Lecture 4 IUK107 Alcohol Ether Phenol PDF

Alcohol, Ether & Phenol Mohamad Shazeli Che Zain, PhD Alcohol Alcohols have general formula: CnH2n+1 OH The –OH is functional group for alcohol. When –OH group is directly connected with the benzene ring is called phenol. The old name of benzene is “phene” So the name became...

Alcohol, Ether & Phenol Mohamad Shazeli Che Zain, PhD Alcohol Alcohols have general formula: CnH2n+1 OH The –OH is functional group for alcohol. When –OH group is directly connected with the benzene ring is called phenol. The old name of benzene is “phene” So the name became phene + ol = phenol  Alcohols contain an OH group connected to a a saturated C (sp3) Phenols contain an OH group connected to a carbon in a benzene ring Structure of alcohol The functional group of an alcohol is an - OH (hydroxyl) group bonded to sp3- hybridized carbon. The oxygen atom of an alcohol is also sp3 hybridized. Two sp3 hybrid orbitals of oxygen form s bonds to atoms of carbon and hydrogen, and the remaining two sp3 hybrid orbitals each contain an unshared pair of electrons. A Lewis structure and a ball-and-stick model of methanol, CH3OH bond angle 108.9°, very close to the perfectly tetrahedral angle of 109.5°. Nomenclature of alcohol Step 1: Locate the longest chain that contain as –OH group attached to one of the carbon atoms. Name the parent alkane. Step 2: Replace the –e at the end of the name of the parent alkane with –ol. Step 3: Add a position number before the root of the name to indicate the location of the –OH groups. Nomenclature of alcohol Step 4: if there is more than one –OH group, leave the –e in the name of the parent alkane, and put the appropriate prefix (di-, tri- or tetra-) before the suffix –ol. Step 5: Name and number any other branches on the main chain. Add the name of these branches to the prefix. Put the name together: prefix+root+suffix. Physical properties of alcohol Alcohol consists of: a non-polar (alkane-like) chain a polar hydroxyl group Thus, alcohols might be water-soluble, or not (it depending on the length of the carbon chain). Physical properties of alcohol We learned that boiling points of the alkanes increase with increasing chain length. The same is true for alcohols. Alcohols with more than one hydroxyl group (polyhydroxy alcohols) have higher boiling points than monohydroxy alcohols. Hydroxyl groups are very polar because of significantly different electronegativities. Hydrogen bonding can form between alcohol molecules. Physical properties of alcohol The reason for the difference of boiling points of almost equal molecular weight compounds. The water-solubility of alcohols depends on the length of the alkyl chain in the alcohol. Monohydroxy alcohols having chains longer than three carbons are not very water-soluble. Physical properties of alcohol Polyhydroxy alcohols are more soluble because they have more opportunities for hydrogen-bonding with water. Alcohols have higher boiling points than alkanes of the same chain length (because they hydrogen bond to each other; the intermolecular forces for alkanes are only London forces). Alcohols of a given chain length are far more water-soluble than alkanes. Hydrogen bonding Hydrogen bonding is a strong intermolecular attraction between the hydrogen atom from an N-H, O-H, or F-H group on one molecule, and a nitrogen, oxygen, or fluorine atom on another molecule. Other forces of attraction The attractive forces between polar molecules are called dipole-dipole interactions. These forces cause polar molecules to cling to each other. Dispersion forces or London forces are attractive forces resulting from mutual and complementary polarization that occur between the covalent molecules. These forces are usually very weak for small molecules, but they strengthen as the size of the molecule increase. Types of alcohol Alcohols are classified into three types: Alcohols can be classified as primary (1°), secondary (2°), or tertiary (3°) depending on the number of alkyl groups attached to the carbon bearing the –OH group. Primary alcohols Secondary alcohols Tertiary alcohols Synthesis of alcohol from alkene ACID-CATALYZED HYDRATION OF ALKENES Water adds to alkenes in the presence of an acid catalyst following Markovnikov’s rule Because rearrangements often occur, the acid-catalyzed hydration of alkenes has limited usefulness as a laboratory method Synthesis of alcohol from alkene