Alcohol Reactions Flashcards

Hydroxy Compounds: Structural and Optical Isomerism

• Structural and optical isomerism in hydroxy compounds should be understood.

Physical Properties of Hydroxy Compounds

• The physical properties of hydroxy compounds should be stated.

Classification of Alcohols

• Alcohols are classified into primary (1°), secondary (2°), and tertiary (3°) alcohols.

Preparation of Alcohols

• Alcohols like ethanol can be prepared from:

  • Fermentation process.

  • Hydration of ethene in industries.

Reactions of Alcohols

• Reactions of alcohols include:

  • Oxidation

  • Dehydration

  • Reaction with Na (sodium)

  • Formation of haloalkanes

  • Esterification

  • Acylation

Tests for Alcohols

• Tests to determine the class and type of alcohols:

  • Lucas test

Uses of Alcohols

• Alcohols are used as:

  • Antiseptic

  • Solvent

  • Fuel

Acidity of Water, Phenol, and Alcohol

• The relative acidity of water, phenol, and alcohol should be explained, with reference to:

  • Inductive effects

  • Resonance effects

Preparation of Phenols

• Phenols can be prepared from the cumene process.

Reactions of Phenols

• Reactions of phenols with:

  • Na (sodium)

  • NaOH (sodium hydroxide)

  • Acyl chloride

  • Electrophilic substitution in the benzene ring

Tests for Phenol

• Tests for phenol include:

  • Bromine water

  • Aqueous iron(III) chloride

Use of Phenol

• Phenol is used in the manufacture of:

  • Cyclohexanol

  • Nylon-6,6

Reactions of Alcohols Overview

• The reactions of alcohols to be discussed include: oxidation, dehydration, reaction with Na, formation of haloalkanes, esterification, and acylation.

Oxidation of Alcohols

• Oxidation products depend on the class of alcohol used (1°, 2°, 3°).

• Oxidation is achieved by treating alcohols with oxidizing agents.

• Common oxidizing agents:

  • Chromic acid (K2Cr2O_7/H+) (orange)

  • Acidified potassium permanganate ($KMnO_4/H^+$) (purple)

  • Pyridinium chlorochromate (PCC)

• Oxidation of 1° alcohol gives aldehyde or RCOOH, depending on experimental conditions.

• Oxidation of 2° alcohol gives ketone.

• 3° alcohols are not easily oxidized (i.e., not oxidized under normal conditions).

Oxidation Reactions

• 1° alcohol oxidation:

  • CH3C(H)2OH$(1° alcohol)$[O] \rightarrow CH3CHO$(aldehyde)$[O] \rightarrow CH3COOH$(carboxylic acid)</p></li></ul></li><li><p>2° alcohol oxidation:</p><ul><li><p>$CH3CH(OH)CH3$(2° alcohol)$[O] \rightarrow CH3C(O)CH3$(ketone)</p></li></ul></li><li><p>3° alcohol oxidation:</p><ul><li><p>$(CH3)3COH$(3° alcohol)$[O] \rightarrow$no reaction</p></li></ul></li></ul><h3 collapsed="false" seolevelmigrated="true">Oxidation with Chromic Acid</h3><ul><li><p>Chromic acid is prepared by dissolving either chromium(VI) oxide ($CrO3$) or potassium dichromate ($K2Cr2O7$) in sulfuric acid ($H2SO4$).</p></li><li><p>It is a strong oxidizing agent that can oxidize 1° alcohol to carboxylic acid.</p></li><li><p>Example:</p><ul><li><p>$CH3(CH2)6CH2OH$$\xrightarrow{K2Cr2O7, H2SO4}$$CH3(CH2)6COOH $</p></li></ul></li></ul><h3 collapsed="false" seolevelmigrated="true">Oxidation with Acidified Potassium Permanganate</h3><ul><li><p>It is a common and cheaper alternative to other oxidizing agents.</p></li><li><p>A strong agent that oxidizes 1° alcohol to carboxylic acid.</p></li><li><p>Example:</p><ul><li><p>$CH3CH2CH2OH$$\xrightarrow{KMnO4, H2SO4}$$CH3CH2COOH$</p></li></ul></li></ul><h3 collapsed="false" seolevelmigrated="true">Oxidation with PCC</h3><ul><li><p>Sarret-Collins reagent is a special oxidizing agent to convert a primary alcohol exclusively into an aldehyde.</p></li><li><p>Is formed when$CrO_3$is added into excess pyridine and is known as PCC.</p></li><li><p>PCC does not oxidize carbon with a double bond.</p></li></ul><h3 collapsed="false" seolevelmigrated="true">Dehydration of Alcohols</h3><ul><li><p>Alcohols are converted into alkenes via elimination reaction where water is eliminated.</p></li><li><p>One molecule of water is eliminated from the adjacent carbon atom.</p></li><li><p>Common dehydrating agents and conditions:</p><ol><li><p>Conc.$H2SO4$, Δ, 180 °C</p></li><li><p>85$H3PO4$, Δ, 350 °C</p></li><li><p>Alumina,$Al2O3, Δ, 350 °C

• The ease of acid-catalyzed dehydration of alcohol is in the order of: 1° < 2° < 3°

• If using dehydrating agents at a lower temperature (140°C), it will give (symmetrical) ethers.

