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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