Chapter 11 Halogen Derivatives Part 2 – Chemistry free study material by TEACHING CARE online tuition and coaching classes
- Reimer-Tiemann reaction : Chloroform reacts with phenol when heated in presence of sodium hydroxide or potassium The product formed is salicylaldehyde.
C H OH + CHCl
- 3NaOH ¾¾65¾°C ® C H OH + 3NaCl + 2H O
6 5 3
6 4 CHO 2
- Carbylamine reaction (Isocyanide test) : This reaction is actually the test of primary amines. Chloroform, when heated with primary amine in presence of alcoholic potassium hydroxide forms a derivative called isocyanide which has a very offensive
RNH2 + CHCl3 + 3KOH(alc.) ¾¾D ®
- 3KCl + 3H2O
This reaction is also used for the test of chloroform.
- It is used as a solvent for fats, waxes, rubber, resins, iodine,
- It is used for the preparation of chloretone (a drug) and chloropicrin (Insecticide).
- It is used in laboratory for the test of primary amines, iodides and
- It can be used as anaesthetic but due to harmful effects it is not used these days for this
- It may be used to prevent putrefaction of organic materials, e., in the preservation of anatomical species.
(5) Tests of chloroform
- It gives isocyanide test (Carbylamine test).
- It forms silver mirror with Tollen’s
- Pure Chloroform does not give white precipitate with silver
Iodoform or tri-iodomethane, CHI3
Iodoform resembles chloroform in the methods of preparation and properties.
- Laboratory preparation : Iodoform is prepared in the laboratory by heating ethanol or acetone with iodine and
Ethanol : CH3CH2OH + I2 ¾¾® CH3CHO+ 2HI
CH3CHO + 3I2 ¾¾® CI3CHO+ 3HI
CI3CHO + KOH ¾¾® CHI3 + HCOOK
Tri – iodoacetaldehyde
CH3COCH3 + 3I2 ¾¾® CI3COCH3 + 3HI
CI3COCH3 + KOH ¾¾® CHI3 + CH3COOK
Iodoform Pot. acetate
Sodium carbonate can be used in place of KOH or NaOH. These reactions are called iodoform reactions.
- Industrial preparation : Iodoform is prepared on large scale by electrolysis of a solution containing ethanol, sodium carbonate and potassium The iodine set free, combine with ethanol in presence of alkali to
form iodoform. The electrolysis carried out in presence of CO2
and the temperature is maintained at 60-70°C.
K + + I –
K + + e – ® K
2I – ® I 2 + 2e –
K + H O ¾¾® KOH + 1 H
2 2 2
KOH is neutralised by CO2 : C2 H5OH + 4 I2 + 3Na2CO3 ¾¾® CHI3 + HCOONa + 5 NaI + 3CO2 + 2H2O
- It is a yellow crystalline
- It has a pungent characteristic
- It is insoluble in water but soluble in organic solvents such as alcohol, ether,
- It has melting point 119°C. It is steam
(3) Reactions of iodoform
Hydrolysis Potassium formate
Reduction Red P/HI
CH º CH
C H NC
C6H5NH2+KOH (alc.) 6 5
Iodine vapours, 4CHI3+3O2 ® 4CO + 6I2 + 2H2O
(Less stable than CHCl3)
Yellow precipitate of AgI
(This reaction is not given by chloroform)
- Uses : Iodoform is extensively used as an antiseptic for dressing of wounds; but the antiseptic action is due to the liberation of free iodine and not due to iodoform When it comes in contact with organic matter, iodine is liberated which is responsible for antiseptic properties.
(5) Tests of iodoform
- With AgNO3 : CHI3
gives a yellow precipitate of AgI .
- Carbylamine reaction :
on heating with primary amine and alcoholic KOH solution, gives an
offensive smell of isocyanide (Carbylamine).
- Iodoform reaction : With I 2
and NaOH or
I 2 and
Na2CO3 , the iodoform test is mainly given by ethyl
(CH3 – C– H),
a-methyl ketone or 2-one
(- C– CH3),
secondary alcohols or
(-CHOH × CH3)
and secondary alkyl halide at
C2 (-CHCICH3 ) . Also lactic acid ( CH3 – CHOH – COOH) ,
Pyruvic acid (CH3 – C– COOH) and methyl phenyl ketone (C6 H5 – C– CH3 ) give this test.
It is the most important tetrahalogen derivative of methane.
