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Aqa a level chemistry > Organic Chemistry - carboxylic acids > Flashcards

Organic Chemistry - carboxylic acids Flashcards

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1
Q

dissociation of carboxylic acids

A

-carboxylic acids = weak acids = partially dissociate to form H+ ions in solution

-smaller carboxylic acids dissolve in water because they can form hydrogen bonds with other molecules of water

COOH –> COO- + H+

-carboxylic acid salts are stabilised by delocalisation

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2
Q

ethanol structural formula

A

CH3-CH2-OH

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3
Q

test for carboxylic acids

A

The effervescence caused by production of CO2
with carboxylic acids with solid Na2CO3 or
aqueous NaHCO3 can be used as a functional
group test for carboxylic acids

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4
Q

uses of esters

A

Esters are sweet smelling
compounds that can be used in
perfumes and flavourings.
For use in perfumes they need to be non toxic, soluble in solvent such as
ethanol, volatile (turns into gas easily), and not react with water.

Esters can be used as solvents
for polar organic substances.
Ethyl ethanoate is used as a
solvent in glues and printing inks.

Although polar, they do not form hydrogen bonds (reason: there is no
hydrogen bonded to a highly electronegative atom).
They have a lower b.p. than the hydrogen-bonded carboxylic acids

They are also almost insoluble in water.
Esters can be used as
plasticisers for polymers.
Often pure polymers have limited flexibility because the polymer chains
cannot move over each other.
Incorporating some plasticiser into the polymer allows the chains to move
more easily and the polymer can become more flexible

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5
Q

hydrolysis of esters

A

i) with acid
reagents: dilute acid (HCl)
conditions: heat under reflux

ii) with sodium hydroxide
reagents: dilute sodium hydroxide
conditions: heat under reflux

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6
Q

carboxylic acids

A

-carboxylic acids = weak acids = partially dissociate to form H+ ions in solution

-smaller carboxylic acids dissolve in water because they can form hydrogen bonds with other molecules of water

-carboxylic acid salts are stabilised by delocalisation

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7
Q

acid + base

A

-acid + base –> salt + water

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8
Q

acid + metal carbonate

A

-acid + metal carbonate –> salt + CO2 + H2O

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9
Q

acid + metal

A

-acid + metal –> salt + hydrogen

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10
Q

metal oxide

metal hydroxide

A

-metal oxide –> metal salt + water

-metal hydroxide- -> metal salt and water

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11
Q

HCL + metal carbonate

A

HCl + Na2CO3 –> NaCl + CO2 + H2O

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12
Q

ethanoic acid + sodium carbonate

A

CH3COOH + Na2CO3 –> CH3COONa + CO2 + H2O

Ethanoic acid + sodium carbonate –> sodium ethanoate + carbon dioxide + water

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13
Q

structural formula of a carboxylic acid

A

Structural formula of a carboxylic acid

e.g propanoic acid = CH3-CH2-COOH

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14
Q

formation

A

Propanoic acid + sdoium hydroxde –> sodium propanoate + H2O

Carboxylic acids can react in the presence of an acid catalyst to make esters

Carboxylic acids = weak acids

HCl dissociates to H+ and Cl-

Carboxylic acids like ethanoic acid dissociate into ethanoate ions and hydrogen ions

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15
Q

observation when adding sodium hydrocarbonate to ethanoic acid

A

Observation when adding sodium hydrocarbonate to ethanoic acid:

-effervescence when CO2 gas is evolved

-colourless solution of sodium ethanoate

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16
Q

functional group of carboxylic acids

A

-carbon is open to attack from nucleophilles

-oxygen from C=O can be attacked by postively paired species

-H+ may be lost as it is behaving like an acid

Carboxylic acid + metal –> salt + hydrogen

Acid plays the role of a catalyst in the hydrolysis of esters

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17
Q

acyl chlorides and anhydrides

A

-general formula = RCOCl

-all carboxylic acids contain a carbonyl group

-SOCl2 = oxidation state of sulfur = +4

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18
Q

room temp

A

Oil = liquid at room temperature

Solid at room temperature = fat

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19
Q

acid anhydride

A

-formation of this is a reversible reaction

-2 molecules of ethanoic acid can be dehydrated to ethanoic anhydride

-general formula = RCOOCOR

-two acyl (carbonyl) groups bonded to the same oxygen atom.

