Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~5~
The present invention relatefi to the making of benzidine pigments.
Among the objects of the present invention is the provision of a novel
process for inexpensively making benzidine pigments.
According to the present invention benzidine pigments are prepared from
azoxybenzenes having the formula:
xl x2
in which X , X , Y and Y are selected from the class consisting of hydrogen,
chlorine, methyl, methoxy, ethoxy, sulfo and carboxyl.
The azoxybenzene is essentially completely reduced to the corresponding hydra-
zobenzene by technical NaHS in aqueous solution at a pH between about 8 and about
10, and at a temperature of 50 to 100 C, the solution is then cooled to precipi-
tate out the hydrazobenzene, the precipitated hydrazobenzene is filtered off,
washed, and in the resulting crude condition subjected to benzidine rearrangement,
diazotization and coupling.
It is preferred to carry out the reduction in an aqueous solution that
contains water-miscible organic solvent that increases the solubility of the
azoxybenzene in the hot reducing solution, but is essentially inert to the re-
actants. Examples of such organic solvents include lower alcohols having 1 to 4
carbon atoms, ethyleneglycol partially etherified so it has an ether group con-
taining 1 to 4 carbons, dimethyl sulfoxide, dimethyl formamide and morpholine.
'Lhe crude hydrazobenzene is recovered from the reducing treatment in
very good yields ranging from about 72 to about 88%, and is sufficiently pure
that it can be directly converted to -the final dye without further purification
~ ~5~
of the hydrazobenzene or the dichlorobenzidine. The process of the present in-
vention is accordingly well suited for commercial use to reduce the cost of manu-
facturing the benzidine dyes.
A feature of the present invention is that it is not even necessary to
use a pure or even a carefully prepared NaHS reactant. The technical material
available on the market does an admirable job of effecting the desired reduction
and does so even if it contains large quantities of impurities such as sodium
thiosulfate, an ingredient sometimes found in substantial quantities in technical
NaHS.
On the other hand the presence of sodium thiosulfate or any of the
other impurities normally found in technical NaHS is not needed for the purpose
of the invention, and all types of technical grades of NaHS give substantially
the same results. An excess of NaHS reagent should be used and the reaction mix-
ture preferably tested to ascertain that essentially noné of the unreduced ma-
terial is present therein, before terminating the reducing step. One convenient
way for making such a test on the reaction mixture is to ascertain the absence
of starting azoxy derivative by thin layer chromatographic separation of the
mixture under reduction.
The crude hydrazobenzene is transformed into the desired product by
first subjecting it to benzidine rearrangement as by means of a mineral acid such
as aqueous HCl of 25 to 33% strength, preferably 30%, or H2SO4 of for example
about 45% strength. More specific descriptions of such benzidine rearrangement
are in "Methoden der organischen Chemie" (Houben-Weyl), 4th edition (1957), Georg
Thieme Verlag, Stuttgart, Vol. XI/l, pages 839 to 848; and "Unit Processes in
Organic Synthesis" by Ph. Groggins, 5th edition, McGraw-Hill Company, Inc., New
York.
The dichlorobenzidine derivatives formed can be diazotized without the
intermediate isolation and purlfication and the coupling of the resulting tetrazo
--2--
~)5~3Z'~'~
compounds is carried out in usual and known manner. See in this connection
"Farbenchemie" by H.E. Fierz-David and L. slangley, 5th edition (1943), Springer
Verlag Wien, pages 230 to 250, particularly pages 249/250 (diazotizing), and
pages 250 to 281, particularly pages 270 to 281 (coupling).
