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Experiment 8BQualitative Analysis II
Introduction
• Qualitative analysis of an unknown organic
compound is an indispensible tool in experimental
organic chemistry. This method is done in order to
determine the possible structures of an
unknown sample. The different functional groups
present in an organic compound are identified by
reacting the sample with different reagents that react
that gives a visible result. It is an indispensable tool
in experimental organic chemistry as well as other
fields such as the study of natural products and
biochemistry.
Sodium Metal
• Results
Tests for Alcohols
Sample Visible ResultStructure/Formula of compound
responsible for visible results
n-butyl
alcoholEvolution of gas H2
Sec-butyl
alcoholEvolution of gas H2
Tert-butyl
alcoholEvolution of gas H2
Sodium Metal
• Type of Reaction: Acid-Base Reaction
• General Formula:
Tests for Alcohols
Sodium Metal
• Mechanism
Tests for Alcohols
sodium
alkoxidebubbles
Sodium Metal
• Complications
– Dealing with sodium metal can be exciting.
Make sure that all samples are dry before
proceeding with test.
Tests for Alcohols
Sodium Metal
1. What property of alcohol is demonstrated in the reaction with Na metal? What is the formula of the gas liberated?
– The alcohol exhibits acidic property in the reaction with Na metal. The hydrogen atom is replaced by Na producing H2 shown in the reaction:
– 2 R–O–H + 2 Na 2 R–O(–)Na(+) + H2
(http://www2.uni-siegen.de/~pci/versuche/english/v44-1-1.html)
Tests for Alcohols
Sodium Metal
2. Dry test tube should be used in the
reaction between the alcohols and Na
metal. Why?
– A dry test tube should be used because Na
metal is highly reactive with water and may
ignite violently due to the H2 gas produced
(http://www2.uni-siegen.de/~pci/versuche/english/v44-1-1.html)
Tests for Alcohols
Lucas Reagent (HCl/ZnCl2)
• Results
Tests for Alcohols
Sample Visible Result
Structure/Formula of
compound responsible
for visible results
n-butyl No layer None
Sec-butyl
alcohol
Formation of
layers(CH3)2CHCl + H2O
Tert-butyl
alcohol
Formation of
layers(CH3)3CCl + H2O
Lucas Reagent (HCl/ZnCl2)
• Type of Reaction: Nucleophilic Substitution
• Substrate:
• Attacking Agent: Cl-
• General Formula:
Tests for Alcohols
Lucas Reagent (HCl/ZnCl2)
• Mechanism (SN1 for 2º and 3º ROH)
Tests for Alcohols
insoluble layer
Lucas Reagent (HCl/ZnCl2)
• Mechanism (SN2 for 1º ROH)
Tests for Alcohols
insoluble layer
Lucas Reagent (HCl/ZnCl2)
• ZnCl2 is a Lewis acid that complexes strongly
with the lone-pairs oxygen. This weakens the C-
O bond and creates a better leaving group.
• ZnCl2 also enhances the reactivity of the HCI by
polar coordination.
Tests for Alcohols
Lucas Reagent (HCl/ZnCl2)
• Complications
– The test applies only to those alcohols soluble
in the reagent (monofunctional alcohols lower
than hexyl and some polyfunctional alcohols).
Tests for Alcohols
Lucas Reagent (HCl/ZnCl2)
3. Why is the Lucas test not used for alcohols
containing more than eight carbon atoms?
– The Lucas test applies only to alcohols soluble in
Lucas reagent (monofunctional alcohols with less
than 6 carbons and some polyfunctional alcohols).
Long chains of carbon makes the compound nonpolar
and the –OH group less functional. This results to the
insolubility of the alcohol in the reagent, rendering the
test ineffective.
Tests for Alcohols
Lucas Reagent (HCl/ZnCl2)
4. Explain why the order of reactivity of the
alcohols toward Lucas reagent is 3°>2°>1°?
