Alcohols, Ether and Epoxide, Lecture notes of Organic Chemistry

Download Alcohols, Ether and Epoxide and more Lecture notes Organic Chemistry in PDF only on Docsity! Alcohols Alcohols contain the -OH functional group. General formula — The first part of the name of an alcohol is according to the longest carbon atom sequence. The second part of the name is -ol. A number will be included to indicate the position of the alcohol group. H H om om °. AN ™ AK a Pentanol or pentan-1-ol Pentan-2-ol 3-methylbutan-2-ol Types of Alcohol There are three types of alcohol; primary, secondary and tertiary. They are classified according o the number of carbon groups attached to the carbon with the OH group. i i Rog Ol R-¢-O-H H-¢-O-H R-¢-O-H H R H H Primary Secondary Tertiary No or one carbon (R) group attached to the carbon with the OH group is a primary alcohol. Two carbon (R) groups attached to the carbon with the OH group is a secondary alcohol. Three carbon (R) groups attached to the carbon with the OH group is a tertiary alcohol. methanol doesn’t have anything attached to the C-atom, so it doesn’t fit the classification. alcohols can be produced from sugarcanes. Physical properties of alcohols The OH group can take part in hydrogen-bonding, both as a donor (H is sufficiently 5+) and as an acceptor (through the two lone pairs on the oxygen atom). As a result alcohols have higher melting and boiling points than hydrocarbons of comparable molar mass. They are also more soluble in water because of H-bonding: ethanol is miscible with water in all proportions. As the non-polar hydrocarbon chain becomes longer, it becomes harder for water to dissolve the alcohol: from C4 alcohols are less soluble, and don’t mix with water. Reactions of Alcohols Combustion All alcohols undergo combustion to form carbon dioxide and water. For example the equation for the combustion of butanol is as follows; CaHsOH + 602 > 4CO2 + 5H20 Reaction with sodium | effervescence is seen All alcohols react with sodium. 2ROH + 2Na > 2RONa + H2 This equation is similar to the reaction of sodium with water, except that an alkoxide is formed rather a hydroxide. e.g. Ethanol and sodium 2C2HsOH + 2Na > 2C2HsONa + H2 Sodium ethoxide Reaction with phosphorus pentachloride All alcohols react with phosphorus pentachloride. This is used as a test for the -OH group. The presence of the OH group can be shown by adding phosphorus pentachloride to the compound. A reaction takes place forming hydrogen chloride which Ont | as 3 white fumes. In the reaction with phosphorus pentachloride a chloro group replaces the -OH group. e.g. Propanol and phosphorus pentachloride CH3sCH2CH20H + PCls > CH3sCH2CH2Cl + POCls + HCl Phosphorus oxychloride Reaction with other halogenating agents Alkyl bromides can be made from the reaction of an alcohol with HBr. HBr is made in situ from KBr and H2SO« forms bromoalkanes during heating under reflux. C2HsOH + HBr > C2HsBr + H20 Alkyl chlorides can be made by refluxing the alcohol with conc. HCl in the presence of ZnCl2 C2HsOH (I) + HCl (g) > C2HsCl (I) + H20 (I) lodoalkanes can be made in a reaction phosporus triiodide from iodine and red phosporus. 3C2HsOH + Pl3 > 3C2Hsl + H3PO3 The relative reactivities of alcohols in halogenation are tertiary > secondary > primary alcohol. E eee Tool Edit Help: Que =" > Oo “a3 2 -|DEr =| rr Z Heat co cwensen ea 2 Loar shape ed Lod al gs 2 O Fig HUR = ¢@ © BG Once the carboxylic has been formed, it needs to be separated from the reaction mixture and other products. This is done by Distillation is used to separate a volatile product from a mixture of involatile substances, or substances that have a boiling point of at least 50°C higher than the component being collected. Heat two miscible liquids can be separated using simple distillation Alcohols and Ethers are common products of nucleophilic substitution reaction. -10- Alcohols, Ethers, & Epoxides Chapter 9 Naming Ethers ¢ Simple ethers are usually assigned common names. To do so: « Name both alkyl groups bonded to the oxygen, arrange these names alphabetically, and add the word ether. ¢« For symmetrical ethers, name the alkyl group and add the prefix “qi-” . " CH3-O-G—CH2CHg CH3CH,—O—CH2CH3 methyl CHg ethyl ethyl sec-butyl diethyl ether sec-butyl methyl ether Alphabetize the b of butyl before the m of methyl. epoxides are heterocylic Naming Epoxides * Epoxides can be named in three different ways: epoxyalkanes, oxiranes, or alkene oxides. C2 \ A A (Po Heo _e1 HoyS CH CH3 H CH3CH3 CHg 1,2-epoxycyclohexane 1,2-epoxy-2-methylpropane cis-2,3-epoxypentane position 2 Number the ring beginning o! O at the O atom. 7\ LA CH3S/\-H 2 3 7 \ CH; H oxirane 2,2-dimethyloxirane O T\ CH,=CH, ———> sC—-C,, Hf 8H ethylene H H ethylene oxide oxirane Preparation of Alchols and Ethers ¢ Alcohols and ethers are both common products of nucleophilic substitution. mewvene CH3,CH,—Br + | “OH CH3CH,CH,—Cl + | “OCH, CH3CH,—Br + | ~OCH,CH3 Sy2 > Sy2 ———- Sy2 —> product | CH3CH»- -OH CH3CH2CH»- -OCH3 CH3CH»- -OCH,CH, alcohol unsymmetrical ether symmetrical ether ¢ The preparation of ethers by the method shown in the last two equations is called the Williamson ether synthesis. Mechanism of Ether Cleavage This bond is cleaved by an mechanism. | Hg buy \ This bond is cleaved by an mechanism. Uses of Alcohol, Ether and Epoxides Uses of alcohol 1. Used as an ingredient in alcoholic beverages e.g. wine and beer 2. Used to produce methylated spirit (meth) |methylated spirit= denatured alcohol Methylated spirit is ethanol mixed with small amounts of methanol, which is poisonous, making it unfit for consumption. Methylated spirit is used as a component of household cleaning products, usually glass contains 10% methanol in ethanol 3. Used asa fuel Ethanol burns cleanly to form carbon dioxide and water. Using ethanol as fuel does not contribute much to pollution. Ethanol is usually mixed with gasoline to produce 'gasohol", which is about 10-20% ethanol. Using ethanol as a fuel reduces our reliance on natural fossil fuels such as petrol. 4. Used as a solvent Ethanol is commonly used as an organic solvent to dissolve organic compounds which are insoluble in water. E.g. used in cosmetics such as perfumes; used in medicines such as disinfectants; used in toiletries such as after-shave lotions Use of ether e Being flammable and volatile it is used in cold weather to start a diesel or petrol engine. It is also used as a refrigerant. e Ethers are used as anantisepticin order to prevent infection when an injection is administered into the body. e A cotton ball is dipped in ether and skin is disinfected before an injection is allowed to pierce the skin. e Diethyl ether is used as an anaesthetic in hospitals. Anesthetics help in making people go to sleep or become unconscious during surgery. Use of epoxides Ethylene epoxide/has many uses including generation of surfactants and detergents. e Epoxy glues and structural materials are a result of epoxides reaction with amines. e It is used as a stabilizer in materials like PVC. They are also used in manufacture of Epoxy resin that has low viscosity and without compromising strength and physical properties. Epoxides are also used in things like insecticides, aerosols, resins and chemical intermediates. Prepared By: Ramisa Anjum