Question

Describe the role of the melting point depression phenomenon in this Solventless Aldol Experiment.

the Eperiment:

Experimental Procedure:
1. in test tube, mix two solid reactants with spatula until an oil forms (melting point depression):

In a small test tube, mix 0.25 g 3,4-dimethoxybenzaldehyde and 0.20 g 1-indanone. Crush the
solids completely, using a glass rod or metal spatula. Caution: Avoid pressing hard on the
bottom of the test tube. Continue stirring until a yellowish oil forms.
2. Add 50 mg of finely ground NaOH. Caution: Avoid contact with NaOH!
3. Stir the mixture thoroughly and continuously, scraping and crushing any solids which are
present, until the whole mixture becomes solid. Allow another 15 minutes for the reaction to complete.
4. Quench the reaction by adding 10% aqueous HCl solution (2 mL). Scrape the solid off the
walls of the test tube and break up any chunks. Using pH paper, check that the mixture is acidic
(pH < 3).
5. Isolate the solid product by vacuum filtration with a small Hirsch funnel and 1 cm filter paper,
using small portions of water to rinse any remaining solid from the test tube.
6. Recrystallize from aqueous ethanol: Place the solid in a 50 mL erlenmeyer flask, and place 20
mL 9:1 ethanol/water in another 50 mL erlenmeyer flask. Heat the ethanol/water on a hot plate.
Add small portions of hot ethanol/water to dissolve the solid product, while warming both flasks
on the hot plate. Use only the minimum amount of solvent needed to dissolve the solid (less than
20 mL). Allow the mixture to cool to room temperature on the benchtop, then cool the product in
an ice bath for a few minutes. Isolate the crystalline solid by vacuum filtration with a small
Hirsch funnel and 1 cm filter paper, allowing vacuum to pull air through the product for several
minutes to ensure complete dryness.

Answer 1

From, the knowledge of colligative property we know that melting point of a pure solid is lowered when other substance is mixed with it. Melting point depression depends on number of solute particles.  

In the given reaction, when the reactants are mixed their melting point decreases and they converted to liquid form and mix well. Therefore there is no requirement of solvent. Most reactions need solvents. These solvents are the major sources of industrial waste. Therefore not requirment of solvent reduces the waste of chemicals. So in this reaction, melting point depression phenomenon has an important role towards green chemistry.