Organic Chemistry

EXERCISE 1

PROPERTIES THAT DISTINGUISH ORGANIC FROM INORGANIC COMPOUNDS

Organic CompoundsInorganic Compound

Flammableyesno

Melting Pointlowhigh

Boiling Pointlowhigh

Solubility in waterno (for most)yes

Solubility in non-polar liquidsyesno

Type of bondingcovalentionic

Reactions occur between:moleculesions

Atoms per moleculemanyfew

Structurecomplexsimple

Electrolytenoyes

Organic compounds are unstable. They are combustible, with many having no sharp melting points, decomposing, and charring at moderately high temperature.

Most are non-electrolytes.

Most organic compounds contain the same kind and number of atoms but they exhibit different sets of properties.

Organic chemical reactions are relatively slow.

Name of TestTest CompoundResult

Ignition Tests

a. FlammabilityEthyl alcoholFlammable

WaterNon-flammable

b. CharringSucrosePositive

C12H22O11 + O2 + heat CO2 + 11H2O + 11C

Sodium chlorideNegative

Calcium carbonateNegative

Name of TestTest CompoundObservationType of Bond

Solubility TestsNaphthalene in waterInsoluble

Naphthalene in etherSolubleCovalent bond

Urea in waterPartially solubleH-bonding

Urea in etherSolubleCovalent bond

Sodium chloride in waterSolubleIonic bond

Sodium chloride in etherInsoluble

Name of TestTest CompoundObservation

Electrical Conductivity1M sucroseNon-electrolyte

1M sodium chlorideElectrolyte

95% ethyl alcoholNon-electrolyte

n-hexaneNon-electrolyte

EXERCISE 2

QUALITATIVE TESTS FOR ELEMENTS IN ORGANIC COMPOUNDS

Carbon and hydrogen are the predominant elements found in organic compounds.

Next common elements are: oxygen, nitrogen, sulfur, phosphorus, halogens chlorine, bromine, and iodine.

Least common elements include: arsenic, antimony, mercury, and other metals.

A. Test for Carbon and Hydrogen

Test compound: Glucose (C6H12O6)

Carbon and hydrogen are detected qualitatively by heating a mixture of the given substance with dry copper (II) oxide in a glass tube.

C6H12O6 + CuO CO2 + H2O

CO2 + Ca(OH)2 CaCO3 + H2O

Glucose + CuO

heat

CO2

water vapor

gets trapped in lime water

Calcium carbonate

Water

The presence of carbon is indicated by the formation of white precipitate.

The presence of hydrogen is indicated by the formation of droplets of water in the cool end of the tube.

Copper (II) oxide acts as a catalyst.

B. Test for Nitrogen

Name of test: Soda-Lime Test Test compound: Urea

Soda-lime: NaOH-CaO (2:1 solid mixture)

Nitrogen is usually detected by the formation of Prussian blue after the sodium fusion.

CO(NH2)2 + heat NH3 + CO2 CO2 + Ca(OH)2 CaCO3 + H2O

When heated with soda lime, urea decomposes and the nitrogen in the form of amino nitrogen (-NH2) will liberate ammonia gas.

Red litmus paper changes to blue.

C. Test for Halogen

Name of test: Beilstein Test Test compound: Chloroform (CHCl3)

An organic halogen compound imparts a green color flame when burned upon the surface of a copper wire.

The copper oxide formed from the copper wire reacts with the halogens to form the cuprous halide, which burns with a green flame.

Chlorine is the compound responsible for turning the flame green.

Name of test: Silver Nitrate Test Test compound: Monochloroacetic acid

Formation of insoluble silver halide upon treatment with silver nitrate in the presence of dilute nitric acid.

Nitric acid is necessary to remove cyanide and sulfide ions, otherwise, they form precipitates silver cyanide is white and silver sulfide is black that interfere with the detection of halogens.

Silver chloride white precipitate.

