carbonyls Flashcards
what is the carbonyl functional group?
C=O
why do carbonyl compounds react with nucleophiles
the C=O bond is polarised, with the carbon being partially positive. which is susceptible to attack by nucleophiles
how are aldehydes prepared
aldehydes are made from the oxidation of a primary alcohol using acidified potassium dichromate, gentle heating and distillation
describe how aldehydes and ketones can be distinguished using acidfied potassium dichromate
aldehydes can be oxidised to carboxylic acids when refluxed with acidified K2Cr2O7.During this process, the solution turns from orange to green
Ketones, however, do not undergo oxidation with acidfied potassium dichromate so the solutions stays orange
name and outlinethe mechanism for the reaction
nucleophillic addition
what is the general equation for the reduction of a ketone, RCOR’ with a reducing agent [H]
RCOR’ + 2[H]–> RCH(OH)R’
name the reducing agent used in the reduction of aldehydes and ketones to alcohols
NaBH4
Outline the mechanism
name the mechanism in the reaction between carbonyl compounds and hydrogen cyanide
nucleophillic addition
why is the reaction between carbonyl compounds and hydrogen cyanide useful
it provides a way of fincreasing the length of the carbon chain by 1 carbon atom
what type of product is formed in the reaction of an aldehyde or ketone with hydrogen cyanide
hydroxynitrile
how and why is hydrogen cyanide generates in situ for the reaction with aldehydes and ketones
HCN is generated in situ by mixing potassium cyanide or sodium cyanide with a dilute acid. HCN is a toxic gas
what is the general equation for the reaction of an aldehyde (RCHO) with HCN
RCHO + HCN –> RCH(OH)CN
how are ketones prepared
ketones are made from the oxidation of a secondary alcohol using acidified potassium dichromate and heating under reflux
what is the test for a carbonyl group
add 2,4-DNPH, compounds containing a carbonyl group will produce a yellow or orange ppt
2.4-DNPH is usually dissolved in methanol and sulfuirc acid as Brady’s r
How can you determine the identity of a carbonyl compound using 2,4-DNPH
- add 2,4-DNPH to the carbonyl compound and an orange ppt will form
- filter the ppt and purify it by recrystallisation
- measure the melting point of the ppt
- compare the melting point to a database
name 2 tests to distinguish between aldehydes and ketones
- Tollen’s reagent
- acidified potassium dichromate
what is Tollens’ reagent
solution containing the conplex ion [Ag(NH3)2]+ formed by the addition of ammonia to silver nitrate
explain how aldehydes and ketones can be distinguished using Tollens’ reagent
Aldehydes are oxidised to carboxylic acids when warmed with Tollens, forming a silver mirror due to the reduction of Ag+ to Ag
ketones dont react with tollens
why are carboxylic acids soluble in water
C-O and O-H bonds are polar
explain whether carboxylic acids are strong or weak acids
weak acids as they only partially dissociate when dissolved in water
HCOOH ->< H+ + HCOO-
describe the reactions of carboxylic acids with metals
carboxylic acids react with metals in redox reactions to form hydrogen gas and a carboxylate salt/ The metal visbily dissapears as it is oxidised
2HCOOH + Mg –> (HCOO)2Mg + H2
describe the reactions of carboxylic acids with metal oxides
neutralisation reactions to form a carboxylate salt and water
2HCOOH + CaO –> (HCOO)2Ca + H2O
describe the reactions of carboxylic acids with metal carbonates
neutralisation reaction to form a carboxylate salt, water , CO2
2HCOOH + Na2CO3 –> 2HCOONa + H2O + CO2
describe the chemical test to identify the presence of a carboxyl group
reaction with sodium carbonate or sodium hydrogencarbonate to produce carbon dioxide gas
outline 3 types of reaction that can be used to produce carboxylic acids
- oxidation of primary alcohols and aldehydes with acidfied K2Cr2O7 under reflux
- hydrolysis of nitriles with dilute acid or alkali followed by acidfication
- hydrolysis of esters with dilute acid or alkali with heat followed by acidification
