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Organic Synthesis and

Analysis

ORGANIC SYNTHESIS AND ANALYSIS

Distinguishing between different OrganicCompounds

It is possible to compare most of the organic compoundsthat you have coveredthrough simple chemical tests. A number of these tests arecovered below.

Test for alkenes

Due to the fact that they undergo electrophilic

additionwith bromine, alkenes will decolourise

bromine water.

To test:

Add few drops on bromine water to your sample.

Shakethe mixture.

If:

the bromine decolourisesthen an alkene is present.

the bromine does not decolourise no alkene is present.

Test for haloalkanes

If you heat haloalkanes with dilute sodium hydroxide halide

ions are produced due to a nucleophil ic substitution

reaction.

To test:

Add aqueous sodium hydroxide to your sample.

Heat the mixture and then allow it to cool.

Add dilute nitric acid followed by aqueous silver nitrate.

If:

a white precipitatethat is soluble indilute

ammonia forms then a chloroalkane was present.

a cream precipitatethat is soluble inconcentrated ammoniaforms then a

bromoalkanewas present.

a yellow precipitatethat is insolublein ammoniaforms then an iodoalkane

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Organic Synthesis

Distinguishing between

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was present.

Test for aldehydes

It is possible to oxidisedaldehydes using a mild oxidising agent

like Tollens reagent or Fehlings solution.

Tollens reagent:

Add Tollens reagent to your sample.

Heat the mixture.

If:

a silver mirror forms then analdehyde is present.

Fehlings solution:

Add Fehlings solution to your sample.

Heat the mixture.

If:

a brick-red precipitateforms an aldehyde is

present.

Test for carboxylic acids

Carboxylic acids are able to free carbon dioxidefrom

carbonates.

To test:

Add sodium carbonate solution to your sample.

If:

effervescenceis produced and the gas causes the

lime water to become milkythen a carboxylic acid is

present.

Test for acyl chlorides

Chloride ionsare released readily by acyl

chlorides which produces the gas, hydrogen

chloride .

To test:

Add water slowly to your sample.

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If:

white, misty fumesare produced then an

acyl chloride is present.

Test for amines

Amines are alkaline.

To test:

Add universal indicator to your sample.

If:

it turns blue/purpleand has a fishy smellthen an

amine is present.

Test for alcohols

When sulphuric acidis present, alcohols will react with carboxylic acidsto produce

esters.

To test:

Add ethanoic acid followed by sulphuric

acid to your sample.

Heat the mixture.

If:

the mixtures begins to smell swee t and fruitythen an alcohol was present.

Distinguishing tests for primary, secondary and tertiary alcohols

All react differently when oxidised:

primaryalcohols form aldehydes

secondaryalcohols form ketones

tertiaryalcohols cannot be oxidised

To test:

Add dilute sulphuric acid and potassium dichromate to your mixture.

Warm the mixture gently.

If:

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the mixture turns greenthan a primary or secondary alcohol is present.

the mixture does not turn greenthen a tertiary alcohol is present.

If the mixture turns green then add Fehlings mixture and heat again.

If:

a brick-red precipitateforms then a primary alcohol w as present.

no brick-red precipitateforms then a secondary alcohol was present.

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