Note: Descriptions are shown in the official language in which they were submitted.
7 ~ 13
This invention pertains -to a process i-or the prepara-
tion of 2-aryl-2H-benzotriazoles and derivatives thereof. More
particularly, the invention relates to a nove:L process for pre-
paring 2-aryl-2H-benzotriazoles whereby high yields of the
desired products are obtained and effluent pollution problems
occurring with present processes for making such products are
essentially eliminated.
Heretofore, the conversion of an ortho-nitroazobenzene
to the corresponding 2-aryl-2H-benzotriazole has been accom-
plished 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 hydroxide solutions to
give good yields of the corresponding 2-aryl-2H-benzotriazoles.
Ammonium sulfide, alkali sulfides, zinc with ammonia at
go-loooc,sodiumhydrosulfide and zinc with hydrochloric acid
have also been used as the chemical reducing agents for this
transormation as disclosed in U.S. Pa-tent 2,362,988. The use
of ammonium sulfied 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 absence
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.
~'
~ 77~3
Electrolytic reduction of o-nitroazobenzenes was
reported by H. Itomi, Mem. Coll. Sci. Kyoto Imp. Univ., 12A,
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 embodiments
and conditions with a major impurity being formed, namely the
corresponding o-aminoazobenzene.
The widely used zinc dust and sodium hydroxide
chemical reducing system for transforming o-nitroazobenzenes
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-
benzotxiazoles varied from 30 to 85% depending on the specific
o-nitroazobenzene intermediate reduced.
The known chemical and electrolytic reduction pro~
cesses for preparing 2-aryl-2H-benzotriazoles are not practi-
cal 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 zinc
sludge which is of increasing environmental concern.
The preparation in good yield of the isomeric, but
chemically distinct lH-benzotriazoles by the catalytic reduc-
tion in alkaline medium of o-nitrophenylhydrazine and
selected pheynl ring substituted alkyl and perfluoroalkyl
-- 3 --
r
:
':
7~3
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 avo~iding severe
pollution and environmental problems.
A further object of this invention is to prepare 2-aryl-2H-
benzotriazoles by reducing and cyclizing the corresponding o-nitroazobenzene
under certain conditions hereinafter set forth in greaterdetailwhereby 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 I
Rl ~ ~ N / ~ 5
wherein Rl is hydrogen or chlorine, R2 is hydrogen, chlorine, lower alkyl of
1 to 4 carbon atoms, lower alkoxy of l to 4 carbon atoms, 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 wil~h alkyl groups,
said alkyl groups having 1 to 8 carbon atoms, cycloalkyl of !, to 6 carbon
atoms, carboalkoxy of 2 to 9 carbon atoms, chlorine carboxy ethyl or aryl
alkyl of 7 to 9 carbon atoms, R4 is hydrogen, lower alkyl of l 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, cycloaklyl of 5 to 6
carbon atoms or arylalkyl of 7 to 9.carbon atoms, which comprises reducing
and cyclizing the corresponding o-nitroazobenzene with hydrogen at a
temperature in the range of from about 20C to about lOO~C and at a pressure
.~
~4~71!3
in the range of from about 15 psig (1.05 kg/cm2, 1 atmosphere) to about
1000 psig ~70 kg/cm2, 66 atmospheres) while mixed in an aqueous alkaline
medium having a pH greater than lO 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 hydrogenati~n catalyst cannot be palladium, and recovering the
desired 2-aryl-2H-benzotriazole.
Taken in its broadest aspect~ one embodiment of the present invention
provides 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 reducing conditions in an aqueous alkaline
medium in the presence of a hydrogenation catalyst selected from the group
consisting of the noble metals of group VIII of the Periodic Table, and
recovering the desired 2-~2-hydroxy-5-methyl)-2H-benzotriazole.
A further embodiment of this invention is found in a process for
the production of 2-~2-hydroxy-5-methyl-
-4a-
~; `
~4~7 ~8
`phenyl)-2H-benzotriazole which comprises treating 2-nitro-2'-
hydroxy-5'-methylazobenzene with hydrogen at a temperature in
the range of from about 20C to about 100C and at a pressure
in the range of about 1 atmosphere to about 66 atmo6pheres in
an aqueous alkaline medium in the presence of a hydrogenation
catalyst comprising a noble metal of Group VIl of the
Periodic Table, removing the noble metal catalyst by filra-
tion, lowering the pH of the aqueous system to a value less
than 10 to precipitate the desired product, and recovering
the desired 2-(2-hydroxy-5-methylphenyl3-2H-benzotriazole by
conventional procedures.
