Chemistry for Health Sciences II Lectures 12-13 Term 3, 2024 PDF

Chemistry for Health Sciences II Two credits Term 3, 2024 King Saud bin Abdulaziz University for Health Sciences (Lectures 12-13) Objectives: At the end of these lectures, students should be able to: Write IUPAC names for alcohols, phenols, ethers, epoxides, and thiols. Write structural formulas for...

Chemistry for Health Sciences II Two credits Term 3, 2024 King Saud bin Abdulaziz University for Health Sciences (Lectures 12-13) Objectives: At the end of these lectures, students should be able to: Write IUPAC names for alcohols, phenols, ethers, epoxides, and thiols. Write structural formulas for the above functional groups. Explain the physical properties (boiling point & solubility) of the above functional groups. Identify and classify primary, secondary and tertiary alcohols. Recognize the medical uses of alcohols. Recognize and write the reactions to prepare alcohols (i.e. hydration of alkenes, hydrogenation of aldehydes/ketones). Recognize and write the reactions of alcohols (i.e. dehydration based on Zaitsev's Rule and oxidation reactions). Alcohols: Structure and Physical Properties An organic compound containing a hydroxyl group attached to an alkyl group Alcohols have the general formula R-OH H H H H OH H Physical Properties of Alcohols Hydroxyl group is polar Hydrogen Bonds are intermolecular forces working between different molecules – High boiling points relative to their molar masses due to ability to hydrogen bond A hydrogen bond is a dipole-dipole attraction between hydrogen atom of one molecule which is bonded to another strong electronegative atom (N, O, S etc..) of the other molecule in a polar bond. CH3CH2CH2OH CH3CH2CH2CH3 b.p. = 97.2oC b.p. = -0.5oC Alcohols have higher boiling points than hydrocarbons of comparable M.W. because of Hydrogen Bonding between different alcohol molecules Alcohols are soluble in water because of Hydrogen Bonding between alcohol and water Physical Properties of Alcohols In homologous series, as MW increases b.p. increases, but solubility in water decreases. Alcohol Classification Alcohols: Nomenclature IUPAC: based on the longest chain containing the OH carbon The -e of the alkane name is replaced with -ol The chain is numbered from the end giving the -OH carbon the lower number The name is prefixed with the number indicating the position of the OH group Alcohol has priority over multiple bonds, halogens, and alkyl groups. For cyclic alcohols, the OH is at C-1 IUPAC Name of Alcohols CH3 CH3 CH CH CH3 OH 1. Name the parent compound – 4 carbons = butane 2. Replace the –e with –ol = butanol 3. Number the parent chain to minimize number of carbon with the –OH group = number from right to left 4. Identify, name, and number all substituents = methyl on C-3 3-methyl-2-butanol IUPAC Name of Alcohols CH3 CH3CH2OH Ethanol (Ethyl alcohol) CH3CCH2CH2CH3 OH 2-Methyl-2-pentanol CH3CHCH2CH2CH2CH3 OH 2-Hexanol HO Br 2 3 1 H3C 5 4 CH3 3-bromo-2-pentanol IUPAC Name of Alcohols 1. Determine longest chain with OH Blue chain is longer; however, Red chain contains OH 6 5 4 3 2 1 CH3CH2CH2CH2CHCH2OH C CH2CH2CH3 1 2 2-propyl-1-hexanol 3 C Write IUPAC Name of Cyclic Alcohol CH3 OH 1. Name the parent compound – 6 carbon ring = cyclohexane 2. Replace the –e with –ol = cyclohexanol 3. Number the ring to minimize number of carbon with the –OH group = number counterclockwise 4. Identify, name, and number all substituents = methyl on C-3 3-Methylcyclohexanol OH must be at C-1 Common Names of Alcohols CH3 CH3 C CH3 OH t-butyl alcohol CH3 CH CH3 OH isopropyl alcohol The common names for alcohols consist of the alkyl cycloalkyl group name or , a space, and the word alcohol Examples OH OH 2 3 4 5 1 6 Cyclohexanol 