Document Text Contents
Page 1
Haloform reaction
From Wikipedia, the free encyclopedia
Jump to: navigation, search
The haloform reaction is a chemical reaction where a haloform (CHX3, where X is a halogen) is
produced by the exhaustive halogenation of a methyl ketone (a molecule containing the R-CO-
CH3 group) in the presence of a base.
[1]
R may be H, alkyl or aryl. The reaction can be used to
produce CHCl3, CHBr3 or CHI3.
Contents
1 Scope
2 Mechanism
3 Uses
4 Iodoform test
5 History
6 References
[edit] Scope
Substrates that successfully undergo the haloform reaction are methyl ketones and secondary
alcohols oxidizable to methyl ketones, such as isopropanol. The only primary alcohol and
aldehyde to undergo this reaction are ethanol and ethanal, respectively. 1,3-Diketones such as
acetylacetone also give the haloform reaction. Beta-ketoacids such as acetoacetic acid will also
give the test upon heating. The halogen used may be chlorine, bromine, or iodine. Fluoroform
(CHF3) cannot be prepared from a methyl ketone by the haloform reaction due to the instability
of hypofluorite, but compounds of the type RCOCF3 do cleave with base to produce fluoroform
(CHF3); this is equivalent to the second and third steps in the process shown above.
[edit] Mechanism
In the first step, the halogen disproportionates in the presence of hydroxide to give the halide and
hypohalite:
http://en.wikipedia.org/wiki/Haloform_reaction#mw-head
http://en.wikipedia.org/wiki/Haloform_reaction#p-search
http://en.wikipedia.org/wiki/Halogen
http://en.wikipedia.org/wiki/Halogenation
http://en.wikipedia.org/wiki/Ketone
http://en.wikipedia.org/wiki/Base_(chemistry)
http://en.wikipedia.org/wiki/Haloform_reaction#cite_note-0
http://en.wikipedia.org/wiki/Hydrogen
http://en.wikipedia.org/wiki/Alkyl
http://en.wikipedia.org/wiki/Aryl
http://en.wikipedia.org/wiki/Chloroform
http://en.wikipedia.org/wiki/Bromoform
http://en.wikipedia.org/wiki/Iodoform
http://en.wikipedia.org/wiki/Haloform_reaction#Scope
http://en.wikipedia.org/wiki/Haloform_reaction#Mechanism
http://en.wikipedia.org/wiki/Haloform_reaction#Uses
http://en.wikipedia.org/wiki/Haloform_reaction#Iodoform_test
http://en.wikipedia.org/wiki/Haloform_reaction#History
http://en.wikipedia.org/wiki/Haloform_reaction#References
http://en.wikipedia.org/w/index.php?title=Haloform_reaction&action=edit§ion=1
http://en.wikipedia.org/wiki/Aldehyde
http://en.wikipedia.org/wiki/Ethanol
http://en.wikipedia.org/wiki/Ethanal
http://en.wikipedia.org/wiki/Acetylacetone
http://en.wikipedia.org/wiki/Acetoacetic_acid
http://en.wikipedia.org/wiki/Fluoroform
http://en.wikipedia.org/wiki/Hypofluorite
http://en.wikipedia.org/wiki/Fluoroform
http://en.wikipedia.org/w/index.php?title=Haloform_reaction&action=edit§ion=2
http://en.wikipedia.org/wiki/Hydroxide
http://en.wikipedia.org/wiki/File:Haloform_Reaction_Scheme.png
Page 2
X2 + OH−→ XO−+ X− + H
+
(X = Cl, Br, I) (Unbalanced)
If a secondary alcohol is present, it is oxidized to a ketone by the hypohalite (hydroxide
depicted below should be hypohalite and the water≡H2O should be hypohalic acid≡HXO):
If a methyl ketone is present, it reacts with the hypohalite in a three-step process:
(1) R-CO-CH3 + 3 OX
-
→ R-CO-CX3 + 3 OH−
(2) R-CO-CX3 + OH− → RCOOH + −CX3
(3) RCOOH + −CX3 → RCOO− + CHX3
The detailed reaction mechanism is as follows:
Under basic conditions, the ketone undergoes keto-enol tautomerization. The
enolate undergoes electrophilic attack by the hypohalite (containing a halogen
with a formal +1 charge). When the α position has been exhaustively
halogenated, the molecule undergoes a nucleophilic acyl substitution by
hydroxide, with −CX3 being the leaving group stabilized by three electron-
withdrawing groups. The −CX3 anion abstracts a proton from either the
carboxylic acid formed or the solvent, and forms the haloform.
