Appendix - Chemical Test, Routes of Synthesis

Appendix APPENDIX

1

Chemical tests for functional groups

Homologous series/ Typical compound

Functional group(s)

Alkanes CH3CH3 ethane

C – C and C–H

Alkenes CH2 = CH2 ethene

C=C

Chemical tests/Observations Add liquid bromine in ultraviolet light (or sunlight): White fumes of HBr liberated; decolourisation of bromine occurs slowly (a) Add Br2 in CCl4 at room temperature: Decolourisation of bromine occurs immediately CH2 = CH2 + Br2 → CH2BrCH2Br (b) Add acidified KMnO4 at room temperature: Decolourisation of KMnO4 occurs immediately CH2 = CH2 + [O] + H2O → CH2 – CH2 ⏐ ⏐ OH OH (a) Insert a glowing splint into the hydrocarbon hydrocarbons: Burns with smoky flame

Aromatic hydrocarbons

(b) Add concentrated nitric(v) acid and concentrated sulphuric acid at 55 °C: Yellow oil with bitter almond smell produced

benzene

NO2 + HNO3 (HONO2)

Alkylbenzenes

– CH3

CH3

+ H2O

Add alkaline KMnO4 and boil: Decolourisation of KMnO4; brown precipitate of MnO2 formed ⎯ CH3 + 3[O]

methylbenzene

H2SO4

⎯ COOH + H2O

Comment Oxidation of the side chain is more effective in alkaline than acidic conditions. Haloalkanes R–X where R is an alkyl group; X is Cl, Br or I

C–X

Add silver nitrate in alcohol and warm: White precipitate for C – Cl group; cream-coloured precipitate for C – Br group; yellow precipitate for C – I group

Alcohols CH3CH2OH ethanol

– OH

(a) Add solid PCl5: White fumes of HCl liberated C2H5OH + PCl5 → C2H5Cl + POCl3 + HCl(g) (b) Add glacial ethanoic acid and a few drops of concentrated sulphuric acid and heat: Fragrant fruity smell of ester liberated CH3COOH + C2H5OH → CH3COOC2H5 + H2O Appendix

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Homologous series/ Typical compound Aldehydes CH3CHO ethanal

Functional group(s) H ⏐ –C=O

Chemical tests/Observations (a) Add 2,4-dinitrophenylhydrazine at room temperature: Yellow-orange precipitate formed NO2 CH3CHO + H2NNH ⎯

⎯ NO2

NO2 CH3CH = NNH ⎯

⎯ NO2 + H2O

(b) Add ammoniacal silver nitrate (Tollens’ reagent) and warm: CH3CHO + 2Ag+ + H2O → CH3COOH + 2Ag + 2H+ (c) Add Fehling’s solution (alkaline copper(II) complex) and heat: CH3CHO + 2Cu2+ + 2H2O → CH3COOH + Cu2O + 4H+ Ketones CH3COCH3 propanone

O 储 –C–C–C

(a) Add 2,4-dinitrophenylhydrazine at room temperature: Yellow-orange precipitate formed CH3

NO2

C = O + H2NNH ⎯ CH3

CH3 ⎯ NO2

NO2

C = NNH ⎯

⎯ NO2 + H2O

CH3

(b) Add Tollens’ reagent or Fehling’s solution and heat: No reaction Carboxylic acids CH3COOH ethanoic acid

O 储 – C – OH

(a) Add Na2CO3 solution at room temperature: Effervescence and carbon dioxide gas liberated 2CH3COOH + Na2CO3 → 2CH3COONa + CO2 + H2O (b) Add ethanol and a few drops of concentrated sulphuric acid and heat: Fragrant, fruity smell of ester liberated

Ethanoate ions CH3COO–

O 储 –C–O–

(a) Add dilute sulphuric acid, then warm: Vinegar smell liberated CH3COO– + H+ → CH3COOH (b) Add iron(III) chloride solution: Dark red solution produced 3CH3COO– + Fe3+ → (CH3COO)3Fe

