organics- carboxylic acids and derivatives Flashcards
what is a carboxylic acid
the name given to the family of compounds that contain the carboxyl functional group, -COOH
what is the general formula of a carboxylic
CnH2n+1COOH which can be shortened to just RCOOH
what is the nomenclature of a carboxylic acid
alkan + oic acid and there is no need to add numbers as COOH is always on no 1
what are weak carboxylic acids
Carboxylic acids with fewer than six carbon atoms per molecule are water-soluble
This is because water molecules can hydrogen-bond with the functional group
In aqueous solution they are only slightly ionised, to give low concentrations of hydronium ions and alkanoate ions (often called carboxylate ions)
where does the position of eq lie for weak acids
due to the partial dissociation means that the position of the equilibrium lies to the left and that the concentration of H+ is much smaller than the concentration of the carboxylic acid
how do carboxylic acids react with aqueous solution of sodium carbonate and sodium hydrogen carbonate
salt of acid + CO2 + H2O
conc of hydrogen ions is sufficient and produce carbon dioxide
These reactions are a useful test for the possible presence of a carboxylic acid:
Sodium carbonate: 2RCOOH + Na2CO3 → 2RCOO-Na+ + CO2 + H2O
Ionic equation with carbonates: 2RCOOH + CO32- → 2RCOO- + CO2 + H2O
Sodium hydrogen carbonate: RCOOH + NaHCO3 → RCOO-Na+ + CO2 + H2O
Ionic equation with hydrogen carbonates: RCOOH + HCO3- → RCOO- + CO2 + H2O
how are esters produced
esters are formed from the condensation reaction between an alcohol and carboxylic acid in the presence of a concentrated strong acid catalyst e.g. sulfuric or hydrochloric acid
This reaction is often referred to as esterification
A condensation reaction involves the elimination of a small molecule not always water
Esterification is one example of a condensation reaction as water is eliminated from the acid and alcohol reacting together
eg ethanol + ethanoic acid = ethyl ethanoate + water
what are esters
a carboxylic acid derivative which contains the ester group, -COO-
An ester is named after the parent carboxylic acid from which it is derived
what is the nomenclature for an ester
Remove the -oic acid suffix from the parent carboxylic acid and replace with -oate
The alkyl chain attached to the oxygen atom of the -COO- group is then added as the first word in the name
This part of the name comes from the alcohol, e.g. propanol becomes propyl
what are some of the uses of esters
Like aldehydes and ketones, esters are important chemicals in the flavourings and fragrances industry
Esters have a fruitier and sweeter smell than aldehydes and ketones and are responsible for many natural flower scents and flavours
Synthetic esters can also be used as artificial fruit flavours in confectionary products e.g. ethyl methanoate is used as a raspberry ester fragrance
Aromas and tastes are often due to complex mixtures of different esters
how can esters be used to test for an alcohol and carboxylic acids
An unknown substance can be warmed with a carboxylic acid such as ethanoic acid in the presence of concentrated sulfuric acid (catalyst)
Excess acid with its pungent vinegary smell can be removed by adding warm aqueous sodium carbonate solution
If the remaining mixture has a sweet smell of an ester, this confirms the presence of an alcohol
The warmth of the solution then causes the ester to evaporate and the sweet smell is easily detected
how can esters be used as plasticisers and what are they
which are additives mixed into polymers to increase the flexibility of the polymer
Poly(chloroethene) better known as PVC, is a strong rigid polymer suitable for making drainpipes and guttering
When a suitable plasticising ester is added, it can be made into cling film which is soft and pliable
An ester plasticiser works by penetrating between the polymer chains and increasing the distance between them
This then weakens the polar effects of the carbon-chlorine bond and the rigidity of the 3D structure if reduced allowing the polymer chains to slide over one another
how are PVC chains so strong
