Alcohols Flashcards
Why do alcohols have higher melting and boiling points than their analogous alkanes?
- ethanes strongest IMF is van de walls
- Ethanols strongest bonds are hydrogen bonds
Why are short alcohols soluble in water? Why do alcohols become less soluble as chain length increases?
- water and short chain alcohols both contain hydroxyl group and this can form hydrogen bonds with each other
- as chain length increases, as the non-polar hydrocarbon chain cannot form hydrogen bonds, a greater part of the molecule is unable to form H bonds with water molecules
Why are alcohols useful from chemical synthesis?
- as they are used as intermediates and as solvents
- used as starting materials for the production of many other substances
What are the conditions for fermentation?
- glucose
- 35C
- anaerobic
- yeast
Why must air be kept out of the reaction vessel (fermentation)
- to prevent ethanol from oxidising (ethanol acid)
Does fermentation have high or low atom economy?
- low
What does hydration mean?
- adding water across double bond
What are the conditions for hydration of ethenol?
- 573K
- 60-70atm
- H3PO4 catalyst
What is a biofuel?
- fuel made from renewable resources
What does carbon neutral mean?
- the CO2 released by burning fuels is absorbed by plants from which it was obtained
Why might ethanol not be described as a carbon neutral fuel?
- uses energy for all steps
- transport + fertiliser + machinery in farming
Aldehydes ketones and carboxylic acids contain…
- the C=O (carbonyl) functional group
What is the functional group for an aldehyde
Suffix-al
What is the functional group for a ketone?
- suffix-one
What is a carboxylic acid>
- R-COOH
- suffix-oic acid
What is the strongest IMF in an aldehyde?
- dipole-dipole
Describe the oxidation of primary alcohols
- primary alcohols can be oxidised to aldehydes
- aldehydes can be further oxidised to carboxylic acids
What is the oxidising agent in the oxidation of primary alcohols?
- acidified potassium dichromate
- H+/K2Cr2O7
Describe the colour of potassium dichromate
- K2Cr2O7 is orange due to the presence of Cr2O7 2- ions
- when it oxidises a primary alcohol or an aldehyde it turns green as Cr2O72- ions are reduced to Cr3+ ions
How is ethanol oxidised?
- distillation
- produces an aldehyde + water
- H+ in H+/K2Cr2O2 is supplied by a dilute acid
- oxidising agent is added to alcohol to ensure it is never in excess
- mixture is heated gently and distilled immediately
- to maximise the yield for aldehyde the temperature must be kept below boiling point of the alcohol and the collecting vessel should be cool
- ethanal has a boiling point of 21C so it vaporises as soon as it forms
- CH3CH2OH + [O] -> CH3CHO + H2O
How is an alcohol/aldehyde oxidise to a carboxylic acid?
- reflux
- the H+/Kr2Cr2O7 is supplied by a concentrated acid and is added in excess
- orange to green
- after refluxing for around 20 mins, the ethanol I acid that is formed has a boiling point of 118C. The apparatus is rearranged to that for distillation, so it can be distilled off along with any water
What is the general equation of an alcohol to a carboxylic acid?
- R-CH2OH + 2[O] -> R-COOH + H2O
- 2 Oxidation steps
- H2O is producded in step 1 only
What is the equation for the oxidation of ethanol -> ethanoic acid?
CH2CH2OH + 2[O] > CH3COOH + H2O
Describe oxidation of secondary alcohols
- secondary alcohols are oxidise to ketones using H+/K2Cr2O7 under reflux conditions
- orange to green
- byproduct of water
