C26. Compounds Containing the Carbonyl Group (A2) Flashcards
What are carbonyls?
C=O functional group compounds, Carbon to oxygen double bond
How are aldehydes and ketones prepared?
Oxidise primary alcohol to form aldehydes; Oxidise secondary alcohols to form ketones
What’s the oxidising agent used for oxidation of aldehydes and ketones?
Acidified potassium dichromate K2Cr2O7 with sulfuric acid H2SO4
What colour change is evident when K2Cr2O7 is reduced?
Alcohol oxidised; Orange to green
What colour change is evident when KMnO4 is reduced?
Alcohol oxidised; Purple to colourless
How do you form carboxylic acids from primary alcohols?
Oxidation; Heat reaction mixture under reflux; Aldehyde produced but evaporates and condenses into mixture; Oxidised further into carboxylic acid
Why are ketones resistant to being oxidised?
No readily available hydrogen atoms; Extremely strong oxidising agent needed; Oxidation will likely oxidise ketones destructively, breaking C-C bond
How do you distinguish between aldehydes and ketones?
Weak oxidising agents; Tollens reagent and fehling’s solution; Or acidified potassium dichromate
Describe the silver mirror test.
Tollens’ reagent, ammoniacal silver nitrate [Ag(NH3)2]+; Colourless; Warmed gently with aldehyde, oxidises aldehyde; Causes [Ag(NH3)2]+ ion to reduce to solid Ag; Silver mirror formed
How is Tollens’ reagent formed?
Aqueous ammonia is added to a solution of silver nitrate
Describe the Fehling’s test.
Fehling’s solution (blue), Copper(II) complex ions solution is an oxidising agent; Aldehyde warmed with Fehling’s solution, aldehyde oxidised to carboxylic acid; Brick red precipitate formed, copper(I) oxide
Describe a common reducing agent for reduction of carbonyls.
Sodium tetraborohydride NaBH4(-); In aqueous solution (acidic solvent used to provide the H+ ion), generates hydride ion nucleophile :H-; Hydride ion reduces carbonyl group but not strong enough to reduce C=C; Due to high electron density of C=C and attraction to C=O; Nucleophilic addition
Describe the mechanism of nucleophilic addition of HCN to carbonyl groups.
Electrons from double bonds, C=O, move to O; CN- attacks C from C=O; Lone pair from O- attracts H+ ion;
Why does the nucleophilic addition of HCN to ketones and aldehydes result in optical isomers?
Planar shape of carbonyl group, CN- can attack from either side of the carbonyl group; Forming enantiomers
Describe the physical properties of carbonyls.
Carbonyl group is strongly planar; Permanent dipoles-dipole forces between molecules; High boiling point relative to molecular mass, less than OH though; Highly reactive due to electronegativity difference; Nucleophiles attack C; Unsaturated so addition reactions are applicable;
Describe the mechanism for nucleophilic addition reaction between carbonyls.
Nu: attacks C, double bond moves to O; O: attracts H; H+ from solvent; (R)(R)C(Nu)(OH)
How are aldehydes converted into primary alcohols?
Reduction; H+ from solvent acts as a nucleophile; :H-
How are ketones converted into secondary alcohols?
Reduction; H+ from solvent acts as a nucleophile; :H-
What functional groups does carboxylic acids contain?
Carbonyl group C=O; Hydroxyl group O-H
Describe the physical properties of carboxylic acids.
Able to form hydrogen bonds w H2O molecules; Acids up to butanoic acids are H2O soluble; Acids form hydrogen bonds w each other in solid state; High melting point relative to molecular mass; Characteristic smells, ethanoic acid - vinegar
How do you name esters?
Chain with carbonyl group is main chain, -oate side; Named by parent alcohol (ethyl), parent acid (ethanoate)
How do you name esters?
Chain with carbonyl group is main chain, -oate side; Named by parent alcohol (ethyl), parent acid (ethanoate)
Describe the different methods carboxylic acids could react?
C+ is open to attack from nucleophiles; O- from C=O is open to attack from positively charged species; H+ lost as H+, behaving as acid
Describe the formation of esters.
Carboxylic acids react with alcohol in presence of strong hot acid catalyst; Reversible reaction; Producing ester and water; Condensation reaction
Describe the hydrolysis of esters.
Carbonyl carbon atom has delta+ charge, attacked by H2O, acting as weak nucleophile; In presence of strong acid catalyst; Forming alcohol and carboxylic acid
Describe the hydrolysis of esters in presence of a base catalyst?
Salt of the acid is produced, rather than acid itself; Equilibrium is not established, resultantly more product; Ester + H2O =Hot H2SO4=> Carboxylic acid + Alcohol =NaOH=> Salt + H2O
Describe the mechanism for base hydrolysis of an ester.
:OH- attacks carbonyl carbon, double bond moves into oxygen; :O- moves back into single bond, forming double bond, single bond moves into O; Hydroxyl H bond moves into O, :O- moves to H
What’s the difference between a fats and an oil?
Oils are liquid in room temperature; Fats are solid
What’s the IUPAC name of glycerol?
Propane-1,2,3-triol
How are fats and oils hydrolysed?
Acidic conditions forming a mixture of glycerol and fatty acids; Or boil with sodium hydroxide forming glycerol and sodium salts of the three acids
What can salts formed from base hydrolysis of fats and oils be used as?
Soaps
Describe the properties of glycerol and its uses.
3 O-H bonds, readily forms hydrogen bonds; Very soluble in water: Used in pharmaceutical and cosmetics, attracts water and prevents drying out; Medicine, toothpaste; Solvent in food industry, food colouring
Describe the alternative fuel source to crude oil.
Biodiesel; renewable; Oils deprived from crops, rape seed, triglyceride ester; Oil reacted w/ methanol w/ strong alkali catalyst to produce methyl esters (biodiesl)
Describe the alternative fuel source to crude oil.
Biodiesel; renewable; Oils deprived from crops, rape seed, triglyceride ester; Oil reacted w/ methanol w/ strong alkali catalyst to produce methyl esters (biodiesel)
What is acylation?
Process by which acyl group is introduced into another molecule;
What are acid derivatives?
Compounds w/ acyl group as part of their structure; Acid chlorides; Acid anhydrides; Derived from carboxylic acids; General formula, RC(=O)Z
What’s the functional group of acid chlorides and what’s their nomenclature?
C(=O)Cl; -Oyl chloride
What’s the functional group of acid anhydrides and what’s their nomenclature?
RC(=O)OC(=O)R’; -Oic anhydride
What are the factors affecting how readily nucleophiles attack the acyl group?
RC(=O)Z
Magnitude of delta+ charge on carbonyl carbon; Electron releasing or attracting power of Z; How easily Z is lost; How strong the nucleophile is
List the order of reactivity of nucleophiles that acyl chlorides and acid anhydrides.
Primary amines; Ammonia; Alcohol; Water
How do acyl chlorides and acid anhydrides react with strong nucleophiles?
Addition elimination reactions, nucleophiles are neutral so lose hydrogen ion when reacting
Describe the hydrolysis reaction, addition elimination reaction, between ethanoyl chloride and water?
:O- attacks C, = moves into O-; :O- moves back into single bond forming double bond, single bond moves into Cl, cutting it; H2O, H moves into O, cutting it; CH3COOH and HCl formed
Why do industries use ethanoic anhydride over ethanoyl chloride?
Cheaper; Less corrosive; Does not react with water as readily; Safer as byproduct is is ethanoic acid rather than hydrogen chloride
oWhat’s the IUPAC name of aspirin?
2-ethanoyloxybenzenecarboxylic acid