– The reaction of alcohols with Lucas reagent is a
nucleophilic substitution reaction. In an Sn1 reaction,
the rate determining step is the carbocation. The
carbocation is most stable in a tertiary alcohol and is
therefore formed faster than a secondary and a
primary carbocation. (Solomons and Fryhle)
Tests for Alcohols
Potassium Dichromate
• Results
Tests for Alcohols
Sample Visible Result
Structure/Formula of
compound responsible for
visible results
n-butyl Blue-green soln Cr3+
Sec-butyl Blue-green Cr3+
Tert-butyl Yellow-orange Cr2O72-
Potassium Dichromate
• Type of Reaction: Reduction-Oxidation
• General Formula:
Tests for Alcohols
Potassium Dichromate
• Mechanism
Tests for Alcohols
Potassium Dichromate
• Mechanism
Tests for Alcohols
Potassium Dichromate
• Mechanism
Tests for Alcohols
chromate ester
elimination
green
(due to chromium ion, Cr3+)
Potassium Dichromate
• For 1º ROH, RCHO products are further
oxidized to form RCOOH
Tests for Alcohols
Potassium Dichromate
• Tertiary alcohols do not react because there will
not be any b-hydrogens to eliminate.
Tests for Alcohols
Potassium Dichromate
• Complications
– Aldehydes, which also give a positive test, are
better characterized in other ways. The color
usually develops in 5 - 15 seconds.
– Enols may give a positive test.
– Phenols give a dark colored solution which is
not blue-green like a positive test.
Tests for Alcohols
Potassium Dichromate
5. Illustrate with equations the reactions of the following alcohols with Potassium Dichromate solution:
Proof that dichromate is a strong oxidizing reagent in an acidic sol’n (ε0= 1.33 V) (ε0 = −0.13 V)
• n-butylalcohol
– CH3CH2CH2CH2OH + Cr2O72- CH3CH2CH2CHO + [O]
CH3CH2CH2COOH
• sec-butylalcohol
– CH3CH2CH(OH)CH3 + Cr2O72- CH3CH2COCH3 + H2O
• tert-butylalcohol– (CH3)3COH + Cr2O7
2- no reaction
Tests for Alcohols
Ferric Chloride
• Results
Tests for Phenols
Sample Visible Result
Structure/Formula of
compound responsible for
visible results
Phenol Brown-black Fe(OAr)3
Catechol Brownish Fe(OAr)3
Resorcinol Brownish green Fe(OAr)3
a-naphthol Purple solution Fe(OAr)3
Ferric Chloride
• Type of Reaction: Complexation
• General Formula:
Tests for Phenols
Ferric Chloride
• Mechanism
Tests for Phenols
blue to violet color
Ferric Chloride
• Complications
– Not all phenols or enols give positive results.
– Most oximes, hydroxamic acids, and sulfinic acids give a positive test.
– Bulky groups on the benzene ring, especially in the ortho position, may cause the experiment to show a negative result.
– Activating groups attached to the ring decreases the wavelength caused by less electron excitation, thus causing a different color of positive result.
Tests for Phenols
Bromine Water
• Mechanism
Tests for Phenols
Sample Visible Result
Structure/Formula of
compound responsible
for visible results
Phenol Light brown 2,4,6-tribromophenol
Catechol Dark solutionBromination of benzene
ring
Resorcinol Yellow with precipitate Tribromoresorcinol
a-naphthol Dark cloudy solution 2,4-dibromo-1-naphthol
Bromine Water
• Type of Reaction: Electrophilic Substitution
• Substrate: ArOH
• Attacking Agent: Br+
• General Formula:
Tests for Phenols
brown to black solution
yellow Br color is removed
Bromine Water
• Mechanism
Tests for Phenols
Bromine Water
• The aromatic ring is activated by the hydroxy
group, therefore, it can react by electrophilic
addition
Tests for Phenols
Bromine Water
• Complications
– Mercaptans react readily.
– HBr is generated, but will not be observed
since the reagent is aqueous.
Tests for Phenols
Millon’s (Hg(NO3)2 in H2O)
• Results
Tests for Phenols
Sample Visible Result
Structure/Formula of
compound responsible for
visible results
PhenolDark upper layer, light
bottomHg complex with phenols
Catechol Dark solution Hg complex with phenols
Resorcinol Dark purple Hg complex with phenols
a-naphthol Greenish yellow Hg complex with phenols
Millon’s (Hg(NO3)2 in H2O)
• Type of Reaction: Electrophilic Addition
and Complexation
• Substrate: Ar-OH and tyrosine
• Attacking Agent: Hg(NO3)2
• General Formula:
Tests for Phenols
• Mechanism
1. Nitration of aromatic ring
2. Complexation with mercuric ion
• Produces: red complexes and ppt
Tests for Phenols
Millon’s (Hg(NO3)2 in H2O)
6. What functional group is responsible for
the observed result in Millon’s test?
