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Alevel Organic Chemistry > Alcohols > Flashcards

Alcohols Flashcards

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1
Q

Naming alcohols

A

These have the ending-ol and if necessary the position number for the OH group is added between the name stem and the –ol

If the compound has an –OH group in addition to otherfunctional groups that need a suffix ending then the OH can be named with the prefix hydroxy-

If the re are two or more -OH groups then di, tri are used.
Add the ‘e’ on to the stem name though eg propane1,2,3triol

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2
Q

Bond angles in alcohols

A

All the H-C-H bonds and C-C-O are 109.5o (tetrahedral shape), because there are 4 bonding pairs of electrons repelling to a position of minimum repulsion.

The H-O- C bond is 104.5o (bent line shape), because there are 2 bonding pairs of electrons and 2 lone pairs repelling to a position of minimum repulsion. Lone pairs repel more than bonding pairs so the bond angle is reduced.

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3
Q

Boiling points of acohols

A

The alcohols have relatively low volatility and high boiling points due to their ability to form hydrogen bond between alcohol molecules.

Smaller alcohols can dissolve in
water because they can form
hydrogen bonds to water molecules.

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4
Q

Primary alcohols

A

Primary alcohols are alcohols
where 1 carbon is attached to
the carbon adjoining the
oxygen.

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5
Q

Secondary alcohols

A

Secondary alcohols are alcohols
where 2 carbon are attached to
the carbon adjoining the oxygen.

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6
Q

Tertiary alcohols

A

Tertiary alcohols are alcohols
where 3 carbon are attached to
the carbon adjoining the oxygen

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7
Q

What is the oxidising agent that causes alcohols to oxidise

A

Potassium dichromate K2Cr2O7

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8
Q

Partial oxidation of primary alcohols

A

Reaction: primary alcohol —> aldehyde

Reagent: potassium dichromate (VI) solution and dilute sulfuric acid.

Conditions: (use a limited amount of dichromate) warm gently and distil out the aldehyde as it for

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9
Q

Naming aldehydes

A

An aldehyde’s name ends
in–al.
It always has the C=O bond on the first carbon of the chain so it does not need a number in its name

When writing the formulae of aldehydes in a condensed way write CHO and not COH e.g.CH3CH2CHO

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10
Q

Equation for oxidation of primary alcohol propan-1-ol

A

CH3CH2CH2OH + [O] —> CH3CH2CHO + H2O

[O] represents O from oxidising agent.

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11
Q

Observation for partial and full oxidation of primary alcohols

A

Observation: the orange dichromate ion
(Cr2O7 2-) reduces to the green Cr 3+ ion

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12
Q

Distilation

A

In general used as separation technique to separate an organic product from its reacting mixture.

In order to maximise yield collec e collection flask can be cooled in ice to help improve the yield of distillate ted, only collect the distillate at the approximate boiling point of the desired aldehyde and not high

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13
Q

Key points for setting up distilation method

A

The bulb of the thermometer should be at the T junction connecting to the condenser to measure the correct boiling point

The water goes in to the bottom of the condenser to go against gravity. This allows more efficient cooling and prevents back flow of water.

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14
Q

Why are elctrical heaters often used to heat organic chemicals

A

Electric heaters are often used to heat organic chemicals. This is because organic chemicals are normally highly flammable and could set on fire with a naked flame.

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15
Q

Full oxidation of primary alcohols

A

Reaction: primary alcohol —> carboxylic acid

Reagent: potassium dichromate(VI) solution and dilute sulfuric acid

Conditions: use an excess of dichromate, and heat under reflux: (distil off product after the reaction
has finished)

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16
Q

Equation of full oxidation of propan1ol

A

H3CH2CH2OH + 2[O] —> CH3CH2COOH + H2O
propan-1-ol —> propanoic acid

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17
Q
A
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18
Q

What is reflux

A

Reflux is used when heating organic reaction mixtures for long periods. The condenser prevents organic vapours from escaping by condensing them back to liquids.

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19
Q

Why is the reflux never sealed at the end of the condenser?

A

Never seal the end of the condenser as the build up of gas pressure could cause the apparatus to explode. This is true of any apparatus where volatile liquids are heated including the distillation set up.

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20
Q

Why are antibumping granules added to the flask in both distilation and reflux

A

To prevent vigorous, uneven boiling by making small bubbles form instead of large bubbles.

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21
Q

Drawing and labelling reflux accurately

A

It’s important to be able to draw and label this apparatus accurately.
• Don’t draw lines between flask and condenser.
• Don’t have top of condenser sealed
• Condenser must have outer tube for water that is sealed at top and bottom
• Condenser must have two openings for water in and out
that are open

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22
Q

Oxidation of secondary alcohols

A

Reaction: secondary alcohol —> ketone

Reagent: potassium dichromate(VI) solution and dilute sulfuric acid.

Conditions: heat under reflux

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23
Q

Naming ketones

A

Ketones end in-one
When ketones have 5C’s or more in a chain then it needs a number to show the position of the double
bond. E.g. pentan-2-one

