Chapter 15: Alcohols Flashcards
What is the general formula and functional group of Alcohols
- CnH2n+1OH
- Have a hydroxyl group (-OH) attached to the hydrocarbon chain
How do you name alcohols
- Find longest chain -OH is attached to
- Place the -OH on the lowest possible number for the chain
- Remove -e from alkane and add -ol
- Use numbers to show position isomers
What do you do if there is more than 1 hydroxyl group (more than 1 -OH)
- Use names to say how many (di, tri, tetra)
- e.g propane 1, 2, 3 - triol
In alcohols what are the shapes and bonding angles
- The oxygen atom has 2 bonding pairs and 2 lone pairs
- The C-O-H bond angle is 105 (104.5). Angle of tetrahedron is squeezed down in presence of lone pairs
What are the different classification of alcohols and give examples
- Primary alcohol (1º) - has -OH group at the end and attached to carbon that is attached to 1 other carbon (e.g Propan-1-ol)
- Secondary alcohol (2º) - has -OH group in the body of the chain and -OH attached to carbon that is attached to 2 other carbons (e.g propan-2-ol)
- Tertiary alcohol (3º) - has -OH group attached to a C bonded to 3 other C. (e.g methyl propan-2-ol)
What are the Physical Properties of alcohols
- High melting and boliling points (-OH group means hydrogen bonding occurs between molecules)
- Water soluble
- The -OH group can hydrogen bond to water molecules but non-polar hydrocarbon can’t
- Longer chain (non-polar hydrocarbon chain dominates) - insoluble
- Shorter chain soluble in water (hydrogen bond pre-dominates)
What is a substances boiling point a measure of
- A substances boiling point is a measure of the intermolecular forces present between particles
- Noble gases show a gradual increase in boiling points, hydrides (element joined to H) also show trend
What is the formula of ethanol and what are the 2 ways it can be produced
- C2H5OH
- By product of anaerobic respiration (fermentation of alcohols)
- Manufacture industrially with ethene (hydration of ethene)
Why are alcohols and ethanol important
- Alcohols are used as intermediates and easily made and converted into other compounds
- Ethanol used as intermediate in the manufacture of other organic compounds and used in cosmetics, perfumes
What is fermentation of alcohols
(conditions, raw materials, raw material type, type of process, reaction rate, purity of ethanol)
- Fermentation is a process where glucose is converted to alcohol as a byproduct of anarobic respiration in yeast (C6H12O6→2C2H5OH + 2CO2)
- Conditions: 35ºc, normal atmospheric pressure, catalyst: enzyme in yeast zymase, aqueous and anaerobic
- Raw material (type): Carbohydrate crop (renewable)
- Type of process: batch (stop/start)
- Reaction rate (slow)
- Purity of ethanol - impure (needs fractional distillation) Once fermenting solution has 15% ethanol (enzymes dont work) removed by FD (78ºC BP 100º H20)
What happens if there is oxygen in fermentation
- Oxygen can oxidise ethanol to ethanoic acid
- C2H5OH + 2[O] →CH3COOH + H2O
Apart from fermentation, what is the other way to produce ethanol
- Making ethanol from crude oil
- Ethene is produced when crude oil fractions are cracked
- Ethene is hydrated, water added across double bond
- Ethene is mixed with steam (H2O(g)) and passed over a catalyst consisting of Silicon dioxide coated with phosphoric acid (H3PO4)
- Hydration means addition of water to a compound
What is the conditions of the Hydration of ethene to produce ethanol
Raw materials (type), Type of process, Reaction rate, Purity of ethanol
- Conditions: Temperature = 300ºC, Pressure = 70atm, Catalyst = conc phosphoric acid
- Raw materials (type) : Crude oil (finite)
- Type of process: Continuous
- Reaction rate: Fast
- Purity of ethanol: Pure
What can ethanol be used for and what is a biofuel
- Can be burnt as a fuel (burned in excess oxygen to produce carbon dioxide and water)
- C2H5OH + 3O2 →2CO2 + 3H2O
- A biofuel is a fuel produced from biological resources
What is an advantage and disadvantage of fermentation of alcohols at 35ºC rather than 25ºC and What does carbon neutral mean
- Advantage: Ethanol is produced at a faster rate
- Disadvantage: More energy is used/ required in the reaction
- Carbon neutral - No net production of CO2 in the atmosphere
- Ethanol can be manufactured by the direct hydration of ethene and by the fermentation of sugars. What is meant by hydration?