D. Test for Oxygen

Name of test: Ferrox Test Test compounds: Acetone, ethyl alcohol, gasoline, benzene

Ferrox paper is prepared by soaking filter paper in methanol containing equal amounts of ferric chloride and ammonium thiocynate.

In the presence of oxygen, a deep red color is distributed between the filter paper and the test compound.

The test showed positive results for acetone and ethyl alcohol.

E. Test for Sulfur

Name of test: Lead Acetate Test Test compounds: Albumin

The presence of sulfur is detected by the production of brownish-black lead sulfide when albumin is treated with lead acetate in the presence of acetic acid.

Acetic acid prevents the formation of other insoluble lead salts.

The production of brownish-black precipitate is due the presence of cysteine the amino acid part of albumin.

EXERCISE 3

Separation and Purification of Organic Compounds

QUALITATIVE TESTS FOR ELEMENTS IN ORGANIC COMPOUNDS

Recrystallization is a highly effective method for the purification of organic substances that exists already as crystals.

Processes Involved in Recrystallization

1. Dissolving the material to form a saturated solution in a suitable solvent at an elevated temperature.

Properties of a Desirable Solvent

a. Dissolves the solute easily at an elevated temperature, but only sparingly at a lower temperature.

b. Gives no chemical reaction with the solute.

c. Sufficiently volatile so that it may be removed easily from the purified crystals.

2. Filtering while hot to remove any suspended insoluble particles.

3. Letting crystallization process

Stages of Recrystallization

1. Removal of impurities, which may retard or inhibit crystal formation.

Samples that contain colored impurities maybe treated with decolorizing carbon to give rise to colorless solution.

Impurities are adsorbed by the active surface of the decolorizing carbon.

Animal charcoal is less effective at high than at low temperature.

The reason for operating at high temperature is to keep the substances from being crystallized in solution.

2. Nucleus formation

Spontaneous nucleus formation is caused by the orientation and aggregation of sufficient number of molecules, which may give rise to a crystal nucleus.

Methods of Inducing Crystal Formation

1. Seeding the process of adding a small crystal of pure material to induce the crystallization process.

2. Scratching the sides or bottom of a container with a glass rod provides sharp edges upon which crystal growth may occur.

3. Encouragement of growth of crystals to visible form.

Growth of crystals maybe encouraged by stirring or agitation, which results in distribution of the nuclei throughout the solution.

Crystal growth in supersaturated solutions may be inhibited as a result of restricted motion of the molecules.

A. Recrystallization of Benzoic Acid

Benzoic acid + NaCl + Methylene blue

heat

+ activated charcoal

filter

activated charcoal + methylene blue

colorless solution

rapid cooling

slow cooling

water coarse crystals water

fine crystals

wash with cold distilled water

Benzoic acid crystals

Benzoic acid crystals

+

+

hot distilled water

hot distilled water

+

+

HNO3

HNO3 +

+

AgNO3

AgNO3

Colorless solution

Colorless solution

with crystals

with crystals

Cloudy solution: NaCl + AgNO3 NaNO3 + AgCl

B. Decolorization of Brown Sugar

Brown sugar + water

Brown sugar solution

Brown sugar solution

Heat

+ Activated carbon

filter

activated charcoal + brown pigment Colorless solution

EXERCISE 4

Separation and Purification of Organic Compounds

SUBLIMATION

Sublimation the direct conversion of a substance from solid to gas without passing through the liquid state.

It can be applied when the components of a solid mixture differ appreciably in their vapor pressures.

As a separation process, it involves gentle heating of the mixture in a confined container until the component with high vapor pressure changes into vapor phase, while the component with the lower vapor pressure is left in the container.

As a purification process, it also depends on the difference of volatility. Less volatile or non-volatile impurities remain as residue while the sublimate is being formed.

Sublimate the crystals, deposit, or material obtained when a substance is sublimated.

High vapor pressure

Low melting point

More volatile

Residue the solid particles that remained on the dish.

