Chapter 14 Alcohols, Phenols, and Ethers

Transcription

1 Chapter 14 Alcohols, Phenols, and Ethers Homework- 8, 12, 20, 34, 36, 42, 46, 58, 74, Bonding Characteristics of Oxygen Atoms in Organic Compounds Already seen that Carbon forms 4 bonds and Hydrogen 1 bond Oxygen in organic compounds normally forms 2 bonds 2 single bonds 1 double bond 1

2 14.2 Structural Characteristics of Alcohols An alcohol is an organic compound in which an OH group is bonded to a saturated carbon atom The functional group of OH is called a hydroxyl group Looked at as structural derivatives of water Same bent shape around the oxygen atom 14.3 Nomenclature for Alcohols Common names exist for alcohols with simple alkyl groups Name of alkyl group + alcohol Isopropyl alcohol, Butyl alcohol. Propyl alcohol 2

3 14.3 Nomenclature for Alcohols IUPAC rules for naming alcohols (single OH) Name the longest chain to which the hydroxyl group is attached Name the chain by dropping the e from the alkane name and add suffix ol Number the chain starting at the end nearest the hydroxyl group and use the appropriate number to indicate the position of the OH Alcohols take precedence of numbering over double and triple bonds as well as halogens Name and locate any other substituents In alcohols where the OH is attached to a carbon atom in a ring, the hydroxyl group is assumed to be on carbon 1 3

4 14.3 Nomenclature for Alcohols Name the following alcohols 14.3 Nomenclature for Alcohols Polyhydroxy alcohols, alcohols with more than 1 OH, can be named with only a slight modification to the IUPAC rules -ol of alcohol name is substituted with alternate ending 2 OH s is a diol 2 OH s is a triol Etc 4

5 14.4 Isomerism for Alcohols Alcohols can have structural and positional isomers Structural if C is moved Positional if OH is moved Ex C 4 H 9 OH 14.5 Important Commonly Encounter Alcohols Methanol Sometimes called wood alcohols from early preparation methods Current method of preparation CO + 2 H 2 CH 3 OH Good for fuel internal combustion engines Good solvent Paints, shellacs, varnishes Toxic, in liver produces formaldehyde (causes blindness) and formic acid (causes acidosis of blood) 1 oz can cause optic nerve damage 5

6 14.5 Important Commonly Encounter Alcohols Ethanol Ethanol is the alcohol found in beverages Produced by fermentation of yeast Yeasts can grow in the presence of up to only about 14% alcohol, but the concentration of alcohol in the final product can be increased by distillation. To produce absolute ethanol a small amount of benzene is added and the mixture is again fractionally distilled. The resulting ethanol is water free, for processes that require it. However, several ppm of benzene remains, so consumption by humans leads to distinctive liver damage Important Commonly Encounter Alcohols Ethanol (cont) Used in industry as solvent (perfumes, paints and in chemical reactions) Made from petroleum feedstocks, typically by the catalytic hydration of ethylene with sulfuric acid as catalyst. This process is cheaper than the production by fermentation. CH 2 =CH 2 +H 2 O CH 3 CH 2 OH Ethanol for industrial use is normally made unfit for human consumption ("denatured") by the inclusion of small amounts of substances that are either toxic (such as methanol) or unpleasant (such as denatonium). Ethanol is used as a fuel (often mixed with gasoline) and in a wide variety of industrial processes. Used in antifreeze products for its low melting point. A solution of 70-85% of ethanol is commonly used as a disinfectant. It kills organisms by denaturing their proteins and dissolving their lipids and is effective against most bacteria and fungi, and many viruses. 6

7 14.5 Important Commonly Encounter Alcohols Isopropyl Alcohol 70% ipa - 30%water solution is rubbing alcohol Good as a disinfectant Bitter taste Toxicity twice that of Ethanol Poisoning can occur through skin absorption, oral ingestion, or inhalation Symptoms from ingestion, inhalation or absorption of large quantities (>150mL) include flushing, headache, dizziness, mental depression, nausea, vomiting, anesthesia, and coma. Few fatalities b/c vomiting keeps much of the alcohol from getting into the system 7

8 14.5 Important Commonly Encounter Alcohols Ethylene Glycol & Propylene Glycol Two simplest diols, also glycols A glycol is a diol in which the 2 OH s are on adjacent carbon atoms Colorless, odorless, high boiling pt liquids Year-round antifreeze, airplane de-icers Starting material for polyester fibers Ethylene Glycol is Extremely toxic Metabolizes to oxalic acid which crystallizes in kidneys and causes renal damage Propylene Glycol is essentially nontoxic Metabolized to pyruvic acid a chemical normally found in the body Used as solvent for many drugs 14.5 Important Commonly Encounter Alcohols Glycerol Contains 3 hydroxyl groups Clear, thick liquid Part of human fat metabolism Biological Antifreeze Used in lubrication High affinity for water Used in soaps and skin lotions Used in candies and icings to prevent sugar crystallization 8

