Topic 18 Organic chemistry 3

Question 1

What is benzene?

Answer 1

Benzene is a cyclic, planar molecule with the molecular formula C6H6
Carbon has 4 valent electrons. Each carbon is bonded to 2 other carbons and 1 hydrogen atom. The final electron is in a p - orbital which sticks out above and below the polar ring

Question 2

How is the delocalised ring in benzene made?

Answer 2

The lone electrons in the p orbital combine to form a delocalised ring of electrons
Due to the delocalised electron structure, all the C-C bonds in the molecule are the same. They have the same bond length.

Question 3

Different benzene structures

Answer 3

Benzene is normally drawn in the skeletal formula. This structure shows benzene with double bonds. It’s called Kekule’s structure. He thought there was alternating double and single bonds.

The other structure shows the delocalised electron system and you will be more likely to see this. Remember there is a hydrogen attached to each carbon. These aren’t shown in the skeletal formula

Question 4

Benzene stability

Answer 4

Benzene is actually more stable than the theoretical alternative which is cyclohexa-1,3,5-triene (kekule’s model)
We measure the stability of benzene by comparing the enthalpy change of hydrogenation in benzene and cyclohexa-1,3,5-triene.

Cyclohexene has 1 double bond. The enthalpy change of hydration is -120KJmol-1. If benzene has 3 double bonds we would expect an enthalpy change of hydrogenation of -360KJmol-1. However, when we measure the enthalpy change if hydrogenation for benzene, it is lower at -208KJmol-1.
Energy is required to break bonds and is released to form bonds. This suggests more energy is required to break bonds in benzene than cyclohexa-1,3,5-triene
This suggests benzene is more stable. This is due to the delocalised structure.

Question 5

Combustion of benzene

Answer 5

Burns in oxygen to produce CO2 and water if burned completely. This is no different to burning a standard hydrocarbon.
2C6H6 + 15O2 —-> 12CO2 + 6H2O
In reality, carbon doesn’t burn completely as there isn’t enough oxygen in the air. As a result, we hey a lot of unreacted carbon atoms (soot) and a black smoky fame is observed

Question 6

Addition of bromine to an alkene (Electrophilic addition)

Answer 6

Alkenes have a double bond and undergo electrophilic addition
Adding Br2 water to an alkene causes a colour change from orange to colourless
Bromine is the electrophile and adds to the alkene forming a dibromoalkane (colourless)

Br2 is polarised as the electrons in the double bond repels electrons in Br2
An electron pair in the double bond is attracted to delta+ bromine and forms a bond. This breaks the Br-Br bond.
A carbocation is formed and Br- is attracted to C+
Colourless 1,2-dibromoalkane is formed.

Question 7

Reaction of arenes (electrophilic substitution)

Answer 7

They undergo electrophilic substitution
Benzene has a high electron density as it has a delocalised ring of electrons. This is attractive to electrophiles (electron-loving substances)
As we have seen, benzene is stable so unlike traditional alkenes, they don’t undergo electrophilic addition as this would disrupt the stable ring of electrons
Instead, they undergo electrophilic substitution where a hydrogen or functional group on the benzene ring is substituted for the electrophile

Question 8

What are the 2 ways to name arenes?

Answer 8

You can name the benzene at the end - Bromobenzene or nitrobenzene etc
Or you can name them as if phenyl (C6H5) is a functional group - Phenol or Phenylamine etc

Question 8

What are the 4 mechanisms you should know for electrophilic substitution?

Answer 8

Friedel crafts Acylation
Friedel crafts Alkylation
Halogenation
Nitration

Question 9

What is an arene?

Answer 9

Aromatic compounds are molecules that contain a benzene ring, they are also known as arenes.

Question 9

How does electrophilic substitution occur?

Answer 9

Delocalised electrons are attracted to the carbocation. 2 electrons move to form a bond which breaks the ring and a + charge develops.
The electrons in the C-H bond move to neutralise the + charge and reform the ring. H is substituted
Need a very strong Electrophile to react. Can be created using a halogen carrier catalyst.
Typically, aluminium halides, iron and iron halides

Question 10

What are friedel crafts reactions?

Answer 10

Benzene is used widely in pharmaceuticals and dye stuffs however due to the stability of benzene it is difficult to react. Friedel crafts help to solve the problem.

