Isomerism 2 Flashcards
1
Q
Optical isomerism
A
2
Q
What is optical isomerism?
A
optical isomerism occurs when a carbon atom has four different atoms or groups of atoms attached to it.
3
Q
What do all optical isomers have?
A
asymmetrical atom or a chiral centre
4
Q
When a molecule has a chiral centre..?
A
there are 2 non-superimposable isomers that are mirror images of each other
5
Q
give an example of optical isomerism?
A
2-chlorobutane - chlorine group, ethyl group, methyl group and a hydrogen atom attached
6
Q
what does non-superimposable mean?
A
means you can not stack one form exactly on top of the other.
7
Q
what categories do spoons fall into?
A
mirror images and superimposable
8
Q
what categories do books fall into?
A
superimposable but not mirror images
9
Q
what categories do hands fall into?
A
non-superimposable and mirror images
10
Q
for optical isomerism which two categories do they need to fall into?
A
must be non-superimposable and mirror images
11
Q
what is the difference between optical isomers and enantiomers?
A
Enantiomers have the same physical properties except that they differ in their effect on the plane of polarised light (instead they are optically active)
12
Q
when does plane-polarised light vibrate?
A
only in one plane
13
Q
How many enantiomers can we have?
A
2
14
Q
in which ways will these enantiomers rotate?
A
one enantiomer will rotate the plane of the polarised light clockwise (+)
the other enantiomer will rotate the plane of polarised light anticlockwise (-)
15
Q
how can we measure the rotation of light?
A
using a polarimeter
16
Q
how exactly does this work?
A
by observing the polarised light coming out towards the observer
17
Q
Which two forms can enantiomers take?
A
Dextrorotary and Laevorotary
18
Q
If an enantiomer takes the Dextrorotory form then..?
A
the light appears to have turned to the right (clockwise) to form a positive (+) dextrorotary enantiomer
19
Q
If the enantiomer takes a Laevorotary form then light…?
A
appears to have taken a left turn (anticlockwise) to form a negative enantiomer (-)
20
Q
Draw out the polarimeter and label which each part does what
A
A - light source produces light vibrating in all directions
B - polarising filter only allows through light vibrating in one direction
C - plane polarised light passes through the sample
D - if substance is optically active it rotates the plane of polarised light
E - analysing filter is turned so that light reaches a maximum
F - direction of rotation is measure coming towards the observer
21
Q
what would be classed as an optically inactive mixture?
A
a mixture of equal amounts of both enantiomers (50:50) is optically inactive because the optical effects of each enantiomer cancel each other out
22
Q
And what would this mixture be referred to as?
A
Racemate/ racemic mixture
23
Q
Optical isomerism is important in..?
A
Biochemistry
24
Q
why is only one enantiomer formed in nature?
A
when optically active molecules are made in nature, only one enantiomer is formed. this is because biological systems involve enzymes that are stereospecific in their action.
*in nature, the molecule is made by enzymes that are stereospecific in their action.
* the enzyme will be a single enantiomer that will only react with one enantiomer to make a single enantiomer.
25
What biological system is an example of something opticaly active?
enzymes
26
How many enantiomers can enzymes react with?
only one enantiomer and can only produce one enantiomer as a result of a reaction
27
Give an example
only the (+) enantiomer of glucose is absorbed by the human body. the (-) enantiomer passes through the body unchanged.
Also amino acids exist as single enantiomers too e.g alanine
28
the properties of all optically active enantiomers are..?
all identical
29
the properties of optically active enantiomers are all identical except...?
in reactions with other optically active substances
30
what is meant by enzymes are sterospecific?
they can distinguish between enantiomers and catalyse the reactions of only one pair of isomers
31
why can enantiomers have different smells?
this is because our sense receptors are chiral protein molecules
32
what molecules is naturally occurring chemical with two enantiomers?
Carvone
33
what does carvone taste like?
one tastes like caraway seeds while the other has a spearmint flavour
34
Chirality in the pharmaceutical industry
35
What is drug action determined by and why can Drug action can have different effects?
drug action can be determined by the stereochemistry of the molecule and different optical isomers can have different effects
36
In optically active drugs only...?
one enantiomer will produce an effect on the body
37
if only one enantiomer works, why are drugs usually a racemic mixture?
for economical reasons - separation of the enantiomers is very costly
38
What drug is a chiral molecule and can exist as two enantiomers?
Thalidomide
39
What was Thalidomide used for?
used to treat anxiety and morning sickness in pregnant women
40
what did side effects did this have?
many gave birth to children with deformities and missing limbs
41
After research, how thalidomide caused birth defects, explain how?
it turned out only one enantiomer was effective and safe, its optically active counterpart was not. The major problem was that a mixture of isomers was formed.
( after than was banned worldwide but still babies left with defects)
42
why have drug companies been encouraged to develop single enantiomer products/drugs?
such products are safer and more effective than the racemate
43
Give an example of a single enantiomer drug?
Ibuprofen acts much faster as the (+) enantiomer than when administered as a racemate
44
Questions
45
explain why the compound CH3CH2(NH2)COOH can exist as an enantiomer?
It can exist as an enantiomer as it has a chiral structure. there are 4 different groups are attached to the 2nd carbon
46
explain why the compound CH3CH(NH2)COOH occur only in nature as a (-) enantiomer?
In nature, the molecule is made by enzymes that are stereospecific in action. The enzyme will be a single enantiomer that will only react with one enantiomer to make a single enantiomer
47
Draw two enantiomers of the above carboxylic acid
48
After exercise Lactic acid builds up in the muscle cells of the body and causes fatigue. what will be the difference between this lactic acid and that prepared in a laboratory?
Muscle cell lactic acid will be a single enantiomer (made by enzymes that are stereospecific in their action.) Which will rotate the plane of polarised light. Lab made lactic acid will be a racemate mixture (50:50 of both enantiomers) and wll not rotate the plane of polarised light - optical effects cancel out.
49
How could we differenciate between 2 optical isomers of lactic acid?
One will rotate the plane of polarised light clockwise (+) and one will rotate the plane of polarised light anticlockwise (-) by the same amount
50
Aldehydes and Ketones - oxidation and reduction
51
Why is the carbon oxygen bond polar? also why does it react with acid?
- the oxygen atom is more electronegative than the carbon atom
- the oxygen atom draws the electrons in the double bond towards itself
- the oxygen atom becomes slightly neg(-) charges and the carbon becomes slightly pos(+) charged
- the pos(+) carbon atom is electron deficient and is attacked by nucleophiles readily
52
what are nucleophiles?
lone pair of electrons that can donate to form a covalent bond
53
What are alcohols oxidised by?
Acidified potassium dichromate
54
what are primary alcohols oxidised to form?
aldehydes
55
secondary alcohols are oxidised to form?
ketones
56
general formula for aldehydes and ketones?
CnH2nO
57
what is the difference between aldehydes and ketones?
aldehydes have a hydrogen atom attached to the carbonyl atom
58
What is the test for aldehydes?
aldehydes can be further oxidised to carboxylic acids in an excess of the oxidising agent.
(so aldehydes are mild reducing agents)
59
Tollen's reagent results for both aldehyde and ketone?
when tollens is warmed with an aldehyde a silver mirror is produced, the aldehyde has been oxidised to a carboxylic acid.
ketones do not react with tollens
60
Fehlings solution results when warmed with an aldehyde?
when an aldehyde is warmed with fehlings a brick red precipitate is formed. the aldehyde is oxidised to a carboxylic acid
ketones do not react with fehlings
61
Reduction of Aldehydes and Ketones
62
aldehydes can be reduced to...?
primary alcholos
63
Ketones can be reduced to..?
secondary alcohols
64
How can reduction of aldehydes and ketones take place, by which processes?
Catalytic hydrogenation and reactions with reducing agents such as NaBH4
65
Catalytic hydrogenation
66
What catalyst is used to reduce Aldehydes and ketones?
Nickel catalyst
67
why can the C=O bond go undergo catalytic hydrogenation in the same way as C=C?
because the C=O bond is saturated in the same way that C=C bond is saturated when alkenes undergo catalytic hydrogenation
68
what happens when these bonds undergo catalytic hydrogenation
these bonds become saturated
69
Show a displayed formula of the catalytic hydrogenation of butanone?
what temperature is needed for this reaction?
150 DEGREES
70
How are aldehydes and ketones reduced using NaBH4?
aldehydes and ketones are reacted with sodium tetrahydridoborate(III) and adds hydrogen via a nucleophilic attack on the slightly positive carbon of the carbonyl group
71
why can nucleophiles not attack alkenes?
therefore..?
electron rich double bond repels nucleophiles. therefore, reagents such as NaBH4 can be used to SELECTIVELY REDUCE aldehydes and ketones
72
What are the reaction conditions needed for the Nucleophilic addition of the hydride ion?
- NaBH4 OR LIBH4 in aqueous solution
73
Draw out the full mechanism of the nucleophillic addition of the hydride ion.
explain this mechanism in steps
1. carbonyl group of an aldehyde or ketone is attacked by a nucleophile, an addition rection occurs and the carbon double bond becomes a single bond
2. reagents such as NaBH4 and LiBH4 provide the hydride ion (:H-)
3. An oxyanion intermediate is formed which gains a proton (H+) from the solvent (e.g water/weak acid)
4. the reaction with NaBH4 is normally carried out in aqueous solution
74
Show the mechanism for the reduction of ethanal by NaBH4
75
Show the mechanism for the reduction of propanone by NaBH4
76
why is reduction using NaBH4 preferred to reduction using Catalytic hydrogenation in compounds that have multiple functional groups?
NaBH4 is capable of selectively reducing the carbonyl group. H2/Ni does not select what it reduces - tends to reduce anything present that can be reduced
77
In what conditions does Reduction with NaBH4 take place?
In Aqueous conditions
78
Nucleophilic addition reaction of aldehydes and ketones with KCN followed by dilute acid
79
what do Aldehydes and ketones form when undergoing nucleophilic reactions with KCN and dilute acid
hydroxynitriles
80
Draw the reaction mechanism for nucleophilic addition reaction of aldehyde (ethanal) and ketone (butanone + propanone) with KCN followed by dilute acid. explain the mechanism in steps + include the final products
the :CN- (from the KCN) acts as a nucleophile and attacks the electron deficient slight positive carbon atom of the carbonyl group
- the anion then gains a proteon from the (H+) from the dilute acid
Products aldehyde: 2-hydroxypropanenitrile
products butanone: 2-hydroxy-2-methylbutanenitrile
products propanone: 2-hydroxy-2-methylpropanenitrile
81
When is a chiral centre produced in a ketone?
only when the starting ketone is asymmetrical
82
Nucleophilic addition of hydrogen cyanide to aldehydes and ketones
83
what do aldehydes and ketones form with hydrogen cyanide?
hydroxynitriles
84
why is this reaction rarely carried out?
due to the highly toxic nature of HCN gas
85
What is the overall equation for the reaction between ethanal and Hydrogen cyanide?
---> 2-hydroxypropanenitrile
CH3CHO + HCN ----> CH3CH(OH)CN
86
What is the overall equation for the reaction between butanone and Hydrogen cyanide?
----> 2-hydroxy-2-methylbutanenitrile
CH3COCH2CH3 + HCN ---> CH3CH2C(OH)(CH3)CN
87
What is the overall equation for the reaction between propanone and Hydrogen cyanide?
----> 2-hydroxy-2-methylpropanenitrile
CH3COCH3 + HCN ---> (CH3)2C(OH)CN
88
What are the hazards of using KCN?
- KCN is highly toxic and HCN is extremely toxic and can lead to death
- If there is a risk of HCN a fume cupboard should be used
- hydrogen cyanide is also highly flammable
89
why is the addition of the -CN group very useful in organic synthesis?
because it increases the number of carbon atoms in the molecules and so increases the chain length
90
What are the other advantages of the -CN group?
- easily converted into other functional groups once it has been added to a molecule
- the -CN can be converted into a -COOH (a carboxylic acid by hydrolysis
- the -CN group can be reduced to -CH2NH2 (an amine) by catalytic hydrogenation
91
How can 2-Hydroxypropanenitrile be hydrolysed and reduced to form what products?
CH3CH(OH)CN ------H2O+H+----> CH3CH(OH)COOH (hydrolysis to form carboxylic acid)
CH3CH(OH)CN ----- H2/N2-----> CH3CH(OH)CH2NH2 (reduced via catalytic hydrogenation to form a amine)
92
the reaction of aldehydes and ketones with acidified KCN produces racemic mixture.
Title
93
what happens when ethanal is reacted with KCN. What does it produce?
forms 2-hydroxypropanenitrile - which has a chiral centre
94
when this product is made in a labarotory what is produced?
an optically inactive (+_) racemic mixture
95
what is a racemic mixture?
a mixture of equal amounts of each enantiomer (50:50) and is optically inactive because both of the optical effects of each enantiomer cancel out
96
why is a racemic mixture produced?
because the carbonyl group is planar so attack by the :CN- nucleophile is equally likely from either side of the plane
97
What does the hydrolysis (in acidic conditions) of 2-hydroxypropanenitrile lead to?
the formation of the racemate ( ±) 2 hydroxypropanoic acid (lactic acid)
98
where is this mixture (±) of lactic acid found?
in sour milk
99
when is the (+) enantiomer of lactic acid formed?
during the contraction of muscle cells
100
reduction of an unsymmetrical ketone gives a? Give an example of a reaction?
racemic mixture
e.g CH3COCH2CH3 + 2[H] --------> CH3CH(OH)CH2CH3
(butanone makes butan-2-ol)
101
why is a racemic mixture produced when a ketone is reduced?
carbonyl group is planar so attack by the nucleophile is equally likely from both sides of the plane
102
When But-2-ene reacts with HBr in an electrophilic addition reaction, what is formed? why?
A racemic mixture of 2-Bromobutane
because the C=C double bond is planar so attack by the H-Br electrophile is equally likely from either side of the plane
103
Write a series of reactions to show how 2-hydroxypropanoic acid can be synthesised from ethanol.
1. oxidation of ethanol to produce ethanal
2, then we can react ethanal with potassium cyanide followed by dilute acid. to form 2-hydroxypropanenitrile
3. Acidic hydrolysis of 2-hydroxypropanenitrile makes 2-hydroxypropanoic acid (reagents = h20/h+)
104
Carboxylic acids and Esterification
105
what is the functional group of carboxylic acids?
COOH - also refferred to as the carboxyl group
106
How do we name carboxylic acids?
we begin from the COOH group - so this is carbon number 1
107
what is this also the same for?
same for other functional groups such as nitriles, aldehydes
108
How are carboxylic acids made?
by oxidising a primary alcohol or an aldehyde
109
what are primary alcohols oxidised by?
to form?
acidified potassium dichromate 6 to form aldehydes
ethanol + [O] -------> ethanal + water
110
these aldehydes can be further oxidised by..? to form?
an excess of Acidified potassium dichromate 6 to form a carboxylic acid
111
What is the main property of a carboxylic acid?
What does this allow carboxylic acids to do?
it's a weak acid
so can react with metals, bases (alkali's) - neutralisation and metal carbonates and hydrogencarbonates
112
when reacted with metals what does a carboxylic acid make?
metal + acid ------> salt and Hydrogen
113
draw a symbol and word equation to show the reaction between magnesium and ethanoic acid?
Mg + 2CH3CHOOH --------> (CH3COO-)2 Mg2+ + H2
magnesium + ethanoic acid --------> magnesium ethanoate + hydrogen
114
when reacted with bases, what do carboxylic acids make?
Base + acid -----> salt + water
115
Draw a symbol and word equation to show the reaction between sodium hydroxide and ethanoic acid.
NaOH + CH3COOH -----------> CH3COO-Na+ + H2O
sodium hydroxide + ethanoic acid -------> sodium ethanoate + water
116
what does a metal carbonate and a metal hydrogencarbonate make when reacted with a carboxylic acid?
Salt + water + CO2
117
Draw a symbol and word equation to show the reaction between calcium carbonate and propanoic acid.
CaCO3 + 2 CH3CH2COOH -------> (CH3CH2COO-)2 Ca2+ + H2O + CO2
calcium carbonate + propanoic acid ------> calcium propanoate + water + co2
118
Draw a symbol and word equation to show the reaction between sodium hydrogencarboate and ethanoic acid.
NaHCO3 + CH3COOH -----> CH3COOH- Na+ + H2O + CO2
sodium hydrogencarbonate + ethanoic acid ------> soium ethanoate + water + co2
119
what is the test and positive result for a carboxylic acid?
Sodium hydrogen carbonate - bubbles of CO2 gas
120
explain why carboxylic acids, have a low Ka value?
they are weak acids, so only slightly disassociate with water
121
what is the carboxylate anion?
part of the salt made when carboxylic acids react tor form a salt
122
what is the charge on the carboxylate anion?
single negative charge - the single negative charge is shared between the two oxygens
123
Draw a diagram to show how the single charges are shared between the 2 oxygen atoms
124
Esterification
125
How are esters made?
reacting carboxylic acids with alcohols in the presence of a small quantity of a strong acid catalyst (concentrated sulphuric acid H2SO4) to make esters
126
What type of reaction is esterification?
reversible
127
what is the functional group of esters?
COOR
R - is an alkyl group
128
Water is eliminated in the reaction, so is also referred to as a....?
condensation reacation
129
why is this way of making an ester not good?
because the reaction is reversible and so there is a low yield
130
Draw a word equation to show what a carboxylic acid + alcohol makes an ester
carboxylic acid + ester ---> conc h2SO4 --> ester + water
131
Write equations and draw the displayed formula of the reactants and products for the following reactions :
Move to next sildes
132
ethanoic acid and ethanol ---------->
ethyl ethanoate and water
133
propanoic acid and butan-1-ol ---------->
134
2-methylpropanoic acid + butan-2-ol -------->
135
Benzene carboxylic acid + propan-1-ol ----->
136
Esters
137
how are esters made and what type of reaction is esterification?
carboxylic acids react with alcohols in the presence of concentrated sulphuric acid to make esters (a reversible reaction)
138
esters have...? smells?
what do esters smell like?
pleasant - often described as having a sweet and fruity smell
139
what are esters commonly used in?
1. perfumes
2. artificial food flavourings
3. plasticisers (make polymers more flexible)
4. solvents (for polar organic compounds)
140
when drawing esters, we draw the part of the ester which is derived from the acid on the.. and the part of the aclcohol on the...?
acid first (on the left) and then the part of the alcohol on the right
141
But when naming ester, the name of the ester which is derived from the acid is .... and the part from the alcohol is..?
acid is written after the alcohol. The name derived from the alcohol is written first then the acid.
142
the alcohol group is written first as what group?
an alkyl group
143
the second part of the name is from the carboxylic acids and named?
as an oate - so changes from ethanoic to ethanoate
144
what type of isomers are esters?
functional group isomers - same molecular formula different functional group (same func. group as COOH)
145
what is the backwards reaction of esterification?
ester hydrolysis
146
Esters can undergo hydrolysis in two way, what are they?
In acidic or alkaline solution
147
how do we hydrolyse an ester in acidic solution?
by refluxing an ester with water and in the presence of concentrated sulphuric acid catalyst (H2SO4)
148
Draw a word equation to show this reaction
Ester + water--------Conc. H2SO4⇌
carboxylic acid + alcohol
149
draw the word equation to show the acidic hydrolysis of ethyl ethanoate?
ethyl ethanoate + water ----Conc. H2SO4 ----> ethanoic acid + ethanol
150
How can we hydrolyse an ester in alkaline solution?
esters can be hydrolysed by boiling in NaOH
151
Why is boiling an ester with NaOH solution better?
boiling an ester with NaOH is quicker and produces a higher yield of product as the reaction goes to completion.
152
draw a word equation for this hydrolysis?
ester + sodium hydroxide ----> sodium salt of carboxylic acid + alcohol
153
draw the symbol equation for this reaction?
RCOOR' + NaOH -----> RCOO- Na+ R'OH
154
Draw the symbol and word equation for the alkaline hydrolysis of methyl ethanoate?
methyl ethanoate + sodium hydroxide -----> sodium ethanoate + methanol
CH3COOCH3 + NaOH ----> CH3COO- Na+
+ CH3OH
155
Draw the symbol and word equation for the alkaline hydrolysis of ethyl methanoate?
ethyl methanoate + sodium hydroxide ----> sodium methanoate + ethanol
CH3COOCH2CH3 + NaOH -------->HCOO-Na+ + CH3CH2OH
156
What happens when an excess of dilute HCL or dilute H2SO4 is added to the sodium salt of a carboxylic acid?
The carboxylic acid is then reformed
157
Hydrolysis of naturally occurring esters
158
What are examples of naturally occurring esters?
Fats and oils
159
Why do we hydrolyse naturally occurring esters such as oils and fats?
to make useful products such as soap and glycerol
160
give an example of solid esters?
Give an example of liquid esters?
- occurs in animal fats
- vegetable oils are liquid esters
161
most oils and fats are esters of which glycerol molecule?
propane 1,2,3-triol (glycerol) with 3 long chain carboxylic acids (often called fatty acids)
162
What are these esters long chain of fatty acids also called?
triglycerides (tri-esters)
163
What are the most common fatty acids (long -chain carbocylic acids) and how and where are they found?
a) octadecanoic acid (stearic acid) - a saturated fatty acid (no C=C) - found in animal fats
b) octadeca-9-enoic acid (oleic acid) - cis-mono-unsaturated (1 c=c) - found in most fats and olive oil
c) octadeca-9,12-dienoic acid (linoleic acid) - (2 C=C) - found in vegetable oils (soybean + corn oil )
164
What happens when fats (triglycerides) are boiled with sodium hydroxide?
they form glycerol (propane-1,2,3-triol) and a mixture of sodium salts of the 3 component acids - (SOAP) (sodium octadecanoate)
165
draw the word and symbol equation of hydrolysing triglycerides with sodium hydroxide?
166
which homologous series does glycerol belong to?
alcohol - OH
167
why id glycerol highly viscous?
hydrogen bonding occurs between the molecules
168
why is glycerol added to wine?
to increase both sweetness and viscosity
169
why does glycerol attract water molecules?
glycerol easilt form hydrogen bonds and therefore attracts water.
170
this property of being able to attract water molecules means that glycerol helps to prevent?
materials drying up too quickly
171
therefore, glycerol is added to..?
cosmetics, food, and glue
172
Biodiesel
173
what is biodiesel?
an fuel that can be used in normal diesel engines
174
where is biodiesel mainly obtained from?
mainly obtained from vegetable oils suh as rapeseed ooils, sunflower oiol, or soybean oil,. (not from crude oil)
175
what are some of the good properties of biofuel?
renewable fuel and carbon neutral
176
how can vegetable oils be converted into biodiesel (and glycerol) ?
by reacting it with methanol in the presence of a catalyst (base or acid)
177
what is biodiesel a mixture of?
a mixture of methyl esters of long-chain carboxylic acids
178
how are these methyl esters formed?
in a transesterification reaction
179
what is a transesterification reaction?
is a reversible reaction in which an ester reacts with an alcohol (usually in excess) to form a new ester and a new alcohol.
180
Draw an equation which outlines every transesterification reaction?
Alcohol + Ester ⇌ New alcohol + New Ester
181
So if we reacted Propyl Butanoate in an excess of methanol with an acid or base catalyst what would be our products?
methyl Butanoate + Propan-1-ol
182
And we can apply this to the transesterification of biodiesel ↑
How many moles of an methanol would we need and why?
3 moles of the reacting alcohol (methanol) to form 3 new esters
183
draw a word and symbol equation to show the transesterification of vegetable oil (triglycerides) to make biodiesel + glycerol.
vegetable oils (triglycerides) + methanol -------> methyl esters of long-chain fatty acids (BIODIESEL) + glycerol (propane1,2,3-triol)
184
Adding an excess of methanol does what to the reversible reaction?
drives equilibrium to the right to increase the yield of biodiesl
185
why do we convert vegetable oil to a mixture of methyl esters of fatty acids?
why is it better?
makes the fuel less viscous
186
why is biodiesel mixed with petrodiesel?
improves fuel lubricity.
187
what is the advantage of biodiesel than petrodiesel?
cleaner burning - so less pollutants made
188
How can the glycerol by-product be used?
made into soap, cosmetics, glue and food - however there are new uses for glycerol being explored
189
what is a downside of biodiesel?
farmers may stop planting staple food crops in favour of biodiesel cash crops - so might lead to food shortage
190
Acyl chlorides and Acid anhydrides
191
what are acyl chlorides and acid anhydrides?
derivates of carboxylic acids
192
in Acyl chlorides what is the OH replaced by?
CL group/ atom
193
in acid anhydrides what replaces the OH group?
RCOO- group
194
what do these replacements do?
make the resulting molecule more reactive than the corresponding carboxylic acid
195
what is the functional group of acyl chlorides
-COCl functional group
196
why are acyl chlorides attacked by nucleophiles?
Both the O and the Cl are more electron negative than the carbon atom. the C=O and the C-Cl bonds are polar. The slightly positive carbon atom is electron deficient and is therefore very readily attacked by nucleophiles
197
how do we name acyl chlorides?
the oic acid suffic is replaced by oyl chloride
198
explain why acid anhydrides are readily attacked by nucleophiles?
the Oxygen is more electronegative than the slight positive carbon. both oxygens are polar the carbon atom is electron deficient and therefore readily attacked by nucleophiles
199
how do we name acid anhydrides?
the oic acid is replaced by oic anhydride
200
what is acylation?
is the addition of an acyl group (R-C=O) to a molecule
201
what can both the acid anhydride and acyl chloride provide?
the acyl group for the acylation of another molecule
202
what do both acid anhydrides and acyl chlorides have that make them more susceptible to a nucleophilic attack?
a slightly positive carbon atom
203
what properties do they both have?
good leaving groups, CL- and OCOR respectively
204
what are good leaving groups?
'Good leaving groups' are stable species that are liberated during a chemical reaction.
205
because acyl chlorides and acid anhydrides have good leaving groups, this makes them more...?
reacative than the corresponding carboxylic acids
206
Acyl chlorides and acid anhydrides take part on acylation reactions via which mechanism?
they react with nucleophiles via nucleophilic addition-elimination
207
What are the four nucleophiles that attack acid anhydrides and acyl chlorides?
1. water (Hydrolysis)
2. alcohols
3. ammonia
4. primary amines
208
What are the products of the above reaction with acyl chlorides?
1. water forms carboxylic acids
2. alcohols form esters
3. Ammonia forms Amides
4. primary amines form N-substituted amides
209
Name and Draw out the mechanism as well as the symbol and word equation of the reaction between ethanoyl chloride with water, include the products made.
reactants: CH3COCL + H20 (Ethanoyl chloride + water0
products: CH3COOH + HCl (ethanoic acids and Hydrogen chloride)
210
Name and Draw out the mechanism and word/symbol equation of the reaction between ethanoyl chloride and methanol, include the products made.
Reactants : CH3COCL + CH3OH (Ethanoyl chloride + methanol)
Products: CH3C00CH3 + HCl (Methyl ethanoate + hydrogen chloride)
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Name and Draw out the mechanism as well as the symbol and word equation of the reaction between ethanoyl chloride and Ammonia, include the products made.
reactants: CH3COCL + 2NH3 (Ethanoyl chloride + ammonia
products: CH3CONH2 + NH4Cl ethanamide + Ammonium chloride
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Name and Draw out the mechanism as well as the symbol and word equation of ethanoyl chloride with Primary amine = methylamine, include the products made.
Reactants: CH3COCL + 2CH3NH2 (ethanoyl chloride + methylamine)
Products: CH3CONHCH3 + CH3NH3+CL-
( N-methylethanamide + methyl-ammonium chloride)
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How do we name amides?
the suffic - amide is used when naming amides
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what is an N-substituted amide?
one (or two) of the hydrogen atoms attached o the nitrogen atom have been replaced by an alkyl group
e.g N-ethylpropanamide, there is an ethyl group and a hydrogen attached to the nitrogen instead of two hydrogens
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Acylation of Acid Anhydrides
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What are the 4 nucleophiles acid anhydrides react with and what products are formed?
1. water (hydrolysis) to form 2 carboxylic acids (no other byproduct made)
2. Alcohols make ester and (carboxylic acid)
3. Ammonia makes Amide + (ester)
4. Primary amine makes a N-substituted amide + (branched ester)
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name and draw out the mechanism as well as the symbol and word equation for the reaction between ethanoic anhydride and water, include the products made
Reactants: (CH3CO)2O + H2O ( ethanoic anhydride + water)
Products: 2 CH3COOH (ethanoic acid)
218
name and draw out the mechanism as well as the symbol and word equation for the reaction between ethanoic anhydride and Methanol, include the products made
Reactants: (CH3CO)2O + CH3OH) ( ethanoic anhydride + methanol)
Products: CH3COOCH3 +CH3COOH (methyl ethanoate + ethanoic acid)
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name and draw out the mechanism as well as the symbol and word equation for the reaction between ethanoic anhydride and Ammonia, include the products made
Reactants: (CH3CO)2O + 2NH3) ( ethanoic anhydride + Ammonia)
Products: CH3CONH2 + CH3COO-NH4+ (ethanamide + ammonium ethanoate )
220
name and draw out the mechanism as well as the symbol and word equation for the reaction between ethanoic anhydride and Primary amine = methylamine, include the products made
Reactants: (CH3CO)2O + 2NH3) ( ethanoic anhydride + Ammonia)
Products: CH3CONHCH3 + CH3COO-CH3NH3+ (N-methylethanamide + methylammonium ethanoate )
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Note: May not be asked to draw out mechanisms but examiner may be cheeky
222
How can we distinguish between Acid Anhydrides and Acyl Chlorides
- add water
- measure the pH with a pH meter
- pH ≈ 3 for ethanoic anhydride
- pH ≈ 0/1 for acyl chloride
223
why is the pH roughly 3 for an acid anhydride?
Draw out a symbol equation to show this reaction
this is because only ethanoic acid (weak acid) is made when ethanoic anhydride reacts with water.
(CH3CO)2O + H20 ----> 2 CH3COOH
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Why is the pH roughly 0/1 for a Acyl Chloride?
This is becuase when ethanoyl chloride reacts with water HCL (strong acid) is also made in addition to ethanoic acid
CH3COCL + H20 ----> CH3COOH + HCl
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MAKING ASPIRIN
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what is the chemical name for Aspirin?
2-ethanoyloxybenzenecarboxylic acid
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What is Aspirin mostly used for?
Aspirin is the most commonly used drug of all time as an analgesic (pain killer)
228
How is Aspirin made?
by reacting salicylic acid with either ethanoyl chloride or ethanoic anhydride
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What is the chemical name for salicylic acid?
2-hydroxybenzoic acid
230
Draw a reaction mechanism to show how Aspirin is made by reacting Salicylic with Ethanoyl chloride?
makes Aspirin and Hydrogen chloride
231
Draw a reaction mechanism to show how Aspirin is made by reacting salicylic acid with ethanoic anhydride?
makes aspirin and ethanoic acid - CH3COOH
232
What are hydroxybenzene molecules?
Phenols
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What can phenols do?
Act as nucleophiles
234
Industrially how is aspirin made?
aspirin is made by industrially by reacting salicylic acid with ethanoic anhydride
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What are the advantages of making Aspirin with ethanoic anhydride compared to ethanoyl chloride?
- ethanoic anhydride is cheaper
- ethanoic anhydride is less corrosive (less dangerous to use)
- ethanoic anhydride is less reactive and less susceptible to hydrolysis
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FINISH
