ORGANIC COMPOUNDS ALCOHOLS

Alcohols

Homologous series of organic compounds containing a hydroxyl functional group (–OH) bonded to a carbon atom.

General formula of unbranched alcohols

$$C_n H_{2n+1}OH$$

Reason alcohols are polar molecules

The electronegative oxygen atom in the hydroxyl group polarizes the bond, creating partial positive and negative charges.

Reason alcohols have higher boiling points than corresponding alkanes

Alcohols form intermolecular hydrogen bonds between molecules, which are much stronger than the weak dispersion forces between alkanes and require more thermal energy to overcome.

Two industrial methods of manufacturing ethanol

Fermentation of glucose and catalytic addition of steam to ethene (hydration).

Raw materials and biological catalyst used in fermentation

Aqueous glucose ($C_6 H_{12} O_6$) and enzymes provided by yeast.

Essential reaction conditions for glucose fermentation

Anaerobic environment (absence of oxygen), temperature maintained at $25\,^{\circ}\text{C}$ to $30\,^{\circ}\text{C}$, and yeast enzymes.

Products of the fermentation of glucose

Ethanol and carbon dioxide.

Balanced chemical equation for the fermentation of glucose

$$C_6 H_{12} O_6 \rightarrow 2C_2 H_5 OH + 2CO_2$$

Role of yeast in the fermentation process

Provides biological enzymes (such as zymase) that catalyze the conversion of glucose into ethanol and carbon dioxide.

Reactants for the direct industrial synthesis of ethanol from an alkene

Ethene and steam.

Conditions required for catalytic hydration of ethene

Phosphoric acid catalyst ($H_3 PO_4$), a temperature of $300\,^{\circ}\text{C}$, and a pressure of $60\,\text{atm}$ ($6000\,\text{kPa}$).

Balanced chemical equation for the hydration of ethene

$$C_2 H_4 + H_2 O \rightarrow C_2 H_5 OH$$

Advantages of manufacturing ethanol via fermentation

Uses renewable plant-based feedstocks, requires low operating temperatures, and operates at atmospheric pressure.

Disadvantages of manufacturing ethanol via fermentation

Slow batch process, produces an impure/dilute ethanol mixture requiring energy-intensive fractional distillation, and uses land that could grow food.

Advantages of catalytic addition of steam to ethene

Continuous process, rapid reaction rate, high percent yield, and directly yields pure ethanol.

Disadvantages of catalytic addition of steam to ethene

Relies on finite, non-renewable crude oil fractions and requires high energy input to sustain elevated temperatures and pressures.

Ethanol production method that runs as a continuous process

Catalytic addition of steam to ethene.

Reason ethanol is widely used as a solvent

It is a polar solvent capable of dissolving both polar substances (via hydrogen bonding) and non-polar organic substances (via its ethyl group).

Industrial and consumer applications of ethanol as a solvent

Perfumes, cosmetics, printing inks, and adhesives.

Reason ethanol is utilized as an alternative automotive fuel

It is renewable, has a high octane rating, and combusts more cleanly than fossil fuels with reduced soot and particulate emissions.

Composition of E10 fuel

10% ethanol and 90% gasoline.

Composition of E85 fuel

85% ethanol and 15% gasoline.

Composition of E100 fuel

100% pure ethanol.