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CHEM231 Lab Manual 2013/14

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Organic Chemistry -1 (Practical)

CHEM 231

________________________________________________________________________

Laboratory Manual 2013/2014

Pepared by

Dr. Khaid Shadid & Prof. Dr. Abdulfatah Haikal

Islamic University in Madinah


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Melting Point Determination

Identity and Purity of Solid Organic Compounds

Objectives

• To introduce the technique of melting point determination.

• To use the concept of melting points for identification and characterization of organic

compounds.

• Properly fill and use a capillary melting point tube.

• Determine accurate melting point ranges for a wide variety of organic substances.

Introduction

The melting point of a solid can easily and accurately be determined using only a small

amount of material. In combination with other measurements, melting point information can

provide rapid confirmation of the identity of unknown substances.

The method of capillary melting point determination involves placing a small amount of

sample in the bottom of a narrow capillary tube that has been closed at one end. The melting

point is then determined using a melting point apparatus (as in Figure) that simultaneously

heats both the sample tube and a thermometer. The temperature range over which the

substance melts is recorded.

Melting is said to begin when the first indication of liquid is seen. The end of the melting

point range is the temperature at which all of the solid material has become a liquid.

Some pure materials possess a very narrow melting range, perhaps as little as 0.5-1.0 °C,

while more typically a 2-3 °C range will be observed. You will usually see data recorded as, for

example, mp 232-234 °C. Though formally denoting the melting range, this piece of data is

almost universally referred to as the melting point (mp).


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For the most accurate results, the rate of heating should be kept relatively low, especially for low-

melting samples, to ensure that the thermometer reading represents as accurately as possible

the true temperature experienced by the sample tube (since the transfer of heat within the

apparatus is relatively slow). With this fact in mind, it is sensible when recording a melting

point of an unknown material to perform a trial run where the temperature range is increased

relatively rapidly in order to ascertain a rough melting range. The determination is then

repeated by heating rapidly to within around twenty degrees of the expected melting point and

then very carefully increasing the temperature the remaining few degrees until the melting

point is reached.

Apparatus for manual melting point determination.

"Mel-temp" device (left) and hot oil method (right).

Melting Points as Criteria of Purity. Thermodynamics tells us that the freezing point of a pure

material falls as the amount of an impurity is increased. The presence of an impurity in a

sample will both lower the observed melting point and cause melting to occur over a broader

range of temperature. Generally, a melting temperature range of 0.5-1.0 °C is indicative of a

relatively high level of purity. It follows that for a material whose identity is known, an estimate

of the degree of purity can be made by comparing melting characteristics with those of a pure

sample.


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Melting Points of Urea and Succinic Acid

1. Determine the melting point range of urea, then the melting point range of succinic acid .

2. The capillary melting point tubes should be filled by crushing the sample to a fine

powder on a watch glass with the end of a glass rod and then introducing this powder to

the tube by pressing the open end into the powdered sample.

3. Once a 4-5 mm depth of powder has been introduced, the tube should be turned over.

Tap the sealed end of the tube on a hard surface to compact all of the material at the

bottom.

4. Assemble the melting point apparatus as in the figure above.

5. Record the melting point range of both urea and cinnamic acid.

Compound Melting Range, °C

Acetanilide 113.5-114

Salicylic Acid 158.5-159

Sulfanilamide 165-166

Benzoic Acid 121.5-122

p-Terphenyl 210-211


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Melting Point Determination Report Sheet Melting Points of Urea and Succinic acid Melting Range Melting Range Trial 1 Trial 2 (if needed) Succinic acid ---------------- --------------- Urea ---------------- ---------------

Note

See How to fill the melting point capillaries

1. Pack the capillary tube by pressing the open end gently into a sample of compound to be analyzed. Crystals will stick in the open end of the tube.

The solid should fill the tube to a depth of 2-3 mm. Tap the bottom of the capillary on a hard surface so that the

crystals pack down into the bottom

Name:----------------------


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Recrystallization

A purification Technique for Solids

Objectives

1. To understand the concept behind recrystallization and its usefulness in organic synthesis.

2. Learn how to choose the correct solvent for recrystallization.

Introduction

Crystallization may be defined as the process in which a solid compound precipitates from a

saturated solution in the form of crystals. Saturation is usually effected through cooling or

evaporation. - Purification by recrystallization depends on the following facts:

1. Different solids have different solubilities in a given solvent.

2. Most solids are more soluble in hot than in cold solvents.

a crystallized compound

When the impure solid is dissolved in a minimum volume of a suitable hot solvent and the

resulting solution is gradually cooled, saturation and eventual crystallization of the pure

compound occurs.

Impurities in a solid are of two kinds: soluble and insoluble and recrystallization involves the

removal of both to purify a solid. Insoluble impurities are first removed by gravity filtration of

the hot solution while the soluble impurities remain dissolved in the cold saturated solution

(mother liquor) after precipitation of the desired compound. The pure crystals are separated from

the supernatant liquid by suction filtration.


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Generalized Experimental Procedure:

1. Recrystallization involves the following sequence of steps:

2. Selection of a suitable solvent.

3. Preparation of the solution.

4. Hot Filtration (Gravity Filtration).

5. Cooling.

6. Collecting and Drying of Crystals.

Each step will now be discussed more fully.

1. Selection of a suitable solvent

A suitable solvent for recrystallization should possess the following important properties:

1. Dissolve a large amount of the solid to be purified at high temperature.

2. Dissolve impurities readily at low temperatures (= soluble impurities) or not at all even at the

boiling point (= insoluble impurities).

