CARBOXYLIC ACIDS AND ESTERS

carboxylic acids

contian the carboxyl functional group -COOH

carboxylic acids are weak acids

in water they partially dissociate into carboxylate ion and H+ ion

the dissociation of carboxylic acids is a reversible reaction

but the equilibrium lies on the LEFT ebcause most of the molecuels DONT dissociate

carboxylic acids react with carbonates (CO₃^2-) or hydrogen carbonates (HCO₃^-)

to form a salt, carbon dioxide and water

esterification

heating carboxylic acids with an alcohol in the presence of a strong acid catalyst produces an ester

concentrated sulfuric acid/ hydrochloric acid/ phosphoric acid

all strong catalysts that can be used

naming an ester

• (alcohol)-ly (carboxylic acid)-oate

esters are sweet smelling

useful for perfumes/drink flavours/sweet flavour

esters are polar liquids

dissolve other polar organic compounds

esters have low boiling points

evaporate easily from mixtures making them good solvents in glues and printing inks

esters make good plasticisers

added to plastics during polymerisation to make the plastic more flexible

hydrolysis

the splitting of a substance by water

there are two types of hydrolysis of esters

• acid hydrolysis

• base hydrolysis

acid hydrolysis of esters

splits esters into an acid and an alcohol

acid hydrolysis of ester conditions

reflux ester with dilute acid: HCl/H2SO4

reservible reactions to require alot of water to shift the equilibrium over to the right so you get lots of product

base hydrolysis conditions

reflux the ester with dilute alkali: NaOH

OH- ions from the base react with the ester and you get a carboxylate ion and an alcohol

animal fats and vegetable oils are

esters of glycerol and fatty acids

fatty acids

long chain carboxylic acids

glycerol

propane-1,2,3-triol

fatty acids can be saturated

no double bonds

fatty acids can also be unsaturated

double bond

most fat/oil is made from the fatty acid chain

so the chain gives them their properties

fats have mainly saturated hydrocarbon chains ncreasing the van der waals forces between them

this means higher temperatures are needed to melt them and they are solid at room temperature

oils have undasurated hydrocarbon chains, the double bonds bend the chain and dont pack well together, decreasing the effect of van der waals forces

so theyre easier to melt and are liquids at room temeprature

you can hydrolyse oils in base hydrolysis by heating them with sodium hydroxide

OH- from the sodium hydroxide reacts with the fat/oil to form a carboxylate ion and an alcohol.

the alcohol that is formed is glycerol

and the carboxylate ions combine with Na+ to form a sodium salt AKA SOAP

you can convert the sodium salt back into a long chain carboxylic acid (fatty acid) by adding HCl

the H+ ions displace the Na+ to form the carboxylic acid

vegetable oils make good vehicle fuels when converted into biodiesel

reacting vegetable oil with methanol using a strong alkali: KOH/NaOH as a catalyst to produce a mixtuer of methyl esters of of long chain fatty acids(biodiesel)

biodiesels are thought to be carbon neutral

because when you grow crops they absorb the same amount of CO2 produces when theyr burned

energy is used to make fertilizer, plant the crops, harvest the crops, convert into oil

this enrgy comes from fossil fuels so the process is not carbon neutral overall

acyl (acid) chlorides functional group

COCl

acyl chloride general formula

C_nH_2n-1OCl

acyl chloride naming

-oyl chloride and the carbon atoms are numbered with accordance to the carbon with the functional group

reactions of acyl chlorides

involve Cl being substituted by oxygen/nitrogen with misty fumes of hydrogen chloride produced

acyl chloride reacts vigorously with cold water producing a carboxylic acid

acyl chloride + alcohol → (vigorously+ at room temp) produces an ester

this is a faster method of esterification

acyl chloride + ammonia → (vigorously @ room temp) produces amides

acyl chloride + primary amines → (vigorously @ room temp) produces N-substituted amide

acyl chloride reactions all have the same mechanism

nucleophilic addition-elimination

nucleophilic addition elimination reactions have 2 steps

• nucleophile adds onto the acyl chloride, displacing the Cl- ion

• the hydrogen leaves to create an acyl chloride derivative

step 1 of addition elimination:

• nucleophile attacks delta +ve carbon on acyl chloride

• pair of electrons transferred from C=O to just oxygen so the nucleophile can bond with the carbon

