Dear learners of Class 12, today we are going to discuss chapter 13 Amin's part 4. After this discussion, you will be able to understand the Dizonium salts, describe the method of preparation of Dizonium salts, explain their importance in the synthesis of a series of aromatic compounds, including azodiz. Dizonium salts are one of the most reactive derivatives of aromatic primary amines, but are quite unstable in nature. Primary aliphatic amines form highly unstable alkyl Dizonium salts. Primary aromatic amines form erine Dizonium salts, which are stable for a short time in solution at low temperatures of 273 to 278 Kelvin. The stability of erine Dizonium ion is explained on the basis of resonance. Benzene Dizonium chloride is prepared by the reaction of aniline with nitrous acid at 273 to 278 Kelvin. Nitrous acid is produced in the reaction mixture by the reaction of sodium nitrite with hydrochloric acid. The conversion of primary aromatic amines into Dizonium salts is known as Dizonium salts. Due to its instability, the Dizonium salt is not generally stored. And is used immediately after its preparation. Let us understand the physical properties of the Dizonium salts. Benzene Dizonium chloride is a colorless crystalline solid. It is readily soluble in water and is stable in cold, but reacts with water when warmed. It decomposes easily in the dry state. Benzene Dizonium fluoroborate is water insoluble and stable at room temperature. The reactions of Dizonium salts can be broadly divided into two categories namely reactions involving displacement of nitrogen and reactions involving retention of dye as a group. Let us understand the reactions involving displacement of nitrogen in detail. Dizonium group being a very good leaving group is substituted by other groups such as chloride, bromide, iodide, cyanide and hydroxyl which displaced nitrogen from the aromatic ring. The nitrogen formed escapes from the reaction mixture as a gas. Replace Ben by haline or cyanide iron. The chloride, bromide and cyanide nucleophiles can easily be introduced in the benzene ring in the presence of copper plus iron. This reaction is called Sanmeh reaction. Alternatively chlorine or bromine can also be introduced in the benzene ring by treating the Dizonium salt solution with corresponding halogen acid in the presence of copper powder. This is referred as Gatermann reaction. The yield in Sanmeh reaction is found to be better than Gatermann reaction. Replace Ben by iodide iron. Iodine is not easily introduced into the benzene ring directly but when the Dizonium salt solution is treated with potassium iodide, Ido benzene is formed. Replace Ben by fluoride iron. When erine Dizonium chloride is treated with fluoroboric acid, erine Dizonium fluoroborite is precipitated which on heating decomposes to yield eryloid. Replace Ben by hydrogen. Certain mild reducing agents like hypophosphorus acid, phosphinec acid or ethanol reduce Dizonium salts to erines and themselves get oxidized to phosphorus acid and ethanol respectively. Replace Ben by hydroxyl group. If the temperature of the Dizonium salt solution is allowed to rise up to 283 Kelvin, the salt gets hydrolyzed to phenol. Replace Ben by nitro group. When Dizonium fluoroborite is heated with aqueous sodium nitride solution in the presence of copper, the Dizonium group is replaced by nitro group. Let us understand the reactions involving retention of Dizogrupe and these reactions are known as coupling reactions. The azure products obtained here have an extended conjugate system having both the aromatic rings joined through the nitrogen-nitrogen bond. These compounds are often colored and are used as dyes. Benzine Dizonium chloride reacts with phenol in which the phenol molecule at its para position is coupled with the Dizonium salt to form para hydroxyazobenzine. This type of reaction is known as coupling reaction. Similarly, the reaction of Dizonium salt with aniline yields para amino azobenzine. This is an example of electrophilic substitution reaction. Methylorane is a very useful indicator in acid-based titrations is a product of the coupling reactions. From the reactions discussed, it is clear that the Dizonium salts are very good intermediates for the introduction of fluorides, chlorides, bromides, iodides, cyanides, hydroxyl and nitrogrups onto the aromatic ring. Aryl fluorides and iodides cannot be prepared by direct halogenation. The cyanogrop cannot be introduced by nucleophilic substitution of chlorine in chlorobenzine, but cyanobenzine can be easily obtained from Dizonium salt. Thus, the replacement of diazogrop by other groups is helpful in preparing those substituted aromatic compounds which cannot be prepared by direct substitution in benzene or substituted benzene. To summarize this discussion, let us recall the points discussed. Dizonium salts are formed as a result of carrying diazotization reaction of aniline. Structure of Dizonium salt is supposed to be derived from ammonium salt, such as ammonium chloride by replacing three hydrogen atoms with nitrogen atom and the fourth by a phenyl group. Dizonium salts are highly reactive chemically and are helpful in the synthesis of a large number of aromatic compounds. Benzine diazonium chloride participates in coupling reactions with phenol and aniline under ice cold conditions to form colored compounds known as azodise. Before we end this discussion, let me leave you with an assignment. You are expected to explain the following conversions as mentioned on the screen. Nitrogen benzene into aniline, ethyenoic acid into methenamine, aniline into aniline into methenamine into methenamine, four nitrotoluene into two bromobenzoeic acid. I hope you understood all the concepts discussed in this discussion. Wishing you all happy times ahead, take care, stay safe and stay healthy.