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Chemistry > Topic 17 + grignard reagents > Flashcards

Topic 17 + grignard reagents Flashcards

1
Q

Why are carboxylic acids acidic?

A

because they can donate the H in the -COOH group

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2
Q

What happens to the H in the -COOH when carboxylic acids form salts?

A

the H is replaced by a positive metal ion

—-O(-)Na(+) [sodium ethanoate eg.)

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3
Q

Boiling point of carboxylic acids

A

higher boiling points that alcohols (and alkanes)

  • form hydrogen bonds between two molecules of carboxylic acid to produce a dimer

(between delta positive hydrogen and lone pair on oxygen) AKA between the acidic H (from C-OH) and carbonyl O

  • also additional london forces?
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4
Q

Solubility of carboxylic acids in water

A

hydrogen bonds form between carboxylic acid and water molecules

solubility decreases as chain length increases
because the alkyl groups interrupt the hydrogen bonding for water molecules but then for london forces in replacement. This means the energy released when forming london forces does not exceed the energy required to break the hydrogen bonding in molecules = no solubility.

Carboxylic acids of up to 4 carbons are soluble in water because the energy required to break the hydrogen bonds in water is the same as the energy released when hydrogen bonds between the carboxylic acid and water form

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5
Q

What happens when methanol is oxidised?

A

technically it should go to a carboxylic acid (methanoic acid) but in practice the oxidation can go all the way to carbon dioxide and water

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6
Q

6 ways to prepare carboxylic acids?

A

1) oxidation of primary alcohols
2) oxidation of aldehydes
3) acid/alkali hydrolysis of nitriles
4) grignard + CO2
5) acid/alkali hydrolysis of esters (ester + water –> carboxylic acid + alcohol) OR (ester + alkali –> salt + alcohol then protonate salt to produce carboxylic acid)
6) acyl chloride + water –> carboxylic acid + HCl

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7
Q

Half equation for oxidation of dichromate ions (orange to green)

A

Cr2O7 2- + 14H+ + 6e- ———> 2Cr3+ + 7H2O

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8
Q

Conditions for preparing carboxylic acids from primary alcohols/aldehydes?

What is the other product?!

A
  • potassium dichromate (VI) with sulphuric acid
  • heat under reflux
  • produces H20 as well!!!
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9
Q

full equation for primary alcohol to carboxylic acid (eg. ethanol)

A

CH3CH2OH + 2[O] —-> CH3COOH + H2O

2[O] because 2 lots of oxygen, one bit from to aldehyde and second bit to carboxylic acid

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10
Q

What does heating under reflux do and what do you do when the reaction is done and the carboxylic acid has formed?

A

Heating under reflux prevents any aldehyde formed from escaping before it has time to be converted to a carboxylic acid

Mixture distilled when reaction is complete (get aqueous solution of the acid)

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11
Q

Name two ways nitriles can be formed

A

halogenoalkane + cyanide ions

aldehyde/ketone + HCN (makes hydroxynitriles)

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12
Q

Name two ways to convert nitriles into carboxylic acids

which is usually better

A
  • acid hydrolysis of nitriles (this bad boi is better)

- alkaline hydrolysis of nitriles

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13
Q

3 things about acid and alkali hydrolysis to prepare carboxylic acids

A
  • heat under reflux
  • dilute acid (eg. HCl) // alkali solution (eg. NaOH)
  • distill off carboxylic acid from mixture once formed
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14
Q

Steps of alkaline hydrolysis of nitriles

A

NITRILE + WATER + ALKALI —-> SALT + AMMONIA

ethanenitrile —> sodium ethanoate (with ethanoate ions ofc) + NH3

CH3CN + H2O + OH- ———-> CH3COO- + NH3

Add HCl:
1) CH3COO- + H+ ——> CH3COOH (protonation)

2) NH3 + H+ ——> NH4Cl

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15
Q

4 things that acyl chlorides react with (spec)

A
  • water
  • alcohols
  • concentrated ammonia
  • amines
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16
Q

acyl chloride + water

A

carboxylic acid + HCl

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17
Q

acyl chloride + alcohol

A

ester + HCl

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18
Q

acyl chloride + concentrated ammonia

A

amide + HCl

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19
Q

acyl chloride + amine

A

secondary substituted amide + HCl

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20
Q

acyl chloride + water

knowledge

A
  • hydrolysis reaction
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21
Q

carboxylic acid + alcohol

A

ester + water

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22
Q

Name the acid hydrolysis of esters equation

acid catalyst

A

ester + water –> carboxylic acid + alcohol (reversible so reaction does not go to completion)
(acid catalyst)

