2.5 Alcohols

General formula of alcohol
■ Alcohol

	►	General formula: CnH2n+1OH with n = 1, 2, 3, 4 ....
	►	A series of molecular organic compounds containing one or more hydroxyl functional group (OH) attached to a saturated carbon atom.
	►	Simplest homologous series of alcohol is considered to be a derivative of the alkane by replacing one hydrogen atom by a hydroxyl group (OH).

■ Molecular formula of the first ten alcohol members.

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Number of carbon, n Molecular formula CnH2n+1OH 1 CH3OH 2 C2H5OH 3 C3H7OH 4 C4H9OH 5 C5H11OH 6 C6H13OH 7 C7H15OH 8 C8H17OH 9 C9H19OH 10 C10H21OH

Nomenclature of alcohol and their isomers
■ Naming alcohols according to the IUPAC system

	►	Each member of the alkane series has a name suffix-anol
	►	Prefixes is connected with the suffix-anol give their name alcohol. Number of carbon, n Prefix Name of alkane: Prefix + suffix-anol 1 Meth Methanol 2 Eth Ethanol 3 Prop Propanol 4 But Butanol 5 Pent Pentanol 6 Hex Hexanol 7 Hept Heptanol 8 Oct Octanol 9 Non Nonanol 10 Dec Decanol
	►	Alcohol shows isomerism start from propanol. The position of the functional group, OH group, need to be mentioned in the nomenclature of alcohol.
	►	The steps are the same as those used for naming the isomers of alkanes with one additional step(Use a smallest number to indicate the position of the functional group, OH group).
	►	Example: ○ Longest carbon chain: 3 carbon atoms Alcohol : propanol Position of the OH groups: C1 atom Position of the branch CH3 group: C2 atom Name of alcoholic isomers : 2-methylpropan-1-ol ○ Longest carbon chain: 3 carbon atoms Alcohol : propanol Position of the OH groups: C2 atom Position of the branch CH3 group: C2 atom Name of alcoholic isomers : 2-methylpropan-2-ol

■ This video provides a brief introduction to electrochemistry.

✍ Worked-example 2.5(a) Name the structural formulae of the following alcohols. 3-methylbutan-1-ol 2,2-dimethylpentan-1-ol 3,2,4-trimethylhexan-2-ol Solution: The following animation shows the method used to draw the structural formulae of alcohols.

✍ Worked-example 2.5(b) Based on the molecular formula of the given alcohols, draw their structural formulae. 2-metilpentan-1-ol 2,3-dimethylhexan-1-ol Solution: The following animation shows the method used to draw the structural formulae of alcohols.

Industrial production of ethanol
■ Ethanol

	►	The most important alcohol.
	►	Commonly used as a solvent or starting material in the manufacture of other organic compounds.
	►	A key component in beer, wine and other types of spirits.
	►	Industrial synthesis of ethanol. ○ From alkenes ○ From glucose by fermentation

■ From alkenes

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In the industry, ethanol is prepared by the reaction of steam with ethene (C2H4) at 300°C and a pressure of 60 atmospheres by using phosphoric acid (H3PO4) as the catalyst according to the following equation: ○ C2H4 + H2O → C2H5OH + H2O

■ From glucose by fermentation

	►	Most fruits and cereals contain carbohydrates such as sucrose and starch . The large molecules of starch can be broken down by enzymes from yeast to glucose. ○ $C_{12}{H}_{22}{O}_{11}+H_2\stackrel{\mathit{yeast}}{\to }{\mathrm{C}}_6{H}_{12}{O}_6+{\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_7$ ${\mathrm{(C}}_6{H}_{10}{O}_5\mathrm{)n}+{\mathrm{nH}}_2\mathrm{O}\stackrel{\mathit{yeast}}{\to }{\mathrm{nC}}_6{H}_{12}{O}_6$
	►	Then zymase enzyme is used to to convert glucose into ethanol and carbon dioxide. This process is called fermentation and is represented by the following equation: ○ $C_6{H}_{12}{O}_6\stackrel{\mathit{yeast}}{\to }{\mathrm{2C}}_2{H}_5\mathit{OH}+{\mathrm{2CO}}_2$
	►	Distillation process is used to purify ethanol from the other product of fermentation.

■ This video contains information on the production of ethanol.

Laboratory Activity 2.5.1 : Preparation of Ethanol

Physical properties of alcohol ethanol
■ Physical properties of ethanol

	►	Volatile, colorless liquid that has a strong characteristic odor.
	►	Low melting point and boiling point.
	►	Soluble in water and many organic solvents, including acetic acid, acetone, benzene and toluene.
	►	An organic solvent that can dissolve certain organic compounds such as ink and varnish.

■ Physical properties of alcohol series:

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Alcohol Molecular formula Molecular mass Boiling point (°C) Density (gdm-3 Physical state Methanol CH3OH 32 63 0.798 Liquid Ethanol C2H5OH 46 73 0.789 Liquid Propanol C3H7OH 60 97 0.804 Liquid Butanol C4H9OH 74 118 0.810 Liquid Pentanol C5H11OH 88 157 0.815 Liquid

■ Changes in the physical properties when going down the homologous series of alcohols.