2,3-dimethyl-1-cyclohexanol 2,3-dimethylcyclohexanol H3C OH 2 3 4 5 1 6 CH3 3-ethyl-5-methyl-1-cyclohexanol 3-ethyl-5-methylcyclohexanol Phenol More Examples H CH2OH OH phenylmethanol (benzyl alcohol) CH2 CHCH2OH 2-propen-1-ol (allyl alcohol) cyclohexanol (cyclohexyl alcohol) Name the following alcohols by the IUPAC system: You do it H OH OH ClCH2CH2OH Organic Chem. Hart-Chap. 7 14 Examples Write a structural formula for the following: You do it 3-penten-2-ol cyclobutanol 3-bromopropanol The hydroxyl group is named as a substituent when it occurs in the same molecule with carboxylic acid, aldehyde, or ketone functionalities, which have priority in naming. Examples are: CHO OH CO2H But OH OH m-hydroxybenzoic acid p-hydroxybenzaldehyde NO2 p-nitrophenol (not p-hydroxynitrobenzene) Organic Chem. Hart-Chap. 7 16 Medically Important Alcohols Methanol – Colorless and odorless liquid – Used as a solvent – Toxic, can cause blindness and death if ingested – Can be used as a fuel CH3 OH Ethanol An odorless and colorless liquid Widely used as a solvent The alcohol in alcoholic beverages – Derived from fermentation of carbohydrates – Beverage produced varies with the starting material and the fermentation process 2-Propanol (Isopropyl alcohol) Colorless, but has a slight odor Commonly called rubbing alcohol Toxic when ingested Used as a: – Disinfectant – Astringent – Industrial solvent CH3 CH CH3 OH 1,2-Ethanediol (Ethylene glycol) Used as automobile antifreeze Has a sweet taste, but is extremely poisonous Added to water – Lowers the freezing point – Raises the boiling point CH2 CH2 OH OH Reactions Involving Alcohols Preparation of Alcohols Hydration – Addition of water to the carbon-carbon double bond of an alkene produces an alcohol – Requires a trace of acid as a catalyst Preparation of Alcohols Hydrogenation – Addition of hydrogen to the carbon-oxygen double bond of an aldehyde or ketone produces an alcohol – A type of addition reaction – Also considered a reduction reaction – Requires Pt, Pd, or Ni as a catalyst Dehydration of Alcohols Alcohols dehydrate with heat in the presence of strong acid to produce alkenes Dehydration is a type of elimination reaction – A molecule loses atoms or ions from its structure – Here –OH and –H are removed / eliminate from adjacent carbon atoms to produce an alkene and water – A reversal of the hydration reaction that forms alcohols Copyright © 2017 McGraw-Hill Education. Permission required for reproduction or display Dehydration of Alcohols to Alkenes Alcohols can be dehydrated by heating them with a strong acid. H2SO4 CH3CH2OH OH H2C 160°C H2SO4 CH2 + H2O + H2O 140°C (79-87%) 24 Dehydration of Alcohols to Alkenes CH3 H3C C H3C OH H2SO4 C heat CH3 H3C CH2 + H2O (82%) 25 Zaitsev’s Rule Some alcohol dehydration reactions produce a mixture of products Zaitsev’s rule states that in an elimination reaction the alkene with the greatest number of alkyl groups on the double bonded carbon is the major product of the reaction Predict the Product of Dehydration What are the major and minor products when 3methyl-2-butanol is dehydrated? – Zaitsev’s rule states that in an elimination reaction the alkene with the greatest number of alkyl groups on the double bonded carbon is the major product of the reaction Examples: Zaitsev’s Rule 28 Oxidation of Alcohols  Remember, we distinguish three types of alcohols: R R R CH2 OH CH OH R' 10 R C R 20 OH 30 Dehydrogenation (oxidation) is possible for 10 and 20 only leading to aldehydes and ketones, respectively. O R O R H aldehyde R' ketone 29 Oxidation of Alcohols 30 Strong Oxidizing Agents: CrO3/H2SO4 (Jone’s reagent) O - Mild Oxidizing Agent: O Pyridinium chlorochromate HO Cr OH (PCC) O H O Cr Cl N O PCC 31 Oxidation of Alcohols Primary alcohols