Question

In: Chemistry

Why is not possible to recrystallize ASA using a single-solvent recrystallization from water, as is done...

Why is not possible to recrystallize ASA using a single-solvent recrystallization from water, as is done with acetanilide?

Solutions

Expert Solution

Acetyl salicylic acid is soluble in ethanol but very poor soluble in water , this is due to fact

Compared to water, ethanol has a hydrophobic carbon chain. In this sense, water can at best dissolve the carboxylic acid and polar portion of aspirin - and other polar compounds even the methylester may not be adequately dissolved in water. ... The ethyl side chain, here in ethanol is a hydrocarbon side chain, can form Vander waal (VDW) forces with hydrophobic benzene

aspirin, a sylicylate derivative:

has:

A bulky benzene ring (hydrophobic)
A benzoic acid group (hydrophilic)
An methylester group (polar)

Compared to water, ethanol has a hydrophobic carbon chain. In this sense, water can at best dissolve the carboxylic acid and polar portion of aspirin - and even the methylester may not be adequately dissolved.

In ethanol, the alcohol group can form favourable hydrogen bonds with carboxylic acid and dipole interactions with the ester group. The ethyl side chain, which is a hydrocarbon side chain, can form VDW forces with hydrophobic benzene.

Also due to intramolecular H bonding bitweeb two adjecead group reduces water solubility of ASA further

Thuse due to this solubility difference

Now coming to our question

Ethanol is added to completely dissolve everything. Then cold water is added to precipitate out the aspirin only but not other impuritiea

What you're altering is the temperature/composition of the solvent, that is, the quality of the solvent. You have to look at the solvent as a whole with properties intermediary to that of the pure components, not as two separate solvents.

For above reason we mentioned at start, the impurities in aspirin are more soluble in cold water+ethanol than in ethanol alone, because acetylsalicylic acid is more apolar than the impurities, so acetylsalicylic acid precipitates selectively in cold water. The impurities can be unreacted reagents, like salicylic acid, which is more soluble in cold water than acetylsalicylic acid due to being more polar.

.


Related Solutions

Extraction of Trimyristin from Nutmeg Lab 1. Why is acetone a good solvent to recrystallize the...
Extraction of Trimyristin from Nutmeg Lab 1. Why is acetone a good solvent to recrystallize the trymyristin? What are the disadvantages? 2. Assume that the amount of trimyristin in nutmeg is 20% by weight. What would be the expected amount to be recovered from the 7.00g of nutmeg? 3. Calculate your percent recovery using the expected recovery amount (expected 20% of the sample you weighed). 4.If the melting point of the purified trimyristin was done before it was completely dry...
Explain why you chose your recrystallization solvent. What properties did this solvent have that made it...
Explain why you chose your recrystallization solvent. What properties did this solvent have that made it the best for recrystallization?
A chemist decided to try and recrystallize (purify) quinidine from acetone solvent. The solubility of quinidine...
A chemist decided to try and recrystallize (purify) quinidine from acetone solvent. The solubility of quinidine in acetone is 1.0 g dissolves in 3.0 mL of hot acetone and 100 mg dissolves in 1.0 mL of cold acetone. If he started with 0.35 g impure quinidine, what is the minimum amount of solvent he should use to recrystallize the impure solid? Is acetone a good choice of solvent?
1. Water is the best choice for use as a crystallization solvent whenever possible. Why? 2....
1. Water is the best choice for use as a crystallization solvent whenever possible. Why? 2. Why do you crystallize your product as slowly as possible? 3. Why would n-propyl alcohol, CH3CH2CH2OH be more soluble in water than n-propyl bromide, CH3CH2CH2Br?
1) Why is methanol a good solvent for recrystallization of cholesterol?   2) What chemical differences are...
1) Why is methanol a good solvent for recrystallization of cholesterol?   2) What chemical differences are needed between extraction solvent and re-crystallization solvent?
explain the possible advantages of using urea and cinnamic acid for recrystallization and the properties of...
explain the possible advantages of using urea and cinnamic acid for recrystallization and the properties of these solvent are important.
4. What is the most important criterion in choosing a recrystallization solvent? 5.  Using resonance, briefly (less...
4. What is the most important criterion in choosing a recrystallization solvent? 5.  Using resonance, briefly (less than 20 words) explain why only the alcohol (phenol) is acetylated and not the carboxylic acid.
Why is cyclohexane used as a solvent in this experiment instead of water? Water is much...
Why is cyclohexane used as a solvent in this experiment instead of water? Water is much safer and much cheaper.
Give reasons why or why not its possible to remove all water from an ethanol-water mixture...
Give reasons why or why not its possible to remove all water from an ethanol-water mixture using distillation.
Water makes life possible as a solvent for biological molecules. What electrical properties allow it to...
Water makes life possible as a solvent for biological molecules. What electrical properties allow it to do this?
ADVERTISEMENT
ADVERTISEMENT
ADVERTISEMENT