- From methane : Chlorination of methane with excess of chlorine at 400°C yields impure carbon
CH4 + 4Cl2 ¾¾400¾°¾C ® CCl4 + 4 HCl
Methane used in this process is obtained from natural gas.
- From carbon disulphide : Chlorine reacts with carbon disulphide in presence of catalysts like iron, iodine, aluminium chloride or antimony
CS2 + 3Cl2 ¾¾® CCl4 +
further reacts with CS2 to form more of carbon tetrachloride.
CS2 + 2S2Cl2 ¾¾® CCl4 + 6S
Carbon tetrachloride is obtained by fractional distillation. It is washed with sodium hydroxide and then distilled to get a pure sample.
- From propane : Propane is reacted with chlorine at about 400°C and at a pressure of 70-100
C3 H8 + 9Cl2 ¾¾He¾at ®
(2) Physical properties
- It is a colourless liquid having characteristic
- It is non-inflammable and It has boiling point 77°C.
- It is insoluble in water but soluble in organic
- It is an excellent solvent for oils, fats, waxes and
- Chemical properties : Carbon tetrachloride is less reactive and inert to most organic However, the following reactions are observed.
- Reaction with steam (Oxidation) : Carbon tetrachloride vapours react with steam above 500°C to form phosgene, a poisonous
CCl4 + H2O ¾¾500¾°¾C ®
Phosgene (Carbonyl chloride)
- Reduction : It is reduced by moist iron filling into
CCl4 + 2H ¾¾Fe /¾H2¾O ® CHCl3 + HCl
- Hydrolysis : On heating with aqueous potassium hydroxide it forms carbon dioxide which combines with potassium hydroxide to give KCl and potassium carbonate (Inorganic salts).
CCl4 + 4 KOH ¾¾-4K¾¾Cl ®[C(OH)4 ] ¾¾-2H¾2¾O ® CO2 ¾¾2KO¾H ® K2CO3 + H2O
- Reaction with phenol (Reimer-tiemann reaction) : It combines with phenol in presence of sodium hydroxide to form salicylic
C H OH + CCl
¾¾+ 4 N¾aO¾H ® C H OH + 4 NaCl + 2H O
6 5 4
6 4 COOH 2
- It is used as a fire extinguisher under the name pyrene. The dense vapours form a protective layer on the burning objects and prevent the oxygen or air to come in contact with the burning
- It is used as a solvent for fats, oils, waxes and greases, resins, iodine
- It finds use in medicine as helmenthicide for elimination of hook
Vinyl chloride or chloroethene, CH2=CHCl
- Synthesis : Vinyl chloride can be synthesised by a number of methods described below:
- From ethylene chloride : It is easily prepared in the laboratory by the action of dilute alcoholic solution of potassium hydroxide on ethylene
CH 2 Cl
+ Alc. KOH
- KCl + H 2O
Ethylene chloride Vinyl chloride
Vinyl chloride can also be obtained from ethylene chloride by thermal decomposition at 600-650°C.
CH 2 Cl
CHCl + HCl
- From ethylene : Free radical chlorination of ethylene at 500°C yields vinyl
CH2 = CH2 + Cl2 ¾¾500¾°¾C ® CH2 = CHCl
- From acetylene : Vinyl chloride is obtained by controlled addition of HCl on acetylene. Acetylene is
passed through dilute hydrochloric acid at about 70°C in presence of This method is also used for its manufacture.
CH º CH + HCl ¾¾HgC¾l2 ® CH2 = CHCl
as a catalyst to form vinyl chloride.
- Properties : It is a colourless gas at room Its boiling point is –13°C. The halogen atom in
vinyl chloride is not reactive as in other alkyl halides. However, addition reactions.
C = C
bond of vinyl chloride gives the usual
The non-reactivity of chlorine atom is due to resonance stabilization. The lone pair on chlorine can participate in delocalization (Resonance) to give two structures.
. . – +
CH2 = CH – Cl ¬¾® C H2 – CH = Cl
The following two effects are observed due to resonance stabilization.
- Carbon-chlorine bond in vinyl chloride has some double bond character and is, therefore, stronger than a pure single
- Carbon atom is
C – Cl
bond length is shorter (1.69Å) and stronger than in alkyl
halides (1.80Å) due to
hybridization of the carbon atom.