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 80C, and most preferably from
about 40C to about 70C.
A specific embodiment of the invention is exemplified
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 temperature
in the range of from about 20C to about 100C and at a
pressure in the range of from about 1 to about 66 atomos-
pheres in an aqueous alkaline medium in the presence of a
hydrogenation catalyst comprising palladium composited on
charcoal, and recovering the desired 2-(2-hydroxy-5-methyl-
phenyl)-2-benzotriazole.
~5~7~
Other objects and embodimetns will be found in the
following, further detailed description of this invention.
The use of organic solvents when catalytically re-
ducing 2-nitroazobenzenes to form 2-aryl-2H-benzotriazoles
has inherent disadvantages. One desadvantage is economic in
nature involving the cost and recovery of the solvent, and
the other is the well known hazard of using low boiling sol-
vents when hydrogenating nitro compounds.
In order to avcid the use of organic solvents, the
reduction of 2-nitro-2' hydroxy-5'-methylazobenzene was car-
ried out in an aqueous alkaline solution employing sufEicient
sodium hydroxide to convert the water-insoluble azobenzene
intermediate into the corresponding water~soluble sodium
phenolate salt. A hydrogenation catalyst comprising palladium
composited on carbon was used and the reduction and cycliza-
tion effected at a hydrogen pressure of from about 1 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 77~. However, higher pressures up to about
66 atmospheres may be also used with equivalent results.
-- 6 --
~L~5~7~1~
While many of the 2-nitro-2'-hydroxyazobenzene inter-
mediates useful in this invention have such a combination of
chemical and physical properties that they can be converted
in strong aqueous alkaline solution into the corresponding
water-soluble alkali phenolate salts, other 2-nitro-2'-
hydroxyazobenzene intermediates because of their more hydro-
carbon nature remaining essentially insoluble in these strong
aqueous alkaline solutions. In order to facilitate required
close proximity of the catalyst, hydrogen and o-nitroazo-
benzene intermediate in this heterogeneous reaction, the use
of a wetting or dispersing agent is required.
In the process according to the invention the 2-nitro-
2'-hydroxyazobenzenes insoluble in strong aqueous alkaline
solution are employed as dispersions in water. The term dis-
persion is used in the present invention to describe any fine
distribution of the 2-nitro-2'-hydroxyazobenzenes. Dispersions
are produced by adding dispersing agents to the aqueous alkali
and the appropriate 2-nitro-2'-hydroxyazobenzne compound
mixtrue in a concentration between 0.1% and 5% by weight, and
preferably between 0.5~ and 3% by weight, of the dispersing
agent~ It is frequently necessary to stir very rapidly at the
same time. This rapid stirring should be maintained after
addition of the noble metal catalyst and during the hydro-
genation reaction itself to maximize contact between the
various components of this heterogeneous system.
~47 i~13
Examples of dispersing agents which can be used
according to the invention are dispersing agents from e.g.
Ullmann, Encyklopaedie der Technischen Chemie, Third Edition,
Volume 16, 1965, pages 724-741.
In the case of the anionic surface-active a~ents, the
anion is shown. The cation is generally an alkali metal ion.
In the case of the cationic surface-active agents, the cation
is shown. The anion is generally a chloride or methosulfate
ion.
In the list below, the symbols denote the following:
R denotes a long-chain alkyl radical,
R' denotes a short alkyl radical or H, and
X denotes an alkylene radical, for example -(CH2)n , with
n = 1-3.
