (after 
recrystallisation). 
Example 4 
157.6 g of benzamidine hydrochloride (purity: 99.4%) are reacted with 300 
ml of water, 112.9 g of ethyl chloroformate and 160 g of a 50% solution of 
sodium hydroxide as in Example 3(a). Then 300 ml of .RTM.Dowtherm solvent 
are run into the suspension. After heating to 70.degree. C. and separating 
the aqueous phase, the solvent (.RTM.Dowtherm) phase is heated to 
170.degree. C. under a vacuum of 200 mbar, while distilling ethanol and 
urethane from the mixture. When the reaction is complete, the precipitated 
product is cooled to 70.degree. C., treated with 200 ml of methanol and 
then isolated by filtration at room temperature. The filter product is 
washed with methanol and dried at 120.degree. C. under vacuum. The yield 
is 108 g (86% of theory). Analysis by thin-layer chromatography shows a 
pure product which does not have to be recrystallised. 
PREATION OF THE CHLORO-S-TRIAZINE INTERMEDIATE 
Example 5 
24.9 g 2-hydroxy-4,6-diphenyl-s-triazine are heated to 80.degree. C. in 175 
ml of xylene (mixture of isomers). After addition of 2 ml of dimethyl 
formamide, 13.1 g of thionyl chloride are run in over 30 minutes. The 
reaction mixture is subsequently stirred for 30 minutes at 
85.degree.-90.degree. and thereafter for 3 hours at 
125.degree.-130.degree.. The resultant solution is concentrated to dryness 
by evaporation, giving 26 g (=97.1% of theory) of the compound of formula 
##STR8## 
with a melting point of 139.degree.-140.degree.. 
PREATION OF THE FINAL PRODUCTS 
Example 6 
124.6 g of 2-hydroxy-4,6-diphenyl-1,3,5-s-triazine are suspended in 600 ml 
of xylene (mixture of isomers) and, after addition of 3 ml of dimethyl 
formamide, heated to 100.degree. C. With good stirring, 71.4 g of thionyl 
chloride are run in at 100.degree.-105.degree. C. over 1 hour. The thin 
suspension is stirred for 1hour at the same temperature and then heated to 
125.degree.-130.degree. C. until it has dissolved completely. After 
cooling to 100.degree. C., 100 ml of the xylene mixture is distilled from 
the solution. The solution is cooled to 60.degree. C. and 73.3 g of 
anhydrous aluminium chloride (Merck) are added over 1 hour. The mixture is 
heated again to 80.degree. C. and, with good stirring, a suspension of 
66.1 g of 1,3-dihydroxybenzene in 100 ml of xylene (mixture of isomers) is 
added over 30 minutes. To bring the reaction to completion, the reaction 
mixture is stirred for a further 5 hours at 85.degree. C. To the reaction 
mixture is thereafter added a mixture of 450 ml of water and 50 ml of 30% 
hydrochloric acid. After heating to 100.degree. C., the xylene mixture is 
removed from the reaction mixture by steam distillation. The precipitated 
solid is isolated by filtration at 80.degree. C., washed free of acid with 
hot water and dried at 80.degree.-90.degree. C. under vacuum. The product 
is purified by treatment at 90.degree. C. with a mixture of dimethyl 
formamide/water in the ratio 7:3, giving 151.8 g (=88% of theory) of the 
compound of formula 
##STR9## 
with a melting point of 272.degree.-273.degree..