Methanoate ions HCOO–

O 储 H–C–O–

(a) Add ammoniacal silver nitrate solution, then warm: Grey precipitate or silver mirror of metallic silver formed HCOOH + Ag2O → 2Ag + CO2 + H2O (b) Add concentrated sulphuric acid and heat: Carbon monoxide liberated which burns with a blue flame HCOO– + H+ → H2O + CO

Benzoate ions COO–

O 储 C6H5 – C – O –

(a) Dissolve the organic salt in water, then add dilute hydrochloric or sulphuric acid to the aqueous solution obtained: White precipitate of benzoic acid formed ⎯ COO– + H+

2

⎯ COOH

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Homologous series/ Typical compound

Functional group(s)

Chemical tests/Observations (b) Add iron(III) chloride solution: Buff-coloured precipitate formed ⎯ COO– + Fe3+

3

Amides CH3CONH2 ethanamide Aliphatic primary amines C2H5NH2 ethylamine

⎯ COO)3Fe

(

– CONH2

Add aqueous sodium hydroxide, then warm: Ammonia gas liberated; it forms white fumes with hydrogen chloride gas CH3CONH2 + NaOH(aq) → CH3COONa + NH3

– NH2

Add sodium nitrite (NaNO2), followed by dilute hydrochloric acid, then warm: Effervescence occurs NaNO2/HCl RNH2 + O = N – OH ⎯⎯⎯⎯⎯→ ROH + N2 + H2O (HNO2) nitrous acid

Acyl chloride CH3COCl ethanoyl chloride

O 储 – C – Cl

(a) Add ethanol and shake: White fumes of HCl liberated On pouring reaction mixture into a beaker of water, fragrant smell of ester produced CH3COCl + C2H5OH → CH3COOC2H5 + HCl (b) Add aqueous silver nitrate at room temperature: White precipitate of silver chloride formed CH3COCl + AgNO3 + H2O → CH3COOH + AgCl + HNO3

Amino acids H2NCH2COOH aminoethanoic acid

Phenols

– CHCOOH ⏐ NH2 OH

OH

Add copper(II) sulphate solution: Dark blue solution of copper(II) complex formed (a) Add bromine water at room temperature: Decolourisation of bromine water and white precipitate formed OH

OH Br

phenol

Br

+ 3Br2

+ 3HBr Br

(b) Add iron(III) chloride solution at room temperature: Purple solution produced Arylamines NH2

NH2

(a) Add bromine water at room temperature: Decolourisation of bromine water and white precipitate formed NH2

phenylamine

Br

NH2

+ 3Br2

Br + 3HBr

Br

(b) Add sodium chlorate(I) solution: Purple solution produced

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APPENDIX

2

Tests to distinguish between organic compounds

(A) Aliphatic Organic Compounds To distinguish between

Chemical tests

Observations

Alkene and alkane (or cycloalkane)

Add Br2 in CCl4

Alkene: Immediate decolourisation Alkane (or cycloalkane): No reaction

Alcohol and ether

Add PCl5

Alcohol: White fumes of HCl Ether: No reaction

CH3CH2OH and CH3OH

Iodoform (triiodomethane) test: Add I2 in NaOH(aq), then warm

C2H5OH: Yellow precipitate of iodoform (CHI3) formed (positive test) CH3OH: No visible reaction

CH3CH2OH and CH3CH2CH2OH

Iodoform test

C2H5OH: Positive iodoform test CH3CH2CH2OH: No reaction

CH3CHCH3 and CH3CH2CH2OH ⏐ OH

Iodoform test

CH3CH(OH)CH3: Positive iodoform test CH3CH2CH2OH: No reaction

Aldehyde (RCHO) and ketone (RCOR')