7~
Anionic surface~acti~re _ ~ents
_
a) Salts of carboxylic acids
R-COO Soaps
R-CONH-X-COO
R
~CH-S02NH-X-COO
_ Modified soaps with inter-
-O-X-COO
mediate members
R-S-X-COO
R-S02 -X-COO
b) Sulfuric acid Sulfated oils and fatty acids
esters
R-CH-X-C~ Sulfated esters
I - \OR'
R-CH-X-C~ Sulfated amides
OSO3
R-OSO3 Alkylsulfates
O Sulfated fatty acid monoglyce-
H rides and others
-
R-CONH-X-OSO3 Sulfated fatty acid alkylol-
amides
R-O-X-OSO Sulfated ethers
7,f~
c~ Alkylsulfonates
R~H-R' Simple alkyl.sulfonates
~3
CH2--COOR \ Sulfosuccinic acid esters
03S-CH--coo~ I . ,
RCOO-X-S03
R-COI-X-So3 Alkylsulfonates with`intermediate
R' members
R - ~ O-X-S03
d) Alkylarylsulfonates
R ~ ~lkylnaphthalenesulfona~es
S03
R--~ ~ Alkylbenæ~esulIonates
S03
e) Surface-active agents with less customary anionic groups
O Alkylphosphates (variQus kinds~
Il / O ..
R ~ ~ O
Salts o~ alkylbenzenephosphonic ac.ids
- 10 -
7 7 1~
Cationic sur~ace~active agents
a) Amine sal,s
,~
R-NH3
2 ¦ Primary, secondary and tertiary
+ ~ ~mine salts
R-NH R' I
1. ./ ..
R--COO--X--NH~2
` ~ ¦ Primary, secondary and ~ertiary
R--CONHX-NHR2
~ amine salts with intermediate members
R-O- X --NHR2
b} Quaternary ammonium salts
R'
~+
R-~ -R' (Also with intermediate members, as
Ri in ~he case of amine salts)
c) Phosphonium salts d) Sulfonium salts
~' R'
R-P~-R' and R-5
R ~
A~lphoteric surface-ac~ive agents
I .
~N~X-COO- Betaines
R'
7 a 8
I ~ _
R - N-X-SO Sulfobetaines
R'
R - N-X-O-S03 Sulfate-betaines
R'
Non-ionic surface-active agents
a) Ethylene oxide adducts
R-(O-CH -CH ) -OH Alkyl-polyethylene
glycols
,
R ~ (O-CH2-CH2)n-OH Alkylphenyl-polyethylene
glycols
R CO(O CH2 C 2)n Acyl-polyethylene glycols
H-(O-CH2-CH2)n-(O-~H-cH2)m ( CH2 2 n Oxethylated poly-
H3 propylene glycols
b) Further non-ionic surface-active agents
2 o 2 Fatty acid monoglycerides
H
R-COO-c6Hll04 Anhydrous sorbitol mono-
fatty acid esters
R-CONH-X-OH
R-CON-X-OH ) Fatty acid alkylolamides
X-OH
R-COO-cl2H210lo Sucrose mono-fatty acid
esters
- 12 -
4771~
Effective dispersing agents are found in the cationic,
anionic and non-ionic compound classes. Among the preferred
dispersing agents are long chain amines, amine salts of long
chain acids, alkyl polyethylene glycols, alkylphenyl poly-
ethylene glycols, polyhydroxyalkyl monoesters of fatty acids
and the like. The following may be m~ntioned as illustrative
examples: sorbitan monooleate, sorbitol monooleate, lauryl
polyethylene glycol, p-dodecylphenyl polyethylene glycol,
octadecylamine salts, diethanolamine salt of myristic acid and
the like. Particularly effective as wetting agents were the
polyhydroxyalkyl monoesters of fatty acids such as sorbitan
monooleate (Span. 80).
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 VIIIof the Periodic
Table, the preferred metal comprising palladium although it is
comtemplated within the scope of this invention that the
other noble metals such as platinum, rhodium, ruthenium,
osmium and iridium may also be used, although not necessarily
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 alumi-
na. A particularly effective support comprises charcoal.
Very small quantities of catalysts are required to
- 13 -
`7~
effect the reductive cyclization of this invention. Amounts of noble metal
catalyst as low as about 0.001 to 0.0015 mol/mol of the o-nitroazobenzene to be
reduced are eEfective.
~ lore catalyst can be used, but using amounts over 0.005 mol/mol of the
o-nitroazobenzene is generally neither needed nor economically attractive.
me noble metal catalysts of this invention can be generally used
interchangeably with one another in the instant 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 a
palladium catalyst results in the reductive cyclization to the 2-aryl-2H-benzo-
triazole, but the chlorine atom is also concomitantly cleaved off. However, sub-
stitution of palladium by rhodium, the latter which appears to be a milder, more
selective catalyst, results in the preparation of the 2-aryl-2H-benzotriaZOle
still containing the chlorine atom. According by when the preparation of a
2-aryl-2H-benzotriazole containing chlorine on either or both aromatic rings is
inv~lved, a rhodium catalyst should be used and the use of a palladium catalyst
should be avoided. A preferred catalyst for the reductive cyclization of a
2-nitroazobenzene intermediate substituted with chlorine to the corresponding
chlorine substituted 2-aryl-2H-benzotriazole is rhodium composited on charcoal.
