Download EXPERIMENT 4 Objectives Principles

EXPERIMENT 4
PREPARATION OF CYCLOHEXENE FROM CYCLOHEXANOL
(For Students)
Objectives
1) Be able to synthesize cyclohexene from cyclohexanol via an alcohol
dehydration reaction.
2) Be able to classify alkanes and alkenes using chemical reaction test
Principles
In this experiment some properties of hydrocarbons will be studied. Simple
tests which provide a means of distinguishing between saturated hydrocarbons
(alkanes) and unsaturated hydrocarbons (alkenes) will be carried out. An
alkene (cyclohexene) will be prepared by dehydration of an alcohol
(cyclohexanol).
Alcohol dehydration is an acid catalyzed elimination reaction, which can be
performed by strong, concentrated mineral acids such as phosphoric acid.
OH
H3PO4
cyclohexanol
b.p. 161oC
+ H2O
cyclohexene
b.p. 83oC
From the reaction above, cyclohexene is the only alkene that can be
formed under these conditions. Cyclohexene and water are removed via
azeotropic distillation to drive the equilibrium to product. Traces of acid in crude
product are removed by treatment with sodium carbonate solution. A final wash
with water removes any remaining carbonate.
Cyclohexene is an unsaturated hydrocarbon. In chemistry, a hydrocarbon
is any chemical compound that consists only of the elements carbon (C) and
hydrogen (H). The major classes of hydrocarbons are alkanes, alkenes, alkynes
and aromatic hydrocarbons. The alkanes are the least reactive class, because
they contain only carbon and hydrogen and they have no reactive functional
groups. There are a number of simple tests that may be used to differentiate
alkanes from alkenes. These tests are based upon the reactivity of alkenes with
a variety of reagents to which the alkanes are insensitive. In this experiment,
1
you can distinguish between cyclohexene (alkene) and cyclohexane (alkane)
using chemical reaction tests; bromine and permanganate tests.
1) Bromine test using bromine in chloroform (Br2/CHCl3)
R C C
H H
Br H
R C C
H Br
R + Br2
R
Solutions of bromine in CHCl3 have an intense red-orange color. When
Br2 in CHCl3 is mixed with an alkane, no change is initially observed. When
it is mixed with an alkene or alkyne, the color of Br2 rapidly disappears.
2) Permanganate Test (Baeyer’s test)
3 R C C
H H
R +
2KMnO4 + 4H2O
OH OH
3R C
C R + 2MnO2 + 2KOH
H
H
The disappearance of the purple color of potassium permanganate and
the appearance of brown precipitate (MnO2) is a positive test. The alkenes
are readily oxidized by potassium permanganate to form diols. The alkanes
in this situation are not react with the potassium permanganate.
Procedure
Part A : Preparation of cyclohexene by dehydration of cyclohexanol
OH
H3PO4
heat
1)
2)
3)
Transfer 10 g of cyclohexanol to a 100 mL round-bottomed flask, in
addition to 5 mL of 85% H3PO4. Thoroughly mix the solution by swirling it.
Add a few boiling chips, and assemble the flask for fractional distillation
(Figure 1) using a 25 mL graduated cylinder in a ice-water bath as a
receiver. (cyclohexene is very volatile and it will evaporate very rapidly)
Start circulating the cooling water in the condenser and heat the reaction
flask using a heating mantle (do not heat too high). The temperature of the
distilling vapor should be regulated so that it does not exceed 100°C.
2
4)
5)
When white fumes appear in the round bottom flask, and a few milliliters of
liquid remains in the reaction flask, discontinue the distillation.
Transfer the distillate* in a small separatory funnel and add about 10 mL of
10% aqueous Na2CO3. Swirl the solution slowly at first and then shake
vigorously to neutralize the solution.
6) Allow the layers to separate, drain and test the pH of the aqueous layer
(bottom layer). Repeat the neutralization until the aqueous layer is basic to
litmus. (The aqueous layer is discarded)
7) Repeat washing the organic layer with 10 mL of water.
