AQA Chemistry Unit 4 with Anon_98

Scroll to see replies

Advantages and possible disadvantages of producing and using biodiesel as a substitute for diesel.

Advantages:

- Formed from a renewable resource and therefore potentially is more carbon neutral than diesel from petroleum

- Produces less harmful particulates

- No sulphur to remove

Disadvantages:

- Expensive to produce

- May use land which would otherwise be used to produce food crops

- Fuel economy is less with diesel from petroleum

Reply 61

Anon_98

Compounds containing the carbonyl group – Acylation –Topic 5.

Brb, taking a break.

Reply 62

Anon_98

Compounds containing the carbonyl group – Acylation –Topic 5.

Alright, so there are 4 reactions you need to know with acyl chlorides + acid anhydrides.

Reactions of water, alcohol, ammonia and amines.

~

So, first we'll start with water + an acyl chloride.

Example: Ethanoyl chloride with water.

Condensed equation: CH3COCl + H2O --------------> CH3COOH + HCl

Conditions: Room temperature

Observations: Fairly vigorous reaction, White fumes with ammonia.

~

Now water with an acid anhydride.

Example: Ethanoic anhydride with water.

Condensed equation: (CH3CO)2 + H2O --------------> 2CH3COOH

Conditions: Heat.

Observations: Much less reactive than the acyl chloride.

Reply 63

Anon_98

Next, we'll do the reaction with alcohols.

So, first we'll start with an alcohol + an acyl chloride.

Example: Ethanoyl chloride with methanol.

Condensed equation: CH3COCl + CH3OH --------------> CH3COOCH3 (methyl ethanoate) + HCl

Conditions: Room temperature

Observations: Fairly vigorous reaction, Steamy fumes.

~

Now alcohol with an acid anhydride.

Example: Ethanoic anhydride with Ethanol.

Condensed equation: (CH3CO)2 + CH3CH2OH --------------> CH3COOCH2CH3 (ethyl ethanoate) + CH3COOH (ethanoic acid)

Conditions: Reflux

Reply 64

Anon_98

Now we'll do the reaction with ammonia.

So, first we'll start with an ammonia+ an acyl chloride. - which is an acid-base reaction.

Example: Ethanoyl chloride with ammonia.

Condensed equation: CH3COCl + 2NH3 --------------> CH3CONH2 (ethanamide) + NH4⁺Cl^-

Conditions: Room temperature

Observations: Very vigorous reaction, White fumes.

~

Now ammonia with an acid anhydride.

Example: Ethanoic anhydride with Ammonia.

Condensed equation: (CH3CO)2 + 2NH3 --------------> CH3CONH2 (ethanamide) + CH3COO^-NH4⁺(ammonium ethanoate)

Conditions: Reflux

Reply 65

Anon_98

Finally, the reaction with amines.

So, first we'll start with an amine + an acyl chloride. - which is an acid-base reaction.

Example: Ethanoyl chloride with methylamine.

Condensed equation: CH3COCl + 2CH3NH2 --------------> CH3CONHCH3 (N-methyl ethanamide)+ CH3NH3⁺Cl^-(Methyl ammonium chloride)

Conditions: Room temperature

Observations: Very vigorous reaction, White fumes.

~

Now an amine with an acid anhydride.

Example: Ethanoic anhydride with ethylamine.

Condensed equation:(CH3CO)2 + 2CH3CH2NH2 --------------> CH3CONHCH2CH3 (N-ethyl ethanamide) + CH3COO^-CH3CH2NH3⁺(ethyl ammonium ethanoate)

Conditions: Reflux

Reply 66

Anon_98

Nucleophillic addition- elimination mechanisms

Alright, so you need to be able to outline the mechanisms for water, alcohols, ammonia + amines ONLY with acyl chlorides.

I'll start with water, I'll draw it below:

Reply 67

Anon_98

NUCLEOPHILIC ADDITION -ELIMINATION MECHANISM FOR AN ACYL CHLORIDE AND WATER.

Posted from TSR Mobile

1465848601420.jpg13.2KB

Reply 68

Anon_98

Now I'll do the mechanism for an acyl chloride with an alcohol, specifically - methanol.

Below:

Reply 69

Anon_98

NUCLEOPHILIC ADDITION - ELIMINATION MECHANISM FOR AN ACYL CHLORIDE AND AN ALCOHOL. (methanol)

Posted from TSR Mobile

1465849125937.jpg13.2KB

Reply 70

Anon_98

Now I'll do the mechanism for an acyl chloride with ammonia.

Below:

Reply 71

Anon_98

NUCLEOPHILIC ADDITION- ELIMINATION MECHANISM FOR AN ACYL CHLORIDE AND AMMONIA.

Posted from TSR Mobile

1465849761408.jpg15.8KB

Reply 72

Anon_98

Lastly, the mechanism for an acyl chloride with an amine, specifically - methylamine.

Below:

Reply 73

Anon_98

NUCLEOPHILIC ADDITION -ELIMINATION MECHANISM FOR AN ACYL CHLORIDE AND AN AMINE. (methylamine)

Posted from TSR Mobile

1465851901626.jpg16.6KB

Reply 74

Anon_98

Industrial advantages of ethanoic anhydride over ethanoyl chloride in the manufacture of aspirin:

- Cheaper than the acyl chloride ·

- Less dangerous to handle than the acyl chlorides since less corrosive ·

- Less vulnerable to hydrolysis by moisture(easier to store)

Advantages and disadvantages of using ethanoyl chloride over ethanoic acid in making esters:

Advantages:

- Greater yield;

- Faster reaction

- Less energy required

- Product easier to separate·

Disadvantages:

- Ethanoyl chloride more hazardous to handle

- Harder to store

Reply 75

Anon_98

Aromatic chemistry – Bonding –Topic 6.

Description of the bonding in benzene:

- Planar i.e. all 12 atoms in a single plane·

- All C-C bonds identical in length and intermediate between typical single and double bonds·

- All bond angles are 120^o i.e. perfect hexagon·

- 1 electron from each of the C atoms is delocalised in the ring

Reply 76

Anon_98

Aromatic chemistry – Delocalisation stability –Topic 6.

The delocalisation confers energetic stability on the molecule.

The estimation of the enthalpy change when the Kekule structure reacts with hydrogen(hydrogenation) to form cyclohexane is -120kJ

If you assume that the three double bonds in the Kekule structure behave independently on each other, the enthalpy change of hydrogenation would be three times the value for cyclohexane, therefore:

-120 x 3 = -360kJ

Benzene, however, only releases 208kJ of energy.

So, the difference between these two values. I.E. The delocalisation energy is 152kJ

Benzene must be energetically more stable than the Kekule structure by 152kJ

Reply 77

Anon_98

Aromatic chemistry – Electrophillic substitution –Topic 6.

Alright, so firstly I'll just draw the general mechanism for substitution of an electophile, E⁺.

Reply 78

Anon_98

Posted from TSR Mobile

1465854397910.jpg13.2KB

Reply 79

Anon_98

Aromatic chemistry – Nitration –Topic 6.

Nitration reaction.

Reagents: Concentrated HNO3 and Concentrated H2SO4.

Conditions: Warm to 50C, but not above to minimise further substitution.

Mechanism name: Electrophillic substitution.

Name of reactive inorganic species: Nitronium ion.

Equation for the generation of the nitronium ion : HNO₃ + 2H₂SO₄ --------> NO₂⁺ + 2HSO₄^- + H₃O⁺

Alright, I'm going to draw out the mechanism for this below: