40Chloroform

📚
CHLOROFORM
▢ Introduction:
  • •
    Trihalogen derivative of methane
  • •
    Discovered by Liebig, 1831
  • •
    Name proposed by Dumas → hydrolysis gives formic acid
  • •
    Earlier use → surgical anaesthetic
  • •
    Current anaesthetic use → rare; liver damage risk
▢ Preparation:
❖ Lab Method:
◉ Principle: Dry distillation: ethanol/acetone + bleaching powder solution
◉ Yield: ≈ 40%
◉ Overall Reaction:
  1. \(CH_3CH_2OH \xrightarrow{CaOCl_2/H_2O/\Delta} CHCl_3 + (HCOO)_2Ca\)
  2. \(CH_3COCH_3 \xrightarrow{CaOCl_2/H_2O/\Delta} CHCl_3 + (CH_3COO)_2Ca\)
◉ Bleaching Powder:
  1. \(CaOCl_2 + H_2O \rightarrow Ca(OH)_2 + Cl_2\)
  2. Available chlorine → oxidizing + chlorinating agent
◉ From Ethanol:
  1. Oxidation: \(Cl_2 + H_2O \rightarrow 2HCl + [O]\)
  2. \(CH_3CH_2OH + Cl_2 \rightarrow CH_3CHO + 2HCl\)
  3. Chlorination: \(CH_3CHO + 3Cl_2 \rightarrow CCl_3CHO + 3HCl\)
  4. Hydrolysis: \(CCl_3CHO + Ca(OH)_2 \rightarrow CHCl_3 + (HCOO)_2Ca\)
◉ From Acetone:
  1. Chlorination: \(CH_3COCH_3 + 3Cl_2 \rightarrow CCl_3COCH_3 + 3HCl\)
  2. Hydrolysis: \(CCl_3COCH_3 + Ca(OH)_2 \rightarrow CHCl_3 + (CH_3COO)_2Ca\)
  3. No oxidation step
❖ Other Methods:

Table 1: Other Methods of Chloroform Preparation

Method
Reaction
Note
Halogenation of methane
\(CH_4 + Cl_2 \xrightarrow{h\nu} CH_3Cl + CH_2Cl_2 + CHCl_3 + CCl_4\)
mixture
Reduction of \(CCl_4\)
\(CCl_4 + 2[H] \xrightarrow{Fe/H_2O\ steam} CHCl_3 + HCl\)
large scale; impure; mainly solvent
From chloral hydrate
\(CCl_3CH(OH)_2 \xrightarrow{NaOH/distillation} CHCl_3 + HCOONa + H_2O\)
pure chloroform
◉ Chloral Hydrate Stability:
  • •
    Stable geminal diol
  • •
    Reason → intramolecular H-bonding between Cl and H of \(-OH\)
❖ Industrial Preparation:
  • •
    Ethanol/acetone + aq. \(NaCl\) electrolysis
  • •
    Electrolysis → \(Cl_2 + NaOH\)
  • •
    \(CH_3CH_2OH/CH_3COCH_3 \xrightarrow{Cl_2+NaOH} CHCl_3\)
▢ Properties:
❖ Physical Properties:
  • •
    Sweet-smelling colourless liquid
  • •
    Practically insoluble in water
  • •
    Soluble in alcohol, ether, organic solvents
  • •
    Non-inflammable
  • •
    Vapour may burn with green flame
  • •
    Anaesthetic → unconsciousness
❖ Chemical Properties:
◉ Oxidation:
◈ Reaction: \(CHCl_3 + [O] \xrightarrow{light+air} COCl_2 + HCl\)
◈ Product: Diethyl carbonate → non-poisonous
◈ Prevention:
  • •
    Dark-coloured bottle
  • •
    Bottle filled up to brim
  • •
    Light + air cut off
  • •
    1% ethyl alcohol added
◈ Phosgene Removal: \(COCl_2 + 2C_2H_5OH \rightarrow CO(OC_2H_5)_2 + 2HCl\)
◈ Methyl Isocyanate: \(CH_3NH_2 + COCl_2 \rightarrow CH_3NCO\)
◈ Bhopal Gas Tragedy: Caused by methyl isocyanate
◉ Test Before Anaesthetic Use:

Table 1: Pure vs Impure Chloroform

Reagent
Pure \(CHCl_3\)
Impure \(CHCl_3\): \(COCl_2 + HCl\)
Blue litmus
No change
Turns red
\(AgNO_3\)
No reaction
White ppt. \(AgCl\)
conc. \(H_2SO_4\)
No reaction
Yellow solution
◉ Reduction:
  • •
    \(CHCl_3 \xrightarrow{Zn/HCl/C_2H_5OH} CH_2Cl_2 + HCl\)
  • •
    \(CHCl_3 \xrightarrow{Zn/H_2O/\Delta} CH_4 + 3HCl\)
◉ Chlorination: \(CHCl_3 + Cl_2 \xrightarrow{UV\ light} CCl_4 + HCl\)
◉ Hydrolysis:
  • •
    \(CHCl_3 + 3NaOH \rightarrow HC(OH)_3 + 3NaCl\)
  • •
    \(HC(OH)_3\) → unstable orthoformic acid
  • •
    \(HC(OH)_3 \rightarrow HCOOH + H_2O\)
  • •
    \(HCOOH + NaOH \rightarrow HCOONa + H_2O\)
  • •
    \(CHCl_3 + aq.KOH \rightarrow HCOOK + 3KCl + 2H_2O\)
◉ Reaction With conc. \(HNO_3\):
  1. \(CHCl_3 + HNO_3 \rightarrow CCl_3NO_2 + H_2O\)
  2. Product → chloropicrin / nitrochloroform
  3. Nature → liquid, poisonous
  4. Use → insecticide + tear gas / war gas
◉ Reaction With Acetone:
  1. \(CH_3COCH_3 + CHCl_3 \xrightarrow{NaOH} (CH_3)_2C(OH)CCl_3\)
  2. Product → chloretone
  3. Chloretone → colourless crystalline solid
  4. Use → hypnotic drug
  5. Hypnotic → sleep-inducing
◉ Hypnotic Drugs:
  • •
    Chloretone
  • •
    Paraldehyde
  • •
    Hypnone
◉ Tear Gases:
  • •
    Chloropicrin
  • •
    Benzoyl chloride \((C_6H_5COCl)\)
◉ Reaction With Ag: \(2CHCl_3 + 6Ag \xrightarrow{\Delta} HC\equiv CH + 6AgCl\)
◉ Carbylamine Reaction / Isocyanide Test:
◈ General: \(R-NH_2 \xrightarrow{CHCl_3+KOH/\Delta} R-NC + KCl + H_2O\)
◈ Positive: Only \(1^\circ\) amines: aliphatic/aromatic
◈ Product: Isocyanide → unpleasant/offensive smell
◈ Uses:
  1. Test of primary amines
  2. Test of chloroform
◈ Examples:
  1. \(CH_3CH_2NH_2 \xrightarrow{CHCl_3+KOH/\Delta} CH_3CH_2NC\)
  2. \(C_6H_5NH_2 \xrightarrow{CHCl_3+KOH/\Delta} C_6H_5NC\)
◉ Reimer-Tiemann Reaction: Listed reaction
◉ Reaction With Sodium Ethoxide: \(CHCl_3 + 3NaOC_2H_5 \rightarrow HC(OC_2H_5)_3 + 3NaCl\)
◉ Product: Ethyl orthoformate
▢ Uses:
  • •
    Solvent → fats, waxes, rubber, resins, iodine
  • •
    Preparation → chloretone, chloropicrin
  • •
    Laboratory test → primary amines, iodides, bromides
  • •
    Anaesthetic → historical; now avoided due to harmful effects
  • •
    Excess inhalation → liver damage; similar with \(CCl_4\)
  • •
    Preservation of organic materials/anatomical specimens
  • •
    Major modern use → manufacture of Freon refrigerant R-22
▢ Freons:

Table 1: Freon Examples

Freon
Formula
Freon-14
\(CF_4\)
Freon-13
\(CF_3Cl\)
Freon-12
\(CF_2Cl_2\)
Freon-11
\(CFCl_3\)
CFCs → refrigerants; replacement tried due to ozone layer destruction.
▢ Physiological Impact:
  • •
    Inhalation → CNS depression
  • •
    Vapour → headache, fatigue, dizziness
  • •
    Chronic exposure → liver + kidney damage
▢ Tests of Chloroform:
  • •
    Carbylamine / isocyanide test positive
  • •
    Tollens' reagent → silver mirror
  • •
    Pure \(CHCl_3\) + aq. \(AgNO_3\) → no white ppt.
  • •
    Reason → \(C-Cl\) covalent; no ionization to \(Cl^-\)
📚
IODOFORM \(CHI_3\)
▢ Introduction:
  • •
    Yellow crystalline solid
  • •
    Pungent characteristic odour
  • •
    Preparation/properties resemble chloroform
▢ Preparation:
❖ From Ethanol: \(CH_3CH_2OH + 4I_2 + 6NaOH \xrightarrow{\Delta} CHI_3\downarrow + HCOONa + 5NaI + 5H_2O\)
❖ From Acetone: \(CH_3COCH_3 + 3I_2 + 2Na_2CO_3 \xrightarrow{\Delta} CHI_3\downarrow + CH_3COONa + 3NaI + 2CO_2\)
❖ Alkali Options:
  1. \(NaOH\)
  2. \(KOH\)
  3. \(Na_2CO_3\)
▢ Reactions:
❖ Antiseptic Action:
  • •
    Used for wound dressing
  • •
    Actual antiseptic → free iodine
  • •
    Iodoform itself → not antiseptic
▢ Tests of Iodoform:
❖ With (AgNO_3): \(CHI_3\) → yellow ppt. \(AgI\)
❖ Carbylamine Reaction: \(CHI_3 + 1^\circ amine + alc.KOH \xrightarrow{\Delta}\) isocyanide → offensive smell
❖ Iodoform Test / Iodoform Reaction:
◉ Positive Groups:
  1. \(CH_3CO-Z\)
  2. \(CH_3CH(OH)-Z\)
◉ Reagents:
  1. \(NaOI\)
  2. \(I_2 + aq.NaOH\)
  3. \(I_2 + aq.Na_2CO_3\)
  4. \(I_2 + aq.NaHCO_3\)
◉ Observation: Yellow ppt. of \(CHI_3\)
◉ Z: Atom/group without lone pair
◉ Negative Condition: Z with lone pair → resonance → no iodoform test

Table 1: Iodoform Test: Positive vs Negative

Compound
Result
Reason
\(CH_3CHO\)
positive
only aldehyde giving test
\(CH_3COCH_3\)
positive
methyl ketone
\(CH_3COC_2H_5\)
positive
methyl ketone
\(C_6H_5COCH_3\)
positive
methyl ketone
\(C_2H_5OH\)
positive
oxidized to acetaldehyde
\(CH_3CH(OH)CH_3\)
positive
\(CH_3CH(OH)-\) group
\(CH_3COCH_2CH_2CH_3\)
positive
methyl ketone
\(HCHO\)
negative
no \(CH_3CO-\)
\(CH_3CH_2COCH_2CH_3\)
negative
no methyl ketone
\(C_6H_5CHO\)
negative
no \(CH_3CO-\)
\(CH_3OH\)
negative
not ethanol type
\(CH_3CH_2CH_2OH\)
negative
not \(CH_3CH(OH)-\)
\(CH_3COOH\)
negative
acid
\(CH_3COCl\)
negative
acid derivative
\(CH_3CONH_2\)
negative
acid derivative
\(CH_3COOCH_3\)
negative
acid derivative
\(CH_3COOCOCH_3\)
negative
acid derivative
Ethyl acetoacetate \(CH_3COCH_2COOC_2H_5\)
negative
active methylene iodination preferred
❖ Important Notes:
  • •
    Acids + acid derivatives → negative
  • •
    Ethanol → only primary alcohol positive
  • •
    Acetaldehyde → only aldehyde positive
  • •
    Ethyl acetoacetate → negative despite \(CH_3CO-\)
❖ Distinction Tests:

Table 1: Iodoform Test Applications

Pair
Positive
Negative
Methanol vs Ethanol
Ethanol
Methanol
Ethanol vs Propan-1-ol
Ethanol
Propan-1-ol
Propan-1-ol vs Propan-2-ol
Propan-2-ol
Propan-1-ol
Pentan-2-one vs Pentan-3-one
Pentan-2-one
Pentan-3-one
Iodoform vs Chloroform + \(AgNO_3\)
Iodoform → yellow ppt. \(AgI\)
Chloroform → no ppt.
📚
READ AND DIGEST
  • •
    Carbylamine reaction → only primary amines
  • •
    Pure chloroform + bromoform → colourless liquids
  • •
    Iodoform → yellow solid
  • •
    Chloretone → hypnotic / sleep-inducing medicine
  • •
    Phosgene → poisonous war gas
  • •
    Chloropicrin → tear gas + insecticide
  • •
    Halothane \((CF_3CHClBr)\) → general inhalational anaesthetic; replaces diethyl ether
  • •
    \(CCl_4\) → fire extinguisher under name pyrene
  • •
    \(CCl_4\) resists hydrolysis with boiling water due to non-availability of d-orbitals in C
  • •
    \(C_2Cl_6\) / hexachloroethane → artificial camphor
  • •
    Freon-12 → refrigerant + propellant + industrial solvent
  • •
    \(C_2H_5Cl\) → local anaesthetic
Q1.
Chloroform is chemically
Q2.
Chloroform was discovered by
Q3.
The name chloroform was proposed by Dumas because its hydrolysis gives
Q4.
Chloroform is now rarely used as anaesthetic mainly because it may cause
Q5.
In laboratory, chloroform is commonly prepared by dry distillation of ethanol or acetone with
Q6.
In preparation of chloroform from ethanol and bleaching powder, the first important step is
Q7.
In preparation of chloroform from ethanol, acetaldehyde is chlorinated to form
Q8.
In preparation of chloroform from acetone and bleaching powder, which step is not required?
Q9.
Bleaching powder helps in chloroform preparation mainly because it supplies
Q10.
Pure chloroform can be prepared from chloral hydrate by heating with
Q11.
Chloral hydrate is stable because of
Q12.
Large-scale preparation of chloroform may be done by reduction of
Q13.
Industrial preparation of chloroform involves electrolysis of aqueous NaCl with ethanol or acetone because electrolysis produces
Q14.
Chloroform is generally
Q15.
Chloroform is practically insoluble in
Q16.
Chloroform is stored in dark-coloured bottles filled up to brim mainly to prevent
Q17.
On exposure to light and air, chloroform forms poisonous
Q18.
The poisonous product formed by oxidation of chloroform is chemically
Q19.
Why is about 1% ethyl alcohol added to chloroform?
Q20.
Impure chloroform containing HCl and phosgene turns blue litmus
Q21.
Pure chloroform with aqueous AgNO3 gives
Q22.
Impure chloroform gives white precipitate with AgNO3 due to presence of
Q23.
Reduction of chloroform with Zn/HCl in alcohol gives mainly
Q24.
Reduction of chloroform with Zn and water on heating gives
Q25.
Chlorination of chloroform in ultraviolet light gives
Q26.
Hydrolysis of chloroform with aqueous KOH finally gives
Q27.
The unstable intermediate formed during hydrolysis of chloroform is
Q28.
Chloroform reacts with concentrated nitric acid to form
Q29.
Chloropicrin is chemically
Q30.
Chloropicrin is used as
Q31.
Chloroform reacts with acetone in presence of NaOH to form
Q32.
Chloretone is used as
Q33.
Which of the following is a hypnotic drug?
Q34.
Carbylamine reaction is given by chloroform with alcoholic KOH and
Q35.
The offensive smell in carbylamine reaction is due to formation of
Q36.
Carbylamine reaction is used as a test for
Q37.
Chloroform reacts with sodium ethoxide to form
Q38.
When chloroform is heated with silver powder, the main organic product is
Q39.
Major modern use of chloroform is in manufacture of
Q40.
Chloroform is used as solvent for
Q41.
Iodoform has formula
Q42.
Iodoform is generally
Q43.
Iodoform test gives
Q44.
Which aldehyde gives positive iodoform test?
Q45.
Which of the following gives iodoform test?
Q46.
The only primary alcohol giving iodoform test is
Q47.
Which functional group gives iodoform test?
Q48.
Which alcohol group gives positive iodoform test?
Q49.
Which of the following gives positive iodoform test?
Q50.
Which of the following does not give iodoform test?
Q51.
Pentan-2-one and pentan-3-one can be distinguished by iodoform test because
Q52.
Methanol and ethanol can be distinguished by iodoform test because
Q53.
Iodoform itself is not the actual antiseptic; antiseptic action is due to
Q54.
Iodoform with AgNO3 gives
Q55.
Iodoform can be distinguished from chloroform by AgNO3 because
Q56.
Ethyl acetoacetate gives negative iodoform test despite having CH3CO− group because
Q57.
Which reagent can be used for iodoform test?
Q58.
Halothane is used as
Q59.
Carbon tetrachloride is used as fire extinguisher under the name
Q60.
Freon-12 has formula
Q61.
Hexachloroethane is also called