As coupling components there can be used those of the acetoacetanilide,
pyrazolone and 2,3-hydroxynaphthoic arylamide series usually applied in the manu-
facture of benzidine dyes, such as, for instance, acetoacetylamino-benzene,
acetoacetylamino-2-methylbenzene, acetoacetylamino-2,4-dimethylbenzene,
acetylamino-4-methyibenzene, acetoacetylamino-4-chloro-2-methylbenzene, acetoace-
tylamino-2-methoxybenzene, acetoacetylamino-2, 4-dimethoxybenzene, acetoacety-
lamino-2,5-dimethoxybenzene, acetoacetylamino-2,5-dimethoxy-4-chlorobenzene,
acetoacetylamino-2-chlorobenzene, 1-phenyl-3-methyl-5-pyrazolone, 1-(4'-methyl)-
phenyl-3-methyl-5-pyrazolone, 1-chlorophenyl-3-methyl-5-pyrazolone, l-methoxy-
phenyl-3-methyl-5-pyrazolone, 1-phenyl-3-carbethoxy-5-pyrazolone, 2,3-hydroxyna-
phthoic anilide and 2,3-hydroxynaphthoic 0-anisidide.
The benzidine pigments are obtained according to the process of the
present invention in a yield of about 86 to 90 per cent of the theory, referred
to the corresponding hydrazobenzene intermediate.
The following examples serve to illustrate the inven-tion but are not
intended to limit it thereto, the designated parts being by weight unless other-
wise noted.
Example 1
85 Parts of an aqueous solution of technical grade sodium hydrosulfide
(containing 35 percent NailS and 12 percent Na2S203) were slowly added over 90
minutes to a mixutre of 53.4 parts of 2,2'-dichloroazoxybenzene in 133.5 parts
of methanol at room temperature~ Subsequently, the reaction mixture was refluxed
at 70C to 75C for a period of 2.1/2 hours. The pH of the reaction mixture was
found to be between the values of 9 and 9.4. during this period. After this
period a test showed the absence of the starting material, and the reaction
--3--
~ ~5~
mixture was cooled down to 0C to 5C to precipitate the hydrazobenzene, which
was then filtered off and washed with water until alkali-free. After drying be-
low 70C, 40.3 parts of 2,2'-dichlorohydrazobenzene of a melting point of 85C to
87C, were obtained, this representing a yield of 80 percent of the theory.
The same result is achieved if isopropanol is used instead of methanol.
Also if there is used an aqueous solution of technical sodium hydro-
sulfide essentially free of sodium thiosulfate, and the sodium hydrosulfide is in
the proportion of about 2.0 to 3.0 moles per mole 2,2'-dichloroazoxybenæene, and
it is reacted as described above in this Example, practically the same result is
achieved as to the yield and purity of the 2,2~-dichlorohydrazobenzene.
40 Parts of 2,2'-dichlorohydrazobenzene obtained as in Example 1 were
added to 400 parts of hydrochloric acid of 30 percent strength at a temperature
of 0C to 5C in 4 hours and then stirred at room temperature overnight. The
temperature of the solutlon was then raised to 50C in 5 hours, and the solution
stirred for another 30 minutes at this temperature. Rearrangement to 3,3'-di-
chlorobenzidine was then complete, as shown by the absence of 2,2'-dichlorohydra-
zobenzene in the thin layer chromatographic separation of the reaction mixture.
The reaction mixture was accordingly cooled down by dilution with 2000
parts of,ice water to 0C to 5C and diazotized with 20.5 parts of sodium nitrite.
After 4 parts of charcoal had been added to the diazo liquid so prepared, the
solution was clarified.
Separately a solution of 52,5 parts of acetoacetylaminobenzene in 230
parts of water and 36 parts of sodium hydroxide was charged with 56 parts of
acetic acid and thereby adjusted to pH 5 to 6. The solution was cooled to 0 C
to 5 C and charged with the aforesaid clarified diazo liquid while neutralizing
the solution with aqueous sodium acetate solution. Coupling was affected at pH
4 to 5. After completion of the reaction the resulting precipitation was fil-
tered, washed with water and dried below 70C. 88.5 Parts of Pigment Yellow
~:)5~2~
12 (C.I. 21090) representing a yield of 89 percent of the theory, referred to
the hydrazobenzene compound, were obtained as a greenish yellow powder with ex-
cellent application properties.
