Boiling point Second Class

Experimental Organic Chemistry

Zainab Amer Sallal Department of chemistry, College of Science, University of Baghdad

Boiling Points

• The boiling point of a pure liquid compound

is also a characteristic physical property.

• Bp’s are dictated by the degree of van-der-

Waals, hydrogen bonding, and dipole-dipole

interactions between molecules.

• Bp determination does not help to indicate

purity, as bp is affected less by impurities.

Boiling Points

• Bp is defined as the temperature at which

the vapor pressure of the liquid exactly

equals the pressure exerted on it.

Therefore, correction for current

atmospheric pressure is required.

(P mm Hg / 760 mm Hg) x measured

bp = corrected bp

Procedure

1.Place a few milliliters of a known liquid organic compound in a small

test tube.

2.Into the test tube, place the capillary tube with closed end upward.

3.Clamp the test tube to a ring stand and immerse a thermometer in the

test tube. Be sure to clamp the thermometer to the ring stand as well.

4. Fill a 250 mL beaker 3/4 full with water and place on the hot plate.

Carefully lower lower the test tube and thermometer combination into the

beaker of water so that the test tube is immersed half way in the water.

5.Begin to heat the hot plate/water slowly. As the liquid approaches its

boiling point, a

few bubbles will be observed flowing out of the end of the capillary tube.

When a steady steam of bubbles are observed, turn off the hot plate and

allow the contents of the test tube to cool.

6.As the contents of the test tube cools, observe the capillary tube

carefully. When the liquid begins to flow into the capillary tube, record

the temperature of the liquid as its boiling point temperature.

Experimental Organic

Chemistry

Melting point Second class

Zainab Amer Sallal Department of chemistry, College of Science,

University of Baghdad

Remember physical properties?

A substance’s (or a molecule’s) physical properties include: • State • Color & odor • Refractive index • Density • Solubility • Melting & boiling points

solid liquid gas

Crystalline matrix is held together by inter- molecular forces.

Heat

Fusion or

mp

Heat

vaporization or bp

D&D p.175-6

Liquid crystals

Liquid crystals are sometimes called a mesophase because they have more order than a liquid, but less than a crystal. Molecules involved are often rod-like and have disc-like arenes.

nematic

smectic

The more ordered smectic state is due to stronger intermolecular forces.

D&D p.178-9

Melting point

The temperature at which a solid becomes a liquid. Characteristic of molecule can be used to determine identity & purity.

Four factors influence (and increase) melting point: 1. Molecular symmetry 2. Molecular polarity 3. H-bonding 4. Molecular weight

Both conformation & orientation also matter

Pentane mp = - 130°C

2,2-dimethylpropane mp = -17°C

Benzoic acid = 2 H-bonds Benzoic alcohol = 1 H-bond

D&D p.179-83

Even vs. odd chain length

The ability of molecules to pack together tightly influences intermolecular interactions & melting point.

• Tighter packing increases melting point

Bruice p98

Pure substances also have higher mps. Why?

It’s easier for identical molecules to pack together evenly & tightly.

A mixture of molecules of different shapes & lengths does not pack efficiently, so fewer interactions.

Melting point & shape

So even chains pack tighter than odd. And molecules with spherical shapes have unusually high melting points.

www.cem.msu.edu

Molecule

Shape

Boiling point °C

Melting point °C

pentane linear 36 -130

hexane linear 69 -95

heptane linear 98 -91

octane linear 126 -57

nonane linear 151 -54

decane linear 174 -30

tetramethylbutane (8C)

spherical 106 +100

Notice that even-numbered chains have higher mp than odd. Spherical molecules pack more efficiently than elongated (linear) molecules. The shape of spherical molecules is stable. But the rotation of all bonds in long alkanes gives them shifting shapes that are less likely to settle in a solid (packed & crystalline) form.

Examples: melting point

Which has the higher melting point and why? 1) Hexane or cyclohexane?

2) Cyclopentanethiol or cyclopentanol?

Cyclohexane, because it has

higher symmetry

SH

D&D p.179-83

OH

The alcohol because it is able to form H-bonds.

mp 6.47 C

mp -95 C

bp 130 C bp 140 C

Recrystallisation

Experimental Organic Chemistry

Recrystallization

Second class

Zainab Amer Sallal Department of chemistry, College of Science, University of Baghdad

Recrystallisation

Temperature >>

TL TH

Theory:

The degree of solubility of most compounds in a given solvent rises with

temperature. In other words, the higher the temperature the greater the mass of

the compound which will remain in solution. This can be represented in

general terms in graphical form as follows.