Experimentally: the suitable solvent is determined through solubility tests.

This is done by shaking about 0.1 g of the powdered solid with ~2 mL of the given solvent in a

dry test tube. If the entire solid has nearly dissolved in the cold solvent, the solvent considered

unsuitable. If not, the mixture is heated gently to the boiling point with stirring. If most of the

solid did not dissolve, the solvent is also unsuitable.

If a substance is found to be too soluble in one solvent and insoluble in another, then a mixture

of both solvents (solvent pair) may be used. In such cases, the solvents must be completely

miscible. The compound to be recrystallized is dissolved in the solvent in which it is very

soluble and then the other solvent is added gradually at the boiling point until a slight turbidity

occurs. The solution is then allowed to stand at room temperature to effect slow crystallization

before chilling in ice.


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Table: Common solvents for Recrystallization

Solvent b.p., ◦C Particulars of Solvents

Water 100 To be used whenever suitable

Methanol 65 Flammable, toxic

Ethanol 78 Flammable

Acetone 56 Flammable

Chloroform 61 Non-flammable, vapor toxic

Cyclohexane 81 Flammable

Ethyl acetate 78 Flammable

2. Preparation of the solution

To prepare the hot solution, the finely divided solid is placed in an Erlenmeyer (conical) flask

and the selected solvent is added in small portions. The mixture is stirred and heated to boiling

after each addition, until the solid dissolves completely. A slight excess of the solvent is usually

added to compensate for any losses (through evaporation) during hot filtration.

NOTE: Decolorizing charcoal may added at this stage if the solution is colored due to colored

impurities.

The flask should be removed from the heat source before adding charcoal to it, otherwise

bumping will occur.


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3. Hot Filtration (Gravity Filtration)

Filtration of the hot solution is necessary to remove insoluble impurities. Upon addition to the

funnel, the solution will cool rapidly and this can cause unwanted precipitation. This can be

minimized, or avoided, by using a fluted filter paper and a stemless funnel placed on top of a

beaker on a hotplate containing a few milliliters of the recrystallization solvent.

4. Cooling

Cooling the filtered solution will allow crystals to form. The rate of cooling plays a role in

determining the size of the crystals that form: fast cooling will tend to generate more crystals of

small size, slow cooling can allow largest crystals to form. The best compromise of speed,

convenience, and crystal quality, is simply to let the solution cool to room temperature on the

lab bench. To ensure maximum recovery of material, the solution should be cooled in an ice-

water bath after the solution has reached room temperature.

NOTE: Scratching of the inner surface of the glass can help in crystal formation.


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5. Collecting and Drying of Crystals

When the crystallization is complete, the crystals need to be collected by suction filtration using

a Buchner funnel to ensure rapid and complete removal of the solvent. Transfer the crystalline

material as a suspension to the filter, being careful to never fill the funnel over half full. Most of

the time, it will be difficult to completely transfer all of the crystals to the funnel, quantitatively,

so it will be necessary to add a small amount of ice-cold solvent to the flask to help facilitate the

transfer of all of the crystals. The crystals are then washed with a little more ice-cold solvent to

remove any final impurities that may remain on the surface of the crystals. This solvent should

be as cold as possible to keep the crystals from redissolving.

The crystals are finally dried in an oven or allowed to air-dry, in case the melting point is low,

by spreading them over a sheet of paper.


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Experimental

� Selection of Solvent

Perform solubility tests on anthracene, salicylic acid, benzoic acid, and sodium benzoate in

water, alcohol, and ligroin as follows:

With a spatula take about 0.1 g of the powdered solid and place in a dry test tube. Start by

dissolving it in about 2 mL of solvent with stirring. If insoluble, heat the mixture to boiling (in

water bath) and observe the solubility. The results should allow the selection of a suitable

solvent for each compound.

� Recrystallization of an impure unknown

Weigh about 1 g of the impure unknown and recrystallize it from the solvent you have

selected.(By making a solubility tests on pure unknown to choose the suitable solvent).

Make sure you use the minimum volume of solvent; otherwise the amount of recovered

product will be small. Determine the weight and melting point of the purified compound.


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Recrystallization

Report Sheet

� Selection of Recrystallization Solvent

Compound

Solubility

Suitable

Solvent Water Alcohol Ligroin

Cold Hot Cold Hot Cold Hot

Sodium benzoate

Salicylic acid

Anthracene

Benzoic Acid

Name:---------------------


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Procedure for Crystallization

The photos below illustrate the process of crystallization.

Heat some solvent to boiling. Place

the solid to be recrystallized in an

Erlenmeyer flask.

Pour a small amount of the hot

solvent into the flask containing the

solid.

Swirl the flask to

dissolve the solid.

Place the flask on the steam bath to

keep the solution warm.

If the solid is still not dissolved, add

a tiny amount more solvent and

swirl again.

When the solid is all in

solution, set it on the bench

top. Do not disturb it!


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After a while, crystals should

appear in the flask.

You can now place the flask in an ice

bath to finish the crystallization process.

You are now ready to filter the solution to isolate the crystals. Please see the section on vacuum

filtration. After your crystals are filtered from the solution, put them on a watch glass as shown below.

Here is the filter paper with crystals

on it.

Carefully scrape the crystals onto

the watch glass.