– Phenol interacts with nitric acid, nitrated
phenol reacts with mercury and mercury salts
are formed. This reaction accounts for the
observed positive result in Millon’s test.
Tests for Phenols
Millon’s (Hg(NO3)2 in H2O)
2,4-dinitrophenylhydrazine
• Results
Tests for Aldehydes and Ketones
Sample Visible Result
Structure/Formula of
compound responsible for
visible results
Formaladehyde Yellow ppt 2,4-dinitrophenylhydrazone
AcetaldehydeOrange,
brown(heated)2,4-dinitrophenylhydrazone
Acetone Orange ppt 2,4-dinitrophenylhydrazone
Benzaldehyde Orange ppt 2,4-dinitrophenylhydrazone
2,4-dinitrophenylhydrazine
• Type of Reaction: Nucleophilic Addition
• Substrate:
• Attacking Agent:
• General Formula:
Tests for Aldehydes and Ketones
2,4-dinitrophenylhydrazine
• Mechanism
Tests for Aldehydes and Ketones
2,4-dinitrophenylhydrazine
• Mechanism
Tests for Aldehydes and Ketones
yellow to red ppt
2,4-dinitrophenylhydrazine
• Complications
– Some ketones give oils which will not solidify.
– Some allylic alcohols are oxidized by the
reagent to aldehydes and give a positive test.
Tests for Aldehydes and Ketones
2,4-dinitrophenylhydrazine
7. Why is it disadvantageous to use a strong acid catalyst in the reaction of aldehyde or ketone with 2,4-DNPH?– The use of a strong acid reverses the sequence of the
reaction. Instead of the nucleophilic attacking the substrate followed by the electrophile, in the presence of a strong acid, the weaker ucleophile attacks the carbon to stabilize the forming hemiacetal. Water abstracts the H+ of the hemiacetal. Hemiacetals are less stable and will form acetals which do not show the visible changes expected of the test.
Tests for Aldehydes and Ketones
2,4-dinitrophenylhydrazine
8. Show the mechanism for the reaction of
acetaldehyde with the following reagents:
a. 2,4 – DNPH
Tests for Aldehydes and Ketones
2,4-dinitrophenylhydrazine
8. Show the mechanism for the reaction of
acetaldehyde with the following reagents:
a. 2,4 – DNPH
Tests for Aldehydes and Ketones
Bisulfite
• Mechanism
Tests for Aldehydes and Ketones
Sample Visible Result
Structure/Formula of
compound responsible for
visible results
Formaldehyde Ppt formation H2CH(OH)SO3- Na+
Acetaldehyde Ppt formation H3C(OH) SO3- Na+
Acetone No Ppt H3CC(OH)SO3- Na+
Benzaldehyde Ppt formation (C6H6)CH(OH)SO3- Na+
Bisulfite
• Type of Reaction: Nucleophilic Addition
• Substrate:
• Attacking Agent:
• General Formula:
Tests for Aldehydes and Ketones
Bisulfite
• Mechanism
Tests for Aldehydes and Ketones
insoluble
Bisulfite
• Complications
– Aryl methyl ketones form the precipitate
slowly or not at all.
– Addition complex stable only in neutral
solution.
Tests for Aldehydes and Ketones
Bisulfite
8. Show the mechanism for the reaction of
acetaldehyde with the following reagents:
b. NaHSO3
Tests for Aldehydes and Ketones
Schiff’s Test (Fuschine in NaHSO3 solution)
• Results
Tests for Aldehydes and Ketones
Sample Visible ResultStructure/Formula of compound
responsible for visible results
Formaldehyde Purple
Acetaldehyde Red-purple
Acetone No change
Benzaldehyde purple
• Type of Reaction: Nucleophilic Addition and
Elimination
• Substrate:
• Attacking Agent: Schiff’s Reagent
• General Formula:
Tests for Aldehydes and Ketones
Schiff’s Test (Fuschine in NaHSO3 solution)
• Schiff’s Reagent (fuchsia/pink)
– (bis-N-sulfinic acid of p-rosaline hydrochloride) aka
fuchsin-aldehyde reagent or Leucosulfonic acid
Tests for Aldehydes and Ketones
Schiff’s Test (Fuschine in NaHSO3 solution)
• Mechanism
Tests for Aldehydes and Ketones
Schiff’s Test (Fuschine in NaHSO3 solution)
• Product: Quinoid Dye (purple/magenta)
Tests for Aldehydes and Ketones
Schiff’s Test (Fuschine in NaHSO3 solution)
• Complications
– In this test the reagent should not be heated, and the
solution tested should not be alkaline.