there is intermolecular attraction bwt the delta positive and delta negative
this creates dipoles that attract adjacent polymer chains
how are esters used as solvents
-low toxicity and volatiltiy
eg
Ethyl ethanoate is a common solvent which has the beneficial properties of low toxicity and low volatility (its boiling point is 77˚C) as well as being relatively cheap
This makes it an ideal solvent for use in glues, fragrances and nail varnishes
give some examples of naturally occuring esters
Triglycerides found in animal fat and olive oil are naturally occurring esters
They are tri-esters of glycerol (propane-1,2,3-triol) and fatty acids (long chain carboxylic acids) such as stearic acid (CH3(CH2)16COOH)
The reaction of 1 mole of glycerol with 3 moles of a fatty acid in the presence of an acid catalyst leads to the formation of the triglyceride whereby 3 moles of water are eliminated
describe the process of ester hydrolysis
- where esters are broken down to carboxylic acids and alcohols
-acidic conditions - carboxylic acids + alcohols are formed but the reaction is slow and reversible- under reflux - eq mixture is established- meaning not fully complete
-alkali conditions -to completion - for the salt of the carboxylic acid and an alcohol - saponification
-the salt produced requires further acidification to turn into a carboxylic acid
what is biodiesel
Biodiesel is made from renewable vegetable oils rather than nonsustainable petrochemicals
-triglyceride oils are converted to esters of methanol making them less viscous
how is biodiesel produced- biodiesel from rapeseed oil
transesterification
The triglyceride is converted, or transesterified, into the less viscous fatty acid methyl ester (FAME) using methanol
-converted using methanol
However, it is more common to use an alkaline catalyst such as NaOH / KOH
The transesterification is reversible, so an excess of methanol is used to drive the equilibrium to the right
Under optimum conditions this process can produce a very successful yield of 98%
add on CH3 to the lipid/fatty acid
give an example of ester hydrolysis
Name the products and write equations for the following hydrolysis reaction:
Ethyl ethanoate with hot dilute sulfuric acid solution
Methyl propanoate by hot sodium hydroxide solution
Answer:
Answer 1: Ethanoic acid and ethanol
CH3COOCH2CH3 + H2O ⇌ CH3COOH + CH3CH2OH
Answer 2: Sodium propanoate and methanol
CH3CH2COOCH3 + NaOH → CH3CH2COONa + CH3OH
how are soaps produced
by a process known as saponification
-Vegetable oils and animal fats can be hydrolysed in alkaline conditions with aqueous sodium hydroxide to form soaps
-Soaps are carboxylate salts of long-chain carboxylic acids, known as fatty acids
When triglycerides / fats are hydrolysed in hot alkaline conditions, the product is a mixture containing glycerol (propane-1,2,3-triol) and the salts of the fatty acids, soaps
-boil lipid with KOH to produce 3 salts of fatty acids and a glycerol
what are acyl chlorides
they are derivatives of carboxylic acids that are built from acyl groups
how are acyl chlorides named
substitution of the -OH group by a chlorine atom
Acyl chlorides are named by identifying the parent hydrocarbon chain and adding the suffix -oyl chloride
They can also be named by removing the -oic acid from the carboxylic acid and adding -oyl chloride
what are acid anhydrides
derivatives of carboxylic acids
how are acid anhydrides named
formed by substitution of the -OH group by an alkanoate
Acid anhydrides are named by identifying the parent hydrocarbon chain and adding the suffix -oic anhydride
They can also be named by removing the -oic acid from the carboxylic acid and adding -oic anhydride
how can acyl chlorides undergo nucleophilic addition via elimination
In nucleophilic addition-elimination reactions, the nucleophilic addition of a small molecule across the C=O bond takes place followed by elimination of a small molecule
examples are
Hydrolysis
Reaction with alcohols to form esters
Reaction with ammonia and primary amines to form amides
describe the process of elimination via hydrolysis/water
The hydrolysis of acyl chlorides results in the formation of a carboxylic acid and HCl molecule