It is a reaction where an acyl group (RCO-) or an alkyl group (R-) is added onto a benzene molecule. After the acyl or alkyl group is added to the benzene structure, it is weaker and it makes it easier to modify it further to make useful products.

To add onto the benzene ring, the electrophile must have a very strong + charge. Acyl groups have a + charge but it isn’t + enough. We can use a halogen carrier to act as a catalyst which will produce a much stronger electrophile with a stronger + charge.

In the Friedel crafts reactions, we need to react an acyl chloride or halogenoalkane with the halogen carrier in order to create a strong + electrophile

Question 11

Friedel crafts Acylation

Answer 11

To make the powerful + electrophile we use AlCl3 as the halogen carrier
RCOCl + AlCl3 —> RCO+ + AlCl4-

AlCl3 accepts a pair of electrons away from the acyl group. As a result, the polarisation increases and a carbocation is formed. A stronger electrophile is now produced which can now react with benzene.

Now we have the electrophile, we need to react it with benzene
Look at the paper for the mechanism
The delocalised electrons are attracted to the carbocation. 2 electrons move to form a bond that breaks the ring and a + charge develops.
The AlCl4- is then attracted to the + charged ring and 1 of the chlorine atoms breaks away to form a bond with the hydrogen
The electrons in the C-H bond move to neutralise the + charge and re form the ring

Question 12

Friedel crafts alkylation

Answer 12

To make the powerful electrophile we use AlCl3 as the halogen carrier
RCl + AlCl3 —-> R+ + AlCl4-
AlCl3 accepts a pair of electrons away from the halogenoalkane. As a result, a carbocation is formed. This stronger electrophile can now react with benzene

Now we have made the electrophile, we need to react it with benzene to make a less stable alkylbenzene under reflux and with a dry ether solvent.
Look at the paper for the mechanism

The delocalised electrons are attracted to the carbocation. 2 electrons move to form a bond which breaks the ring and a + charge develops
The negative AlCl4- is then attracted to the + charged ring and one of the cl atoms breaks away to form a bond with the hydrogen
The electrons in the C-H bond move to neutralise the + charge and re-form the ring

Question 13

Alcohol based groups adding to benzene ring

Answer 13

Look at the paper for the mechanism
If we use an electrophile that contains an alkyl chain with (OAlCl3)- then this can add an alcohol-based group to a benzene ring
This works in a similar way to other Friedel crafts reactions as the oxygen in the group has a lone pair of electrons which allows it to act as a nucleophile

Question 14

Nitration of benzene

Answer 14

Nitrating benzene is useful as it allows us to make dyes for clothing and explosives
If we heat benzene with a conc nitric acid and sulfuric acid we form nitrobenzene. However, like we have seen before, we need to make a powerful electrophile first.

The 1st step is to make the Electrophile, We react sulfuric acid with nitric acid.
H2SO4 + HNO3 —-> H2NO3+ HSO4-
The H2NO3+ decomposes to form the electrophile (Nitronium ion NO2+)
H2NO3+ —–> NO2+ + H2O

We now use the NO2+ and react with benzene to produce nitrobenzene
Look at the paper for the mechanism
The nitronium ion is attacked by the benzene ring forming an unstable + charged ring
The electrons in the C-H bond move to reform the delocalised electron ring
Nitrobenzene is formed and a H+ is formed which reacts with HSO4- formed in the previous reaction to make H2SO4 again. It is a catalyst.
A temp of below 55 degrees will ensure a single NO2 substitution. Above this will result in multiple substitutions

Question 15

What are phenols?

Answer 15

They have a hydroxyl group attached to the benzene ring (OH)
Carbon with the OH group will always be carbon 1
Phenols are more reactive than benzene due to the electron density in the ring being higher
Electrophilic substitution is more likely to occur with phenol than with benzene due to the OH group and orbital overlap.
The electrons in the P orbital of the oxygen overlaps with the delocalised ring structure and so they are partially delocalised into the pi system.
The electron density increases within the ring structure and so is more susceptible to attack from the electrophiles.

Question 16

Aspirin

Answer 16

It is an ester and is made by reacting ethanoic anhydride or ethanoyl chloride and salicylic acid. Aspirin and ethanoic acid is made.
Ethanoyl anhydride is used instead of ethanoyl chloride because:
- It is safer as it’s less corrosive, doesn’t produce harmful HCL gas and doesn’t react vigorously with water
- It is cheaper

Question 17

How do phenols react?

Answer 17

Phenols partially dissociate which means they’re weak acids. From phenol to phenoxide and H+

Phenols react with alkalis to form a salt and water. Phenol + NaOH —> Sodium phenoxide + water

Phenols can react with bromine water. This is because phenols are more reactive than benzene. We observe the brown bromine water decolourising. Phenol + 3Br2 —-> 2,4,6 - tribromophenol + 3HBr
As OH is an electron-donating group, substitution occurs at carbon 2,4,6. The product smells of antiseptic and is insoluble in water

Phenols can react with dilute nitric acid. Phenols react with this to produce nitrophenols as phenols are more reactive than benzene. Remember with benzene we need concentrated nitric acid and sulfuric acid as a catalyst. 2 isomers are produced, 2-nitrophenol and 4-nitrophenol

Question 18

What is an amine?

Answer 18

It is derived from ammonia molecules and all contain a nitrogen atom where hydrogens are replaced with an organic group
Can be primary, secondary, tertiary, quaternary ion and phenylamine(primary)
Nonaromatic amines are known as aliphatic amines - doesn’t have a benzene ring

Question 19

What are the 2 ways of making aliphatic amines?

Answer 19

Made by reacting halogenoalkane with excess ammonia
Made by reducing a nitrile

Question 20

Making aliphatic amine through reacting halogenoalkane with excess ammonia

Answer 20

With each step we add halogenoalkane. Look at paper for mechanism
Here the methylamine (primary) reacts with chloroethane (halogenoalkane) to form a secondary amine
2CH3NH2 + CH3CH2CL —-> CH3NHCH2CH3 + CH3NH3 + CL-

In this example, we look at the mechanism for chloroethane reacting with excess ammonia. Look at paper for mechanism
Ammonia is a nucleophile that attacks the delta+ on the carbon. An intermediate is formed (alkylammonium) with a +N and a Cl- ion. A second ammonia gives up a lone pair of electrons to hydrogen which breaks away from the salt. A primary amine and ammonium chloride salt is produced

However, the downside is that we have an impure product as this mechanism produces secondary, tertiary and quaternary salts too. This occurs as primary amines still have a lone pair of electrons on the nitrogen so also act as a nucleophile. The amine can react with any remaining halogenoalkanes to produce a secondary amine, then reacts further to make tertiary and quaternary salts

Question 21

Makin aliphatic amines by reducing nitrile (catalytic hydrogenation)

Answer 21

You reduce nitrile by using a nickel catalyst and hydrogen gas
It is the cheapest way to produce primary amines
It is called catalytic hydrogenation and unlike using halogenoalkane as seen before, this reaction reduces primary amines only, so a pure product is made.
High temp and pressure required.

We can also look at reducing nitriles using a strong reducing agent (LiAlH4) and dilute acid.
It is more expensive than using H gas and a Ni or Pt catalyst. LiAlH4 is expensive.
Reaction is called reduction and we use [H] to symbolise it. This is dissolved in a non-aqueous solvent such as dry ether
Use LiAlH4 and a dilute acid

Question 22

Making aromatic amines (reducing nitro compounds)

Answer 22

Made by reducing nitro compounds such as nitrobenzene. Look at paper for mechanism
1. We heat, under reflux, nitrobenzene with concentrated HCL and tin to form a salt like C6H5NH3+Cl-
2. Salt from 1) is reacted with an alkali such as NaOH to produce an aromatic amine such as phenyl amine

Question 23

Amines as a base

Answer 23

They have a lone pair of electrons that allows them to accept a proton and hence act as a base.
A proton bonds to an amine via a dative covalent bond.
Both electrons on the bond originate from the lone pair on the N.
The strength of the base is dependent on the availability of the lone pair of electrons on the N. The higher the electron density, the more available they are.
Electron density in the nitrogen is dependent on the type of group attached to the nitrogen

Question 24

What is the order of base strength between aromatic amines, ammonia and primary aliphatic amines?

Answer 24

The weakest is aromatic amines
The strongest is primary aliphatic amines
Look at paper for shading of electron density

Benzene is an electron-withdrawing group so it pulls away from nitrogen into the ring structure. Electron density at nitrogen reduces so lone pair availability is reduced and aromatic amines are less basic
Alkyl groups are electron-pushing groups so they push electrons towards nitrogen. Electron density at Nitrogen increases so lone pair availability is increased and primary aliphatic amines are more basic

Question 25

Amine stability

Answer 25

It can hydrogen bond with water so some have the ability to dissolve.
The LP of electrons on the nitrogen can form H bonds with the H atoms on water molecules. The LP on oxygen can also form H bonds with hydrogen on the amine.

However, only smaller amines will dissolve. Larger ones have longer hydrocarbon components and are non-polar and these can disrupt the hydrogen bonding with water molecules.
If the amine is large enough then the London forces between the non-polar hydrocarbon chain will be stronger than they H bonding between the N and H on water molecules. This means larger amines will not dissolve.

Question 26

Amines and complex ions

Answer 26

Amine reacts with copper complex ions to form a deep blue solution
This copper complex is formed by dissolving copper (II) sulfate in water
If we add a small amount of butyl amine to copper sulfate solution, a pale blue precipitate is formed [Cu(OH)2(H2O)4] as the amine removes 2 H+ acting as a base

If we can add more butylamine then 4 of the ligands will be exchanged with the amine forming the complex which is deep blue solution. Look at paper

Question 27

Amines and acyl chlorides

Answer 27

Acyl chlorides react with butylamines. The Cl is substituted for a N. Reaction with primary amines produces N-substituted amides. This is a vigorous reaction that produces a white-solid product.
Ethanoylchloride + butylamine —-> N-butylethanamide + Hcl
Look at paper
Overall reaction is CH3COCl + 2C4H9NH2 —–> CH3CONHC4H9 + [C4H9NH3]+Cl-

Question 28

Amines react with acids and form alkaline solutions

Answer 28

Amines are bases so react with acids to form salts however unlike traditional acid and base reactions, they don’t form water.
C4H9 +HCL —-> C4H9NH3+CL-

Smaller amines are soluble in water and dissolve to form alkaline solutions. Unlike some bases where there is an OH group; amines react with water to produce the OH- ion which makes the solution basic.
C4H9NH2 + H2O —–> C4H9NH3+ + OH-

Question 30

Amides

Answer 30

They are derivatives of carboxylic acids and have the functional group CONH2
Look at paper for diagram of amide and N-substituted amide.

Question 31

Making amides

Answer 31

Acyl chlorides react with ammonia and primary amines

Reaction with ammonia produces amides:
Ethanoyl chloride + NH3 —–> Ethanamide + HCL
Vigorous reaction and a white misty fume of HCL is produced

Reaction with primary amines produces N-substituted amides
Ethanoyl chloride + CH3NH2 —–> N-Methylethanamide + Hcl
Vigorous reaction and white misty fumes of HCL is produced

Question 32

Condensation polymers

Answer 32

Condensation polymerisation is where 2 different monomers with at least 2 functional groups react together. When they react, a link is made and water is eliminated. The link determines the type of polymer produced

Question 33

What are the types of polymers?

Answer 33

Polypeptides - found in proteins
Polyamides - found by reacting diamines and dicarboxylic acids
Polyesters - formed by reacting a diol and dicarboxylic acids together

Question 34

Polyamides

Answer 34

Amide links are formed wen dicarboxylic acids react with diamines. We have to use dicarboxylic acids and diamines as they have functional groups either side which allows for chains to be formed. Look at paper

Question 35

Polyesters:

Answer 35

Ester links are formed when dicarboxylic acids react with diols

Question 36

Condensation polymers

Answer 36

We can work out the monomer from the polymer chain
The monomer can be determined bt finding the repeat unit. We look for either an amide link(HN-CO) or an ester link (CO-O)
The monomer can be formed by breaking the bonds in these links and add H or OH to either end of both molecules. Look at paper

Question 37

Hydrolysis

Answer 37

Condensation polymers can be hydrolysed (split using water)) to produce the original monomers. It is just the reverse of polymerisation.
To determine the monomer units produced we break the bond in the middle of the amide or ester link of the repeat unit
Then we add OH and H to each of the monomer units.
Look at paper

Question 38

Amino acids

Answer 38

They have an amino group (NH2) and a carboxyl group (COOH)
They are amphoteric which means they have acidic and basic properties
Amino acids have an organic side chain (represented by R) with the exception of glycine where R is hydrogen
Amino acids are chiral molecules as they have 4 different groups around a central carbon atom. They rotate plane polarised light

Question 39

How to name amino acids - 2 ways

Answer 39

Common and systematic
1. Find the longest carbon chain
2. Number the carbons
3. Note the number where the NH2 group sits
4. Name any other groups

Question 40

What are zwitter ions?

