organics- carboxylic acids and derivatives

Question 1

what is a carboxylic acid

Answer 1

the name given to the family of compounds that contain the carboxyl functional group, -COOH

Question 2

what is the general formula of a carboxylic

Answer 2

CnH2n+1COOH which can be shortened to just RCOOH

Question 3

what is the nomenclature of a carboxylic acid

Answer 3

alkan + oic acid and there is no need to add numbers as COOH is always on no 1

Question 4

what are weak carboxylic acids

Answer 4

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)

Question 5

where does the position of eq lie for weak acids

Answer 5

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

Question 6

how do carboxylic acids react with aqueous solution of sodium carbonate and sodium hydrogen carbonate

Answer 6

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

Question 7

how are esters produced

Answer 7

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

Question 8

what are esters

Answer 8

a carboxylic acid derivative which contains the ester group, -COO-
An ester is named after the parent carboxylic acid from which it is derived

Question 9

what is the nomenclature for an ester

Answer 9

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

Question 10

what are some of the uses of esters

Answer 10

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

Question 11

how can esters be used to test for an alcohol and carboxylic acids

Answer 11

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

Question 12

how can esters be used as plasticisers and what are they

Answer 12

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

Question 13

how are PVC chains so strong

Answer 13

there is intermolecular attraction bwt the delta positive and delta negative
this creates dipoles that attract adjacent polymer chains

Question 14

how are esters used as solvents

Answer 14

-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

Question 15

give some examples of naturally occuring esters

Answer 15

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

Question 16

describe the process of ester hydrolysis

Answer 16

• 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

Question 17

what is biodiesel

Answer 17

Biodiesel is made from renewable vegetable oils rather than nonsustainable petrochemicals
-triglyceride oils are converted to esters of methanol making them less viscous

Question 18

how is biodiesel produced- biodiesel from rapeseed oil

Answer 18

transesterification
The triglyceride is converted, or transesterified, into the less viscous fatty acid methyl ester (FAME) using methanol
Acids and alkalis can both be used to catalyse the reaction
An acid works by protonating the carbonyl group
An alkali works by deprotonating the alcohol / 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%

Question 19

give an example of ester hydrolysis

Answer 19

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

Question 20

how are soaps produced

Answer 20

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

Question 21

what are acyl chlorides

Answer 21

they are derivatives of carboxylic acids that are built from acyl groups

Question 22

how are acyl chlorides named

Answer 22

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

Question 23

what are acyl anhydrides

Answer 23

derivatives of carboxylic acids

Question 24

how are acyl anhydrides named

Answer 24

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

Question 25

how can acyl chlorides undergo nucleophilic addition via elimination

Answer 25

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

Question 26

describe the process of elimination via hydrolysis

Answer 26

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 HC

Question 27

describe the process of elimination via the formation of esters

Answer 27

Acyl chlorides can react with alcohols to form esters
The esterification of acyl chlorides is also a nucleophilic addition-elimination reaction
The alcohol adds across the C=O bond
A HCl molecule is eliminated

Question 28

describe the process of elimination via the formation of amides

Answer 28

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

Question 29

mechanism for hydrolysis of acyl chloride

Answer 29

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

Question 30

mechanism for formation of esters via acyl chloride

Answer 30

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

Question 31

the mechanism for the formation of amides via acyl chloride

Answer 31

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

Question 32

how do u name/ draw an ester

Answer 32

take the OH off the carboxylic acid
take a H of the alcohol and bond together

Question 33

what is important to remember when drawing the etser hydrolysis reaction for ester + salt

Answer 33

put the O as a negative charge
put the Na as a positive charge

Question 34

what are lipids

Answer 34

naturally occurring esters that consist if 3 long chain carboxylic acids and a molecule of glycerol

Question 35

what is the IUPAC name of glycerol

Answer 35

propane-1,2,3-triol

Question 36

what are unsaturated fatty acids known as

Answer 36

oils and have C=C

Question 37

what are saturated fatty acids known as

Answer 37

fats and no C=C

Question 38

what is the general process of acylation

Answer 38

replace one of the H of nucleophile with an acyl group
eg acyl chloride or anyhydride

Question 39

what is produced when an acid anhydride reacts with an alcohol

Answer 39

ester
carboxylic acid
-add the alchol on to the ester linkage but without the water

Question 40

how to write mechanism for acyl chloride + alcohol

Answer 40

-take out Cl of acyl chloride and H of alcohol
-bolt the rest together to form ester

Question 42

What is the salt called produced by saponification

Answer 42

Carboxylate salt

Question 43

Suggest why aqueous ethanol is a suitable solvent when heating the coconut oil with KOH.

Answer 43

Allow to dissolve both oil and KOH
To act as a mutual solvent OR To ensure reactants are miscible