Halogenoalkanes :
Halogenoalkanes :
(CnHenX) an alkane in which one or m o re
of the hydrogen atoms have been replaced by a
halogen .
8 + 5-
Carbon-Halogen bond polar dipole halogenoalkanes are susceptible to nucleophilic attack the d Carbon substitution
·
is so this means on occu rs
,
Nucleophile : a
species with a lone pair of electrons that can be donated to an electron-deficient species
Nucleophilic substitution :
Preparation of alcohols : Reflux :
out
Water
Cag
condenser
H nucleophile Of , provided by NaOH allows prolonged heating of
#18
is
·
OH
·
,
+
5
H -
C -
C -
C -
C) + C
↳
·
Mechanism nucleophilic substitution or water in volatile chemicals w/out loss
↑
:
Ith Ith
hydrolysis water
·
top of condenser must be open
Ground
if using -
solvent & reagent
OH- ·ning
in
:
A slow reaction has to be heated doesn't explode
·
so So
hoa
1-Chloropropane Propan-1-o ·
In an
open flask much of liquids would
·
Water in from bottom
evaporate low it has time to absorb
yield heat
So
·
hydroxide ion acts as base ·
So Reflux is used . heat
Elimination :
1-bromopropane Propene
Elimination involves the loss of small molecule to
CH3
reaction produce double bond
·
-
H H20 a
:
a
H Br -
+
C = C OH-
HBr +
The alkali (NaOH must be dissolved in ethanol wh out any water to avoid substitution
·
H
-
I H
% OH The halogen must be attached to carbon which
·
is next to the carbon w/ the halogen attached
If halogenoalkane unsymmetrical than alkene be formed (E-Z isomerism)
·
is more one can
,
hydroxide ion acts base
·
as
Testing for halide ion :
Different halogens :
Same test but dilute nitric acid must
Electronegativity decreases halogen
- ·
: a s size of increases
be added before silver nitrate to neutralise . Bond strength Substitution
: involves breaking C-X bond ,
So more
energy required to break bond with 'strongest' dipole
the NaOH , if not ,
brown ppt forms :
AgOH -bond strength dominates the order of the rate of
hydrolysis
-rate of reaction :
tertiary halogeno alkanes react fastest due to
alkyl groups which reduce the positive charge on the carbon
Uses :
making it easier to release the
halogen
Solvents :
·
have polar bond & non-polar alkyl chain so can
Anaesthetics :
Polymers
of organic substances
·
Can act general anaesthetics
·
Made of halogeno hydrocarbons
variety
as
mix with a
Non-flammable be used Chloroform & Mickey Finn used in the past e
.
g polychloroethene (PVC) used in
packaging
·
were
processes of
· -
so c a n in
.
degreasing &
dry cleaning
& revolutionised
surgery polytetrafluoroethe (PTFE) used for non-sticky surfaces
-
Some of these still used anaesthesia , . halothane
·
a re in e .
g
Refrigerants
·
boiling temperatures close to room temp Adverse environmental effects of CFCs
Chosen for non-flammable
non-toxicity & volatile Nowadays, limited found to be toxic & CFCs damage to earth's
layer
·
is
many
·
use as were cause ozo n e
,
The layer prevents harmful UV radiation So depletion skin
. dichloro-fluoromethane reaching earth's surface
2
g
·
. ozone . can cause cancer
·
The process involves radical substitution Ozone layer contains Oz molecules .
Cl .
+
Oz - Cl0 . +
02
Why the C-F bond C-Cl bond ? Alternatives
·
is
stronger than :
C10 : +
03 + Cl .
202
because fluorine alkanes : However have
is much smaller atom
get problem inflammability
·
a ,
so can -
a on
closer to the carbon atom ,
therefore the attraction
-
HFCs : radicals not formed when exposed to UV radiation due to the strength of the bond
between &
greater
shared
pair of electrons nuclei is .
, 18/03/25
·
Making alcohol : ethanol boiling point : 78
%
C ·
As alcohol chain
increases there are
,
1) Fermentation
less H-bonds So compare
& bio
we
:
enzyme catalyst Polar so can form
chain
length
CHizOg(aq) 2(HgOH(1) +
COz(g) hydrogen bonds
·
You separate the product
2) Industrial :
by distillation H
* -
H
c
1)
-
Alcohol
Electrophilic addition of HO to ethene Shorter
·
chains soluble in water
a re
+
if it Yo
(Hy(g) Hz0(g) +
300 %
CHgOH(g) DH -49KJmol
= :
60-70 atm
HzPOn Catalyst
hydrogen adds to carbon w/ most
hydrogens elimination & dehydration of alcohols to form alkenes :
H HH H
H
Hy
C
H- -
↑
H
C C
-
=
H -
c -
H H
Syo +H
- -I
+
H
I
it ↑
Hu H HT
T
A
C-C
-
H- H + Hz0 C = C
↑
H H20
:
0 -
H # H
/
H
H %: 0
.