Let the crystal finish drying on the

watch glass.

http://orgchem.colorado.edu/hndbksupport/filt/filtration.html#vacfilt

http://orgchem.colorado.edu/hndbksupport/filt/filtration.html#vacfilt


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Boiling Point and Distillation

Identify and Purify of Liquid Organic Compounds

Distillation as a method for the Separation of Liquids

Objectives

1. Distillating a pure liquid (acetone) and determining its boiling point.

2. Separating a mixture of acetone and water by simple distillation.

3. Separating a mixture of acetone and water by fractional distillation.

4. Compare the efficiency of each type of distillation.

Introduction

The boiling point of a pure organic liquid is a physical property of that liquid. It is

defined as the temperature at which the total vapor pressure of the liquid is equal to the

external (atmospheric) pressure.

Boiling points can be determined using the technique of simple distillation.

Simple Distillation is the condensation of vapors from a boiling liquid and collection of

the condensed vapors in a receiving vessel.

Fractional Distillation is equivalent to several repeated simple distillations.

Distillation is a technique that is used to:

- obtain a boiling point of a pure liquid.

- purify a mixture of liquids based on boiling point differences among compounds.


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Background

Boiling Points of Pure Liquids

The boiling point of a pure liquid depends on the following variables:

1- Nature of intermolecular attractive forces: H-bonding, dipole-dipole, or London forces.

2- Molar masses: boiling point increases with molar mass.

3- Shape of molecules: among isomers having the same functional group, straight chain molecules

have higher boiling points than corresponding branched ones (less molecular surface area).

Boiling Points of Solutions

The effect of any solute, A, on the boiling point of a liquid B, depends on the nature of A:

If A is less volatile than B:

the total vapor pressure of the solution is lower at any given temperature.

the boiling point of the solution is higher than that of pure B.

Example: a solution of sugar in water.

If solute A is more volatile than B:

the total vapor pressure of the solution is higher at any given temperature.

the boiling point of the solution is lower than that of pure B.

Example: a solution of acetone and water.

Simple and Fractional Distillation

- In practice, separation of a liquid mixture into its components by a single distillation

(simple distillation) is possible when the boiling points of the components are 80 degrees or

more apart.

- For mixtures of liquids having boiling points much less than 80 degrees apart, separation

can be achieved only by fractional distillation. The basic idea behind fractional

distillation is the same as simple distillation only the process is repeated many times. It

uses a fractionating column which provides a large surface area for continuous heat

exchange between the hot ascending vapor and the cooler descending liquid, thus

resulting in a series of evaporations and condensations leading to separation of the two

components.


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The Apparatus

A typical set-up for simple distillation is given in Figure 2 below.

Simple Distillation Apparatus

1: Heat source, 2: Round bottom flask, 3: Still head, 4: Thermometer, 5: Condenser, 6: Cooling water in

7: Cooling water out , 8: Distillate/receiving flask, 9: Vacuum/gas inlet, 10: Still receiver, 11: Heat control

12: Stirrer speed control , 13: Stirrer/hot plate, 14: Heating (Oil/sand) bath, 15: Stirrer bar/anti-bumping

granules , 16: Cooling bath.

Observe the following practical points:

1- The boiling flask should not be more than half full.

2- Boiling stones are added to the liquid to prevent bumping.

3- Each ground joint should be greased to ensure a completely sealed system.

4- Cooling water in the condenser should enter at the lower end and exit at the upper end. This

ensures that the condenser jacket is always full of water.

5- The bulb of the thermometer should be below the opening of the side arm so as to measure the

temperature at which liquid and vapor are in equilibrium.

http://en.wikipedia.org/wiki/Image:Simple_distillation_apparatus.png


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The photo below is for a fractional distillation set-up. The only difference between this set-up and that of

a simple distillation set-up is the inclusion of a fractionating column (Figure 4) between the round

bottom flask and the Y-adaptor (still head).

Fractional Distillation Apparatus Fractionating Columns

Experimental

Determination of Boiling Point (bp) of Pure Acetone

Arrange a simple distillation apparatus. Introduce about 20 mL of acetone and a few boiling

stones in a 50 mL round-bottomed flask. Heat gently so that the distillate collects in the receiver

drop by drop. Make sure that there is a drop of liquid hanging from the bulb of the thermometer

to ensure that the thermometer is reading the correct bp. Absence of this drop indicates

superheating. Wait until 1-2 mL of the distillate have been collected before recording the

temperature. Continue the distillation until about 2 mL of residue are left in the distillation flask,

and record the temperature again. Keep the acetone for the following part.

Separation of a Mixture

(Simple Distillation)

Make a mixture of the two liquids (acetone-water) 20 mL each and pour it into a 100 mL round

bottomed flask. Carry out a simple distillation as before and collect five fractions in the following

boiling ranges: 50-62, 62-72, 72-82, 82-95 plus the fifth fraction which is the residue. Measure the

volume of each fraction and record the results.


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(Fractional Distillation)

Combine the five fractions and pour into a 100 ml round-bottomed flask, attach the fractionating

column and proceed as for simple distillation. Measure the volume of each fraction as before and

record your results.


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Boiling Point and Distillation

Report Sheet

Simple Distillation of Pure Acetone

Boiling point of pure acetone: ---------

Separation of a Mixture of Acetone and Water

1.

Fraction Boiling Range, °C Volume of Distillate, mL

Simple Fractional

Composition

I 50-62

II 62-72

III 72-82

IV 82-95

V residue

2. Plot the boiling point versus the volume of distillate for the acetone-water mixtures using

simple and fractional distillation.