(a) Silver mirror test: Add Tollens’ reagent, then warm

Aldehyde: Silver mirror formed Ketone: No reaction

(b) Add Fehling’s solution, then heat

Aldehyde: Reddish-brown precipitate of Cu2O formed Ketone: No reaction

CH3COCH2CH2CH3 and CH3CH2COCH2CH3

Iodoform test

CH3COCH2CH2CH3: Positive iodoform test CH3CH2COCH2CH3: No reaction

HCOOH (or its salts) and CH3COOH (or its salts)

Acidified KMnO4 and heat

HCOOH (or its salts): Decolourisation of KMnO4 CH3COOH (or its salts): No reaction

COOH (or its salts) and ⏐ COOH CH3COOH (or its salts)

Acidified KMnO4 and heat

COOH (or its salts): Decolourisation of ⏐ KMnO4 COOH CH3COOH (or its salts): No reaction

COOH and HCOOH ⏐ COOH

Add concentrated sulphuric acid, then heat

COOH: Gives CO(g) and CO2(g) ⏐ (limewater turns milky) COOH HCOOH: Only CO(g) liberated which has no effect on limewater

CH3COONH4 and CH3CONH2

Add FeCl3 solution

CH3COONH4: Dark red colouration due to formation of (CH3COO)3Fe CH3CONH2: No visible reaction

H2NCH2COOH and ClCH2COOH

Add copper(II) sulphate solution

H2NCH2COOH: Deep blue colouration formed ClCH2COOH: No reaction

4

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To distinguish between COOC2H5 and CH3COOC2H5 ⏐ COOC2H5

CH3CH2Br and CH3CH2Cl

Chemical tests

Observations

Reflux with NaOH(aq); distill off the ethanol produced; acidify the residual solution; add KMnO4 solution

COOC2H5: KMnO4 decolourised ⏐ COOC2H5

Add silver nitrate in ethanol and warm

CH3CH2Br: Yellow precipitate formed CH3CH2Cl: White precipitate formed

CH3COOC2H5: No reaction

(B) Aromatic Compounds To distinguish between

Chemical tests

Observations

C6H5CH3 and benzene

Add KMnO4 in alkaline solution, then boil

C6H5CH3: KMnO4 decolourised and brown precipitate formed Benzene: No reaction

CH3C6H4OH and C6H5CH2OH

(a) Bromine water

CH3C6H4OH: Decolourisation and white precipitate formed C6H5CH2OH: No reaction

(b) PCl5

C6H5CH2OH: White fumes CH3C6H4OH: No reaction

C6H5CHO and C6H5COCH3

Add Tollens’ reagent, then warm Comment Fehling’s solution cannot be used, as C6H5CHO has no effect on Fehling’s solution

C6H5CHO: Silver mirror formed C6H5COCH3: No reaction

C6H5CH2CHO and CH3C6H4CHO

Add Fehling’s solution, then heat

C6H5CH2CHO: Yellow-orange precipitate of Cu2O formed CH3C6H4CHO: No reaction

C6H5CH2Cl and C6H5Cl

Add AgNO3 in ethanol, then heat

C6H5CH2Cl: White precipitate C6H5Cl: No reaction

CH3C6H4COOH and CH3C6H4OH

Add Na2CO3 solution at room temperature

CH3C6H4COOH: Effervescence, CO2 liberated CH3C6H4OH: No reaction

CH3C6H4NH2 (or C6H5NH2) and C6H5CH2NH2

Add bromine water

CH3C6H4NH2 (or C6H5NH2): Bromine decolourised and white precipitate formed C6H5CH2NH2: No reaction

(C) Aliphatic and Aromatic Compounds To distinguish between Benzene and hexane

Chemical tests Add nitrating mixture (concentrated HNO3 + concentrated H2SO4) at 55 °C

Observations Benzene: Yellow oil formed Hexane: No visible reaction

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To distinguish between

Chemical tests

Observations

(a) Br2 in CCl4 (or bromine water)