- 14 -
As hereinbefore stated, the reduction is effected at
reducing conditions including a temperature within the range
of from about 20C to about 100C, a pressure ranging from
about 1 to about 66 atmospheres and with sufficient aqueous
alkaline solution to convert the hydroxy-substituted o-nitro-
azobenzenes into their corresponding water-soluble or water-
dispersed alkaline phenolate salts. The water-soluble alkaline
phenolate salts are prepared by adding the appropriate hydroxy-
substituted o-nitroazobenzene to an aqueous alkaline solution
of sodium hydroxide, potassium hydroxide, lithium hydroxide,
sodium carbonate, potassium carbonate, ammonia, barium-
hydroxide, calciumhydroxide or the like. The preferred alkali-
ne solution comprises from about 5 to about 15 % by weight
sodium hydroxide in water. When using this aqueous alkaline
solution, it is possible at the end of the reduction and cyc-
lizationreaction to remove the catalyst by filtration for
further recycling of desired while leaving the desired 2-aryl-
2-H-benzotriazole product in aqueous solution as its alkaline
salt in the case of the water-soluble salts.
In the case of the water-dispersed alkaline phenolate
salts, it is necessary to have an appropriate dispersing agent
also present in the system. In these cases the recovery of
the catalyst requires precipitation of the curde
- 15 -
71!~
2-aryl-2H-benzotriazole product, separation by filtration of
the curde product contaminated by the noble metal catalyst,
dissolving the crude product in an organic solvent such as
toluene, xylene, petroleum mineral spirits, cyclohexane,
hexane, chlorobenzene, ethylene dichloride and the like, and
isolation of the noble metal catalyst by filtration. The crude
product now in organic solution is extracted with warm mineral
acid such as 70% sulfuric acid and then recrystallized by
conventional procedures.
Isolation of a product in good yield and acceptable
purity is another feature of this invention. The aqueous alkali
solution of the desired hydroxy-substituted 2-aryl-2H-benzo-
triazole salt, preferably the sodium salt, is acidified with
aqueous mineral acid, preferably sulfuric acid or hydrochloric
acid, to a pH of lO or 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 curde product
may be further purified by one of several procedures to give
purified products of high purity in yields in the range of 70
to 80~. A variety of trace by-products are formed during the
reduction of o-nitroazobenzens. These include the correspon-
ding o-aminoazobenzenes, o-aminohydrazobenzenes,o-phenylene-
diamine, anilines, aminophenols and l,2,3-benzotriazoles. Most
of these by-product impurities are removed by an acid-
preferably sulfuric acid, wash followed by an alcohol, prefer-
ably isopropanol, wash and finally a water wash of the crude
- 16 -
.~;
~47~
2H-benzotriazole produc~. Al-ternatively, the crude produc~ may
be dissolved in an organic solvent, such as toluene, and the
impurities extractd by an aqueous acid solution, and the pro-
duct isolated then from organic solution by conventional pro-
cedures.
The process of this invention may be effected in any
suitable manner and may comprise either a batch or continuous
type of operation. For example, when a batch-type operation
is used, a quantity of the hydroxy-substituted o-nitroazo-
benzene, water, sufficient alkali, such as sodium hydroxide,
to prepare the water-soluble or water-dispersed alkaline
phenolate salt along with the catalyst such as palladium
composited on charcoal and dispersing agent if needed 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 autoclave and the contents thereof
are then heated, if needed, to the desired reaction tempera-
ture and maintained thereat with agitation until slightly more
than the theoretical amount of hydrogen is adsorbed and the
reduction reaction is complete. At the end of this time the
excess pressure is vented, the aqueous alkaline solution,
usually warm, is subjected in the case of the water-soluble
alkaline phenolate salts to filtration, preferably under an
inerte atmosphere such as nitrogen or argon, to remove the
catalyst. The solution is then brought to room temperature
and acidified with mineral acid solution to precipitate the
- 17 -
~ `~
r~ 7~
desired hydroxy-substituted 2-aryl~2H-benzotriazole crude
product, which ~ay be optionally further purified by treatment
with aqueous acid and recrystallization from an organic
solvent.
