WM cdhg: Organic reactions (alcohols & phenols); green chemistry Flashcards
What is an elimination reaction?
One in which a small molecule is removed from a larger one, leaving the latter unsaturated.
- What conditions are required for the reaction between alcohols and halide ions?
- What type of reaction occurs?
- What is the mechanism?
- What is produced?
- HCl / H2SO4
- Substitution
- Nucleophilic substitution
- Haloalkane + water
Acid catalyst protonates C-OH carbon, making it more δ+ and thus susceptible to nuc attack
- What conditions are required for the conversion of alcohols to alkenes?
- Give two names for the type of reaction which occurs.
- Heated Al2O3 / conc. H2SO4, reflux
- Dehydration, elimination
Name, and give the formula for, a strong oxidising agent which will oxidise the hydroxyl group on alcohols.
Acidified dichromate(VI) solution
Cr2O7(aq)2- / H+(aq)
- Which of primary, secondary and tertiary alcohols react with acidified dichromate(VI) solution?
- Describe and explain what is observed
- Primary + secondary
- Mixture turns from orange to green. Orange dichromate(VI) (Cr2O72-) ions are reduced to green chromate(III) (Cr3+) ions
- Give two names for the type of reaction which occurs between primary or secondary alcohols and acidified dichromate(VI) solution.
- Describe what happens to the hydroxyl group.
- Oxidation, condensation
- -OH group oxidised to C=O (carbonyl) group: one hydrogen removed from oxygen + another from carbon to which oxygen is bonded
State what is produced when acidified dichromate(VI) solution is added to a primary alcohol and the mixture is:
- Distilled
- Refluxed
- Distilled: aldehyde
- Refluxed: carboxylic acid
State what is produced when acidified dichromate(VI) solution is added to a secondary alcohol and the mixture is:
- Distilled
- Refluxed
- Distilled: ketone
- Refluxed: ketone (no further oxidation; would involve breaking strong C-C bond)
State what is produced when acidified dichromate(VI) solution is added to a tertiary alcohol and the mixture is:
- Distilled
- Refluxed
Alcohol is not oxidised under either condition.
(No hydrogen available to remove from carbon atom to which hydroxyl group is bonded)
Draw a diagram showing what is produced when acidified dichromate(VI) solution is added to ethanol and the mixture is:
- Distilled
- Refluxed
Write an equation, using full structural formulae, for the reaction between acidified dichromate(VI) solution and propan-2-ol. Represent the former with [O].
Name a test for phenol. Describe and explain what is observed when phenol is present.
- Test with neutral iron(III) chloride solution
- Mixture changes from colourless to purple since C=C–OH (enol) group forms purple complex with Fe3+ ions
Write equations to show how ethanol and phenol act as acids.
C2H5OH(aq) ⇌ C2H5O-(aq) + H+(aq)
C6H5OH(aq) ⇌ C6H5O-(aq) + H+(aq)
Rank the acidic strength of the following compounds in decreasing order:
- Phenols
- Water
- Carboxylic acids
- Ethanol
Carboxylic acids > phenol > water > ethanol
How do phenols and carboxylic acids react with:
- Alkalis (strong bases)?
- Carbonates (weak bases)?
Phenol + alkali → salt + water
Carboxylic acid + alkali → salt + water
Phenol + carbonate: no reaction
Carboxylic acid + carbonate → salt + water + CO2
Remember that phenols are less reactive than carb acids, and carbonates are less reactive than alkalis.
Write the symbol equation for the reaction between ethanoic acid and sodium hydroxide.
CH3COOH + NaOH → CH3COONa + H2O
- Write the skeletal equation for the reaction between phenol and sodium hydroxide.
- Name the organic product.
Sodium phenoxide
Write the symbol equation for the reaction between ethanoic acid and sodium carbonate.
2CH3COOH + Na2CO3 → 2CH3COONa + CO2 + H2O
State and explain what would be observed on the addition of sodium carbonate to:
- Phenol
- Propanoic acid
- No change; phenol does not react with carbonates
- Fizzing; gaseous CO2 produced
- Name two reagents which can be used to esterify alcohols. For each, state any conditions required.
- State which reaction is reversible.
- Carboxylic acids, with conc. H2SO4 / HCl
- Acid anhydrides (no catalyst)
Reaction with carb acids is reversible (with acid anhydrides goes to completion)
Explain why acid anhydrides are preferable to carboxylic acids as a reagent for the esterification of alcohols.
- Acid anhydrides react completely with alcohols (reverse reaction is negligable):
- Leaving group is -OCOO ion
- Delocalisation makes it stabler and a worse nucleophile than OH- leaving group from carb acids
- Less likely to attack ester
- Acid anhydrides give higher yield of ester
Stability in solution: Cl- ions > carboxylate ions > OH- ions
- Give the skeletal equation for the reaction of ethanol with ethanoic acid.
- Name the organic product.
Ethyl ethanoate
Give the symbol and word equations for the reaction of ethanol with ethanoic anhydride.
What reagent(s) and conditions are needed to esterify phenols?
Acid anhydride, alkaline conditions
Carboxylic acids aren’t reactive enough for phenols. OH in phenols is less reactive than in alcohols bc delocalisation acts as “electron vampire”, making nucleophilic oxygen less δ-
Write the word and symbol equation for the synthesis of phenyl ethanoate from phenol.
Phenol + ethanoic anhydride → phenyl ethanoate + ethanoic acid
C6H5OH + (CH3CO)2O → CH3COOC6H5 + CH3COOH
The systematic name of salicylic acid is 2-hydroxybenzoic acid.
Name two ways in which it could be esterified.
- React phenol group with acid anhydride
- React carboxyl group with alcohol, in presence of conc. HCl / H2SO4
The systematic name of salicylic acid is 2-hydroxybenzoic acid.
Draw two synthetic pathways for the esterification of salicylic acid, naming any conditions required.
Draw the skeletal formulae of all reagents and products, and give the systematic names of the organic products.
Image labelled “ethanol” is actually methanol. Q is general but A is ethyl and methyl esters respectively.
What is green chemistry?
The development of chemical processes which are as sustainable and environmentally friendly as possible.
Suggest 3 principles of green chemistry which maximise sustainability.
- Maximise atom economy
- Minimise energy usage (catalysis, temp, pressure)
- Use renewable feedstock
Suggest 4 principles of green chemistry which reduce waste production.
- Maximise atom economy
- Reduce number of reagents + synthetic steps
- Catalysis
- Real-time process monitoring
Suggest 5 principles of green chemistry which minimise health and safety issues.
- Use less hazardous reagents
- Design less hazardous products (immediate + during degradation in environment)
- Use less hazardous solvents
- Use less hazardous processes (minimise gas/fire/explosions)
