Experiment 5: Acid-Base Extraction

What is liquid-liquid extraction based on?

It is based on the transfer of soluble substances from one liquid phase into another liquid phase based on solubility differences. Very useful technique when solubility differences exist between compounds

Most often, what are the phases in a liquid-liquid extraction?

Most often, there is a water or water-based (aqueous) solution and the other phase is an organic solvent which is immiscible with water.

What is the distribution coefficient

For a given compound, the solubility differences between solvents is quantified as the distribution coefficient K = C2/C1 where C2 and C1 are the concentrations at equilibrium between the two phases

Most organic compounds are more soluble in organic solvents than in water, by a distribution coefficient of K >4. How can some organic compounds be altered chemically to become more water soluble?

Organic compounds can be converted to their water-soluble salt forms if they belong to:
1. Organic acids (carboxylic acids which are strong organic acids and phenols which are weak organic acids)
2. Organic bases includes amines

How can organic acids be converted into water soluble forms?

An organic acid, when treated with an aqueous solution of their inorganic base such as (NaOH strong base or NaHCO3 weak base) Salts are ionic and in general ions are water soluble but not soluble in organic solvents.

How can organic bases (amines) be converted to their salt form?

When treated with an inorganic acid (such as HCl hydrochloric Acid) in an aqueous solution

In the experiment, a mixture of two compounds had to be separated. How would you separate Aspirin, if mixed with Phenacetin?

1. Aspirin, also known as acetylsalicyclic acid is a Carboxylic Acid, to convert this acid into its salt so that it can be soluble in the aqueous layer, an inorganic base should be used such as NaHCO3. Phenacetin would remain in the organic layer.
2. Once

In the experiment, a mixture of two compounds had to be separated. How would you separate Caffeine, if mixed with Phenacetin?

1. Caffeine, is a bitter, white crystalline xanthine alkaloid that acts as a stimulant, it's an amine. When treated with HCl, it becomes soluble in the aqueous layer and Phenacetin would remain in the organic layer.
2. Once separated, the salt from caffei

In the experiment, a mixture of two compounds had to be separated. How would you separate Aspirin, if mixed with Caffeine?

1. Aspirin, also known as acetylsalicyclic acid is a Carboxylic Acid, to convert this acid into its salt so that it can be soluble in the aqueous layer, an inorganic base should be used such as NaHCO3. Caffeine would remain in the organic layer.
2. Once s

What type of apparatus is used in the extraction procedure to separate the two liquid layers?

A separatory funnel

How do you use a separatory funnel?

1. Pour liquid to be extracted
2. Pour Solvent, close using glass stopper
3. Shake vigourously, with stopcock closed, while inverted open stopcock every 30 seconds to allow gasses to come out.
4. Once equilibrium is reached (reaction has taken place) stop

Lets say you have Naphthalene, a neutral compound and benzoic acid, a carboxylic acid in an organic solvent, dichloromethane. How would you separate them?

Add an aqueous solution of either 5% NaOH or saturated NaHCO3 to extract the benzoic acid in its salt form in the aqueous layer.

Phenols are weak organic acids and are partially water soluble, substituted phenols are not. Will a weak inorganic base make a phenol water soluble?

No, a weak inorganic base, such as NaHCO3 will not deprotinate phenols, stronger bases such as NaOH are needed to convert the phenol to its ionic salt

A mixture of benzoic acid (strong acid) and p-methoxphenol (weak acid) dissolved in dichloromethane need to be separated. Which solvent would work best? 5% NaOH, a strong base or NaHCO3, a weak base? Explain

5%NaOH would deprotinate both weak and strong acid so separation could not be achieved, however the weaker base, NaHCO3, would only be able to deprotinate the stronger benzoic acid into its salt and it could be separated in the aqueous layer.

You have a mixture of 4 compounds!!! An amine, A strong acid, a weak acid and a neutral compound, what do you do?

1. Add HCl, extract the Amine salt
2. Add weak base, extract the strong acid salt
3. Add strong base, extract the weak acid salt
4. Organic layer remains with neutral compound (not chemically altered)

How do you convert the salts back into their original form?

You have to alter the pH, the amine needs to be basified so that it is no longer soluble in the acid. You do this by adding concentrated NaOH till the solution becomes basic (pH of 10ish)
Likewise, salts from acids need to be acidified by adding concentra

True or False:
When doing acidification of a salt, it's better to use 1 N HCL (dilute) than 6 N HCL (concentrated)

False, it's better to use the concentrated version! Since it's better to recrystallize from less aqueous volume! Geez, I just realized all my true and false are false! LOL

Transferring a solute from one solvent to another is called?

Extraction

You have two layers of liquid and you need to determine which is aqueous, how do you do this?

Add a few drops of water to both layers. If the drops dissolve, then that is the aqueous layer, if the drops added form isolated drops, that is an organic layer.