Differentiate primary, secondary and tertiary alcohol by oxidation and dehydrogenations method. It is acidic and dissolve in bases to form salt. Answer: These materials are added so that the ethanol will not be used for beverage purposes. (iii) Ethyl acetate from ethanol Answer: (i) Friedel-Crafts reaction – alkylation of anisole : Anisole undergoes Friedel- Crafts reaction i.e., the alkyl and aryl group is introduced at ortho and para-positions by reaction with alkyl halide and aryl halide in the presence of anhydrous aluminium chloride (Lewis acid) as catalyst. Question 8. Ans: Acid catalysed dehydration of primary alcohols to ethers occurs by SN 2 reaction involving nucleophilic attack by the alcohol molecule on the protonated alcohol molecule. (iv) 1-Methoxyethane Name the primary alcohol which gives iodoform test. (a) Ethyl ether NCERT s olutions for class 12 chemistry chapter 11 Alcohols, Phenols and Ethers - This article covers NCERT solutions for class 12 chemistry chapter 11 Alcohols, Phenols and Ethers. Download NCERT solutions for alcohol phenol and ether part 2 as PDF. Answer: Question 21. This page looks at the mechanism for the acid catalysed dehydration of a simple primary alcohol like ethanol to give an alkene like ethene. Is it a continuous process ? Write the equations for the preparation of phenol using these reagents. Allylic alcohols are (ii) and (vi). Question 5. Why ? Download PDF's. If carbon tetrachloride is used in place of chloroform, salicylic acid is obtained as the main product. Tertiary alcohols tend to be easier to dehydrate and primary alcohols to be the hardest. It can follow either an S N 1 or S N 2 mechanism . The alcohol involved in reaction plays two roles: one alcohol molecule acts as a substrate while the other acts as a nucleophile. The addition of diborane to alkene to form trialkyl boranes followed by their oxidation with alkaline hydrogen peroxide to form alcohol is called hydroboration-oxidation. (i) Diethyl ether from Ethanol: Explain in brief. (i) When ethyl alcohol is heated in excess of cone. The secondary and tertiary alcohol being highly crowded under go dehydration in acid presence to form alkene.Hence, preparing of ethers by acid dehydration of secondary or tertiary is not a suitable method. Answer: The alcohols presented E1 on BPO₄, E2 on Ca₃(PO₄)₂ and E1cB on Sm₂O₃. The boiling point of ethanol is higher than methoxymethane because of the presence of strong intermolecular hydrogen bonding between ethanol molecule. The reactions showing acidic character of phenols are : Phenol on being heated with Zn powder forms ………………. The choice of the mechanism depends on whether the protonated alcohol loses water before or simultaneously upon the attack of a second alcohol molecule. Alcohols, Phenols and Ethers Objective Type Questions. Methylated spirit is 90% ethanol to which nauseating materials like methyl alcohol, pyridine or mineral naphtha have been added. (iii) Pentan-l-ol using a suitable alkyl halide ? Class 12 Chemistry Alcohols Phenols Ethers: Preparation of Alcohols: Preparation of alcohols: It can be prepared by following methods: From Haloalkane: When any haloalkane reacts with aqueous KOH it undergoes nucleophilic substitution and leads to the formation of alcohol and potassium halide . The 1° alcohol gets protonated. (a) Phenol Question 14. When 3-methylbutan-2-ol is treated with HBr, the following reaction takes place: E2 mechanism includes the elimination of a proton and hydroxyl group from alcohol which is concerted without formation of ionic intermediate. (i) Reaction with sodium : Phenol reacts with Na to give H2 gas. The protonation of the hydroxyl group successfully converts the leaving group from hydroxide ion to water. Answer: It works on the counter current principle and the steam and wash travel in opposite directions through the still. The base-catalyzed loss of water from β hydroxy carbonyl compounds is one of the examples of elimination reaction which involves a sp³ hybridized carbon atom that follows the E1cB pathway. (a) C6H5OH The following compound reacts with phthalic acid to give acid-base indicator : (ii) Ethanol from diethyl ether Answer: Answer: Alcohol is ………………. On the other hand ethoxide ion and ethanol do not represent resonance thus negative charge is on oxygen of ethoxide ion whereas charge displacement occur in phenoxide ion. (i) 2,2,4-Trimethyl pentan-3-ol The pyroligneous acid is taken in a copper vessel and distilled. Write the mechanism of acid catalysed dehydration of ethanol to give ethene. (b) Cu/300°C, Question 5. Answer: Methyl alcohol obtained by fractional distillation is about 95% pure. Dehydrate the given alcohol. Describe the laboratory method of preparation of diethyl ether. Or, So, this method is called Williamson continuous etherification process but actually we cannot get ether continuously. The secondary and tertiary alcohol being highly crowded under go dehydration in acid presence to form alkene.Hence, preparing of ethers by acid dehydration of secondary or tertiary is not a suitable method. (b) Reaction with PCl5 In the presence of sulphuric acid, dehydration of ethanol at 443 K gives ethane, and we get ethoxyethane at 413 K. It is the best method to prepare ether with necessary alcohol. HCl and anhydrous ZnCl2. Question 13. On the other hand, hydrocarbons cannot form hydrogen bonds with water molecules and hence are insoluble in water. The acid consumed in step I is released in Step 3. (b) Cone. Reaction of ether with HI is used for the detection of what ? Question 11.1. Resonating structures of p-nitro phenoxide ion. CBSE has reduced the syllabus for class 