OXYMERCURATION-DEMERCURATION Alkenes react with Hg(OAc)2 in a mixture of THF and water to produce (hydroxyalkyl)mercury compounds The (hydroxyalkyl)mercury compounds can be reduced to alcohols with NaBH4. Oxymercuration-demercuration is highly regioselective (favor bond formation at particular atom) Synthesis of alcohol from alkene HYDROBORATION-OXIDATION Addition of the elements of water to a double bond can be achieved through hydroboration, followed by oxidation and hydrolysis of the organoboron intermediate to an alcohol and boric acid. Synthesis of alcohol From alkyl halide: Alkyl halides are hydrolyzed to the corresponding alcohols on boiling with aqueous alkali (NaOH or KOH) or moist silver oxide (Ag2O). Synthesis of alcohol Reduction of aldehydes & ketones: The aldehydes and ketone compounds are best reduced by complex metal hydrides, such as lithium aluminum hydride (LiAlH4) or sodium borohydride (NaBH4). Reaction of alcohols Two general classes of reaction At the carbon of the C–O bond At the proton of the O–H bond Reaction of alcohols Reaction of alcohol with sodium (Na) metals: If a small piece of sodium is dropped into ethanol, it reacts steadily to give off bubbles of hydrogen gas and leaves a colorless solution of sodium ethoxide. The anion component is an alkoxide. Reaction of alcohols Dehydration of alcohols: Alcohols undergo dehydration (lose of water) when heating with concentrated sulfuric acid or phosphoric acid. Reaction of alcohols Oxidation of alcohols: Primary and secondary alcohols can be oxidized to aldehydes and ketones, respectively. Tertiary alcohols are not oxidized. Can be accomplished by inorganic reagents, such as KMnO4, CrO3, and Na2Cr2O7 or by more selective, expensive reagents Reaction of alcohols OXIDATION OF PRIMARY ALCOHOLS To aldehyde: pyridinium chlorochromate (PCC, C5H6NCrO3Cl) in dichloromethane. Other reagents produce carboxylic acids Reaction of alcohols OXIDATION OF SECONDARY ALCOHOLS Effective with inexpensive reagents such as Na2Cr2O7 in acetic acid PCC is used for sensitive alcohols at lower temperatures Reaction of alcohols Esterification of alcohols: Alcohol react with carboxylic acid and produce ester. Ether any of a class of organic compounds characterized by an oxygen atom bonded to two alkyl or aryl groups. Nomenclature of ether Simply lists (in alphabetical order) both groups that are attached to the oxygen atom and adds the word ether. Nomenclature of ether IUPAC substitutive names are used for more complicated ethers and for compounds with more than one ether linkage Ethers are named as alkoxyalkanes, alkoxyalkenes, and alkoxyarenes. The RO– group is an alkoxy group Cyclic ethers Physical properties of alcohol & ether Alcohols have much higher b.p. than comparable ethers or hydrocarbons. The molecules of alcohols can associate with each other through hydrogen bonding, whereas those of ethers and hydrocarbons cannot. Physical properties of alcohol & ether Ethers have boiling points that are comparable with those of hydrocarbons of the same molecular weight. Ethers are able to form hydrogen bonds with compounds such as water. Synthesis of ether ETHERS BY INTERMOLECULAR DEHYDRATION OF ALCOHOLS Dehydration to an ether usually takes place at a lower temperature than dehydration to an alkene. Et2O is the predominant product at 140°C; ethane is the major product at 180°C Synthesis of ether THE WILLIAMSON SYNTHESIS OF ETHERS Reaction of ether A. Dialkyl ethers react with very few reagents other than acids. Reactive sites of a dialkyl ether: C–H bonds and –O– group. Ethers resist attack by nucleophiles and by bases. The lack of reactivity, coupled with the ability of ethers to solvate cations makes ethers especially useful as solvents for many reactions. Reaction of ether B. The oxygen of the ether linkage makes ethers basic ⇒ Ethers can react with proton donors to form oxonium salts. Reaction of ether C. Heating dialkyl ethers with very strong acids (HI, HBr, and H2SO4) cleaves the ether linkage: Reaction of ether Hydrolysis of epoxide Epoxides are cyclic ethers with three- membered rings (IUPAC: oxiranes). Phenol Phenol Phenols are compounds in which the hydroxyl group is attached directly to a benzene ring. They are polar compounds because of the polar hydroxyl group. Phenols are found in fragrances and flavourings and are also used as preservatives and germicides. Phenol Not exactly the same as alcohols