CH2Br – CHBrCl
CH3 – CHBrCl
CH2 = CHCl
- C H
- C H ú
ê Polyvinyl chloride (PVC) ú
- Uses : The main use of vinyl chloride is in the manufacture of polyvinyl chloride (PVC) plastic which is employed these days for making synthetic leather goods, rain coats, pipes, floor tiles, gramophone records, packaging materials,
Allyl iodide or 3-iodopropene-1, ICH2CH = CH2
- Synthesis : It is obtained,
- By heating allyl chloride with sodium iodide in Allyl chloride required in the reactions is prepared
either by chlorination of propene at 500°C or by action of
CH3CH = CH2 + Cl2 ¾¾500¾°¾C ® CH2 – CH = CH2
on allyl alcohol.
Or 3 C H 2 – CH = CH 2 + PCl3 ¾¾He¾at ® 3 C H 2 – CH = CH 2 + H3 PO3
C H 2 – CH = CH2 + NaI ¾¾Ace¾to¾ne ® C H 2 – CH = CH 2 + NaCl
This is halogen- exchange reaction and is called Finkelstein reaction.
- By heating glycerol with HI.
+ 3HI ¾¾- 3 H¾¾O ®
- Properties : It is a colourless It boils at 103.1°C.The halogen atom in allyl iodide is quite reactive. The p-orbital of the halogen atom does not interact with p–molecular orbital of the double bond because these are
separated by a saturated sp3 -hybridized carbon atom. Thus, the halogen atom in allyl halides can be easily
replaced and the reactions of allyl halides are similar to the reaction of alkyl halides.
In terms of valence bond approach, the reactivity of halogen atom is due to ionisation to yield a carbonium ion which can stabilize by resonance as shown below,
= CH – CH2
= CH – CH2
- CH = CH2
] + I –
Substitution reactions : Nucleophilic substitution reactions occur,
= CH – CH2OH
CH2 = CHCH2I
= CH – CH2CN
= CH – CH NH
2 2 2
CH = CH – CH OCH
2 2 3
Allyl methyl ether
CH = CH – CH NO
2 2 2
Addition reactions : Electrophilic addition reactions take place in accordance to Markownikoff’s rule.
CH2 = CH – CH2 I + Br2 ¾¾® CH2 Br × CHBr × CH2 I ;
Allyl iodide is widely used in organic synthesis.
CH2 = CH – CH2 I + HBr ¾¾® CH3CHBrCH2 I
In these compounds the halogen is linked directly to the carbon of the benzene nucleus.
- Nomenclature : Common name is aryl halide IUPAC name is halo-arene.
Example : Cl Br
(3) Methods of preparation
- By direct halogination of benzene ring
¾¾Lew¾is a¾c¾id ®
X + HX
Lewis acid = FeX3 , AlX3 ,Tl(OAC)3 ;
X 2 = Cl2 , Br2
- From diazonium salts
C6H5Br C6H5I C6H5F
C H NH
¾¾NaN¾O2¾, H¾Cl ® Å –
6 5 2
C6 H5 N 2 Cl
- Hunsdiecker reaction : C6 H5COO– Ag + ¾¾B¾r2 ® C6 H5 Br + CO2 + AgBr
- From Aryl thalium compound :
(4) Physical properties
ArH + Tl(OOCCF3 )3 ¾¾-CF¾CO¾¾H ®
ArTl(OOCF3 )2 ¾¾KI ® ArI
Aryl thallium trifluoroacetate
- Physical state : Haloarenes are colourless liquid or crystalline
- Solubility : They are insoluble in water, but dissolve readily in organic Insolubility is due to inability to break hydrogen bonding in water. Para isomer is less soluble than ortho isomer.
- Halo-arenes are heavier than
- P. of halo-arenes follow the tend. Iodo arene > Bromo arene > Chloro arene.
(5) Chemical properties
Inert nature of chlorobenzene : Aryl halides are unreactive as compared to alkyl halides as the halogen atom in these compounds is firmly attached and cannot be replaced by nucleophiles. Such as OH–, NH –,CN – etc.
Thus delocalization of electrons by resonance in aryl halides, brings extra stability and double bond character
between C – X bond. This makes the bond stronger and shorter than pure single bond. However under vigorous
conditions the following nucleophilic substitution reactions are observed,
- Nucleophilic displacement : C6 H5 Cl ¾¾NaO¾H,¾350¾°¾C ® C6 H5OH
- Electrophilic aromatic substitution
H2SO4 NO2 +
- Wurtz – fittig reaction : C6 H5 Br + CH3 Br ¾¾N¾a ® C6 H5CH3 + 2NaBr
- Formation of grignard reagent : C6 H5 Br ¾¾M¾g ® C6 H5 MgBr
- Ullmann reaction
2 I Cu +
- Freons : The chloro fluoro derivatives of methane and ethane are called Some of the derivatives
difluoroethane). These derivatives are non-inflammable, colourless, non-toxic, low boiling liquids. These are stable upto 550°C. The most important and useful derivative is CF2Cl2 which is commonly known as freon and freon-12.