In the case of ~he water,dispersed alkaline phenolate
salts, the mixture is just brou~ht to room temperature and
acidified with mineral acid solution. The insoluble hydroxy-
substituted 2-aryl-2H-benzotriazole crude product containing
therein the noble metal catalyst residue is then dissolved in
a solvent, such as toluene. The solution of the crude product
is then filtered to remove the catalyst residue and the
crude product is further purified as described above.
It is also contemplated within the scope of this
invention that the preparation of the 2-aryl-2H-benzotriazoles
by the reduction and cyclization o o-nitroazobenzenes may
also be effected in a continuous manner, although not neces-
sarily with equivalent results. For example, when a continous
type operation is used, the hydroxy-substituted o-nitroazo-
benzene starting material is premixed with, and dissolved or
dispersed in an aqueous alkaline solution, said solution or
dispersion fed continuously to a reaction zone which is main-
tained at the proper operating conditions of temperature and
pressure and which contains the hydrogenation catalyst.
Hydrogen is pressurized into the reaction zone by a separate
means. After desired residence time, the reactor effluent is
- 18 -
77~3
continuously dischared and the effluent Solution is acidified
to isolate the desired product. Due to the nature of the
catalyst employed, a particularly effective continuous type
of operation comprises a fixed bed of catalyst subjected to
either an upward of downward flow of the reaction solution.
If it is desirable to carry out the reduction as a two-step
process with a different operating temperature for each step,
two reaction zones in series each operating at the preferred
temperature range or the specific reduction step involved
may be used.
The re~duction of o-nitroazobenzenes to the correspon-
ding 2-aryl-2H-benzotriazoles is a two-step process as out-
lined below.
-- 19 --
C)H
R~ 0\ 1 5 _ep 1 ~_
R2 --`N2 \/\ R4
~ , /
OH
~f ~ N~ R4
2 ~ N / ~--~
.
`. . .'
Stf~p 2
0
R~ N~
X3
- 20 ~
,
~ 7~
Step 1 - The reduc~ioll o the o-nitroazobenzene to the
N-o~ybenzotriclzole derivative proceeds rapidly and exoth~r-
mically even at low temperatuxe under the process conditions
o~ this invent.ion.
Step ~ - Th~ reduction o the N oxybenæo~riazole in~.ermediate
to the corresponding 2-aryl-~H-benzotriazole product goes
more slowly. This reduction can be ~reatly expedited by
adding more cata7yst, raising the temperature, increasing
the hydrogen pressure or by combination of these fac~.ors.
Genexally, the reaction ceases when the N-oxy in
termediate is completely reduced to the corresponding 2-aryl-
2H-benzotriazole making for facile control of this cata1.ytic
hy~rogenation process~ H~ever, with some hi~hly substituted
benzotriazoles, reduction should be stopped when ~he appropri~
ate amount of hydrogen has been absorbed and reacted to prevent
further reductive cleavage of the desired 2-aryl-2H-benzotria--
zoles prepared. In some cases with Raney nic~el at room
temperature, reduction pxoceeds beyond the desired benzotria-
zol~ product to the correspondin~ 4,~,6,7~tetrailydrobenzotr.ia-
zole compounds as undesired by produc's.
Specifically, the instant invention pro~rides an
improved process for production of compounds having the
~ormula I
- 21 -
7~
O~I ~S
N ~ ~ ~R4
R3
~herein
Rl lS hydrogen or chloriIIe~
R~ ;s hydrogen, chlorine, lower alk~yl of 1 to 4
carbon atoms, 10~7er alkoxy of 1 to ~ carbon aiams, carbo-
alkoxy o~ 2 to 9 car~on atoms, carboxy or -S03H,
~ 3 ig alkyl of 1 to 12 carbon atoms, ~l};oxy of 1
to 4 carbon atoms, phenyl, phenyl subst~tuted wlth alkyl
gxoups, said alkyl groups having 1 to 8 carbon atoms, cyclo-
al~yl of 5 to 6 carbon atoms, carboalkoxy o~ 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
~toms, lower alkoxy of 1 to 4 carbon atoms, chlorine or
hydroxyl, and
3~5 is hyclrogen, alkyl of 1 to 12 carbon atoms,
chlorine, cyc loalkyl o 5 to ~ carbon atoms or arylalkyl of
7 to ~ carbon a~oms.
