organicsynthesis knockhardy publishing 2015 specifications
TRANSCRIPT
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ORGANICORGANIC
SYNTHESISSYNTHESIS
KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING20152015
SPECIFICATIONSSPECIFICATIONS
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INTRODUCTION
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KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING
ORGANIC SYNTHESISORGANIC SYNTHESIS
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CONTENTS• Introduction
• Functional groups
• Extending a carbon chain
• Chiral synthesis - introduction
• Nucleophilic addition
• Nucleophilic substitution
• Synthetic methods
ORGANIC SYNTHESISORGANIC SYNTHESIS
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ORGANIC SYNTHESISORGANIC SYNTHESIS
Involves the preparation of new compounds from others.
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ORGANIC SYNTHESISORGANIC SYNTHESIS
Involves the preparation of new compounds from others.
Many industrial processes involve a multi stage process where functional groups are converted into other functional groups.
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ORGANIC SYNTHESISORGANIC SYNTHESIS
Involves the preparation of new compounds from others.
Many industrial processes involve a multi stage process where functional groups are converted into other functional groups.
When planning a synthetic route, chemists must consider...
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ORGANIC SYNTHESISORGANIC SYNTHESIS
Involves the preparation of new compounds from others.
Many industrial processes involve a multi stage process where functional groups are converted into other functional groups.
When planning a synthetic route, chemists must consider...
• the reagents required to convert one functional group into another
• the presence of other functional groups - in case also they react
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ORGANIC SYNTHESISORGANIC SYNTHESIS
Involves the preparation of new compounds from others.
Many industrial processes involve a multi stage process where functional groups are converted into other functional groups.
When planning a synthetic route, chemists must consider...
• the reagents required to convert one functional group into another
• the presence of other functional groups - in case also they react
• the conditions required - temperature, pressure, catalyst
• the rate of the reaction
• the yield - especially important for equilibrium reactions
• atom economy
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ORGANIC SYNTHESISORGANIC SYNTHESIS
Involves the preparation of new compounds from others.
Many industrial processes involve a multi stage process where functional groups are converted into other functional groups.
When planning a synthetic route, chemists must consider...
• the reagents required to convert one functional group into another
• the presence of other functional groups - in case also they react
• the conditions required - temperature, pressure, catalyst
• the rate of the reaction
• the yield - especially important for equilibrium reactions
• atom economy
• safety - toxicity and flammability of reactants and products
• financial economy - cost of chemicals, demand for product
• problems of purification
• possibility of optically active products
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ORGANIC SYNTHESISORGANIC SYNTHESIS
Involves the preparation of new compounds from others.
Many industrial processes involve a multi stage process where functional groups are converted into other functional groups.
When planning a synthetic route, chemists must consider...
• the reagents required to convert one functional group into another
• the presence of other functional groups - in case also they react
• the conditions required - temperature, pressure, catalyst
• the rate of the reaction
• the yield - especially important for equilibrium reactions
• atom economy
• safety - toxicity and flammability of reactants and products
• financial economy - cost of chemicals, demand for product
• problems of purification
• possibility of optically active products
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ORGANIC SYNTHESISORGANIC SYNTHESIS
Functional groupsFunctional groups
Common functional groups found in organic molecules include...
alkene
hydroxyl (alcohols)
haloalkane
carbonyl (aldehydes & ketones)
amine
nitrile
carboxylic acid
ester
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ORGANIC SYNTHESISORGANIC SYNTHESIS
Involves the preparation of new compounds from others, for example…
ESTERSESTERS
ALKANESALKANES ALKENESALKENES
HALOGENOALKANESHALOGENOALKANES
ALCOHOLSALCOHOLS
AMINESAMINES
ALDEHYDESALDEHYDES
KETONESKETONES
CARBOXYLIC ACIDSCARBOXYLIC ACIDS
POLYMERSPOLYMERS
NITRILESNITRILES
DIBROMOALKANESDIBROMOALKANES
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EXTENDING A CARBON CHAINEXTENDING A CARBON CHAIN
Rationale
Methods HaloalkanesCarbonyl compounds (aldehydes and ketones)Aromatic (benzene) rings
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POTASSIUM CYANIDE
Reagent Aqueous, alcoholic potassium (or sodium) cyanideConditions Reflux in aqueous , alcoholic solutionProduct Nitrile (cyanide)Nucleophile cyanide ion (CN¯)
Equation e.g. C2H5Br + KCN (aq/alc) ——> C2H5CN + KBr(aq)
Mechanism
NUCLEOPHILIC SUBSTITUTIONNUCLEOPHILIC SUBSTITUTION
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POTASSIUM CYANIDE
Reagent Aqueous, alcoholic potassium (or sodium) cyanideConditions Reflux in aqueous , alcoholic solutionProduct Nitrile (cyanide)Nucleophile cyanide ion (CN¯)
Equation e.g. C2H5Br + KCN (aq/alc) ——> C2H5CN + KBr(aq)
Mechanism
Importance extends the carbon chain by one carbon atomthe CN group can be converted to carboxylic acids or amines.
