题目

甲基橙的制备及产率测定

提问时间：2021-03-18

答案

请参考Pittsburg州立大学上的制备方法（对氨基苯磺酸先重氮化后与二甲苯胺偶联）：
Diazotisation:
In a 250 mL beaker place 5 mL of a 5% solution of sodium carbonate.Dilute it with water to about 12 mL,and then add 0.0075 moles of sulphanilic acid.(Check whether you have the hydrate or anhydrous,this corresponds to 1.3 grams anhydrous or 1.5 grams of the hydrate.) Stir until dissolved.Warm if necessary.You may need to add a bit more sodium carbonate,but do not add more than one mL!Dissolve 0.45 grams of sodium nitrite in 6.0 mL of water.Add to the above solution.
Cool in an ice bath to about 4 degrees.Add drop by adrop a solution of 1.0 mL concentrated HCl diluted with 1.0 mL of water.Check to be sure the solution is strongly acidic (Congo red) at the end of this step,if not add a bit more acid.
Coupling:
to 0.8 mL of dimethyl aniline in a test tube add 0.4 mL of glacial acetic acid and mix.Add this solution to the diazonium salt solution prepared above,stir strongly during the addition.Let stand 10 minutes.
Neutralise the sollution by adding 0.9 grams of solid NaOH in 3 mL of water.The red colour will change to bright yellow orange.Methyl orange will immediately begin to separate.Add 3 grams of NaCl to precipitate it more completely.Filter on a Büchner funnel,and crystalise from hot water.5 to 6 grams of how water are required for each gram of material.Do not use too much water!Filter hot using fluted filter paper and a conical funnel.Allow to cool.Methyl orange separates as an intensely coloured solid.Chill in ice bath and collect the solid using a Büchner funnel.
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