carboxylic acids and derivatives Flashcards
carboxylic acids are weak acids. meaning
they slightly dissociate/ionise when in solution
how can you test for them
react with carbonates. forms CO2 as a gas and can bubble through limewater to confirm its presence.
the reaction observes fizzing and bubbling
–
any reaction with c acid I’d slower because they are weak acids so barely donate protons
why can they form H bonds with water
they have O-H bonds. difference in electronegativity and the high mass to charge ratio of H gives it a strong delta positive charge
the lone pair of electrons on the O in H2O is attracted to it forming H bonds, due to imf
as the chains get longer this solubility reduces
what happens to the structure of the c acid when it loses H as an ion and becomes a salt
COO-
but the double bond between C=O kinda spreads out so its more like
O
I (-ve)
C –O
the delocalised -ve charge cloud stabilises the ion
what makes a c acid more acidic (a stronger acid)
ACID STRENGTH IS BASED ON ITS CONJUGATE ASE, THE CARBOXYLATE ION
- SHORTER CHAIN LENGTH
- alkyl groups are elctron releasing
- when there are longer chains there are more alkyl groups which push electron density onto COO- ion once it forms making it more negative, and less stable
- so acid is less strong - acid is less likely to donate proton and become unstable - ELECTRONEGATIVE ATOMS IN CHAIN
- they are electron withdrawing because of their electronegativity
- so they take away e- density from COO- ion, make it less negative and more stable
reaction for ester formation
conditions
esterification
// is a reversible reaction:
acid + alcohol <=> ester + water
// conditions: conc H2SO4 (strong acid catalyst), heat under reflux
very slow reaction, can have low yield bc reversible
how do you name an ester
__yl __oate
-yl part derived from alcohol (how many Cs on the C-O side of the COO f group)
-oate part derived from c acid (how many Cs on the C=O side of the COO f group)
how is an ester formed
the -OH from the acid and H from the alcohol react to form water
So the C on the carbonyl group bonds to the O remaining on the alcohol
f group of esters
RCOOR
O
||
R-C-O-R
uses of esters
used in food flavourings and perfumes because they are sweet smelling compounds
they have low BPs and make good solvents for other polar molecules
used in plasticisers (substance added to material to make it more flexible bc polymer chains can now move over eachother) to increases elasticity and softness of materials.
[[ where else in the course do we encounter plasticisers ]]
used to make rigid pvc (addition polymer (long chain molecule), alkene) more flexible. there are strong imfs between pvc molecule chains because large Mr means many electrons so strong VdWs, but plasticiser disrupts the layers weakening the IMFs
plasticised pvc is used for cable wire insulation, clothing (waterproof and sport)
fats and oils are
how are they formed
triglycerides, a type of lipid. these are esters because they are formed by the reaction between glycerol (propane123triol) and 3 fatty acids of variable chain length
so vegetable oils and animal fats are esters of propane-1,2,3-triol (glycerol)
why are fats solid and oils liquid
fats tend to have saturated fatty acid chains so chain is linear. so stronger IMFs
oils tend to have unsaturated fatty acid chains so chain is bended, but bends only occur if Z isomerism. so weaker IMFs
glycerol undergoes esterification to form
triglyceride esters
the H on all of its OH groups and the OH from the COOH group of three fatty acids react to form triglyceride esters AND don’t forget 3 waters
in what two ways can esters be hydrolysed
hydrolysis in acidic conditions to form an alcohol and a carboxylic acid (reverse of esterification) by adding water. is a reversible reaction so will shift to reactants side to decrease conc water, increasing yeild of reactants, thereby hydrolysing the ester
hydrolysis in alkaline conditions to form soap, known as saponification
ester hydrolysis in acidic conditions
strong acid catalyst is needed for this reversible reaction
simple reverse reaction,
the backwards reaction to:
an alcohol and c acid <=> ester and water
conditions:
- dilute strong acid
- heat under reflux
- lit just the backwards of alcohol + acid
hydrolysis of esters in alkaline conditions:
- what happens
- conditions
- use
WHAT HAPPENS
ester and NaOH in aqueous solution (ratio 1:3) will react to form salt of fatty acids and glycerol.
the triglyceride is hydrolysed to form glycerol and fatty acid chains which have COO- f group carboxylate instead of COOH. this reacts with the Na+ or whatever cation to form 3 salts of the fatty acid as well as the glycerol
triglyceride+ 3NaOH -> 3salts of fatty acid and glycerol (OH- bonds with glycerol that doesn’t have any of its OH groups)
CONDITIONS
boiled with metal hydroxide as reagent
excess NaOH ensures ester hydrolysis
USE
the fatty acid salts are used as soaps because they have hydrophilic and hydrophobic properties. so grease and water can mix
as well as soap, triglycerides can produce biodiesel
what is biodiesel
renewable biofuel derived from biological sources like vegetable oils, animal fats or recycled greases
it is a mixture of methyl esters of long chain carboxylic acids
reaction to form biodiesel
vegetable oils and methanol in presence of KOH (strong alkali) catalyst
- lipid is broken down into 3 fatty acids and glycerol by reaction with KOH
- these fatty acids are converted into three new ester using methanol. methanol reacts with fatty acids to form methyl (__oate (depends on formula of long chain fatty acids)) esters.
- overall the KOH is not used up and so acts as a catalyst
how could biodiesel potentially be a carbon neutral fuel
why is it’s production kinda bad
no net release of carbon dioxide to the atmosphere because the same amount of CO2 released when the fuel is burned is absorbed from the crops it was made from during photosynthesis
its production uses a lot of farmland instead of using it for food production
acyl chloride
structure
naming
byproduct
leaving group that allows for acylation
functional group
O
I I
R-C-Cl , always at the end of a molecule
suffix is always -oyl chloride
HCl
Cl
how do you test for the presence of an acyl chloride
add acidified silver nitrate
chloride leaves acyl chloride as an ion, and forms a white ppt when ionically bons to silver
Ag+ (aq) + Cl- (aq) –> AgCl (s)
whats the mechanism of acylation
acylation: replacing a H atom on a molecule with an acyl group (RCO)
nucleophilic addition elimination
what molecules can an acyl chloride be attacked by, which get acylated
what is the product formed
acyl chlorides (and acid anhydries) contain a polar C=O bond and a strongly electronegative Cl atom so the C is delta +ve. so susceptible to attack by:
water ——— carboxylic acid
ammonia ———- amide
1y amine ———- N substituted amide (one of the Hs in NH2 is smth else)
alcohols ——- ester
they all have a LP on the O or N. therefore they can act as nucleophiles