• Alcohols with four or more carbon atoms usually give a mixture of alkenes.

• Follow Zaitsev’s rule to determine the major product: When isomeric alkenes are obtained in an elimination reaction, the alkene having the greater number of substituents on the double bond generally predominates, i.e., alkene with the greater number of alkyl groups attached to –C=C– is the most stable.

• Examples:

  • (i) CH3CH2CH(OH)CH3$$\xrightarrow{Conc. H2SO4, 180°C}$$CH3CH=CHCH3$(2-butene, major product) +$CH3CH2CH=CH2$(1-butene)</p></li><li><p>(ii)$(CH3)2CHCH(OH)CH3$$\xrightarrow{H2SO4, 180°C}$$(CH3)2C=CH2$(2-methyl-1-butene) +$CH3CH=C(CH3)_2$(2-methyl-2-butene, major product)</p></li><li><p>(iii) Cyclohexanol$\xrightarrow{H2SO4, 180°C} 1,2-dimethylcyclohexane (major product)

Reaction with Active Metals

• Due to its acidity, alcohols react with reactive metals such as lithium, sodium, and potassium to liberate hydrogen gas.

• This reaction produces alkoxide ions, which are strong nucleophiles and strong bases, and often needed in synthesis.

• The more acidic the alcohols, like methanol and ethanol, react rapidly with sodium.

• Tertiary alcohols react very slowly with sodium; hence, potassium, which is more reactive, is used to complete the reaction in a convenient amount of time.

Formation of Haloalkanes with Hydrogen Halide (HX)

• Halogen atom substitutes hydroxyl group.

• For the same HX, the reactivity increases in the order of: Phenol (no reaction) < 1° < 2° < 3° < benzyl alcohol

• For example: CH3CH2OH + HBr \rightarrow CH3CH2Br + H_2O$</p></li></ul><h3 collapsed="false" seolevelmigrated="true">Lucas Test</h3><ul><li><p>For the same alcohol, the reactivity increases in the order of:$HCl < HBr < HI$</p></li><li><p>It is a test to differentiate between 1°, 2°, and 3° alcohols based on the difference in reactivity of the classes of alcohols toward$HCl$.</p></li><li><p>The reactions produce haloalkanes, which are insoluble white precipitates.</p></li><li><p>Lucas reagent is prepared by mixing concentrated$HCl$with$ZnCl_2$(catalyst).</p></li><li><p>On treatment with Lucas reagent:</p><ul><li><p>3° alcohol – cloudiness is observed immediately.</p></li><li><p>2° alcohol – cloudiness is observed within 5 to 10 minutes.</p></li><li><p>1° alcohol – no cloudiness is observed after 10 minutes.</p></li></ul></li></ul><h3 collapsed="false" seolevelmigrated="true">Formation of Haloalkanes with Phosphorus Halide (PX)</h3><ul><li><p>A substitution reaction that gives haloalkanes.</p></li><li><p>$PX = PCl3, PCl5, PBr3, PI3$</p></li></ul><h3 collapsed="false" seolevelmigrated="true">Formation of Haloalkanes with Thionyl Chloride (SOCl₂)</h3><ul><li><p>The reaction is carried out in the presence of pyridine.</p></li><li><p>$R-OH + SOCl2 \xrightarrow{pyridine} R-Cl + SO2 + HCl$</p></li><li><p>Example:</p><ul><li><p>Cyclohexanol +$SOCl2 \xrightarrow{pyridine}$Chlorocyclohexane +$SO2 + HCl$</p></li></ul></li></ul><h3 collapsed="false" seolevelmigrated="true">Esterification</h3><ul><li><p>Alcohol reacts with carboxylic acids to form esters and water.</p></li><li><p>Reaction is catalyzed by a strong acid (concentrated sulfuric acid).</p></li><li><p>Alcohol is a nucleophile; carboxylic acid is an electrophile.</p></li><li><p>Need a large excess of the alcohol or the acid to achieve good yield.</p></li><li><p>General equation:</p><ul><li><p>$RCOOH + R'OH \xrightarrow{H^+} RCOOR' + H_2O$</p></li></ul></li><li><p>Examples:</p><ul><li><p>(i)$HCOOH$(methanoic acid) +$CH3CH2OH$(ethanol)$\xrightarrow{H^+}$$HCOOCH2CH3$(ethyl methanoate) +$H_2O$</p></li><li><p>(ii)$CH3COOH$(ethanoic acid) + Cyclohexanol$\xrightarrow{H^+}$Cyclohexyl ethanoate +$H2O$</p></li><li><p>(iii)$(CH3)2CHCOOH$(2-methylpropanoic acid) +$(CH3)2CHOH$(2-propanol)$\xrightarrow{H^+}$$(CH3)2CHCOOCH(CH3)2$(isopropyl 2-methylpropanoate) +$H_2O$</p></li></ul></li></ul><h3 collapsed="false" seolevelmigrated="true">Acylation</h3><ul><li><p>Alcohol reacts with acyl/acid chlorides to form esters and water.</p></li><li><p>A more powerful way to form an ester.</p></li><li><p>An exothermic reaction.</p></li><li><p>General equation:</p><ul><li><p>$R'OH + RCOCl \rightarrow RCOOR' + HCl$$