Identificayion test for aldehyde ketkne
Answers
Abstract
The aim of this experiment was to identify which functional groups the various chemicals and unknown substances belonged to using the different reaction tests. The main purpose was to determine the reactions of Aldehydes and Ketones. Aldehydes and Ketones are organic compounds consisting of the carbonyl functional group. Aldehydes contain their carbonyl group at the end of the carbon chain and are susceptible to oxidation while Ketones contain theirs in the middle of the carbon chain and are resistant to oxidation. Jones’s Test, Tollen’s Reagent and Iodoform Reaction were the three tests used to determine the reactions of aldehydes and ketones. The Chromic Anhydride test caused Aldehydes to turn blue, and Ketones orange. The Tollen’s Reagent test caused the oxidation of aldehydes thus forming a mirror-like image in the test tube rendering it a positive test and the Iodoform reaction produced a yellow precipitate in the test tube which concluded the presence of an aldehyde.
Introduction
The carbon-oxygen double bond is one of the most important functional groups, due to its ubiquity, which are involved in most important biochemistry processes. Reactivity of this group is ruled by the electron imbalance in the πorbitals of the bond between a more electronegative and a carbon atom. This carbon atom is more likely to undergo a nucleophillic attack, especially if the oxygen is protonated. If the carbonyl group has hydrogen’s in the α-position, it can tautomerise to the enol, thus, Keto tautomer can become Enol tautomer.
Aldehydes and Ketones are organic compounds that consist of the carbonyl functional group, C=O. The carbonyl group that consists of one alkyl substituent and one hydrogen is the Aldehyde and those containing two alkyl substituents are called Ketones. These two organic compounds undergo reactions that are related to the carbonyl group, however,
, they can be distinguished due to their “susceptibility to oxidation” (1)
The carbonyl of an aldehyde is always at the end of the carbon chain whereas the carbonyl of a Ketone can lie anywhere within the carbon chain. These two organic compounds are found abundantly in nature. Since the carbonyl group is polar, aldehydes and ketones have a larger dipole moment. In the carbonyl group, the positive carbon atom will be attacked by nucleophiles. (1)
Addition reactions can be undergone by carbonyl groups. Since Aldehydes have the hydrogen atom attached to it, it makes them more susceptible to oxidation, which is the loss of electrons. However, Ketones lack the hydrogen atom in their carbonyl group and are therefore resistant to oxidation. Small Aldehydes and Ketones are easily dissolved in water but as the chain increases in length, its solubility decreases. (1)
In this experiment, the Chromic Anhydride (Jones’s Test), Tollen’s Reagent and the Iodoform reaction were used to test for the presence of aldehydes and ketones. Jones’s Test is an organic reaction for the oxidation of alcohols to carboxylic acids and ketones. This oxidation is very rapid and exothermic with high yields. Tollen’s Reagent was used to determine whether a substance is an aldehyde or ketone, which shows that aldehydes are easily oxidized while ketones are not. The Iodoform reaction would have a positive result if there is a pale yellow precipitate.
The aim of this experiment was to identify the reactions of Aldehydes and Ketones and which functional groups the unknown substances and known chemicals belonged to, using the different reaction tests.