Transcript Hydrocarbons and Fuels - Calderglen High School

Hydrocarbons and Fuels
Alkanes, Alkenes, and Alkyne,
Halogen derivatives, Aromatic
Hydrocarbons, Petrol,
Alternative fuels,
Index
Carbon chemistry introduction
Alkanes and Alkenes
Alkynes
Halogen derivatives, CFC’s
Aromatic hydrocarbons
Fuels
Organic Chemistry, the
Chemistry of Carbon
Originally chemical compounds were divided into 2 classes:
Inorganic or Organic
Organic compounds were derived from living things. It
was believed that they contained a ‘vital force’ and could
not be made from inorganic compounds.
Carbon has the ability to CATENATE, forming
covalent bonds with its own atoms.
H
C
C
H
Organic Chemistry
Organic chemistry is basically the study of compounds
containing carbon
(with the exclusion of oxides and carbonates)
There are so many compounds containing carbon that a
whole branch of chemistry is devoted to their study.
Organic molecules may be
as simple as methane,
CH4
or more complicated
such as cholesterol
HO
Alkanes and Alkenes
Alkane general formula
C n H 2n+2
Alkene general formula
C n H 2n
Structural formula
H
H
H
H
C
C
C
H
H
H
H
Straight Chain
H
H C H
H
H
H C C C
H
H
Name
No C’s
Meth
Eth
Prop
But
Pent
Hex
Hept
Oct
1
2
3
4
5
6
7
8
Branched Chains and unsaturated
CH3CH2CH3
CH3 (CH2)2CH3
CH3CH2CH3
Condensed formula
Molecular formula
C3H7
Naming Compounds of
Carbon
Alkanes
1.
2.
3.
4.
5.
Identify the longest chain
Identify the ‘branches’ and name them.
Number the carbon atoms on the longest chain, at the end giving
the lowest numbers for the branches.
Write the branches in alphabetical order.
If there are more branches with the same name
use di, tri etc
Naming Compounds of
Carbon
Alkenes
1.
2.
3.
4.
5.
Identify the longest chain, that contains a double bond.
Identify the ‘branches’ and name them.
Number the carbon atoms on the longest chain, starting from
the end nearest the double bond. Pick the lowest number to
describe the position of the double bond.
Write the branches in alphabetical order.
If there are more branches with the same name
use di, tri etc
Naming Organic Compounds
H
H
H
H
H
H
H
CH3
C
C
C
C
C
C
C
H
CH2
H
H
H
CH2
H
CH3
CH2
1. Decide on the type of compound
(ie. consider functional group)
2. Select the longest chain
3. Name the compound
with the branched chains
in alphabetical order.
H
CH3
alkane
10 C’s  decane
7-ethyl-3-methyldecane
H
H
C2H5 H
C
C
C
C = C
H
CH3
H
H
1. Decide on the type of compound
(ie. consider functional group)
2. Select the longest chain
3. Number the C atoms so that
the functional group has the
lowest number
4. Name the compound
with the branched chains
in ascending order.
CH3
H
alkene
7 C’s  heptene
hept-2-ene
5,5-dimethylhept-2-ene
H
H
CH3
H
H
H
C
C
C
C
C
H
CH3
Cl
H
H
1. Decide on the type of compound
(ie. consider functional group)
2. Select the longest chain
H
halogen (chloroalkane)
5 C’s  pentane
3. Name the compound
3-chloro-2,2-dimethylpentane
with the branched chains
and halogen in alphabetical order.
STRUCTURAL ISOMERISM
There are two types
1. Chain isomerism.
Here the isomers have different arrangements of carbon
atoms or different chains. For example there are two
compounds with the molecular formula C4H10
H
H
H
H
H
C
C
C
C
H
H
H
H
butane
H
H
H
H
H
C
C
C
H
CH3 H
H
2-methylpropane
Here, you can see that 2-methylpropane has a side chain.
2. Position Isomerism.
Here the isomers have the same carbon skeleton and
functional group but the position of the functional group
is different.
H
H
H
H H
H
H
C
C
C
H
H
Cl
H
H
1-chloropropane
H
H
H
H
C
C
C
H
H
OH
propan-1-ol
H
C
C
C
H
Cl
H
H
H
H
C
C
C
H
OH
H
H
2-chloropropane
H
propan-2-ol
H
Reaction of Alkenes
Reaction with Hydrogen, hydrogenation, an addition reaction
H H H
H C C C
H
H
+
H-H
Propene
H H H
H C C C H
H H H
Propane
Reaction with halogens,
H H H
H C C C
H
H
+
Br-Br
Orange/red
H Br Br
H C C C H
H H H
1,2 dibromopropane
colourless
Reaction with Hydrogen Halides
H H H
H C C C
H
H
+
H
H-I
H
H
I
C
C
C
H
H
H
H
2 -iodopropane
Normally the H from the
halide attaches to the C
which already has the
most hydrogen’s.
or
H
H
H
I
C
C
C
H
H
H
H
1 -iodopropane
Alkyne family CnH2n-2
Ethene
HC CH
C2H2
CaC2 + 2 H2O
H
C
C
Ca(OH)2 + C2H2
Addition reactions with H2 similar to alkenes.
but two stages are possible
Ni Catalyst 150 oC
1st
H
C
C
H
+
H2
Ethene
2nd
H
C
C
H
+
H2
Ethane
H
H
H
Halogen Derivatives
Halogenalkanes and Halogenalkenes
CHCl3
Chloroform
CCl2F2
Freon
CH3CCl3 Correcting fluid
CF2=CF2 Gortex, Teflon
CCl2=CCl2 Solvent for grease
Degreasing agent
CCl
4
CCl2H2
Paint Stripper
CH2=CHCl Vinyl chloride
2-bromo-2-chloro-1,1,1-trifluorethane Halothane
Lava lamps, non-polar alkanes and chloroalkanes
mixed with polar water.
