Comprehensive Notes on Alcohols

Alcohols

• Alcohols are organic molecules with a hydroxyl functional group (-OH) attached.

• The -OH group makes alcohols polar; polarity decreases as the carbon chain increases.

• Bartender joke about "OH juice" and wanting dilute ethanol.

Ethanol Production

• Ethanol is produced industrially from ethene, called ‘synthetic ethanol’.

• Used for industrial solvents or cleaners like methylated spirits; generally not for drinking due to being denatured.

• About 20% of ethanol production is synthetic.

Negative effects of synthetic ethanol.

Drinkable Ethanol Production

• Most ethanol is produced by fermentation: microorganisms act on carbohydrates to produce other compounds without oxygen.

• Fermented products include ethanol, cheese, penicillin, ginger beer, and beer.

Breaking it down

• Yeast breaks down carbohydrates.

• Glucose (C6H12O6) passes into the yeast cell and is converted to ethanol (C2H5OH) and carbon dioxide (CO2).

• $C<em>6H</em>{12}O<em>6 \rightarrow C</em>2H<em>5OH + CO</em>2$

Special Conditions for Fermentation

• Temperature: Enzymes function up to about 45°C. Fermentation is exothermic, so the reaction container must be kept cool.

• Acidic Conditions: Slightly acidic conditions are required for optimum yeast performance.
  *Negative effects of bioethanol: High blood pressure, heart disease, stroke, liver disease, and digestive problems. Cancer of the breast, mouth, throat, esophagus, voice box, liver, colon, and rectum. Weakening of the immune system, increasing the chances of getting sick. Learning and memory problems, including dementia and poor school performance. Liver cirrhosis. slurred speech · impaired balance, coordination, vision and reflexes · unstable emotions · nausea and vomiting

• Aqueous and Dilute: Prevents excessive ethanol concentrations that can poison the yeast.

• Anaerobic Conditions: Oxygen converts ethanol to ethanoic acid (vinegar), so it must be excluded.

Classifying Alcohols

• Alcohols are classified based on the number of alkyl groups attached to the carbon bonded to the -OH group:

  • Primary (1°) alcohols: The carbon attached to the -OH group is attached to only ONE alkyl group.

  • Also called terminal alcohols because the functional group is on the end of the hydrocarbon chain.

  • Secondary (2°) alcohols: The carbon attached to the -OH group is attached to TWO alkyl groups.

  • Tertiary (3°) alcohols: The carbon attached to the -OH group is attached to THREE alkyl groups.

Example

$Pentane-1,2,3-triol$

Alcohol Nomenclature

• Drop the '-e' from the parent alkane name and replace it with '-ol'.

  • Example: Ethane → Ethanol

• For alcohols other than methanol or ethanol, include the position of the functional group.

  • Example: Propan-1-ol

• Use prefixes to signify the number of alcohol groups, similar to alkenes and alkynes.

  • Example: Hexan-3,4-diol

• Assign numbers to give the lowest position to the functional group.

  • Example: Butan-2,2-diol is preferred over Butan-3,3-diol.

• For branched alcohols, ensure the functional group has the lowest possible position number.

  • Example: 5,6-dimethyl-heptan-3-ol

Oxidation of Alcohols

• Alcohols can be oxidized into aldehydes, ketones, carboxylic acids, and esters.

• The product depends on whether the alcohol is primary, secondary, or tertiary.

• Acidified potassium dichromate ($Cr<em>2O</em>7^{2-}/H^+$) is used as an oxidizing agent.

Oxidation of Primary Alcohols

• Primary alcohols oxidize in two steps using $Cr<em>2O</em>7^{2-}/H^+$. The reaction requires heat.

  1. First, they become an aldehyde (terminal double-bonded O).

     • $R-CH<em>2OH \xrightarrow{Cr</em>2O_7^{2-}/H^+, heat} R-CHO$

  2. Then, with excess oxidizing agent, the aldehyde further oxidizes into a carboxylic acid.

     • $R-CHO \xrightarrow{Cr<em>2O</em>7^{2-}/H^+, heat} R-COOH$

Oxidation of Secondary Alcohols

• Secondary alcohols oxidize in only one step using $Cr<em>2O</em>7^{2-}/H^+$, which involves heat.

• A secondary alcohol oxidizes into a ketone (non-terminal double-bonded O).

  • $R<em>1-CHOH-R</em>2 \xrightarrow{Cr<em>2O</em>7^{2-}/H^+, heat} R<em>1-CO-R</em>2$

Oxidation of Tertiary Alcohols

• Tertiary alcohols do not oxidize without breaking a C-C bond.

  • $R<em>1-COH(R</em>2)-R<em>3 \xrightarrow{Cr</em>2O_7^{2-}/H^+, heat} No Reaction$

Colorful Oxidation

• If the alcohol has been oxidized, the dichromate must have been reduced.

• Reduction equation: $6e^- + 14H^+ + Cr<em>2O</em>7^{2-} \rightarrow 2Cr^{3+} + 7H_2O$

• Dichromate ion ($Cr<em>2O</em>7^{2-}$) is orange, and chromium (III) ions ($Cr^{3+}$) are green.

• A color change from orange to green indicates oxidation has occurred.

• This distinguishes primary and secondary alcohols from tertiary alcohols because tertiary alcohols show no color change (the solution remains orange).