Mdm Rohazita Bahari ERT 102 Organic Chemistry 2017 2018 Alcohols & Ethers Mdm Rohazita Bahari ERT 102 Organic Chemistry 2017 2018

Alcohols & Ethers Alcohols and ethers are organic derivatives of water where one or both H atoms are replaced by R groups. H-O-H  R-O-H  R-O-R’ Water Alcohol Ether

Alcohols Functional group is -OH, the hydroxyl group, bonded to a tetrahedral carbon Nomenclature Rules Same as for Alkenes and Alkynes except you only drop the -e, and add -ol! propane propanol

Nomenclature of Alcohols 1) Select the longest chain that contains the carbon bonded to the -OH group, and number the chain to give the carbon bonded to the -OH group the lowest number The -OH group takes precedence over alkyl groups, double bonds, triple bonds, and halogens!!!

Nomenclature of Alcohols 2) Change the suffix by dropping the -e, and adding -ol. Use the number to show location. In cycloalkanes, start numbering from the carbon bonded to the -OH. 3) Name and number substituents and list them in alphabetical order.

Naming Alcohols 1. The parent chain must contain the –OH group. Change parent ending to “-ol”. 2. Give the –OH the lowest possible number. 6,6-dimethyl-3-heptanol

Alcohol Nomenclature 1º methanol methyl alcohol ethanol ethyl alcohol 3º 2º 2-propanol isopropyl alcohol 2-methyl-2-propanol tert-butyl alcohol

OH > C=C > R, X 4-methyl-2-pentanol 4-chloro-2-methyl-2-pentanol 2,6-dichloro-4-methyl-4-octanol

OH > C=C > R, X 4-penten-2-ol 5-chloro-3-hexen-2-ol 3-chloro-2-ethyl-2-buten-1-ol

Naming Alcohols 3. When the –OH group is attached to a ring, it is assumed to be at carbon #1. 2-methylcyclopentanol (NOT 2-methyl-1-cyclopentanol)

Classification We classify alcohols as 1o, 2o, and 3o, depending on the classification of the carbon they are bonded to.

Multiple -OH’s present Molecules with 2 -OH’s are named as diols Molecules with 3 -OH’s are named as triols (Note: you do not drop the -e when using diol, triol, etc) Compounds with 2 -OH’s are refered to as glycols

Physical Properties of Alcohols The most important physical property is their polarity Both the C-O bond and the O-H bond are polar covalent bonds Thus alcohols are polar molecules They also have the ability to hydrogen bond. These factors lead to higher B.P’s, M.P’s. etc

Physical Properties of Alcohols Because of increase London forces (van der Waals forces) between larger molecules, the B.P. of all types of compounds, including alcohols, increase as molecular weight increases Alcohols are much more soluble in H2O due to their H-bonding capacity. As MW increases, the water solubility of alcohols decreases This is because the hydrocarbon portion of the molecule dominates.

Reactions of Alcohols Acidity of Alcohols -Alcohols are considerably weaker acids than carboxylic acids, but can lose their hydrogen in an acid-base reaction.

Methanol Methanol was once prepared by the destructive distillation of wood. Wood alcohol. Toxic, causes blindness in low doses (15 mL). Routinely used as a solvent and starting material. Methanol used by the chemical industry is prepared by the catalytic reduction of carbon monoxide. CO + 2 H2 CH3OH 250°C Cu/ZnO/Al2O3

Ethanol H2C=CH2 + H2O CH3CH2OH Prepared by the fermentation of grains and sugars. Grain alcohol. Used in alcoholic beverages. The largest single use of ethanol is as a motor fuel and fuel additive (replaces MTBE). 5 billion gallons are prepared (primarily from corn) annually in the U.S. for fuel uses. Ethanol used by the chemical industry is prepared by the acid-catalyzed hydration of ethylene. H2C=CH2 + H2O CH3CH2OH 250°C H3PO4

The Polar -OH Group The physical properties of the alcohols are strongly influenced by the polar -OH group. Electrostatic Potential Map Negatively polarized oxygen Methanol Neutral methyl group Positively polarized hydrogen

Boiling Points The polar -OH group allows hydrogen bonding to take place in alcohols. These strong intermolecular forces result in higher than expected boiling points. - + CH3CH2CH2OH CH3CH2Cl CH3CH2CH2CH3 Compound MW (g/mol) BP (°C) 58 -0.5 65 12.5 60 97

Ethers Structure- functional group is a Oxygen bonded to 2 carbons Simplest ether is dimethyl ether

Nomenclature of Ethers The common naming system is used for simple ethers: List the alkyl groups bonded to the oxygen in alphabetical order, followed by the work “ether”.

Ether Nomenclature diethyl ether ethyl methyl ether cyclohexyl methyl ether cyclooctyl ethyl ether

Crown Ethers Large rings consisting repeating (-OCH2CH2-) or similar units Named as x-crown-y x is the total number of atoms in the ring y is the number of oxygen atoms 18-crown-6 ether: 18-membered ring containing 6 oxygens atoms Central cavity is electronegative and attracts cations

18-Crown-6

Uses of Crown Ethers Complexes between crown ethers and ionic salts are soluble in nonpolar organic solvents Creates reagents that are free of water that have useful properties Inorganic salts dissolve in organic solvents leaving the anion unassociated, enhancing reactivity

Physical Properties of Ethers Ethers are polar compounds The oxygen has a partial minus charge, the carbons bonded to the oxygen have a partial positive charge Ether have very weak intermolecular forces which results in low boiling points