Name:----------------------


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Chromatography

A Separation and Purification Technique

Introduction

Chromatography is a technique that may be used:

1. to separate the components of a mixture as well as 2. to identify organic substances and 3. examine their purity.

Chromatography encompasses several techniques such as column, thin-layer, paper, gas

liquid, etc.

Two principles are basically involved in Chromatography: adsorption (as in thin-

layer Chromatography) and partition (as in paper Chromatography), and certain terms are

common to both types of Chromatography.

In adsorption Chromatography, separation depends on the selective desorption of the

components of a mixture by the eluent (mobile phase) from the surface of a solid

adsorbent (stationary phase). The adsorbent may be packed in a column (Column

Chromatography) or spread as a thin layer on a glass plate as in thin-layer

Chromatography.

In partition Chromatography, separation depends on partition of the components of a

mixture between the stationary and mobile phases. The mobile phase may be a

liquid (liquid-liquid partition Chromatography) or a gas (gas-liquid partition

Chromatography).


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ANALYSIS OF CHROMATOGRAMS:

In thin layer and paper Chromatography, substances are characterized by their Rf values

(retardation factor). The Rf-value is a number (less than one) which is characteristic of a

compound for a given adsorbent and developing solvent.

The retention factor, or Rf, is defined as the distance traveled by the compound divided by

the distance traveled by the solvent.

For example, if a compound travels 2.1 cm and the solvent front travels 2.8 cm, the Rf is 0.75:

The Rf for a compound is a constant from one experiment to the next only if the

chromatography conditions below are also constant:

solvent system

adsorbent

thickness of the adsorbent

amount of material spotted

temperature

Since these factors are difficult to keep constant from experiment to experiment, relative Rf

values are generally considered. “Relative Rf” means that the values are reported relative to a

standard, or it means that you compare the Rf values of compounds run on the same plate at the

same time.

The larger an Rf of a compound, the larger the distance it travels on the TLC plate. When

comparing two different compounds run under identical chromatography conditions, the


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compound with the larger Rf is less polar because it interacts less strongly with the polar

adsorbent on the TLC plate. Conversely, if you know the structures of the compounds in a

mixture, you can predict that a compound of low polarity will have a larger Rf value than a

polar compound run on the same plate.

The Rf can provide corroborative evidence as to the identity of a compound. If the identity of a

compound is suspected but not yet proven, an authentic sample of the compound, or standard,

is spotted and run on a TLC plate side by side (or on top of each other) with the compound in

question. If two substances have the same Rf value, they are likely (but not necessarily) the same

compound. If they have different Rf values, they are definitely different compounds. Note that

this identity check must be performed on a single plate, because it is difficult to duplicate all the

factors which influence Rf exactly from experiment to experiment.

In gas-liquid chromatography, compounds are characterized by their retention times.

THIN-LAYER CHROMATOGRAPHY (TLC):

This is one application of adsorption chromatography in which an adsorbent, usually silica gel

or alumina, is spread out as a thin layer on an inert surface, such as a glass plate or microscope

slide. The mixture is applied at one end of the coated plate and, as the mobile phase (a liquid)

moves up the solid adsorbent by capillary action, the adsorbed components of the mixture get

desorbed and carried along at different rates by the moving solvent. Adsorption of the

components of the mixture, on the surface of the adsorbent, occurs to differing extents

depending on their structural features and polarity. The more strongly adsorbed a given

compound is, the slower it is transported by the mobile phase, and conversely, the more weakly

adsorbed the compound is, the faster it is transported up the stationary phase. The result is that

the components of the mixture are separated into different zones or spots.

Separation by thin-layer chromatography


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Separation by thin-layer chromatography depends on:

1. the kind and activity of the adsorbent (stationary phase). 2. the polarity of the eluent (mobile phase). 3. the chemical nature of the components of the mixture.

The most common adsorbents employed in TLC are silica (SiO2.xH2O) and alumina (Al2O3.

xH2O), and the activity of these adsorbents is largely determined by their water content. For a

given adsorbent and compound, the greater the polarity of the eluent, the greater is its ability to

dislodge a compound from the surface of the adsorbent, and therefore the higher the Rf-value.

Eluting power of solvents:

Acetic acid > Ethyl alcohol > Acetone > Diethyl ether > Dichloromethane > Hexane.

GENERALIZED EXPERIMENTAL PROCEDURE

Preparation of TLC Plates. Large glass plates (20x20 cm) are commonly used for quantitative separations, while microscope slides are usually used for qualitative purposes. A homogeneous slurry of the adsorbent in a volatile organic solvent (chloroform or dichloromethane) is poured over the glass plates and allowed to air-dry at room temperature. Microscope slides can be coated, two at a time, by dipping them into the slurry for sometime then holding them vertically to air-dry. The jar of adsorbent must be shaken thoroughly before each use to homogenize the slurry.

Spotting. The mixture to be analyzed is dissolved in a suitable solvent (1% solution). With a drawn capillary tube, a small amount of this solution is spotted on the TLC plate about 1 cm from the bottom. The spots should have a diameter not larger than 1-2 mm, since larger spots result in "tailing" and overlapping of close spots. Once the solvent evaporates from the spots, the plate is ready for developing.

Development of the Chromatogram. The eluent, also called developing solvent, is chosen on the basis of the nature and polarity of the compounds being studied. It is best to choose the solvent that will give a satisfactory separation within the range of 0.2-0.8 Rf values. The plate is placed in a developing chamber (e.g. a covered beaker) containing the solvent and lined with filter paper soaked in the solvent to help saturate the atmosphere with solvent vapors. When the solvent front reaches the finish line, the plate is removed from the beaker and placed on the bench top to air-dry.


