Compounds Conataining The Carbonyl Group Flashcards
Physical properties of carbonyl compounds
Carbonyl group strongly polar so permanent dipole-dipole forces so boiling point higher than alkanes of similar length but lower than alcohols. Short chain aldehydes and ketones mix completely with water as H bonds form between the O in C=O and the H of the water. The longer the chain, the less soluble.
How is addition of hydrogen cyanide made safer?
Use sodium or potassium cyanide followed by the addition of dilute HCl
What is a common reducing agent for aldehydes and ketones?
Sodium tetrahydridoborate (NaBH4). Generates nucleophile H- with lone pair (hydride ion)
Mechanism for reduction of carbonyl compounds (nucleophilic addition)
Arrow from lone pair of H- to delta+ C of C=O and arrow from double bond to O. Arrow from new lone pair on O- to H+ (from solvent) aldehydes form a primary alcohol. Ketones form a secondary alcohol. In equations [H] is used for reducing agent.
How to name a carboxylic acid with a benzene ring
Suffix is carboxylic acid.
Physical properties of carboxylic acids
Short chain ones are completely soluble in water as hydrogen bonds form between O on water and H on OH and between H on water and O on C=O. The acids also for H bonds with each other (C=O to OH) so have higher meting point than alkanes if similar mass.
How are esters derived?
They are derived from carboxylic acids where the H from the OH is replaced by a hydrocarbon group. This is through reacting them with alcohols (by product of water). The reaction is reversible and sped up using a strong acid catalyst.
Uses of esters
Flavourings and perfumes. Solvents and plasticisers. Fats and oils are esters with longer carbon chains.
Describe a carboxylate ion
Formed when the H from the OH is lost from a carboxylic acid. The negative charge is shared over the whole carboxylate group (COO-). This délocalisation makes the ion more stable.
How can an ester be split up?
Through hydrolysis. It reacts with water to from the original carboxylic acid and alcohol. The water acts as a weak nucleophile. It is a reversible reaction and sped up using a strong acid catalyst. Can happen at room temperature.
What happens when a base is used as a catalyst for hydrolysis of esters?
The reaction isn’t reversible so there is more product in the mixture. The salt of the original carboxylic acid is produced rather than the acid itself. Water is also produced.
What is the arrangement of oils and fats?
They contain three molecules of long chain carboxylic acids called fatty acids. Fats and oils are based on glycerol so are referred to as triglycerides.
What is glycerol?
Propane- 123-triol
What does hydrolysis of fats in acid conditions produce?
Mixture of glycerol and the components of fatty acids
What does hydrolysis of fats by boiling with NaOH produce?
Glycerol and mixture of sodium salts (soaps) of the three acids which formed part of the ester.
How do soaps work?
The sodium salts dissociate. The RCOO- has two distinct ends. One is a long, non-polar hydrocarbon chain which will mix with grease. The other is the COO- group which is polar and ionic so mixes with water. It allows grease and water to mix.
Uses of glycerol
Used in pharmaceutical and cosmetic preparations (attracts water so stops them from drying out). Solvent in many medicines. Food colourings. Plasticiser.
What is acylation?
Process by which the acyl group (RC=O) is introduced into another molecule.
What is an acid derivative?
An organic compound related to a carboxylic acid with the general formula of RCOZ and contain an acyl group.
What is the order or reactivity for reactions with acyl chlorides and acid anhydrides?
Primary amine > ammonia > alcohol > water
What are the products of addition-elimination reactions for each reactant?
Amine to N-substituted amide. Ammonia to amide. Alcohol to ester. Water to carboxylic acid.
General mechanism for addition-elimination reactions
Arrow from lone pair of nucleophile to delta+ carbon of C=O and arrow from double bond to O of C=O. Arrow from new lone pair on O- to new C-O bond and arrow from C-Cl bond to Cl. Arrow from Nu-H bond to Nu+. Forms HCl.
Why is ethanoic anhydride preferred to ethanoyl chloride as an acylating agent?
Cheaper, less corrosive, not as reactive with water, by-product safer (ethanoic acid compared to HCl)
Why is the minimum volume of hot water added in recrystallisation of aspirin?
To obtain a saturated solution, to increase yield, enable crystallisation on cooling.
Why is the solution filtered hot in recrystallisation of aspirin?
To remove insoluble impurities and prevent crystals forming during filtration.
Why is the filtrate cooled in ice in recrystallisation of aspirin?
To increase the amount of crystals that are formed.
Why are the crystals washed in cold water in recrystallisation of aspirin?
To remove soluble impurities. Using hot water would dissolve some of the crystals.
How to determine the melting point of aspirin
Heat melting point tube in an oil bath. Heat slowly near the melting point.
What is the process called to produce biodiesel from vegetable oils?
Transesterification
Mechanism for nucleophilic addition with HCN
Arrow from lone pair on CN- to δ+ C of C=O and arrow from C=O bond to O. Arrow from lone pair of new O- to H+. Forms hydroxynitrile.
How is biodiesel made?
React vegetable oils (like rape seed oil) with methanol with strong alkali catalyst. Forms a mixture of methyl esters of long chain carboxylic acids which is the biodiesel.
Apparatus for filtration under reduced pressure
Conical flask with side arm which goes to a tube connected to tap or vacuum pump (tube doesn’t always need to be shown). Büchner funnel (more rectangular than Y-shaped) with filter paper in with air tight connection to flask. No cut off connections.
How to purify an organic liquid
Put distillate of impure product in separating funnel. Wash product by adding either sodium hydrogencarbonate solution or saturated NaCl solution. Allow layers to separate in funnel and run tap to discard aqueous layer. Run organic layer in clean dry conical flask and add spatulas of drying agent. Carefully decant liquid into distillation flask and distill to collect pure product.
Why is the separating funnel inverted periodically and the tap opened?
To release the pressure due to CO2 being formed from the reaction of left over acid with sodium hydrogencarbonate.
Why would saturated NaCl solution be used to wash the impure organic liquid?
It helps separate the organic layer from the aqueous layer.
What are the criteria for a good drying agent for an organic liquid?
Be insoluble in the organic liquid. Not react with the organic liquid.