Cyclohexene: Bromine decolourised Benzene: No reaction

(b) Acidified KMnO4 at room temperature

Cyclohexene: KMnO4 decolourised Benzene: No reaction

C6H5COOC2H5 and CH3COOC2H5

Reflux the esters with aqueous NaOH, distill off the ethanol produced, add excess sulphuric acid to the residual liquid

C6H5COOC2H5: White precipitate of C6H5COOH formed CH3COOC2H5: No precipitate formed

C6H5CHO and CH3COCH3

(a) Add Tollens’ reagent, then warm

C6H5CHO: Silver mirror formed CH3COCH3: No reaction

(b) Iodoform (triiodomethane) test

C6H5CHO: No reaction CH3COCH3: Yellow precipitate of CHI3 formed (positive test)

(a) Na2CO3 solution at room temperature

CH3COOH: Effervescence; CO2 liberated C6H5OH: No reaction

(b) Bromine water at room temperature

CH3COOH: No reaction C6H5OH: White precipitate of 2,4,6-tribromophenol formed

(a) Bromine water at room temperature

C6H5OH: White precipitate of 2,4,6tribromophenol formed C2H5OH: No reaction

(b) Iodoform test

C6H5OH: No reaction C2H5OH: Positive iodoform test

C6H5NH2 and C2H5NH2

Add bromine water at room temperature

C6H5NH2: White precipitate of 2,4,6-tribromophenylamine formed C2H5NH2: No reaction

C6H5CONH2 and C2H5NH2

Add NaOH(aq) and heat

C6H5CONH2: Ammonia gas liberated C2H5NH2: No reaction

C6H5CONH2 and C2H5CONH2

Add NaOH(aq), then boil; add excess sulphuric acid to the reaction mixture on cooling

C6H5CONH2: Ammonia gas liberated; on acidification, white precipitate of C6H5COOH formed C2H5CONH2: Ammonia gas liberated; on acidification, no precipitate formed

Cyclohexene and benzene

CH3COOH and C6H5OH

C6H5OH and C2H5OH

6

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H2O

250 °C

O2/Ag

+

CH3CHBrCH3

Terylene

CO2 + H2O

r HB

NaOH reflux

C2H5X

NH3

4

H2SO4

K2Cr2O7

CH3CHBrCH2Br

CH3CH2CHO

CH3CH(OH)CH3

Br2

LiAlH4

K2Cr2O7/H+

CH3COCH3

H2SO4 heat

CH3CH2COOH

CO2 + H2O

MnO4–/H+

HCOOH

Mg ether

C2H5CH2OH

HCHO + acid

RCHO + acid

(CH3)3Pb

CH3Li

R CHOH C2H5

Li ether

C2H5OH

C

O

R R ’ C—OH C2H5

R R’