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24
Q

Can ketones oxidise further

A

There is no further oxidation of the ketone under these conditions

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25
Can tertiary alcohols be oxidised by potassium dichromate?
Tertiary alcohols cannot be oxidised at all by potassium dichromate: This is because there is no hydrogen atom bonded to the carbon with the -OH group
26
Distinguishing between Aldehydes and Ketones
Aldehydes can be further oxidised to carboxylic acids whereas ketones cannot be further oxidised. This is the chemical basis for two tests that are commonly used to distinguish between aldehydes and ketones.
27
Tollens’ Reagent - Reagent: and conditions
Tollens’ reagent formed by mixing aqueous ammonia and silver nitrate. The active substance is the complex ion of [Ag(NH3)2]+ Heat gently
28
Reaction of tollens reagent
aldehydes only are oxidised by Tollens’ reagent into a carboxylic acid. The silver(I) ions are reduced to silver atoms
29
Observation witn tollens reagent
With aldehydes, a silver mirror forms coating the inside of the test tube. Ketones result in no visible change
30
Example equation of a reaction with tollens reagent.
CH3CHO + 2Ag+ + H2O —> CH3COOH + 2Ag + 2H+
31
Fehlings solution reagent and conditions
Fehling’s solution Reagent: Fehling’s solution containing blue Cu 2+ ions. Conditions: heat gently
32
Fehlings solution reaction
Reaction: aldehydes only are oxidised by Fehling’s solution into a carboxylic acid. The copper (II) ions are reduced to copper(I) oxide
33
Fehlings solution observation
Aldehydes :Blue Cu 2+ ions in solution change to a red precipitate of Cu2O. Ketones do not react
34
Example equation of fehlings solution reaction
CH3CHO + 2Cu2+ + 2H2O —> CH3COOH + Cu2O + 4H+
35
How can the presence of carboxylic acid be tested
The presence of a carboxylic acid can be tested by addition of sodium carbonate. It will fizz and produce carbon dioxide.
36
Reaction of Alcohols with Dehydrating Agents
Reaction: Alcohol —> Alkene Reagents: Concentrated sulfuric or phosphoric acids Conditions: warm (under reflux) Role of reagent: dehydrating agent/catalyst Type of reaction: acid catalysed elimina
37
What is a dehydration reaction
Dehydration Reaction: removal of a water molecule from a molecule
38
Reaction of Alcohols with Dehydrating Agents eg propan1ol
Propan-1-ol —> propene CH3CH2CH2OH —> CH2=CHCH3 + H2O
39
When is more than one product formed when alcohols react with dehydrating agents
Some 2o and 3o alcohols can give more than one product, when the double bond forms between different carbon atoms
40
Example of alcohols producing two products with dehydrating agents.
Butan-2-ol can form both alkenes but-2-ene although more but-2-ene would be formed But-2-ene could also exist as E and Z isomers
41
What does producing alkenes from alcohols do
Producing alkenes from alcohols provides a possible route to polymers without using monomers derived from oil.
42
What are the two ways ethanol can be formed
Comparing two methods for producing ethanol: Fermentation or industrial formation from ethene
43
Equation for fermentation
Glucose —> ethanol + carbon dioxide C6H12O6 —> 2 CH3CH2OH + 2 CO2
44
Conditions for fermentation
The conditions needed are: •Yeast •No air •temperatures 30 –40oC
45
What is the optimum temperature for fermentation and why
The optimum temperature for fermentation is around 38oC At lower temperatures the reaction is too slow. At higher temperatures the yeast dies and the enzymes denature
46
Why is fermentation done in an absence of air?
Fermentation is done in an absence of air because the presence of air can cause extra reactions to occur. It oxidises the ethanol produced to ethanoic acid (vinegar)
47
What are the advantages of fermentation
•sugar is a renewable resource •production uses low level technology / cheap equipment
48
What are the disadvantages of fermentation
•batch process which is slow and gives high production costs •ethanol made is not pure and needs purifying by fractional distillation •depletes land used for growing food crops
49
Essential conditions for extrancting ethanol from ethene
high temperature 300°C high pressure 70 atm strong acidic catalyst of conc H3PO4
50
Reagent for extracting ethanol from ethene
Reagent: ETHENE - from cracking of fractions from distilled crude oil
51
What type of reaction is extracting ethanol from ethene
Type of reaction: Hydration/addition Definition: Hydration is the addition of water to a molecule
52
Equation for extracting ethanol from ethene
CH2=CH2 (g) + H2O (g) —> CH3CH2OH (l)
53
Advantages for extracting ethanol from ethene
faster reaction •purer product •continuous process (which means cheaper manpower)
54
Disadvantages for extracting ethanol from ethene
•high technology equipment needed (expensive initial costs) •ethene is non-renewable resource (will become more expensive when raw materials run out) •high energy costs for pumping to produce high pressure
55
What is a biofuel
A biofuel is a fuel produced from plants
56
What does carbon nuetral mean
The term carbon neutral refers to “an activity that has no net annual carbon (greenhouse gas) emissions to the atmosphere”
57
When is ethanol reffered to as a biofuel
Ethanol produced from fermentation is a biofuel. It can be argued that ethanol produced from this method is classed as carbon–neutral because any carbon dioxide given off when the biofuel is burnt would have been extracted from the air by photosynthesis when the plant grew. There would be no net CO2 emission into the atmosphe
58
Equations to show no net contribution to CO2 (removal of co2)
Removal of CO2 by photosynthesis 6 CO2 + 6 H2O —> C6H12O6 + 6 O2 6 CO2 molecules are removed from the atmosphere when the plants grow
59
Equations to show no net contribution to CO2 (production of CO2 by fermentation and combustion)
C6H12O6 —> 2 CH3CH2OH + 2 CO2 2 CH3CH2OH + 6O2 —> 4 CO2 + 6 H2O When 1 molecule of glucose is fermented 2 molecules of CO2 is emitted. The two ethanol molecules produced will then produce 4 molecules of CO2 when they are combusted. Overall for every 6 molecules of CO2 absorbed, 6 molecules of CO2 are emitted. There is no net contribution of CO2 to the atmospher
60
Why is production of ethanol not carbon nuetral
This does not take into account any energy needed to irrigate plants, fractionally distil the ethanol from the reaction mixture or process the fuel. If the energy for these processes comes from fossil fuels then the ethanol produced is not carbon neutra;
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Alevel Organic Chemistry (6 decks)

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