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The boiling point and the density of alcohol increases almost just with each additional methylene group, CH2.

■ Comparison between alkanes and alcohols.

	►	The boiling point for alcohol is higher than the corresponding alkanes because of the existence of OH group. Hydroxyl group, OH, causes the alcohol molecules bond to each other stronger. Thus, more heat energy is required to overcome them.
	►	In contrast to the corresponding alkanes, lower alcohols such as ethanol in the homologous series is liquid that is soluble in water at room temperature. This is because the hydroxyl group, OH, in the alcohol molecule will form hydrogen bonds with water molecules. However, higher alcohol usually is a waxy solid at room temperature and insoluble in water.

Chemical properties of ethanol
■ Chemical properties of ethanol

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Chemical reaction of ethanol: ○ Combustion reaction ○ Dehydration reaction ○ Oxidation reaction ○ Esterification reaction

■ This video contains information on the chemical properties of ethanol

■ Combustion

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Ethanol burns readily in air with a non-smoky blue flame to produce carbon dioxide and water according to the following equation: ○ C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l)

■ Dehydration

	►	Ethanol can be dehydrated (removal of water) to ethylene (C2H4) as the following equation: ○ $C_2{H}_5\mathit{OH}(l)\begin{array}{c}\to \\ \mathit{dehydration}\end{array}{C}_2{H}_4(g)+H_{2}O(l)$
	►	The dehydration reaction on ethanol can be carried out in two methods. ○ Ethanol vapour, C2H5OH is passed over a heated catalyst such as porcelain chips, porous pot or aluminium oxide, Al2O3. ○ Ethanol C2H5OH is heated under reflux at 180℃ with excess concentrated sulphuric acid, H2SO4.

■ Oxidation of ethanol

	►	Ethanol can be oxidized by the oxidizing agent to ethanoic acid. ○ ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}(\mathrm{l})+2\mathrm{[}\mathrm{O}\mathrm{]}\begin{array}{c}\to \\ \mathrm{oxidation}\end{array}\mathrm{C}{\mathrm{H}}_3\mathrm{COOH}(\mathrm{l})+{\mathrm{H}}_2\mathrm{O(l)}$
	►	Oxidation reaction of ethanol with the oxidising agent such as acidified potassium dichromate(VI) solution and acidified potassium manganate(VII) ○ Observation with acidified potassium dichromate(VI), K2Cr2O7: solution changes from orange to green. Observation with acidified potassium manganate(VII) K Mn O4: purple colour of solution is decolourized.

■ The esterification reaction of ethanol

	►	In the presence of concentrated sulphuric acid as drying agent and also as catalysts, ethanol reacts with carboxylic acids to produce esters.
	►	Ester is a chemical compound that smells like fragrant fruit.
	►	The esterification reaction between ethanol and ethanoic acid is shown in the following equation: $\begin{array}{c}{C}_2{H}_5\mathit{OH}\\ \mathit{ethanol}\end{array}+\begin{array}{c}{\mathit{CH}}_3\mathit{COOH}\\ \mathit{ethanoic}\mathit{acid}\end{array}\iff \begin{array}{c}{\mathit{CH}}_3{\mathit{COOC}}_2{H}_5\\ \mathit{ethyl}\mathit{ethanoate}\end{array}+H_{2}O$ Observation: A fragrant compound that smells like fruit is produced.

Laboratory Activity 2.5.2 : Chemical Properties of Ethanol

Prediction on the chemical properties of other alcohols
■ Chemical properties of other alcohols

	►	All the members of the alcohol homologous series have the same functional group, that is, hydroxyl, -OH, group.
	►	Thus, the other alcohol members should be able to exhibit similar chemical properties as ethanol, C2H5OH.
	►	Based on the reaction of ethanol, the chemical properties of other alcohols can be predicted. ○ Complete combustion: Alcohol + oxygen ➝ carbon dioxide + water ○ Dehydration reaction: $\text{Alcohol}\begin{array}{c}\to \\ \text{dehydration}\end{array}\text{alkene}$ ○ Oxidation reaction: $\text{Alcohol}\begin{array}{c}\to \\ \text{oxidation}\end{array}\text{carboxylic acid}$ ○ Esterification reaction: Alcohol + carboxylic acid ➝ Ester + water

■ Uses of alcohol in everyday life

	►	Alcohol as fuel.
	►	Alcohol as solvent.
	►	Alcohol in the medical field.
	►	Manufacture of cosmetic products.
	►	Alcoholic drinks

Alcohol abuse
■ Alcoholic drinks

	►	Contain ethanol.
	►	Produced from the fermentation of glucose by yeast through fermentation.

■ Effects of Excessive Alcohol Consumption

	►	Can damage liver cells, reduce the production of bile, cause cirrhosis of the liver and hepatitis.
	►	Slows down the rate of nerve impulse transmission and affects the central nervous system.
	►	In severe cases, continuous consumption of alcohol may cause death.