Freon or freon-12
is prepared by treating carbon tetrachloride with antimony trifluoride in the
presence of antimony pentachloride as a catalyst. 3CCl4 + 2SbF3 ¾¾SbC¾l5 ® 3CCl2 F2 + 2SbCl3
Or it can be obtained by reacting carbon tetrachloride with hydrofluoric acid in presence of antimony pentafluoride.
CCl4 + 2HF ¾¾Sb¾F5 ® CCl2 F2 + 2HCl
Under ordinary conditions freon is a gas. Its boiling point is –29.8°C. It can easily be liquified. It is chemically inert. It is used in air-conditioning and in domestic refrigerators for cooling purposes (As refrigerant). It causes depletion of ozone layer.
- Teflon : It is plastic like substance produced by the polymerisation of tetrafluoroethylene (CF2 = CF2) . Tetrafluoroethylene is formed when chloroform is treated with antimony trifluoride and hydrofluoric
CHCl3 ¾¾Sb¾F3 ® CHF2Cl ¾¾800¾°¾C ® CF2 = CF2
HF – HCl
On polymerisation tetrafluoroethylene forms a plastic-like material which is called teflon.
nCF2 = CF2 ¾¾®(-CF2 – CF2 -)n
Teflon is chemically inert substance. It is not affected by strong acids and even by boiling aqua-regia. It is stable at high temperatures. It is, thus, used for electrical insulation, preparation of gasket materials and non-sticking frying pans.
- Acetylene tetrachloride (Westron), CHCl2∙CHCl2 : Acetylene tetrachloride is also known as sym. It is prepared by the action of chlorine on acetylene in presence of a catalyst such as ferric chloride, aluminium chloride, iron, quartz or kieselguhr.
CH º CH + 2Cl2 ¾¾®
CHCl2 × CHCl2
In absence of catalyst, the reaction between chlorine and acetylene is highly explosive producing carbon and
HCl. The reaction is less violent in presence of a catalyst.
It is a heavy, non-inflammable liquid. It boils at 146°C. It is highly toxic in nature. Its smell is similar to chloroform. It is insoluble in water but soluble in organic solvents.
On further chlorination, it forms penta and hexachloroethane. On heating with lime (Calcium hydroxide), it is converted to useful product westrosol (CCl2 = CHCl) .
2CHCl2 – CHCl2 + Ca(OH)2 ¾¾® 2CHCl = CCl2 + CaCl2 + 2H 2 O
Both westron and westrosol are used as solvents for oils, fats, waxes, resins, varnishes and paints, etc.
- p-Dichlorobenzene : It is prepared by chlorination of
It is a white, volatile solid having melting point of 325 K, which readily sublimes. It resembles chlorobenzene in their properties.
It is used as general insecticides, germicide, soil fumigant deodorant. It is used as a larvicide for cloth moth and peach tee borer.
- DDT; 2, 2-bis (p-Chlorophenyl) –1,1,1-trichloroethane : It is synthesised by heating a mixture of
chloral (1mol) with chlorobenzene (2mol) in the presence of concentrated
– C =
Cl3C – C
Properties and uses of D.D.T.
- D.T. is almost insoluble in water but it is moderately soluble in polar solvents.
- D.T. is a powerful insecticide. It is widely used as an insecticide for killing mosquitoes and other insects.
Side Effects of D.D.T. : D.D.T. is not biodegradable. Its residues accumulate in environment and its long term effects could be highly dangerous. It has been proved to be toxic to living beings. Therefore, its use has been abandoned in many western countries. However, inspite of its dangerous side effects, D.D.T. is still being widely used in India due to non-availability of other cheaper insecticides.
- BHC (Benzene hexachloride), C6H6Cl6 : It is prepared by chlorination of benzene in the presence of
Uses : It is an important agricultural pesticide mainly used for exterminating white ants, leaf hopper, termite, etc. It is also known by the common name gammaxene or lindane or 666.
