Question

The Diels-Alder reaction is one of the most useful in organic chemistry because it allows for the formation of rings: The reactor initially has only the diene and the dienophile. The product stream has 55 mole% of the ring and 17 mole% of diene. Calculate the fractional conversion of the limiting reactant and the percentage by which the other reactant is in excess. If we assume that we can do this reaction continuously, pick a basis for the feed and determine theextent of reaction.R = CH3.

Answer 1

Diels-Alder reaction is conjugate addition reaction

One reactant - conjugated diene

Another reactant - alkene

Example

1,3 butadiene + ethene ---- cyclohexene (1)

Product stream has 55 mol% of ring and

17 mol% diene

Remaining percentage is alkene

Product stream :

17 mol % diene

55 mol% ring

28 mol% alkene

Product basis : 100 mol

Moles of diene = 100(0.17) = 17 moles

Moles of ring = 100(0.55) = 55 moles

Moles of alkene = 100(0.28) = 28 moles

According to stiochiometry , for 55 moles of ring, we need 55 moles diene and 55 moles alkene

Feed analysis

Moles of diene = 55 +17 = 72 moles

Moles of alkene = 55+28 = 83 moles

Stiochiometric ratio of alkene : diene = 1:1

Actual ratio of alkene : diene = 83:72 =1.1527

So alkene is excess reactant and diene is limiting reactant

Fractional conversion of diene = (72-17) /72 =0.7638

% excess of alkene =( (83-72) /(72)) (100) =15.277%

Feed basis :

155 moles/h

Moles of alkene = 155(1.1527/2.1527) = 83 moles

Moles of diene = 72 moles

% conversion of limiting reactant = 76.38%

Extent of reaction = 72(0.7638) = 55 moles/h

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