Electrostatic Potential Map Negatively polarized oxygen The Ethers Ethers lack the polar -OH group and therefore do not have hydrogen bonding. Electrostatic Potential Map Diethyl ether Negatively polarized oxygen Neutral ethyl group Neutral ethyl group

Reactions of Ethers Like alkanes, they are resistant to most chemical reactions Therefore, they are ideal to use as solvents

Diethyl Ether 2 CH3CH2OH CH3CH2OCH2CH3 + H2O Was once widely used as an anesthetic. Highly flammable. Presently used as a solvent. Prepared by the sulfuric acid-catalyzed dehydration of ethanol. 2 CH3CH2OH CH3CH2OCH2CH3 + H2O H2SO4

Boiling Points Ethers have weak intermolecular forces, which results in low boiling points. Low molecular weight ethers are highly volatile. CH3CH2CH2CH2OH CH3OCH3 Compound MW (g/mol) BP (°C) CH3CH2OH CH3CH2OCH2CH3 46 78.5 46 -25 74 117.2 74 34.5

Alcohols & Ethers Alcohols and ethers have very different chemical and physical properties. This is due to the polar -OH group that’s present in alcohols but absent in ethers. ROR’ ROH Compound BP Polarity Hydrogen-Bonding? Reactive? Uses starting materials polar yes high yes non-polar no low no solvents

Reactions: OXIDATION & REDUCTION ALCOHOL Reactions: OXIDATION & REDUCTION

Basic need to know Type of alcohol What is carbonyl group Oxidation Reduction

Type of alcohol PRIMARY ALCOHOL SECONDARY ALCOHOL TERTIARY ALCOHOL

Carbonyl group Aldehyde Ketone Carboxylic Acid Ester What is carbonyl group? Aldehyde Ketone Carboxylic Acid Ester

oxidation reduction Is the loss of electrons (e-) and loss of hydrogen atom Up charge Is the gain of electrons (e-) and gain of hydrogen atom Reduce charge

A reaction involving electron transfer Called it as redox reaction example: Fe + CuSO4 FeSO4 + Cu

Oxidation-Reduction An oxidation reduction reaction or a redox reaction is one which electron transfer occurs In organic chemistry this tends to have a significance more on par of oxygen content Oxidation reactions as ones in which carbon gains bonds to oxygen Reduction reactions as ones in which carbon atoms lose bonds to oxygen.

oxidation Just to take a look at oxidations. We can oxidize primary or secondary alcohols A tertiary alcohol cannot be oxidized because that carbon cannot already has three bonds to other carbons. So, there are not any bonds that can be replaced to give carbon more bonds to oxygen. It is going to be possible to gain more oxygen here

oxidation For oxidation, we usually used PCC, Pyridinium chlorochromate to get aldehyde for primary alcohols & ketone for secondary alcohols It is a reagent in organic synthesis used primary for oxidation of alcohols. We use Jones oxidation (CrO3 + H2SO4) to get carbocyclic acid for primary alcohols and ketones for secondary alcohols.

reduction Carbonyl compound to alcohol Use different reducing agents and again these have different strengths. Sodium borohydrate (NaBH4) and Lithium aluminum hydride (LiAlH4) LiAlH4 more stronger than NaBH4. NaBH4 only reduce aldehyde and ketones LiAlH4 can reduce aldehyde, ketones including carboxylic acid and ester.

Oxidation and Reduction Carboxylic Acid REDUCTION Aldehyde / Ketone Alcohol Alkane Oxidation: Increase C-O bonds Reduction: Increase C-H bonds

Common Reducing Agents Sodium borohydride (NaBH4) is a mild reducing agent. aldehyde 1º alcohol ketone 2º alcohol

Common Reducing Agents Lithium aluminum hydride (LiAlH4) is a strong reducing agent. carboxylic acid 1º alcohol

Predict the Products

Common Oxidizing Agents Pyridinium chlorochromate (PCC) (C5H6NCrO3Cl) is a mild oxidizing agent. 1º alcohol aldehyde 2º alcohol ketone

Common Oxidizing Agents Chromium trioxide (CrO3) and sodium dichromate (Na2Cr2O7) are strong oxidizing agents. 1º alcohol carboxylic acid 2º alcohol ketone

Predict the Products

The Williamson Ether Synthesis Is the reaction that converts alcohol (R-OH) into ethers (R-O-R). The 1st step in this reaction is forming the conjugate base of the alcohol (called an alcoxide) by reacting the alcohol with sodium metal. This reaction forms hydrogen gas (H2) as a bioproduct.

The Williamson Ether Synthesis R can be 1º, 2º, 3º, or cycloalkyl. 2 ROH + 2 M  2 ROM + H2 alcohol M = Na, K RO- + R’X  ROR’ + X- SN2 alkoxide alkyl halide ether R can be 1º, 2º, 3º, or cycloalkyl. R’ should be methyl or 1º.

Synthesis of Diethyl Ether via the Williamson Synthesis Diethyl ether is a symmetrical ether. 2 CH3CH2OH + 2 Na  2 CH3CH2ONa + H2 ethanol sodium ethoxide CH3CH2O- + CH3CH2I  CH3CH2OCH2CH3 + I- SN2 ethoxide ion ethyl iodide diethyl ether

Synthesis of tert-Butyl Methyl Ether via the Williamson Synthesis tert-Butyl methyl ether is an asymmetrical ether. SN2 + This is the better route nucleophile tert-butyl methyl ether E2 + + base 2-methylpropene