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20
Q

nucelophillic addition-elimination

A

When 2 pi bonds break and a sigma bond forms this is called an eliminaton reaction

This reacton shown above is a nucelophilic addition-elimination

Butanoyl chloride + propanol –> propyl butanoate + HCl (this reaction must take place in ahydrous conditions)

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21
Q

forming esters equation

A

Carboxylic acid + alcohol ⇌ ester + water

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22
Q

conditions for esterification

A

-Esterfication includes a concentrated acid catalyst e.g sulfuric acid

-heat

-little water

O-C=O = ester bond

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23
Q

propanoic acid + methanol

A

Propanoic acid + methanol ⇌ methylpropanoate + H2O

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24
Q

methanoic acid + propan-2-ol

A

Methanoic acid + propan-2-ol ⇌ methylethyl ethanoate + waer

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25
acid hydrolysis of esters
-ester + water ⇌ carboxylic acid + alcohol -reversible reaction Conditions --> acid catalyst e.g sulfuric acid, heat, excess water, 60 degrees
26
base hydrolysis of esters
-non-reversible reaction -ester + KOH -> R=O-C-O-K + alcohol -e.g ethyl acetate + sodium hydroxide --> sodium acetate + ethanol
27
uses of esters
-Vegetable oils and animal fats are esters of propane-1,2,3-triol (glycerol). -Vegetable oils and animal fats can be hydrolysed in alkaline conditions to give soap (salts of long-chain carboxylic acids) and glycerol. -Biodiesel is a mixture of methyl esters of long-chain carboxylic acids. -Biodiesel is produced by reacting vegetable oils with methanol in the presence of a catalyst.
28
types of fats
-saturated fat = only single bonds = high melting point = solid at room temp -unsaturated fat = double bonds = liquid at room temp due bends/kinks in hydrocarbon chain -trans fat = hydrogen atoms on opposite sides of double carbon bond = no bending = formed via partial hydrogenation of unsaturated fats
29
fat molecule
Fat molecule = 1 glycerol molecule and 3 fatty acids
30
soaps
Soaps = sodium salts formed when triglycerides are hydrolysed using NaOH and heat -salts dissociates into Na+ and RCOO- in solution. RCOO- molecules have one end which mixes with water and one end that mixes with organic grease. Allows grease + water to mix Fatty acid + NaOH --> salt + glycerol = base hydrolysis of fats
31
biodiesel
-renewable as it is made from vegetable oils -triglycerides are reacted with methanol with NaOH catalyst to form glycerol and methyl esters which can be used as fuel -this s known as a transesterifcation reaction where the alcohols group swap
32
delocalisation
The delocalised ion has equal C-O bond lengths. If delocalisation did not occur, the C=O bond would be shorter than the C-O bond. The pi charge cloud has delocalised and spread out. The delocalisation makes the ion more stable and therefore more likely to form. -Increasing chain length pushes electron density on to the COO- ion, making it more negative and less stable. This make the acid less strong. E.g propanoic acid is less acidic than ethanoic acid
33
acid anhydride
R(CO)2O
34
acyl chloride
RCOCl
35
propanoic anhydride + ethylamine
ehtyl propanamide + CH3CH2C=OO- + H2N-CH3-CH2
36
acyl chloride reactivity
Acyl chlorides react more violently with water than acid anhydride Carboxylic acids need a catalyst to react with alcohols Order of reactivity: Acyl chlorides --> acid anhydride --> carboyxlic acids (most to least reactive) Acyl chlorides = most open to nucelophillic attack
37
Oil + methanol
Oil + methanol --> biodiesel + glycerol Methanol = CH3OH Biodiesel = R-O=C-O-CH3 Glycerol = 3x CH2OH
38
what is acylation
-the process where an acyl group is added to another molecule
39
acyl chloride + alcohol
Acyl chloride + alcohol (R-O-H) --> R-O=C-O-R (ester) + HCl
40
propanoyl chloride reactions
Propanoyl chloride + ethanol --> ethyl propanoate + HCl Propanyol chloride + water --> propanoic acid + HCl
41
ethanoyl chloride + ammonia
ethanoylchloride + ammonia (NH3) --> ethyl amine + Cl- + NH4+
42
reaction of CH3CH2COCl with ammonia
nucelophilic addition elimination
43
CH3CH2CH2Cl with excess ammonia
nucelophilic subsiution
44
Ethanoic anhydride + methylamine -->
methylammonium ethanoate + methylammonia
