Phenolpthalein :

A solution of 250 g ofphthalic anhydridein 200g of concentratedsulfuric acidis prepared withcareful heating. It is cooled to 115° C, and treated with500 g ofphenol, and the mixture is then heated at115-120° Cfor 10-12 hours, care being taken that the temperaturedoes not exceed 120° C. The reaction mixtureis then poured intoboiling water, and the excess ofphenolremoved by steamdistillation. The granular yellow solid is extracted withdilutecaustic soda, which dissolves out the phenolphthalein,leaving behind a by-product, phthalein anhydride. Aftercooling, the liquid is filtered, acidified withacetic acid,mixed with a few drops of hydrochloric acid, and left tostand for 24 hours. The crude phenolphthalein, a sandy yellowpowder, is then filtered off and dried. The further purification ofphenolphthalein is performed bycrystallization. 10 gof the air-dried crude phenolphthalein are boiled under reflux for90 minuteswith 60 gof absolute alcohol and 5 gofactivated charcoalto two-thirds theiroriginal volume, and treated with water. The milky liquiddeposits, on standing, crystals of phenolphthalein mixedwith a gummy impurity. To remove this, the alcoholicsolution is added to water, in the proportion of 40 grams to320 mlthe mixture is vigorously shaken, and after standingfor a short time separated quickly from the precipitatedresin. The solution is then heated, when the milkinessdisappears, a white crystalline powder being precipitated.This is filtered off, washed with water, and dried at a lowtemperature. A further quantity is obtained by removalby distillation of the alcohol from the filtrate. The yield ofphenolphthalein is75 %, calculated from the weight of phthalicanhydride employed.Phenolphthaleinforms a white powder, almost insolublein water; readily soluble in alcohol. It melts at250-253° C and dissolvescompletely in sodium or potassium hydroxide solution.

Phenolphthaleinis oftenusedas an indicator in acid–base titrations. For this application, it turns colorless in acidic solutions and pink in basic solutions. ...Phenolphthaleinis slightly soluble in water and usually is dissolved in alcohols forusein experiments.

Methyl Orange :

The 4-diazobenzenesulfonic acid (4-sulfobenzene-1-diazonium) is dissolved in the smallestpossible quantity of dilutesodium hydroxide,kept cold with ice, and the liquid is pouredinto a solution of the calculated amount ofdimethylanilinemixed withacetic acid. The sodiumsalt of the methyl orangethereupon separates in shining,reddish-yellow, laminar crystals.These crystals are filtered off and recrystallizedfrom hot water. If a warm solution ofthe salt is treated with dilute hydrochloricacid in moderate excess, the free base of methyl orange is precipitatedas a shining, reddish violet, crystallinepowder.

For the preparation of the methyl orange without the isolation the diazo compound – 4-diazobenzenesulfonic acid is used and the reaction is carried by the following procedure.

1 molesulfanilic acidis dissolvedin exactly 1 mole dilutesodium hydroxide, treatedwith 1 molesodium nitrite, and then 1 mole hydrochloric acid is added in the cold. Thissolution is treated straight away with 1 moledimethylanilinein a little hydrochloric acid,and sodium hyroxide is again added. The sodiumsalt of the methyl orange soon separates out. The precipitationmay be rendered more complete byadding common salt.

Methyl orangeis a pH indicator frequentlyusedin titrations because of its clear and distinct colour change. Because it changes colour at the pH of a midstrength acid, it is usuallyusedin titrations for acids.