carboxylic acids and derivatives

Question 1

carboxylic acids are weak acids. meaning

Answer 1

they slightly dissociate/ionise when in solution

Question 2

how can you test for them

Answer 2

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

Question 3

why can they form H bonds with water

Answer 3

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

Question 4

what happens to the structure of the c acid when it loses H as an ion and becomes a salt

Answer 4

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

Question 5

what makes a c acid more acidic (a stronger acid)

Answer 5

ACID STRENGTH IS BASED ON ITS CONJUGATE ASE, THE CARBOXYLATE ION

1. 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
2. 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

Question 6

reaction for ester formation

conditions

Answer 6

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

Question 7

how do you name an ester

Answer 7

__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)

Question 8

how is an ester formed

Answer 8

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

Question 9

f group of esters

Answer 9

RCOOR

O
||
R-C-O-R

Question 10

uses of esters

Answer 10

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.

Question 11

[[ where else in the course do we encounter plasticisers ]]

Answer 11

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)

Question 12

fats and oils are

how are they formed

Answer 12

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)

Question 13

why are fats solid and oils liquid

Answer 13

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

Question 14

glycerol undergoes esterification to form

Answer 14

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

Question 15

in what two ways can esters be hydrolysed

Answer 15

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

Question 16

ester hydrolysis in acidic conditions

Answer 16

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

Question 17

hydrolysis of esters in alkaline conditions:
- what happens
- conditions
- use

Answer 17

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

Question 18

as well as soap, triglycerides can produce biodiesel

what is biodiesel

Answer 18

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

Question 19

reaction to form biodiesel

Answer 19

vegetable oils and methanol in presence of KOH (strong alkali) catalyst

1. lipid is broken down into 3 fatty acids and glycerol by reaction with KOH
2. 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.
3. overall the KOH is not used up and so acts as a catalyst

Question 20

how could biodiesel potentially be a carbon neutral fuel

why is it’s production kinda bad

Answer 20

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

Question 21

acyl chloride

structure
naming
byproduct
leaving group that allows for acylation

Answer 21

functional group
O
I I
R-C-Cl , always at the end of a molecule

suffix is always -oyl chloride

HCl

Cl

Question 22

how do you test for the presence of an acyl chloride

Answer 22

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)

Question 23

whats the mechanism of acylation

Answer 23

acylation: replacing a H atom on a molecule with an acyl group (RCO)

nucleophilic addition elimination

Question 24

what molecules can an acyl chloride be attacked by, which get acylated

what is the product formed

Answer 24

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 9one of the Hs is smth else)
alcohols ——- ester

they all have a LP on the O or N. therefore they can act as nucleophiles

Question 25

describe the mechanism generically of acylation

Answer 25

1. nucleophile donate LP to C. C=O bond goes to O
2. O is now :O- , it gives back its LP to the C-O bond and this causes C-Cl bond to go to Cl
3. O
   II
   R-C-Nu

Question 26

what other molecule can you do nucleophilic addition elimination with?

structure
f group
ex

Answer 26

acid anhydrides

their name indicates that there will be two C chains effectively

ethanoic anhydride for ex is CH3COOCOCH3
O O
II II
f group is R-C-O-C-R

useful to think about it as if: for whatever they give eg butanoic anhydride, imagine two butanoic acids react and a water (hydr- like hydride) is removed (anhydride). forms that structure

Question 27

acid anhydrides have similar reactivity so

whats the difference between them?

Answer 27

their leaving groups
acyl chlorides - Cl
acid anhydrides - one side of the central O so ROCO-

their byproducts
acyl chlorides - mostly HCl
acid anhydrides - mostly RCOOH

Question 28

how is aspirin made

why is ethanoic anhydride used > ecyl chlorides

Answer 28

2- hydroxybenzoic acid which contains a phenol group. In the reaction the phenol group is turned into an ester by reacting it with the reactive ethanoic anhydride.

cheaper, less corrosive, less vulnerable to hydrolysis, less dangerous to use

Question 29

aspirin - organic solid prac

ester - organic liquid prac

Answer 29

lol