Write a notes on fermentation. (i) Reimer-Tiemann reaction : When phenol is treated with chloroform in presence of aqueous sodium hydroxide at 60°C, o-Hydroxy benzaldehyde (Salicylaldehyde) and p-Hydroxy benzaldehyde are formed. The syn elimination products are made when the groups are eliminated from the same side of the molecule and anti-elimination products are made when the groups are removed from the opposite side. Reaction of ether with HI is used for the detection of what ? Question 15. Since the rate of skeletal isomerization of isobutene to n-butene is comparatively lower than the rate of formation of n-butene in dehydration, the n-butene is a primary product. (ii) The iodide is treated with silver nitrite to form nitroalkane. Dehydration of secondary and tertiary alcohols in acidic conditions follows the E1 method. The pyroligneous acid is taken in a copper vessel and distilled. Answer: Mechanism. (i) 1-Ethoxy-2-methylpropane Most of the steam condenses and the alcohol vapours condenses in the condenser. (iv) 2,3 – Diethylphenol Answer: (ii) What is the reaction of diethyl ether with HI acid ? Answer: (ii) Ethanol from diethyl ether Which is used for poisoning the alcohol: Manufacture of methanol: By the destructive distillation of wood: Dried wood is heated (350°C) in closed retorts for about 3 hours. If a blue colour is obtained, the alcohol is secondary. (c) CO2 H2SO4 gives, 2,4,6-Trinitro-phenol (Picric acid). Pro Lite, Vedantu (d) Cone. When yeast is mixed in glucose solution and kept at proper conditions, ethyl alcohol is formed as a result of fermentation. HCl Or, This is an important chapter and hence requires an indepth knowledge of the topics. Answer: Question 21. From Haloalkanes:-. Class 12 - Chemistry - Alcohols Phenols Ethers. Write mechanism of this reaction. Download PDF's. Question 11. It is a good ferment. Write chemical reaction for the preparation of phenol from chloroben zene. Mechanism : (i) Protonation of alcohol by H 2 SO 4 (ii) Removal of water (iii) Elimination of β-hydrogen in the form of proton by base (bisulphate ion) Secondary alcohol needs about 100⁰C in 75% H₂SO₄ and primary can only be dehydrated at 170⁰C in 95% H₂SO₄ which are under extreme conditions. (ii) Nitration of anisole : Anisole reacts a mixture of concentrated sulphuric and nitric acids to yield a mixture of ortho and para nitroanisole. Purification: Ether contain ethanol, water and sulphuric acid as impurities. This is the old method and is used at present also. C2H5Br + C2H5ONa → C2H5OC2H5 + NaBr (Hint : The secondary carbocation formed in step-II rearranges to a more stable tertiary carbocation by a hydride ion shift from 3rd carbon atom.) Answer: (b) Ethyl alcohol This mixture is subjected to fractional distillation to separate methyl alcohol (b.p. When a relatively stable carbocation is produced by dehydration of a protonated alcohol an E1 elimination can take place. Question 23. This is an important chapter and hence requires an indepth knowledge of the topics. (i) 2-Methylbutan-2-ol Dehydration is an elimination reaction of an alcohol involves the loss of an OH from one carbon and an H from an adjacent carbon. Question 2. (b) Hydrogen bond 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. Question 7. Phenol is more acidic than ethanol. (d) p – nitrophenol. Match the following : (a) Alcohol has higher density than water (a) Phenol Step-II: Nucleophilic attack by water on carbo-cation to yield protonated alcohol. The dehydration process of both secondary and tertiary alcohols involves the formation of a product called the carbocation intermediate. The dehydration of alcohol series done by Thomke over BPO ₄, Ca ₃ (PO ₄) ₂ and Sm ₂ O ₃ determined the mechanism by 2 precise criteria, uptake of deuterium from deuterated catalysts into produced olefin and un-reacted alcohol. Diethyl ether does not reacts with Na. 