CARBOXYLIC ACIDS AND DERIVATIVES

How do you name carboxylic acids?

• name from the carboxylic end

• end in -oic acid

• if there are 2 carboxylic groups it will be -dioic acid

What type of acids are carboxylic acids?

• weak acids in water and slightly dissociate

• strong enough to displace carbon dioxide from carbonates

How soluble are carboxylic acids in water?

smaller carboxylic acids dissolve in water, however solubility decreases when the length of the chain increases, as they can no longer make hydrogen bonds

How are carboxylic acid salts stabilised?

• by delocalisation

• makes dissociation more likely

• delocalised ion has equal C-O bond lengths and if delocalisation didn’t occur, the C=O bond would be shorter than the C-O bond

• pi charge cloud has delocalised and spread out, making it more stable and more likely to form

What effects the strength of carboxylic acids?

• number of alkyl groups

• number of electronegative elements

How does the number of alkyl groups affect the strength of carboxylic acids?

• increasing the chain length pushes electron density on the COO- ion making it more negative and less stable

• this makes it less strong

How does having electronegative atoms affect the strength of carboxylic acids?

• electronegative atoms withdraw electron density from the COO- ion making it less negative and more stable

• this makes the acid more strong

What forms when a carboxylic acid and a metal react?

acid + metal → salt + hydrogen

What forms when a carboxylic acid and an alkali react?

acid + alkali → salt + water

What happens when a carboxylic acid and a carbonate react?

acid + carbonate → salt + water + carbon dioxide

How can you test for carboxylic acids?

• add a carbonate

• effervescence due to carbon dioxide produced

What happens when carboxylic acids react with alcohols?

• in the presence of a strong acid catalyst

• forms esters and water

• heat under reflux

How do you name esters?

• the alcohol which joined (the O-C) section ends with -yl

• the carboxylic acid containing the C=O bond is -anoate

What’re uses of esters?

• sweet smelling compounds used for perfumes and flavourings

• used as solvents for polar organic substances

• used as plasticisers for polymers

What’re properties of esters?

• don’t react with water

• used in perfumes

• non-toxic

• soluble in solvent

• volatile

• don’t form hydrogen bonds

• lower boiling point than hydrogen-bonded carboxylic acids

• insoluble in water

What’re the 2 ways to hydrolyse esters?

• heating with acid

• with sodium hydroxide

How are esters hydrolysed using acid?

• reagents - dilute acid

• conditions - heat under reflux

• reverse reaction of ester formation

• forms a carboxylic acid and an alcohol

• does not give a good yield of the products

How are esters hydrolysed using sodium hydroxide

• reagents - dilute sodium hydroxide

• conditions - heat under reflux

• reaction goes to completion

• using excess sodium hydroxide ensures the ester is completely hydrolysed

• forms a sodium salt and alcohol

• addition of a strong acid to the salt will convert it to a carboxylic acid

What’re the steps in hydrolysing ethyl benzoate?

1. liquid ethyl benzoate can be hydrolysed by sodium hydroxide by heating under reflux for 30 mins

2. allow the mixture to cool to room temperature

3. add hydrochloric acid

4. a precipitate of benzoic acid will be produced that can be filtered off using suction filtration

5. benzoic acid can be purified

Why is sodium benzoate soluble in water but benzoic acid isnt?

benzene ring is non-polar

What’re fats and oils?

• esters of glycerol and long chain carboxylic acids (fatty acids)

• vegetable oils and animal fats can be hydrolysed to give soap, glycerol and long chain fatty acids

What is glycerol?

• propane-1,2,3-triol

• forms hydrogen bonds very easily

• readily soluble in water

• used in cosmetics, food and glues

How does soap work?

• long chain carboxylic acids produced by the hydrolysis of fats

• polar CO2- end is hydrophilic and mixes with water

• long non-polar hydrocarbon chain is hydrophobic and mixes with grease

• allows grease and water to mix and be washed away

What is biodiesel?

mixture of methyl esters of long chain carboxylic acids

How can vegetable oils be converted into biodiesel?

by the reaction with methanol in the presence of a strong alkali catalyst

How is biodiesel produced from vegetable oils carbon-neutral?

• any carbon dioxide given off when the biofuel is burnt would’ve been extracted from the air by photosynthesis when the plant grew

• doesn’t take into account any energy needed to irrigate plants, extract the oil, heat the reaction with methanol mixture or process the fuel

What’re acyl chlorides?

• more reactive than carboxylic acids

• Cl is classed as good leaving groups

• ends with -oyl chloride

• mostly give off HCl

What’re acid anhydrides?

• similar reactivity to acyl chlorides

• mostly give off RCOOH

What happens when acyl chlorides react with water?

• form a carboxylic acid

• reagent - water

• conditions - room temp

• observation - steamy white fumes of HCl

What happens when acid anhydrides react with water?

• form a carboxylic acid

• reagent - water

• conditions - room temp

What is nucleophilic addition elimination mechanism between water and an acyl chloride?

What happens when an acyl chloride reacts with alcohol?

• forms an ester

• reagent - alcohol

• conditions - room temp

• observation - steamy white fumes of HCl

What happens when acid anhydrides react with alcohol?

• forms an ester

• reagent - alcohol

• conditions - room temp

What is the nucleophilic addition elimination mechanism between an acyl chloride and an alcohol?

Why is it preferred to make esters from acyl chlorides compared to carboxylic acids?

• quicker reaction

• not a reversible reaction

What happens when acyl chlorides react with ammonia?

• forms a primary amide

• reagent - ammonia

• conditions - room temp

• observation - white smoke of NH4Cl

What happens when acid anhydrides react with ammonia?

• forms a primary amide

• reagent - ammonia

• conditions - room temp

What is the nucleophilic addition elimination reaction between an acyl chloride and ammonia?

How do acyl chlorides react with primary amines?

• forms a secondary amide

• reagent - primary amine

• conditions - room temp

How do acid anhydrides react with primary amides?

• forms a secondary amide

• reagent - primary amine

• conditions - room temp

What is the nucleophilic addition elimination mechanism between an acyl chloride and a primary amine?

Why are acid anhydrides used instead of acid chlorides?

• cheaper

• less corrosive

• less vulnerable to hydrolysis

• less dangerous to use

What’re the steps involved in purifying aspirin?

1. dissolve the impure compound in a minimum volume of hot solvent

2. hot filter the solution through filter paper quickly

3. cool the filtered solution by inserting a beaker in ice

4. suction filtrate with a buchner flask and funnel to separate out crystals

5. wash the crystals with distilled water

Why do you use a minimum volume of hot solvent?

• appropriate solvent is one which will dissolve both compound and impurities when hot and one in which the compound doesn’t dissolve well when its cold

• minimum volume is used to obtain a saturated solution and enable crystallisation on cooling

Why do you hot filter the solution?

removes any insoluble impurities and heat will prevent crystals reforming during filtration

Why do you cool the solution using ice?

• crystals reform but soluble impurities remain in solution as they’re present in small quantities

• ice will increase the yield of crystals

Why do you suction filtrate?

reduces the pressure and speeds up filtration

Why do you wash crystals with distilled water?

removes soluble impurities

How is the yield lost due to recrystalisation?

• crystals lost when filtering or washing

• some product stays in solution after recrystallisation

• other side reactions occurring

What happens to the melting point if impurities are present?

• melting point will be lowered

• sample will melt over a range of temperatures

How do you find the melting point of a substance?

• place the substance in a capillary tube

• place a thermometer in some heating oil

• heat slowly near the melting point

• measure the point which it melts

How do you verify the degree of impurity?

compare the experimentally determined melting point value with one quoted in a data source