Hence an appropriate solvent

(or solvent mixture) is one

which will dissolve both

compound and impurities at or

near its boiling point and one

in which the compound itself

does not dissolve well at or

near room temperature.

Recrystallisation

Dissolve the impure compound in a minimum volume of hot (near boiling)

solvent.

Add solid to solvent

Place beaker in

water bath

Heat mixture to

dissolve solid

with stirring

Add additional

solvent until

fully dissolved

Recrystallisation

Pure crystals

of the

desired

compound

Impurities

remaining

in solution

Solution cooling slowly

Recrystallisation

Transfer

crystals

into funnel

Followed by

remainder of

solution

Apply suction

Recrystallisation

Cover crystals

with a little cold

solvent

Apply suction

Experimental Organic Chemistry

Distillation

Second class

Zainab Amer Sallal Department of chemistry, College of Science, University of Baghdad

Distillation • Distillation is used to separate two liquids of

sufficiently different boiling points.

• An equilibrium between vaporizing and condensing in a distillation column allows for the separation of liquids.

• Most of the lower boiling liquid is collected in a receiver vial while most of the higher boiling liquid remains in the original flask.

• The separation process is improved upon by conducting subsequent re-distillations (simple distillation, Fig. 5.5) or increasing column surface area (fractional distillation, Fig. 5.7).

Simple Distillation • 1. Add 60 mL of 20% ethanol-water mixture in a 100-mL

round-bottomed flask from the macroscale kit.

• 2. Add boiling chips.

• 3. Assemble apparatus for simple distillation as shown in Fig 5.10 (page 100). Ensure that all the connections are tight. The bulb of the thermometer should be below the opening into the side arm of the distillation head.

• 4. Heat the flask strongly on the thermo well (no sand) until boiling begins, then adjust the heat until the distillate drops at a regular rate of one drop per second.

• 5. Record both the temperature and volume of distillate at regular intervals. Remember to record the temperature at the first drop of distillate and then after every milliliter that you collect.

• 6. After 50 mL of distillate is collected, discontinue distillation and save your distillate for fractional distillation.

• 7. Working in the hood, place 3 drops of the distillate using a Pasteur pipette on a Pyrex watch glass and try to ignite it.

Procedure:

1. Make a table in your lab record book of Temperature, oC vs.

Volume, mL.

2. Pour 30 mL of the compound into your 50 mL round bottom flask

and add 2 boiling chips. Place the round bottom flask in a heating

mantle and clamp the round bottom flask. Set up the simple

distillation apparatus shown in Figure 1.

3. Start the water running slowly through the condenser and have the

instructor check the set up before starting to heat the flask. Make sure

the heating mantel is plugged into the Variac, not directly to the

socket.

4. Regulate the heat control, starting at position 5-6 and decreasing to

a lower numerical value on the heat control, so that the rate of

distillation is no more than about 1 drop every 2 seconds. Collect the

distillate in the graduated cylinder. Record the temperature after every

2 mL of distillate.

Experimental Organic Chemistry

Steam distillation

Second class

Zainab Amer Sallal Department of chemistry, College of Science, University of Baghdad

Steam distillation : is a special type of distillation (a separation process)

for temperature sensitive materials like natural aromatic compounds. It

once was a popular laboratory method for purification of organic

compounds, but has become less common due to the proliferation

of vacuum distillation. Steam distillation remains important in certain

industrial sectors.

Many organic compounds tend to decompose at high sustained

temperatures. Separation by distillation at the normal (1 atmosphere)

boiling points is not an option, so water or steam is introduced into the

distillation apparatus. The water vapor carries small amounts of the

vaporized compounds to the condensation flask, where the condensed

liquid phase separates, allowing easy collection. This process effectively

enables distillation at lower temperatures, reducing the deterioration of the

desired products. If the substances to be distilled are very sensitive to heat,

steam distillation may be applied under reduced pressure, thereby reducing

the operating temperature further.

Principle

When a mixture of two practically immiscible liquids is heated

while being agitated to expose the surface of each liquid to the

vapor phase, each constituent independently exerts its

own vapor pressure as a function of temperature as if the other

constituent were not present. Consequently, the vapor pressure

of the whole system increases. Boiling begins when the sum of

the vapour pressures of the two immiscible liquids just exceeds

the atmospheric pressure (approximately 101 kPa at sea level).