- Give 1 advantage and 1 disadvantage of manufacturing ethanol by fermentation rather than hydration
How is Fermentation known to be Carbon neutral
- Addition of water/steam
- Advantage: Low technology, renewable feedstock, allowed for ususe in drinks, perfumes, considered to be green
- Disadvantage: Slow, low yield, significant land use, has to be distilled, labour intensive
What is a redox reaction and What happens in reduction and oxidation
- A redox reaction has a simultaneous reduction and oxidation reaction
- Reduction:
- Gain of H
- Loss of O
- Oxidation:
- Gain of O
- Loss of H
What is Redox reaction in alcohols, what does an oxidising agent do and what is the common oxidising agent in oxidising alcohols
- Alcohols can be oxidised to other products depending on the type of alcohol
- A substance that oxidises another is called an oxidising agent
- A common oxidising agent is acidified dichromate (VI) ions, (H+/Cr2O72-)
- Often provided by sulfuric acid mixed with potassium dichromate solution
In redox reactions in alcohols what happens to the Potassium dichromate ions
- Potassium dichromate ions are orange
- They can be reduced to green Chromium (III) (Cr3+)
- This happens when the dichromate ions oxidise something else
- This means they act as oxidising agents
What happens when a Primary alcohol is oxidised
- It produces an aldehyde and can be further oxidised to produce carboxylic acids
- Oxidising ethanol to ethanal- excess alcohol, little oxidising agent - distillation remove product as it is made - stop from being oxidised further
- Oxidising ethanol to ethanoic acid - conc sulfuric acid - excess dichromate used, mixture is refluxed, vapour condenses and drips back into the reaction flask, eventually all oxidised to acid. After 20mins distil ethanoic acid with water
What happens when a secondary alcohol is oxidised
- Ketones are produced and not oxidised further
Why are tertiary alcohols not oxidised
- Oxidation needs C-C bond not C-H bond
What are aldehydes and ketones and their differences
- Both have C=O group (carbonyl group) Aldehydes suffix -al and have carbonyl group at the end of the chain
- Ketones have suffix one and have carbonyl group in the body
What are the different tests to test for aldehydes or ketones
- Tollens Reagent: Ammonical silver nitrate solution. (silver nitrate dissolved in ammonia)
- Aldehydes produce a silver mirror effect inside the container. Ag(NH3)2+ +e-→Ag + 2NH3
- Silver I complex reduced to Ag when aldehyde is oxidised
- Fehlings Solution: Blue solution of Copper (II) ions dissolved in sodium hydroxide
- Aldehydes reduce Cu2+ to a brick red Cu+ percipitate. The aldehydes oxidised to an acid Cu2+ e —> Cu+
Outline a simple procedure to allow you to determine whether A is primary, secondary or tertiary alcohol
- Mix the alcohol with warm acidified Potassium dichromate (K2CR207) - lack of reaction is tertiary alcohol
- Distillation of initial product for 1 or 2
- Effect on tollens reagent or fehlings solution on oxidation product identifies primary or secondary alcohol.
How can alkenes be produced from alcohols
- By acid catalysed elimination reactions
- Alkenes produced by this method can be used to produce addition polymers without using monomers derived from crude oil.
EXAM Q: Alcholic drink has methanol, ethanol, ethanal, ethanoic acid and phosphoric acid
- Identify how alcohol in the drink was produced
- Suggest a test to confirm presence of ethanal
- Explain how ethanal and ethanoic acid were produced from ethanol
- Hydration of ethene - phosphoric acid is only used in this technique
- Tollens/Fehlings/Benedicts turms silver with aldehydes or brick red percipitate
- Oxidation - ethanol excess with no reflux produces ethanal and water
- Excess oxidising agent with reflux produces ethanoic acid
What are elimination reactions
- Molecule is removed (for example water) dehydration of alcohols is an elimination reaction
- Water molecule made from -OH group and H next to this group
What is the apparatus for an elimination reaction (dehydration) and what are the conditions
- Elimination reactions remove small molecules
- This is always water in alcohols
- This forms alkens and Isomeric products can be produced (Aluminium oxide is used as a catalyst
- Hot conc sulfuric or phosphoric acid at 180 degrees
