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Preparation of P-toluenesulfonic Acid (PTSA)

The purpose of the experiment:
To learn preparation of aryl sulfonic acid with aromatic sulfonation reaction;
To consolidate the use, reflus and recrystallization opearation of water knockout trap.

The principle of the reaction:
The main reaction:

The vise reaction:

Steps:

Reflux reaction: adding 25 mL Toluene into the 50 mL round-bottom flask first. Then adding 5.5 ml concentrated sulfuric acid slowly, while the flask is being shaken. At last, throwing several grains of zeolite into the flask. Heating and refluxing the flask on asbestos network for 2h till the volume of liquid in the water knockout trap to be 2 mL.

Equipments:

a  Reaction device     b  Filtration device

Product separation: keep the reactants to be cool. Put the reactants into 60 mL erlenmey flask. Adding 1.5 mL water till there is some crystal coming out. Stirring the reactants slowly with glass rod. When the reactants become solid, filtering the reactants with Buchner funnel. Pressing the reactants to remove Toluene and p-toluenesulfonic acid and getting crude product 15g.
  • Purification: To get pure p-toluenesulfonic acid (PTSA http://ru.p-toluenesulfonicacid-ptbba.com ), the crude product should be recrystallized. Dissolving 12g crude product with 6 mL water in 50mL beaker ( or large test tube). Passing hydrogen chloride gas into the solution till there is some crystal coming out. When the hydrogen chloride gas is being ventilated, some measures should be taken to avoid “suck down”. Sucting and filtering the precipitated crystals with Buchner funnel rapidly and then wash the rest crystals with small amount of concentrated hydrochloride acid. After squeezing the water out with glass stopper, store the solid in dryer.

     

    Notice:

    While the concentrated sulfonic acid was dropped in, the flask must be shaken and the dropping rate should be slow with burette.
    The heating strength should be under control.
    Stirring when the crystals come out.