Question

please calculate the

1.theoretical yield,

2.percent yield, and

3. overall percent yield from benzaldehyde.

my products weight was 2.137 g

experiment was "Isolation of Tetraphenylcyclopentadienone, then Recrystalization of Tetraphenylcyclopentadienone"

HERE IS MY PROTOCOL I FOLLOWED TO GET MASS OF 2.137 g

THIS IS ALL AVAILABLE INFORMATION!!!

Add 1.5 g benzil, 1.5 g dibenzyl ketone, and 12 mL absolute ethanol to a 50-mL round-bottom flask. Place a magnetic stir bar in the flask. Attach a condenser, having lightly greased the joint. Stir and heat the mixture at 70ºC (with the condenser running) until the solids dissolve. Then raise the temperature to 80ºC with continued stirring. Using a 9" Pasteur pipette, add dropwise 2.25 mL of ethanolic potassium hydroxide solution through the condenser into the flask; make an effort to prevent any drops from contacting the condenser walls (each drop should fall directly into the reaction mixture). The mixture will immediately turn a dark purple. Once you have added the potassium hydroxide, raise the temperature to about 85ºC. Stir the mixture at this temperature for 15 minutes.

Isolation of Tetraphenylcyclopentadienone

At the end of the heating period, remove the flask from the heat and allow it to cool to room temperature. Then place the flask in an ice-water bath for 5 minutes to complete the crystallization of the product. Collect the deep purple crystals on a Büchner funnel by vacuum filtration. Wash the crystals with 3 4-mL portions of ice-cold 95% ethanol; this wash solvent should be used to transfer crystals from the round-bottom flask to the Büchner funnel if they do not all come out when the mixture is initially poured into the funnel. After air-drying the crystals for a few minutes, complete the drying in a 100ºC-oven for a few minutes.

Recrystallizing Tetraphenylcyclopentadienone

Recrystallize your tetraphenylcyclopentadienone from a 1:1 mixture of 95% ethanol and toluene; approximately 24 mL of this solvent mixture will be required per gram of tetraphenylcyclopentadienone, but remember to only add the minimum boiling solvent necessary to dissolve the solute. Recover the crystals by vacuum filtration (as above) and redetermine the melting point.

Weigh the dried product and calculate the percent yield. Also calculate the overall percent yield from benzaldehyde. Determine the melting point. If the melting point is not within 2ºC of the literature value, you should recrystallize your product (see below).

Answer 1

One mol of benzil reacts with one mol of dibenzyl kenote to give one mol of Tetraphenylcyclopentadienone. As per the molecular weights of the reactants and product, 210 gm of benzil reacts with 210 gm of dibenzyl kenote to give 384 gm of Tetraphenylcyclopentadienone. Please find the diagram below.

Therefore, 1.5 gm of benzil will react with 1.5 gm of dibenzyl kenote to give (1.5X384)/210 = 2.743 gm of Tetraphenylcyclopentadienone.

1. Theoretical yield = 2.743 gm

2. Percent yield = (weight of the final product / theoretical yield) X 100 = (2.137 /2.743) X100 = 77.91 %

3. overall percent yield from benzaldehyde.

This is not possible to find out from the information provided. Complete protocol does not use benzaldehyde anywhere.