– When the test is used on an unknown, a
simultaneous test on a known aldehyde and a known
ketone should be performed for comparison.
Tests for Aldehydes and Ketones
Schiff’s Test (Fuschine in NaHSO3 solution)
9. Why is the Schiff’s test considered a general
test for aldehydes?
– Differentiation of aldehydes from ketones becomes
the main purpose of using Schiff’s test since it cannot
distinguish one kind of aldehyde from another.
Tests for Aldehydes and Ketones
Schiff’s Test (Fuschine in NaHSO3 solution)
• Results
Tests for Aldehydes and Ketones
Sample Visible Result
Structure/Formula of
compound responsible
for visible results
Formaladehyde Silver mirror Ag
Acetaldehyde Silver mirror Ag
Acetone Clear None
Benzaldehyde Silver mirror Ag
Tollen’s Test (Ag(NH3)2OH)
Tollen’s Test (Ag(NH3)2OH)
• Type of Reaction: Reduction-Oxidation
• Reducing Agent:
• Oxidizing Agent: Ag(NH3)2+
• General Formula:
Tests for Aldehydes and Ketones
• Mechanism
Tests for Aldehydes and Ketones
Tollen’s Test (Ag(NH3)2OH)
silver mirror
• Complications
– The test tube must be clean and free of oil if a silver
mirror is to be observed.
– Easily oxidized compounds give a positive test. For
example: aromatic amine, some phenols, a-alkoxy
and a-dialkylaminoketones.
Tests for Aldehydes and Ketones
Tollen’s Test (Ag(NH3)2OH)
10.What test will you use to differentiate
each of the following pairs? Give also the
visible result.
– Acetaldehyde and acetone
• Schiff’s reagent: acetaldehyde – purple solution;
acetone – no reaction
• Tollen’s test: acetaldehyde – silver mirror; acetone
– no reaction
Tests for Aldehydes and Ketones
Tollen’s Test (Ag(NH3)2OH)
10.What test will you use to differentiate each of the following pairs? Give also the visible result.– Acetaldehyde and bezaldehyde
• Acetaldehyde and benzaldehyde can be distinguished from each other using the Bisulfite test since it is also an indication whether the sample is an aliphatic aldehyde or an aromatic aldehyde. Aldehyde will react faster than benzaldehyde because an aromatic ring makes the compound more electron-rich, making the compound less susceptible to nucleophilic attack. Both will form a red precipitate due to cuprous oxide.
Tests for Aldehydes and Ketones
Tollen’s Test (Ag(NH3)2OH)
Iodoform Test (NaOH/I2KI)
• Results
Tests for Aldehydes and Ketones
Sample Visible Result
Structure/Formula of
compound responsible
for visible results
Formaladehyde None None
Acetaldehyde Yellow Ppt CHI3
Acetone Yellow Ppt CHI3
Benzaldehyde None None
Iodoform Test (NaOH/I2KI)
• Type of Reaction: Nucleophilic Addition + Substitution
• Substrate: I+
• Attacking Agent: OH-
• General Formula:
Tests for Aldehydes and Ketones
addition substitution
Iodoform Test (NaOH/I2KI)
• Mechanism: Secondary alcohols/ethanol with an
adjacent methyl group are oxidized to methyl
ketones/ethanal by iodine bleach.
Tests for Aldehydes and Ketones
Iodoform Test (NaOH/I2KI)
• Mechanism (Nucleophilic Addition Part)
Tests for Aldehydes and Ketones
Iodoform Test (NaOH/I2KI)
• Mechanism (Nucleophilic Substitution Part)
Tests for Aldehydes and Ketones
yellow
ppt
Iodoform Test (NaOH/I2KI)
• Complications
– Test will not be positive if the R group is a di-
ortho substituted aryl group.