Example 2
80.4 Parts of an aqueous solution of technical sodium hydrosulfide con-
taining 35 percent NaHS and 8 percent Na2S203, were added to a mixture comprising
53.4 parts of 2,2'-dichloroazoxybenzene in 130 parts oE ethanol at room tempera-
ture. Subsequently, the reaction mixture was brought to 65 C within 1 hour and
further refluxed at 75 C to 78C for further 3 hours. During the heating the
pH was kept in the range 9 to 9.4. The reaction mixture was then cooled down to
0 C to 5C and the hydrazobenzene derivative filtered off and washed with water
until alkali-free. After drying below 70C, 37.3 parts of 2,2'-dichlorphydrazo-
benzene of melting point of 86 C were obtained, this representing a yield of 74
percent of the theory.
Practically the same yield and purity of 2,2'-dichlorohydrazobenzene is
obtained when the technical NaHS is free of thiosulfate.
50.6 Parts of 2,2'-dichlorohydrazobenzene thus obtained were added to
190 parts of hydrochloric acid of 30 percent strength at a temperature of 0C to
5 C in 4 hours. The reaction mixture was kept at this temperature for another 4
hours and then stirred at room temperature overnight. Subsequently, the tempera-
ture of the solution was raised to 50 C in 5 hours and stirred for another 30
minutes at this temperature. The foregoing test showed that the re-arrangement
to 3,3'-dichlorobenzidine was completed. The reaction mixture was then cooled
down with 3000 parts of ice water to 0 C to 5 C and diazotised with 26.2 parts of
sodium nitrite. After the addition of 2 parts of charcoal to the diazo liquid
so obtained, the solution was clarified b~ filtration.
In the meantime, a solution of 70.1 parts of acetoacet-0-toluidide in
700 parts of water and 25 parts of solium hydroxide was charged with 40 parts of
--5--
2~2
acetic acid. The pH was then adjusted to 5 to 6 with a solution oE 160 parts of
sodium hydroxide and 370 parts of glacial acetic acid in 500 parts of water. The
final solution was cooled to 0c to 5C and charged to the aforesaid clarified
diazo liquid. The pH-value during the resulting coupling was maintained at 4 to
5 by means of sodium acetate. After completion of the coupling, the reaction
mixture was boiled for 1 to 1-1/2 hours, thereafter filtered, washed with water
and finally dried below 70 C. 115.6 Parts o~ Pigment Yellow 14 (C.I. 21095) was
obtained as a yellow powder with excellent application properties, this repre-
senting a yield of 88 percent of the theory, referred to the hydrazobenzene com-
pound.
In place of acetoacet-o-toluidide used in the above example, if one
uses acetoacet-p-toluidide, one obtains Pigment Yellow 55 (C.I. 21096) in 86% of
theory yield.
Example 3
50.6 Parts of 2,2'-dichlorohydrazobenzene obtained according to
Example 1 were added to 200 parts of hydrochloric acid of 30 percent strength at
a temperature of 0 C to 5 C in 4 hours. The rearrangement to 3,3'-dichloroben-
zidine was completed by stirring the solution at room temperature overnight and
for 5 hours at 50 C. The reaction mixture was then cooled down with ice water
to 0 C to 5C and diazotized with 26.5 parts of sodium nitrite. After the addi-
tion of 2 parts of charcoal the diazo liquid was clarified.
A coupling solution of 78 parts of acetoacet-o-chloroanilide in 250
parts of water and 24 parts of caustic soda was charged with 37 parts of acetic
acid and the pH adjusted to 5 to 6 by adding an a~ueous solution of sodium acetate.
The reaction mixture was cooled to 0 C to 5 C and charged to the aforesaid clari-
fied diazo liquid. During the coupling a pH-value of 4 to 5 was maintained.
After completion of the coupling the liquid was boiled for 1 hour, the formed
;~?S~
pigment iltered, washed with water and dried below 70C. There were obtained
124.5 parts of high quality Pigment Yellow 63 (C.I. 21091) as a yellow powder,
this representing a yield of 89 percent of the theory, referred to the hydrazo-
benzene compound.
