When Acetaldehyde Is Treated With Fehling’s Solution?


Fehling’s test gives a reddish-brown precipitate of CuO2 when it reacts with aldehydes or ketones having an α- hydrogen. As we know from the structures of benzaldehyde and acetaldehyde; benzaldehyde has no α- hydrogens whereas acetaldehyde has 3 α- hydrogens.

Does Fehling’s solution react with aldehyde?

The reaction requires heating of aldehyde with Fehling’s Reagent which will result in the formation of a reddish-brown colour precipitate. Hence, the reaction results in the formation of carboxylate anion. However, aromatic aldehydes do not react to Fehling’s Test. Moreover, ketones do not undergo this reaction.

Which gives positive Fehling’s solution test?

The Glucose structure has an aldehyde group and due to which it gives a positive test for Fehling’s solution. Thus, the right answer is (B) Glucose.

What reacts with Fehling’s solution?

Fehling’s solution is a solution used to differentiate between water soluble aldehyde and ketone functional groups. The substance to be tested is heated together with Fehling’s solution; a red precipitate indicates the presence of an aldehyde. Ketones (except alpha hydroxy ketones) do not react.

Which is not give Fehling test?

Fehling’s test is a chemical test, basically used to differentiate aldehyde and ketone functional groups. … Out of all the given options, only sucrose will not give a positive test as it is a disaccharide and does not contain free aldehyde or ketone group, the rest three sugars will give positive test.

Which does not give Fehling Solution?

Aldehydes such as benzaldehyde, lack alpha hydrogens and cannot form an enolate and thus do not give a positive test with Fehling’s solution which is comparatively a weaker oxidizing agent than Tollen’s reagent, under usual conditions.

Which does not give Fehling’s solution test?

Ketones apart from alpha-hydroxy-ketones do not give positive Fehling’s test as they are not oxidized easily. Aldose monosaccharides and ketose monosaccharides both give positive Fehling’s test. Presence of glucose in urine can be determined using Fehling’s test. It helps to know whether the person is diabetic or not.

What is the action of hydroxylamine on acetaldehyde?

We have to know that the reaction between acetaldehyde with hydroxylamine is. condensation reaction. In this reaction, a molecule of acetaldehyde is condensed with hydroxylamine to form Acetaldoxime. As this reaction is a condensation reaction, a molecule of water is eliminated.

Which among the following does not give red precipitate with Fehling’s solution?

Because acetone require stronger oxidizing agent and hence not oxidized with Fehling solution to give brick red ppt.

What happens when I acetaldehyde reacts with Fehling Solution II acetic acid reacts with phosphorus pentachloride?

i) When acetaldehyde is heated with Fehling’s solution than a red precipitation is formed. ii) When acetic acid is heated with phosphorus pentachloride than acetyl chloride is obtained and in this reaction -COOH is converted into -COCL group.

Why ketones do not give Fehling test?

The copper(II) complex in Fehling’s solution is an oxidizing agent and the active reagent in the test. … Ketone does not react with the Fehling’s solution unless they are alpha-hydroxy ketones. Acetone is not alpha-hydroxy ketone so it will also not reduce the Fehling’s solution.


Does Pivaldehyde give Fehling’s test?

Aldehydes that lack alpha hydrogens, such as benzaldehyde or pivalaldehyde (2,2-dimethylpropanal) cannot form an enolate and thus do not give a positive Fehling’s test result under usual conditions.

Why aromatic aldehydes do not give Fehling’s test?

In aromatic aldehydes, the -CHO group is attached to a benzene ring. Due to resonance, carbonyl group’s C acquires a double bond character with the benzene which is very strong to break. The oxidizing agents like Cu2+ are unable to break that bond, so such aldehydes are unable to show fehling’s test.

Which aldehyde does not react with Fehling solution?

Which of the following compound does not react with Fehling’s solution? Aromatic aldehyde i.e., C6H5CHO are not able to reduce Fehling solution but it gives Cannizaros reaction with alkali.

Why is Fehling solution used?

Fehling’s solution is a chemical reagent used to differentiate between water-soluble carbohydrate and ketone functional groups, and as a test for reducing sugars and non-reducing sugars, supplementary to the Tollens’ reagent test.

Which test is not given by aldehydes?

Aromatic aldehydes do not respond to Fehling’s test. An aqueous solution of the compound may be used instead of an alcoholic solution. Formic acid also give this test.

Is lactose positive in Fehling’s test?

Likewise, some disaccharides such as maltose and lactose contain a hemiacetal. They are also reducing sugars that give a positive Fehlings, Benedict, or Tollens test (picture of lactose positive test is further below).

Does starch give a positive Fehling test?

Positive Fehling’s test: reddish brown ppt ( glucose, fructose, lactose) Negative Fehling’s test: No red ppt (sucrose, starch)

Which sugar does not reduce Fehling solution?

The reason why sucrose is a non-reducing sugar is that it has no free aldehydes or keto group. Additionally its anomeric carbon is not free and can’t easily open up its structure to react with other molecules.

What is the formula of Fehling solution?

Typically, the L-tartrate salt is used. The deep blue active ingredient in Fehling’s solution is the bis(tartrate) complex of Cu 2+. The net reaction between an aldehyde and the copper(II) ions in Fehling’s solution may be written as: RCHO + 2 Cu 2+ + 5 OH → RCOO + Cu 2O + 3 H 2O.

How does glucose react with Fehling’s solution?

The reducing sugar, when treated with Fehling’s solution, forms a precipitate. This is because reducing sugar has a free aldehyde or ketone group. The formula of glucose is CH2OH(CHOH)4CHO. So, when the glucose reacts with Fehling’s solution it forms red ppt and gluconic acid.

Why ketones do not react tollens?

Tollens’ reagent oxidizes an aldehyde into the corresponding carboxylic acid. Ketones are not oxidized by Tollens’ reagent, so the treatment of a ketone with Tollens’ reagent in a glass test tube does not result in a silver mirror (Figure 1; right).

Can ketones reduce Fehling’s solution?

Generally, a ketone does not reduces Tollen’s reagent and Fehling’s solution.