CH3COOC2H5

CH3COOH

H2SO4

CH3CONH2

C2H5OH

alloy Na/Pb heat

COOH

NH3

C2H5MgX Grignard reagent

CH3I

aspirin

NaOH

P/I2

Cr2O72–/H+

HCHO

OH

CH3COCl

OCOCH3 COOH

PCl5

K2Cr2O7/H+

CH3OH

CH3COOH

KCN alc. reflux

C2H5NH3+

CH3CN

(CH3CH2)4Pb CO + H2O

4

H+

K2Cr2O7/H+

LiAlH4

CH3CHO

C2H5ONa

H–

O

O

ux

refl

2

HS

C2H5NH2

Na

K2Cr2O7/H+

CH3COOC2H5

NaOH, reflux

KCN alcohol Na/C2H5OH C2H5CN

H 2 SO H 4 2O

CH3CH=CH2

H2SO4 180 °C

C2H5CH2OH

HNO2

O 2

H C2H5HSO4

Pb

a/

KMnO4/H+

1

C2H5OC2H5

H2

, SO 4

C2H5CH2NH2

C2H4

C 80 °

O4

30 0 20 atm 0° C

H 2S

N

COOH

COOH

K2Cr2O7/H

CH2OH

CH2OH

CH2

O

nO

CH2

4

H2,Ni 200 °C

KM

C2H5OH

CH3COOH

(CH2)n

5

OH H 2

C

SO 2

H HX

C2H6

Na

C2H4Br2

C

0° 14

NaOH, reflux

COOH

O2

HOOC

5

OH H

HN 2

3

/C

H

+

/H 4

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SO

Br 2 2

APPENDIX Routes for the synthesis of aliphatic compounds

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7

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Cl

NH3+Cl–

l HC

Sn/HCl

600 °C

Fe2O3

NHCOCH3

CH3COCl

5 °C

HNO2

CH3 cumene

C—CH3

H

LiAlH4

H, C 2H 5O eat h l, C H

/H +

CH=CH2

N=N

OH

N2+Cl–

OH

70 °C

H2O

Cl

H2SO4

H H

H 2, N 0° i C 20

OH

100 °C

—C—C— ( )n H

CH3

C—CH3

O—OH

COOH

K2Cr2O7/H+

—CH2OH

polymerisation

O2, 120 °C

4

nO

KM

C—OC2H5

O

CHO

LiAlH4 HNO3

Br2

OH

OH

Br

OH

heat

K2Cr2O7/H+

Br

N=N

Br

nylon

O

OH

heat

COCl, NaOH

NH2(CH2)6NH2

HOOC(CH2)4COOH

+ CH3COCH3

H2, Ni 200 °C

OH

+

Cl

Cl

NO2

C2H5

CH3CH=CH2

250 °C, 25 atm, H3PO4

O4 /H +

NH2

KMn

C—CH3

O

CrO2Cl2

—N 2

Cl

Cl

CH3Cl/AlCl3

CH3

4

Cl

Cl

u.v.

2

l3 lC m /A 0 at H 4 C 2 °C, 0 5 2

Cl ,

Cl

2

,F

e

i ,N H 2 °C 0 20

HNO3/H2SO4

CO

CH

15 OH Na 0 °C , 30 atm

55 °C

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Cl

8 CO2Na +

NaOH (aq) reflux

C—O

O

O–Na+

4

3

APPENDIX Routes for the synthesis of aromatic compounds

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APPENDIX

5

Organic compound Alkene, cycloalkene or alkyne

Reactions of bromine with organic compounds Observations Immediate decolourisation

Reaction type/Equations Electrophilic addition reaction CH2 = CH2 + Br2 → CH2BrCH2Br Br + Br2 Br

H – C ≡ C – H + 2Br2 → CHBr2CHBr2 Phenol or phenylamine

Decolourisation and white precipitate formed

Electrophilic substitution reaction OH Br

Br

– OH + 3Br2

+ 3HBr Br Br

NH2

– NH2 + 3Br2

Br + 3HBr

Br

Aldehyde or ketone

No reaction with bromine alone; decolourisation occurs only in the presence of a dilute acid

Substitution reaction CH3COCH3 + Br2 → BrCH2COCH3 +HBr

Alkanes or cycloalkanes

Decolourisation occurs slowly in uv light or sunlight; no reaction in the dark at room temperature

Free radical substitution reaction RH + Br2 → RBr + HBr

Benzene or alkylbenzene

No reaction with bromine alone; decolourisation occurs only in the presence of a halogen carrier such as iron filings

Electrophilic substitution reaction + Br2 CH3

⎯ Br + HBr CH3

+ 2Br2

CH3

Br +

+ 2HBr Br

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APPENDIX

Reactions of aqueous sodium hydroxide with organic compounds

6

Reaction type

Organic compound(s)

Alkaline hydrolysis

Haloalkane (alkyl halide)

