Denigés' reagent for qualitative analysis

The Denigés' reagent is a reagent used for qualitative analysis.

Denigés' reagent is used to detect isolefin or tertiary alcohols which can be easily dehydrated to form isoolefin in the presence of acid. Treatment of solutions containing either isolefin or tertiary alcohols with this reagent will result in the formation of a solid yellow or red precipitate

How Synthesis Denigés' reagent

Despite the different stoichiometry in these mixtures which varies the concentration of the reagent, they all follow the same idea of adding HgO to distilled water and concentrated sulfuric acid. The Denigés' reagent is ultimately mercury(II) sulfate in an aqueous solution.

• 5 grams of mercury(II) oxide (HgO) is dissolved in 40 mL of distilled water. The mixture is slowly stirred, while 20 mL of concentrated sulfuric acid is added. After adding an additional 40 mL of distilled water, the solution is stirred until the HgO is completely dissolved.

• The Denigés' reagent can also be prepared by dissolving 5 grams of HgO in 20 mL of concentrated sulfuric acid and 100 mL of distilled water.

• The Denigés' reagent can be modified by using nitric acid in place of sulfuric acid

Benedict reagent Benedict's solution Benedict's test

Benedict reagent Benedict's solution Benedict's test

What is Benedict's Reagent?

Benedict's reagent also called Benedict's solution or Benedict's test) is a chemical reagent.

Benedict's reagent is used as a test for the presence of reducing sugars. This includes all monosaccharides and the disaccharides, lactose and maltose.

 Even more generally, Benedict's test will detect the presence of aldehydes (except aromatic ones), and alpha-hydroxy-ketones, including those that occur in certain ketoses. Thus, although the ketose fructose is not strictly a reducing sugar, it is an alpha-hydroxy-ketone, and gives a positive test because it is converted to the aldoses glucose and mannose by the base in the reagent.

The copper sulphate in Benedict's solution reacts with reducing sugars.

One litre of Benedict's reagent can be prepared from 100 g of anhydrous sodium carbonate, 173 g of sodium citrate and 17.3 g of copper(II) sulfate pentahydrate.

It is often used in place of Fehling's solution.

Benedict's reagent contains blue copper(II) ions (Cu²⁺) which are reduced to copper(I) ions (Cu⁺). These are precipitated as red copper(I) oxide which is insoluble in water.

This reagent is used to test for sugars. 
The disacarides (Sucrose, Lactose and Maltose) doesn't give a positive result with just the reagent, but there is a round about method I'm going to show in a future video

Baeyer's reagent

Baeyer's reagent : used in organic chemistry as a qualitative test for the presence of unsaturation, such as double bonds or triple bond .

The bromine test is also able to determine the presence of unsaturation.

Baeyer's reagent is an alkaline solution of potassium permanganate, which is a powerful oxidant Reaction with double or triple bonds (-C=C- or -C≡C-) in an organic material causes the color to fade from purplish-pink to brown.

 It is a syn addition reaction.

 Aldehydes and formic acid (and formic acid esters) also give a positive test

The brown solid manganese(IV) oxide precipitates out of solution when potassium permanganate reacts with a double or triple bond.

Notes : Baeyer's reagent, named after the German organic chemist Adolf von Baeyer