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AS Chemistry > Alcohols > Flashcards

Alcohols Flashcards

1
Q

Primary, Secondary, Tertiary Alcohol

A

Carbon bonded to the -OH group is attached to less than or equal to 1,2,3 carbons atoms

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2
Q

Combustion of Alcohols

A

CO2 + H2O

Slightly luminous flame

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3
Q

Substitution RXNs (alcohols) to form HalogenoalkanesWhat happens?

A

OH attached to the C atom is replaced by a halogen atom

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4
Q

Making HCl for Substitution of Alcohols to form Halogenoalkanes

A

in situ NaCl(aq) + H2SO4(aq) –> NaHSO4 + HCl(g)

practicality

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5
Q

Substituting a Chloride ion into alcohol (e.g. ethanol) to form an R-X Chemical 1?

A

SOCl2 - sulfur dichloride oxide

most preferred as gases escape

useful with larger alcohols

C2H5OH + SOCl2 –> C2H5Cl + HCl(g) + SO2(g)

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6
Q

Substitution RXNs (alcohols) to form HalogenoalkanesWhy does it happen?

A

C with OH group is partially +ve as O is more EN than C

==> C is open to nucleophilic attack

Initial attack is by the partially -ve X atom bonded in Hydrogen Halide

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7
Q

Substitution RXNs (alcohols) to form HalogenoalkanesConditions

A

Heat under reflux

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8
Q

Substituting a Chloride ion into alcohol (e.g. ethanol) to form an R-XChemical 2?

A

PCl5 - phosphorous (V) chloride

                   room temp.   C2H5OH + PCl5 --> C2H5Cl + HCl(g) + POCl3

PCl3 can also do it, but requires heating (higher Eact)

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9
Q

HCl(g) - colour, smell, pH

A

colourless, fumes (looks misty), pungent, acidic (blue litmus to red)

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10
Q

Test for hydroxyl group

A

add PCl5 / SOCl2

causes HCl(g) - a “steamy fume” - to come off

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11
Q

Making Bromo/Iodoalkanes

Products + Reactants

A

Use PBr3/PI3

e.g. heat
3C2H5OH + PBr3 –> 3C2H5Br + H3PO3
heat
3C2H5OH + PI3 –> 3C2H5I + H3PO3

NB different products from PCl5

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12
Q

Chemical for making R-Cl with 2°/3° alcohols?

A

(conc) HCl / ZnCl2

ZnCl2 is a catalyst

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13
Q

Obervations for Lucas test

A

1° - do not react
2° - cloudy after few mins
3° - cloudy immediately (due to immediate formation of R - Cl which is immiscible in water)

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14
Q

Lucas Test

A

Distinguish between water soluble alcohols

with (conc) HCl / ZnCl2

ZnCl2 is a catalyst

R-OH + HCl(aq) –> R-Cl(l) + H2O(l)

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15
Q

Methods for making ROHs

A
  1. Nucleophilic Substitution
  2. Hydration (Electrophilic Addition) of Alkenes
  3. Reduction ( aldehydes + ketones )
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16
Q

Methods for making ROHs 1.

A

R-X + NaOH(aq) –> ROH + NaX(aq)

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17
Q

Methods for making ROHs 2.

A

H2O + alkene

H2SO4 / H3PO4 catalyst

300°C

70atm - elevated temperature and pressure

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18
Q

Methods for making ROHs 3.

A

Reduction of Aldehydes/Ketones

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19
Q

Making Methanol

A

Cu
CO + 2H2 –> CH3OH

Catalysed hydrogenation of CO from synthesis gas/syngas

100atm, 200-300°C

20
Q

Uses of Alcohols x2

A
  1. Beverages - beer (4%)- wine (12%)- spirits (35-40%)

2. Fuel- on its own- Gasohol (20% alcohol, 80% petrol) - reduces pollution

21
Q

Uses of Alcohols x2

A
  1. Preservative-biological specimens

4. Solvent- dissolves both ionic & covalent molecules

22
Q

Making Ethanol

A

Anaerobic fermentation of glucose

C6H12O6 –> 2C2H5OH + 2CO2

23
Q

Boiling points of ROHs

Why?Trend?

