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Alcohols Flashcards

1
Q

Alcohols are a family of….

A

molecules that contain the hydroxyl functional group, -OH

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2
Q

general formula

A

CnH2n+1OH

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3
Q

what does the complete combustion of alcohol produce

A

carbon dioxide and water

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4
Q

Three ways to convert alcohols to halogenoalkanes

A

Chlorination

Bromination

Iodination

replacing the hydroxyl group in an alcohol molecule with a halogen atom

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5
Q

explain chlorination

A

Phosphorus(V) chloride is added to alcohol at room temperature

phosphoryl chloride and hydrogen chloride

CH3CH2CH2OH + PCl5 → CH3CH2CH2Cl + POCl3 + HCl

Chlorination of tertiary alcohols can be carried out in a different way by mixing (shaking) with hydrochloric acid at room temperatureThis reaction will not occur with primary or secondary alcohols.
(CH3)3CCl + H2O

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6
Q

explain bromination

A

warmed mixture of potassium bromide and 50% concentrated sulfuric acid with the reacting alcohol

2KBr + H2SO4 → K2SO4 +2HBr

CH3CH2CH2CH2OH + HBr → CH3CH2CH2CH2Br + H2O

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7
Q

explain iodination

A

using a mixture of red phosphorus and iodine with the alcohol whilst heating under reflux

2P + 3I2 → 2PI3

3C2H5OH + PI3 → 3C2H5I + H3PO3

formation of phosphoric acid

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8
Q

what is dehydration

A

done by heating the alcohol with concentrated phosphoric acid
similar to the elimination reaction of a halogenoalkene
The OH group and hydrogen of adjacent carbons are removed forming a C=C bond

CH3CH2OH → CH2=CH2 + H2O

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9
Q

What can primary alcohols oxidise to form

A

form aldehydes which can undergo further oxidation to form carboxylic acids

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10
Q

Secondary alcohols can be oxidised to form

A

ketones

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11
Q

what do tertiary alcohols form when oxidised

A

do not undergo oxidation

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12
Q

what are the oxidising agents of alcohols

A

Acidified potassium dichromate(VI), K2Cr2O7

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13
Q

what happens to dichromate ions when alcohols are oxidised

A

When alcohols are oxidised the orange dichromate ions (Cr2O72-) are reduced to green Cr3+ ions

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14
Q

what happens when primary alcohol is added to oxidising agent and warmed

A

The aldehyde product has a lower boiling point than the alcohol reactant so it can be distilled off as soon as it forms

If the aldehyde is not distilled off, further refluxing with excess oxidising agent will oxidise it to a carboxylic acid

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15
Q

what about ketone when distilling off

A

Since ketones cannot be further oxidised, the ketone product does not need to be distilled off straight away after it has been formed

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16
Q

formula for carboxylic acid

A

CnH2n+1COOH

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17
Q

formula for aldehydes

A

CnH2n+1CHO

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18
Q

Ketone formula

A

CnH2nO

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19
Q

how can you determine -OH group

A

If you add PCl5 to an unknown liquid the evolution of steamy fumes (HCl gas)

20
Q

how can you determine the presence of an aldehyde group

A

oxidising agent Fehling

should go to red precipitate otherwise remain blue

21
Q

what is Feeling’s solution

A

alkaline solution containing copper(II) ions which act as the oxidising agent

22
Q

what happens when feelings solution is warmed with aldehyde

A

aldehyde is oxidised to a carboxylic acid and the Cu2+ ions are reduced to Cu+ ions

The carboxylic acid formed will be neutralised to a carboxylate ion (the -COOH will lose a proton to become -COO- )

The carboxylate ion (-COO-) will form a salt with a positively charged metal ion such as sodium (-COO-Na+)

clear blue solution turns opaque due to the formation of a red precipitate, copper(I) oxide

23
Q

Can you do Fehling’s solution on ketone

A

Ketones cannot be oxidised and therefore give a negative test when warmed with Fehling’s solution