9 14.6 Physical Properties of Alcohols Alcohol molecules have both polar and nonpolar character Physical properties of an alcohol depend on whether the polar or nonpolar portion dominates Depends upon the length of the chain and number of OH s 14.6 Physical Properties of Alcohols Boiling points For terminal alcohols the boiling point increases as the length of the chain increases Increasing London Forces Alcohols with more than 1 OH have significantly higher boiling points than their monohydroxy counterparts Increased hydrogen bonding Branching effects alcohol boiling points in the same manner as in Hydrocarbons Water solubility Small monohydroxy alcohols are soluble in water C>3 solubility rapidly decreases for monohydroxy alcohols Diols and triols are more soluble than monohydroxyl alcohols Increased hydrogen bonding with water 9

10 14.6 Physical Properties of Alcohols Hydrogen Bonding of Alcohols Alcohols have Higher boiling points than their alkane counterpart Alcohols have Much Higher solubility in water than their alkane counterpart Difference is due to hydrogen bonding More interactions therefore more energy needed Alcohols H-Bond w/ themselves Alcohols H-Bond w/ water 14.7 Preparation of Alcohols The general method for preparing alcohols is the Markovnikov addition of water to an alkene An addition method is the addition of H 2 to a carbonyl group (C=O) 10

11 14.8 Classification of Alcohols Alcohols are classified based on the type of carbon the OH is attached to Reactions of Alcohols Alcohols can undergo many reactions we will only look at 4 Combustion Dehydration Oxidation Halogenation Combustion- A reaction of an alcohol with oxygen to form carbon dioxide and water CH 3 CH 2 OH + 3 O 2 2 CO H 2 O 11

12 14.9 Reactions of Alcohols Dehydration- A reaction in which the components of water (H & OH) are removed from a single reactant or 2 reactants (H from one & OH from another) Alcohol dehydration is an intramolecular dehydration both H & OH removed from one molecule An example of an elimination reaction, a reaction in which 2 groups or 2 atoms on neighboring carbon atoms are removed, or eliminated, from a molecule, leaving a multiple bond between the carbon atoms 14.9 Reactions of Alcohols Dehydration of an alcohol can sometimes result in more than one alkene product Follow Zaitsev s Rule The major product in an intramolecular dehydration reaction is the alkene that has the greatest number of alkyl groups attached to the carbon atoms of the double bond 12

13 14.9 Reactions of Alcohols Intermolecular dehydration can also occur Occurs when reaction is carries out at a lower temperature Still have loss of water Only occurs with a primary alcohol Called a Condensation Reaction- A reaction in which 2 molecules combine to form a larger one while liberating a small molecule, usually water 14.9 Reactions of Alcohols Oxidation A carbon atom in an organic cmpd is considered oxidized if it loses H s or gains O s in a redox reaction A carbon atom in an organic cmpd is considered reduced if it loses O s or gains H s in a redox reaction Opposite processes Some alcohols readily undergo oxidation while others do not Depends upon the type of alcohol Primary and Secondary alcohols readily undergo oxidations by mild oxidizing reagents but tertiary alcohols do not 13

14 14.9 Reactions of Alcohols Mild Oxidation reagents include (Oxidize 1º & 2º alcohols) Potassium Permanganate (KMnO 4 ) Potassium Dichromate (K 2 Cr 2 O 7 ) Chromic Acid (H 2 CrO 4 ) The net product of oxidation varies depending upon type of alcohol oxidized and the extent of oxidation Primary Alcohol- aldehyde of carboxylic acid Secondary Alcohol- ketone Tertiary Alcohol- No product 14.9 Reactions of Alcohols General oxidation reactions of 1 and 2 alcohols 14

15 14.9 Reactions of Alcohols Halogenation In an alcohol halogenation reaction a halogen atom is substituted for the OH producing an alkyl halide Unlike halogenation of an alkane this reaction only produces 1 product Preferred method of halogenation Can be performed with Cl or Br 3 R-OH + PX 3 + heat 3 R-X + H 3 PO 3 15

16 14.11 Structural Characteristics of Phenols A phenol is an organic compound in which an OH group is attached to a carbon atom that is part of an aromatic carbon ring system Generic formula for a phenol is Ar-OH where Ar stands for aryl group (the benzene ring) Nomenclature for Phenols Phenol is an IUPAC approved name Rules for naming phenol are very close to that of naming benzene derivatives -OH always at position 1 Ortho, meta, and para still used 16

