Chem 120 10.4 ALCOHOLS AND PHENOLS

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Chem 120 10.4 ALCOHOLS AND PHENOLS

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Chapter 10.4 ALCOHOLS AND PHENOLS

12.1 Alcohols: Structure and Physical Properties : 

12.1 Alcohols: Structure and Physical Properties An organic compound containing a hydroxyl group attached to an alkyl group Alcohols have the general formula R-OH

Physical Properties : 

Physical Properties R-O-H has a structure similar to that of water Hydroxyl group is very polar Hydrogen bonds can form readily

Alcohol Boiling Points : 

Alcohol Boiling Points Alcohols have abnormally high boiling points relative to their molecular weights due to their ability to hydrogen bond Hydrogen bonds Hydrogen bonds in Ethane

Trends in Alcohol Boiling Points : 

Trends in Alcohol Boiling Points

Solubility : 

Solubility Low molecular weight alcohols (up to 5-6 carbons) are soluble in water Very polar Hydrogen bond with the water molecule CH3CH2OH very soluble CH3OCH3 barely soluble CH3CH2CH2CH2OH, 7 g per 100 mL HOCH2CH2CH2CH2OH is very soluble (two OH groups)

High Molecular Weight Alcohol Solubility : 

High Molecular Weight Alcohol Solubility As molecular weight increases, alcohols become insoluble in water Still polar Ratio of hydroxyl groups to carbons in the chain determines solubility Diols and triols are more soluble than those with only a single hydroxyl group

12.2 Alcohols: Nomenclature : 

12.2 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 For cyclic alcohols, the OH is at C-1

Naming Alcohols : 

Naming Alcohols 3-methyl-2-butanol Name the parent compound – 4 carbons = butane Replace the –e with –ol = butanol Number the parent chain to minimize number of carbon with the –OH group = number from right to left Identify, name, and number all substituents = methyl on C-3

Naming Alcohols : 

Naming Alcohols 3-methylcyclohexanol OH must be at C-1 Name the parent compound – 6 carbon ring = cyclohexane Replace the –e with –ol = cyclohexanol Number the ring to minimize number of carbon with the –OH group = number counterclockwise Identify, name, and number all substituents = methyl on C-3

Common Names of Alcohols : 

Common Names of Alcohols The common names for alcohols consist of the alkyl group name, a space, and the word alcohol t-butyl alcohol isopropyl alcohol

12.3 Medically Important Alcohols : 

12.3 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

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 Ethanol

2-Propanol : 

Colorless, but has a slight odor Commonly called rubbing alcohol Toxic when ingested Used as a: Disinfectant Astringent Industrial solvent 2-Propanol

12.5 Reactions Involving Alcohols : 

12.5 Reactions Involving Alcohols Preparation of Alcohols Hydration Addition of water to the carbon-carbon double bond of an alkene produces an alcohol A type of addition reaction called hydration Requires a trace of acid as a catalyst

1,2-Ethanediol : 

Used as automobile antifreeze Has a sweet taste, but is extremely poisonous Added to water Lowers the freezing point Raises the boiling point 1,2-Ethanediol

1,2,3-Propanetriol : 

Very viscous, thick Has a sweet taste Non-toxic Highly water soluble Used in: Cosmetics Pharmaceuticals Lubricants Obtained as a by-product of fat hydrolysis 1,2,3-Propanetriol

12.4 Classification of Alcohols : 

12.4 Classification of Alcohols Alcohols, depending on the number of alkyl groups attached to the carbinol carbon, are classified as: Primary Secondary Tertiary Carbinol carbon is the carbon bearing the hydroxyl group

Structures of Different Alcohol Categories : 

Structures of Different Alcohol Categories

12.5 Reactions Involving Alcohols : 

12.5 Reactions Involving Alcohols Preparation of Alcohols Hydration Addition of water to the carbon-carbon double bond of an alkene produces an alcohol A type of addition reaction called hydration Requires a trace of acid as a catalyst

Preparation of Alcohols : 

Hydrogenation Addition of water 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 Preparation of Alcohols

Dehydration of Alcohols : 

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

Zaitsev’s Rule : 

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 : 

Predict the Product of Dehydration What are the major and minor products when 3-methyl-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

Oxidation Reaction of Primary Alcohols : 

Oxidation Reaction of Primary Alcohols Primary alcohols usually oxidize to carboxylic acids With some care (using CrO3 as the reagent) an aldehyde may be obtained

Oxidation Reaction of Secondary Alcohols : 

Oxidation Reaction of Secondary Alcohols Secondary alcohols oxidize to ketones This reaction is also an elimination of 2H The usual oxidizing agent is a Cr(VI) species Tertiary alcohols do not oxidize as there is no H on the carbonyl carbon to remove

12.7 Phenol : 

12.7 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)

Phenol Derivatives : 

Phenol Derivatives Widely used in healthcare as: Germicides Antiseptics Disinfectants

Phenol Reactivity : 

Phenol Reactivity Phenols are acidic, but not as acidic as carboxylic acids They react with NaOH to give salt and water

12.8 Ethers : 

12.8 Ethers Ethers have the formula R-O-R R can be aliphatic or aromatic Ethers are slightly polar due to the polar C=O bond Do not hydrogen bond to one another as there are no –OH groups

Ether Physical Properties : 

Ether Physical Properties Ethers have much lower boiling points than alcohols due to the lack of hydrogen bonding

Common Names of Ethers : 

Common Names of Ethers Common names for ethers consist of the names of the two groups attached to the O listed in alphabetical order (or size) and followed by ‘ether’ Each of the three parts is a separate word Name: Isopropyl methyl ether Ethyl phenyl ether

IUPAC Nomenclature of Ethers : 

IUPAC Nomenclature of Ethers The IUPAC names for ethers are based on the alkane name of the longest chain attached to the oxygen The shorter chain is named as an alkoxy substituent Alkane with the -ane replaced by -oxy e.g., CH3CH2O = ethoxy CH3CH2CH2CH2CH2-O-CH3 1-methoxypentane

Reactivity of Ethers : 

Reactivity of Ethers Chemically, ethers are moderately inert Do not normally react with reducing agents or bases Extremely volatile Highly flammable = easily oxidized in air Symmetrical ethers may be prepared by dehydrating two alcohol molecules Requires heat and acid catalyst

Medical Uses of Ethers : 

Medical Uses of Ethers Ethers are often used as anesthetics Accumulate in the lipid material of nerve cells interfering with nerve impulse transmission Today halogenated ethers are used routinely as general anesthetics Less flammable Safer to store and to work with Diethyl ether - First successful general anesthetic Penthrane

12.9 Thiols : 

12.9 Thiols Thiols have the formula R-SH Similar in structure to alcohols with S replacing O Disulfides have the formula R-S-S-R R may be aliphatic or aromatic Name is based on longest alkane chain with the suffix –thiol position indicated by number 3-methy-1-butanethiol

Thiols and Scent : 

Thiols and Scent Thiols, as many other sulfur-containing compounds can have nauseating aromas Defensive spray of skunks Onions and garlic Compare with pleasant scents above

Naming Thiols : 

Naming Thiols

Reaction Schematic : 

Reaction Schematic Alcohol Aldehyde NO REACTION Ketone Dehydration If primary If tertiary If secondary + H+ and heat Alkene Hydration Carbonyl Reduction Oxidation

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