Organic Chemistry - carboxylic acids Flashcards
dissociation of carboxylic acids
-carboxylic acids = weak acids = partially dissociate to form H+ ions in solution
-smaller carboxylic acids dissolve in water because they can form hydrogen bonds with other molecules of water
COOH –> COO- + H+
-carboxylic acid salts are stabilised by delocalisation
ethanol structural formula
CH3-CH2-OH
test for carboxylic acids
The effervescence caused by production of CO2
with carboxylic acids with solid Na2CO3 or
aqueous NaHCO3 can be used as a functional
group test for carboxylic acids
uses of esters
Esters are sweet smelling
compounds that can be used in
perfumes and flavourings.
For use in perfumes they need to be non toxic, soluble in solvent such as
ethanol, volatile (turns into gas easily), and not react with water.
Esters can be used as solvents
for polar organic substances.
Ethyl ethanoate is used as a
solvent in glues and printing inks.
Although polar, they do not form hydrogen bonds (reason: there is no
hydrogen bonded to a highly electronegative atom).
They have a lower b.p. than the hydrogen-bonded carboxylic acids
They are also almost insoluble in water.
Esters can be used as
plasticisers for polymers.
Often pure polymers have limited flexibility because the polymer chains
cannot move over each other.
Incorporating some plasticiser into the polymer allows the chains to move
more easily and the polymer can become more flexible
hydrolysis of esters
i) with acid
reagents: dilute acid (HCl)
conditions: heat under reflux
ii) with sodium hydroxide
reagents: dilute sodium hydroxide
conditions: heat under reflux
carboxylic acids
-carboxylic acids = weak acids = partially dissociate to form H+ ions in solution
-smaller carboxylic acids dissolve in water because they can form hydrogen bonds with other molecules of water
-carboxylic acid salts are stabilised by delocalisation
acid + base
-acid + base –> salt + water
acid + metal carbonate
-acid + metal carbonate –> salt + CO2 + H2O
acid + metal
-acid + metal –> salt + hydrogen
metal oxide
metal hydroxide
-metal oxide –> metal salt + water
-metal hydroxide- -> metal salt and water
HCL + metal carbonate
HCl + Na2CO3 –> NaCl + CO2 + H2O
ethanoic acid + sodium carbonate
CH3COOH + Na2CO3 –> CH3COONa + CO2 + H2O
Ethanoic acid + sodium carbonate –> sodium ethanoate + carbon dioxide + water
structural formula of a carboxylic acid
Structural formula of a carboxylic acid
e.g propanoic acid = CH3-CH2-COOH
formation
Propanoic acid + sdoium hydroxde –> sodium propanoate + H2O
Carboxylic acids can react in the presence of an acid catalyst to make esters
Carboxylic acids = weak acids
HCl dissociates to H+ and Cl-
Carboxylic acids like ethanoic acid dissociate into ethanoate ions and hydrogen ions
observation when adding sodium hydrocarbonate to ethanoic acid
Observation when adding sodium hydrocarbonate to ethanoic acid:
-effervescence when CO2 gas is evolved
-colourless solution of sodium ethanoate
functional group of carboxylic acids
-carbon is open to attack from nucleophilles
-oxygen from C=O can be attacked by postively paired species
-H+ may be lost as it is behaving like an acid
Carboxylic acid + metal –> salt + hydrogen
Acid plays the role of a catalyst in the hydrolysis of esters
acyl chlorides and anhydrides
-general formula = RCOCl
-all carboxylic acids contain a carbonyl group
-SOCl2 = oxidation state of sulfur = +4
room temp
Oil = liquid at room temperature
Solid at room temperature = fat
acid anhydride
-formation of this is a reversible reaction
-2 molecules of ethanoic acid can be dehydrated to ethanoic anhydride
-general formula = RCOOCOR
-two acyl (carbonyl) groups bonded to the same oxygen atom.