[edit] Uses
This reaction was traditionally used to determine the presence of a methyl
ketone, or a secondary alcohol oxidizable to a methyl ketone through the
iodoform test. Nowadays, spectroscopic techniques such as NMR and infrared
spectroscopy are preferred because they require small samples, may be non-
destructive (for NMR) and are easy and quick to perform.
It was formerly used to produce iodoform and bromoform and even chloroform
in industry.
[citation needed]
In organic chemistry, this reaction may be used to convert a terminal methyl
ketone into the appropriate carboxylic acid.
[edit] Iodoform test
http://en.wikipedia.org/wiki/Hydroxide
http://en.wikipedia.org/wiki/Carboxylic_acid
http://en.wikipedia.org/wiki/Carboxylic_acid
http://en.wikipedia.org/wiki/Carboxylate
http://en.wikipedia.org/wiki/Nucleophilic_acyl_substitution
http://en.wikipedia.org/wiki/Hydroxide
http://en.wikipedia.org/wiki/Electron-withdrawing_group
http://en.wikipedia.org/wiki/Electron-withdrawing_group
http://en.wikipedia.org/w/index.php?title=Haloform_reaction&action=edit§ion=3
http://en.wikipedia.org/wiki/Secondary_alcohol
http://en.wikipedia.org/wiki/Haloform_reaction#Iodoform_test
http://en.wikipedia.org/wiki/NMR_spectroscopy
http://en.wikipedia.org/wiki/Infrared_spectroscopy
http://en.wikipedia.org/wiki/Infrared_spectroscopy
http://en.wikipedia.org/wiki/Iodoform
http://en.wikipedia.org/wiki/Bromoform
http://en.wikipedia.org/wiki/Chloroform
http://en.wikipedia.org/wiki/Wikipedia:Citation_needed
http://en.wikipedia.org/wiki/Organic_chemistry
http://en.wikipedia.org/w/index.php?title=Haloform_reaction&action=edit§ion=4
http://en.wikipedia.org/wiki/File:Iodoform_reaction.png
Page 3
negative and positive iodoform test
When iodine and sodium hydroxide are used as the reagents, a positive reaction
gives iodoform. Iodoform (CHI3) is a pale-yellow substance. Due to its high
molar mass caused by the three iodine atoms, it is solid at room temperature (cf.
chloroform and bromoform). It is insoluble in water and has an antiseptic smell.
A visible precipitate of this compound will form from a sample only when either
a methyl ketone, ethanal, ethanol, or a methyl secondary alcohol is present.
[edit] History
The haloform reaction is one of the oldest organic reactions known.
[2]
In 1822,
Serullas reacted ethanol with iodine and sodium hydroxide in water to form
sodium formate and iodoform, called in the language of that time hydroiodide of
carbon. In 1831, Justus von Liebig reported the reaction of chloral with calcium
hydroxide to chloroform and calcium formate. The reaction was rediscovered by
Adolf Lieben in 1870. The iodoform test is also called the Lieben haloform
reaction. A review of the Haloform reaction with a history section was
published in 1934.
[3]
[edit] References
1. ^ Chakrabartty, in Trahanovsky, Oxidation in Organic Chemistry, pp 343-370,
Academic Press, New York, 1978
2. ^ László Kürti and Barbara Czakó (2005). Strategic Applications of Named
Reactions in Organic Synthesis. Amsterdam: Elsevier. ISBN 0-12-429785-4.
3. ^ Reynold C. Fuson and Benton A. Bull (1934). "The Haloform Reaction".