Answer 40

Amino acids sometimes exist as zwitter ions.
This is a molecule with both + and - ions. Zwitterins only exist as the amino acids isoelectric point
The isoelectric point is the PH at which the average overall chiral charge is 0. This is dependent on the R group.

If the PH is lower than the isoelectric point, then COO- is likely to accept an H+
A zwitterion is likely to be formed when at a PH at the isoelectric point. Both the carboxyl group and amino group are ionised
If the PH is higher than the isoelectric point, then NH3+ is likely to lose a H+

Question 41

What is Thin Layer chromatography?

Answer 41

TLC allows us to separate and identify amino acids as they have different solubilities
TLC uses a stationary phase of silica or alumina mounted on a glass/metal plate. A pencil baseline is drawn and drops of amino acid mixtures are added
Place the plate in a solvent - the baseline must be above the solvent level
Leave until solvent has moved up to near the top of the plate. Remove and mark the solvent front and allow it to dry.
It works by the amino acid mixture spots dissolving in the solvent. Some chemicals may not dissolve as much and stick to the stationary phase quickly. What we are left with is a chromatogram.
We can identify the amino acids using the positions on the chromatogram

Question 42

Calculating RF value

Answer 42

The number of spots on the plate tell you how many aminoacids make up the mixture
The amino acids can be identified by calculating the RF value and comparing these to a library of known RF values

RF = distance travelled by spot / distance travelled by solvent
Rf values are fixed for each amino acid however this changes if the temp, solvent or makeup of the TLC plate changes

Question 43

Grignard reagents

Answer 43

They are used to help carbon carbon bond formation, which is very difficult normally
They are an oranomagnesium compound that are made by reacting a halogenoalkane with magnesium in dry ether.
R-X + Mg —-> RMgX

Question 44

Grignard reagent reacting with CO2

Answer 44

Carboxylic acids can be made
R-MgBr + CO2 —-> RCOCl + MgBrCl
Dry ether and dilute HCL

A new C-C bond is formed when the R breaks off the Grignard reagent and bonds with the C in CO2. This in turn breaks a C=O bond to form R-COO-
Finally, the Cl protonates the R-COO- to form the carboxylic acid

It occurs in 2 steps:
1) In dry ether, we bubble CO2 in Grignard reagent
2) We add a dilute acid to the solution

Question 45

Grignard reagent reacting with carbonyl compounds

Answer 45

Alcohols can be made by reacting Grignard reagent with aldehydes and ketones
R-MgBr + RCOR —-> CRRROH + MgBrCl

A new C-C bond is formed when the R breaks off the Grignard reagent and bonds with the C in the carbonyl group. This breaks a C=O bond. Finally the HCL protonates to form alcohol

Same 2 steps as before:
1) In dry ether, we bubble CO2 in the Grignard reagent
2) We add a dilute acid to the solution

Question 46

What are all the functional groups, their features and typical reactions?

Answer 46

Alkane:
C-C. Unreactive, non-polar bond. Typical reaction is radical substitution.

Alkene:
C=C. Electron rich double bond, non-polar bond. Typical reaction is electrophilic addition

Alcohol:
C-OH. LP on oxygen can act as a nucleophile, polar C-OH bond. Typical reactions - Esterification and nucleophilic substitution, dehydration/elimination and nucleophilic substitution

Aromatic compounds:
C6H5. Delocalised electron ring, stable. Typical reactions - Electrophilic substituiton

Haloalkane:
C-x. Polar C-X bond. Nucleophilic substitution and elimination

Nitrile: C-C=N(triple bond not double). Electron deficient carbon centre. Typical reactions are reduction and hydrolysis

Amine:
C-NR2. LP on N is basic, can act as a nucleophile. Typical reactions are nucleophilic substitution and neutralisation

Aldehydes and ketones:
C=O. polar C=O bond. Typical reactions are nucleophilic addition, oxidation of aldehydes and reduction

Carboxylic acids:
COOH. Electron deficient carbon centre. Typical reactions are Esterification and neutralisation

Ester:
RCOOR. electron deficient carbon centre. Typical reactions are hydrolysis

Acyl chloride:
Electron deficient carbon centre. Typical reactions are Nucleophilic addition-elimination, condensation and Friedel crafts acylation.