Tests for Aldehydes and Ketones
Iodoform Test (NaOH/I2KI)
11.What structural feature in a compound is
required for a positive iodoform test? Will
ethanol give a positive iodoform test? Why or
why not?
– Ketones and alcohols with a methyl group directly
adjacent to a carbonyl group or a carbon atom
bearing a hydroxyl group react with an alkaline
solution of iodine to produce a yellow solid, iodoform.
Ethanol will give a positive result because it can be
oxidized to an aldehyde with a methyl group attached
to a carbonyl group.
Tests for Aldehydes and Ketones
Iodoform Test (NaOH/I2KI)
12.Show the mechanisms for the iodoform using
acetaldehyde as the test sample:
Tests for Aldehydes and Ketones
• Results
Tests for Aldehydes and Ketones
Sample Visible Result
Structure/Formula of
compound responsible for
visible results
Formaladehyde Brick Red Precipitate Cu2O
Acetaldehyde Brick Red Precipitate Cu2O
Acetone None No rxn
Benzaldehyde Brick Red Precipitate Cu2O
Fehling’s Test [Cu(C4H4O6)2]4-
Fehling’s Test [Cu(C4H4O6)2]4-
• Type of Reaction: Reduction-Oxidation
• Reducing Agent: (reducing sugar)
• Oxidizing Agent: [Cu(C4H4O6)2]4-
• General Formula:
Tests for Aldehydes and Ketones
• Fehling’s Reagent: Sodium tartrate, NaOH and
CuSO4 forming a copper-tartrate complex
Tests for Aldehydes and Ketones
Fehling’s Test [Cu(C4H4O6)2]4-
• Mechanism
Tests for Aldehydes and Ketones
Fehling’s Test [Cu(C4H4O6)2]4-
• Mechanism
Tests for Aldehydes and Ketones
Fehling’s Test [Cu(C4H4O6)2]4-
brick red ppt
• Complications
– None.
Tests for Aldehydes and Ketones
Fehling’s Test [Cu(C4H4O6)2]4-
• Results
Tests for Aldehydes and Ketones
Test Samples Visible Result
Structure Formula of
Compound Responsible
for the Visible Result
Glucose Violet Ring
1% Sucrose Violet Ring
Maltose Violet Ring
1% Boiled Starch Violet Ring
Molisch (a-naphthol in ethanol)
Molisch (a-naphthol in ethanol)
• Type of Reaction: Nucleophilic Substitution
• Substrate: furfural or hydroxymethylfurfural
• Attacking Agent: a-naphthol
• General Formula:
Tests for Aldehydes and Ketones
• Mechanism
– Dehydration of Hexose Sugar by H2SO4 (elimination)
Tests for Aldehydes and Ketones
Molisch (a-naphthol in ethanol)
• Mechanism
– Dehydration of Pentose Sugar by H2SO4 (elimination)
Tests for Aldehydes and Ketones
Molisch (a-naphthol in ethanol)
• Mechanism
Tests for Aldehydes and Ketones
Molisch (a-naphthol in ethanol)
• Mechanism
Tests for Aldehydes and Ketones
Molisch (a-naphthol in ethanol)
• Mechanism
Tests for Aldehydes and Ketones
Molisch (a-naphthol in ethanol)
violet
Benedict’s Test [Cu3(citrate)2]
• Results
Tests for Aldehydes and Ketones
Sample Visible Result
Structure/Formula of
compound responsible for
visible results
Glucose Brick Red Precipitate Cu2O
Maltose Brick Red Precipitate Cu2O
Sucrose Brick Red Precipitate Cu2O
Boiled starch No change No rxn
• Type of Reaction: Reduction-Oxidation
• Reducing Agent: (reducing sugar)
• Oxidizing Agent: Cu3(citrate)2
• General Formula:
Tests for Aldehydes and Ketones
Benedict’s Test [Cu3(citrate)2]
• Benedict’s Reagent: Sodium citrate, CuSO4 and
NaHCO3 forming copper-citrate
Tests for Aldehydes and Ketones
Benedict’s Test [Cu3(citrate)2]
• Mechanism
Tests for Aldehydes and Ketones
Benedict’s Test [Cu3(citrate)2]
• Mechanism
Tests for Aldehydes and Ketones
Benedict’s Test [Cu3(citrate)2]
brick red ppt
• Complications
– Not general for simple aldehydes and ketones.