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Visualization of Spots. Compounds on the plate are located according to their characteristics:

a). If the spots are colored, they can be observed in ordinary light.

b). If the compounds are colorless, they can be seen under UV-light where they appear as dark

spots on a white background.

c). Colorless spots may also be located with an indicator. Most organic compounds form

complexes with iodine giving dark brown spots when the plate is exposed to iodine vapor.

Sulfuric acid may also used to make colorless spots visible. Most organic compounds turn black

when sprayed with sulfuric acid.

COLUMN CHROMATOGRAPHY: تم إضافة هذا الجزء المهم باألسفل الرتباطه الوثيق بما سبق لكنة غير مطلوب

In column chromatography, the stationary phase, a solid adsorbent, is placed in a vertical

glass (usually) column and the mobile phase, a liquid, is added to the top and flows down

through the column (by either gravity or external pressure). Column chromatography is

generally used as a purification technique: it isolates desired compounds from a mixture.

The mixture to be analyzed by column chromatography is applied to the top of the column.

The liquid solvent (the eluent) is passed through the column by gravity or by the application of

air pressure. An equilibrium is established between the solute adsorbed on the adsorbent and

the eluting solvent flowing down through the column. Because the different components in the

mixture have different interactions with the stationary and mobile phases, they will be carried

along with the mobile phase to varying degrees and a separation will be achieved. The

individual components, or elutants, are collected as the solvent drips from the bottom of the

column.

Column chromatography is separated into two categories, depending on how the solvent

flows down the column. If the solvent is allowed to flow down the column by gravity, or

percolation, it is called gravity column chromatography. If the solvent is forced down the

column by positive air pressure, it is called flash chromatography, a "state of the art" method

currently used in organic chemistry research laboratories. The term "flash chromatography" was

coined by Professor W. Clark Still because it can be done in a “flash."


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Columns Packed Column Column Chromatography

The Adsorbent

Silica gel (SiO2) and alumina (Al2O3) are two adsorbents commonly used by the organic chemist

for column chromatography. These adsorbents are sold in different mesh sizes, as indicated by

a number on the bottle label: “silica gel 60” or “silica gel 230-400” are a couple examples. This

number refers to the mesh of the sieve used to size the silica, specifically, the number of holes in

the mesh or sieve through which the crude silica particle mixture is passed in the

manufacturing process. If there are more holes per unit area, those holes are smaller, thus

allowing only smaller silica particles go through the sieve. The relationship is: the larger the

mesh size, the smaller the adsorbent particles.

Adsorbent particle size affects how the solvent flows through the column. Smaller particles

(higher mesh values) are used for flash chromatography, larger particles (lower mesh values)

are used for gravity chromatography. For example, 70–230 silica gel is used for gravity columns

and 230–400 mesh for flash columns.

Alumina is used more frequently in column chromatography than it is in TLC. Alumina is quite

sensitive to the amount of water which is bound to it: the higher its water content, the less polar

sites it has to bind organic compounds, and thus the less “sticky” it is. This stickiness or activity

is designated as I, II, or III, with I being the most active. Alumina is usually purchased as

activity I and deactivated with water before use according to specific procedures. Alumina

comes in three forms: acidic, neutral, and basic. The neutral form of activity II or III, 150 mesh,

is most commonly employed.


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The Solvent

The polarity of the solvent which is passed through the column affects the relative rates at

which compounds move through the column. Polar solvents can more effectively compete with

the polar molecules of a mixture for the polar sites on the adsorbent surface and will also better

solvate the polar constituents. Consequently, a highly polar solvent will move even highly polar

molecules rapidly through the column. If a solvent is too polar, movement becomes too rapid,

and little or no separation of the components of a mixture will result. If a solvent is not polar

enough, no compounds will elute from the column. Proper choice of an eluting solvent is thus

crucial to the successful application of column chromatography as a separation technique. TLC

is generally used to determine the system for a column chromatography separation. Often a

series of increasingly polar solvent systems are used to elute a column. A non-polar solvent is

first used to elute a less-polar compound. Once the less-polar compound is off the column, a

more-polar solvent is added to the column to elute the more-polar compound.

Interactions of the Compound and the Adsorbent

Compounds interact with the silica or alumina largely due to polar interactions.

Analysis of Column Eluents

If the compounds separated in a column chromatography procedure are colored, the progress

of the separation can simply be monitored visually. More commonly, the compounds to be

isolated from column chromatography are colorless. In this case, small fractions of the eluent

are collected sequentially in labeled tubes and the composition of each fraction is analyzed by

thin layer chromatography. (Other methods of analysis are available; this is the most common

method and the one used in the organic chemistry teaching labs.).

This Figures shows the use of column chromatography

1 2 3 4 5 …..

Column Chromatography


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Alcohols

Classification and tests

Objective:

1. Determine chemical and physical properties of alcohols.

2. Classify an alcohol as primary, secondary, or tertiary.

3. Perform a chemical test to distinguish between the classes of alcohols.

4. Write the formulas of the oxidation products of alcohols

Structures of Alcohols

Alcohols are organic compounds that contain the hydroxyl group (–OH). The simplest alcohol

is methanol. Ethanol is found in alcoholic beverages and preservatives, and is used as a solvent.

2-Propanol (isopropanol), also known as rubbing alcohol, is found in astringents and perfumes.