17 14.13 Physical and Chemical Properties of Phenols Phenols are low-melting solids or oily liquids at room temp Only slightly soluble in water Weak acidic properties Ar-OH + H 2 O H 3 O + + Ar-O - (phenoxide ion) Most Physical properties are different to those of alcohols Both Flammable Do NOT undergo dehydration reaction Cannot be oxidized with mild oxidizing agents (can be with stronger agents) Both undergo halogenation reactions Have antiseptic (living) and disinfectant (inanimate) properties Occurrence and Uses for Phenols 2% solutions of phenol are used as antiseptics Used in mouthwashes and throat lozenges Chloroseptic/Sucrets Concentrated phenol causes skin burns Carcinogen Lysol contains a phenol derivative for disinfecting 17

18 14.14 Occurrence and Uses for Phenols Some phenols also possess antioxidant activity An antioxidant is a substance that protects other substances from being oxidized by being oxidized itself in preference to the other substance Used on foods as BHT and BHA Vitamin E is a natural phenolic antioxidant Occurrence and Uses for Phenols Many phenols are also used as flavoring agents and/or antibacterial agents as well as cause adverse effects 18

19 14.15 Structural Characteristics of Ethers An ether is an organic compound in which an oxygen atom is bonded to 2 carbons atoms by single bonds General Formula R 1 - O-R 2 where R can be any alkyl or aryl group, but not a Hydrogen Similar to water H-O-H in shape Structural Characteristics of Ethers Alcohols and ethers with the same number of carbon atoms and the same degree of saturation are structural isomers. 19

20 14.16 Nomenclature for Ethers Common names for ethers are formed by naming the 2 hydrocarbon groups attached to the oxygen atom and adding the word ether When both groups are the same di- prefix is used Ethyl Methyl Ether Nomenclature for Ethers In the IUPAC nomenclature system ethers are named as substituted hydrocarbons The smaller hydrocarbon chain and the oxygen are called an alkoxy group, an are considered a substituent on the larger hydrocarbon chain An alkoxy group is an OR group, an alkyl (or aryl) group attached to an oxygen atom 20

21 14.16 Nomenclature for Ethers IUPAC steps for naming an ether are Select the longest carbon chain and use its name as the base name Change the yl ending of the other hydrocarbon group to oxy to obtain the alkoxy group name Place the alkoxy name, with a locator number, in front of the base chain name Nomenclature for Ethers Name the following ethers 21

22 14.16 Nomenclature for Ethers MTBE, Methyl tert-butyl ether Used in gasoline to raise octane levels since 1979 Now being used in larger amounts so that the fuel is cleaner burning But MTBE is making its way into water supply from car emissions Choice clean air or clean water? Physical and Chemical Characteristics of Ethers Boiling points of ethers are similar to those of alkanes but much lower than those of alcohols Due to the absence of Hydrogen bonding between ether molecules Ethers are more soluble than alkanes in water b/c they can H-bond with water 22

23 14.18 Physical and Chemical Characteristics of Ethers Ethers are very flammable Ethers react slowly with air to form unstable hydroperoxides Hydroperoxides represent an explosion hazard therefore extra care must be taken when using older supplies of ethers Ethers are unreactive towards acids, bases, and oxidizing agents but do undergo halogenation reactions Prepared by the intermolecular dehydration of a primary alcohol Cyclic Ethers Cyclic ethers contain ether functional groups within a ring system Cyclic ethers are examples of heterocyclic organic compounds A heterocyclic organic compound is a cyclic organic compound in which 1 or more of the carbon atoms in the ring have been replaced with atoms of other elements Normally O or N 23

24 14.20 Sulfur Analogs of Alcohols Many organic compounds containing oxygen have sulfur analogs S and O in same group of periodic table therefore have similar electron configurations and properties A thiol is the sulfur analog of an alcohol contain sulfhydryl groups A sulfhydryl group is the SH functional group A thiol is an organic compound in which a sulfhydryl group is present Older term for thiols is mercaptans General structure of R-SH Sulfur Analogs of Alcohols Important properties of thiols are low boiling points and a strong disagreeable odor The smell of a skunk is that of a thiol Thiols are also the source of odors and smells of many foods as well Can form disulfide bonds H-S-S-H Important in proteins Reversible 24

25 14.21 Sulfur Analogs of Ethers Sulfur analogs of ethers also exist A thioether is an organic compound in which a sulfur atom is bonded to 2 carbons atoms by single bonds General formula R 1 -S-R 2 Also have strong characteristic odors 25