8) Transfer the organic layer to a dried 50 mL Erlenmeyer flask. Add
anhydrous Na2SO4 to the flask and swirl occasionally until the solution is
dry and clear (about 10-15 min).
9) By gravity filtration using cotton wool, filter the cyclohexene into a dried
100 mL round-bottomed flask. Add boiling stones and distill the mixture
through a simple distillation apparatus (dry your original distillation
equipment by first washing with water and then acetone). Collect the
fraction boiling between 80 and 85°C in a tared and dried 50 mL receiving
flask that is cooled in ice. Do not distill to dryness.
10) Weigh cyclohexene product and calculate the total yield.
* distillate = A liquid condensed from vapor in distillation
distilland = The material in the distillation apparatus that is to be distilled.
Thermometer
Water out
Water in
Condensor
Fractionating
column
ice-water bath
Heating mental
Figure 1: a fractional distillation apparatus
3
Part B : Test for unsaturation
Samples :
1. Cyclohexane (Alkanes): from the laboratory
2. Cyclohexene (Alkenes): from PART A
1)
Bromine test: Add about 3 drops of samples in dry test tubes. Then, add
about 3-4 drops of a solution of bromine in chloroform. Stopper each tube,
shake, and record any changes. If decolorization occurs, test for hydrogen
bromide with wet litmus.
2)
Permanganate test: To 3 drops of samples in clean test tubes, add 2-3
drops the 0.1% permanganate solution drop by drop with shaking.
Observe the disappearing of the purple color and occurring a brown
precipitate within 1 minute.
Safety Precautions
-
-
Phosphoric acid is a strong acid capable of producing severe burns to skin
or eyes.
Cyclohexanol can be irritating to the respiratory system and skin.
Cyclohexene is not particularly dangerous but is highly flammable and has
an unpleasant smell.
Bromine is highly volatile, toxic, and causes severe skin burns.
Waste Disposal
All contents of your test tubes from bromine test reactions go into
“HALOGENATED organic waste”.
Quiz
Quiz will cover this material and the basic knowledge of hydrocarbons.
4
EXPERIMENT 5
Reactions of Alkyl Halides
(For Students)
Objectives
1)
2)
3)
Be able to classify alkyl halides according to their structures and reactivity.
Understand the relationship between structures and reactivity of alkyl
halides.
Be able to distinguish the differences in SN1 and SN2 reactions.
Principle
Alkyl halides are hydrocarbon compounds containing at least one atom
of halogen directly bonded to an alkyl group. With a general formula R-X,
the halogen atom could be F, Cl, Br, or I. If the halogen atom is attached to
an aromatic ring, the compound will be referred to as an aryl halide. In terms
of reactivity, aryl halides are usually less reactive than alkyl halides.
Most of the reactions for alkyl halides are Nucleophilic Substitution
reaction. Nucleophiles are molecules with high electron density or lone pairs
of electrons, or ions with a negative charge. They can form bond by
donating electrons to another molecule having a position of lower electron
density (electrophiles). Examples of nucleophilic species are: water, amine,
ammonia, cyanide ion, alkoxide ion, and hydroxide ion.
Alkyl halides can react with a number of nucleophilic reagents, both
organic and inorganic species. Therefore, alkyl halides are usually good
starting materials in the synthesis of compounds with other functional
groups.
The reaction may occur by one of two mechanisms designated SN1 or
SN2. Which mechanism operates depends on the structure of the R group
and the reaction conditions.