Hydrolysis C2H5CN + 2H2O ———> C2H5COOH + NH3
Reduction C2H5CN + 4[H] ———> C2H5CH2NH2
NUCLEOPHILIC SUBSTITUTIONNUCLEOPHILIC SUBSTITUTION
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CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITIONCARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION
Reagent potassium cyanide – followed by dilute acid
Conditions reflux
Nucleophile cyanide ion CN¯
Product(s) hydroxynitrile (cyanohydrin)
Equation CH3CHO + HCN ——> CH3CH(OH)CN
2-hydroxypropanenitrile
Notes HCN is a weak acid and has difficulty dissociating into ions
HCN H+ + CN¯
Using ionic KCN produces more of the nucleophilic CN¯
Alternative reagent: HCN catalysed by alkali which shifts the above equilibrium in favour of CN¯
HIGHLY TOXICTAKE GREAT CARE
HIGHLY TOXICTAKE GREAT CARE
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CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITIONCARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION
Mechanism Nucleophilic addition
Step 1 CN¯ acts as a nucleophile and attacks the slightly positive COne of the C=O bonds breaks; a pair of electrons goes onto the O
STEP 1
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CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITIONCARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION
Mechanism Nucleophilic addition
Step 1 CN¯ acts as a nucleophile and attacks the slightly positive COne of the C=O bonds breaks; a pair of electrons goes onto the O
Step 2 A pair of electrons is used to form a bond with H+
Overall, there has been addition of HCN
STEP 2STEP 1
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CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITIONCARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION
Mechanism Nucleophilic addition
Step 1 CN¯ acts as a nucleophile and attacks the slightly positive COne of the C=O bonds breaks; a pair of electrons goes onto the O
Step 2 A pair of electrons is used to form a bond with H+
Overall, there has been addition of HCN
STEP 2STEP 1
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CARBONYL COMPOUNDS - NUCLEOPHILIC ADDITIONCARBONYL COMPOUNDS - NUCLEOPHILIC ADDITION
Mechanism Nucleophilic addition
Step 1 CN¯ acts as a nucleophile and attacks the slightly positive COne of the C=O bonds breaks; a pair of electrons goes onto the O
Step 2 A pair of electrons is used to form a bond with H+
Overall, there has been addition of HCN
STEP 2STEP 1
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FRIEDEL-CRAFTS REACTIONS OF BENZENE - FRIEDEL-CRAFTS REACTIONS OF BENZENE - ALKYLATIONALKYLATION
Overview Alkylation involves substituting an alkyl (methyl, ethyl) group
Reagents a halogenoalkane (RX) and anhydrous aluminium chloride AlCl3
Conditions room temperature; dry inert solvent (ether)
Electrophile a carbocation ion R+ (e.g. CH3+)
Equation C6H6 + C2H5Cl ———> C6H5C2H5 + HCl
Mechanism
General A catalyst is used to increase the positive nature of the electrophile
and make it better at attacking benzene rings.AlCl3 acts as a Lewis Acid and helps break the C—Cl bond.
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FRIEDEL-CRAFTS REACTIONS OF BENZENE - FRIEDEL-CRAFTS REACTIONS OF BENZENE - ACYLATIONACYLATION
Overview Acylation involves substituting an acyl (methanoyl, ethanoyl) group
Reagents an acyl chloride (RCOX) and anhydrous aluminium chloride AlCl3
Conditions reflux 50°C; dry inert solvent (ether)
Electrophile RC+= O ( e.g. CH3C+O )
Equation C6H6 + CH3COCl ———> C6H5COCH3 + HCl
Mechanism
Product A carbonyl compound (aldehyde or ketone)
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EXTENDING A CARBON CHAINEXTENDING A CARBON CHAIN
Rationale
Methods HaloalkanesCarbonyl compounds (aldehydes and ketones)Aromatic (benzene) rings
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CHIRAL SYNTHESISCHIRAL SYNTHESIS
Rationale
Pharmaceutical synthesis often requires the production of just one optical isomer. This is because...
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CHIRAL SYNTHESISCHIRAL SYNTHESIS
Rationale
Pharmaceutical synthesis often requires the production of just one optical isomer. This is because...
• one optical isomer usually works better than the other
• the other optical isomer may cause dangerous side effects
• laboratory reactions usually produce both optical isomers
• naturally occurring reactions usually produce just one optical isomer
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CHIRAL SYNTHESISCHIRAL SYNTHESIS
Rationale
Pharmaceutical synthesis often requires the production of just one optical isomer. This is because...