Similarly by using, in place of acetoacet-o-chloranilide used above,
equivalent amount of acetoacet-o-anisidide, or acetoacetylamino-4-chloro-2,5-
dimethoxybenzene, one obtains Pigment Yellow 17 (C.I. 21105), or Pigment Yellow
83 respectively. One can also employ equivalent amounts of acetoacetylamino-2,
5-dimethoxybenzene in place of acetoacet-o-chloroanilide used above to get a
reproducible grade of Yellow Pigment in very good yields.
_ample 4
50.6 Parts of the crude 2,2'-dichlorohydraæobenzene of Example l were
rearranged to 3,3'-dichlorobenzidine and then diazotized according to Example 1,
2000 parts of a clarified diazo liquid being obtained. Simultaneously, a coupl-
ing solution of 67.8 parts of 1-phenyl-3-methyl-5-pyrazolone were dissolved in
250 parts of water and 16.5 parts of sodium hydroxide. The coupling solution was
cooled to 0C to SC and then charged to the aforesaid clarified diazo liquid.
After completion of the coupling the pigment was filtered, washed with water and
finally dried below 70 C. 108.4 Parts of Pigment Orange 13 (C.I. 21110) equal
to 87 percent of the theory, referred to the hydrazobenzene compound, were ob-
tained as a reddish powder. The pigment had excellent application properties,
the same as the pigment obtained by using commercially available 3,3'-dichloro-
benzidine as starting material.
By using equivalent amounts of l-phenyl-3-carbethoxy-5-pyrazolone in
place of l-phenyl-3-methyl-5-pyrazolone coupled to the crude hydrazobenzene in
the above example, one obt~ins Pigment Red 38 (C.I. 21120) in 89% yield and higl
purity.
1~)5~Z2;2
Example 5
50.6 Parts of the crude 2,2'-dichlorohydrazobenzene of Example 1, were
rearranged to 3,3'-dichlorobenzidine and then diazotized as described in Example
1; 2000 parts of a clarified diazo liquid being obtained.
At the same time, 72.7 parts of 1-p-tolyl-3-methyl-5-pyrazolone was
dissolved in 300 parts of water and 20 parts of caustic soda. 5 Parts activated
carbon were added and the solution clarified by filtration. 32 Parts of glacial
acetic acid were next added to the solution, and the resulting liquid charged to
the aforesaid diaæo liquid maintaining a temperature between 5C to 10C. The pH-
value at the end of the coupling should be acid to congo red.
After completion of the coupling the reaction mixture was boiled for1 hour, and the formed pigment filtered and washed neutral with water. After
drying at below 70 C, 114.5 parts of Pigment Orange 34 (C.I. 21115) were obtained,
this representing a yield of 88 percent of the theory, referred to the hydrazo-
benzene compound.
Example 6
90 Parts of an aqueous solution of technical sodium hydrosulfide con-
taining 35 percent NaHS and 4 percent Na2S2O3 were added to a mixture comprising
51.6 parts of 2,2'-dimethoxyazoxybenzene in 155 parts methanol at room tempera-
ture within 5 hours. Subsequently, the reaction mixture was refluxed at 70 C to75 C for 2-1/2 hours while the pH was maintained between 8.5 and 9.4. After this
period the absence of the starting material was confirmed and the reaction mix-
ture was cooled down to 0 C to 5C, the reduced product that precipitated fil-
tered off and washed with water until alkali-free. After drying below 70 C, 35
parts of 2,2'-dimethoxyhydrazobenzene of a melting point of 100 C to 102C were
obtained, this representing a commercially acceptible grade in a yield of 72 per-
cent of theory.
Prac~ically the same results were achieved if there is used a correspond-
ing camount of ethylene glycol instead of methanol.
If the sodium hydrosulfide solution contains no sodium thiosulfate, and
the amount of sodium hydrosulfide applied is 3.0 moles per mole 2,2'-dimethoxy-
azoxybenzene, the reaction carried out otherwise as described in this Example pro-
duces practically the same yield and purity of the 2,2'-dimethoxyhydrazobenzene.