Low vapor pressure

High melting point

Less or non-volatile

Deposition the process of changing gas to solid without passing through liquid state.

SUBLIMATERESIDUE

Salicylic acid sodium sulfate mixtureSalicylic AcidSodium sulfate

Physical AppearanceNeedle-likePowder-like

PolarityNon-polarPolar

Type of CompoundOrganicInorganic

ObservationColorless solution with salicylic acid crystalsCloudy solution with white precipitate

Salicylic acid + BaCl no reaction

Salicylic acid is an organic compound, while barium chloride is an inorganic compound.

Na2SO4 + BaCl NaCl + BaSO4

Sodium sulfate is a polar inorganic compound that results to white precipitate (barium sulfate) when added with barium chloride.

EXERCISE 5

Separation and Purification of Organic Compounds

DISTILLATION

Distillation is usually employed for the purification of liquid organic substances.

It involves evaporation and condensation.

Evaporation the conversion of liquid to vapor state with the aid of heat

Condensation the process in which vapor turns to liquid by cooling.

Distillate the liquid that passed through the distilling flask.

It requires a distillation flask fitted with a thermometer and a water-cooled condenser.

Boiling chips are also used to prevent bumping by producing a constant steam of bubbles which keeps the liquid in motion.

Boiling point is one of the most important criteria of purity, as it is constant in every pure organic substance at a definite pressure.

Distillation could be used to convert muddy water to potable water.

Solid particles should be allowed to settle and then decanted. Then, the water should be heated to boil in low to moderate fire. It should be below the boiling point of water. This would rid the water of impurities.

The use of distillation is limited to a certain extent because some organic compounds decompose when an attempt is made to distill them at normal atmospheric pressure.

Common Types of Distillation

1. Simple Distillation used to separate a volatile liquid from a non-volatile solute.

a large temperature difference (more than 20) between the boiling points of the component is necessary to obtain efficient separation.

the component which is more volatile will distill over first, in almost pure form at a definite constant temperature, the second component will distill over when the boiling point again remains constant for a long period of time.

2. Fractional Distillation the process of collecting separate fractions according to arbitrary boiling point ranges during the distillation of a mixture of substances.

It is performed readily by means of a special fractioning column.

It cannot be used if the components of a mixture have boiling points very close together because some substances form a constant boiling mixture, also known as azeotropic mixture.

Azeotropic mixture a mixture of liquids of certain definite composition that distills at constant temperature without change in composition.

4. Diminished-Pressure Distillation

.

5. Steam Distillation

Thermometer ReadingVolume of DistillateIgnition TestSodium-Nitroprusside Test

56C 5 mLFlammableRed-wine colored

100C5 mLSlightly flammableLighter color

Sodium-Nitroprusside Test Clinical test for urine. Test for acetone.

EXERCISE 6

Separation and Purification of Organic Compounds

EXTRACTION OF CHLOROPHYLL

Extraction, by the use of solvents, is a frequently used method of withdrawing or substance from a mixture.

It is usually performed using two immiscible solvents. The mixture is first dissolved in one of the liquids and then shaken with the other to distribute the components.

Aside from extraction, it also involves decantation and filtration.

Decantation the process of separating solid-liquid components of mixtures by gently pouring out the liquid so as not to disturb the solids that readily settle at the bottom of the container.

Filtration the process of separating the solid from the liquid by using a porous filter.

Residue the solid particles that remained on the filtering medium.

Filtrate the liquid that passed through the filtering medium.

Water is usually one of the solvents used in the extraction process.

The other liquid is usually a non-polar organic liquid.

Diethyl ether used extensively as an extracting solvent.

organic solvent

high solvent power for hydrocarbons and for oxygen-containing compounds.

Highly volatile. It boils at 34.60C

Fire hazard

Ether slightly soluble in water

Its efficiency can be improved by the addition of a small amount of ionizable salt, such as NaCl.

The increase polar property of the water solution will cause a decrease in the solubility of the organic solute.