Classification of Alcohols

In a primary (1°) alcohol, the carbon atom attached to the –OH group is bonded to one other

carbon atom. In a secondary (2°) alcohol, it is attached to two carbon atoms and in a tertiary (3°)

alcohol to three carbon atoms.


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1. Properties of Alcohols Materials: 4 test tubes, pH paper, stirring rod, methanol, ethanol, 2-propanol, t-butyl

alcohol (2-methyl-2-propanol).

Odor: Place 5 drops of each of the alcohols, phenol to four separate test tubes. Carefully

detect the odor of each.

Solubility in water Add about 2 mL of water (40 drops) to each test tube. Shake and

determine whether each alcohol is soluble or not. If the substance is soluble in water, you

will see a clear solution with no separate layers. If it is insoluble, a cloudy mixture or

separate layer will form. Record your observations.

Acidity Obtain a container of pH paper. Place a stirring rod in one of the alcohols and touch

a drop to the pH paper. Compare the color of the paper with the chart on the container to

determine the pH of the solution. Record your observations. Note: DISPOSE OF ORGANIC SUBSTANCES IN DESIGNATED WASTE CONTAINERS!

2. Oxidation of Alcohols

The Bordwell-Wellman test solution contains potassium dichromate dissolved in sulfuric

acid. It is an orange-yellow solution. The orange-yellow color is due to the Cr2O7 2- ion. The

oxidation number of chromium is +6. This reagent will oxidize primary and secondary

alcohols and, in turn, becomes reduced. The chromium in dichromate is reduced to chromic

ion, Cr+++.

A greenish colored solution results. This color change from orange-yellow to green serves

as an indicator for the presence of a primary or secondary alcohol. A primary alcohol is

oxidized first to an aldehyde, which will be further oxidized to an acid.

Materials: 4 test tubes, methanol, ethanol, 2-propanol, t-butyl alcohol (2-methyl-2-

propanol), 1% potassium dichromate solution, conc. H2SO4

Procedure: Place 3 mL of 1 % of potassium dichromate and 2 drops of conc. H2SO4 in each

of four test tubes. Mix thoroughly and add 2 drops of the alcohols. Shake the tube and Look

for a color change.

If the orange color turns to green in 1–2 minutes, oxidation of the alcohol has taken place. If

the color remains orange, no reaction has occurred. If a test tube becomes hot, place it in a

beaker of ice-cold water. Record your observations.

Caution: Concentrated H2SO4 is corrosive.


30

General reaction equation:

Experimental equation:

Methanol:

Ethanol:

Isopropanol:

2-methyl-2-propanol:

K2Cr2O7

H2SO4

CH3OH HCOOHgreenCr 3+

K2Cr2O7

H2SO4

CH3CH2OH CH3COOHgreenCr 3+

CH3CHCH3

K2Cr2O7

H2SO4 greenCr 3+

OH

C

O

H3C CH3

K2Cr2O7

H2SO4

C

CH3

H3C

CH3

OH No Reaction


31

3. Lucas Test: for Primary, Secondary and Tertiary Alcohols.

The Lucas reagent is a solution of zinc chloride in concentrated HCl. This solution must

be made freshly to get proper results. The test depends on a difference in the rate of

reaction of these alcohols. The general equation for the reaction is:

Tertiary alcohols react IMMEDIATELY. The test tube will get hot, and because

the chloride is insoluble two layers may be apparent, or a cloudy dispersion

forms.

Secondary alcohols will become cloudy in 5 to 10 minutes. If cloudiness does not

appear place test tube in a hot water bath and observe.

Primary alcohols give no reaction in a reasonable length of time.

CAUTION! Lucas reagent contains concentrated hydrochloric acid - Handle It With Care

Procedure

1. Place 1 ml of Lucas reagent in each of three clean test tubes.

2. Add 4 drops of ethanol to one test tube. Shake the test tube to mix the reagents and

notice whether the mixture gets cloudy and how long it takes.

3. In a second test tube place 4 drops of Isopropanol, shake and note how long it takes the

tube to get cloudy.

4. In a third test tube place 4 drops of 2-methyl-2-propanol, shake and note how long it

takes the tube to get cloudy.

5. Record observations on the Report Sheet. Dispose of these reagents in the "Halogenated Organic Liquid Waste" container in the hood.


32

4. Iodoform Test

The iodoform test is used to identify secondary alcohols that have a methyl group on the

alcohol carbon. This type of alcohol will react with I2 in NaOH to give a yellow

precipitate of iodoform, CHI3. The reaction is shown below.

The formation of a yellow precipitate in the test solution is taken as a positive reaction,

and it means that the reactant alcohol was a secondary alcohol with a methyl group on

the alcohol carbon.

Procedure: To test methanol, ethanol and isopropanol, Place about 1 mL of water (20 drops)

in each of 3 test tubes. Add 5 drops of the alcohols to be tested. Add 10 drops of 10% NaOH

and mix by shaking each tube side to side. Add 10 drops of KI/iodine solution and shake to

mix. A yellow precipitate indicates a positive reaction. Record observations on the Report

Sheet.


33

5. Methyl Salicylate (Wintergreen Oil)

1. Transfer about 0.5 g of salicylic acid to clean and DRY large test tube and add 1 mL of

methanol.

2. Holding the top of the tube, tap the bottom with your finger to stir the mixture.

Dissolve the salicylic acid completely in the methanol.

3. Carefully add 3 to 4 drops of concentrated H2SO4 to the mixture (in the hood) and mix

again by tapping the bottom of the tube with your finger.

