CA1058222A - Process for the manufacture of benzidine pigments and hydrazobenzene derivatives in canada - Google Patents

Abstract

PROCESS FOR MANUFACTURE OF BENZIDINE PIGMENTS

Abstract of the Disclosure Benzidine pigments are very off?stir?ly made by reducing certain azoxybenzenes with technical ??? to form in good yield a corresponding hydrazch?????? which can be further reacted in crude condition to make the pigment.

Description

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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 ~)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 ~ ~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

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.

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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.

~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 ~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 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.

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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 ~ ~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.

~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.

;)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.

Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVI-LEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In the process of making a benzidine pigment, the improvement accord-ing to which an azoxybenzene having the formula in which X1,Y2,Y1 and Y2 are selected from the class consisting of hydrogen, chlorine, methyl, methoxy, ethoxy, is essentially completely reduced to the corresponding hydrazobenzene by techni-cal NaHS in aqueous solution at a pH between about 8 and about 10, and at a tem-perature of 50 to 100°C, the solution is then cooled to precipitate out the hydrazobenzene, the precipitated hydrazobenzene is filtered off, washed and in the resulting crude condition subjected to benzidine rearrangement, diazotization and coupling.

2. The combination of claim 1 in which the aqueous solution contains water-miscible organic solvent that increases the solubility of the azoxybenzene in the hot reducing solution, but is essentially inert to the reactants.

3. In the process of making a benzidine pigment, the improvement accord-ing to which an azoxybenzene having the formula in which X1, X2, Y1 and Y2 are selected from the class consisting of hydrogen, chlorine, methyl, methoxy, ethoxy, is essentially completely reduced to the corresponding hydrazobenzene by technical NaHS in aqueous solution at a pH between about 8 and about 10, and at a tempera-ture of 50 to 100°C, the solution is then cooled to precipitate out the hydrazo-benzene derivative, the precipitated hydrazobenzene derivative is filtered off and the filtered off hydrazobenzene derivative is washed to produce in good yield crude dye intermediate suitable without further purification for processing into the final dye.