Aromatic Compounds, Carbonyls and Carboxylic Acids + Nitrogen Chemistry Flashcards
What can an aldehyde be oxidised into?
A carboxylic acid
What is the equation for the oxidation of ethanal?
CH3CHO + [O] → CH3COOH, the reaction mixture is gently heated under reflux
Where do carbonyl compounds have a dipole?
In the C=O functional group
Which part of the C=O bond is attacked and what is it attacked by?
The delta positive carbon atom is attacked by a nucleophile that donates a pair of electrons to the electron deficient carbon
What happens to the C=O bond when the nucleophile attacks the delta positive carbon?
The pi bond breaks and a reactive intermediate is formed, the electron pair is then donated to the neighbouring hydrogen to form an alcohol group and a stable product
What reducing agent is commonly used in nucleophilic addition reactions?
NaBH4
What is hydrogen cyanide and what is its chemical formula?
- A weak acid that partially ionises in solution, its chemical formula is HCN
- HCN + H2O ⇌ CN- + H3O+
- Other sources of CN- include NaCN
Can the cyanide ion directly react with carbonyl compounds?
No, they can only react when the reaction is acidified as the polarity of the C=O bond is increased, which makes the carbonyl group more reactive
What is the role of the acid in the nucleophilic addition reaction between butanal and hydrogen cyanide?
It acts as a catalyst to make the C=O bond more polar which enables the CN- ion to act as an effective nucleophile
When an ester is hydrolysed how are the products named?
Everything before the C=O bond forms part of the carboxylic acid, everything after the C=O bond forms part of the alcohol
What products are formed when methyl propanoate is hydrolysed using water and an acid catalyst?
Propanoic acid + methanol
What is formed when methyl propanoate is hydrolysed using NaOH?
Sodium propanoate + methanol
What is Brady’s reagent?
2,4-DNP, orange transparent mixture
What does Brady’s reagent test for?
- Aldehydes and ketones, when 2,4-DNP is added to a solution containing an aldehyde or ketone, a yellow/orange precipitate is formed
- No precipitate is observed with a carboxylic acid or an ester despite them having the C=O bond
After a positive Brady’s reagent test what test would you use to distinguish between an aldehyde and ketone?
The precipitate formed from the reaction of 2,4-DNP and the aldehyde/ketone can be collected by filtration and purified by crystallisation, this can then be dried and the accurate melting point of the pure product can be measured through experiment
- The melting point for the precipitate can then be compared to database values, this tells you whether it is an aldehyde or a ketone
What is Tollen’s reagent?
A colourless chemical that can be used to distinguish between a ketone and an aldehyde
What is the method for making Tollen’s reagent?
- Sodium hydroxide solution is added to silver nitrate solution until a brown precipitate is formed
- Dilute ammonia is added dropwise until the precipitate redissolves
How does Tollen’s reagent distinguish between a ketone and an aldehyde?
- Tollen’s reagent is a weak oxidising agent, Tollen’s reagent react with aldehydes and a redox reaction takes place
- The silver ions are reduced and the aldehyde functional group is oxidised
- Ag+(aq) + e- → Ag(s) Silver ions are reduced to silver metal which forms a precipitate, this appears as a silver mirror
- RCHO + [O] → RCOOH aldehyde is oxidised to a carboxylic acid
What is the observation when Tollen’s reagent is added to an aldehyde?
A silver mirror is observed
What is the general formula of a carboxylic acid?
CnH2n+1COOH
What is the general formula for an aldehyde?
CnH2n+1CHO
What is the trend in solubility as carboxylic acids get bigger?
- The small carboxylic acids are soluble in water and other polar substances. This is because hydrogen bonds can be formed between the carboxylic functional group and the water molecules
- As the hydrocarbon chain of the carboxylic acid increases in size, the solubility decreases
- This is because only the polar carboxylic acid functional group can form hydrogen bonds with the water molecules
What happens when a carboxylic acid is dissolved in solution?
It partially ionises in solution to form a carboxylate ion and an H3O+ ion
What is the difference between a weak acid and a strong acid?