- 22 -
4~
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 or 2 to 9 carbon atoms such as carbo-
methoxy, carboethoxy, or carbo-n-octoxy.
R3 can be alkyl of 1 to 12 carbon atoms such as methyl,
ethyl, sec-butyl, tert-butyl, amyl, tert-octyl or n-dodecyl.
R3 can also be alkoxy of 1 to 4 carbon atoms such as methoxy,
ethoxy or n-butoxy. R3 is also phenyl substituted with alkyl
groups, said alkyl groups having 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 carboalkoxy or 2 to 9 carbon atoms such
as carbomethoxy, carboethoxy, carbo-n-butoxy or carbo-n-
octoxy. R3 is also arylalkyl or 7 to 9 carbon atoms such as
benzyl, ~-methylbenzyl or ~ dimethylbenzyl.
R4 can be lower alkyl of 1 to 4 carbon atoms such as
methyl, ethyl or n-butyl.
R4 can also be lower alkoxy of 1 to 4 carbon atoms
such as methoxy, ethoxy or n-butyloxy.
R5 can be lower alkyl or 1 to 8 carbon atoms such as
methyl, sec-butyl, tert-butyl, tert-amyl or tert-octyl.
~ 23 -
~S~7~3
R5 can also be cycloalkyl of 5 to 6 carbon atoms such
as cyclopentyl or cyclohexyl. R5 is also arylalkyl of 7 to 9
carbon atoms such as benzyl, a~methylbenzyl or ~,a-dimethyl-
benzyl.
Preferably Rl is hydrogen.
Preferably R2 is hydrogen, chlorine, lower alkyl of
1 to 2 carbon atoms, methoxy or carboxy.
Preferably R3 is alkyl of 1 to 8 carbon atoms,
cyclohexyl, phenyl, chlorine, a-methylbenzyl or carboxyethyl.
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.
~ ost preferably R4 is hydrogen.
Most preferably R5 is hydrogen, chlorine, methyl,
sec-butyl, tert-butyl, tert~amyl, tert-octyl or ~-methyl-
benzyl.
- 24 ~
.
t
~ ~ i
~. :
L7~13
The process involved the reduction of an o-nitroazo-
benzene intermediate of the formula II
R2 N2 ~ R~ (II)
wherein Rl~ R2, R3, R4 und R5 are as described previously.
The s~arting o-nitroazobenzene intermediates are
prepared by coupling the appropriate o-nitrobenzenediazonium
compounds of formula III
1 ~ =N ~ ~
I O ¦ (III)
R~No2
wherein Rl and R2 are as described previously and X is chlo-
ride, sulfate, or other anionic species, but preferably
chloride, with phenols of formula IV
~R5 (V)
which couple in the ortho position tothe hydroxy group.
- 25 -
,
~5~7~3
The o-nitrobenzenediazonium compounds are in turn
prepared by standard diazotization procedures using sodium
nitrite in acid solution with the corresponding o-nitro-
anilines of formula V
R~NH2 (V)
R2 N02
For illustration purposes some specific examples of
compounds of formulas IV and V are listed. These items are
generally available as i~ems of commerce.
ompounds of formula IV
p-cresol
2,4-di-tert-butylphenol
2,4-di-tert-amylphenol
2,4-di-tert-octylphenol
2-tert-butyl-4-methylphenol
4-cyclohexylphenol
4-tert-butylphenol
4-tert-amylphenol
4-tert-octylphenol
2,4-dimethylphenol
3,4-dimethylphenol
4-chlorophenol
2,4-dichlorophenol
- 26 -
71~
3/4-dichlorophen
4-phenylphenol
4-phenoxyphenol
4-o-tolylphenol
4-(3'-tert-octyl)-phenylphenol
ethyl 4-hydroxybenzoate
n-octyl 4-hydroxybenzoate
4-methoxyphenol
4-n-octylphenol
4-n-dodecylphenol
resorcinol
4-(~-methylbenzyl)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-carboxyethylphenol
Preferably compounds of formula IV useful in this
nvention are
p-cresol
2,4-di-tert-butylphenol
2,4-di-tert-amylphenol
2,4-di-tert-octylphenol
- 27 -
7~8
2-tert-butyl-4-methylphenol
4-tert-octylphenol
4-n-octylphenol
4-n-dodecylphenol
resorcinol
2-sec-butyl-4-tert-butylphenol
2-(~-methylbenzyl)-4-methylphenol
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
- 28 -
. :
: .. .