nucelophillic addition-elimination
When 2 pi bonds break and a sigma bond forms this is called an eliminaton reaction
This reacton shown above is a nucelophilic addition-elimination
Butanoyl chloride + propanol –> propyl butanoate + HCl (this reaction must take place in ahydrous conditions)
forming esters equation
Carboxylic acid + alcohol ⇌ ester + water
conditions for esterification
-Esterfication includes a concentrated acid catalyst e.g sulfuric acid
-heat
-little water
O-C=O = ester bond
propanoic acid + methanol
Propanoic acid + methanol ⇌ methylpropanoate + H2O
methanoic acid + propan-2-ol
Methanoic acid + propan-2-ol ⇌ methylethyl ethanoate + waer
acid hydrolysis of esters
-ester + water ⇌ carboxylic acid + alcohol
-reversible reaction
Conditions –> acid catalyst e.g sulfuric acid, heat, excess water, 60 degrees
base hydrolysis of esters
-non-reversible reaction
-ester + KOH -> R=O-C-O-K + alcohol
-e.g ethyl acetate + sodium hydroxide –> sodium acetate + ethanol
uses of esters
-Vegetable oils and animal fats are esters of propane-1,2,3-triol (glycerol).
-Vegetable oils and animal fats can be hydrolysed in alkaline conditions to give soap (salts of long-chain carboxylic acids) and glycerol.
-Biodiesel is a mixture of methyl esters of long-chain carboxylic acids.
-Biodiesel is produced by reacting vegetable oils with methanol in the presence of a catalyst.
types of fats
-saturated fat = only single bonds = high melting point = solid at room temp
-unsaturated fat = double bonds = liquid at room temp due bends/kinks in hydrocarbon chain
-trans fat = hydrogen atoms on opposite sides of double carbon bond = no bending = formed via partial hydrogenation of unsaturated fats
fat molecule
Fat molecule = 1 glycerol molecule and 3 fatty acids
soaps
Soaps = sodium salts formed when triglycerides are hydrolysed using NaOH and heat
-salts dissociates into Na+ and RCOO- in solution. RCOO- molecules have one end which mixes with water and one end that mixes with organic grease. Allows grease + water to mix
Fatty acid + NaOH –> salt + glycerol = base hydrolysis of fats
biodiesel
-renewable as it is made from vegetable oils
-triglycerides are reacted with methanol with NaOH catalyst to form glycerol and methyl esters which can be used as fuel
-this s known as a transesterifcation reaction where the alcohols group swap
delocalisation
The delocalised ion has equal C-O bond lengths. If delocalisation did not occur, the C=O bond would be shorter than the C-O bond. The pi charge cloud has delocalised and spread out. The delocalisation makes the ion more stable and therefore more likely to form.
-Increasing chain length pushes electron density on to the COO- ion, making it more negative and less stable. This make the acid less strong. E.g propanoic acid is less acidic than ethanoic acid
acid anhydride
R(CO)2O
acyl chloride
RCOCl
propanoic anhydride + ethylamine
ehtyl propanamide + CH3CH2C=OO- + H2N-CH3-CH2
acyl chloride reactivity
Acyl chlorides react more violently with water than acid anhydride
Carboxylic acids need a catalyst to react with alcohols
Order of reactivity:
Acyl chlorides –> acid anhydride –> carboyxlic acids (most to least reactive)
Acyl chlorides = most open to nucelophillic attack
Oil + methanol
Oil + methanol –> biodiesel + glycerol
Methanol = CH3OH
Biodiesel = R-O=C-O-CH3
Glycerol = 3x CH2OH
what is acylation
-the process where an acyl group is added to another molecule
acyl chloride + alcohol
Acyl chloride + alcohol (R-O-H) –> R-O=C-O-R (ester) + HCl
propanoyl chloride reactions
Propanoyl chloride + ethanol –> ethyl propanoate + HCl
Propanyol chloride + water –> propanoic acid + HCl
ethanoyl chloride + ammonia
ethanoylchloride + ammonia (NH3) –> ethyl amine + Cl- + NH4+
reaction of CH3CH2COCl with ammonia
nucelophilic addition elimination
CH3CH2CH2Cl with excess ammonia
nucelophilic subsiution
Ethanoic anhydride + methylamine –>
methylammonium ethanoate + methylammonia
water + propanoyl chloride
propanoic acid + HCl
equations
2Ammonia + ethanoyl chloride –> ethanamide + [NH4+Cl-]
Propan-2-ol + ethanoyl chloride –> propan-2-oic acid + HCl
properties of acyl chloride
-reactive
-corrosive
-expensive
-harmful products
properties of acid anhydrides
cheaper
-less corrosive
-safer
-less reactive
why are anhydrides used as acyling agents
Despite acyl chloride having a higher atom economy, acid anhydrides are generally used as acyling agents because its cheaper and less corrosive, doesn’t react with water as readily and safer as biproduct is ethanoic acid not HCl
NH3 + H2O
NH3 (aq) +H2O (l) ⇌NH4+(aq)+OH-(aq)
sodium benzonate
Sodium benzoate is soluble in water because it is ionic. Benzoic acid, however, is insoluble. This is because even though the polar COOH group can form hydrogen bonds, the benzene ring is non-polar. In organic compounds there are often polar parts and non-polar parts. The solubility in water of a compound will controlled by whether the polar or non polar part is of greater importance.