Chemical Reviews 15 (3): 275–309
Haloform Reaction
http://en.wikipedia.org/wiki/Iodoform
http://en.wikipedia.org/wiki/Molar_mass
http://en.wikipedia.org/wiki/Iodine
http://en.wikipedia.org/wiki/Insoluble
http://en.wikipedia.org/wiki/Antiseptic
http://en.wikipedia.org/w/index.php?title=Haloform_reaction&action=edit§ion=5
http://en.wikipedia.org/wiki/Organic_reaction
http://en.wikipedia.org/wiki/Haloform_reaction#cite_note-1
http://en.wikipedia.org/wiki/Ethanol
http://en.wikipedia.org/wiki/Iodine
http://en.wikipedia.org/wiki/Sodium_hydroxide
http://en.wikipedia.org/wiki/Sodium_formate
http://en.wikipedia.org/wiki/Justus_von_Liebig
http://en.wikipedia.org/wiki/Chloral
http://en.wikipedia.org/wiki/Calcium_hydroxide
http://en.wikipedia.org/wiki/Calcium_hydroxide
http://en.wikipedia.org/wiki/Chloroform
http://en.wikipedia.org/wiki/Adolf_Lieben
http://en.wikipedia.org/wiki/Haloform_reaction#cite_note-2
http://en.wikipedia.org/w/index.php?title=Haloform_reaction&action=edit§ion=6
http://en.wikipedia.org/wiki/Haloform_reaction#cite_ref-0
http://en.wikipedia.org/wiki/Haloform_reaction#cite_ref-1
http://en.wikipedia.org/wiki/International_Standard_Book_Number
http://en.wikipedia.org/wiki/Special:BookSources/0-12-429785-4
http://en.wikipedia.org/wiki/Haloform_reaction#cite_ref-2
http://en.wikipedia.org/wiki/File:Jodoformprobe.jpg
http://en.wikipedia.org/wiki/File:Jodoformprobe.jpg
http://en.wikipedia.org/wiki/File:Jodoformprobe.jpg
http://en.wikipedia.org/wiki/File:Jodoformprobe.jpg
Page 4
This reaction has been used in qualitative analysis to indicate the presence of a methyl ketone. The
product iodoform is yellow and has a characteristic odour. The reaction has some synthetic utility in the
oxidative demethylation of methyl ketones if the other substituent on the carbonyl groups bears no
enolizable α-protons.
Mechanism of the Haloform Reaction
The reaction readily proceeds to completion because of the acidifying effect of the halogen substituents.
Chapter 18: Enols and Enolates
The Haloform reaction
Reaction type : Nucleophilic substitution
http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch18/ch18-0.html
http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch18/ch18-0.html
http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch18/ch18-0.html
http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch18/ch18-0.html
Page 5
javascript:popup('ch18-3-2b-a1.html','answer','640','300','center','front');
http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch18/ch18-3-1.html
http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch18/ch18-3-2.html
Page 6
Step 3:
Steps 1 and 2 repeat twice more yielding the
trihalogenated ketone.
Step 4:
The hydroxide now reacts as a nucleophile at the
electrophilic carbonyl carbon, with the C=O becoming a
C-O single bond and the oxygen is now anionic.
Step 5:
Reform the favourable C=O and displace a leaving group,
the trihalomethyl system which is stabilised by the 3
halogens. This gives the carboxylic acid.
Step 6:
An acid-base reaction. The trihalomethyl anion is
protonated by the carboxylic acid, giving the carboxylate
and the haloform (trihalomethane).
Haloform reaction
Compounds which have one of the following structural units, on heating with a halogen (
Cl2, Br2 or I2) in the presence of a base like NaOH or KOH give rise to a haloform
(chloroform, Iodoform).
As in Acetaldehyde, Acetone Ethanol, 2-Propanol
Chloroform
It is prepared by heating bleaching powder [Cl2 + Ca(OH)2 ] and ethanol. It is Chloroform
is formed as a colorless liquid. It is generally preserved in the presence of small amounts
of ethanol (negative catalyst) to prevent the formation of carbonyl chloride that is
phosgene which is highly poisonous.
Chloroform was used as an anesthetic during surgery; it is no longer used now because of
severe side effects like liver and cardiac toxicity. An anesthetic used at present is
Halothane. ( F3CCHBrCl).
Page 7
Net reaction using NaOH as the base
Steps
Note: 1. First step is oxidation of alcohol by the halogen.
Aldehydes and ketones with a methyl group next to the carbonyl group, will also give rise
to haloform.
The difference is the oxidation step will not be there.
Substitution of the three α-hydrogens by halogen atoms take place in the second step.
The hydrogens replaced by halogens are all from the same side of the carbonyl group, in
compounds like
CH3COCH3. Once hydrogen is replaced by halogen the other hydrogen atoms at that carbon
become more acidic causing further substitution at the same place.