Acid anhydride:
RCOOCOR. Electron deficient carbon centre. Typical reaction is esterification

Question 47

What are the 7 reaction types?

Answer 47

Addition reactions :
a double bond is broken and 2 molecules join to form a single product. The functional groups involved are alkene and carbonyl groups

Elimination/dehydration:
A double bond is normally formed when a functional group is removed and released as part of a smaller molecule

Substitution:
A functional group is exchanged for another one

Condensation reactions:
When w molecules join and a small molecule is eliminated

Hydrolysis:
2 smaller molecules are formed by splitting one with water such as breaking polyamides and polyesters

Oxidation:
Normally means the gain of oxygen or loss of H in a reaction

Reduction:
Normally means the loss of oxygen or gain of hydrogen in reactions

Question 48

What are all the reactions that occur from alcohol?

Answer 48

Alcohol —> Alkene (Conc H2SO4/H3PO4 and heat)
Alcohol —-> Aldehyde (K2Cr2O7, H2SO4 and heat primary alcohol in distillation kit)
Alcohol —–> Haloalkane (Sodium halide, H2SO4 at 20 degrees)
Alcohol —-> Ketone (K2CR2O7 H2SO4 heat secondary alcohol under reflux)
Alcohol —–> Iodoalkane (I2, red phosphorus and under reflux)
Alcohol —-> Ester (Carboxylic acid, acid catalyst, heat or acyl chloride)

Question 49

What are all the reactions that occur from Alkene?

Answer 49

Alkene —-> Alkane (H2, Nickel catalyst and 150 degrees)
Alkene —-> Dihaloalkane (Halogen and 20degrees)
Alkene —-> Diol (Acidified KMnO4 at 20 degrees)
Alkene —-> alcohol (Steam H3PO4 at 60 atm and 300 degrees)
Alkene —-> Haloalkane (KOH, ethanol and under reflux)

Question 50

What are the reactions that occur from alkane

Answer 50

Alkane —-> Haloalkane (Halogen and UV light)

Question 51

What are the reactions that occur from carboxylic acids?

Answer 51

Carboxylic acid —-> Alcohol (LiAlH4 forms primary alcohol)
Carboxylic acid —-> Acyl chloride (SOCl2)

Question 52

What are the reactions that occur from aldehyde/ketones?

Answer 52

Aldehyde —-> Carboxylic acids (K2Cr2O7, H2SO4 under reflux)
Aldehyde —-> Alcohol (NaBH4 in methanol and water)
Ketone —-> Alcohol (NaBH4 in methanol and water)
Aldehyde/ketone —-> Hydroxynitrile (KCN H2SO4 at 20 degrees)
Aldehyde/ketone —–> Ester (concentrated H2SO4, alcohol, heat and catalyst)

Question 53

What are the reactions that occur from haloalkane?

Answer 53

Haloalkane —-> Alkene (KOH, ethanol and under reflux)
Haloalkane —-> Alcohol (Warm NAOH, H2O and reflux)
Haloalkane —-> Carboxylic acids (Mg, dry ether, CO2 in dilute acid)
Haloalkane —-> Primary amine (NH3 and heat)
Haloalkane —-> Nitrile (KCN, ethanal and reflux)

Question 54

What are the reactions that occur from nitriles?

Answer 54

Nitrile —> Primary amine ( LiAlH4 + dilute H2SO4 OR H2, Ni/pt catalyst, high them and pressure OR Na, ethanal and under reflux
Nitrile —-> Carboxylic acid (Dilute HCL and under reflux)

Question 55

What are the reactions from Acyl chloride?

Answer 55

Acy chloride —–> Carboxylic acid (H2O at 20 degrees
Acy chloride —–> Primary amide (NH3 at 20 degrees)

Question 56

What are the reactions that occur from Ester?

