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chem
Carbonyls, carboxylic acids, and esters
| Question | Answer |
|---|---|
| Oxidation of aldehydes | Oxidised when in reflux with acidified dichromate ions (K2Cr2O7/H+) to a carboxylic acid e.g. butanal + [O] -> butanoic acid |
| Reduction of carbonyls | Nucleophilic addition with NaBH4 in acidic or aqueous conditions to form primary or secondary alcohols Nucleophile is hydride ion H- e.g. butanal + 2[H] -> butan-1-ol |
| Carbonyl reaction with HCN | Nucleophilic addition with NaCN and H2SO4 Nucleophile is -CN e.g. CH3CH2CHO + HCN -> CH3CH2CH(OH)CN |
| Test for carbonyls | Brady's reagent or 2,4-DNP dissolved in methanol and H2SO4 to produce a orange precipitate if positive for a C=O bond Carbonyl can be identified from melting point of derivative |
| Test for aldehydes | Tollens' reagent to produce a silver mirror if positive Tollens reagent made by reacting AgNO3 with NaOH and dilute NH3 Tollens' reagent and unknown solution heated at 50C to produce silver mirror |
| Distinguishing aldehydes and ketones with Tollens' reagent | Tollens' reagent acts as an oxidising agent, thus does not react with ketones as they cant be oxidised Ag+(aq) + e- -> Ag(s) RCOH + [O} -> RCOOH |
| Solubility of carboxylic acids in water | C=O and O-H are polar so can form hydrogen bonds Carboxylic acids up to 4C are soluble |
| Acid reactions of carboxylic acids | Metal + acid -> salt + H2 Metal oxide + acid -> salt + water Alkali + acid -> salt + water Carbonate + acid -> salt + water + CO2 |
| Esterification of carboxylic acids with alcohols | Heated with concentrated H2SO4 catalyst Carboxylic acid + alcohol -> ester + H2O |
| Esterification of acid anhydrides with alcohols (and phenols) | Acid anhydride + alcohol -> ester + carboxylic acid |
| Acid hydrolysis | Ester in reflux with dilute aqueous acid, broken down by water with acid as the catalyst - opposite of esterification Ester + H2O -> carboxylic acid + alcohol |
| Alkaline hydrolysis | Ester in reflux with aqueous hydroxide ions, irreversible, forms salt of the alkali used Ester + alkali -> carboxylate salt + alcohol |
| Formation of acyl chlorides from carboxylic acids | Reacted with thionyl chloride (SOCl2), reactants are toxic so should be carried out in a fume cupboard Carboxylic acid + SOCl2 -> acyl chloride + SO2(g) + HCl(g) |
| Esterification of acyl chlorides with alcohols and phenols | Acyl chloride + alcohol/phenol -> ester + HCl Can react with phenols as acyl chlorides are more reactive than carboxylic acids |
| Reaction of acyl chlorides to form carboxylic acids | Acyl chloride + H2O -> carboxylic acid + HCl |
| Reaction of acyl chlorides to form primary and secondary amides | Acyl chlorides react with ammonia to form a primary amide Acyl chloride + 2NH3 -> primary amide + NH4Cl Acyl chlorides react with primary amines to form a secondary amide Acyl chloride + primary amine -> secondary amide + chloride salt |
Created by:
silver54331