- A weak acid has a lower concentration of H+ ions, however because dissociation is an equilibrium, when the ions of a weak acid are reacting, more are produced as the ions are used up as the concentration of the products decreases the position of equilibrium shifts towards the products. This means that the same moles of H+ ions will be used in a reaction using both a weak acid and a strong acid but the strong acid will be instantly ionised whereas the weak acid gradually ionises as the reaction takes place
- This means that the rate of reaction will be slower when using the same concentration of a weak acid as a strong acid but they will both produce the same moles of product if the same volume of both is used
What products are formed when sodium reacts with ethanoic acid?
2Na + 2CH3COOH → 2CH3COONa + H2
What products are formed when magnesium oxide reacts with methanoic acid?
MgO(s) + 2HCOOH(aq) → (HCOO)2Mg(aq) + H2O(l)
What products are formed when potassium hydroxide reacts with propanoic acid?
KOH(aq) + CH3CH2COOH(aq) → CH3CH2COOK(aq) + H2O(l)
What products are formed when sodium carbonate reacts with methanoic acid?
Na2CO3(s) + 2HCOOH(aq) → 2HCOONa(aq) + H2O(l) + CO2(g)
How are esters named?
- Everything before the ester linkage is part of the acid and everything after the ester linkage is part of the alcohol
- For example an ester: CH3COOCH3 is named methyl ethanoate
What reactants are used to produce an ester?
A carboxylic acid and an alcohol are heated gently in the presence of a sulfuric acid catalyst, an ester and a water molecule are produced
What are the chemical properties of an ester?
Esters have low boiling points as they aren’t able to form hydrogen bonds between molecules, this means that esters are very volatile
How can esters be separated from the reaction mixture?
Using distillation as the esters are very volatile meaning they can easily be evaporated off and then recollected by condensing the gas produced
Why can’t phenols be used instead of an aliphatic alcohol?
The rate of reaction is too slow, phenols have the delocalised ring making them much more stable than aliphatic alcohols
What is formed in the reaction between ethanoic anhydride and methanol?
- Methyl ethanoate + ethanoic acid
- (CH3CO)2O + CH3OH → CH3COCH3 + CH3COOH
What does the hydrolysis of an ester form?
A carboxylic acid and an alcohol
What are the benefits and cons of producing an ester from an acid anhydride?
The reaction is not reversible meaning a higher yield of the ester product is obtained than using a carboxylic acid
What happens when an ester is refluxed and what catalyst is required?
When esters are refluxed with a catalyst of hot aqueous acids, such as dilute H2SO4 or dilute HCl, the ester will decompose reversibly into a carboxylic acid and an alcohol
What happens when an ester is refluxed with a hot alkali such as NaOH?
- When an ester is heated under reflux with a hot alkali, the ester will decompose into an alcohol and a carboxylate salt
- This reaction is not reversible
- This reaction can be used to make soaps
What is the reaction to produce an acyl chloride?
CH3COOH + SOCl2 → CH3COCl + SO2 + HCl
What do acyl chlorides produce when they react with alcohols?
- They react with alcohols to produce an ester and HCl
- CH3COCl + CH3CH2OH → CH3COOCH2CH3 + HCl
- This reaction is not reversible so therefore has a higher yield of ester than the reaction using a carboxylic acid
How do you name an acyl chloride?
Count the number of carbons in the carbon chain and add to the suffix -oyl chloride
What do acyl chlorides produce when they react with water?
- A carboxylic acid
- CH3COCl + H2O → CH3COOH + HCl
What is the observation of reactions with acyl chlorides that produce HCl?
Steamy fumes are given off
What happens when an acyl chloride reacts with ammonia?
- A primary amide is produced
- CHCOCl + 2NH3 → CHCONH2 + NH4Cl
- Solid ammonium chloride is produced and ethanamide is produces as a white smoke
What happens when an acyl chloride reacts with an amine?
- A secondary amide is produced
- CH3COCl + CH3CH2NH2 → CH3CONHCH2CH3 + HCl
- Ethylamine must be a cold concentrated solution
- N-ethylethanamide is a white solid
What is N-ethylethanamide?
CH3CONHCH2CH3