- :
.
,
7'~
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, carboal-
koxy of 2 to 9 carbon atoms; R3 is phenyl, phenyl substituted
with alkyl groups said alkyl groups have 1 to 8 carbon atoms,
carboalkoxy of 7 to 9 carbon atoms, aralkyl 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, cycloalkyl of
5 to 6 carbon atoms or arylalkyl of 7 to 9 carbon atoms
generally exhibit poor solubility in aqueous alkaline solu-
tion. With such intermediates the use of the dispersing or
wetting agents described previously is generally necessary
in the process of this invention.
The 2-aryl-2H-benzotriazoles have found wide use as
dyestuff intermediates, optical brightner blue fluorescent
agents and selective ultraviolet light absorbing stabilizers
affording valuable protection for fibers, films and a variety
of polymeric structures subject to deterioration by ultra-
violet radiation. These materials have become important items
of commerce.
The 2-aryl-2H-benzotriazoles are complex organic
molecules which require careful synthetic procedures for
their production in good yield and acceptable purity.
- 29 -
9L~5i~7713
The present invention i5 concerned with an improved
process to prepare ultraviolet stabilizers which are substi-
tuted 2-aryl-2H-benzotriazoles. These are distinguished by
a very slight absorption invisible light and very high fast-
ness to light in various subs-trates. 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 benzotriazole 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 benzotrialzole nucleus.
The description, preparation and uses of these
valuable substituted 2-aryl-2~-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 examples 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 what-
soever.
- 30 -
~1S~177~
Example 1
2-(2-Hydroxy-5-methylphenyl)-2H-benzotriazole
rrO a l-liter, lcw pressure, stirred hydrogenation reactor were charged
under nitrogen with low speed stirring at roam temperature 85 grams of 2-nitro-
2'-hydroxy-5'-methylazo~enzene (containing 45% water) dissolved in 37.2 grams of
50% sodium hydroxide solution and 200 grams of water and 1.4 grams of 5% palla-
dium on charccal hydrogenation catalyst slurried in 18 grams of water. The
amount of catalyst is 3% based on the azobenzene intermediate. The reactor was
flushed several times with hydrogen and then pressurized to 5.7 atmospheres with
hydrogen. m e reactor was then heated to 38-40 & and the contents stirred
vigorously. Reaction began occurring readily in the very exothermic first reduc-
tion step of the azobenzene to the N-oxybenzotriazole intermediate. me tempera-
ture gradually increased to the range of 56-58&, and it was maintained at 58-
60 C throughout the remainder of the reaction. The takeup of hydrogen was
monitored throughout the reaction until no more hydrogen was absorbed. m e
hydrogen pressure was maintained on the reactor throughout the reaction in the
5.3-4.7 atmosphere range. Slightly more than the theoretical amDunt of hydrogen
was taken up, but when the reduction of the azobenzene intermediate to the de-
sired 2-aryl-ZH-benzotriazole was ccmplete, further hydrogen absorption ceased.
'me time of the reduction reaction was 2.5 hours.
- 31 -
~-rl
, ~,
~4771~3
The hydrogen remaining in the reactor was then vented, and
a nitrogen atmosphere was reimposed on the reactor contents.
The reactor contents were then filtered under nitrogen
to remove the palladium on charcoal catalyst dispersed there-
in. The recovered catalyst was washed on the filter with a
solution of 4 gra~s of 50~ sodium hydroxide solution and
16 grams of water. This catalyst was then suitable for reuse
in another hydrogenation reaction after further washing.
The combined highly alkaline filtrates containing the
desired product were then cooled to 50C under nitrogen and
25 grams of 70~ sulfuric acid solution was added slowly to
bring the pH of the system to a value of less than 10. The
slurry of a yellow precipitate which forms was held at
65-70C for 15 minutes. The yellow precipitate was then iso-
lated by filtration and successively washed with water at a
temperature of 65-70C, with water at room temperature, with
isopropanol and finally again with water. A yellow crude
product was thus isolated in a yield after drying of 34.4
grams (84% of theory).