General form of the SN1 mechanism
nuc: = nucleophile
X = leaving group (usually halide)
This mechanism involves the formation of a carbocation as the crucial
intermediate in the rate-determining step. The reaction exhibits unimolecular
(or "first-order") kinetics, because only one molecule is involved in the ratedetermining step. Since the mechanism goes through a carbocation, the
leaving group must be attached to either a tertiary or secondary carbon to
stabilize the intermediate. A methyl or primary leaving group will not form a
carbocation. Because the intermediate carbocation, R+, is planar, the central
carbon is not a stereocenter, even if it was a stereocenter in the original
reactant, so the original configuration at that atom is lost. Nucleophilic attack
can occur from either side of the plane, so the product may consist of a
mixture of two stereoisomers. In fact, if the central carbon is the only
stereocenter in the reaction, racemization may occur
General form of the SN2 mechanism
nuc: = nucleophile
X = leaving group (usually halide)
The SN2 reaction involves displacement of a leaving group by a
nucleophile. The rate of an SN2 reaction is second order, as the ratedetermining step depends on the nucleophile concentration, as well as the
concentration of alkyl halide. This reaction works best with methyl and primary
halides because bulky alkyl groups block the backside attack of the
nucleophile, but the reaction does work with secondary halides (although it is
usually accompanied by elimination), and will not react at all with tertiary
halides. In the following example, the hydroxide ion is acting as the
nucleophile and bromide ion is the leaving group: Because of the backside
attack of the nucleophile, inversion of configuration occurs.
Procedure
1. Reaction with NaI in acetone
In this part of the experiment, you will test the reactivity of several alkyl
halides in an SN2 reaction. Iodide ion (I-) is an effective nucleophile in SN2
substitution. In acetone solution, other alkyl halides (alkyl chlorides or
bromides) can be converted to alkyl iodides easily by this method. Although
one might expect such a reaction to be reversible, it can be driven to
formation of R-I by using anhydrous acetone as the solvent. Sodium iodide
(NaI) is soluble in this solvent, but sodium chloride and sodium bromide are
not. If a reaction occurs, a precipitate of sodium chloride or sodium bromide
forms and thus the ion is not available in solution for the reverse reaction.
The mechanism involves a one-step, concerted, SN2 reaction. Therefore,
the reaction occurs most quickly when attack at the carbon that bears the
halogen (X) is least sterically hindered.
Part1
1.
2.
3.
4.
Place 2 drops of n-butyl chloride in a clean and dry test tube.
Add 1 mL of 18% NaI solution in acetone.
Stopper, and shake vigorously.
Record the time required to observe precipitate. If no precipitation
takes place after 5 minutes, place the test tube in a water bath (4550°C) for 6 minutes. Do not allow complete evaporation by adding
acetone to keep the solution at the same level. Record whether
the precipitation take place and the time required.
5. Present the final result and confirm the data with your instructor.
6. Repeat step 1 to 5 with s-butyl chloride, t-butyl chloride, n-butyl
bromide, and bromobenzene.
2. Reaction with AgNO3 in ethanol
The silver nitrate test allows for the identification of alkyl halides by
observing them in an alcoholic silver nitrate environment. The rate at which
the silver halide salt precipitate forms is characteristic of different types of
alkyl halides. You will test the reactivity of several alkyl halides in a SN1
reaction. Organic halides may react with ethanol to form ethyl ethers. When
the ethanol contains silver ion, the rate of reaction increases because the
silver ion acts as an electrophile toward the halogen and helps to break the
carbon-halogen bond. Alkyl chlorides yield an observable silver chloride
precipitate, which is insoluble in ethanol and thus provides an indicator that
a reaction has occurred. In this case, the slow step being the breaking of the
carbon-halogen bond. The carbocation then reacts rapidly with alcohol to
form the ether. Organic halide reactivity parallels the stability of the
corresponding carbocations.
Part 2
1.
2.
3.
4.
Place 2 drops of n-butyl chloride in a clean and dry test tube.
Add 1 mL of 1% AgNO3 in ethanol.
Stopper, and shake vigorously.
Record the time required to observe precipitate. If no precipitation
takes place after 5 minutes, place the test tube in a water bath (4550°C) for 6 minutes. Do not allow complete evaporation by adding
ethanol to keep the solution at the same level. Record whether
the precipitation take place and the time required.
5. Present the final result and confirm the data with your instructor.
6. Repeat step 1 to 5 with s-butyl chloride, t-butyl chloride, n-butyl
bromide, and bromobenzene.
3. Comparison of SN1 and SN2
Blank test:
1. Place 1 mL of ethanol, 5 drops of water, and 2 drops of bromophenol
blue in a test tube.