Haloform reaction
From Wikipedia, the free encyclopedia
Jump to: navigation, search
The haloform reaction is a chemical reaction where a haloform (CHX3, where X is a halogen) is
produced by the exhaustive halogenation of a methyl ketone (a molecule containing the R-CO-
CH3 group) in the presence of a base.
[1]
R may be H, alkyl or aryl. The reaction can be used to
produce CHCl3, CHBr3 or CHI3.
Contents
1 Scope
2 Mechanism
3 Uses
4 Iodoform test
5 History
6 References
[edit] Scope
Substrates that successfully undergo the haloform reaction are methyl ketones and secondary
alcohols oxidizable to methyl ketones, such as isopropanol. The only primary alcohol and
aldehyde to undergo this reaction are ethanol and ethanal, respectively. 1,3-Diketones such as
acetylacetone also give the haloform reaction. Beta-ketoacids such as acetoacetic acid will also
give the test upon heating. The halogen used may be chlorine, bromine, or iodine. Fluoroform
(CHF3) cannot be prepared from a methyl ketone by the haloform reaction due to the instability
of hypofluorite, but compounds of the type RCOCF3 do cleave with base to produce fluoroform
(CHF3); this is equivalent to the second and third steps in the process shown above.
[edit] Mechanism
In the first step, the halogen disproportionates in the presence of hydroxide to give the halide and
hypohalite:
http://en.wikipedia.org/wiki/Haloform_reaction#mw-head
http://en.wikipedia.org/wiki/Haloform_reaction#p-search
http://en.wikipedia.org/wiki/Halogen
http://en.wikipedia.org/wiki/Halogenation
http://en.wikipedia.org/wiki/Ketone
http://en.wikipedia.org/wiki/Base_(chemistry)
http://en.wikipedia.org/wiki/Haloform_reaction#cite_note-0
http://en.wikipedia.org/wiki/Hydrogen
http://en.wikipedia.org/wiki/Alkyl
http://en.wikipedia.org/wiki/Aryl
http://en.wikipedia.org/wiki/Chloroform
http://en.wikipedia.org/wiki/Bromoform
http://en.wikipedia.org/wiki/Iodoform
http://en.wikipedia.org/wiki/Haloform_reaction#Scope
http://en.wikipedia.org/wiki/Haloform_reaction#Mechanism
http://en.wikipedia.org/wiki/Haloform_reaction#Uses
http://en.wikipedia.org/wiki/Haloform_reaction#Iodoform_test
http://en.wikipedia.org/wiki/Haloform_reaction#History
http://en.wikipedia.org/wiki/Haloform_reaction#References
http://en.wikipedia.org/w/index.php?title=Haloform_reaction&action=edit§ion=1
http://en.wikipedia.org/wiki/Aldehyde
http://en.wikipedia.org/wiki/Ethanol
http://en.wikipedia.org/wiki/Ethanal
http://en.wikipedia.org/wiki/Acetylacetone
http://en.wikipedia.org/wiki/Acetoacetic_acid
http://en.wikipedia.org/wiki/Fluoroform
http://en.wikipedia.org/wiki/Hypofluorite
http://en.wikipedia.org/wiki/Fluoroform
http://en.wikipedia.org/w/index.php?title=Haloform_reaction&action=edit§ion=2
http://en.wikipedia.org/wiki/Hydroxide
http://en.wikipedia.org/wiki/File:Haloform_Reaction_Scheme.png
Page 2
X2 + OH−→ XO−+ X− + H
+
(X = Cl, Br, I) (Unbalanced)
If a secondary alcohol is present, it is oxidized to a ketone by the hypohalite (hydroxide
depicted below should be hypohalite and the water≡H2O should be hypohalic acid≡HXO):
If a methyl ketone is present, it reacts with the hypohalite in a three-step process:
(1) R-CO-CH3 + 3 OX
-
→ R-CO-CX3 + 3 OH−
(2) R-CO-CX3 + OH− → RCOOH + −CX3
(3) RCOOH + −CX3 → RCOO− + CHX3
The detailed reaction mechanism is as follows:
Under basic conditions, the ketone undergoes keto-enol tautomerization. The
enolate undergoes electrophilic attack by the hypohalite (containing a halogen
with a formal +1 charge). When the α position has been exhaustively
halogenated, the molecule undergoes a nucleophilic acyl substitution by
hydroxide, with −CX3 being the leaving group stabilized by three electron-
withdrawing groups. The −CX3 anion abstracts a proton from either the
carboxylic acid formed or the solvent, and forms the haloform.
[edit] Uses
This reaction was traditionally used to determine the presence of a methyl
ketone, or a secondary alcohol oxidizable to a methyl ketone through the
iodoform test. Nowadays, spectroscopic techniques such as NMR and infrared
spectroscopy are preferred because they require small samples, may be non-
destructive (for NMR) and are easy and quick to perform.
It was formerly used to produce iodoform and bromoform and even chloroform
in industry.
[citation needed]
In organic chemistry, this reaction may be used to convert a terminal methyl
ketone into the appropriate carboxylic acid.
[edit] Iodoform test
http://en.wikipedia.org/wiki/Hydroxide
http://en.wikipedia.org/wiki/Carboxylic_acid
http://en.wikipedia.org/wiki/Carboxylic_acid
http://en.wikipedia.org/wiki/Carboxylate
http://en.wikipedia.org/wiki/Nucleophilic_acyl_substitution
http://en.wikipedia.org/wiki/Hydroxide
http://en.wikipedia.org/wiki/Electron-withdrawing_group
http://en.wikipedia.org/wiki/Electron-withdrawing_group
http://en.wikipedia.org/w/index.php?title=Haloform_reaction&action=edit§ion=3
http://en.wikipedia.org/wiki/Secondary_alcohol
http://en.wikipedia.org/wiki/Haloform_reaction#Iodoform_test
http://en.wikipedia.org/wiki/NMR_spectroscopy
http://en.wikipedia.org/wiki/Infrared_spectroscopy
http://en.wikipedia.org/wiki/Infrared_spectroscopy
http://en.wikipedia.org/wiki/Iodoform
http://en.wikipedia.org/wiki/Bromoform
http://en.wikipedia.org/wiki/Chloroform
http://en.wikipedia.org/wiki/Wikipedia:Citation_needed
http://en.wikipedia.org/wiki/Organic_chemistry
http://en.wikipedia.org/w/index.php?title=Haloform_reaction&action=edit§ion=4
http://en.wikipedia.org/wiki/File:Iodoform_reaction.png
Page 3
negative and positive iodoform test
When iodine and sodium hydroxide are used as the reagents, a positive reaction
gives iodoform. Iodoform (CHI3) is a pale-yellow substance. Due to its high
molar mass caused by the three iodine atoms, it is solid at room temperature (cf.
chloroform and bromoform). It is insoluble in water and has an antiseptic smell.
A visible precipitate of this compound will form from a sample only when either
a methyl ketone, ethanal, ethanol, or a methyl secondary alcohol is present.
[edit] History
The haloform reaction is one of the oldest organic reactions known.
[2]
In 1822,
Serullas reacted ethanol with iodine and sodium hydroxide in water to form
sodium formate and iodoform, called in the language of that time hydroiodide of
carbon. In 1831, Justus von Liebig reported the reaction of chloral with calcium
hydroxide to chloroform and calcium formate. The reaction was rediscovered by
Adolf Lieben in 1870. The iodoform test is also called the Lieben haloform
reaction. A review of the Haloform reaction with a history section was
published in 1934.
[3]
[edit] References
1. ^ Chakrabartty, in Trahanovsky, Oxidation in Organic Chemistry, pp 343-370,
Academic Press, New York, 1978
2. ^ László Kürti and Barbara Czakó (2005). Strategic Applications of Named
Reactions in Organic Synthesis. Amsterdam: Elsevier. ISBN 0-12-429785-4.
3. ^ Reynold C. Fuson and Benton A. Bull (1934). "The Haloform Reaction".
