Why sulphuric acid not used during the reaction of alcohol with k i

https://chem.libretexts.org/@app/auth/3/login?returnto=https%3A%2F%2Fchem.libretexts.org%2FBookshelves%2FOrganic_Chemistry%2FMap%253A_Organic_Chemistry_(Wade)_Complete_and_Semesters_I_and_II%2FMap%253A_Organic_Chemistry_(Wade)%2F14%253A_Reactions_of_Alcohols%2F14.04%253A_Dehydration_Reactions_of_Alcohols Dehydration of Alcohols to Yield Alkenes One way to synthesize alkenes is by dehydration of alcohols, a process in which alcohols undergo The required range of reaction temperature decreases with increasing substitution of the hydroxy-containing carbon: • 1° alcohols: 170° - 180°C • 2° alcohols: 100°– 140 °C • 3° alcohols: 25°– 80°C If the reaction is not sufficiently heated, the alcohols do not dehydrate to form alkenes, but react with one another to form ethers (e.g., the Alcohols are amphoteric; they can act as both acid or base. The lone pair of electrons on oxygen atom makes the –OH group weakly basic. Oxygen can donate two electrons to an electron-deficient proton. Thus, in the presence of a strong acid, R—OH acts as a base and protonates into the very acidic alkyloxonium ion +OH2 (The pKa value of a tertiary protonated alcohol can go as low as -3.8). This basic characteristic of alcohol is essential for its dehydration reaction with an acid to form alkenes. Mechanism for the Dehydration of Alcohol into Alkene Different types of alcohols may dehydrate through a slightly different mechanism pathway. However, the general idea behind each dehydration reaction is that th...

Q. 4. Account for the following : (i) Sulphuric acid is not used during the reaction of alcohols with KI. (ii) p-methoxybenzyl bromide reacts faster than p-nitrobenzyl bromide with sodium ethoxide to form an ether product. (iii) Organic halogen compounds used as solvents in industry are chlorides rather than bromides and iodides. (iv) Wurtz reaction fails in case of tert-alkyl halides. (v) Alkyl halides are insoluble in water though they contain a polar \( C - X \) bond. (vi) Use of \( CHCl _ \) as anaesthetic is not preferred. asked Jun 3, 2022 in by ( 35 points)

In the presence of sulphuric acid (H2SO4), KI produces HI Since is an oxidizing agent, it oxidizes HI (produced in the reaction to I2). As a result, the reaction between alcohol and HI to produce alkyl iodide cannot occur. Therefore, sulphuric acid is not used during the reaction of alcohols with KI. Instead, a non-oxidizing acid such as H3PO4 is used.

\( \newcommand\) • • • • • • • This page discusses the dehydration of alcohols in the lab to make alkenes—for example, dehydrating ethanol to produce ethene. The dehydration of ethanol to give ethene This is a simple method of making gaseous alkenes such as ethene. If ethanol vapor is passed over heated aluminum oxide powder, the ethanol is essentially cracked to yield ethene and water vapor. To produce a few test tubes of ethene, the following apparatus can be used: This system can be scaled up by boiling ethanol in a flask and passing the vapor over aluminum oxide that is heated in a long tube. Dehydration of alcohols using an acid catalyst The acid catalysts normally used in alcohol dehydration are either concentrated sulfuric acid or concentrated phosphoric(V) acid, H 3PO 4. Concentrated sulfuric acid produces messy results. Because sulfuric acid is also a strong oxidizing agent, it oxidizes some of the alcohol to carbon dioxide and is simultaneously reduced itself to sulfur dioxide. Both of these gases must be removed from the alkene. Sulfuric acid also reacts with the alcohol to produce a mass of carbon. There are other side reactions as well (not discussed here). The dehydration of ethanol to yield ethene In this process, ethanol is heated with an excess of concentrated sulfuric acid at a temperature of 170°C. The gases produced are passed through a sodium hydroxide solution to remove the carbon dioxide and sulfur dioxide produced from side reactions. The ethene is ...