organic reaction scheme

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SYNTHETIC SYNTHETIC ORGANIC ORGANIC CHEMISTRY CHEMISTRY

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Page 1: Organic Reaction Scheme

SYNTHETIC SYNTHETIC ORGANIC ORGANIC

CHEMISTRYCHEMISTRY

Page 2: Organic Reaction Scheme

ESTERSESTERS

REACTIONS OF ORGANIC COMPOUNDSREACTIONS OF ORGANIC COMPOUNDS

ALKANESALKANES ALKENESALKENES

HALOGENOALKANESHALOGENOALKANES

ALCOHOLSALCOHOLS

AMINESAMINES

ALDEHYDESALDEHYDES

KETONESKETONES

CARBOXYLIC ACIDSCARBOXYLIC ACIDS

POLYMERSPOLYMERS

NITRILESNITRILES

DIBROMOALKANESDIBROMOALKANES

CONVERSIONSCONVERSIONS

AMIDESAMIDES

HYDROXYNITRILESHYDROXYNITRILES

ALKYL HYDROGEN SULPHATES

ALKYL HYDROGEN SULPHATES

Page 3: Organic Reaction Scheme

KK

ESTERSESTERS

REACTIONS OF ORGANIC COMPOUNDSREACTIONS OF ORGANIC COMPOUNDS

ALKANESALKANES ALKENESALKENES

HALOGENOALKANESHALOGENOALKANES

ALCOHOLSALCOHOLS

AMINESAMINES

ALDEHYDESALDEHYDES

KETONESKETONES

CARBOXYLIC ACIDSCARBOXYLIC ACIDS

AA

PP

SS

TTGG

TT

NN

RR

POLYMERSPOLYMERS

EE

NITRILESNITRILES

HH

JJ

UU

UUII

BB LL

DD

MM

QQOO

FF

CC

VV

ESTERSESTERS

REACTIONS OF ORGANIC COMPOUNDSREACTIONS OF ORGANIC COMPOUNDS

ALKENESALKENES

HALOGENOALKANESHALOGENOALKANES

ALCOHOLSALCOHOLS

AMINESAMINES

ALDEHYDESALDEHYDES

KETONESKETONES

CARBOXYLIC ACIDSCARBOXYLIC ACIDSNITRILESNITRILES

DIBROMOALKANESDIBROMOALKANES

CONVERSIONSCONVERSIONS

HYDROXYNITRILESHYDROXYNITRILES

ALKYL HYDROGEN SULPHATES

ALKYL HYDROGEN SULPHATES

AMIDESAMIDES

WWWW

XX

XX

YY

Page 4: Organic Reaction Scheme

CHLORINATION OF METHANECHLORINATION OF METHANE

Mechanism free radical substitution

Initiation Cl2 2Cl• radicals created

Propagation Cl• + CH4 CH3• + HCl radicals used and

Cl2 + CH3• CH3Cl + Cl• then re-generated

Termination Cl• + Cl• Cl2 radicals removed

Cl• + CH3• CH3Cl

CH3• + CH3• C2H6 don’t use this as a termination

step in the examSummaryDue to the lack of reactivity of alkanes you need a very reactive species to persuade them to react.Free radicals need to be formed by homolytic fission of covalent bonds.This is done by shining UV light on the mixture (heat could be used).Chlorine radicals are produced because the Cl-Cl bond is the weakest.You only need one chlorine radical to start things off.With excess chlorine you will get further substitution and a mixture of chlorinated products.

AA

CONVERSIONSCONVERSIONS

Page 5: Organic Reaction Scheme

ELECTROPHILIC ADDITION OF HBrELECTROPHILIC ADDITION OF HBr

Reagent hydrogen bromide... it is electrophilic as the H is slightly positive

Condition room temperature

Equation C2H4(g) + HBr(g) C2H5Br(l) bromoethane

Mechanism electrophilic addition

Step 1 As the HBr nears the alkene, one of the carbon-carbon bonds breaks.The pair of electrons attaches to the slightly positive H end of H-Br.The H-Br bond breaks to form a bromide ion.A carbocation (positively charged carbon species) is formed.