RX + NaOH → ROH + NaX CH2XCH2X + 2NaOH → CH2OHCH2OH + 2NaX

Ester

RCOOR' + NaOH → RCOONa + R'OH

Amide

RCONH2 + NaOH → RCOONa + NH3 C6H5NHCOCH3 + NaOH → C6H5NH2 + CH3COONa

Nitrile

RCN + H2O + NaOH → RCOONa + NH3

Ammonium salt

RCOONH4 + NaOH → RCOONa + NH3 + H2O

Amine salt

RNH3+Cl– + NaOH → RNH2 + NaCl + H2O

NaOH as a base

APPENDIX

7

Role of sulphuric acid

Equation(s)

Reactions of sulphuric acid with organic compounds Organic compound(s)

Reaction(s)/Equation(s)

As a catalyst for acid hydrolysis

Ester

RCOOR' + H2O

As a strong acid

Carboxylate

Strong acid displaces weaker acid from its salt RCOONa + H – HSO4 → RCOOH + NaHSO4

Amine

Amines react with acids to form salts RNH2 + H – HSO4 → RNH3+HSO4–

Methanoic acid and ethanedioic acid

Concentrated H2SO4 removes water molecules from HCOOH and H2C2O4 (ethanedioic acid) or their salts on heating

As a dehydrating agent

RCOOH + R'OH

H2SO4

HCOOH ⎯⎯→ CO + H2O H2SO4

H2C2O4 ⎯⎯→ CO + CO2 + H2O As an electrophile in electrophilic addition reactions with alkenes

10

Alkenes

Concentrated H2SO4 reacts with alkenes to form addition products RCH = CH2 + H – OSO3H → RCHCH3 (H2SO4) ⏐ OSO3H

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APPENDIX

Reactions of iron(III) chloride with organic compounds

8

Organic compound(s)

Observation

Salts of carboxylic acid, for example, methanoate (HCOO–) or ethanoate (CH3COO–)

Red solution formed; brown precipitate obtained when boiled

Benzoate COO–

Buff-coloured precipitate formed

benzoate ion

Phenol, phenoxide ion and 2-hydroxybenzoic acid O–

OH

COOH OH

phenol

APPENDIX

phenoxide ion

9

Purple solution formed

2-hydroxybenzoic acid

Uses of potassium manganate(VII) in organic chemistry

(a) To distinguish alkenes from alkanes or cycloalkanes Alkenes decolourise acidified KMnO4 at room temperature or on heating. Alkanes and cycloalkanes do not react with KMnO4. (b) To distinguish between alkenes • Alkenes with a terminal = CH2 group not only decolourise hot, acidified KMnO4, but also liberate carbon dioxide. This is because a terminal = CH2 group is completely oxidised to carbon dioxide and water by hot KMnO4. The remaining RCH = group is oxidised to RCOOH. • Alkenes without a terminal = CH2 group decolourise hot, acidified KMnO4 but do not liberate carbon dioxide. (c) To identify the position of the double bond in an alkene The oxidation products obtained when an alkene reacts with hot, acidified KMnO4 are often used to determine the position of the double bond of an unknown alkene. (d) To distinguish aldehydes from ketones Aldehydes are oxidised by acidified KMnO4 on heating to form carboxylic acids. Thus aldehydes decolourise acidified KMnO4 on heating. In contrast, ketones do not decolourise hot, acidified KMnO4. (e) To distinguish alkylbenzenes from benzene Alkylbenzenes such as ethylbenzene decolourise acidified or alkaline KMnO4 on heating. The alkyl group is oxidised to – COOH, for example, ⎯ CH2CH3 + 6[O]

⎯ COOH + CO2 + 2H2O

ethylbenzene

Benzene does not decolourise hot, acidified or alkaline KMnO4. (f) To distinguish primary or secondary alcohols from tertiary alcohols Primary and secondary alcohols can be oxidised to aldehydes and ketones respectively. Hence, primary and secondary alcohols decolourise hot, acidified KMnO4. Tertiary alcohols are resistant to oxidation and hence do not decolourise hot, acidified KMnO4.

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