While as shown above it may be desi-rable to effect the NaHS reductions
over very limited pH ranges that could be somewhat different for different azoxy-
benzenes, these reductions can take place at any pH within the range of from
about 8 to about lO without materially effecting the results.
50 Parts of crude 2,2'-dimethoxyhydrazobenzene thus obtained were added
to 400 parts of hydrochloric acid of 30 percent strength and rearranged to 3,3'-
dimethoxybenzidine by stirring 18 hours at room temperature and 5 hours at 50 C.
The reaction mixture was cooled down with lO00 parts of ice water and diazotiæed
with 25.8 parts of sodium nitrite. After the addition of 2 parts of charcoal the
diazo liquid was clarified.
Simultaneously, a coupling solution comprising 69.0 parts of l-phenyl-
3-methyl-5-pyrazolone, 48 parts of caustic soda and 250 parts of water was pre-
pared, and this solution run into the aforesaid diazo liquid. After completion
of the coupling, the reaction mixture was boiled for 1 hour, the pigment filtered
and washed neutral with water. After drying below 70 C, 109.5 parts equal to 87
percent of the theory of good quality Pigment Red 41 (C.I. 21200), referred to
the hydrazobenzene compound, were obtained as a reddish powder.
By using equivalent amounts of l-p-toly-3-methyl-5-pyrazolone, or l-
phenyl-3-carbethoxy-5-pyrazolone in place of l-phenyl-3-methyl-5-pyrazolone used
in the above Example, one obtains Pigment Red 37 or Pigment Red 42 respectively
in excellent yields and grades.
1~5~ Z
Examl)le 7
85 Parts of an aqueous solution of technical sodium hydrosulfide contain-
ing 35 percent NaHS and 6.5 percent Na2S203 were added to a mixture comprising
67;2 parts of 292',5,5'-tetrachloroazoxybenzene in 226 parts of methanol at roomtemperature. Subsequently, the reaction mixture was refluxed at 70C for 2 hoursduring which the pH was kept at 9Ø The reaction mixture was then cooled down
gradually to 2C to 5C and the resulting precipitate filtered off and washed with
water until alkali-free. After drying below 70C, 48 parts of 2,2',5,5'-tetra-
chlorohydrazobenzene of a melting point of 123C to 125C were obtained, this re-
presenting a yield of 15 percent of the theory and a good purity.
If the sodium hydrosulfide solution contains no sodium thiosulfate, and
the sodium hydrosulfide is applied in a ratio of 2.0 moles per mole 2,2'-5,5'-
tetrachloroazoxybenzene, the reaction carried out otherwise as described in thisExample provided practically the same result is achieved as to the yield and pur-
ity of the 2,2',5,5'-tetrachlorohydrazobenzene.
64.4 Parts of the 2,2',5,5'-tetrachlorohydrazobenzene were added to 640
parts of hydrochloric acid of 30 percent strength. The reaction mixture was re-
fluxed for 7 to 8 hours, allowed to cool down to room temperature and further
cooled down to 0C to 5C by adding 1000 parts of ice water. To this solution
83.2 parts of an aqueous solution of sodium nitrite of 30 percent strength were
added. ~fter completion of the diazotization and the addition of 5 parts of
charcoal, the diazo liquid was clarified.
~t the same time, 74.0 parts of acetoacet-m-xylidide were dissolved in
700 parts of water and 25 parts of caustic soda. The solution was cooled down
to 0 C by adding ice, charged with 50.6 parts of acetic acid, and the pH adjusted
with aqueous sodium acetate to 5 to 6. The reaction mixture was now charged to
the aforesaid diazo liquid. During the coupling a pH-value of 4 to 5 was main-
tained.