2. Stopper and shake the tube vigorously.
Note:
Bromophenol blue
pH 3 (yellow) – pH 4.6 (blue)
Test A:
1. Place 1 mL of ethanol, 5 drops of water, 2 drops of bromophenol
blue, and 5 drops of n-butyl chloride in a test tube.
2. Stopper and shake the tube vigorously.
3. Observe the result and compare with the blank test.
4. Present the final result and confirm the data with your instructor.
Test B:
1. Place 1 mL of ethanol, 5 drops of water, 2 drops of bromophenol
blue, and 5 drops of t-butyl chloride in a test tube.
2. Stopper and shake the tube vigorously.
3. Observe the result and compare with the blank test.
4. Present the final result and confirm the data with your instructor.
EXPERIMENT 6
Reactions of Alcohols and Phenols
(For Students)
Objectives
1)
2)
To classify alcohols according to their characteristic chemical reactions.
To use the chemical characteristics to differentiate phenols and the three
types of alcohols.
Principles
The alcohols, with a hydroxyl group attached to an alkyl chain, and the
phenols, with the same group attached directly to the aromatic ring, have similar
chemical properties in kind, but may differ considerably in the degree to which
these properties are exhibited. Alcohols are classified as 10, 20 and 30,
depending on the number of carbon atoms connected to the carbon bearing the
OH group. The following experiments are designed to bring out these
similarities and differences, as well as to demonstrate the properties of the
hydroxyl group.
Procedures
1) Water solubility
As the carbon chains of alcohol become longer, alcohol becomes less
polar and more hydrophobic.
1.
2.
3.
4.
5.
Add 10 drops of water into a clean test tube.
Add 5 drops of methanol. Shake and let stand.
Observe whether or not the alcohol is soluble in water.
Present the data and confirm the result with your instructor.
Repeat step 1-3 with ethanol, 1-butanol, cyclohexanol and 0.5 g of phenol.
2) Alkali solubility
Alcohols are weaker acids than water, but the aromatic ring makes
phenols stronger acids than water, which means that they may be neutralized
by stronger bases such as sodium hydroxide.
1.
2.
3.
4.
5.
Place approximately 1 mL of 10% NaOH solution in a clean test tube.
Add 5 drops of 1-butanol. Shake and let stand.
Observe the results.
Present the data and confirm the result with your instructor.
Repeat step 1-3 with cyclohexanol and 0.1 g of phenol.
3) Reaction with metallic sodium
The hydrogen atom of the hydroxyl group can be displaced by active
metals such as sodium. This reaction can be used as an indication of the
1
presence of an –OH group in an unknown compound. The reaction produces
hydrogen gas and the corresponding sodium alkoxide.
1. Place 1 mL of ethanol, 1 mL of 2-propanol and 1 mL of t-butanol in three
separate clean and dry test tubes.
2. Add a very small piece of sodium into each test tube.
3. Observe the result and note the relative rates of reaction.
4. Add a drop of phenolphthalein to the ethanol experiment.
5. Present the data and confirm the result with your instructor.
6. Repeat step 1-3 with phenol, using 0.5 g of phenol dissolved in 3 mL of
toluene.
NOTE: Do not discard sodium into the sink. Add sufficient ethanol to destroy
any unreacted sodium and discard the solution into the waste bottle.
4) Characteristic reactions of phenol
a) Phenols and compounds with the hydroxyl group attached to an
unsaturated carbon atom, give coloration (purple/violet) upon the
addition of ferric chloride solution.
1. Take two test tubes each containing approximately 1 mL of water.
2. Add a few crystals of phenol in one tube and a few drop of ethanol in the
other.
3. Add 5 drops of 1% ferric chloride solution. Note the characteristic color
developed in the phenol tube. This is a standard test for most phenol.
4. Present the data and confirm the result with your instructor.
b) The hydroxyl group of the phenols activates the benzene ring to further
substitution. Bromination using bromine water can proceed smoothly
under very mild conditions.
1. Take two test tubes each containing approximately 1 mL of water.
2. Add a few crystals of phenol in one tube and a few drop of ethanol in the
other.