24
Q

What is Tollens’ reagent

A

aqueous alkaline solution of silver nitrate in excess ammonia solution

25
what happens when Tollens is warmed with an aldehyde
the aldehyde is oxidised to a carboxylic acid and the Ag+ ions are reduced to Ag atoms In the alkaline conditions, the carboxylic acid will become a carboxylate ion and form a salt The Ag atoms form a silver ‘mirror’ on the inside of the tube
26
two techniques for oxidising aldehydes
Heating under reflux Distillation with addition
27
what is heating under reflux
Producing a carboxylic acid for a primary alcohol Producing a ketone for a secondary alcohol any products of oxidation remain in the reaction mixture Products which boil off condense in the vertical condenser then return to the heating flask
28
what does condenser help with
ensure vapour condense and return to the flask for further heating.
29
what is distillation with addition
when we do not want to complete oxidation To obtain an aldehyde rather than carboxylic acid for primary alcohol
30
what is simple distillation
separate a liquid and soluble solid from a solution or a pure liquid from a mixture of liquids
31
what is fractional distillation
separate two or more liquids that are miscible with one another
32
what is solvent extraction and conditions
This method uses a solvent to remove a desired organic product from a reaction mixture Immiscible (does not mix) with the solvent containing the desired organic product The desired organic product should be much more soluble than the added solvent
33
process of solvent extraction
Place the reaction mixture in a separating funnel and add the chosen solvent forming a separate layer Place a stopper in the neck of the funnel and gently shake the contents of the funnel for a while Allow the contents of the funnel to settle into two layers Remove the stopper and open the tap to allow the lower layer to drain into a flask Pour the remaining layer into a clean dry conical flask and add two spatulas of anhydrous magnesium sulfate This will remove water It should be added until there is no further clumping and it can then be removed by gravity filtration
34
explain crystallisation
separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold The solution is heated, allowing the solvent to evaporate, leaving a saturated solution behind The saturated solution is allowed to cool slowly Crystals begin to grow as solids will come out of solution due to decreasing solubility The crystals are collected by filtering the solution, they are washed with cold distilled water to remove impurities and are then allowed to dry
35
how can you test if the solution is saturated after crystallisation
dipping a clean, dry, cold glass rod into the solution If the solution is saturated, crystals will form on the glass rod
36
what happens to temperature from impurities
Impurities present in the liquid will raise its boiling temperature
37
Can you do tollens reagent on Ketones
Ketones cannot be oxidised and therefore give a negative test when warmed with Tollens’ reagent
38
what is stereoisomerism
compounds with same structural formula but atoms have different arrangement
39
how to achieve high yield of aldehyde
distill off immediately
40
give one reason why yield is less than 100%
transfer loss incomplete reaction side reactions
41
6 test for alcohols reagents and observations
bromine water - orange / yellow / brown solution goes colourless carboxylic acid and H2SO4 - smell of an ester acidified potassium manganate - purple to colourless alkaline potassium manganate - purple to green neutral potassium manganate - purple to brown acidified potassium dichromate - orange to green
42
how can you obtain pure dry sample of cyclohexene when reacting cyclohexanol with phosphoric acid and this mixture is warmed in water bath for 15 minutes before distilling the mixture of cyclohexene and water
separate cyclohexene from water using separating funnel IP2 remove the lower aqueous layer because it has a higher density * IP3 suitable drying agent * IP4 separate the cyclohexene from the drying agent * IP5 redistil product * IP6 collect the distillate boiling over between 80 and 86 °C to collect the pure cyclohexene
43
how can alcohol be converted to nitrile
via intermediate product called 1-bromobutane halogenoalkane is heated under reflux with a solution of sodium or potassium cyanide in ethanol. The halogen is replaced by a -CN group and a nitrile is produced
44
why do anti bumping granules give a smoother boil
because it provides a surface area for bubbles to form and prevent large bubbles from forming
45
hydrogen bromide plus alcohol what is cooling a mixture antibumping granules heating under reflux used for
cool the mixture because the reaction (with concentrated sulfuric acid / H2504) is (very) exothermic anti-bumping granules are added to prevent violent / sudden / localised boiling to make sure the vapour / gas condenses Or to prevent vapour escaping (1)
46
describe how to dry the organic layer to prepare for distillation
add magnesium sulfate and leave until solution becomes clear and drying agent dont clump together
47

Chem Mock (34 decks)

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