• the pair of electrons on oxygen reforms the double and the chlorine is kicked off

• this leaves a positively charged nucleophile and a negatively charged chloride ion

step 2 of addition elimination:

• a pair of electrons from the Nu-H bond is transfered to the nuceophile to cancel its charge

• produces an acyl chloride derivative and a hydrogen ion

possible nucleophiles

• H₂O

• CH₃OH

• NH3

• CH₃NH₂

acid anyhydride

formed from 2 identical carboxylic acid molecules joined via an oxygen with the carboxyl group on either side,

the oxygen comes from the OH of 1 of the carboxylic acids

the other OH group and the spare hydrogen are released as water

acid anhydride naming

-oic anhydride

acid anhydrides react similarly to acyl chlorides only less vigorous and producing a carboxylic acid instead of HCl

asprin is an ester

formed by salicylic acid (contains alcohol group) + ethanoic anhydride OR ethanoyl chloride

ethanoic anhydride is preferred in the industry over ethanoyl chloride

• cheaper

• safer (less corrosive)

• reacts more slowly with water

• doesn’t produce dangerous hydrogen chloride fumes

insoluble organic products

can be seperated to remove impurities that do dissolve in water like salts, water or soluble organic compounds like alcohol

organinc layer and aqueous layer ()containing water + impurities) don’t mix

are immiscible

organic layer usually less then than aqueous layer

you can open the stopper on the separating funnel run off the aqueous layer and collect your organic product

if your organic product has impurities you can use another form of separation

solvent extraction

solvent extraction method

• vigorously shaking impure product with an immiscible solvent so they temporarily mix

your product needs to be more soluble in the added immisvible solvent than the one it was initially dissolved in

this was the producr will dissolve in the added solvent and seperate from the solution containing impurities

the solvent containint the product can then be run off

using a separating funnel

using seperation to purify a product will leave trace amounts of water in your product

so it must be dried

add anhydrous salts: MgSO4/CaCl

drying agents which binds to any water rpesent to become hydrated

when you first add the salt it will form clumps

meaning you need to add more

all the water is gone when

you can swirl the mixture and it looks like a snow globe

to remove the drying agent

filter out the mixture

the product of a reaction can still be condaminated with unreacted reagents or unwanted side products

you can remove these by washing the product

distillation seperates liquids with different boiling points

by gently heating a mixture in distilation apparatus

thermometer

placed at the neck of the condenser and shows the boiling point of the substance that is evapourating at any given time

if you know the boiling point of your pure product

you can use ther thermometer to tell you when its evapourating and therefroe when its condesing

if product of reaction has a lower boiling point than the starting materials

the reaction mixture can be heated in distilation aparatus to the product evapourates from the reaction mixture as it forms

if the starting materials have a higher boiling point than the product

as long as the temeprature is controlled, they wont evapourate out from the reaction mixture

mixtures containing volatile liquids can be purified using

redistillation

if a product and its impurities have different boiling points

redistilation can be used to seperate them

the different between distilation and redistilation

you are heating the IMPURE PRODUCT not the reaction mixture

when the liquid you want boils

you place a flash at the open end of the condenserreadt to collect your product

when the thermometer shows the temperature changing

put another flask at the end of the condenser because a different liquid is about to be delivered

is product solid you can silplify it via

recrystalisation

firstly you dissolve your solid product in a HOT solvent to make a saturated solution then le tit cool down

as it cools down the solublilit of the product decreases

once crystals begin to form:

1. add a VERY HOT solvent to the impure solid until is just about dissolves

2. this gives a saturated solution of the impure product

3. leave the solution to cool down slowly so crystals of the product form

4. the impurities stay in the solution as they are rpesent in much smaller amounts than the product so they take much longer to crystalise

5. remove the crystants by filtration and wash them with a ICE COLD solvent

6. dry the crystals leaving you with a much purer solid product

to accurately determine the melting point of an roganic solid

you can use the melting point apparatus

pack a small amount of sample into a glass capilary tube

place inside heating elemt

increase temperature until the sample turns from solid to liquid

measure a melting range from when the solid started to melt to where its fully melted

look up the melting point of the substance in the data book and compare results

impure samples have lower melting points and increase the melting range