Salting-out effect the reduced solubility in water in the presence of an electrolyte.

Petroleum ether Ligroin Benzene Carbon tetrachloride Chloroform Methylene chloride Ethylene dichloride N-butanol slightly soluble in water

Extraction of water-immiscible solvent is useful for isolation of natural products that occur in animal and plant tissues that have high water content.

Extraction

Malunggay + sand

grind

+ hexane + methanol

decant

filter

crushed leaves and sand

green solution

separatory funnel

dark green extract

water-methanol solution

+

anhydrous sodium sulfate

Chlorophyll

EXERCISE 7

Separation and Purification of Organic Compounds

CHROMATOGRAPHY

Chromatography - the process of separating the substances in a complex mixture by their different affinities to the adsorbent.

It is one of the most useful methods of separating the components of minute amount of mixtures.

It used for analyzing mixtures of colored chemicals.

It was invented by a Russian botanist, Mikhail Semyonovich Tsvet, in 1901, while researching on plant pigments.

This technique involves separation of constituent elements of the mixture.

Chromatography is derived from the Greek words, chroma meaning color, and graphein meaning to write. Thus, the word chromatography literally means color writing.

It has two phases:

Stationary Phase refers to the column packing material and is either solid or liquid.

- It is usually a piece of high quality filter paper.

Mobile Phase represents a mobile phase of liquid or gas.

- The mobile phase is a developing solution that travels up the stationary phase, carrying the samples with it.

Components of the sample will separate readily according to how strongly they adsorb on the stationary phase versus how readily they dissolve in the mobile phase.

Different Classification of Chromatographic Methods

1. Adsorption Chromatography (liquid-solid chromatography) utilizes a mobile liquid or gaseous phase that is adsorbed onto the surface of a stationary solid phase. The equilibration between the mobile and stationary phase accounts for the separation of different solutes.

2. Partition Chromatography (liquid-liquid chromatography) uses a thin film formed on the surface of a solid support by a liquid stationary phase. Solute equilibrates between the mobile phase and the stationary liquid.

3. Ion Exchange Chromatography resin (the stationary solid phase) is used to covalently attach anions or cations onto it. Solute ions of the opposite charge in the mobile liquid phase are attracted to the resin by electrostatic forces.

4. Molecular Exclusion Chromatography (gel permeation chromatography) liquid or gaseous phase passes through a porous gel which separates the molecules according to its size. The pores are normally small and exclude the larger solute molecules, but allow smaller molecules to enter the gel, causing them to flow through a larger volume. This causes the larger molecules to pass through the column at a faster rate than the smaller ones.

Thin Layer Chromatography it is usually used as an analytical technique rather than a preparative method.

The stationary phase used is an adsorbent in the form of a thin layer of an inert solid on a supporting material, usually a think sheet of metal or plastic.

The mobile phase is the solvent system used to separate the components of the mixture. Hexane and/or ethyl acetate is commonly used.

Paper Chromatography a method used for testing the purity of compounds and identifying substances.

Technique:

1. Introduce a small spot of the sample on the filter paper.

2. Put the filter paper into a container that has the mobile phase. Make sure the plate touches the mobile phase.

3. The solvent moves up the plate due to capillary action and carries the sample upwards.

4. Remove the filter paper and allow it to dry

5. Spray it with ninhydrin to make the spots more visible.

Ruhemanns Purple - a purple coloration produced by ninhydrin in the presence of an amino acid.

Calculation of Retention Factor (R)

R = distance traveled by the substance_

distance traveled by the solvent

Distance traveled by the solvent = 5.2 cm

Distance traveled by the substance = 3.5 cmHas polar and non-polar end

Water soluble

Absorbs water

It also absorbs other non-polar substances of malunggay

It acts as an agitator

Non-polar

Extracts chlorophyll of malunggay

Non-polar

Absorbs traces of water

Solvent front

3.5 cm

5.2 cm