usually oxidize to carboxylic acids – The symbol [O] represents an oxidizing agent (KMnO4 or H2CrO4) which is used to oxidize a 1o alcohol to carboxylic acid H R C OH H O [O] R C OH The oxidizing agent (pyridinum chlorochromate; PCC) which is used to oxidize a 1o alcohol to an aldehyde H R C OH O PCC R C H H PCC is a more selective oxidizing agent. Oxidation can be stopped at the aldehyde level. O CH3(CH2)6CH2OH PCC CH2Cl2, 25 oC CH3(CH2)6C H octanal 1-octanol PCC is prepared by dissolving CrO3 in hydrochloric acid and then adding pyridine, shown below: CrO3 + HCl + N pyridine N+ H CrO3Cl- pyridinium chlorochromate (PCC) 34 Using any of the Oxidizing agents (KMnO4, H2CrO4 or PCC), Secondary alcohols oxidize to ketones – This reaction is also an elimination of 2H Tertiary Alcohols Do Not Undergo Oxidation Reactions Tertiary alcohols do not oxidize as there is no H on the carbonyl carbon to remove Organic Oxidation and Reduction In organic systems changes may be tracked: Oxidation: – gain of oxygen – loss of hydrogen Reduction: – loss of oxygen – gain of hydrogen Examples: Oxidation Reactions H OH CrO3 H+, acetone (Jones' reagent) cyclohexanol CH3(CH2)6CH2OH 1-octanol O cyclohexanone Jones' reagent CH3(CH2)6CO2H octanoic acid 38 Phenol Phenols are compounds in which the hydroxyl group is attached to a benzene ring – Polar compounds due to the hydroxyl group – Simpler phenols are somewhat water soluble – Components of flavorings and fragrances Phenols have the formula Ar-OH – Ar must be an aromatic ring (e.g., Benzene) Although alcohols and phenols have same functional group, they have some different properties because of the aromaticity of phenol. I. Acid catalysis will break the C-OH bond in alcohol.However, this bond is difficult to break in phenols. CH3 H3C CH3 C O+ CH3 H O+ H H3C C+ t-butyl cation H + H2O CH3 + H a phenyl cation + H2O II. Since Acidity of alcohol is weaker than phenol, treatment of Alcohols with sodium hydroxide does not covert them to their alkoxides. This is because alkoxides are stronger bases than hydroxide Phenols, however, can be converted to phenoxide ions more easily. RO H + NaOH // - RO Na+ + H2O alcohol OH phenol + NaOH - O Na+ + H2O sodium phenoxide Since the resonance stabilization of the phenolate conjugate base is much greater than the stabilization of phenol itself, the acidity of phenol (aromatic alcohol) relative to aliphatic alcohol is increased. Alternatively, aliphatic alcohol can react with stronger base such as sodium hydride or metal as Potassium to form alkoxide ions RO + 2K H alcohol RO H + NaH sodium hydride - 2 RO K+ + potassium alkoxide H2 - RO Na+ + H2 sodium alkoxide Write the equation for the reaction of t-butyl alcohol with potassium metal. CH3 CH3 2 H3C C OH CH3 t-butyl alcohol + 2K 2 H3C - C O K+ + H2 CH3 potassium t-butoxide NOTE: Refer to the same information in Chapter 20, Ethers slide 12 42 Write an equation for the reaction, if any, between. p-Nitrophenol and aqueous potassium hydroxide. Cyclohexanol and aqueous potassium hydroxide. O2N OH + KOH p-nitrophenol - O K+ O2N + H2O potassium p-nitrophenoxide OH + KOH No Rxn cyclohexanol Organic Chem. Hart-Chap. 7 43 Naming Thiols Write the IUPAC name for the thiols shown Thiols and Scent Thiols, as many other sulfur-containing compounds can have nauseating aromas – Defensive spray of North American striped skunk – Onions and garlic Compare with pleasant scents below Disulfide Formation The thiol-disulfide redox pair controls a critical factor in protein structure called a disulfide bridge – Two cysteine molecules (amino acids) can undergo oxidation to form cystine – Forms a new bond called a disulfide bond Copyright © 2017 McGraw-Hill Education. Permission required for reproduction or display