This is a nucleophilic addition-elimination reaction
A water molecule adds across the C=O bond
A hydrochloric acid (HCl) molecule is eliminated
An example is the hydrolysis of propanoyl chloride to form propanoic acid and HCl
describe the process of elimination via the formation of esters
Acyl chlorides can react with alcohols to form esters
The esterification of acyl chlorides is also a nucleophilic addition-elimination reaction
start with an acyl chloride and attack with alcohol
The alcohol adds across the C=O bond
A HCl molecule is eliminated
describe the process of elimination via the formation of amides
Acyl chlorides can form amides with primary amines and ammonia
The nitrogen atom in ammonia and primary amine has a lone pair of electrons which can be used to attack the carbonyl carbon atom in the acyl chlorides
The product is an amide (when reacted with ammonia) or N-substituted amide (when reacted with primary amines)
This is also an example of a nucleophilic addition-elimination reaction as
The amine or ammonia molecule adds across the C=O bond
A HCl molecule is eliminated
mechanism for hydrolysis of acyl chloride
In the hydrolysis of acyl chlorides, the water molecule acts as a nucleophile
Step 1 - Nucleophilic addition; the lone pair on the oxygen atoms carry out an initial attack on the carbonyl carbon
Step 2 - Elimination; this is followed by the elimination of a hydrochloric acid (HCl) molecule
mechanism for formation of esters via acyl chloride
In the esterification reaction of acyl chlorides, the alcohols act as a nucleophile
Step 1 - Nucleophilic addition; the lone pair on the oxygen atoms carry out an initial attack on the carbonyl carbon
Step 2 - Elimination; this is again followed by the elimination of an HCl molecule
the mechanism for the formation of amides via acyl chloride
The nitrogen atom in ammonia and primary amines act as a nucleophile
Step 1 - Nucleophilic addition; the lone pair on the nitrogen atoms carry out an initial attack on the carbonyl carbon
Step 2 - Elimination; this is followed by the elimination of an HCl molecule
Step 3 - Acid-Base reaction; the HCl formed would immediately react with excess ammonia to give ammonium chloride in an acid-base reaction
how do u name/ draw an ester
take the OH off the carboxylic acid
take a H of the alcohol and bond together
what is important to remember when drawing the etser hydrolysis reaction for ester + salt
put the O as a negative charge
put the Na as a positive charge
what are lipids
naturally occurring esters that consist if 3 long chain carboxylic acids and a molecule of glycerol
what is the IUPAC name of glycerol
propane-1,2,3-triol
what are unsaturated fatty acids known as
oils and have C=C
what are saturated fatty acids known as
fats and no C=C
what is the general process of acylation
attack acyl chloride or acid anhydride with a nucleophile
eg H2O, NH3, primary amine or alcohol
what is produced when an acid anhydride reacts with an alcohol
ester
carboxylic acid
-add the alcohol on to the ester linkage but without the water
how to write mechanism for acyl chloride + alcohol
-take out Cl of acyl chloride and H of alcohol
-bolt the rest together to form ester
What is the salt called produced by saponification
Carboxylate salt
Suggest why aqueous ethanol is a suitable solvent when heating the coconut oil with KOH.
Allow to dissolve both oil and KOH
To act as a mutual solvent OR To ensure reactants are miscible
required prac: purify aspirin
why do certain things
The minimum quantity of hot water was used:
To ensure the hot solution would be saturated / crystals would form on cooling
The flask was left to cool before crystals were filtered off:
Yield lower if warm / solubility higher if warm
The crystals were compressed in the funnel
Air passes through the sample not just round it
A little cold water was poured through the crystals:
To wash away soluble impurities
what do u need to write for an equation to show the dissociation of an acid
-acid on one side
-equilibrium sign
-ve ion of acid - without a H
-H+
what will be produced from the hydrolysis of an ester and NaOH or KOH
-carboxylate salt
-alcohol
