organic analysis chemistry part -4

8/14/2019 Organic Analysis Chemistry Part -4

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EXTRACTIONS : SEPARATIONS BASED

UPON SALT FORMATION

The separation of aniline from

toluene

– is effected by extraction withdilute hydrochloric acid.

– The aniline goes into the

aqueous layer as its salt, aniline

hydrochloride.

– Whereas aniline is very soluble

in toluene and virtually insoluble

in water, its hydrochloride salt,

because of its polar nature, is

soluble in water and insoluble in

toluene.



Phenol from Toluene



Mixture contains than 2 compounds????Mixture contains than 2 compounds????

combinations methods of separations.combinations methods of separations. The condition for successful separation The condition for successful separation

is that :is that :

the components be such that a widethe components be such that a wide polarity difference exists polarity difference exists oror

can be induced between any two of can be induced between any two of

them.them.



Extraction of Water Insoluble

Mixtures

These procedures are

used after the water

solubility test

Assumption: all possible fractions are

obtained



Extraction of Water Soluble

Mixtures

If all components of themixture are water soluble,steam distillation is the bestmethod for the separation.

However, it may prove to beunsatisfactory if the mixture isnot chosen carefully thecomponents of the mixtureundergo reaction with eachother or with boiling aqueous

acid or alkali during steamdistillation. Extraction, which does not

involve heating of the mixture,would be preferable.



• Sample:– mixture of acetic

acid, butanol, butyl

acetate, water



Is the separation of the components of a mixture by theselective distribution of the components between a mobile

phase and a stationary phase. Chroma meaning "color" and graphy meaning "written“(Greek). The mobile phase

– Is a liquid or a gas and carries the compounds along acolumn.

The stationary phase – may be composed of various types of materials,

– for example, silica gel in column chromatography. The ability to separate is based on selective and preferential

absorption of these components in the mobile phase by thestationary phase.



Organic chemists are interested in : – gas chromatography (GC) and liquid chromatography (LC).

Gas chromatography is useful for relatively volatile and thermally stable organic

compounds. – This method involves a gaseous mobile phase, which is usually helium or,

less frequently, nitrogen. – The stationary phase is either a liquid adsorbed on a solid support, an

organic compound bonded to a solid support, a solid, or a nonvolatile liquid. Liquid chromatography uses a liquid mobile phase, which is usually a common

organic solvent. –

The stationary phase may consist of a liqUid adsorbed onto a solid support,an organic species spread over a solid support, a solid, or a resin. – Examples of liquid chromatography are

column chromatography, high-performance liquid chromatography (HPLC), and thin layer chromatography (TLC).



Gas Chromatography – 1. The sample should be volatile and reasonably stable to heat.

– 2. Simple gas chromatographs are inexpensive, are easy to operate, andgive results rapidly.

Liquid Chromatography – 1. Duration: With the simple gravity flow columns, the separation of the

components is time consuming.Rapid analyses are carried out with HPLC and flash chromatography.

– 2. Stability: A small percentage of organic compounds may react with thestationary phase of some columns.Proper choice of conditions, in order to prevent undesirable side reactions,allows virtually any organic compound to be analyzed by LC.

– 3. Cost: Flash and other types of column chromatography are fairly cheap;

HPLC has a much higher initial cost, because of the high-quality pumps andcolumn packings that are necessary.



the most rapid, easiest, andmost often applied methodfor accessing Organiccompounds.

the immobile phase is a thinlayer of adsorbent spreadover a sheet of glass or plastic

Compounds can be detectedon TLC sheets in variousways. The simplest is to usea low-power hand-held UVlight.



Developing SolventDeveloping Solvent

IncreasingIncreasing

polaritypolarity Determination of solvent for

TLC

Good – over– under developed



Preparation for TLC



DevelopmentDevelopment



ResultResult

Rf ?



Column ChromatographyColumn Chromatography



Types of Columns Types of Columns



Packed chromatographyPacked chromatography

columncolumn Slurry PackedSlurry Packed

ColumnsColumns

The solvent is usedThe solvent is usedto pack the columnto pack the column..



The column is prepared dry without the use of

solvent and developed just once with a Single

volume of solvent, in contrast to the slurry methodand multiple volumes of solvent in traditional column

chromatography.

Using the dry column technique, columns as long as

6 ft have been packed and mixtures of mass of up to50 g have been separated.



Flash Chromatography

In flash chromatography, the

column is pressurized with a

flow control adaptor attached to the top of the

column to pressure the

column

The flow control adaptor is

attached to an air line at amedium pressure.

Fast separation



High-Performance Liquid

Chromatography (HPLC)



Chemical Tests for Functional Groups

Homework



Spectroscopy

UV

IRMS

NMR

organic analysis chemistry part -4

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