--10--
~5~ 2
After completion of the coupling, the reaction mixture was boiled for 1
hour and filtered. The resulting press cake was washed neutral with water. Afterdrying below 70C, 129~5 parts of Pigment Yellow 81 representing 86 percent yield
of the theory, referred to the hydrazobenzene compound, were obtained as a green-
ish yellow powder. The thus obtained pigment had the same excellent application
properties as the pigment prepared from a commercial pure 3,3',6,6'-tetrachloro-
benzidinle .
Similarly by employing an equivalent amount of acetoacet-4-chloro-2-methyl-
anilide in place of acetoacet-m-xylidide one can obtain Pigment Yellow 113 in 88%
yield.
Example 8
85 Parts of an aqueous solution of technical sodium hydrosulfide contain-
ing 35 percent NaHS and 9 percent ~a2S203 were added to a mixture comprising 65.4
parts of 5,5'-dichloro~2,2'-dimethoxyazoxybenzene in 196 parts of methanol at
room temperature within 90 minutes. The reaction mixture was then refluxed at
70 C to 75 C for a period of 5 hours. The pH had been kept between 9 and 9.4.
After this period the starting azoxybenzene was shown to be all consumed and thereaction mixture was cooled down to 0C to 5C, and the resulting precipitate
filtered off and washed with water until alkali-free. After drying below 70C,
48 parts of 5,5'-dichloro,2,2'-dimethoxyhydrazobenzene of a melting point of 116C
were obtained, this representing yield of 76 percent of the theory.
The reduction is performed with practically the same result if there is
applied a corresponding amount of ethyleneglycol monoethyl ether instead of the
methanol, or if the NaHS solution is free of thiosulfate.
64.4 Parts of crude 5,5'-dichloro-2,2'-dimethoxyhydrazobenzene thus ob-
tained were added to 640 parts of hydrochloric acid of 30 percent strength and
the reaction mixture refluxed for 8 hours. At this point the re-arrangement to
--11--
~5~ Z
6,6l-dichloro-3,3~-dimethoxybenzidine was complete and the reaction m-lxture was
then cooled down with ice water to 0C to 5C, and then diazotized with 90 parts
of an aqueous sodium nitrite solution of 30 percent strength. After the addition
of 5 parts of charcoal the diazo liquid was clarified.
At the same time, 76.6 parts of acetoacet-m-xylidide were dissolved in
760 parts of water and 28 parts of caustic soda. The solution was cooled down to
0C, charged with 51.6 parts of glacial acetic acid and the pH-value adjusted to
5 to 6 by adding an aqueous sodium acetate solution. To this solution the afore-
said dia~o liquid was added maintaining a pH-value of 4 to 5. After the coupling,
the reaction mass was stirred for another 30 minutes and boiled for 1 to 1-1/2
hours. The pigment that precipitated was filtered and washed neutral with water.
After drying at 70C, 131.5 parts of Pigment Yellow 15 (C.I. 21220) equal to 86
percent of the theory, referred to the hydrazobenzene compound, were obtained as
a yellow powder of very good purity.
Example 9
90 Parts of an aqueous solution of technical sodium hydrosulfide (35 per-
cent NaHS, 10 percent Na2S203) were added to a mixture of 45.2 parts of 2,2'-di-
methylazoxyben~ene in 150 parts methanol at 70C to 75C. Subsequently, the re-
action mixture was refluxed at 75C for 4 hours with pH kept between 9 and 9.4.
Thereafter, the reaction mixture was cooled down to 0C to 5C, and the resulting
precipitate filtered off and washed with water until alkali-free. The press-cake
was dried below 70C. There were obtained 35.6 parts of 2,2'-dimethylhydrazoben-
zene of a melting point of 162 C to ]64C, this representing a yield of 84 per-
cent of the theory of acceptable purity.
48 Parts of crude 2,2'-dimethylhydrazobenzene thus obtained were added
to 250 parts of hydrochloric acid of 30 percent ~strength at 0 C to 5 C. The re-
arrangement to 3,3'-dimethylbenzidine was completed by stirring at room tempera-
ture overnight and for additional 5 hours at 50C. The reaction mixture was then
-12-
1~5~ Z
cooled down by adding 2000 parts of ice water and diazotized with 30 parts of
sodium nitrite. After the addition of 4 parts of charcoal to the diazo liquid,
the solution was clarified.