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. (a) Phenyl benzoate Predict the major product of acid catalysed dehydration of: Dehydration is mainly easy when a neighboring double bond is formed. (c) With SOCl2 : Both the alcohols react with SOCl2 to give corresponding alkyl chlorides. In other words, we can say that the C2H5OH molecules are in associated form due to H-bonding so the b.p. (xi) 1-Phenoxyheptane Answer: Write the reactions of Williamson synthesis of 2-ethoxy-3-methylpentane starting from ethanol and 3-methylpentan-2-oI. Write the mechanism of acid dehydration of ethanol to yield ethene. (ii) Ethanol from Diethyl ether : HCl and anhydrous ZnCl2. Answer: Question 10. Question 15. Answer: HNO3 in presence of conc. Resonating structures of p-nitro phenoxide ion. Question 31. In alcohols, no resonance is possible hence the hydrogen atom is more firmly linked to the oxygen. Alcohols can be produced from Alkenes by their Hydration, by passing alkenes through concentrated H 2 SO 4 and then hydrolysis with boiling water gives alcohols.. Answer: Give chemical equation of the following conversion : Understand the Dehydration of Alcohols with E1, E2 Mechanism i.e. Question 20. (b) CH3-OH (ii) Aryl halides and vinyl halides cannot be used as substrate for the preparation of aromatic aliphatic ether because aryl halide and vinyl halides are less reactive towards nucleophilic substitution reaction. The primary alcohols follow the E2 mechanism for elimination reaction while the E1 mechanism is followed by secondary and tertiary alcohols. Primary alcohol dehydrates through the E2 mechanism. of alcohol is 78.4°C and b.p. Alcohol is ………………. whereas phenol is of ………………. From Alkenes:-. Which compound is known as oil of winter green : The 1° alcohol gets protonated. The dehydration of either a tertiary or secondary alcohol is known as an E1 reaction (two-step mechanism), the dehydration of primary alcohol is an E2 (one step mechanism) reaction because of the difficulty encountered in forming primary carbocations. It is acidic and dissolve in bases to form salt. What is the reason that phenol is acidic and alcohol has alkaline effect ? (i) Phenol to Tribromophenol : Phenols readily react with halogens to give polyhalogen substituted compounds. According to Saytzeff rule, the highly substituted product is the major product. Step-III: Deprotonation (loss of proton) to form an alcohol: Question 12. Secondary alcohols lose hydrogen and yield a ketone. (i) Reimer-Tiemann reaction Write name of the enzyme which converts maltose to glucose. (ii) Cyclohexylmethanol using an alkyl halide by an SN2 reaction ? Since, the rate determining step is the formation of carbocation, the ease of dehydration is. (b) Phenyl benzoate It is then washed with water, dried over anhydrous calcium chloride and redistilled. Question 16. (d) Salol. Answer: Stability of the carbocation (I) determines the case of dehydration and order of stability of carbocation is : Answer: Explain, why ortho nitrophenol is more acidic than ortho methoxyphenol ? (ii) 2,5-Dimethyl hexane-1,3-diol. The steps are explained as follows. Question From class 12 Chapter ALCOHOLS, PHENOLS AND ETHERS Give a mechanism for the acid-catalysed dehydration of ethyl alcohol to form diethyl ether. As a result, the incoming substituents are directed to the ortho and para positions in the benzene ring. It is because alkoxides are not only nucleophile but strong bases as well. (ii) Removal of water, (iii) Elimination of β-hydrogen in the form of proton by base (bisulphate ion) The dehydrogenation of alcohol accompanied the dehydration of alcohol over some basic oxides. (c) Reaction with 2,4 dinitrophenyl hydrazine (d) None of these. Generally, it follows a three-step mechanism. Question 6. of alcohol are higher than ethers and alkene ? Answer: For dehydration to take place, the alcohol must be heated to roughly 50⁰C in 5% H₂SO₄. They react with alkyl halide leading to elimination reaction. Give two reactions that show the acidic nature of phenol. For dehydration to take place, the alcohol must be heated to roughly 50, and primary can only be dehydrated at 170. which are under extreme conditions. In this step, the C-O bond breaks which generate a carbocation. Answer: Question 17. In case dehydration of the given alcohol gives two alkenes, then see which alkene will give the desired alcohol. (i) 1°, (ii) 1°, (iii) 1°, (iv) 2°, (v) 2°, (vi) 3°. (a) With ZnCl2-HCl (Lucas reagent) : Butan-l-ol (1° alcohol) does not react with Lucas reagent at room temperature. Mechanism of dehydration of alcohol. Download PDF. Alkenes are formed from alcohol by the dehydration process.Alcohols undergo elimination reaction mechanism (E1 or E2) to form alkenes.This occurs by heating alcohols in the presence of strong acid, for example, H2SO4 at high temperatures. Thus, it is less acidic than o-nitrophenol. In most of the dehydration of alcohol, heat and catalyze are needed in the reaction. 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