Answer 56

Ester —-> Carboxylic acid (Dilute H2SO4, H2O and under reflux with a catalyst OR dilute NaOH under reflux)

Question 57

What are the reactions that occur from Benzene?

Answer 57

Benzene —-> Nitrobenzene ( Conc H2SO4 and HNO3 below 55 degrees) (Nitration)
Benzene —-> Phenylketone (RCOCL, AlCl3 catalyst under reflux and anhydrous conditions) (Acylation)
Benzene —-> Alkylbenzene (Haloalkane, AlCl3, catalyst and under reflux) (Alkylation)
Benzene —–> Halobenzene (Halogen, AlCl3 catalyst and under reflux)

Question 58

What are the reactions that occur from nitrobenzene?

Answer 58

Nitrobenzne —-> Phenylamine ( Conc Hcl, Tin and under reflux. Add NaOH)

Question 59

What are the reactions that occur from phenol?

Answer 59

Phenol —-> Sodium phenoxide (NaOH at 20 degrees)
Phenol —–> 2,4,6 - tribromophenol

Question 60

What is reflux?

Answer 60

Reflux allows strong heating without losing volatile reactants and products. Volatile compounds evaporate and fall back in the flask
The Liebig condenser has cold water running through the wall. When hot evaporating substances hit the colder condenser they turn back into liquid and return to the bottom of the round-bottomed flask to react further.
As we are using flammable liquids, heating is done via a water bath or electric heater called a mantle

Question 61

What is distillation?

Answer 61

It is used when we want to separate substances with different BPs
Gently heating a mixture will result in the compounds separating out in order of BP
If your compound has a lower BP than your starting mixture, you need to heat to the temp of the compound you want to separate. Collect your product in a separate vessel.
If your compound has a higher BP than your starting mixture, you heat to the BP of the compound you want to separate. Your compound will remain in the round-bottomed flask.

Distillation is useful when you want to extract a chemical before it can react any further. Oxidisng primary alcohols can produce aldehydes however if the aldehyde isn’t removed then it will oxidise to a carboxylic acid. Distillation is used to remove the aldehyde.

Question 62

What is steam distillation?

Answer 62

Steam distillation is used when we want to separate substances with high BPs or decompose when heated
If the product is immiscible with water then steam distillation is used to separate compounds that couldn’t be done under standard conditions.

1) The steam is produced and pushed through the impure sample. The steam lowers the BP of the immiscible product and allows for it to be distilled out of the mixture before it decomposes. This method is also useful if the substances we want to separate have a high BP as the steam reduces this. If this is lower then it means we can separate them as lower.

2) If the substance we are trying to collect is less volatile than the constituent substances we are trying to separate it from, then the desired product will evaporate out of the flask with steam

3) This is then condensed and collected in a separate flask

Question 63

Separation and purification

Answer 63

Add the products from distillation into a separating funnel. Add water to dissolve soluble impurities and create an aqueous solution.
After allowing the solution to settle, 2 layers will form.
Top layer - impure product
Bottom layer - Aqueous layer containing water-soluble impurities. Drain this layer off

Now we need to purify our sample through 2 further steps.
Wash the product with another liquid. Add anhydrous CaCl2. This is a dehydrating agent. Invert flask and leave for 20-30 mins

Question 64

Filtration

Answer 64

Gravity filtration - Use if you wish to keep liquid part and dispose of solid
Vacuum filtration - A vacuum is used to separate the liquid and solid components thoroughly. Place a filter paper disc in the Buchner funnel and dampen it slightly to make a seal. Pour the reaction mixture into the Buchner funnel with the vacuum line on. This vacuum creates a reduced pressure in the flask and pulls the liquid through.

Question 65

Recrystallisation

Answer 65

1. Add enough hot solvent to allow the impure solid to dissolve. This means you have a saturated solution of your impure product.
2. Allow the solution to cool down slowly…crystals will form.
3. Your impurities will remain dissolved in solution as there is a smaller quantity of them, it will take them longer to crystallise
4. Filter to get your solid purified crystals. Wash with very cold solvent and dry them off
   Choose solvent carefully - you want the impure solid to dissolve fully in a hot solvent but virtually insoluble when it’s cold