Unit 4.4 - Aldehydes and Ketones (physicsandmathstutor) Flashcards
what is the type of reaction alcohols undergo to form aldehydes and ketones
oxidation
what does oxidising a 1° alcohol produce
aldehyde
what does oxidising a 2° alcohol produce
ketone
what is needed for the oxidation of an alcohol to aldehyde
distillation
why is immediate distillation required for the oxidation of an alcohol –> aldehyde
otherwise will undergo further oxidation = carboxylic acid
what is the oxidising agent used in the oxidation of alcohols
acidified potassium dichromate
what is observed when an alcohol undergoes oxidation by acidified potassium dichromate
orange (dichromate) is reduced to green (chromium ion)
what is observed when acidified potassium dichromate is added to a tertiary alcohol
solution will remain orange
(tertiary alcohols cannot be oxidised)
what does the oxidation of propan-2-ol produce
propanone + water
what does the oxidation of ethanol produce
ethanal + water
what 2 reagents can be used to distinguish between aldehydes and ketones
- tollens’ reagent
- fehling’s reagent
how can tollen’s reagent be used to determine whether you have an aldehyde or a ketone
when warmed with aldehyde, it forms a silver mirror on test tube
how can fehling’s reagent be used to determine whether you have an aldehyde or a ketone
reagent = blue
reagent + aldehyde = brick red ppt
reagent + ketone = no reaction
what type of reaction do aldehydes and ketones undergo to form alcohols
reduction
what type of alcohol will an aldehyde be reduced to
1° alcohol
what type of alcohol will an ketone be reduced to
2° alcohol
what is a common reducing agent used in the reduction of aldehydes and ketones to alcohols
NaBH₄ dissolved in water with methanol
what does the reduction of butanone produce
butan-2-ol
what is the mechanism for the reduction of propanal to propan-1-ol called
nucleophilic substitution
what are the conditions required for the formation of an hydroxynitrile from an aldehyde/ketone
potassium/sodium cyanide + sulfuric acid = hydrogen cyanide
temp = 20°c
why is hydrogen cyanide not added directly to an aldehyde/ketone for a nucleophilic addition reaction
hydrogen cyanide = very poisonous gas, hard to store
what mechanism is used for the formation of 2-hydroxypropanenitrile from ethanal and hydrogen cyanide
nucleophilic addition
why are hydroxynitriles important
can be hydrolysed to form hydroxy acids
useful in cosmetic industry
what type of reaction occurs when aldehydes/ketones react with 2,4-dinitrophenylhydrazine
nucleophilic addition-elimination reaction
(condensation)
how can 2,4-dinitrophenylhydrazine be used to test for aldehydes + ketones
when reacted with aldehyde/ketone, orange-yellow precipitate is formed
how can 2,4-dinitrophenylhydrazine be used to identify specific aldehydes/ketones
- add 2,4-DNP so that ppt forms
- purify solid by recrystallisation
compare M.P of pure crystals formed with M.P of 2,4-DNP of all common aldehydes/ketones
what reagents can be used for the triiodomethane (iodoform) test
iodine and sodium hydroxide solution
or
potassium iodide and sodium chlorate(I) solutions
describe the method and results of the iodoform test (using iodine and sodium hydroxide)
- iodine added to small amount if ketone/aldehyde
- sodium hydroxide added to remove iodine colour
Pale yellow ppt will be formed if aldehyde/ketone is present
what is the iodoform test used to identify
aldehydes/ketones
