CS197993B1 - Process for preparing sulphophthaleines - Google Patents

Description

BACKGROUND OF THE INVENTION The present invention relates to a process for the preparation of sulfonaphthalsins, compounds which are mainly used as analytical indicators.

The following procedures have been described for the preparation of sulfophthalins. When prepared from the acidic ammonium salt of 6-sulphobenzoic acid with the appropriate phenol in the presence of thionyl chloride or phosphorus pentoxide as a condensing agent (Chrzaszczewski, 0.-, Kosiňski M .: Zes,

II., Nauki Mar. - Przyrod. No 3, 145-57 (1957), White E.C., Acrse S.F .; 3. Am.Chem, Soc., 41, 1190 (1919)), an excess of phosphorus pentoxide is used, thereby increasing the consumption of raw materials. Manufacture from saccharin and the corresponding phenol in the presence of sulfuric acid (Freas R., Provine

E.A ,: a.Am.Chem.Soc. 50, 2014 (1928)) provides a low yield over a long reaction time. The reaction of o-sulfobenzoic anhydride with the appropriate phenol and zinc chloride (Orndorf WR, Cornwell RTK: O.Am.Chem.Soc., 48, 985 (1926)) requires difficult handling of zinc chloride, which must be anhydrous and comminuted. necessary to remel it before reaction. Process for preparing from the corresponding phenol and o-sulfobenzoic anhydride in excess, which binds the water-forming reaction (No. Pat. No. 83987} Leminger 0 .: Chemical Industry 5/30 p. 10 (1955 /} White EC, Acrae SF: 3 41, 1190 (1919)) requires a high consumption of expensive anhydride, making the economic balance unfavorable The risk of explosion arises from the production of o-sulfo-benzoic anhydride and the corresponding phenol in the presence of perchloric acid and phosphorous oxychloride as condensing agent (Yarovenko

197 993

197 993

E.Y. , Kondraehova M.F .: Mathody Poluch, Khim-Reaktivov Prap. 1969, No 20, 212-14), aa prepared from o-sulfobenzoic acid chloride and the corresponding phenol in the presence of zinc chloride as condensing agent (Lubs HA, Acree SF: O. Am. Chem. Soc. 38, 2772 (1916)) Sulfophthaleins are also formed by the reaction of o-e-sulfobenzoic anhydride and the corresponding phenol, whereby the water formed is removed ezotropically (Leminger, O., Vodák, Z .: US Pat. 63987), but is not suitable for all phenol derivatives.

The above disadvantages are substantially reduced by the process for producing the eulfophthaleins of the invention. The principle is that the condensation of o-sulfobenzoic anhydride with a compound of the formula OH is carried out

wherein R ₁ and R ₂ are hydrogen or hydroxy or C 1 -C 3 alkyl is carried out in the presence of molten phosphorus pentoxide at 110 to 170 ° C for 1 to 8 hours at a molar ratio of o-sulfobenzoic anhydride reactants compound of formula

OH

wherein R 1 and R ₂ are as defined above: phosphorus pentoxide 1 to 1.4: a: 0.1 to 0.4. After the condensation is complete, the melted fuel is boiled with water? optionally, the unreacted phenol or derivative thereof is distilled off with water vapor and the resulting dye is filtered off with suction. The product can be purified by reprecipitation or recrystallization.

In the production method according to the invention, good yields are achieved while reducing the consumption of one basic expensive raw material.

He did

A 250 ml three-necked flask equipped with a chlorocelciate cap, stirrer and thermometer was charged with 30 g (0.2 mol) of thymol, 23 g (0.125 mol) of o-sulfobenzoic anhydride and 3.5 g (0.025 mol) of phosphorus pentoxide. The mixture was heated with stirring at 120-135 ° C for 4 hours. 20 ml of water are then carefully added to the resulting melt and the unreacted thymol is distilled off with steam. After removal of any unreacted thymol (400 to 700 ml), the precipitate was filtered off with suction and washed with hot water on the filter. Sushi ea at 60 ° C.

Yield 27 g (56% of theory)

Example 2

A 250 ml three-necked flask equipped with a chloro-calcium cap, stirrer and thermometer was charged with 18.8 g (0.2 mol) phenol, 18.5 g (0.1 mol) o-e-sulfobenzoic anhydride and 2.8 g (0). , 02 mol) phosphorus pentoxide. The mixture was heated with stirring for 5 hours

197 993 at 130-140 ° C. Thereafter, 150 ml of water at 60 ° C was added cautiously to the resulting melt and heated from stirring at 100 ° C until the melt disintegrated. The precipitate is filtered while hot and washed on the filter with hot water.

Yield 22.7 g (64% of theory).

The crude product can be purified by dissolving it in an alkaline hydroxide or ammonia solution and precipitating it with a mineral acid or recrystallizing from a suitable organic solvent.

Claims (1)

OBJECT OF THE INVENTION A process for the preparation of sulfophthaleins of the general formula wherein _a ? ₄ is hydrogen or alkyl of 1 to 3 carbon atoms or a hydroxy group, or a combination thereof, by condensation of the o-e-sulfobenzoic acid anhydride with a compound of the formula OH • R < wherein and R ₂ is hydrogen or hydroxy or alkyl of 1 to 3 carbon atoms, characterized in that the condensation is carried out in the presence of phosphorus pentoxide in the melt. at a temperature of 110 to 170 ° C for 1 to 8 hours at a molar ratio of the reactants o-sulphobenzoic anhydride to the compound of the general formula OH wherein R 1 and R ₂ are as defined above for phosphorus pentoxide 1 to 1.4 to 2 to 0.1 to 0.4.