A

Higher than expected for their Mr / Number of Carbons

Polar OH group leads to Hydrogen bonding

Less evident as molecules get bigger (effect of H bonding decreases)

24
Q

Solubility of ROHs

A

ROHs with small Mr values are totally miscible in water

polar part (OH) is significant

(4+ C atoms) As molecules gets bigger, polar part is less significant as effect is blocked by larger non-polar alkyl group

25
Dangers of alcohols
All are toxic to some degree esp. Methanol - a blue dye is added to prevent drinking - causes blindness ( methylated spirits) Ethanol - we consume, can cause liver damage, impair judgement, slows reactions
26
Oxidation of ROHs1°
[O] [O] 1° R-OH --> Aldehydes --> Carboxylic Acids heat under reflux [O] = acidified potassium dichromate/ potassium permanganate K2Cr2O7 / KMnO4 + dil. H2SO4 E.g C2H5OH + [O] --> CH3COH + H2O
27
Oxidation of ROHs 2°
[O] 2° R-OH --> Ketone E.g CH3CH2OH + [O] --> H3C(O)CCH3 + H2O
28
Oxidation of ROHs3°
[O} 3° R-OH --> No RXN Because we need at least 1 H attached to the C to the OH group when oxidation occurs, the H attached to the C is taken away to form a =O bond
29
Colour change for Reduction of K2Cr2O7
Orange to Green
30
Colour change for Reduction of Acidified KMnO4
Purple to Colourless
31
Preparation of Ethanal
Oxidation of Ethanol 50°C C3C2H5OH + Cr2O7 + 8H+ --> CH3CHO + 2Cr3+ + 7H2O Excess alcohol Liebig condensor used to collect ethanal in icebath (B.P of ethanal - 20°C)
32
Acidity of Alcohols
V. V. V. V. V. V. V. V. V. V. weak!!!!!!!!!!! | weaker than H20
33
ROH and Metals
ROH can act as an acid with highly reactive metals e.g Na/K/Li 2C2H5OH + 2Na --> H2 + 2C2H5ONa (sodium ethoxide)
34
Preparation of Ethanoic Acid
[O] [O] C2H5OH --> CH4CHO --> CH3COOH we need to keep the ethanal for further reaction ==> liebig condensor for evaporated ethanl to fall back to Cr2O72- solution heat using reflux to 118°C get rid of H2O and ethanol
35
B.P of Ethanoic Acid
118°C
36
Alcohols to Alkenes
Dehydration
37
Dehydration of Alcohols | Conditions
Al2O3 C2H5OH --> C2H4 + H2O Cotton wool soaked with ROH heat Al2O3 Inverted test tube to collect Alkene - Beware of Suckback
38
Dehydrating Agent(s)
Al2O3 Concentrated H2SO4
39
ROH + Na
ROH + Na --> alkoxide + H2 Na more vigorous than Li
40
What breaks if an ROH reacts with Na/Li/K
O-H bond E.g 2C2H5OH + 2Na --> 2C2H5O-Na+ + H2
41
Conditions and reagents for making R-Xs with alcohols
Heat under reflux Alcohol Conc. H2SO4 H-X
42
Hydrogen bonding with small R-Xs
O atom in OH functional group has 2 lone pairs of electrons and carries a partially -ve charge H atom carries partially +ve charge ==> O atoms will attract H atoms in neighboring molecules
43
What conditions/reagents are required for: | Dehydration of alcohols?
Conc. H+ (H2 SO4) Heat
44
What rule do you apply for the dehydration of asymmetric alcohols?
Zaitsev's Rule (poor get poorer) Major Product: removal of the H from the C atom with the least H substituents Minor: other way
45
What happens in stage 1 for the dehydration of ROHs?
one of the lone pairs of the O atom picks up a H atom from the H2SO4 ===> R - H2O+
46
What happens in stage 2 for the dehydration of ROHs?
bond between the R and H2O+ is broken One H atom is picked up by the O which had initally lost a H atom Bond between H and C now contributes to the new C=C

AS Chemistry (5 decks)

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