hydrolysis of ethylbenzaonate
Hydrolysis of ethylbenzanoate:
ethyl benzoate + NaOH –> sodium benzoate + ethanol
fats and soaps
-Fats and oils are 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 carboxylic (fatty) acids
-Glycerol (propane-1,2,3-triol) forms hydrogen bonds very easily and is readily soluble in water. It is used in cosmetics, food and in glues
acyl chlorides more reactive than carboxylic acids
Acyl chlorides are much more reactive than carboxylic acids
Acid anhydrides have a similar reactivity to acyl chlorides and therefore bring about the same changes in functional groups. The main difference is the by- products. Acyl chlorides mostly give off HCl. Acid anhydrides give off RCOOH
acyl chloride reactions
Acyl chloride + water –> carboxylic acid + HCl
Observation = white steamy fumes of HCl are given off
Acyl chloride + alcohol –> ester + HCl
Acyl chloride + 2NH3 –> primary amide + NH4Cl
acid anhydrides
Acid anhydride + water –> 2 carboxylic acid
Acid anhydride + alcohol –> ester + alcohol
Acid anhydride + 2NH3 –> primary amide + RCO2- + NH4+
benzene
In benzene, 6p orbitals overlap to form a pisystem containing delocalisedelectrons.
ethanoic acid + sodium carbonate
2CH3COOH + Na2CO3 –> 2CH3COONa + H2O + CO2
acid anhydride + alcohol
ester + carboxylic acids
properties of esters
polar
low boiling points
unsaturated fats like vegetable oil
less van der waals = lower boiling points
fat ester =
saturated
fat + 3NaOH –> glycerol + 3soap
soap = RCOO-Na+
oil + methanol
glycerol + methyl ester
3H3C-O-C=O-R
acyl chloride + NH3
amide + HCl
e.g ethananmide
ethanoic anhydride + water
ethanoic acid x2
vegetable oil =
CH2 - O - C=O - CxHx
[
[
CH - O - C=O - CxHx
[
[
CH2-O-C=O-CxHx
give the equation for the reaction of CH3CH2COCl and AlCl3
CH3CH2CO+ + AlCl4-
give the reagent and conditions for ester to alcohol
NaOH
aqueous/warm
fractional distillation to separate alcohol
KCN reagents + conditions
alcoholic
heat
H2
name the type of compound formed by the formula RCOOK
carboxylate salt
use = salt
suggest why aqueous ethanol is a suitable solvent when heating oil with KOH and precatuions
reason = to dissolve both the oil and KOH
precautions = use water bath for heating mixture = prevents risk of fire since ethanol is flammable
reagents for elimination reaction (dehydration)
concentrated H2SO4
Alkene + Br2 = dibromoalkane
dibromoalkane + NAOH –>
diol e.g 1,2dipropanol + 2NABr
why chemists aim to use fewer steps
less energy
high percentage atom economy =
high yield
hazard of phosphoric acid
corrosive
2 ways in which the melting point of crude asprin would differ to pure asprin
lower melting point
range of values
purpose of adding small amount of cold ethanol
remove any soluble impurities
which reaction involves addition-elimination
CH3COCl + C6H5OH –> CH3COOC6H5 + HCl