Halogen Derivatives, CFC’s
Chlorofluorocabons CFC’s
All CFC’s are very unreactive, are not flammable
and not toxic. They are used as flame retardants.
CCl2F2
The first refrigerant, and in aerosols.
CCl3F
Used as a blowing agent to make expanded foam
Recently Hydrofluorocarbons have replaced some CFC’s.
e.g. 1,1,1,2-tetrafluoroethane is used as a refrigerant.
Ozone destruction O3
Chlorofluorocabons CFC’s
CCl3F
Cl
U.V.light
+ O3
ClO + O
CCl2F
+ Cl
ClO + O2
Cl + O2
CFC’s are very stable, lasting for 100 years in the
atmosphere. So over time, CFC’s can reach the
stratosphere. Here, UV radiation attacks the CFC’s
forming free radicals ( ) .
Free radicals react with O3, the reaction is complex,
but one Cl free radical can break down 1 million O3
molecules.
Aromatic Hydrocarbons
F.A. Kekule proposed
the original structure
as a result of a dream.
C6H6 Benzene
HC
HC
CH
CH
CH
CH
The first structures are unstable and the electrons delocalise to
form a much more stable structure.
Aromatic carbon molecules contain the benzene ring.
Aliphatic carbon molecules contain the linear chains of
carbon ring.
Aromatic carbon molecules containing the benzene ring
and aliphatic chains are called Arenes.
Aromatic Properties
Methylbenzene (toluene)
Phenylethene (styrene)
C6H5CH2CH
CH3
CH=CH2
CH3
1,2 - dimethylbenzene
CH3
CH3
1,3 - dimethylbenzene
CH3
The benzene ring does not contain 3 double bonds, and so does not take
part easily in addition reactions. It is insoluble in water, being non-polar.
It burns with a smoky flame as carbon is produced.
Aromatic compounds are used in dyes, herbicides, insecticides fungicides,
Aromatic compounds
Cl
CHCCl3
Poly-aromatic hydrocarbons PAH
Cl
DDT
dichlorodiphenyltrichloroethane
COOH
COOCH3
NHCOCH3
Aspirin
2-ethanoyloxybenzenecarboxcyclic acid
OH
Paracetamol
4-hydroxyphenylethanamide
Petrol
By products from the
combustion of petrol
are CO, CO2, NOx
and unburned Hydrocarbons
Long chain Hydrocarbons tend to burn unevenly in a car engine, causing
‘knocking’. Branched chained hydrocarbons burn more evenly, so prevent
’knocking’.
The alkane 2,2,4,-trimethylpentane has good antiknock properties
This also has a high octane rating, 100.
Straight chain hydrocarbons have
C
C
C
C
C
H a lower octane rating, heptane has an
octane number of 0. Benzene is 106.
Unleaded petrol in UK has octane rating
H
CH3
H
H
H
of 95.
Petrol is a blend of different hydrocarbons and this can change
depending on the season. In the winter you would need a petrol
which was more volatile. Companies change their blend 3 or 4
times a year.
H
H
CH3
H
CH3
H
Petrol
Reforming, this is the process by which straight-chain
alkanes undergo a chemical change to change them into
new, smoother burning compounds.
High temperatures, pressures and a catalyst are used.
Branched-alkanes, cycloalkanes and aromatic compounds
are produced.
Hydrocracking, this takes place at high temperatures
in the presence of hydrogen. Long straight chain
hydrocarbons are changed into small branched chain and
straight chain alkanes.
Alternative Fuels, biofuels
Biogas
Methane, produced by anaerobic respiration
Ethanol
Produced by fermentation, octane rating of 111
Methanol
A liquid, made from steam and methane. Octane
rating of 114, also ‘clean’ burning. Toxic and corrosive
Hydrogen
economy
The dream fuel, but needs electricity to make it.
Fuel Cells
2x more efficient than the internal combustion engine.
Requires a source of hydrogen and oxygen.
Did you know?
CFC’s where replaced by HFC’s which do not degrade the
ozone layer. However, they are greenhouse gases 1200x
more powerful than CO2.
A fridge contains 0.67kg of HFC’s, equivalent to 800 kg
of CO2 . For this reason, some fridges now use HC’s,
such as butane and propane. These are only 3 to 4x as
powerful a green house gas as CO2.
Did you know?
Methane is 23x more powerful a greenhouse gas as CO2.
Sewage methane can replace the use of natural gas for the
generation of electrical power.
Green house emission
Biogas
Fuel
Natural gas
Diesel
Petrol
-5
-4
-3
-2
-1
0
1
2
3
Carbon dioxide (kg) / litre of fuel burned
So why does burning biogas give a negative value?