A solution of 72.3 parts of acetoacetanilide in 500 parts of water and
27.5 parts of caustic soda was separately charged with 40 parts of glacial acetic
acid. The resulting solution was cooled down to 0C to 5C and the pH adjusted
to 5 to 6 by adding an aqueous sodium acetate solution. The aforesaid clarified
dia~o liquid was then charged to it and a pH of 4 to 5 was maintained. After
completion of the coupling the reaction mixture was boiled for 1-1/2 hours, fil-
tered and washed neutral with water. After drying below 70 C, 117.0 parts of
Pigment Orange 15 (C.I. 21130) equal to 88 percent of the theory, referred to the
hydrazobenzene compound, was obtained as a pure reddish powder.
Similarly by using equivalent amount of acetoacet-m-xylidide in place of
acetoacetanilide used in the above Example one obtains a correspondingly pure
Yellow Pigment in 87% yield.
Examp]e 10
82 Parts of an aqueous solution of 35 percent technical sodium hydro-
sulphide, free from sodium thiosulphate, were added to a mixture of 53.4 parts
of 2,2'-dichloroazoxybenzene in 99 parts of dimethyl formamide at 60C - 65C
within one hour. Subsequently, the reaction mixture temperature was raised to
75C and maintained at 70 C - 75 C for 3 hours. The pH of the reaction mixture
was held between 9.5 and 10Ø After this period, the starting material had been
all consumed. Then the reaction mixture was cooled down to 0C, the separated
product was filtered off and washed with water until alkali-free. After drying
below 70 , 44.6 parts of commercial grade 2,2'-dichloro-hydrazobenzene of a
melting point of 85C were obtained, this representing a yield of 88 percent of
the theory.
~0~
Similar result is achieved if the e is employed the same amount of dimethyl
sulfoxide instead of dimethyl formamide in the Example described above.
If there are used in place of 2,2'-dichloroazoxybenzene equivalent amounts
of the other aæoxybenzenes described above and the reactions are carried out other-
wise as described in this Example with either dimethyl formamide or dimethyl sul-
foxide, one obtains the corresponding hydrazobenzene derivatives in yields of 72 -
88% of the theory, in purities sufficiently good enough for direct conversion to
the appropriate pigments.
84 Parts of an aqueous solution of technical sodium hydrosulfide, free
from sodium.thiosulphate, were added to a mixture comprising 53.4 parts of 2,21- -
dichloroazoxybenzene in 140 parts of morpholine at 60C - 65C within 90 minutes.
Subsequently, the reaction temperature was raised to 75C and maintained at that
temperature for 2 1/2 hours. Next the temperature was ~urther raised to 90C and
maintained at that temperature for 1 hour. The pH of the reaction mixture varied
between 9.5-to 10. After this period the absence of the starting material was ~
confirmed. Then the reaction mixture was cooled to 20C and neutralized cautiously
with 400 parts of hydrochloric acid of 15 percent strength at a temperature below
20C. Then the reaction mixture was cooled to 0C to 5C, filtered off and washed
with water until free of chloride. After drying below 70C, 40.1 parts of 2,2'-
dichlorohydrazobenzene of a melting point of 85C to 87C were obtained, this re-
presenting a yield of 79 percent of the theory.
The hydrazobenzene obtained as described above is also sufficiently pure
for conversion to pigments as described in any one of the foregoing Examples 1 to
5.
If there are used equivalent amounts of 2,2'-dimethoxyazoxybenzene, or
2,2',5,5'-tetrachloroazoxybenzene, or 2,2'-dichloro-5,5'-dimethoxyazoxybenzene,
or 2,2'-dicarboxyazoxybenzene, or 3,3'-disulfoazoxybenzene instead of 2,2'-di-
chloroazoxybenzene used in the above example and the reaction is carried out
-14-
~ ~S8'~
otherwise as described in this Example, one obtains the corresponding hydrazo-
benzene in a yield of 72 - 88 percent oE the theory.