The crude product could be further purified by washing
a toluene solution of the crude product with warm sulfuric
acid solution followed by recrystallization from toluene and
isopropanol to give 31.5 grams (77~ theory) of pure material.
.
'78
Example 2
2-(2-Hydroxy-5-methylphenyl)-2H-benzo-triazole
When the materials described in Example 1 are reacted
by exactly the same procedure therein except that the reactor
was pressured to 1 atmosphere of hydrogen rather than 5.7
atmospheres of hydrogen, the yield of the product, 2-(2-
hydroxy-5-methyl-phenyl)-2H-benzotriazole, was comparable to
that reported in Example 1, but the reduction required 5
hours rather than 2.5 hours.
Example 3
2-(2-Hydroxy-5-methylphenyl)-2H-benzotriazole
When using the procedure of Example l,the 5~palladium
on charcoal was replaced by an equivalent amount of 5%
platinum on charcoal, and the reactor pressurized with hydro-
gen to a pressure of 3.3-2 atmospheres throughout the
reaction, the yield of desired product was 40~, with a reduc-
tion reaction time of 6 hours.
All of the azobenzene intermediate was consumed in
this reduction, but the yield of desired product was with
platinum only half of that obtained with the preferred noble
metal catalyst palladium.
~4~7~3
Example 4
2-(2-H~droxy-5-methylphenyl)-2H-benzotriaæole
When using the procedure of Example 1,the 5%palladium
on charcoal was replaced by an equivalent amount of 5%
rhodium on charcoal, the yield of the desired product was
46% of theory with a reduction time of 5.7 hours with the
reactor pressurized with hydrogen to a pressure of 3.3-2-
atmospheres throughout the reaction and with a reaction tem-
perature in the range of 50-80C.
All bf the azobenzene intermediate was consumed in
this reduction, but the yield of the desired product was
considerably less with rhodium -than with the preferred cata-
lyst palladium. Rhodium appeared to fall between palladium
and platinum in effecti~eness, but somewhat closer to plati-
num with this specific product.
Example 5
2-(2-Hydroxy-3,5-di-tert-amylphenyl)-2H-benzotriazole
When using the procedure of Example 1 an e~uivalent
amount of 2-nitro-2'-hydroxy-3',5'-di-tert-amylazobenzene was
substituted for 2-nitro-2'-hydroxy-5'-methylazobenzene, 4
weight % of 5% palladium on charcoal catalyst based on the
azobenzene intermediate was added in two portions and 0.5% by
weight of the wetting agent sorbitan monooleate ISpan 80) was
- 34 -
~ 5~77~3
added to facilïtate dispersion and wetting of the insoluble
azobenzene intermediate, the above noted product was obtained
in a yield of 31.7%.
Example 6
2-(2-H~droxy~5-tert-octylphenyl)-2H-benzotriazole
When using the procedure of Example 1 an equivalent
amount of 2-nitro-2'-hydroxy-5'-tert-octylazobenzene is
substituted for 2-nitro-2'-hydroxy-5'-methylazobenzene, the
above noted product is obtained.
Example 7
5-Chloro-2-(2-hydroxy-3,5-di-tert-butylphenyl)-2H-
benzotriazole
When in Example 1, the 2-nitro-2'-hydroxy-5'-methyllazo-
benzene is replaced by an equivalent amount 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 in t:he presence of
0.5% dispersing agent sorbitan monooleate, 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-butylphenyl)-2H-benzotriazole.
- 35 -
~5~7~3
Example 8
5~Chloro-2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-2H-
benzotriazole
When in Example 1, the 2-nitro-2'-hydroxy-5'-methyl-
azobenzene is replaced by an equivalent amount of 2-nltro-5-
chloro-2'-hydroxy-3'-tert-butyl-5-methylazobenzene and the 5%
palladium on charcoal catalyst is replaced by a lik~ amount
of 5~ rhodium on charcoal catalyst, the above noted product
is obtained when the reaction is carried out in the presence
of 0.5~ dispersing agent sorbitan monooleate.
- 36 -