Note : ® aaaeee conformation of C6 H6Cl6
is most powerful insecticide.
- Perfluorocarbons (PFCs) : Perfluorocarbons
(Cn F2n+ 2 )
are obtained by controlled fluorination of
vapourized alkanes diluted with nitrogen gas in the presence of a catalyst.
C7 H16 + 16F2 ¾¾Vap¾our¾pha¾se, ¾N2 ,¾573¾K ®
These are colourless, odourless, non-toxic, non-corrosive, non-flammable, non-polar, extremely stable and unreactive gases, liquids and solids. These are stable to ultraviolet radiations and other ionising radiations and therefore, they do not deplete the ozone layer like freons.
These are good electrical insulators. These have many important uses such as :
- These are used as lubricants, surface coatings and
- These are used as heat transfer media in high voltage electrical
- These are used for vapour phase soldering, gross leak detection of sealed microchips in electronic industry.
- These are also used in health care and medicine such as skin care cosmetics, wound healing, liquid ventilation, carbon monoxide poisoning and many medical
Organic compounds in which a metal atom is directly linked to carbon or organic compounds which contain
at least one carbon-metal bond are called organometallic compounds.
Example : Methyl lithium
¾¾® CH3Li ; Dialkyl zinc
¾¾® R2Zn ; Alkyl magnesium halide
¾¾® R – Mg – X
(1) Methyl lithium :
- 2Li ¾¾Eth¾er ®
Note : ® High reactivity of CH3 Li
over grignard reagent is due to greater polar character of C – Li bond in
comparison to C – Mg bond.
- CH3 – Li + H × OH ¾¾® CH4 + LiOH
- CH3 – Li + CH2 – CH2 ¾¾® CH3CH2CH2OLi ¾¾H2¾O ® CH3CH2CH2OH + LiOH O
- Li + CO2
C– O – Li ¾¾¾® CH
3COOH + LiOH
- CH3 – Li + H – C = O ¾¾® CH3CH2 – O – Li ¾¾H2¾O ® CH3CH2OH + LiOH
Note : ® Unlike grignard reagents, alkyl lithium can add to an alkenic double bond.
- R – Li + CH2 = CH2 ¾¾® R – CH2 – CH2 – Li
- Dialkyl zinc : First organometallic compound discovered by Frankland in
2RI + 2Zn ¾¾He¾a¾t ® 2R – Zn – I ¾¾He¾a¾t ®
R2 Zn + ZnI 2
Preparation of quaternary hydrocarbon : (CH3 )3 CCl + (CH3 )2 Zn ¾¾®(CH3 )4 C+ CH3 ZnCl
- Grignard reagent : Grignard reagent are prepared by the action of alkyl halide on dry burn magnesium in presence of alcohol free dry
Dry ether dissolves the grignard reagent through solvolysis.
: O : Mg
: O :
Grignard reagents are never isolated in free sate on account of their explosive nature.
Note : ® For given alkyl radical the ease of formation of a grignard reagent is, Iodide > Bromide > Chloride
Usually alkyl bromides are used.
- For a given halogen, the ease of formation of grignard reagent is, CH3 X > C2 H5 X > C3 H7 X……….
- Since tertiary alkyl iodides eliminate HI to form an alkene, tertiary alkyl chlorides are used in their
- Grignard reagent cannot be prepared from a compound which consists in addition to halogen, some
reactive group such as – OH because it will react rapidly with the grignard reagent.
The C – Mg bond in grignard reagent is some what covalent but highly polar.
| d – d +
d – d +
- C Mg X
or R– Mg X
The alkyl group acts as carbanion. The majority of reaction of grignard reagent fall into two groups:
- Double decomposition with compound containing active hydrogen atom or reactive halogen atom
RMgX + HOH ¾¾® RH + Mg(OH)X
; RMgX + D2O ¾¾® RD + Mg(OD)X
RMgX + R‘ OH ¾¾® RH + Mg(OR‘)X ;
RMgX + R‘ NH2 ¾¾® RH + Mg(R‘ NH)X
RMgX + R‘ I ¾¾® R – R‘+MgIX
; RMgX + ClCH2OR‘ ¾¾® RCH2OR‘+MgClX
- Addition reaction with compounds containing
C = O ;
- C º N,
C = S
C = O + RMgX ¾¾®
C– OH + Mg OH
- C º N + RMgX ¾¾® – C = N MgX ¾¾® – C = O + NH 3 + Mg
| O H2 | X