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23
Q

Name the alkali hydrolysis of esters equation

A

ester + alkali –> salt + alcohol

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24
Q

How are polyesters formed

A

dicarboxylic acid + diol

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25
Four things carboxylic acids react with (spec)
1) lithium tetrahydridoaluminate (lithium aluminium hydride) in dry ether 2) bases to produce salts 3) phosphorus(V) chloride (phosphorus pentachloride) 4) alcohols in the presence of an acid catalyst
26
carboxylic acid + LiAlH4 - finish equation - type of reaction - what it forms - general equation - conditions - what doesn't work
------[4H]----> alcohol + water - reduction - forms primary alcohol - RCOOH + 4[H] -----> RCH2OH + H2O *where R is H or hydrocarbon group* (4 H because LiAlH4 has 4 H) - LiAlH4(reducing agent) must be with dry ether because it is very reactive with water - room temp - end of reaction is complex aluminium salt, convert to alcohol by adding dilute sulphuric acid - NaBH4 won’t work in this case as it is not a strong enough reducing agent
27
carboxylic acid + base | 4 things
salt + water - dilute ethanoic acid + NaOH (produces colourless solution of sodium ethanoate) - temp of mixture increases - ionic equation: H+ (aq) + OH- (aq) ---> H2O(l) - NOTE: base could also mean metal hydroxide
28
How can carboxylic acids be reduced to primary alcohols?
- react with LIAlH4 | it'll go from carboxylic acid --- aldehyde ----- primary alcohol
29
Naming esters
prefix - alcohol suffix - carboxylic acid .........yl.......oate eg. propyl methanoate (formed from propanol and methanoic acid)
30
Drawing esters
the atoms from the alcohol connect to the single bonded O in the ester propyl methanoate (atoms from propanol would be connected to single bonded O)
31
carboxylic acid + alcohol - finish equation - type of reaction - general equation - conditions
ester + water - esterification/reversible - R-COOH + R'--OH -------> R-COO-R' + H2O - acid catalyst (H2SO4) - NOTE: R can be H, R' cannot be H
32
two uses of esters
- flavouring | - used as solvents
33
How do you convert carboxylic acids into acyl chlorides?
react with PCl5
34
carboxylic acid + PCl5 - general equation - observation - state of products
-------> acyl chloride + HCL + POCl3 - R-COOH + PCl5 ----> R-COCl + POCl3 + HCl - steamy white fumes - liquid acyl chloride, phosphorus compound -acyl chloride separated by fractional distillation swapping -OH in -COOH for a -Cl eg. ethanoic acid --> ethanoyl chloride
35
general background about acyl chlorides
very reactive, important because used to make a wide range of lots of other things
36
acyl chloride functional group
O II C - Cl
37
ester functional group
xxxxxO xxxxxII R-----C-----O---R'
38
acyl chloride + water type of reaction what replaces what observation conditions ------------------------ MECHANISM
carboxylic acid + HCl - Nucleophilic addition/elimination reaction - Cl is replaced by -OH from the water - steamy white fumes - vigorous at room temperature - cold water (if too high temp the carboxylic acid may dissociate and go on to other reactions) --------------------------------------------------------------- see written flashcard
39
acyl chloride + alcohol ``` type of reaction observation conditions what is the nucleophile what is good about it ```
ester + HCl - Nucleophilic addition/elimination reaction (Cl is eliminated and then H is eliminated and together they form HCl) - steamy white fumes - very exothermic reaction - room temperature - alcohol is the nucleophile - quick and easy way to form an ester
40
acyl chloride + amine
N-substituted amide - nucleophilic addition/elimination - amine is the nucleophile - concentrated solution of the amine - violent reaction producing white solid mixture of N-substituted amide and (methyl)ammoniumchloride XXX
41
acyl chloride + concentrated ammonia reactant aggressiveness observation and what is produced what remains
amide + HCl - concentrated solution of ammonia in water - very violent reaction - mixture of solid ammonium chloride and ethanamide (lots of white smoke) - Some of the mixture remains dissolved in water as a colourless solution. XXX
42
What about aldehydes/ketones makes them susceptible to nucleophilic attack?
the C=O bond has a delta positive carbon which nucleophiles are attracted to
43
How do aldehydes and ketones differ in terms of oxidation?
aldehydes have a H atom attached to the carbonyl group which makes them very easily oxidised. Ketones do not have this so are resistant to oxidation and only very powerful oxidising agents that break C-C bonds can oxidise them
44
What happens to boiling point as aldehyde/ketone chain length increases?
- more electrons - more and stronger london forces - more temporary dipoles
45
Why do aldehydes and ketones have lower boiling points than alcohols?
- they cannot form hydrogen bonds - because all their H atoms are attached to carbon atoms (no H atoms attached directly to the oxygen in the C=O) (which means no delta positive H in one carbonyl for the O in C=O of another carbonyl to bond to)
46
How soluble are aldehydes and ketones?
- smaller ones are soluble because they can form hydrogen bonds with water - but solubility decreases as chain length increases because the alkyl groups interrupt the water's hydrogen bonds but replace them with only london forces so energy required to break the H bonds exceeds to energy released when the london forces formed hence they are not soluble)
47
How do carbonyl groups affect bonding?
They form polar bonds, because oxygen is much more electronegative than carbon
48
What intermolecular forces are present in a mixture of just ketones/a mixture of just aldehydes?
london forces permanent dipole- permanent dipole (attraction between delta negative O of one ketone and the delta positive C of another ketone)
49
For ketones and aldehydes of a similar molecular mass, why do the ketones have a higher boiling point?
ketone's carbonyl group is more polarised than an aldehyde's so stronger permanent dipole-permanent dipole forces between ketone molecules to break
50
Why are small ketones more soluble than small aldehydes?
because of the distribution of alkyl groups around the C=O bond in ketones
51
What are the relative boiling points of aldehydes, ketones, alcohols and alkanes? Why:
alcohol>ketone>aldehyde>alkane Why: alcohol - london, dipole-dipole, hydrogen bonds ketone - london, stronger permanent dipole-permanent dipole than aldehydes aldehyde - london, weaker permanent dipole-permanent dipole than ketones alkanes - london
52
What does the iodoform reaction identify?
presence of a CH3CO group in an aldehyde/ketone
53
Explain the iodoform reaction and positive result
iodine and alkali (NaOH) added to ketone/aldehyde CH3CO group present = yellow precipitate of CHI3 antiseptic smell
54
What types of aldehydes and ketones give a positive result for the iodoform reaction?
- methyl ketones (have a CH3 group attache dto one side of the C=O) - only aldehyde is ethanal (has a CH3 group attached to one side of C=O - all other aldehydes do NOT)
55
What is the equation for the reaction between a carbonyl compound and iodine? (alkali)
CH3CO-R + 3I2 + 4OH- ——> RCOO- + CHI3 + 3I- + 3H20
56
How can Brady's reagent (2-4dnph) be used to test for aldehydes and ketones?
An orange precipitate forms if a carbonyl is present The precipitate can be purified by re-crystallisation Each different carbonyl give a crystal with a different melting point If the melting points are measured and compared to a table of known values, the compound can be identified
57
What is the reagent for reduction of aldehydes and ketones?
- LiAlH4 (reducing agent) in dry ether - ketones are reduced to secondary alcohols - aldehydes are reduced to primary alcohols - [H]
58
How can you distinguish between aldehydes and ketones?
Aldehydes react with Benedict’s, Fehling’s and Tollens’, ketones do not
59
What reagents can be used to oxides aldehydes to carboxylic acids?
Acidified potassium dichromate, Fehling’s, Benedict’s, Tollens’
60
What is the colour change for Fehling’s/Benedict's?
deep blue solution ---> dark red precipitate - heat gently - ONLY aldehydes oxidised Cu2+ reduced to copper (I) oxide
61
What is the colour change for Tollens’?
aldehyde present (ONLY aldehydes are oxidised) - ammoniacal silver nitrate (silver nitrate, sodium hydroxide, ammonia solution) - silver is reduced - colourless solution --> silver mirror
62
Why can tertiary alcohols not be oxidised?
they have no hydrogen attached to the carbon with the OH group
63
Why can't ketones be oxidised?
they have no singular H atom attached to the C=O
64
How are grignard reagents prepared?
- heat under reflux - magnesium turnings with dry ether and halogenoalkane - if reaction not immediate use crystal iodine as catalyst - rub Mg with abrasive to remove oxide layer so halogenoalkane can directly react
65
two reactions of grignard reagents
grignard reagent _ CO2 ----> carboxylic acid grignard reagent + aldehyde/ketone ----> alcohol
66
grignard reagent + CO2
carboxylic acid 1) bubble CO2 through grignard in dry ether 2) add dilute HCl to solution *R from grignard attaches to C, double bond in CO2 breaks to form one single bonded oxygen, H from acid attaches to the single bonded oxygen, Cl from acid attaches to the MgBr (grignard) left over when the R detached) R-MgBr + CO2 ---> R-COOH + MgBrCl
67
grignard reagent + aldehyde/ketone
alcohol 1) bubble aldehyde/ketone through grignard in dry ether 2) add dilute HCl to solution *R from grignard attaches to C, double bond in C=O breaks to form single bond, H from acid protonates by attaching to the now single bond O in C=O, Cl from acid attaches to left over MgBr (grignard) left over when the R detached)
68
How are polyesters formed?
Through condensation polymerisation
69
What are the physical properties of esters?
Colourless liquids with low melting and boiling points, insoluble in water, no hydrogen bonding. Generally pleasant smell.
70
explain alkaline hydrolysis of esters - conditions - advantages over acid hydrolysis - methyl propanoate example word and chemical equation - how would you form a carboxylic acid from this?
ester + alkali --> salt + alcohol - ester heated under reflux with alkali (usually NaOH) - advantages over acid hydrolysis: reaction one way rather than reversible, products easier to separate - methyl propanoate ----> sodium propanoate + methanol - CH3CH2COOCH3 + NaOH ---> CH3CH2COO-Na+ + CH3OH - add a strong dilute acid (HCl) which will protonate the propanoate ions (or whatever they are) in the salt. Carboxylic acid then distilled off.
71
explain acid hydrolysis of esters - conditions - how to make reactions as complete as possible - example word and chemical equation with methyl propanoate
ester + water --> carboxylic acid + alcohol - ester heated under reflux with dilute acid (HCl acts as catalyst) - reversible - to make reaction as complete as possible use excess dilute acid which contains excess water needed - methyl propanoate ---> propanoic acid + methanol - CH3CH2COOCH3 + HC20 -----(H+)----> CH3CH2COOH + CH3OH
72
How are hydroxynitriles formed?
carbonyl + HCN
73
What is a hrydroxynitrile?
has an -OH and a -CN
74
carbonyl + HCN
hydroxynitrile - nucleophilic addition - room temp + pressure - HCN (g) v poisonous so used in solution with KCN (and little sulphuric acid) - nucleophile = cyanIDE ion (:CN-) - HCN adds across the double bond - needs both HCN and :CN- in order to work - pH 4-5 gives fastest reaction - H added may also come from H20 or H30+ in slightly acidic solution
75
How does this equilibrium HCN H+ + CN- affect the carbonyl + HCN mechanism?
the more acidic, the more HCN associates and equilibrium shifts left and so fewer CN- reaction will be slower because the first step requires :CN- to act as the nucleophile.
76
Explain whether a ketone or aldehyde reacting with HCN would give an optically active mixture as a product?
ketone: once the CN has added on, it has 4 DIFFERENT groups around the chiral carbon. original ketone was planar = nucleophile could attack from either side = racemic mixture = NOT optically active original ketone was NOT planar = nucleophile only attacked from one side = optically active mixture forms Aldehyde: When :CN- adds it can never form a product with 4 different groups around a chiral carbon = never produces an optically active product
77
What is beneficial about a slightly acidic solution in the mechanism reacting carbonyls and HCN?
additional H+ increase polarity of C=O bond by attracting e- more strongly to oxygen end so C more delta negative and nucleophile more attracted
78
explain the carbonyl + HCN mechanism really simply
- :CN- attacks delta positive C in C=O of carbonyl - C=O becomes C-O - lone pair on O attracted to H in H-CN (takes H away and forms OH bond) - hyroxynitrile + :CN-
79
2 ways of producing esters
1) acyl chloride + alcohol --> ester + HCl | 2) carboxylic acid + alcohol ---> ester + water
80
all the reactions (general)
- acid/alkali hydrolysis of nitriles - acid/alkali hydrolysis of esters - 4 acyl chloride reactions - 4 carboxylic acid reactions - 2 grignard reactions - 2 reactions to produce nitriles - 2 oxidation reactions to produce carboxylic acids

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