3. Add bromine water slowly. If the color disappears, continue until the color
of the bromine just persists.
4. Present the data and confirm the result with your instructor.
5) Lucas test –Differentiation of primary, secondary and tertiary alcohols
The Lucas test is a test for the ease of replacement of a hydroxyl group
by a halogen atom, according to the reaction:
R OH + HCl
ZnCl2
R Cl
+ H2 O
Since the product (alkyl halide) is insoluble in water, the solution
becomes cloudy and may separate into two layers when the hydroxyl group is
replaced with halogen. This cloudiness or appearance of a second layer
(heterogeneous mixture) is evidence that a reaction has occurred.
2
When Lucas reagent - ZnCl2 / conc. HCl is added to alcohols, H+ from
HCl will protonate the -OH group, so that the leaving group H2O, being a much
weaker nucleophile than OH-, hence can be substituted by nucleophile Cl-.
Lucas' reagent offers a polar medium in which SN1 mechanism is favoured. In
unimolecular nucleophilic substitution, the reaction rate is faster when the
carbocation intermediate is more stable. Therefore, tertiary alcohols react
immediately with Lucas reagent to produce turbidity while secondary alcohols
do so in about five minutes. Primary alcohols do not react appreciably with
Lucas reagent at room temperature. Hence, the time taken for turbidity to
appear is a measure of the reactivity of the class of alcohol with Lucas reagent,
and this is used to differentiate between the three classes of alcohols
1.
2.
3.
4.
5.
6.
Place 10 drops of 1-butanol in a clean dry test.
Add 4 mL of the Lucas reagent.
Stopper and shake well.
Observe the result immediately, after 5 min, and again after 30 min.
Present the data and confirm the result with your instructor.
Repeat step 1-4 with cyclohexanol, t-butanol, and 1 g of phenol.
6) The oxidation reaction
The oxidation of the carbon atom is an important reaction for this class
of compounds. When sodium dichromate is used as the oxidizing agent, the
orange dichromate ion is reduced to the green chromic ion. In this reaction a
chromate ester of the alcohol substrate is believed to be an intermediate, which
undergoes an E2-like elimination to the carbonyl product. The oxidation state of
carbon increases by 2, while the chromium decreases by 3 (it is reduced). The
progress of these oxidations is easily observed. Indeed, this is the chemical
transformation on which the Breathalizer test is based. The secondary alcohols
can be oxidized to ketones, while the oxidation of primary alcohols gives
carboxylic acid. Tertiary alcohols will not be oxidized under these conditions.
1.
2.
3.
4.
5.
6.
Place 3 mL of a 10% solution of sodium dichromate in a clean test tube.
Add 2 drops of concentrated sulfuric acid and mix thoroughly by shaking.
Add 3 drops of ethanol and warm gently (~40-50°C).
Note the odor; observe any change in color of the solution.
Present the data and confirm the result with your instructor.
Repeat step 1-4 with 2-propanol, t-butanol, and phenol.
3
EXPERIMENT 9
SYNTHESIS OF ESTERS AND REACTIONS OF CARBOXYLIC ACIDS
AND THEIR DERIVATIVES
(For Students)
Objectives
1)
2)
To synthesize the esters using acid-catalyzed esterification
To study the reactions of carboxylic acids and their derivatives
Principles
Carboxylic acids are an important class of organic compounds. Other
important classes of compounds called acid derivatives are related to acids but
differ from them in that the hydroxyl portion of the carboxyl function is replaced by
other groups. Among these acid derivatives are the acyl halides, anhydrides, esters
and amides.
O
R
C
OH
carboxylic acid
O
R
O
C
X
acyl halide
R
C
O
O
C
O
R
R
O
C
acid anhydride
OR'
ester
R
C
NH2
amide
Carboxylic acids can be converted to salts by base. Because these salts are
ionic and usually water-soluble, acids that are only slightly soluble in water can be
extracted by aqueous base from a solution in an organic solvent.
