CL 26- carbonyls and carboxylic acids Flashcards
reduction of propanal
equation and reducing agent/ conditions
CH₃CH₂COH + 2[H] –> CH₃CH₂CH₂OH
forms a primary alcohol
NaBH₄ (warm, AQUEOUS)
reduction of propanone
equation and reducing agent/ conditions
CH₃COCH₃ + 2[H] –> CH₃CHOHCH₃
forms a secondary alcohol
NaBH₄ (warm, AQUEOUS)
ethanal with HCN
equation, conditions
CH₃CHO + HCN –> CH₃CH₂CHOHCN
H₂SO₄ + KCN (as HCN is very toxic, so produced ‘in situ’)
purpose of ethanal + HCN
makes the C chain longer
reagent to test for carbonyls
Brady’s reagent (2,4-DNP)
yellow/orange precipitate formed
how can you use the precipitate formed from 2,4-DNP to identify the exact carbonyl?
- impure yellow/orange solid is filtered to separate the solid precipitate from the solution
- solid is then recrystallised to produce a pure sample of crystals
- find the melting point
- compare to database
use of tollen’s reagent
equation to show what’s happening
silver mirror formed when reacted with aldehyde
Ag⁺₍ₐ₎ + e⁻ –> Ag₍ₛ₎
why are carboxylic acids water soluble?
- C=O and O-H bonds are polar so can form hydrogen bonds with water molecules
trend of solubility of carboxylic acids
- as the number of carbons increase (chain length increases), the solubility decreases
- as the non-polar carbon chain has a greater effect on the overall polarity of the molecule
what is an acid anhydride?
formed by the removal of water from two carboxylic acid molecules
equation for forming ethanoic anhydride
2CH₃COOH –> CH₃COOCOCH₃ + H₂O
ethanoic anhydride with methanol
equation
CH₃COOCOCH₃ + CH₃OH –> CH₃COOCH₃ + CH₃COOH
advantages of using an acid anhydride over a carboxylic acid for esterification
- provides better yields
- requires less stringent conditions
- acid anhydrides are easier to handle
advantage of alkaline hydrolysis over acid
- irreversible reaction
- products are easier to separate
- lower production costs
formation of ethanoyl chloride from a carboxylic acid
CH₃COOH + SOCl₂ –> CH₃COCl + SO₂ + HCl