In this way, many organic compounds insoluble in water can be

purified at a temperature well below the point at which

decomposition occurs. For example, the boiling point

of bromobenzene is 156 °C and the boiling point of water is

100 °C, but a mixture of the two boils at 95 °C. Thus,

bromobenzene can be easily distilled at a temperature 61 °C

below its normal boiling point

Applications

Steam distillation is employed in the isolation of essential oils, for

use in perfumes, for example. In this method, steam is passed

through the plant material containing the desired oils. Eucalyptus

oil and orange oil are obtained by this method on an industrial scale.

Steam distillation is also sometimes used to separate intermediate

or final products during the synthesis of complex organic

compounds.

Steam distillation is also widely used in petroleum

refineries and petrochemical plants where it is commonly referred to

as "steam stripping“.

Steam distillation also is an important means of separating fatty

acids from mixtures and for treating crude products such as tall

oils to extract and separate fatty acids, soaps and other

commercially valuable organic compounds.

Experimental Organic Chemistry

fractional distillation Second class

Zainab Amer Sallal Department of chemistry, College of Science, University of Baghdad

Fractional distillation is the separation of

a mixture into its component parts,

or fractions. Chemical compounds are separated

by heating them to a temperature at which one

or more fractions of the mixture will vaporize.

It uses distillation to fractionate. Generally the

component parts have boiling points that differ

by less than 25 °C from each other under a

pressure of one atmosphere. If the difference in

boiling points is greater than 25 °C, a simple

distillation is typically used.

Apparatus

Fractional distillation

An Erlenmeyer flask is used as a receiving flask. Here the

distillation head and fractionating column are combined

in one piece.

heat source, such as a hot plate with a bath

distilling flask, typically a round-bottom flask

receiving flask, often also a round-bottom flask

fractionating column

distillation head

thermometer and adapter if needed

condenser, such as a Liebig condenser or Allihn condenser

vacuum adapter (only required if performing vacuum

distillation; not used in image to the right)

Standard laboratory glassware with ground glass joints,

e.g. quickfit apparatus.

Procedure: 1.Place the 50 mL of distillate from simple distillation experiment

back into the 100-mL round-bottomed flask once it has cooled.

2.Add boiling chips.

3.Assemble the apparatus for fractional distillation as shown in Fig.

5.11 (page 102). Use stainless steel wool that will be provided to

pack the fractionating column.

4.Turn up the heat to the electric flask gradually until the mixture

just begins to boil. Turn off the power and heat slowly as you watch

the ring of condensate rise gradually through the column. This rise

should be gradual so that the column can acquire a uniform

temperature gradient. Make sure the ring has stopped rising and then

increase the heat gradually until distillation starts.

5.Insulate the column with a towel to prevent flooding of the column

as this slows down the distillation.

6.Record temperature for every milliliter of distillate collected and

take more frequent readings as the temperature begins to rise

abruptly.

7.Empty the contents of the graduated cylinder into a 25 mL

Erlenmeyer flask once it fills.

8.Stop the distillation once the second constant temperature is

reached.

9.Repeat the ignition test and note any difference from before.

Qualitative elemental analysis

Zainab Amer Sallal Chemistry Department, College of Science

Qualitative elemental analysis

• Qualitative determination of elements present in organic compounds, remember that all organic compounds will contain C and H, other commonly found elements will be O, N, S, Halogens and various metals. That can be detected by reaction with sodium metal.

• The non polar nature of organic compounds make the detection of N, S and X difficult because organic compounds don't ionize in solution to give ions of these elements. For this reason it necessary to convert this elements into inorganic ions before doing the test.

Elements as nitrogen, sulphur and

halogens (chlorine, bromine and iodine)

may also be present in organic compounds.

These extra elements are usually detected

by Lassaigne's Test that was developed by

the French Chemist Jean Louis Lassaigne

(1843). He is known named for the sodium

fusion test after that.

Sodium is a chemical element with symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table, because it has a single electron in its outer shell, which it readily donates, creating a positively charged ion—the Na+ cation.

Sodium fusion Test or Lassaigne's Test

In this test, the organic compound is fused with metallic sodium

to convert these elements into water soluble sodium salt. This is

achieved by heating the organic substance with sodium metal which

converts the above elements to the corresponding sodium salts:

sulfur is converted to sodium sulfide, nitrogen to sodium cyanide and

halogen to sodium halide.

C, H, N, S, X + Na (excess) Na2S, NaCN, NaX, NaOH, C

(300 C)

Sodium fusion Test or Lassaigne's Test

1- The quantity of sodium elements is small

less than organic compound will be formed

sodium thiocyanide (NaSCN), these

compound effect detected process on

nitrogen so as to increase the sodium

elements to removed these compound.