because the lone pair on oxygen and the ring p system are in conjugation Increases the electron density in the ring activating it towards electrophilic substitution (ortho and para positions) Also decreases the bond strength of O-H making it more acidic than alcohols Nomenclature of phenol Phenols are aromatic compounds that bear a OH groups. IUPAC naming of phenol: hydroxyl groups have higher priority than CH3 groups (or other groups) for ring- numbering. “Phenol”= phenyl alcohol Common names Physical properties of phenol Simplest phenols are liquid or low melting points solids, because of hydrogen bonding phenols have quite high boiling points. Low molecular weight phenols are somewhat soluble in water (9 g per 100 g water), because of hydrogen bonding with water. High molecular weight phenols are insoluble in water. Phenols are colorless, but easily oxidized during purification, unless carefully purified. Due to oxidation some color may be appeared in phenol. Hydrogen bonding in phenol Intra-molecular hydrogen bonding: when the hydrogen bonding takes place within the single molecules. Hydrogen bonding in phenol Inter-molecular hydrogen bonding: when the hydrogen bonding takes place with neighbouring molecules. Effect of hydrogen bonding Compared to meta-and para-nitrophenols, ortho nitrophenols have much lower boiling point and much lower solubility in water. This is because of intermolecular hydrogen bonding and intramolecular hydrogen bonding in the nitrophenol molecules. Synthesis of phenol Diazonium salts react with water to yield phenols: This reaction takes place slowly in the ice-cold solutions of diazonium salts. Reaction of phenol Phenol are weak acid in water, Acidity of phenols plays important role in ionization of phenol into phenoxide ion (Ar-O-), which have full-fledged negative charge, is even more strongly electron releasing than the – OH groups. The most striking chemical property of a phenol is the extremely high reactivity of its ring towards electrophilic substitution reactions. Reaction of phenol Williamson synthesis: phenols can be converted into ethers by reaction in alkaline solutions with alkyl halides. Reaction of phenol Reaction with bromine: Treatment of phenols with aqueous solutions of bromine results in replacement of every hydrogen ortho or para to the –OH group. Application Methanol (CH3OH) Common names: methyl alcohol or wood alcohol Usage: common solvent used in perfumes, other smelly stuff, important industrial starting material. Toxicity: Dangerous if ingested, it can cause blindness and death Appearance: colorless and odourless liquid. Methanol production: made by heating wood in the absence of air -destructive distillation Preparation of alcohol from carbon monoxide: Ethanol (CH3CH2OH) Common names: ethyl alcohol, grain alcohol Uses: common solvent in flavours & medicines. Industrial starting materials. Found in alcoholic beverages. Toxicity: can be ingested at low levels. Appearance: colorless and odourless liquid. Ethanol production: Fermentation - action of yeast on sugar, a waste product of yeast metabolism, complex biochemical process Lab preparation of ethanol from ethene: dil. acid can be used as catalyst Bakelite Phenol and formaldehyde used to prepare first polymeric product called bakelite. Polymers Alcohols and phenols can also be used to prepare new compounds such as plastics, coatings, adhesives, medicines etc. Diols/polyols are important in the synthesis of polymers including alkyd, polyesters, polyurethanes, polyamides etc. Ethers Medicine: Ether was first used as a surgical anesthetic in 1842. It's also used as an antiseptic to disinfect skin before injections. However, ether is highly flammable and has been largely replaced by safer anesthetics. Solvent: Ether is a solvent for many substances, including fats, oils, waxes, perfumes, resins, dyes, gums, and hydrocarbons. Starting fluid: Ether is used as a volatile starting fluid for diesel and gasoline engines in cold weather. Ethers Refrigerant: Ether is used as a refrigerant. Insecticides, miticides, and fumigants: Vapors of certain ethers are used as insecticides, miticides, and fumigants for soil. Flavoring agents: Ethers are used as flavoring agents. Perfumery: Ethers are used in perfumery. Smokeless gunpowder: Ether is used in the manufacture of smokeless gunpowder. Find the functional groups Thank You FOR YOUR ATTENTION [email protected]