Allery Chem YT OCR A 6.1.2 Carbonyl Compounds REVISION

C=O

Aldehydes & ketones have the carbonyl func group

C=O

The difference betw aldehydes & ketones is

the pos of the carbonyl (C=O) group

pos of carbonyl group in aldehydes

on an end carbon

aldehyde ending

\-al

pos of carbonyl group in ketones

on an inner carbon

ketone ending

\-one

Aldehydes are oxidised to carboxylic acids using

oxidising agents

Tollen’s reagent

used to distinguish betw aldehydes & ketones

Tollen’s reagent can be made first then

used to distinguish betw an aldehyde & ketone

To make Tollen’s reagent:

1) silver nitrate solid (colourless)

2) add few drops NaOH - pale brown ppt forms

After making Tollen’s reagent

3) few drops of dilute ammonia until ppt dissolves

4) add aldehyde/ketone to Tollen’s Reagent

5) place in hot water bath (don’t use flame bc a/k flammable)

Tollen’s results when added warm

aldehydes: Tollen’s reduced to silver which coats inside of flask

ketones

no silver ppt formed

used to distinguish betw aldehydes and ketones

Brady’s reagent/2,4-DNP/2,4-dinitrophenylhydrazine

How to use 2,4-DNP

dissolved in conc sulfuric acid and methanol & added to subs under test

2,4-DNP results

If a carbonyl group exists then a bright orange ppt formed. It only reacts with C=O in aldehydes and ketones not carboxylic acids

the orange ppt is

a derivative of a carbonyl compound & diff carbonyl compounds prod diff derivatives

different derivatives of a carbonyl compound have different mp

so can be identified against a library of known mp

reducing agents such as NaBH4 (sodium borohydride/sodium tetrahydridobrate (III))

dissolved in methol & water can reduce a/k

\[H\]

reducing agent

potassium cyanide reacts with carbonyl compounds to produce

hydroxynitriles

potassium cyanide dissociates to form K+ and CN- ions in

acidic solution

hydrogen cyanide (HCN) can also be used instead of KCN however

no acid req

hydroxynitrile

molecule that contains OH & CN

Potassium cyanide risks

1) irritant v dangerous if ingested or inhaled

2) when KCN reacts w moisture it can form the toxic gas hydrogen cyanide

Reduce risks associated with potassium cyanide

1) wear gloves while handling

2) wear safety goggles at all times

3) wear lab coat to prevent clothing contamination

4) fume cupboard to prevent exposure to toxic fumes