4. Place this mixture in the hot water bath for 10 min to complete the reaction.

5. After the reaction is complete, remove the test tube from the water bath and allow it to

cool. Turn off the hot plate under the water bath.

6. After it has cooled, carefully waft the fumes by passing your hand over the top of the

tube toward your nose. Can you smell the minty aroma of wintergreen?

7. If you have difficulty smelling it, you can pour hot water from the water bath into the

tube. The aroma of the methyl salicylate should be apparent after it has mixed with

warm water.

8. Record your observations and answer the questions on the Report Sheet.

COOH

OH

CH3OHH2SO4

COOCH3

OH

H2O


34

Alcohols Report Sheet

1. Solubility in water

Alcohol Structure Solubility

2. Oxidation of Alcohol

Alcohol Reaction equation Observations

3. Lucas Test

Alcohol Structure of Product Observations

4. Iodoform Test

Alcohol Structure of Product Observation

5. Formation of Methyl Salicylate

Alcohol Reaction equation Observation

Name:----------------------


35

Aldehydes and Ketones


Objective:

5. Determine chemical and physical properties of aldehydes and ketones.

6. Perform a chemical test to distinguish between aldehydes and ketones

Structures of Aldehydes and Ketones

The major similarity between an aldehyde and a ketone is the carbonyl group. A

carbonyl group is a carbon atom doubly bonded to an oxygen atom.

C

O

Both molecules have a carbonyl group, the difference the number of carbons bonded to

the carbonyl carbon. An aldehyde will have none or one and a ketone will have two

carbons.

All aldehydes, except formaldehyde, will have a hydrogen atom on one side of the

carbonyl carbon and at least on carbon on the other side.

C

O

HR

All ketones have a carbon on each side of the carbonyl carbon.

C

O

RR

C

O

HH C

O

HCH3 C

O

H

formaldehyde acetaldehyde benzaldehyde

C

O

CH3CH3 C

O

CH3CH3CH2 C

O

CH2CH3CH3CH2

O

Acetone butanone 3-pentanone cyclohexanone


36

H+

H+

1. The Bordwell-Wellman test solution contains potassium dichromate dissolved in sulfuric

acid: This test was used earlier when testing alcohols. Aldehydes are more rapidly oxidized

than ketones due to the hydrogen atom bonded to the -carbon. Aldehydes are oxidized to

carboxylic acids.

R

O

H

[O]

strong oxidizing agent R

O

OH

aldehyde carboxylic acid

Ketones are not readily oxidized, which makes the two functional groups easily

distinguishable. Only under extreme conditions (strong reagents and high temperature) can

ketones be oxidized since the reaction requires the cleavage of a carbon-carbon bond.

Procedure: Add two drops of the carbonyl compound (Acetone, Acetaldehyde, and

Benzaldehyde) to 0.5 mL of the orange reagent (K2Cr2O7) in a test tube. Shake the tube vigorously

and heat in a water bath for about 3 - 4 minutes. Good mixing is essential, especially with water-

insoluble compounds. A few aldehydes may require longer heating; -- aromatic aldehydes are

more difficult to oxidize than aliphatic ones.

Test Tube Rxn:

C

O

HCH3 722 OCrK

C

O

OHCH3

Test Tube Rxn:

C

O

CH3CH3 722 OCrK NR


37

2. Tollen’s Test: Commonly known as the Silver Mirror Test, this distinctive qualitative test

involves the oxidation of aldehydes to their corresponding carboxylic acid. The oxidizing agent

is a silver complex ion [Ag(NH3)+2] which is reduced to a metallic silver which remains on the

walls of the test tube as a mirror. Otherwise, the silver is deposited as a black precipitate.

Tollen’s reagent is prepared by dissolving silver oxide in ammonia:

2 AgNO3 + 2 NaOH Ag2O (s) + H2O + 2 NaNO3

Ag2O (s) + 4 NH3 + H2O 2 Ag(NH3)2 OH

Tollen's Reagent

+ 2 Ag(NH3)2 OHR

O

H R

O

O NH4+ 2 Ag + 3NH3 + H2O

silver

Procedure: add 3 to 4 drops of (Acetaldehyde, Benzaldehyde, and Acetone) to a basic solution of

AgNO3, NH3, ammonia is normally the base, if the test tube shows a mirrored surface, this is a

positive test for an aldehyde, gentle heating may be necessary. Ordinary ketones do not react with

the reagent.

To prepare Tollen's reagent: add 2 mL of 5% silver nitrate, and ONE DROP of 10% (3M) NaOH.

Mix the ingredients THOROUGHLY by STIRRING. If necessary addition of dropwise 2%

ammonia solution.

CAUTION!! Discard any unused Tollen's reagent after you have completed the tests. EXPLOSIVE

PRECIPITATES DEPOSIT ON STANDING!!

Grey Precipitate


38

3. Iodoform Test: The Iodoform test was performed earlier on alcohols. The yellow ppt may be

collected on Buchner, washed with 10% NaOH, and dried. If there is doubt, its m.p. will con-

firm its identity. Since the procedure here is identical with that of the alcohols, this test will be

omitted here.

Iodoform Test for Methyl Ketones

Ketones containing a methyl group attached to the carbonyl give a reaction with iodine (I2) in a

NaOH solution. The reaction produces solid, yellow iodoform, CHI3.

Iodoform, which has a strong medicinal odor, is used as an antiseptic.


39

Aldehydes and Ketones Report Sheet

1. Acetaldehyde:

Physical State: Color: Odor:

2. Benzaldehyde:


3. Acetone:


6. Oxidation of Aldehyde and Ketone

Reaction equation Observations

Acetaldehyde

Benzaldehyde

Acetone

7. Tollen’s Test

Reaction equation Observations

Acetaldehyde

Benzaldehyde

Acetone

8. Iodoform Test

Structure of Product Observation

Acetaldehyde

Benzaldehyde

Acetone

Name:----------------------


40

Carboxylic Acids


Objective:

7. Determine chemical and physical properties of carboxylic acid.

8. Perform a chemical test to distinguish carboxylic acids.

Structures of Carboxylic acids

Carboxylic acids are organic compounds that have a carboxyl group attached to an alkyl

group (R-COOH) or to an aryl group (Ar-COOH). The 'R' may be a hydrogen and the

result is formic acid. They may be mono carboxylated, multi carboxylated, substituted (e.

g., hydroxyl groups), or they may be aromatic

Physical properties

1. Only formic acid, acetic acid, and lactic acid are liquids at room temperature. The

others are solids. 2. Low molecular weight carboxylic acids are soluble in water. Water insoluble acids

dissolve in both sodium hydroxide solution and sodium bicarbonate solution, they

evolve carbon dioxide gas. This is considered as a good simple indication of them.

3. Aromatic carboxylic acids burn with a yellow smoky flame whereas aliphatic ones

bum with a blue flame without smoke.

4. Their boiling points are generally high due to the association through hydrogen


41

bonds: two molecules of the carboxylic acid are held together by two hydrogen bonds

rather than one.

Chemical properties

The acidic properties of carboxylic acids are attributed to the proton of the carboxyl

group. Mono carboxylic acids are weak acids except formic acid, which is the strongest.

The tendency of the alkyl group to release electrons weakens the acid; thus formic acid is

the strongest. On the other hand presence of electron withdrawing groups (such as

halogens) especially on the alpha carbon increases the acidity.

Reactions of carboxylic acids are related to:

The proton as in salt formation reactions.

Removal of the hydroxyl group as in conversion to derivatives such as esters,

amides, or acid chlorides.

Substitution either in the alpha position of aliphatic acids or in the meta position

of aromatic ones.

1. Solubility Test: All aliphatic carboxylic acid are water soluble and change litmus paper from blue

to red color.

All aromatic carboxylic acid are water insoluble. Soluble in 10% NaOH due to its

acicdity

2. General test (Ferric chloride FeCl3 test) The acid solution should be made neutral before performing the test with ferric chloride

solution. This is achieved by adding very dilute ammonia solution drop by drop with

shaking to a solution of about 0.5 g of the solid acid or 2 drops of the liquid acid in 1 mL

water until the medium becomes basic. At this stage the solution is slightly basic. To

make the solution neutral the excess ammonia should be removed by gently heating the

test tube in a water bath with shaking from time to time until the odor of ammonia

disappears. (In case of oxalic, tartaric, citric and lactic acids keep a portion of their

neutral solution for use in calcium chloride test). Cool the solution and then add few

drops of ferric chloride solution to get different colors (solutions or precipitates) as

follows:


42

1. 2. 3. 4.

3. Special test for acetic acid (ester formation)

Acetic acid, on contrary to formic acid, neither can be oxidized by, nor can reduce any of

the reagents applied to formic acid. Instead, it undergoes ester formation reaction:

Mix 1 mL of acetic acid with 2 mL of ethanol in a test tube and add to this mixture 2-3

drops of concentrated sulphuric acid. Heat the test tube in a water bath for 10 minutes,

and then pour the mixture into another test tube containing 5 mL sodium bicarbonate

solution; the characteristic fruity odor of ethyl acetate can be smelt, which indicates the

formation of this ester.

4. Special test for salicylic acid (ester formation)

In addition to the characteristic violet colour obtained with ferric chloride, salicylic acid

can also be detected by ester formation test. In this test methyl salicylate ester separates

out as an organic phase having a characteristic odor.

Follow the same procedure and conditions used for esterification of acetic acid but use

methanol instead of ethanol. Not that methanol is toxic internally so never withdraw it

by mouth to avoid accidental ingestion.

5. Reaction with Na2CO3

Carboxylic acid + Na2CO3 Strong effervescence (CO2 )

6. Reaction with calcium chloride CaCl2 General Carboxylic acid + CaCl2 + NH4OH precipitate 1. Oxalic acid: white ppt will dissolve in dil HCl, will not dissolve in acetic acid 2. Tartaric acid: white ppt with test tube scratching. The ppt will dissolve in acetic

acid 3. Citric acid: white ppt after heating, will not dissolve in acetic acid


43

Carboxylic acid Report Sheet

9. Solubility in water:

Carboxylic acid Structure Solubility

Acetic acid

Oxalic acid

Citric acid

Tartaric acid

Benzoic acid

Salicylic acid

10. Ferric chloride FeCl3:

Carboxylic acid Observation Conclusion

Acetic acid

Oxalic acid

Citric acid

Tartaric acid

Benzoic acid

Salicylic acid

11. Ester forming:


Acetic acid

Salicylic acid

Name:----------------------


44

12. Reaction with Na2CO3:


Acetic acid

Oxalic acid

Citric acid

Tartaric acid

Benzoic acid

Salicylic acid

13. Reaction with calcium chloride CaCl2


Oxalic acid

Citric acid

Tartaric acid

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