– Hydrazine derivatives give a positive test.
Tests for Aldehydes and Ketones
Benedict’s Test [Cu3(citrate)2]
Hinsberg (benzenesulfonyl chloride)
• Results
Tests for Amines
Sample Visible Result
Structure/Formula of
compound responsible for
visible results
Methylamine ppt in acid C6H5SO2NRH
Dimethylamine ppt in base/acid C6H5SO2NR2
Trimethylamine ppt in base R3NHCl
Aniline ppt in baseacid C6H5SO2NRH
n-methylamine ppt in acid C6H5SO2NRH
Hinsberg (benzenesulfonyl chloride)
• Type of Reaction: Nucleophilic Substitution
• Substrate:
• Attacking Agent:
• General Formula:
Tests for Amines
• Mechanism (1º amines)
Tests for Amines
water soluble water insoluble
Hinsberg (benzenesulfonyl chloride)
Hinsberg (benzenesulfonyl chloride)
• Mechanism (2º amines)
Tests for Amines
water insoluble
Hinsberg (benzenesulfonyl chloride)
• Mechanism (3º amines)
Tests for Amines
water insoluble
Hinsberg (benzenesulfonyl chloride)
• Mechanism (3º amines)
Tests for Amines
water soluble
Hinsberg (benzenesulfonyl chloride)
• Complications
– Amphoteric compounds give erroneous results.
– Some sodium salts of benzenesulfonamides of
primary amines are insoluble in the Hinsberg solution
and may appear to be secondary amines.
– Some tertiary amine hydrochloride salts are insoluble
in dilute HCl and water and may also appear to be
secondary amines.
Tests for Amines
Esterification
• Results
Tests for Carboxylic Acid + Derivatives
Sample Visible Result
Structure/Formula of
compound responsible
for visible results
Salicylic acidColorless with
wintergreen odor
methyl 2-
hydroxybenzoate
Esterification
• Type of Reaction: Nucleophilic Substitution
• Substrate:
• Attacking Agent:
• General Formula:
Tests for Carboxylic Acid + Derivatives
Esterification
• Mechanism
Tests for Carboxylic Acid + Derivatives
ester with odor
Esterification
• Complications
– None.
Tests for Carboxylic Acid + Derivatives
Hydrolysis of Benzamide
• Results
Tests for Carboxylic Acid + Derivatives
Sample Visible Result
Structure/Formula of
compound responsible
for visible results
BenzamideRed to blue litmus
Pungent odorammonia
Hydrolysis of Benzamide
• Type of Reaction: Nucleophilic Substitution
• Substrate:
• Attacking Agent: OH-
• General Formula:
Tests for Carboxylic Acid + Derivatives
Hydrolysis of Benzamide
• Mechanism
Tests for Carboxylic Acid + Derivatives
basic and pungent
Hydrolysis of Benzamide
• Complications
– none
Tests for Carboxylic Acid + Derivatives
Hydrolysis of Ester
• Results
Tests for Carboxylic Acid + Derivatives
Sample Visible Result
Structure/Formula of
compound responsible
for visible results
EthylacetateLoss of Sweet
OdorAcetic acid and Ethanol
Hydrolysis of Ester
• Type of Reaction: Nucleophilic Substitution
• Substrate:
• Attacking Agent:
• General Formula:
Tests for Carboxylic Acid + Derivatives
Hydrolysis of Ester
• Mechanism
Tests for Carboxylic Acid + Derivatives
Hydrolysis of Ester
• Complications
– none
Tests for Carboxylic Acid + Derivatives
Hydrolysis of Anhydride
• Results
Tests for Carboxylic Acid + Derivatives
Sample Visible Result
Structure/Formula of
compound responsible
for visible results
Acetic anhydride Acidic Acetic acid
Hydrolysis of Anhydride
• Type of Reaction: Nucleophilic Substitution
• Substrate:
• Attacking Agent: HOH
• General Formula:
Tests for Carboxylic Acid + Derivatives
Hydrolysis of Anhydride
• Mechanism
Tests for Carboxylic Acid + Derivatives
Hydrolysis of Anhydride
• Complications
– Higher aliphatic anhydrides and aromatic anhydrides
are not readily hydrolyzed with water and thus may
not give a positive test.
