Answer to Question #286201 in Organic Chemistry for Gionny barscalli

Question

Topics:Further synthesis and analysis

Q1

Describe a simple chemical test for distinguishing between the following pairs of compounds:

a) cyclohexane and cyclohexene

b) propanol and propanone

c) propan-1-ok and propan-2-ol

Q2

Suggest how the following syntheses could be carried out in the laboratory:

a) chloroethane to ethanoic acid (5 marks detailed explanation)

b) chloroethane to 2-hydroxypropanenitrile (5 mark with detailed explanation)

c) chloroethane to aminoethane (1 mark with detailed explanation)

Answer 1

Q1

1a) To differentiate between cyclohexane and cyclohexene first we need to understand the basic difference between both of them. So, let’s first draw the structure of both cyclic alkane cyclohexane and cyclic alkene cyclohexene organic compounds.

Complete step by step answer:

Cyclic cyclohexane is 1

∘

1∘ saturated hydrocarbon and cyclic cyclohexene is 2

∘

2∘ unsaturated hydrocarbon as cyclohexane has one ring whereas cyclohexene has one ring with one double bond.

Now, we have to consider a test that can differentiate both the compounds easily.

So, let’s take option A first i.e, Bromine water which is an alkene test.

When cyclic cyclohexane is reacted with Bromine water then no reaction occurs butwhen cyclic cyclohexene reacts with bromine water then it gets reacted with bromine water and an alkene with -Br and -OH bond is formed.

1B) propanol and propanone

The key difference between propanal and propanone.

Propanal and propanone are organic compounds. Both these compounds have carbonyl groups. But they fall into two categories because propanal has an aldehyde group with a hydrogen atom attached to the carbonyl group while propanone is a ketone with alkyl or aryl groups attached to the carbonyl group but no hydrogen atoms attached to the carbonyl carbon. Further, propanal and propanone are structural isomers of each other.

1C) propan-1-ol and propan-2-ol

Fehling solution

Oxidation with concentrated H2SO4 followed by reaction with Fehling solution. Propan-1-ol and propan-2-ol upon heating with copper will give propanal (CH3CH2CHO) and propanone (CH3COCH3) which can be distinguished by Fehling solution.

Q2A) chloroethane to ethanoic acid

Firstly we clorinate the ethane in the presence of light, it gives chloroethane. Then it react with KOH and forms ethanol, and in last KMnO4, an oxidising agent, react with ethanol and forms ethanoic acid. Reactions are below:-

CH3-CH3 + Cl2 →→→→ CH3-CH2-Cl + HCl

CH3-CH2-Cl + KOH →→→ CH3-CH2-OH + KCl

CH3-CH2-OH →→KMnO4→→ CH3-COOH

Q2B) chloroethane to 2-hydroxypropanenitrile (5 mark with detailed explanation)

The reaction of aldehydes and ketones with hydrogen cyanide

Hydrogen cyanide adds across the carbon-oxygen double bond in aldehydes and ketones to produce compounds known as hydroxynitriles. For example, with ethanal (an aldehyde) you get 2-hydroxypropanenitrile:

With propanone (a ketone) you get 2-hydroxy-2-methylpropanenitrile:

The reaction isn't normally done using hydrogen cyanide itself, because this is an extremely poisonous gas. Instead, the aldehyde or ketone is mixed with a solution of sodium or potassium cyanide in water to which a little sulphuric acid has been added. The pH of the solution is adjusted to about 4 - 5, because this gives the fastest reaction. The solution will contain hydrogen cyanide (from the reaction between the sodium or potassium cyanide and the sulphuric acid), but still contains some free cyanide ions. This is important for the mechanism.

Q2C)chloroethane to aminoethane (1 mark with detailed explanation)

Formation of Amines

A haloalkane may also be substituted to form an amine.

The reagent used here is concentrated ammonia, NH3.

1-Chloroethane + NH3 (conc) --> Ethanamine (or aminoethane)