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Main uses and production methods of phenolphthalein

Oct. 09, 2019
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Phenolphthalein refers to a chemical product that is in the form of a crystalline powder and is almost insoluble in water. Its characteristics are colorless in acidic and neutral solutions and purplish red in alkaline solution. Often used to detect acid and alkali.


A phenolphthalein stimulant for chronic constipation. It can directly stimulate the intestinal mucosa or activate the nerve endings of the intestinal smooth muscle to increase the propulsion of the intestine. Fluid and electrolyte disorders due to excessive diarrhea. Long-term use can damage the intestinal nervous system and is likely to be irreversible.


Phenolphthalein has many uses, including industrial pharmaceutical raw materials, organic synthesis, indicators, etc., as detailed below.


Phenolphthalein is a weak organic acid which is a colorless lactone structure in a solution of pH < 8.2 and a red quinoid structure when pH > 8.2.


The discoloration range of phenolphthalein is 8.2 to 10.0, so phenolphthalein can only be tested for alkali and cannot be tested for acid.


The hydrazine or hydrazine salt of phenolphthalein is very unstable in an alkaline medium, and it is slowly converted into a colorless carboxylic acid salt; in the case of a concentrated lye, it is immediately converted into a colorless carboxylic acid. Salt type. Therefore, when the phenolphthalein reagent is dropped into the concentrated lye, the phenolphthalein starts to turn red, and soon the red color retreats to become colorless.


Phenolphthalein is a white or slightly yellowish fine crystal that is hardly soluble in water and soluble in alcohol. Therefore, phenolphthalein is usually used as an alcohol solution. When the phenolphthalein reagent is dropped into water or a neutral or acidic aqueous solution, white turbidity may occur because the alcohol may be mutually soluble in water at any ratio to precipitate the phenolphthalein which is poorly soluble in water in the reagent.


The main uses of phenolphthalein are:


(1) pharmaceutical industry pharmaceutical raw materials: pharmaceutical laxatives, can stimulate the intestinal wall, causing intestinal peristalsis to promote bowel movements. Applicable to habitual stubborn constipation, there are many dosage forms such as tablets and suppositories;

(2) For organic synthesis: mainly used in synthetic plastics, especially synthetic phthalazinone polyaryletherketone polyaryletherketone polymers, which have excellent heat resistance, water resistance and resistance. Chemical corrosiveness, heat aging resistance and good processability, many of the fibers, coatings and composite materials made from it are widely used in electronic appliances, mechanical equipment, transportation, aerospace, atomic energy engineering and military;

(3) A reagent for a base indicator, a non-aqueous solution for titration, and a reagent for color layer analysis.


There are two main methods for producing phenolphthalein.


method one

It is prepared by mixing phthalic anhydride with phenol and co-heating with sulfuric acid.


Method Two

160 kg of phenol was melted, maintaining the temperature at 80-90 ° C, while adding 120 kg of phthalic anhydride, 40 kg of zinc chloride, 5.5 kg of sulfuric acid with stirring, the reaction was carried out for 5 h, then the temperature was raised to 180 ° C, and the reaction was carried out for 40 h; After the end, add water, continue to stir, boil with steam, then stop heating, let stand, suck out the upper layer of waste acid solution, wash the precipitate with water to pH>5, spin dry, then wash to colorless, dry below 80 °C. 4 times of industrial ethanol (ω>95%) was added to the dried crude phenolphthalein, and activated carbon was added thereto, and the mixture was heated under reflux with stirring for 5 minutes. Stop heating and filter. The filtrate is concentrated by evaporation, and the ethanol is recovered. When concentrated to a suitable degree, it is rapidly centrifuged and dried, and washed with ethanol for 1 or 2 times, dried, and sieved through a 40 mesh sieve.


Phenolphthalein is a common chemical raw material used in daily life, as an acid-base indicator, a conventional laxative, a synthetic plastic, and the like.


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