45
water + propanoyl chloride
propanoic acid + HCl
46
equations
2Ammonia + ethanoyl chloride --> ethanamide + [NH4+Cl-] Propan-2-ol + ethanoyl chloride --> propan-2-oic acid + HCl
47
properties of acyl chloride
-reactive -corrosive -expensive -harmful products
48
properties of acid anhydrides
cheaper -less corrosive -safer -less reactive
49
why are anhydrides used as acyling agents
Despite acyl chloride having a higher atom economy, acid anhydrides are generally used as acyling agents because its cheaper and less corrosive, doesn’t react with water as readily and safer as biproduct is ethanoic acid not HCl
50
NH3 + H2O
NH3 (aq) +H2O (l) ⇌NH4+(aq)+OH-(aq)
51
sodium benzonate
Sodium benzoate is soluble in water because it is ionic. Benzoic acid, however, is insoluble. This is because even though the polar COOH group can form hydrogen bonds, the benzene ring is non-polar. In organic compounds there are often polar parts and non-polar parts. The solubility in water of a compound will controlled by whether the polar or non polar part is of greater importance.
52
hydrolysis of ethylbenzaonate
Hydrolysis of ethylbenzanoate: ethyl benzoate + NaOH --> sodium benzoate + ethanol
53
fats and soaps
-Fats and oils are esters of glycerol and long chain carboxylic acids (fatty acids) -Vegetable oils and animal fats can be hydrolysed to give soap, glycerol and long chain carboxylic (fatty) acids -Glycerol (propane-1,2,3-triol) forms hydrogen bonds very easily and is readily soluble in water. It is used in cosmetics, food and in glues
54
acyl chlorides more reactive than carboxylic acids
Acyl chlorides are much more reactive than carboxylic acids Acid anhydrides have a similar reactivity to acyl chlorides and therefore bring about the same changes in functional groups. The main difference is the by- products. Acyl chlorides mostly give off HCl. Acid anhydrides give off RCOOH
55
acyl chloride reactions
Acyl chloride + water --> carboxylic acid + HCl Observation = white steamy fumes of HCl are given off Acyl chloride + alcohol --> ester + HCl Acyl chloride + 2NH3 --> primary amide + NH4Cl
56
acid anhydrides
Acid anhydride + water --> 2 carboxylic acid Acid anhydride + alcohol --> ester + alcohol Acid anhydride + 2NH3 --> primary amide + RCO2- + NH4+
57
benzene
In benzene, 6p orbitals overlap to form a pisystem containing delocalisedelectrons.
58
ethanoic acid + sodium carbonate
2CH3COOH + Na2CO3 --> 2CH3COONa + H2O + CO2
59
acid anhydride + alcohol
ester + carboxylic acids
60
properties of esters
polar low boiling points
61
unsaturated fats like vegetable oil
less van der waals = lower boiling points
62
fat ester =
saturated fat + 3NaOH --> glycerol + 3soap soap = RCOO-Na+
63
oil + methanol
glycerol + methyl ester 3H3C-O-C=O-R
64
acyl chloride + NH3
amide + HCl e.g ethananmide
65
ethanoic anhydride + water
ethanoic acid x2
66
vegetable oil =
CH2 - O - C=O - CxHx [ [ CH - O - C=O - CxHx [ [ CH2-O-C=O-CxHx
67
give the equation for the reaction of CH3CH2COCl and AlCl3
CH3CH2CO+ + AlCl4-
68
give the reagent and conditions for ester to alcohol
NaOH aqueous/warm fractional distillation to separate alcohol
69
KCN reagents + conditions
alcoholic heat H2
70
name the type of compound formed by the formula RCOOK
carboxylate salt use = salt
71
suggest why aqueous ethanol is a suitable solvent when heating oil with KOH and precatuions
reason = to dissolve both the oil and KOH precautions = use water bath for heating mixture = prevents risk of fire since ethanol is flammable
72
reagents for elimination reaction (dehydration)
concentrated H2SO4
73
Alkene + Br2 = dibromoalkane dibromoalkane + NAOH -->
diol e.g 1,2dipropanol + 2NABr
74
why chemists aim to use fewer steps
less energy
75
high percentage atom economy =
high yield
76
hazard of phosphoric acid
corrosive
77
2 ways in which the melting point of crude asprin would differ to pure asprin
lower melting point range of values
78
purpose of adding small amount of cold ethanol
remove any soluble impurities
79
which reaction involves addition-elimination
CH3COCl + C6H5OH --> CH3COOC6H5 + HCl
80
suggest one reason why chlorobenzene doesnt react with ammonia under normal conditions
electron rich ring in benzene repels the nucelophille (NH3)
81
esterification conditions
concentrated H2SO4 catayst warm + reflux

Aqa a level chemistry (26 decks)

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