The Reaction Of Alcohols
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What are the products of alcohol elimination reactions?
Alkenes and water
What happens if alcohols burn with insufficient oxygen?
Incomplete combustion occurs, producing carbon monoxide or carbon
What is eliminated in the elimination reaction of alcohols?
A small molecule of water
What type of reaction is the elimination of water from alcohols?
A dehydration reaction
What are the conditions for dehydrating alcohols?
Heat with concentrated sulfuric acid catalyst
Outline the dehydration mechanism reaction where propan-1-ol is dehydrated to propene (alcohol vapour passes over heated aluminium oxide)
Find the correct mechanism, do your own, mark it
What are primary alcohols oxidised to? (A - frthr. ox. CA)
Aldehydes, then further oxidised to carboxylic acids
What are secondary alcohols oxidised to?
Ketones
Can ketones be further oxidised, and why yes/not? (ANS - bcse. frthr. ox. wld. rqre. brkng. CC bnd. dfclt.)
No, because further oxidation would require breaking a C-C bond which is difficult
Are tertiary alcohols easily oxidised, and why? (bcse. thr. /C-H bnd. crbn. brng. OH grp. brk. drng. ox.)
No because there is no C-H bond on the carbon bearing the -OH group to break during oxidation
What reagent is used to oxidise alcohols in AQA chemistry?
Acidified potassium dichromate
What colour change indicates oxidation with potassium dichromate (VI)?
Orange to green
How is a primary alcohol oxidised to an aldehyde? (htd. w/ APD + uss. dstltn. rmve. A frms.)
Heated with acidified potassium dichromate and uses distillation to remove the aldehyde as it forms
Why must aldehyde be removed quickly during oxidation? (prvnt. frthr. ox. CA)
To prevent further oxidation to carboxylic acids
Why is the receiver cooled in ice during aldehyde distillation? (rdce. evap/ lw. blng. ald)
To reduce evaporation of the low - boiling aldehyde
What conditions are needed to oxidise a secondary alcohol to a ketone? (ht. undr. rflx. w/ excs. acdfd. ptsm. dchrmt.)
Heat under reflux with excess acidified potassium dichromate
Why is reflux used in oxidation reactions? (prvnt vltle. prdcts. frm. escpng. cndnsng. thm. bck. rctn. mxtr.)
To prevent volatile products from escaping by condensing them back into the reaction mixture
How are ketones separated after reflux? (D - prdct. vprsd. + cndsd. - sprt. flsk.)
By distillation, where the product is vaporised and condensed into a separate flask
What conditions are used to oxidise a primary alcohol to a carboxylic acid?
Heated under reflux with excess acidified potassium dichromate
What technique is used to oxidise primary alcohol completely to a carboxylic acid?
Refluxing
What is the difference between reflux and distillation in oxidation reactions? (rflx. kps. prdcts. rctn. mxtr. whle. D rmvs. prdcts. frm.)
Reflux keeps products in the reaction mixture, while distillation removes products as they form
Is water formed when an aldehyde is oxidised to a carboxylic acid?
No, water is not formed
Label the reflux apparatus for the oxidation of ethanol to ethanoic acid
• Reflux • Distillation • Water out • Water in • Flask containing primary alcohol with oxidising reagent • Flask containing secondary alcohol with oxidising reagent • Water out • Thermometer • Water in • Heat