10 & 12 exam 2021, date sheet can release soon. (i) 1-Propoxypropane Different types of alcohols may dehydrate through a slightly different mechanism pathway. Draw labelled diagram of coffee still. Give equations of the following reactions: 56°C). (ii) Nitration of anisole : Anisole reacts a mixture of concentrated sulphuric and nitric acids to yield a mixture of ortho and para nitroanisole. (iii) Bromination of anisole in ethanoic acid medium. Give chemical equation of the following conversion: (ii) Phenol to Picric acid : Nitration : On nitration, phenols give a variety of products depending upon the conditions. The carbonyl group plays 2 vital roles, helps in stabilizing the transitional carbanion and it gives additional driving force for elimination in giving improved stability to the neighboring product. Answer: Question 25. (iv) Friedel-Craft’s acetylation of anisole : Question 32. (a) Methyl alcohol, Question 17. (d) Ether. (iv) Methyl magnesium bromide → 2-Methylpropan-2-ol. Williamson’s synthesis is reaction of alkyl halide (1°) with sodium alkoxide to give ether by SN2 mechanism. Due to resonance, the oxygen atom gets a positive charge and attracts the electron pair of the O—H bond and thus facilitates the release of a proton. (iii) 2-Methoxy-2-methylpropane (ii) Benzyl chloride → Benzyl alcohol. (i) A primary alcohol is easily oxidized to an aldehyde and then to an acid both containing the same number of carbon atoms as the original alcohol. Answer: H2SO4 gives, 2,4,6-Trinitro-phenol (Picric acid). Lucas reagent is : Answer: Question 9. (iv) Ethanol from glucose. ... Write the mechanism of acid-catalysed dehydration of ethanol to yield ethene. Hence, they are soluble in water. (iii) Ethyl acetate from ethanol In the first step the -OH is protonated to form a protonated alcohol. NCERT Class 12 Chemistry Solutions for Chapter 11 provides an insight into the various concepts related to alcohols, phenols and ethers. Question 8. (d) Salol. The formation of ethers by dehydration of alcohol is a bimolecular reaction (S N 2) involving the attack of an alcohol. (i) By the hydrolysis of Benzene diazonium salts: Benzene diazonium salt is formed by aromatic primary amine (aniline) with nitrous acid at 0-5°C. (ix) Cyclopent-3-en-l- Answer: (iii) A tertiary alcohol is resistant to oxidation in neutral or alkaline solutions but is readily oxidized by an acid oxidizing agent giving a mixture of ketone and acid each having lesser number of carbon atoms than the original alcohol. Question 20. Question 10. MP Board Textbook Solutions for Class 6 to 12. (b) Phenol, Question 12. Dehydration can be performed in a 3 step mechanism: Dehydration of alcohols follows E1 or E2 mechanism. This is an important chapter and hence requires an indepth knowledge of the topics. Ethyl alcohol and phenol both contain — OH group.
... Know here complete details related to WB class 10 and 12 … ... All CBSE Notes for Class 12 Chemistry Maths Notes Physics Notes Biology Notes. They are categorized as SN₂ reactions in primary alcohols and SN₁  reactions in secondary as well as tertiary alcohols. When one of the groups in unsymmetrical ether is tertiary, then the halide formed is tertiary halide. The carbon dioxide is collected as a by product. How is it prepared ? Share Tweet Share Pin itAs the synthesis is normally performed, a solution of the phenol and alkyl halide is simply heated in the presence of a suitable base such as potassium carbonate: The alkyl halide must be one that reacts readily by an S 2 mechanism. An alkene is produced when dehydration of an alcohol is performed. Oxygen donates two electrons to a proton from sulfuric acid H 2 SO 4, forming an alkyloxonium ion. Classify the following as primary, secondary and tertiary alcohols : (ii) Kolbe- Schmidt reaction : When sodium salt of a phenol is heated with CO2 at 130°C. It involves the formation of a carbocation. The alkene formed will give the desired alcohol on adding a molecule of H2O. Question 5. Answer: Question 4. Question 11.1. Describe the manufacture method of methanol by the destructive distillation of wood. Secondary alcohol gets oxidized to ketones and primary are oxidized to carboxylic acids by the chromic acid. (b) Alcohol is lighter than water (ii) It directs the incoming substituents to ortho and para positions in benzene ring. (i) 1-Ethoxy-2-methylpropane The dehydration of ethanol This alkene will give pentan-2-ol as well as pentan-3-ol. Write equations of the following reactions: Explain mechanism?. In the E1cB mechanism, the initial step of dehydration is the formation of carbanion, which means that a C-H bond is broken in the first step. Ether and alcohol can be distinguished by the following : Class 12 Chemistry Alcohols Phenols Ethers: Preparation of Alcohols: Preparation of alcohols: It can be prepared by following methods: From Haloalkane: When any haloalkane reacts with aqueous KOH it undergoes nucleophilic substitution and leads to the formation of alcohol and potassium halide . (i) Phenoxide ion: In the E2 mechanism, there is a different kind of selectivity, anti and syn elimination. Dehydration of primary alcohol: C H 3 − C H 2 − O H 9 5 % H 2 S O 4 4 4 3 K C H 2 = C H 2 + H 2 O Dehydration of secondary alcohol: What are molasses ? Which is formed on heating ethyl alcohol with bleaching powder : Therefore, the formation of carbocation is said to be the rate determining step. (c) Phenyl acetate Here the carbocation gets rearranged if the result is a more stable carbocation. Show how will you synthesis : This shows the reaction goes through the E1 mechanism. 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