Chemical Reviews 15 (3): 275–309
Haloform Reaction
http://en.wikipedia.org/wiki/Iodoform
http://en.wikipedia.org/wiki/Molar_mass
http://en.wikipedia.org/wiki/Iodine
http://en.wikipedia.org/wiki/Insoluble
http://en.wikipedia.org/wiki/Antiseptic
http://en.wikipedia.org/w/index.php?title=Haloform_reaction&action=edit§ion=5
http://en.wikipedia.org/wiki/Organic_reaction
http://en.wikipedia.org/wiki/Haloform_reaction#cite_note-1
http://en.wikipedia.org/wiki/Ethanol
http://en.wikipedia.org/wiki/Iodine
http://en.wikipedia.org/wiki/Sodium_hydroxide
http://en.wikipedia.org/wiki/Sodium_formate
http://en.wikipedia.org/wiki/Justus_von_Liebig
http://en.wikipedia.org/wiki/Chloral
http://en.wikipedia.org/wiki/Calcium_hydroxide
http://en.wikipedia.org/wiki/Calcium_hydroxide
http://en.wikipedia.org/wiki/Chloroform
http://en.wikipedia.org/wiki/Adolf_Lieben
http://en.wikipedia.org/wiki/Haloform_reaction#cite_note-2
http://en.wikipedia.org/w/index.php?title=Haloform_reaction&action=edit§ion=6
http://en.wikipedia.org/wiki/Haloform_reaction#cite_ref-0
http://en.wikipedia.org/wiki/Haloform_reaction#cite_ref-1
http://en.wikipedia.org/wiki/International_Standard_Book_Number
http://en.wikipedia.org/wiki/Special:BookSources/0-12-429785-4
http://en.wikipedia.org/wiki/Haloform_reaction#cite_ref-2
http://en.wikipedia.org/wiki/File:Jodoformprobe.jpg
http://en.wikipedia.org/wiki/File:Jodoformprobe.jpg
http://en.wikipedia.org/wiki/File:Jodoformprobe.jpg
http://en.wikipedia.org/wiki/File:Jodoformprobe.jpg
Page 4
This reaction has been used in qualitative analysis to indicate the presence of a methyl ketone. The
product iodoform is yellow and has a characteristic odour. The reaction has some synthetic utility in the
oxidative demethylation of methyl ketones if the other substituent on the carbonyl groups bears no
enolizable α-protons.
Mechanism of the Haloform Reaction
The reaction readily proceeds to completion because of the acidifying effect of the halogen substituents.
Chapter 18: Enols and Enolates
The Haloform reaction
Reaction type : Nucleophilic substitution
http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch18/ch18-0.html
http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch18/ch18-0.html
http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch18/ch18-0.html
http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch18/ch18-0.html
Page 5
javascript:popup('ch18-3-2b-a1.html','answer','640','300','center','front');
http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch18/ch18-3-1.html
http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch18/ch18-3-2.html
Page 6
Step 3:
Steps 1 and 2 repeat twice more yielding the
trihalogenated ketone.
Step 4:
The hydroxide now reacts as a nucleophile at the
electrophilic carbonyl carbon, with the C=O becoming a
C-O single bond and the oxygen is now anionic.
Step 5:
Reform the favourable C=O and displace a leaving group,
the trihalomethyl system which is stabilised by the 3
halogens. This gives the carboxylic acid.
Step 6:
An acid-base reaction. The trihalomethyl anion is
protonated by the carboxylic acid, giving the carboxylate
and the haloform (trihalomethane).
Haloform reaction
Compounds which have one of the following structural units, on heating with a halogen (
Cl2, Br2 or I2) in the presence of a base like NaOH or KOH give rise to a haloform
(chloroform, Iodoform).
As in Acetaldehyde, Acetone Ethanol, 2-Propanol
Chloroform
It is prepared by heating bleaching powder [Cl2 + Ca(OH)2 ] and ethanol. It is Chloroform
is formed as a colorless liquid. It is generally preserved in the presence of small amounts
of ethanol (negative catalyst) to prevent the formation of carbonyl chloride that is
phosgene which is highly poisonous.
Chloroform was used as an anesthetic during surgery; it is no longer used now because of
severe side effects like liver and cardiac toxicity. An anesthetic used at present is
Halothane. ( F3CCHBrCl).
Page 7
Net reaction using NaOH as the base
Steps
Note: 1. First step is oxidation of alcohol by the halogen.
Aldehydes and ketones with a methyl group next to the carbonyl group, will also give rise
to haloform.
The difference is the oxidation step will not be there.
Substitution of the three α-hydrogens by halogen atoms take place in the second step.
The hydrogens replaced by halogens are all from the same side of the carbonyl group, in
compounds like
CH3COCH3. Once hydrogen is replaced by halogen the other hydrogen atoms at that carbon
become more acidic causing further substitution at the same place.
