2 - Organics Flashcards
Why is Cracking important?
Converts low-demand fractions into higher demand fractions
Makes useful hydrocarbons not normally found in crude oil
What are the conditions for thermal cracking?
High temp + pressure
Makes high percentage of small alkenes
What are the conditions for catalytic cracking?
High temp + slight pressure + zeolite catalyst
More efficient
Zeoloite catalyst favours the formation of branched and cycloalkanes
What are the pollution problems caused by burning hydrocarbons?
Global warming
Water vapour is a greenhouse gas
Carbon monoxide and carbon from incomplete combustion
Sulphur dioxide - acid rain
Nitrogen oxides - acid rain and acidic water and petrochemical smog
Ways of reducing pollution from hydrocarbon combustion?
Flue gas desulphurisation
Catalytic converters - converts oxides of nitrogen and CO
Describe covalent double bonds.
Sigma - side-on overlap, atomic orbitals between the nuclei
Pi - end on overlap, atomic orbitals above and below
Overlap in two places causes restricted rotation
What is E/Z isomerism?
Both hydrogen atoms on the same side of the double bond - Z
Both hydrogen atoms on the opposite side of the double bond - E
What is the pi bond in an alkene like?
Area of high electron density and can thus attract electrophiles
What is Heterolytic fission?
The breaking of a covalent bond which results in both electrons going to the same atom
Describe electrophilic addition of alkene
A hydrogen halide or halogen will be attracted by the double bond causing a bond to form breaking the double bond and leaving a radical nucleophile which bonds to the second un-bonded carbon.
Describe hydrogenation
Adding hydrogen to saturate the double bond of an alkene using 200 degrees and a nickel catalyst. (Makes alkane)
How is the presence of a double bond detected?
Bromine water that causes a brown to colourless change
What is Markownikoff’s rule?
“The more electronegative part of the electrophile will usually attach itself to the more highly substantiated carbon atom”
What are the major and minor products of electrophilic addition called?
Markownikoff product and the anti-Markownikoff product
What does electrophilic addition of an alkene produce?
Halogeno-alkanes
Describe hydration of an alkene
Addition of steam, at 300 degrees, 60 atmospheres and using a phosphoric acid catalyst. It produces an alcohol.
Advantages of fermentation
Low-tech process
Not use much energy (35-55 degrees)
Uses sugar cane which is renewable
Disadvantages of fermentation
Batch process
Slow process
Unethical
Other than fermentation how can ethanol be produced?
hydration of ethene - adding steam at 300 degrees, 60 atmospheres and a Phosphoric acid catalyst
Advantages of hydration
Fast process
Continuous process
Produces pure ethanol
Disadvantages of hydration
High tech - expensive
Uses a lot of energy
ethene comes from crude oil which is non-renewable
What is produced when burning ethanol?
CO2 and H20
Describe the elimination of alcohols
Elimination reaction of alcohol. Concentrated phosphoric acid (H3PO4) used to remove water and make an alkene.
What does the elimination of alcohols produce?
Alkenes (removal of H2O)
What forms when a primary alcohol is mildly oxidised?
aldehyde (anal) (COH)
What forms when a secondary alcohol is mildly oxidised?
Ketone (anone) (COC)
Why can’t tertiary alcohols be oxidised?
No available H atoms
What is formed when an aldehyde is further oxidised?
Carboxylic acid as an extra oxygen is added (COOH)
What can be used as an oxidising agent?
Concentrated Potassium dichromate
What can be used to test for Aldehydes?
Tollens reagent - forms ‘Silver Mirror’
What is a substitution reaction?
A reaction in which one atom or group of atoms on the organic molecule is directly replaced by another.
How are free radicals formed?
homolytic fission - breaking a covalent bond in which one electron goes to each atom
What are the three steps and conditions for free radical substitution?
Initiation, Propagation, Termination and UV light required
What can be done to make sure the major product is achieved in free radical substitution?
Excess of alkane
What does free radical substitution make?
Halogenoalkanes
What do halogenoalkanes react with?
Nucleophiles as the C-X bond is slightly positive
Describe the reaction of halogenoalkanes and hydroxide ions
Nucleophilic Subsitiution .The hydroxide ion (acting as a nucleophile) attacks the carbon from behind forcing the X atom to leave as an ion. It does this under boiling with reflux with aqueous NaOH or KOH. It makes an alcohol.
Describe the reaction of an alkene and H2SO4
Electrophilic of cold concentrated sulphuric acid + then warm and add water. An alcohol is formed. This is hydrolysis.
Describe the reaction of halogenoalkanes and cyanide ions (CN-)
Nucleophilic substitution. Boiled under reflux with KCN in aqueous ethanol. The Carbon in the cyanide attacks the carbon. CN- ion attacks carbon and halogen ion is formed. It is a very useful reaction for ascending the homologous series as it increases the number of carbons on the chain.
Describe the reaction of halogenoalkanes and ammonia (NH3)
Nucleophilic substitution. Heated with ethanol. Primary amine formed. Halogen ion formed.
Describe the elimination of halogenoalkanes
Produces an alkene. Ethanolic solution of KOH used. OH ion attacks hydrogen, forms water. curly arrows go from ion to H to C-C bond to X. Loss of X. Hydroxide ion acts as nucleophile.
Describe the rates of reaction for the Halogenoalkanes
Increases down group as halogen atom becomes larger, the C-X bond becomes longer, weaker and easier to break thus reacting more quickly.
Describe dehydration.
Elimination reaction of alcohol. Concentrated phosphoric acid (H3PO4) used to remove water and make an alkene.
How to make chloroalkane from alcohol? (Chlorination)
Add PCL, HCL produced, misty white fumes, only works with primary and secondary alcohols.
For tertiary shake with aqueous HCL, water produced
How to make bromoalkane from alcohol? (Bromoalkane)
Warm gently with HBr, makes H20
To make HBr, add KBr to conc H2SO4
KBr + H2SO4 –> KHSO4 + HBr
How to make iodoalkane from alcohol? (iodonation)
Reflux with PI3, makes H3PO3
To make PL3, add Red phosphorus to 3 iodines
2P + 3I2 –> 2PI3
