SUBTOPIC: ALCOHOLS

Functional group:

R-O-H

1) Family: Alcohol2) Name of functional group: Hydroxyl

Uses

Alcohols UsesMethanol SolventEthanol Solvent, alcoholic beverages, antiseptic1,2 –ethanediol Antifreeze in car radiator1,2,3-propanetriol Cosmetics, confectionaryMenthol Cigarette, throat lozenges, toothpaste

NomenclatureAlcohols with I hydroxyl group

1) Identify parent chain, which is the longest continuous carbon chain containing hydroxyl group2) Number the carbon atoms and give the hydroxyl group the lowest no

Eg:

1

2

Alcohols with more than 1 hydroxyl groupsDiols

Triols

Types of alcohol1) Primary alcohol

E.g:

3

2) Secondary alcohol

E.g:

3) Tertiary alcohol

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Physical properties-Use relative strength of secondary interactions to explain the trend in physical properties.

1) Physical states- Liquid at room temperature- Alcohols contain very polar hydroxyl group, therefore can form strong hydrogen bonds

with other alcohol molecules.- Alcohol molecules are held very close to one another by Hydrogen bonds, therefore

liquid at room temperature.- Lower alcohols are volatile liquids.- Diols and triols are very viscous liquids at room temperature.- Diagram:

Alcohol with 1 OH group

Triol

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2) Boiling point/melting point- Alcohols contain very polar hydroxyl groups; therefore can form strong hydrogen bonds

with other alcohol molecules.

- Require a lot of heat/ high temperature to break strong hydrogen bonds, hence have high bp/mp

Non-polar alkanes alcoholsCompounds MW Bp (oC) Compounds MW Bp (oC)

Ethane 30 -87 Methanol 32 64.5

Propane 44 -42 Ethanol 46 78.3n-butane 58 0 1-Propanol 60 97.2n-propane 72 36 1-Butanol 74 117.7n-hexane 86 69 1-Pentanol 88 138.0

Diagram:Bp of water 100 o C Bp of ethanol 78.3 o C

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- Diols and triols have much higher bp/mp because they can form extensive (many) hydrogen bonds with other alcohol molecules. Hence require much higher temp to break many strong hydrogen bonds between alcohol molecules.

Alcohol compounds MW Bp (oC)1-butanol 74 117

1,3-propanediol 76 214

Alcohol compounds MW Bp (oC)1,2-Ethanediol 62 198

1,2,3-propanetriol 92 290

3) Solubility in waterAlcohols with 1 hydroxyl group

-Lower alcohols (alcohols with small molar mass) are very soluble in water because water molecules can completely surround the alcohol molecules. Alcohol molecules, which contain very polar hydroxyl/hydroxyl group, can form strong hydrogen bonds with very polar water molecules.

Diagram:

-Higher alcohols (alcohols with big molar mass) have low solubility in water because even though they contain very polar hydroxyl groups, however, long non-polar hydrocarbon chain outweighs the polarity of hydroxyl group rendering the whole alcohol molecule as less polar or non- polar. Consequently, alcohol molecules cannot form strong hydrogen bonds with very polar water molecules. Hence, they are less soluble in water.

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Diols and triols-very soluble in water despite their molecular size-they have many very polar hydroxyl groups in one molecule-can form extensive strong hydrogen bonds with very polar water molecules, hence very soluble in water.

4) Solvation process- Ethanol can dissolve ionic compounds such as NaCl- Process is known as solvation or hydration- Diagram:

5) Solubility in organic solvent- Soluble in organic solvents such as petrol due to dispersion force interactions between

alcohol molecules and organic solvents..

- Higher alcohols are more soluble in organic solvent due to their ability to form many DF interactions btw alcohol molecules and organic solvent molecules

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Chemical reactionsOxidation reaction using oxidizing agent, Acidified potassium dichromate solution, K2Cr2O7/H+

1) Primary alcohol-Primary alcohol is oxidized by Acidified potassium dichromate solution, K2Cr2O7/H+

(limited amount) into aldehyde. Cr 6+ (orange) in Dichromate anion is reduced in Cr 3+ (green) . If aldehyde were still in contact with the oxidizing agent, it would be further oxidized into carboxylic acid.Annotated eqn:

Limited Cr2O72-

/H+

Eg: R-O-H RCHO Warm

Excess Cr2O72-

/H+

RCHO RCOOH warm

Eg: limited Cr2O7

2- /H+

CH3CH2OH CH3CHO Warm

excess Cr2O72-

/H+

CH3CHO CH3COOH warm

In summary:

-Observe colour change from orange to green

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2) Secondary alcohol-Secondary alcohol is oxidized into ketone

Cr2O72-

/H+

Eg: R-O-H RCOR warm

-Observe colour change from orange to green

3) Tertiary alcohol

-no reaction

-Observe no colour change. Solution remains orange in colour

Using other oxidizing agent1) Other than acidified potassium dichromate, we can also use acidified sodium dichromate or potassium permanganate (purple) to oxidize primary or secondary alcohols into carboxylic acid and ketone respectively.

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FERMENTATIONIntroduction

1) a process to convert one compound into new compound using microorganisms in the absence of oxygen.

2) converts simple sugars (fructose or glucose) in aqueous solution into ethanol using yeast3) anaerobic process4) Simple sugars can be obtained from 2 sources

a. Fruits (glucose and fructose)

b. Hydrolysis of disaccharides and polysaccharides

i. Starches can be hydrolyzed using amylase enzyme into glucose Equation for hydrolysis:

Conditions required for fermentation to occur

1) Yeast to provide zymase enzyme

2) Optimum temp of 30 o C

3) Dilute aqueous solution

4) Slightly acidic condition

5) In the absence of oxygen to prevent the oxidation of ethanol into carboxylic acid ( vinegar)

Fermentation process

1) Simple sugars are fermented in the presence of zymase enzyme to obtain ethanol

Chemical eqn: C6H12O6 (aq) 2 CH3CH2OH(l) + 2 CO2(g)

2) Zymase enzyme provides alternative pathway with lower new activation energy. Hence more simple sugars can overcome low new activation energy and increase rate of reaction.

3) Max conc of ethanol obtained in fermentation is 15% v/v

4) Conc of Ethanol above 15% v/v would kill the yeast, hence cease zymase production

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5) Could increase ethanol concentration via distillation process

6) Uses of concentrated ethanol

a. To make spirits such as whiskey, brandy (30% v/v)b. To produce car fuels called Gasohol (by mixing petrol with ethanol)c. Antisepticd. To avoid oxidation of dilute ethanol into vinegar

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