Tests for Carboxylic Acid + Derivatives
Hydroxamic Acid Test(hydroxylamine hydrochloride)
• Results
Tests for Carboxylic Acid + Derivatives
Sample Visible ResultStructure/Formula of compound
responsible for visible results
EthylacetateBurgundy or magenta
color Hydroxamate complexes
Benzamide Red to violet color Hydroxamate complexes
Acetic anhydrideBurgundy or magenta
color Hydroxamate complexes
BenzoylchlorideBurgundy or magenta
color Hydroxamate complexes
Hydroxamic Acid Test(hydroxylamine hydrochloride)
• Type of Reaction: Nucleophilic Substitution
• Substrate:
• Attacking Agent:
• General Formula:
Tests for Carboxylic Acid + Derivativeshydroxamic acid
Hydroxamic Acid Test(hydroxylamine hydrochloride)
• Formation of Hydroxylamine
• KOH is added to consume the HCl, so that the reaction will not proceed backward
Tests for Carboxylic Acid + Derivatives
• Mechanism for Anhydrides
Tests for Carboxylic Acid + Derivatives
Hydroxamic Acid Test(hydroxylamine hydrochloride)
• Mechanism for Acyl Halides
Tests for Carboxylic Acid + Derivatives
Hydroxamic Acid Test(hydroxylamine hydrochloride)
Hydroxamic Acid Test(hydroxylamine hydrochloride)
• Mechanism for Esters
Tests for Carboxylic Acid + Derivatives
• Mechanism for Amides
Tests for Carboxylic Acid + Derivatives
Hydroxamic Acid Test(hydroxylamine hydrochloride)
• Ferric Hydroxamate Complex Formation
• The solution is acidified by HCl to prevent the
excess base from reacting with FeCl3 (a Lewis Acid)
Tests for Carboxylic Acid + Derivatives
Hydroxamic Acid Test(hydroxylamine hydrochloride)
red/violet/burgundy/magenta color
• Complications
– Some acids will give a positive test.
– Primary and secondary nitro compounds, imides,
some amides, most nitriles, and aldehydes (with no a-
hydrogens give a positive test.
– Some sterically hindered amides fail to react.
Tests for Carboxylic Acid + Derivatives
Hydroxamic Acid Test(hydroxylamine hydrochloride)
Last Guide Question!
13. A colorless liquid has a bp 199-201°C and burns with a smoky flame. The sodium fusion test proved negative for the presence of halogens, nitrogen and sulfur. It was not soluble in water, 5% aqueous sodium hydroxide, or 5% hydrochloric acid. However, it dissolved in sulfuric acid with evolution of heat. It did not give a precipitate with 2,4-DNPH solution and did not decolorize bromine-methylene chloride solution. The unknown liquid did give a positive hydroxamate test and was found to have a saponification equivalent of 136. Identify the unknown liquid.
– Smoky flame indicates that the compound is aromatic. It tested negative for 2,4-DNPH, telling us that it is neither an aldehyde nor a ketone. Negative tests for bromine in methylene chloride solution also indicates that it is neither an alcohol nor a phenol. A positive test for hydroxamate test tells us that it is an acid derivative, which can undergo saponification—therefore it is an ester. Finally, an aromatic ester with a boiling point range of 199-201oC is methyl benzoate.
References
• http://chemed.chem.purdue.edu/genchem/topicreview/bp
/ch9/active.php
• http://www.biologie.uni-hamburg.de/b-
online/library/newton/Chy251_253/Lectures/Oxidation_of
_Alcohols/Oxidation.html
• http://homepages.ius.edu/DSPURLOc/c122/ket.htm
• http://www.curvedarrowpress.com/partd/tollens.html
• http://web.pdx.edu/~wamserc/C335W99/Fans.htm
• http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/
amine1.htm
• http://www.demochem.de/p30_Z_mol-e.htm
References
• Hornback, J.M. (2006). Organic Chemistry. 2nd Ed.
Belmont, CA: Thomas Brooks/Cole.
• Shriner, R.L. (2004). Systematic Identification of Organic
Compounds. NJ: John Wiley and Sons Inc.
• Vogel, A.I. (1989). Vogel’s Textbook of Practical Organic
Chemistry 5th Ed. UK: Longman Group.