Step 2 The bromide ion behaves as a nucleophile and attacks the carbocation.Overall there has been addition of HBr across the double bond.Note that unsymmetrical alkenes will give a mixture of isomeric products.

BB

CONVERSIONSCONVERSIONS

Page 6: Organic Reaction Scheme

Reagent bromine (liquid or dissolved in tetrachloromethane, CCl4 )

Conditions room temperature. No catalyst or UV light required.

Equation C2H4(g) + Br2(l) CH2BrCH2Br(l) 1,2 - dibromoethane

Mechanism electrophilic addition

It is surprising that bromineshould act as an electrophileas it is non-polar. The Br2 molecule is polarised by the region of high electron density around the double bond.

CC ELECTROPHILIC ADDITION OF BROMINEELECTROPHILIC ADDITION OF BROMINE

CONVERSIONSCONVERSIONS

Page 7: Organic Reaction Scheme

DIRECT HYDRATION OF ALKENESDIRECT HYDRATION OF ALKENES

Reagent steam

Conditions high pressure

Catalyst c. H3PO4 (phosphoric acid)

Product alcohol

Equation C2H4(g) + H2O(g) C2H5OH(g) ethanol

Use ethanol manufacture

Comments It may be surprising that water needs such vigorous conditions to react with ethene. It is a highly polar molecule and you would expect it to be a good electrophile.

However, the O-H bonds are very strong so require a great deal of energy to be broken. This necessitates the need for a catalyst.

DD

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Page 8: Organic Reaction Scheme

HYDROGENATION (REDUCTION)HYDROGENATION (REDUCTION)EE

Reagent hydrogen

Conditions nickel catalyst - finely divided

Product alkanes

Equation C2H4(g) + H2(g) C2H6(g) ethane

Use margarine manufacture

CONVERSIONSCONVERSIONS

Page 9: Organic Reaction Scheme

POLYMERISATION OF ALKENESPOLYMERISATION OF ALKENES

ETHENE

EXAMPLES OF ADDITION POLYMERISATION

PROPENE

TETRAFLUOROETHENE

CHLOROETHENE

POLY(ETHENE)

POLY(PROPENE)

POLY(CHLOROETHENE)

POLYVINYLCHLORIDE PVC

POLY(TETRAFLUOROETHENE)

PTFE “Teflon”

FF

CONVERSIONSCONVERSIONS

Page 10: Organic Reaction Scheme

AQUEOUS SODIUM HYDROXIDE

Reagent aqueous* sodium (or potassium) hydroxideConditions reflux in aqueous solution (SOLVENT IS IMPORTANT)Product alcoholNucleophile hydroxide ion (:OH¯)

Equation C2H5Br(l) + NaOH(aq) C2H5OH(l) + NaBr(aq)

Mechanism nucleophilic substitution

*WARNING It is important to quote the solvent when answering questions.A different reaction (elimination) takes place when ethanol is the solvent.

NUCLEOPHILIC SUBSTITUTIONNUCLEOPHILIC SUBSTITUTIONGG

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Page 11: Organic Reaction Scheme

NUCLEOPHILIC SUBSTITUTIONNUCLEOPHILIC SUBSTITUTION

AMMONIA

Reagent aqueous, alcoholic ammonia (in EXCESS)Conditions reflux in aqueous, alcoholic solution under pressureProduct amineNucleophile ammonia (:NH3)

Equation C2H5Br + 2NH3 C2H5NH2 + NH4Br

Mechanism nucleophilic substitution You need to show the removal of the proton here by another ammonia molecule to form NH4Br

Notes The equation shows two ammonia molecules.Excess ammonia is used to prevent further substitution (SEE NEXT SLIDE)

HH

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Page 12: Organic Reaction Scheme

NUCLEOPHILIC SUBSTITUTIONNUCLEOPHILIC SUBSTITUTION

AMMONIA

Why excess ammonia?The second ammonia molecule ensures the removal of HBr, effectively as NH4Br.

A large excess ammonia ensures that further substitution doesn’t take place - see below.

ProblemThe amine produced is also a nucleophile (lone pair on N) and can attack another molecule of the original halogenoalkane to produce a 2° amine. This in turn is a nucleophile and reacts further producing a 3° amine and, eventually, a quarternary ammonium salt.

C2H5NH2 + C2H5Br HBr + (C2H5)2NH diethylamine, a 2° amine

(C2H5)2NH + C2H5Br HBr + (C2H5)3N triethylamine, a 3° amine

(C2H5)3N + C2H5Br (C2H5)4N+ Br¯ tetraethylammonium bromide, a 4° salt

HH

CONVERSIONSCONVERSIONS

Page 13: Organic Reaction Scheme

POTASSIUM CYANIDE

Reagent aqueous, alcoholic potassium (or sodium) cyanideConditions reflux in aqueous , alcoholic solutionProduct nitrile (cyanide)Nucleophile cyanide ion (:CN¯)

Equation C2H5Br + KCN C2H5CN + KBr(aq)

Mechanism nucleophilic substitution

Importance It extends the carbon chain by one carbon atom.The CN group can then be converted to carboxylic acids or amines.

Hydrolysis C2H5CN + 2H2O C2H5COOH + NH3

Reduction C2H5CN + 4[H] C2H5CH2NH2

NUCLEOPHILIC SUBSTITUTIONNUCLEOPHILIC SUBSTITUTIONII

CONVERSIONSCONVERSIONS

Page 14: Organic Reaction Scheme

REDUCTION OF NITRILESREDUCTION OF NITRILESJJ

CONVERSIONSCONVERSIONS

Reagent nickel catalyst and H2

Product amine

Equation C2H5CN + 4[H] C2H5CH2NH2 propylamine

Note that lithium tetrahydridoaluminate(III), LiAlH4, would achieve exactly the same effect. This reagent is not on your exam however.

Page 15: Organic Reaction Scheme

HYDROLYSIS OF NITRILESHYDROLYSIS OF NITRILESKK

CONVERSIONSCONVERSIONS

Reagent waterConditions reflux in acidic or alkaline conditionsProduct carboxylic acid

Equation C2H5CN + 2H2O C2H5COOH + NH3

Page 16: Organic Reaction Scheme

ELIMINATIONELIMINATION

Reagent alcoholic sodium (or potassium) hydroxide

Conditions reflux in alcoholic solution (SOLVENT IS IMPORTANT)

Product alkene

Equation C3H7Br + NaOH(alc) C3H6 + H2O + NaBr

Mechanism elimination

The OH¯ ion acts as a base and picks up a proton.The proton comes from a C atom next to the one bonded to the halogen.The electron pair moves to form a second bond between the carbon atoms.The halogen is displaced and overall there is ELIMINATION of HBr.

With some unsymmetrical haloalkanes, a mixture of isomeric products may be formed.

LL

CONVERSIONSCONVERSIONS

Page 17: Organic Reaction Scheme

ELIMINATION OF WATER (DEHYDRATION)ELIMINATION OF WATER (DEHYDRATION)

Reagent/catalyst conc. sulphuric acid (H2SO4) or conc. phosphoric acid (H3PO4)

Conditions reflux at 180°C

Product alkene

Equation C2H5OH(l) CH2 = CH2(g) + H2O(l)

Mechanism (NO LONGER NEEDED FOR YOUR EXAM)

Step 1 Protonation of the alcohol using a lone pair on oxygen.Step 2 Loss of a water molecule to generate a carbocation.Step 3 Loss of a proton (H+) to give the alkene.

NoteAlcohols with the OH in the middle of a chain can have two ways of losing water. In Step 3 of the mechanism, a proton can be lost from either side of the carbocation.

This gives a mixture of alkenes from some unsymmetrical alcohols.

LL

CONVERSIONSCONVERSIONS

Page 18: Organic Reaction Scheme

OXIDATION OF PRIMARY ALCOHOLSOXIDATION OF PRIMARY ALCOHOLS

Primary alcohols are easily oxidised to aldehydes by acidified (with H2SO4) K2Cr2O7 (turns green from orange)

e.g. CH3CH2OH(l) + [O] CH3CHO(l) + H2O(l)

It is essential to distil off the aldehyde before it gets oxidised to the acid

CH3CHO(l) + [O] CH3COOH(l)

NN

The aldehyde has a lower boiling point so distils off before being oxidised further.

OXIDATION TOALDEHYDES

DISTILLATION

OXIDATION TOCARBOXYLIC ACIDS

REFLUX

The aldehyde condenses back into the mixture and gets oxidised to the acid.

CONVERSIONSCONVERSIONS

Page 19: Organic Reaction Scheme

OXIDATION OF ALDEHYDESOXIDATION OF ALDEHYDES

Aldehydes are easily oxidised to carboxylic acids

e.g. CH3CHO(l) + [O] CH3COOH(l)

• one way to tell an aldehyde from a ketone is to see how it reacts to mild oxidation• ALDEHYES are EASILY OXIDISED• KETONES are RESISTANT TO MILD OXIDATION• reagents include TOLLENS’ REAGENT and FEHLING’S SOLUTION

TOLLENS’ REAGENTReagent ammoniacal silver nitrate solutionObservation a silver mirror is formed on the inside of the test tubeProducts silver + carboxylic acidEquation Ag+ + e- Ag

FEHLING’S SOLUTIONReagent a solution of a copper(II) complex Observation a red precipitate forms in the blue solution Products copper(I) oxide + carboxylic acidEquation Cu2+ + e- Cu+

OO

CONVERSIONSCONVERSIONS

Page 20: Organic Reaction Scheme

OXIDATION OF SECONDARY ALCOHOLSOXIDATION OF SECONDARY ALCOHOLS

Secondary alcohols are easily oxidised to ketones

e.g. CH3CHOHCH3(l) + [O] CH3COCH3(l) + H2O(l)

The alcohol is refluxed with acidified (with H2SO4) K2Cr2O7

However, on prolonged treatment with a more powerful oxidising agent they can be further oxidised to a mixture of acids with fewer carbon atoms than the original alcohol.

As far as your exam is required, they cannot be oxidised past ketones with acidified K2Cr2O7.

PP

CONVERSIONSCONVERSIONS

Page 21: Organic Reaction Scheme

REDUCTION OF CARBOXYLIC ACIDS REDUCTION OF CARBOXYLIC ACIDS (NOT NEEDED FOR YOUR EXAM)(NOT NEEDED FOR YOUR EXAM)

QQ

Reagent/catalyst lithium tetrahydridoaluminate(III), LiAlH4

Conditions reflux in ethoxyethane

Product aldehyde

Equation CH3COOH(l) + 2[H] CH3CHO(l) + H2O(l)

CONVERSIONSCONVERSIONS

Page 22: Organic Reaction Scheme

REDUCTION OF ALDEHYDESREDUCTION OF ALDEHYDESRR

Reagent sodium tetrahydridoborate(III), NaBH4

Conditions warm in water (aqueous conditions)

Product primary alcohol

Mechanism nucleophilic addition

Equation C2H5CHO(l) + 2[H] C3H7OH(l)

Mechanism only need to show the H+ here

CONVERSIONSCONVERSIONS

Page 23: Organic Reaction Scheme

REDUCTION OF KETONESREDUCTION OF KETONESSS

Reagent sodium tetrahydridoborate(III), NaBH4

Conditions warm in water

Product secondary alcohol

Mechanism nucleophilic addition (see aldehydes for an example)

Equation CH3COCH3(l) + 2[H] CH3CH(OH)CH3(l)

CONVERSIONSCONVERSIONS

Page 24: Organic Reaction Scheme

ESTERIFICATIONESTERIFICATION

Reagent(s) carboxylic acid, alcohol, strong acid catalyst (eg. conc. H2SO4)

Conditions heat under reflux

Product ester

Equation CH3CH2OH(l) + CH3COOH(l) CH3COOC2H5(l) + H2O(l)

Notes Concentrated H2SO4 is also a dehydrating agent. It removes

water as it is formed causing the equilibrium to move to the rightand thus increasing the yield of ester.