O
R
C
O
OH
+ NaOH
R
C
O-Na+
+ H2O
Acyl halides are usually prepared by the reaction of the corresponding acid
with an inorganic halide such as PCl3, PCl5 or thionyl chloride. Acid anhydrides can
be prepared by dehydrating acids whereas esters can be obtained by the reaction
of alcohols with acids or their derivatives. The acid-catalyzed reaction of an alcohol
with a carboxylic acid is the most common is used for such preparation. Amides
can be prepared by heating ammonium salts of acids or by the reaction of
ammonia or primary or secondary amines with various acid derivatives.
Most reactions of acid derivatives involve attack of a nucleophile on the
carbonyl carbon.
Name & ID
The preparation of ester
Background
Esters are found in many natural products, contributing to the aromas of
bananas, oranges, pineapples and other fruits. The structure of ester determines
its scent. By reacting different alcohols and carboxylic acids, you can produce
esters of varying scents.
There are many different synthetic methods for synthesizing esters, but two of
the most common are acid-catalyzed Fischer esterification of a carboxylic acid ad
alcohol and condensation of acid chloride with an alcohol or an alkoxide.
The Fischer esterification is an equilibrium reaction in which an acid and an
alcohol combine to produce the ester and water. For example, the acid catalyzed
reaction for the formation of ethyl acetate from acetic acid and ethanol.
O
O
H+
H3C
C
OH + CH3CH2OH
H3C
C
OCH2CH3 + H2O
To drive the equilibrium towards completion, either the carboxylic acid or the
alcohol is used in excess. Alternatively, if the ester has a significantly different
boiling point than the alcohol or acid, the ester can be separated from the acid
and alcohol by distillation.
A second synthetic route to esters is through an acid chloride. This method
can be used for any carboxylic acid, but it is especially good for malodorous acids.
Work up and purification are simplified, since only stoichiometric amounts of the
alcohol can be used.
O
O
H3C
C
Cl + CH3CH2OH
Technique
Reflux
Extraction using separatory funnel
Simple distillation
base
H3C
C
OCH2CH3
Name & ID
Procedure
Part A Preparation of fruity ester
Each group will get unknown carboxylic acid and alcohol.
Pour the unknown alcohol (0.046 mol) and carboxylic acid (0.12 mol) into a 50
mL round bottom flask. Carefully add 1.5 mL of concentrated sulfuric acid to the
contents of the flask. Add boiling stones to the mixture.
Assemble the reflux apparatus. Bring the mixture to boil using a heating
mantle. Heat the mixture under reflux for 1 hour. Remove the heating source and
allow the mixture to cool to room temperature. Pour the cooled mixture into the
separatory funnel and carefully add 20 mL of distilled water. Rinse the reaction
flask with 5 mL of distilled water and pour the rinsing into the separatory funnel.
Stopper the funnel and shake it several times. Separate the lower aqueous layer
from the upper organic layer. Discard the aqueous layer after making certain that
the correct layer has been saved.
The crude ester in the organic layer contains some acids which can be
removed by extraction with 5%NaHCO3 solution. Carefully add 10 mL of 5%
NaHCO3 to the organic layer contained in the separatory funnel. Swirl the
separatory funnel gently until carbon dioxide gas is no longer evolved. Remove
the lower layer, and repeat the above extraction with 10 mL of 5% NaHCO3
Remove the lower layer and check to see whether it is basic to litmus. (If it is not
basic, repeat the procedure with additional 10 mL portions of 5% NaHCO3 until
the aqueous layer is basic) Discard the basic washings and extract the organic
layer with one 10-mL portion of water. Add 10 mL of saturated sodium chloride to
aid in layer separation. Carefully separate the lower layer and discard it. When the
ester has been removed, pour the ester from the top of the separatory funnel into
a flask. Add about 2 g of anh MgSO4 to dry the ester.
Assemble a simple distillation apparatus, carefully decant the ester into the
distillating flask. Add boiling stones and distill the ester. Collect the fraction and
observe the boiling range. Weigh the product.
Tell your instructor what the smell of your fruity ester is and what a pair of
unknown compounds you got should be (see Table). Check also the boiling range
of your obtained ester from your instructor.