The hydrazobenzene derivatives so obtained are sufficiently pure for con-
vèrsion to appropriate pigments according to the processes as described in Examples
1 to 9.
Example 12
85 Parts of an aqueous solution of 36 percent technical sodium hydrosul-
phide, containing 1 percent sodium thiosulphate, were added to a mixture compris-
ing 51.6 parts of 2,2'-dimethoxy~æoxybenzene in 100 parts dimethyl sulfoxide at
60C within one hour. Subsequently, the temperature of the reaction mixture was
raised to 75C and maintained at 70C - 75C for 2 1/2 hours. The pll of the
reaction mixture was maintained between 9.5 and 10Ø After this period the start-
ing material was shown to be entirely reduced. Then the reaction mixture was
cooled down to 0C, the separated product was filtered off and washed with water
until alkali-free. After drying below 70C, 43.0 parts of high quality 2,2'-di-
methoxyyhydrazobenzene of a melting point of 100C to 102C were obtained, this
representing a yield of 88 percent of the theory.
Practically the same result is obtained if there is used the same amount
of dimethyl formamide instead of dimethyl sulfoxide in the Example described above.
Crude 2,2'-dimethoxyhydraæobenzene obtained by either of the above two
methods can be converted to the Pigment Reds 37, 41 and 42 according to the pro-
cedure described in Example 6 in 87 - 90 percent yields.
Example 13
50 Parts of crude 2,2'-dimethoxyhydrazobenzene prepared as described in
Example 6 were rearranged to 3,31 dimethoxybenzidine and then diazotized as des-
cribed in Example 6, and a clarified diazo solution was prepared.
-15-
~LQSE~ Z
At the same time, 96.8 parts of 2,3-hydroxynaphtlloic anilide was dissolved
in 1000 parts of water and 76 parts of caustic soda. 3 Parts of activated carbon
were added and the solution clarified. This solution was run into a mixture of
400 parts of water and 120 parts of acetic acid and sufficient ice, so that pre-
cipitation occurred at O C - 5C and the pH was adjusted to 5 to 6 by adding, if
necessary, an aqueous sodium acetate solution. To this resulting mixture, the
aforesaid diazo liquid was added in two hours, maintaining a pH value of 4.5-5.5.
After the coupling, the reaction mass was stirred for another one hour, filtered
and the product washed neutral with water. After drying below 70C, 146 parts of
high quality.Pigment Blue 25 (C.I. 21180), equal to 89.5 percent of the theory,
referred to the hydrazobenzene compound, was obtained.
Similarly~ by using equivalent amount of 2,3-hydroxynaphthoic o-anisidide
in place of 2,3-hydroxynaphthoic anilide used in the above Example, one obtains
good quality Pigment Blue 26 (C.I. 21185) in 87% yield.
Other azoxybenzenes suitable for reduction pursuant to the process of the
process of the present invention are:
2,2'-disulfo-5,5'-dicarboxy azoxybenzene
2,2'-diethoxy azoxybenzene
2,2'-dimethyl-5,5'-disulfo azoxybenzene
mixed azoxybenzenes resulting from the prior reduction of a mixture of
ortho nitrobenzoic acid and nitrobenzene.
l'he presence of two or more sulfo groups in the azoxybenzene molecule makes
it practical to use water as the only solvent for the NaHS reduction step of the
present invention. The presence of one sulfo group or of one or more carboxy
groups in that molecule enables the use of less organic solvent in that step than
is exemplified above.
In general the NaHS concentration in the reducing solution should be at
least 5 weight percent, preferably 10 weight percent, of the total solution. The
total quantity of NaHS should be at least 2 mols for every mol of the azoxybenzene.
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;)5~
Obviously many modifications and variations of the present invention are
possible in the light of the above teachings. It is, therefore, to be understood
that within the scope of the appended claims the invention may be practised other-
wise than as specifically described.
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