Aldehydes and ketones are two important classes of organic compounds which are widely used in the synthesis of a variety of other organic compounds. Due to the polarity of the carbonyl group, they undergo nucleophilic addition reactions. Broadly speaking, these addition reactions are of two types- one in which simply the addition of the nucleophilic reagent occurs across \(>C=O\) bond and the other in which addition is followed by the elimination of a molecule of water. A number of ammonia derivatives such as hydroxylamine, hydrazine, phenylhydrazine, 2,4-dinitrophenylhydrazine, and semicarbazide belong to the second category of reactions. These derivatives are used for the identification and characterization of aldehydes/ketones. Both types of nucleophilic addition reactions are influenced by steric and electronic factors. In general, aliphatic aldehydes are more aromatic aldehydes. The aliphatic aldehydes reduce both Fehling's solution and Tollen's reagent but aromatic aldehydes reduce only Tollen's reagent. Like aldehydes, aromatic ketones are less reactive than aliphatic ketones towards nucleophilic addition reactions.

Phenols and carboxylic acids are acidic in nature. Both dissolve in \(NaOH\) solution and turn blue litmus red. However carboxylic acids are much stronger acids than phenols and decompose \(NaHCO_3\) with the evolution of \(CO_2\) but phenols do not. Both electron-donating and electron-withdrawing substituents influence the acid strength of aliphatic as well as aromatic acids. Unlike all other aliphatic acids, formic acid has reducing properties and also does not show reactions of the alkyl group.

Structure of Brady's reagent is ______.

The correct answer is 2.

Brady's reagent, also known as 2,4-dinitrophenylhydrazine (DNPH), is a chemical reagent used to identify and characterize carbonyl compounds, particularly aldehydes and ketones. It is a red-orange solid that is typically dissolved in a mixture of methanol and sulfuric acid to form a solution.

When an aldehyde or ketone is added to Brady's reagent, a condensation reaction occurs, resulting in the formation of a dinitrophenylhydrazone. Dinitrophenylhydrazones are typically colorful solids with well-defined melting points, which can be used to identify the specific carbonyl compound.

Applications of Brady's Reagent

Brady's reagent is a valuable tool for organic chemists due to its simplicity, sensitivity, and selectivity. It is commonly used in qualitative analysis to identify the presence of carbonyl groups in organic compounds. It can also be used to quantitatively determine the concentration of carbonyl compounds in a mixture.

Here are some specific applications of Brady's reagent:

1. Identification of aldehydes and ketones: Brady's reagent can be used to distinguish between aldehydes and ketones based on the color of the dinitrophenylhydrazone formed. Aldehydes typically form yellow or orange dinitrophenylhydrazones, while ketones form red or orange-red dinitrophenylhydrazones.
2. Characterization of carbonyl compounds: The melting point of the dinitrophenylhydrazone formed with Brady's reagent can be used to identify the specific carbonyl compound. Each carbonyl compound has a unique melting point for its dinitrophenylhydrazone derivative.
3. Determination of carbonyl concentration: Brady's reagent can be used to quantitatively determine the concentration of carbonyl compounds in a mixture by spectrophotometry. The absorbance of the solution containing the dinitrophenylhydrazone is measured, and the concentration of the carbonyl compound is determined using a calibration curve.

Safety Precautions

Brady's reagent is a hazardous substance and should be handled with care. It is flammable, toxic, and can cause skin irritation. When working with Brady's reagent, it is important to wear appropriate personal protective equipment, including gloves, goggles, and a lab coat.

In summary, Brady's reagent is a versatile and valuable tool for organic chemists, providing a simple and effective method for identifying and characterizing carbonyl compounds. Its applications range from qualitative analysis to quantitative determination of carbonyl concentrations. However, due to its hazardous nature, it is essential to handle Brady's reagent with care and follow proper safety precautions.