2Na + NaSCN NaCN + Na2S

Sodium Fusion (TEST FOR SULFUR, NITROGEN, AND HALOGEN)

Sodium fusion Test or Lassaigne's Test

2- Add a small quantity of alcohol (ethanol or methanol) to the test

tube to remove the excess unreacted sodium:

Na + C2H5OH NaOC2H5 + H2

3- Sodium element is dangerous can react vigorously with water

resulting in explosion therefore sodium element is kept dipped in

liquid paraffin or kerosene oil to prevent exposure to moisture.

Sodium fusion Test or Lassaigne's Test

1- Detection of Nitrogen :-

If nitrogen is present in the compound, the Lassaigne's extract would contain sodium cyanide (NaCN) formed during fusion. It is converted to sodium ferrocyanide on treating with ferrous sulphate. On further treating it with ferric chloride, a prussian blue complex, ferric ferrocyanide is formed.

Sodium fusion Test or Lassaigne's Test

2- Detection of Sulphur

A- Sodium nitroprusside test :

During the preparation of Lassaigne's extract, sulphur from the organic compound reacts with sodium to form sodium sulphide. It gives a voilate colour with sodium nitroprusside due to the formation of sodium thionitroprusside.

Sodium fusion Test or Lassaigne's Test

B- Lead acetate test :

Sodium sulphide (Na2S) formed during the preparation of Lassaigne's extract

reacts with lead acetate to yield lead sulphide as black precipitate.

CH3COOH

Na2S + (CH3COO)2Pb Pb2S + 2CH3COONa Black ppt

Sodium fusion Test or Lassaigne's Test

Sodium fusion Test or Lassaigne's Test

Sodium fusion Test or Lassaigne's Test

Experimental Organic Chemistry

preparation of aspirin

Second class

Zainab Amer Sallal Department of chemistry, College of Science, University of Baghdad

Aspirin, acetylsalicylic acid, was first synthesized in 1893

by Felix Hofmann, a chemist for the German firm of Bayer. This

compound had the medicinal properties of salicylic acid, an

extract of willow bark, without the unpleasant taste or the high

degree of irritation of the mucous membranes lining the mouth,

gullet, and stomach.

Aspirin is both an organic ester and an organic acid. It is

used extensively in medicine as a pain killer (analgesic) and as a

fever-reducing drug (antipyretic). When ingested, acetylsalicylic

acid remains intact in the acidic stomach, but in the basic

medium of the upper intestinal tract, it hydrolyzes forming the

salicylate and acetate ions. However, its additional physiological

effects and biochemical reactions are still not thoroughly

understood.

Aspirin (molar mass of 180.2 g/mol) is prepared by

reacting salicylic acid (molar mass of 138.1 g/mol) with acetic

anhydride (molar mass of 102.1 g/mol).

Procedure

1-Weigh out 2.0 g of salicylic acid. Place it in a 125-mL

Erlenmeyer flask.

2-Add 5 mL of acetic anhydride. Swirl the flask to wet the

salicylic acid crystals. Add 5 drops of concentrated sulfuric acid,

H2SO4 , to the mixture.

3-Gently heat the flask in a boiling water bath for about 10

minutes.

4-Remove the flask from the hot water bath and add 10 mL of

ice water to decompose any excess acetic anhydride. Chill the

solution in an ice bath until crystals of aspirin no longer form,

stirring occasionally to decompose residual acetic anhydride.

5-Set up a vacuum filtration apparatus. Wet the filter paper in the

Buchner funnel with 1-2 mL of distilled water.

EXPERIMENTAL ORGANIC

CHEMISTRY

PREPARATION OF METHANE

SECOND CLASS

ZAINAB AMER SALLAL

Department of chemistry, College of Science, University of Baghdad

Methane is an odorless, colorless and flammable gas. It is used

primarily as fuel to make heat and light. It is also used to manufacture organic

chemicals. Methane can be formed by the decay of natural materials and is

common in landfills, marshes, septic systems and sewers. Methane can form an

EXPLOSIVE mixture inair at levels as low as 5 percent.

LaboratoryMethod:

(A) Principle : In the laboratory, methane is prepared by heating a mixture of

anhydrous sodium acetate and soda lime (NaOH + CaO).

CH3COONa + NaOH (CaO) --------> CH4 + Na2CO3

Sodium acetate Soda lime mathane

(B) Procedure : Anhydrous sodium acetate and soda lime are taken in the ratio

1:3 by weight and are mixed immediately. The intimate mixture of sodium

acetate and soda lime thus prepared is taken in a dry hard glass test tube

fitted with a cork through which a delivery tube passes. The hard glass test tube

is now heated strongly when methane is evolved. The first part of the evolved

gas is allowed to escape to remove the air inside the test tube. Methane thus

produced is collected in a gas jar by the downward displacement of water.

preparation of methane

(C) Purification : Methane thus prepared contains traces of ethylene,

acetylene, hydrogen and moisture as impurities:-

(I) Acetylene is removed by passing the impure gas through ammonia cuprous chloride solution.

C2H2 + CuCl2 + NH3 -----------> C2Cu2 + 2HCl

(II) Ethylene and moisture are removed by passing the gas through fuming sulphuric acid.

C2H4 + H.HSO4 --------------> C2H5HSO4

(III) The gas is then mixed with excess of oxygen and the gas is passed over palladium heated at 100°C. H22 is removed by absorbing it in alkaline pyrogallate solution. The gas is then passed through conc.H2SO4 to remove water produced by the action of H2 and O2 and then collected over mercury present in methane is converted to water. [Soda lime is used instead of NaOH alone in the preparation of methane from sodium acetate. This is because of the fact that, soda lime is cheap, less hygroscopic, does not fuse and attack so readily as caustic soda]

Experimental Organic Chemistry

Azo Compound

Third class

Zainab Amer Sallal Department of chemistry, College of Science, University of

Baghdad

What are azo compounds? Contain the -N=N- group.

Where R and R’ are arene groups more stable than

alkyl groups.

Azo group is stabilised by becoming part of extended

delocalised system.

Result of a coupling reaction between a diazonium salt and

a coupling agent.

Azo group

Diazonium salts

Only stable salts are aromatic - not particularly stable.

Lose -N+N as N2(g)

Electron rich benzene ring stabilises the -N+N group but decomposition occurs above about 5oC.

Add cold soln. sodium nitrite (NaNO2) to arylamine soln. In dilute acid below 5oC.

Diazotisation.

Prepare fresh and use immediately.

N+N Cl-

How the salt is made.

Acid reacts with sodium nitrite to form unstable

nitrous acid.

NaNO2 (aq) + HCl (aq) HNO2 (aq) + NaCl (aq)

Nitrous acid reacts with the arylamine.

+ HNO2 + H+ N+N + 2 H2O NH2

phenylamine benzenediazonium ion

Diazo coupling reactions A diazonium salt reacts with

another compound containing

a benzene ring called a

coupling agent.

Diazonium salt acts as an

electrophile - reacts with

benzene ring of coupling

agent.

Coloured precipitate of azo

compound immediately forms.

Important use as dyes.

Coupling with phenols Benzenediazonium salt and alkaline phenol gives a

yellow orange azo compound

Benzenediazonium salt and alkaline naphthalen-2-ol

gives a red azo compound.

Coupling with amines Diazonium salts couple with arylamines.

Benzenediazonium salt and phenylamine gives a yellow azo compound.

Use different diazonium salts and coupling agents to make different colours.

Azo compounds are stable so dyes do not fade.

Organic Chemistry

Amines

By

Zainab Amer Sallal

M. Sc. Chemistry Department of chemistry, College of Science, University of Baghdad

Amines

• Amines are organic nitrogen compounds,

formed by replacing one or more hydrogen

atoms of ammonia (NH3) with alkyl groups.

• Amines are classified as 10, 20, or 30 based on

the number of alkyl groups bonded to the

nitrogen atom.

• Like ammonia, the amine nitrogen atom has a

nonbonded electron pair, making it both a base

and a nucleophile.

• As a result, amines react with electrophiles to

form quaternary ammonium salts—compounds

with four bonds to nitrogen.

Amines

Amines with N—H bonds show characteristic

absorptions in their IR spectra:

1- 10 Amines show two N—H absorptions at 3300-3500 cm-1.

2- 20 Amines show one N—H absorption at 3300-3500 cm-1.

3- Because 30 amines have no N—H bonds, they do not absorb in

this region in their IR spectra.

Amines

Interesting and Useful Amines

Amines

Preparation of Amines:

Amines

Amines

Synthetic Dyes :

Amines

Cotton binds dyes by hydrogen bonding interactions

with its many OH groups. Thus, Congo red is bound to

the cellulose backbone by hydrogen bonds.

Synthetic Dyes

Amines

Prontosil and other sulfur containing antibiotics are

collectively known as sulfa drugs.

Prontosil is not the active ingredient itself—In cells,

it is metabolized to sulfanilamide, the active drug.

Sulfa Drugs

Amines