-
H
if
Combustion of alcohols >
-
fuels
·
alcohol can come
from fermentation ,
GHsOH +
302 >
-
2(0z +
3H20 So could be carbon neutral
,
w/ out
less likely
incompletely it contains
requiring crude oil
-
to combust to alkene
compared as
oxygen
Oxidising primary alcohol >
-
aldehyde Oxidising a
secondary
alcohol <Ketone
O
CHzCHaCHy-OH + [O] >
-
CHzCHeCH +HzO OH O
↑
[O] -HC-C-CH H
HFC-CH
+
Oxidation state of carbon increased from -2 to - (average) ,
so oxidation
CH3CHaC +
[O] >
-
CHyCHzC" -
OH
·
We cannot oxidise it further as it would need to break C-H bonds
oxidation number
of carbon
changes from -" to -3 ,
so oxidised
Oxidation of Ht
alcohols
using acidified potassium dichromate acidified by HzSOG for
:
Oxidising agent is Potassium or Sodium dichromate Primary alcohols + [O] aldehyde + water
in
CO" + Ge Zcr +Ho aldehyde + [0] >
-
carboxylic acid
Nat
Secondary alcohol + [Ob >
-
Ketone +
H
Tertiary alcohols don't oxidise
Acidified potassium dichromate (VI) changes color from
orange
to
green
Fermentation v .
Hydration of ethene
Hydration of ethene Fermentation
Equipment complex set up required Simple equipment
Issues around Biofuels :
Raw materials non-renewable (crude oil) renewable (Sugar cane) Pros :
Type of process continuous Batch
-
Renewable raw materials where as fossil fuels aren't
,
Rate of reaction fast slow (several days)
-
Carbon neutral :
plants photosynthesise before being burnt
Very
Pure ethanol Not country has fossil fuels also less affected by changes in
price
Quality
I
dilute solution every
-
of product
Cons
burning
:
Atmospheric effects fossil fuels carbon neutral
Land less space to & forests destroyed
high temp & pressure low temp Cheap
use
grow crops some are
-
:
Reaction conditions .
.
Increases cost
-
Use of water & fertilisers : can strain local resources & pollute
-
Maybe not
actually carbon neutral e .
.
g transport & deforestation .
Dehydration of alcohols : elimination w/ conc HSOG or
heating w/ Al Os
Halogenoalkanes :
(CnHenX) an alkane in which one or m o re
of the hydrogen atoms have been replaced by a
halogen .
8 + 5-
Carbon-Halogen bond polar dipole halogenoalkanes are susceptible to nucleophilic attack the d Carbon substitution
·
is so this means on occu rs
,
Nucleophile : a
species with a lone pair of electrons that can be donated to an electron-deficient species
Nucleophilic substitution :
Preparation of alcohols : Reflux :
out
Water
Cag
condenser
H nucleophile Of , provided by NaOH allows prolonged heating of
#18
is
·
OH
·
,
+
5
H -
C -
C -
C -
C) + C
↳
·
Mechanism nucleophilic substitution or water in volatile chemicals w/out loss
↑
:
Ith Ith
hydrolysis water
·
top of condenser must be open
Ground
if using -
solvent & reagent
OH- ·ning
in
:
A slow reaction has to be heated doesn't explode
·
so So
hoa
1-Chloropropane Propan-1-o ·
In an
open flask much of liquids would
·
Water in from bottom
evaporate low it has time to absorb
yield heat
So
·
hydroxide ion acts as base ·
So Reflux is used . heat
Elimination :
1-bromopropane Propene
Elimination involves the loss of small molecule to
CH3
reaction produce double bond
·
-
H H20 a
:
a
H Br -
+
C = C OH-
HBr +
The alkali (NaOH must be dissolved in ethanol wh out any water to avoid substitution
·
H
-
I H
% OH The halogen must be attached to carbon which
·
is next to the carbon w/ the halogen attached
If halogenoalkane unsymmetrical than alkene be formed (E-Z isomerism)
·
is more one can
,
hydroxide ion acts base
·
as
Testing for halide ion :
Different halogens :
Same test but dilute nitric acid must
Electronegativity decreases halogen
- ·
: a s size of increases
be added before silver nitrate to neutralise . Bond strength Substitution
: involves breaking C-X bond ,
So more
energy required to break bond with 'strongest' dipole
the NaOH , if not ,
brown ppt forms :
AgOH -bond strength dominates the order of the rate of
hydrolysis
-rate of reaction :
tertiary halogeno alkanes react fastest due to
alkyl groups which reduce the positive charge on the carbon
Uses :
making it easier to release the
halogen
Solvents :
·
have polar bond & non-polar alkyl chain so can
Anaesthetics :
Polymers
of organic substances
·
Can act general anaesthetics
·
Made of halogeno hydrocarbons
variety
as
mix with a
Non-flammable be used Chloroform & Mickey Finn used in the past e
.
