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
Ace Ahead Chem (Appendix) 3rd (11/11/08).indd 7
SO
Br 2 2
APPENDIX Routes for the synthesis of aliphatic compounds
Appendix
7
11/13/08 12:36:38 PM
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
Ace Ahead Chem (Appendix) 3rd (11/11/08).indd 8
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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