Organic synthesis

Question 1

Give the reagent and conditions for ester to alcohol

Answer 1

M1 NaOH

1
M2     Aqueous/(warm)
Ignore alcoholic / conc / dil.
1
M3     (Fractional) distillation or described

Question 2

how to distinguish between a tertiary alcohol and a primary alcohol.

Answer 2

1. K2Cr2O7 / H+
2. KMnO4 / H+

Primary alcohol

1 (Orange) goes green Penalise wrong starting colour

2. (purple) goes colourless / decolourises allow goes brown

Tertiary alcohol

1. no change / no observable reaction
2. no change / no observable reaction

Question 3

how to distinguish between a ketone and an aldehyde

Answer 3

1- Fehling’s / Benedict’s

2- Tollens’ / [Ag(NH3)2]+

3- K2Cr2O7/ H+

4- I2 / NaOH

Ketone

1- no change / no observable reaction

2- no change / no observable reaction

3- no change / no observable reaction

4- yellow ppt

aldehyde

1 - Red ppt

2- Silver mirror

3- (Orange) goes green Penalise wrong starting colour

4- o change / no observable reaction

Question 4

How do you test for an acyl chloride

Answer 4

H Acyl chloride
AgNO3
(white) ppt

Na2CO3/NaHCO3 named carbonate
Effervescence or CO2 or fumes or exothermic

water
fumes

named indicator
acid colour

Named alcohol
Smell or fumes

Named amine or ammonia
fumes

Question 5

A chemist has discovered that the labels have fallen off four bottles each of which contains a different organic liquid. These liquids are known to be propan-2-ol, propanal, hexene and 1-bromopropane.
Suggest a series of test-tube reactions which a chemist could use to confirm the identities of the four compounds. State the reagents used and the observations expected.

Answer 5

Acidified potassium dichromate(VI)
1
Turns green with propan-2-ol and propanal
1
No reaction with hexene and 1-bromopropane
1
Tollens with propan-2-ol and propanal
1
only propanal gives silver mirror
1
Bromine water
1
Decolourised by hexane
1
No reaction with 1-bromopropane
1
Warm NaOH followed by acidified AgNO3
1
White ppt with 1-bromopropane
1

Question 6

Heptane can be obtained from the catalytic cracking of hexadecane (C16H34) at a high temperature.
Identify a suitable catalyst for this process.
Give one condition other than high temperature.
Give an equation for the catalytic cracking of one molecule of hexadecane to produce one molecule of heptane, one molecule of cyclohexane and one other product.

Answer 6

Zeolite OR aluminosilicate
Allow porous pot / aluminium oxide / alumina / silica / silicon dioxide
M1
Slight/moderate pressure
Slightly above atmospheric – allow 1-5 atmospheres / 100-500kPa
M2
C16H34 → C7H16 + C6H12 + C3H6

Question 7

Explain, with the aid of equations, why a single radical can cause the decomposition of many molecules of ozone.

Answer 7

Cl●

M1
Cl● + O3 → ClO● + O2
Penalise absence of dot once in the equations
M2
ClO● + O3 → Cl● + 2O2
Allow dot anywhere on the radical
Apply the list principle in the equations and penalise
M3
Cl● is regenerated (and causes a chain reaction in the decomposition of ozone)

Question 8

what observation would you see when an alcohol and ethanol chloride react

Answer 8

Misty fumes / steamy fumes as very exothermic reaction so steamy HCl is produced

Question 9

Consider the following conversion.
benzene to cyclohexane
Identify a reducing agent for this conversion.
State the empirical formula of the product.
State the bond angle between the carbon atoms in the starting material and the bond angle between the carbon atoms in the product.

Answer 9

H2 (Ni / Pt) but penalise wrong metal
NOT Sn / HCl, NaBH4 etc.

CH2

In benzene 120°

In cyclohexane 109° 28’ or 109½°
Allow 108° - 110°

Question 10

in the conversion of a ketone to an alcohol

explain why the product formed is optically inactive.

Answer 10

M1 Planar C=O (bond / group)
Not just planar molecule
1
M2 Attack (equally likely) from either side
Not just planar bond without reference to carbonyl
1
M3 (about product): Racemic mixture formed OR 50:50 mixture or
each enantiomer equally likely