• one optical isomer usually works better than the other
• the other optical isomer may cause dangerous side effects
• laboratory reactions usually produce both optical isomers
• naturally occurring reactions usually produce just one optical isomer
Example Aldehydes and ketones undergo nucleophilic addition with cyanide (nitrile) ions;
CH3CHO + HCN ——> CH3CH(OH)CNethanal 2-hydroxypropanenitrile
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CHIRAL SYNTHESISCHIRAL SYNTHESIS
Example
Aldehydes and ketones undergo nucleophilic addition with cyanide ions
CH3CHO + HCN ——> CH3CH(OH)CNethanal 2-hydroxypropanenitrile
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CHIRAL SYNTHESISCHIRAL SYNTHESIS
Example
Aldehydes and ketones undergo nucleophilic addition with cyanide ions
CH3CHO + HCN ——> CH3CH(OH)CNethanal 2-hydroxypropanenitrile
Problem - the C=O bond is planar
- the nucleophile can attack from above and below
- there is an equal chance of each possibility
- a mixture of optically active isomers is produced- only occurs if different groups are attached to the C=O
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CHIRAL SYNTHESISCHIRAL SYNTHESIS
Example
Aldehydes and ketones undergo nucleophilic addition with cyanide ions
CH3CHO + HCN ——> CH3CH(OH)CNethanal 2-hydroxypropanenitrile
Problem - the C=O bond is planar
- the nucleophile can attack from above and below
- there is an equal chance of each possibility
- a mixture of optically active isomers is produced- only occurs if different groups are attached to the C=O
CN¯ attacksfrom above
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CHIRAL SYNTHESISCHIRAL SYNTHESIS
Example
Aldehydes and ketones undergo nucleophilic addition with cyanide ions
CH3CHO + HCN ——> CH3CH(OH)CNethanal 2-hydroxypropanenitrile
Problem - the C=O bond is planar
- the nucleophile can attack from above and below
- there is an equal chance of each possibility
- a mixture of optically active isomers is produced- only occurs if different groups are attached to the C=O
CN¯ attacksfrom below
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CHIRAL SYNTHESISCHIRAL SYNTHESIS
Example CH3CHO + HCN ——> CH3CH(OH)CNethanal 2-hydroxypropanenitrile
CN¯ attacksfrom above
CN¯ attacksfrom below
MIRROR IMAGES
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CHIRAL SYNTHESISCHIRAL SYNTHESIS
Example CH3CHO + HCN ——> CH3CH(OH)CNethanal 2-hydroxypropanenitrile
CN¯ attacksfrom above
CN¯ attacksfrom below
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CHIRAL SYNTHESISCHIRAL SYNTHESIS
Example CH3CHO + HCN ——> CH3CH(OH)CNethanal 2-hydroxypropanenitrile
ANIMATIONANIMATION
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CHIRAL SYNTHESISCHIRAL SYNTHESIS
Consequences • isomers have to be separated to obtain the effective one
• separation can be expensive and complicated
• non-separation leads to
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CHIRAL SYNTHESISCHIRAL SYNTHESIS
Consequences • isomers have to be separated to obtain the effective one
• separation can be expensive and complicated
• non-separation leads to
larger doses needed
possible dangerous side effects
possible legal action
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CHIRAL SYNTHESISCHIRAL SYNTHESIS
Consequences • isomers have to be separated to obtain the effective one
• separation can be expensive and complicated
• non-separation leads to
larger doses needed
possible dangerous side effects
possible legal action
Solution • use natural chiral molecules as starting materials
• use stereoselective reactions which give one isomer
• use catalysts which give a specific isomer
• use enzymes or bacteria which are stereoselective
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CHIRAL SYNTHESISCHIRAL SYNTHESIS
Consequences • isomers have to be separated to obtain the effective one
• separation can be expensive and complicated
• non-separation leads to
larger doses needed
possible dangerous side effects
possible legal action
Solution • use natural chiral molecules as starting materials
• use stereoselective reactions which give one isomer
• use catalysts which give a specific isomer
• use enzymes or bacteria which are stereoselective
Other examples Nucleophilic substitution of haloalkanes
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NUCLEOPHILIC SUBSTITUTIONNUCLEOPHILIC SUBSTITUTION
Problems There are two possible mechanisms
SN2
This produces just one optical isomer with reversed optical activityCalled SN2 because two species are involved in the rate determining step.
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NUCLEOPHILIC SUBSTITUTIONNUCLEOPHILIC SUBSTITUTION
Problems There are two possible mechanisms
SN1
This produces a racemic mixture of two optical isomersCalled SN1 because one species is involved in the rate determining step.
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NUCLEOPHILIC SUBSTITUTIONNUCLEOPHILIC SUBSTITUTION
Problems There are two possible mechanisms
SN2
This produces just one optical isomer with reversed optical activityCalled SN2 because two species are involved in the rate determining step.
SN1
This produces a racemic mixture of two optical isomersCalled SN1 because one species is involved in the rate determining step.
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MODERN SYNTHETIC METHODSMODERN SYNTHETIC METHODS
The following methods can be used to synthesise a single optical isomer
Enzymes / bacteriaEnzymes / bacteria
Chiral chemicalsChiral chemicals
Chiral catalystsChiral catalysts
Natural chiral moleculesNatural chiral molecules
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©2015 JONATHAN HOPTON & KNOCKHARDY PUBLISHING©2015 JONATHAN HOPTON & KNOCKHARDY PUBLISHING
THE ENDTHE END
ORGANICORGANIC
SYNTHESISSYNTHESIS