Organic Chemistry - Separations and Purifications

MCAT Chapter 12

Extraction

combines two immiscible liquids, one of which easily dissolves the compound of interest

aqeuous phase

polar layer and dissolves compounds with H bonding or polarity

Organic phase

nonpolar layer and dissolves nonpolar compounds

Wash

reverse of extraction, small amount of solvent that dissolves impurities is run over the compound of interest

Filtration

isolates a solid from a liquid

Gravity filtration

used when product of interest is in the filtrate, hot solvent is used to maintain solubility

Vacuum filtration

used when product of interest is the solid. A vacuum is connected to the flask to pull solvent through more quickly

Recrystallization

The product is dissolved in minimum amount of hot solvent. If the impurities are more soluble, crystals will reform while the flask cools, excluding the impurities

Distillation

separates liquids according to differences in their boiling points, the liquid with lowest boiling point vaporizes first and is collected as the distillate

Simple distillation

used if boiling points are under 150 C and are at least 25 C apart

vacuum distillation

should be used if boiling points are over 150 C to prevent degradation of product

Fractional Distillation

Should be used if boiling points are less than 25 C apart because allow more refined separation of liquids by boiling points

Chromatography

use two separate compounds based on physical or chemical properties

Stationary phase

usually a polar solid

Mobile Phase

runs through the stationary phase and is usually a liquid or gas, this elutes the sample through the stationary phase

Thin layer and paper chromatography

used to identify a sample

Reverse phase chromatography

uses nonpolar card with polar solvent

Column chromatography

Utilizes polarity, size affinity to separate compounds based on their physical or chemical properties

Ion exchange chromatography

beads coated with charged substances to bind compound opposite charge

size exclusion chromatography

beads have smaller pores which trap smaller compounds and allow larger compounds to travel through faster

affinity chromatography

column made to have high affinity for compounds by coating beads with receptor or antibody to compound

Gas chromatography

separates vaporizable compounds according to how well the adhere to absorbient in the column

High performance liquid chromatography

similar to column chromatography but uses sophisticated computer mediated solvent and temperature gradients. It is used if sample size is signal or if forces such as capillary action will affect results