Uses of esters Esters are fairly unreactive but that doesn’t make them useless.Used as flavourings, plasticisers and solvents.

Naming esters Named from the alcohol and carboxylic acid which made them...

CH3OH + CH3COOH CH3COOCH3 + H2O

from ethanoic acid CH3COOCH3 from methanol

METHYL ETHANOATE

TT

CONVERSIONSCONVERSIONS

Page 25: Organic Reaction Scheme

HYDROLYSIS OF ESTERSHYDROLYSIS OF ESTERSUU

Reagent(s) dilute acid or dilute alkali

Conditions heat under reflux

Product carboxylic acid and an alcohol

Equation CH3COOC2H5(l) + H2O(l) CH3CH2OH(l) + CH3COOH(l)

Notes If alkali is used for the hydrolysis the salt of the acid is formed.

CH3COOC2H5(l) + NaOH(aq) CH3CH2OH(l) + CH3COO-Na+(aq)

CONVERSIONSCONVERSIONS

Page 26: Organic Reaction Scheme

BROMINATION OF ALCOHOLS BROMINATION OF ALCOHOLS (NOT NEEDED FOR YOUR EXAM)(NOT NEEDED FOR YOUR EXAM)

Reagent(s) conc. hydrobromic acid HBr or sodium (or potassium) bromide and concentrated sulphuric acid

Conditions reflux

Product haloalkane

Equation C2H5OH(l) + conc. HBr(aq) C2H5Br(l) + H2O(l)

Mechanism The mechanism starts off in a similar way to dehydration(protonation of the alcohol and loss of water) but the carbocation(carbonium ion) is attacked by a nucleophilic bromide ion in step 3.

Step 1 Protonation of the alcohol using a lone pair on oxygen.

Step 2 Loss of a water molecule to generate a carbocation (carbonium ion).

Step 3 The bromide ion behaves as a nucleophile and attacks the carbocation.

VV

CONVERSIONSCONVERSIONS

Page 27: Organic Reaction Scheme

Reagent conc. H2SO4

Equation C2H4 + H2SO4 CH3CH2OSO3H

Mechanism electrophilic addition

WW ELECTROPHILIC ADDITION OF SULPHURIC ELECTROPHILIC ADDITION OF SULPHURIC ACIDACID

CONVERSIONSCONVERSIONS

Note that if the resulting ethyl hydrogen sulphate is heated in water, HYDROLYSIS takes place producing an alcohol (ethanol) and regenerating the H2SO4. Hence the sulphuric acid has acted as a catalyst overall.

C2H5OSO3H + H2O C2H5OH + H2SO4

Page 28: Organic Reaction Scheme

Reagent hydrogen cyanide, HCN

Conditions heat under reflux (alkaline conditions)

Product haloalkane

Equation CH3 CHO + HCN CH3CH(OH)CN 2-hydroxypropanenitrile

Mechanism

XX NUCLEOPHILIC ADDITION IN ALDEHYDES NUCLEOPHILIC ADDITION IN ALDEHYDES AND KETONESAND KETONES

CONVERSIONSCONVERSIONS

Watch out for the possibility of optical isomerism in hydroxynitriles.

Page 29: Organic Reaction Scheme

Conditions anhydrous conditions here (depends on the nucleophile used)

Equation eg. CH3 COCl + CH3NH2 CH3COONHCH3 + HCl

N-methylethanamide

Mechanism nucleophilic addition-elimination need to show H+ being lost also (this mechanism doesn’t, but should)

YY NUCLEOPHILIC ADDITION-ELIMINATIONNUCLEOPHILIC ADDITION-ELIMINATION

CONVERSIONSCONVERSIONS

Remember that in industry, acid anhydrides are the preferred method for acylation reactions like this, not acyl chlorides as shown here. This is for three reasons:

• secondary product is a carboxylic acid, not HCl (and so is less corrosive)

• anhydrides are cheaper to use

• anhydrides are less susceptible to hydrolysis