g polychloroethene (PVC) used in
packaging
·
were
processes of
· -
so c a n in
.
degreasing &
dry cleaning
& revolutionised
surgery polytetrafluoroethe (PTFE) used for non-sticky surfaces
-
Some of these still used anaesthesia , . halothane
·
a re in e .
g
Refrigerants
·
boiling temperatures close to room temp Adverse environmental effects of CFCs
Chosen for non-flammable
non-toxicity & volatile Nowadays, limited found to be toxic & CFCs damage to earth's
layer
·
is
many
·
use as were cause ozo n e
,
The layer prevents harmful UV radiation So depletion skin
. dichloro-fluoromethane reaching earth's surface
2
g
·
. ozone . can cause cancer
·
The process involves radical substitution Ozone layer contains Oz molecules .
Cl .
+
Oz - Cl0 . +
02
Why the C-F bond C-Cl bond ? Alternatives
·
is
stronger than :
C10 : +
03 + Cl .
202
because fluorine alkanes : However have
is much smaller atom
get problem inflammability
·
a ,
so can -
a on
closer to the carbon atom ,
therefore the attraction
-
HFCs : radicals not formed when exposed to UV radiation due to the strength of the bond
between &
greater
shared
pair of electrons nuclei is .
, 18/03/25
·
Making alcohol : ethanol boiling point : 78
%
C ·
As alcohol chain
increases there are
,
1) Fermentation
less H-bonds So compare
& bio
we
:
enzyme catalyst Polar so can form
chain
length
CHizOg(aq) 2(HgOH(1) +
COz(g) hydrogen bonds
·
You separate the product
2) Industrial :
by distillation H
* -
H
c
1)
-
Alcohol
Electrophilic addition of HO to ethene Shorter
·
chains soluble in water
a re
+
if it Yo
(Hy(g) Hz0(g) +
300 %
CHgOH(g) DH -49KJmol
= :
60-70 atm
HzPOn Catalyst
hydrogen adds to carbon w/ most
hydrogens elimination & dehydration of alcohols to form alkenes :
H HH H
H
Hy
C
H- -
↑
H
C C
-
=
H -
c -
H H
Syo +H
- -I
+
H
I
it ↑
Hu H HT
T
A
C-C
-
H- H + Hz0 C = C
↑
H H20
:
0 -
H # H
/
H
H %: 0
.
-
H
if
Combustion of alcohols >
-
fuels
·
alcohol can come
from fermentation ,
GHsOH +
302 >
-
2(0z +
3H20 So could be carbon neutral
,
w/ out
less likely
incompletely it contains
requiring crude oil
-
to combust to alkene
compared as
oxygen
Oxidising primary alcohol >
-
aldehyde Oxidising a
secondary
alcohol <Ketone
O
CHzCHaCHy-OH + [O] >
-
CHzCHeCH +HzO OH O
↑
[O] -HC-C-CH H
HFC-CH
+
Oxidation state of carbon increased from -2 to - (average) ,
so oxidation
CH3CHaC +
[O] >
-
CHyCHzC" -
OH
·
We cannot oxidise it further as it would need to break C-H bonds
oxidation number
of carbon
changes from -" to -3 ,
so oxidised
Oxidation of Ht
alcohols
using acidified potassium dichromate acidified by HzSOG for
:
Oxidising agent is Potassium or Sodium dichromate Primary alcohols + [O] aldehyde + water
in
CO" + Ge Zcr +Ho aldehyde + [0] >
-
carboxylic acid
Nat
Secondary alcohol + [Ob >
-
Ketone +
H
Tertiary alcohols don't oxidise
Acidified potassium dichromate (VI) changes color from
orange
to
green
Fermentation v .
Hydration of ethene
Hydration of ethene Fermentation
Equipment complex set up required Simple equipment
Issues around Biofuels :
Raw materials non-renewable (crude oil) renewable (Sugar cane) Pros :
Type of process continuous Batch
-
Renewable raw materials where as fossil fuels aren't
,
Rate of reaction fast slow (several days)
-
Carbon neutral :
plants photosynthesise before being burnt
Very
Pure ethanol Not country has fossil fuels also less affected by changes in
price
Quality
I
dilute solution every
-
of product
Cons
burning
:
Atmospheric effects fossil fuels carbon neutral
Land less space to & forests destroyed
high temp & pressure low temp Cheap
use
grow crops some are
-
:
Reaction conditions .
.
Increases cost
-
Use of water & fertilisers : can strain local resources & pollute
-
Maybe not
actually carbon neutral e .
.
g transport & deforestation .
Dehydration of alcohols : elimination w/ conc HSOG or
heating w/ Al Os