After you know the right combination of carboxylic acid and alcohol you got,
calculate the percentage yield.
Name & ID
Table Selected ester flavors and fragrances
Complete this table before starting the experiments.
Write down the structures of carboxylic acids, alcohols and esters.
Find out the boiling range of the esters from the references.
Carboxylic
acid
Acetic acid
alcohol
Ester
b.p.
Isoamyl alcohol
Isoamyl acetate
Propionic acid
Isobutyl alcohol
Isobutyl propionate
rum
Anthranilic
acid
Methyl alcohol
Methyl anthranilate
grape
Acetic acid
Benzyl alcohol
Benzyl acetate
peach
Butyric acid
Methyl alcohol
Methyl butyrate
apple
Butyric acid
Ethyl alcohol
Ethyl butyrate
pineapple
Acetic acid
Octyl alcohol
Octyl acetate
orange
Acetic acid
n-Propyl alcohol
n-propyl acetate
banana
pear
Name & ID
Part B
Reactions of carboxylic acids and their derivatives
During waiting for the reaction in part A complete.
experiments in Part B.
Carefully perform the
Samples: formic acid, acetic acid, oxalic acid, benzoic acid, methyl benzoate and
acetanilide
1. Solubility Experiments
a) Solubility in water
Use approximately 2 drops of liquid sample or 0.1 g of solid sample,
dissolve in water 3 mL.
Observe the solubility in water and record your observation.
b) With 5% NaOH solution
Use the same amount of sample mentioned above, dissolve in 5% NaOH
solution
Observe the solubility in 5% NaOH solution and record your observation.
c) With 5% NaHCO3 solution
Use the same amount of sample mentioned above, dissolve in 5%
NaHCO3 solution.
Observe the solubility in 5% NaHCO3 and gas evolved, record your
observation.
2. Sodium hydroxamate reactions
Place a drop of methyl benzoate in a test tube, add 0.5 M NH2OH.HCl in
ethanol 1 mL. Add 20% NaOH until the solution become basic. Warm up
the mixture on the water bath and cool down, then add 1M HCl until the
solution become acidic or the brown precipitate dissolve. Add 5% FeCl3 1
drop or until permanent color could be observed.
Record your observation. Compare with benzoic acid.
3. Reaction with Tollens’ reagent
Place approximately 4 mL of Tollens’ reagent in 5 tubes. Add formic acid
and acetic acid 5 drops each in the first two tubes. For the other two tubes,
add oxalic acid and benzoic acid 0.1 g each. The last tube is used as a
blank.
Record your observation. Compare with the blank tube.
4. Reaction with KMnO4
Prepare 5 tubes. Add conc. H2SO4 1 drop, distilled water 1 mL and 0.3%
KMnO4 in each tube. Add formic acid and acetic acid 5 drops each in the
first two tubes. For the other two tubes, add oxalic acid and benzoic acid
0.1 g each. Gently shake. Warm all 5 test tubes on the water bath for 1
min. The last tube is used as a blank.
Record your observation. Compare with the blank tube.
Name & ID
Caution: Extreme care must be exercised to avoid contact with concentrated
sulfuric acid. It will cause serious burns if it is spilled on the skin. If it comes in
contact with the skin or clothes, it must be washed off immediately with excess
water. In addition, sodium bicarbonate may be used to neutralize the acid.
Clean up all spills immediately.
Reference
1. “Introduction to Organic Laboratory Techniques: A Small Scale Approach”,
Pavia, Lampman, Kriz and Engel, Brooks/Cole, 2nd Ed, 2005.
2. “Theory and Practice in the Organic Laboratory” Landgrebe, Brooks/Cole, 5th
Ed, 2005.
3. “Microscale and Miniscale Organic Chemistry Laboratory Experiments”
Schoffstall, Gaddis, Druelinger, McGraw Hill, 2nd Ed, 2004.
4. “Organic Chemistry”, Solomon and Fryhle, John Wiley & Sons, 8th Ed, 2004.