CS203377B1 - Process for preparing 1-/1'-methyl-3-nitrobenzenazo/2-naphthole - Google Patents

Description

This invention relates to the preparation of 1- / 1 ^- -raethyl-3 '- nitrobenzenazo / -2-naphthoic tolu formula I

In an acidic environment, which allows the electrochemical indication of the diazo compound in the reaction mixture and thus the control of the coupling process.

The compound of formula (I) is an insoluble azo pigment used for the preparation of inks, oil paints and the like.

The synthesis consists of coupling 3-nitro-4-toluenediazonium chloride with 2-naphthol. According to the prior art, 3-nitro-4-toluidine is diazotized in hydrochloric acid at 0 ° C with a 2.5 N sodium nitrite solution and the resulting diazo compound solution is scrubbed with carboraffin. The azo component solution is prepared by dissolving 2-naphthol with the addition of sodium hydroxide at elevated temperature. Coupling is accomplished by admixing the diazonium salt solution at pH 8 to 10.

The progress of the coupling is monitored by indicating excess diazo compound by dropwise reaction with an alkaline solution of R-salt or H-acid on paper. The indicated indication is not the most accurate and, due to its difficulty, it is suitable only for the non-automated production process. In order to obtain the prerequisites for the automation of production, it is necessary to replace the prior art diazo reagent method with a physical method, such as polarographic or potentiometric, but their use is determined by the pH sensitivity of the electrodes to the diazonium salt.

A disadvantage of the prior art pigment preparation process is an alkaline medium having a pH greater than 7, in which the function of the electrodes is greatly reduced or completely impossible and the diazo compound in the reaction mixture cannot be indicated during coupling. As a result, automatic regulation of the reaction reaction is prevented. Since 1- (1'-methyl-3'-nitrobenzenazo) -2-naphthol is one of the pigments whose production is increasing, it appears necessary to monitor the possibilities of optimization and automation of its production, which is not possible with the current method of indicating the diazo compound.

We have now found a process for preparing 1- (1'-methyl-3'-nitrobenzenazo) -2-naphthoate by diazotizing 3-nitro-4-toluidine in hydrochloric acid and coupling 3-nitro-A-toluenediazonium chloride for purification with 2-naphthol, The solution according to the invention is characterized in that the solution of 3-nitro-4-toluenediazonium chloride is admixed according to the electrochemical indication with constant pH control of 4.5 to 6.5 to a suspension of 2-naphthol having a pH of 5.4 to 5.6 at 10 to 40 ° C, the coupling mixture is filtered and after completion of the reaction, the resulting azo dye is washed with water and dried.

The coupling is carried out by dissolving the 2-naphthol. in water with the addition of sodium hydroxide at 40 ° C. The pH is adjusted to 4.5 to 6.5, preferably 5.5, with acetic acid or dilute acetic acid. A diazo compound solution is admixed to the fine suspension of the azo component at a temperature of 10 to 40 ° C, preferably 20 ° C, according to the data of the electrochemical sensor, which, in conjunction with automatic control, guarantees its optimum value in the reaction mixture. Simultaneously with the pH regulator, the medium is treated with a 2.5-10 N NaOH solution, preferably 10 N, to a pH of 4.5 to 6.5, preferably 5.5. In this way, an optimum reaction progress is ensured, which is completed in 6 to 12 minutes after allowing the appropriate volume of diazo compound. The pigment slurry was heated to 70-80 ° C, filtered, washed with water until the reaction disappeared from chloride ions and dried at 70-90 ° C.

The process of the invention provides 1- (1'-methyl-3 '' - nitro-benzoazo) -2-naphthol β with a yield of 98 to 99%, which is 3 to 4% more than the prior art, furthermore the pigment has good coloristic properties. 2-naphthol content up to 1 X.

The following example illustrates the preparation process of the invention. Unless otherwise indicated, all parts are by weight.

Example

A. Diazotization of 3-nitro-4-toluidine

77.52 d of 3-nitro-4-toluidine was added with stirring to 360 d of 5 N HCl and diluted with 216 d of water. The diazo component suspension is cooled to 0 ° C and diazotized by the sequential addition of I 2 O d 5% sodium nitrite solution. After completion of the reaction, 1.5 g of carborafine are added and the suspension is filtered after 5 minutes.

B. Coupling

The beakers were charged with 5,150 d of water and 65 d of 10 N NaOH and dissolved in this solution at 40 ° C with 72 d of 2-naphthol which precipitated with 31 d of acetic acid. A diazo compound solution was successively added to the resulting asocomponent suspension at pH 5.4-5.6 and 20 ° C according to potentiometric indication associated and controlled. The pH of the reaction mixture was maintained at 5.2-5.5 by the addition of 10 N NaOH solution. After the coupling (about 12 minutes), the pigment slurry, which is almost without master, is heated to 75 ° C for 15 minutes and then filtered. After washing the cake and drying it, 150.6 d of a red pigment is obtained.

Claims (1)

A process for the preparation of 1- (1'-methyl-3'-nitrobenzenazo) -2-naphthol by diazotizing 3-nitro-4-toluidine in hydrochloric acid and coupling the resulting 3-nitro-4-toluenediazonium chloride after purification. with 2 naphthol, characterized in that the solution of 3-nitro-4-toluenediazonium chloride is admixed according to the electrochemical indication under constant pH control to a value of 4.5 to 6.5 into euapension of 3-naphthol with a pH value of 5.4 to 5.6 at 10 to 40 ° C, the coupling mixture is filtered after completion of the reaction and the azo dye obtained is washed with water and dried.