Synthesis dihydroxytriptycene of from anthracene and p-benzoquinone

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BACKGROUND

Aim: To prepare dihydroxytriptycene from anthracene and p-benzoquinone.

Principle: It is an associative type of reaction, like Dials-Alder reaction (pericyclic) but more a free radical reaction occurring in the last step. Two different products are possible and due to change of stereochemistry, both containing a new bicyclic structure. The substituents point “down” towards the diene in the endo orientation and the bridge is sticking “up”. The substituents point “up” away from the diene in the exo product. “Endo” and “exo” terms the orientation of the substituents on the dienophile (benzoquinone) with the diene. The final enol form (dihydroxytriptycene) is more stable than the keto form.1

Reaction:

Mechanism:

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REQUIREMENTS

Chemicals:     

  • Anthracene – 1.8 g
  • P-Benzoquinone – 1.098 g
  • Xylene – 10 ml
  • KOH – 0.5 g
  • 20% HCl

Apparatus:     

  • Conical flask
  • Beaker
  • Pipette
  • Glass rod
  • Buchner funnel

PROCEDURE

Weigh and transfer the solid anthracene into a round bottomed flask (RBF). Weigh and transfer p-benzoquinone to the same RBF. Dissolve the mixture of solid 10 ml of xylene. The resulting solution is then boiled under reflux for 45 min. Allow the solution mixture to cool to room temp and to allow adducting to crystallize. Collect the solid product with suction and spread on a filter paper to allow residual solvent to evaporate. The p-benzoquinone-anthracene obtained above is weighted (1.27 g) in a conical flask and a solution of 0.5 g of KOH in 50 ml of ethanol is added.

The mixture is heated on a stream bath until all the adduct has dissolved (approx. 5 min). Dilute the solution with 50 ml of water, cool in an ice bath and neutralize the base carefully using 20% HCl, until the solution will be acidic. Filter the precipitated dihydroxytriptycene by suction, and spread to dry in air. Recrystalize the crude product using xylene as solvent and the mass is dried.

Calculation:

Here limiting reagent is anthracene; hence yield should be calculated from its amount.

C14H10 = Molecular formula of anthracene

C20H14O2 = Molecular formula of dihydroxytriptycene

Molecular weight of anthracene = 178 g/mole

Molecular weight of dihydroxytriptycene = 286 g/mole

Theoretical yield:

178 g anthracene forms 286 g dihydroxytriptycene

Therefore, 1.8 g anthracene will form …….? (X) g dihydroxytriptycene

= 2.89 g

Theoretical yield = 2.89 g

Practical yield = ————- g

% Yield = (Practical Yield)/(Theoretical Yield) × 100

CONCLUSION

Dihydroxytriptycene was synthesized and the percentage yield was found to be………..%

REFERENCES

  1. Carbon-Rich Compounds: From Molecules to Materials edited by Michael M. Haley, Rik R. Tykwinski published by WILEY-VCH (2006); Page No. 12.

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