+2 UNIT 15 PAGE- 3
CYANIDES AND ISOCYANIDES
Cyanides and isocyanides are isomeric compounds. Both of these are derivatives of hydrocyanic acid which is known to exist in the following two isomeric forms.
The class of organic compounds obtained by the replacement of the H-atom of hydrogen cyanide by an alkyl or the aryl group is called cyanides or nitriles. Their general formula is :
(where R is any alkyl group and Ar is any aryl group)
The functional group of cyanides is the cyano or the nitrile group, i.e., -C º N .
The class of organic compounds obtained by the relacement of H- atom of hydrogen isocyanide by alkyl or aryl group is called isocyanides or isnitriles. They are also called carbylamines. Their general formula is :
(where R is any alkyl group and Ar is any aryl group)
The functional group of isocyanides is the isocyano or isonitrile group, i.e.,
Thus from the above discussion , it follows that :-Cº N : group can be attached to the alkyl or aryl group either through alkyl or aryl group either through the carbon or through the nitrogen atom. Such a group can be linked through two different sites is called ambident group.
Structure
In cyanides , both C and N are sp-hybridised.
One of the sp-hybridised orbital of C overlaps with sp-hybridised orbital on N to form a C- N , s-bond. The sp-hybridised orbital of C overlaps with an sp3-orbital of carbon of alkyl group to form a R-C , s-bond. The second sp-orbital of N , however, contains a lone pair of electrons.
Both C and N are now left with two mutually perpendicular p-orbitals which overlap sideways to form two p-bonds. The orbital structure of alkyl cyanides is shown in Fig.
The orbital structure of alkyl cyanides
Like cyanides both C and N atoms in isocyanides are also sp-hybridised with the following points of difference :
(i) One of the sp-hybridised orbital of C contains a lone pair of electron. Further one of the two unhybridised p-orbitals contains one electron while the other is empty.
(ii) The two sp-hybridised orbitals of N contain one electron each. Further , one of the unhybridised p-orbitals contains a lone pair of electrons while the other is singly occupied.
Now one sp-hybridised orbital of N overlaps with the sp-hybridised orbital of C forming a N - C, s-bond. The other sp-hybridised orbital on N overlaps with sp3-hybridised orbital on C atom of the alkyl group to form R-N , s-bond. The other sp-orbital of C , however, contains a lone pair of electrons.
Now each of the N and C atoms have one half-filled p-orbital which overlap to form a p-bond. N is left with a p-orbital which has a pair of electrons while C has a p-orbital which is empty. Therefore pp-pp - back bonding occurs to form additional p-bond. The orbital structure of isocyanides is depicted in Fig.
Orbital structure of alkyl isocyanides
Nomenclature
(a) Cyanides : Common names of cyanides are obtained by adding the word cyanide to the name of the alkyl or aryl group.
They are also named as derivatives of the acids they give upon hydrolysis. In this system of nomenclature, the terminal –ic acid from the common name of the acid is replaced by the suffix -onitrile. For example, CH3CN on hydrolysis gives acetic acid. Therefore, the common name of CH3CN is :
Acetic acid - ic acid + onitrile = Acetonitrile
IUPAC Names : In the IUPAC system, alkyl cyanides are called alkanenitriles. The longest chain containing the carbon atom of the -CN group is selected as the parent alkane. The positions of the substituents on the parent alkane are indicated by arabic numerals with carbon atom of -CN group always getting number 1. For example,
Ethane + nitrile = Ethanenitrile
The common and IUPAC names some important alkyl and aryl cyanides are given below.
Structural formula | Common name | IUPAC name |
CH3CN | Methyl cyanide or Acetonitrile | Ethane nitrile |
CH3CH2CN | Ethyl cyanide or Propiononitrile | Propanenitrile |
CH3CH2CH2CN | n-Propyl cyanide or Butyronitrile | Butanenitrile |
CH3CH(CH3)CN | Isopropyl cyanide or Isobutyronitrile | 2-Methylpropanenitrile |
CH2=CHCN | Vinyl cyanide or Acrylonitrile | 2-propenenitrile |
C6H5CN | Phenyl cyanide or Benzonitrile | Benzenenitrile |
For further illustration, consider the IUPAC names of following compounds.
According to 1993 recommendations for IUPAC nomenclature of organic compounds, nitriles in which -CºN group may be considered to have replaced the -COOH group(s) of an acid named by a ‘carboxylic acid’ suffix are named by replacing the suffix by the word carbonitrile. For example,
(b) Isocyanides
For naming isocyanides, the word iso is prefixed to the name of the corresponding cyano / nitrile compound. Thus CH3NC is named as methyl isocyanide or acetoisonitrile. In another mode of nomenclature, the suffix carbyl amine is added to the name of the alkyl group. Thus, CH3NC is called methylcarbylamine.
Methods of Preparation
1. From alkyl halides
Alkyl cyanides are easily prepared by heating an alkyl halide with an aqueous ethanolic solution of sodium or potassium cyanide.
A small amount of methyl isocyanide is also formed in the above reaction. However, if silver cyanide is used instead of NaCN or KCN , the chief product is an isocyanide.
For example,
A small amount of methyl cyanide is also formed in the above reaction.
Aryl cyanides cannot be prepared by this method since aryl halides are almost unreactive towards nucleophilic substitution reactions.
Explanation
This reaction is an example of nucleophilic substitution reaction in which -:CºN: ion acts as the nucleophile. In the cyanide ion , both the carbon and nitrogen atoms have a pair of electrons. Therefore either the carbon or the nitrogen atom can act as the electron donor to the alkyl halide. Such nucleophilic species which have more than one site for reaction are called ambident nucleophiles. Thus CN- ion is an ambident nucleophile.
Alkali metal cyanides are predominantly ionic. In principle, the reaction can occur either through carbon or nitrogen. But in practice , the reaction occurs through carbon since C -C bonds are stronger than C- N bonds and hence alkyl cyanides are the chief products. On the other hand, silver cyanide is predominantly covalent. Consequently only nitrogen electron pair is available for bond formation. As a result, alkyl isocyanides are the chief products.
2. From arenediazonium salts
Aryl cyanides can be easily prepared by the action of sodium or potassium cyanide on a suitable arenediazonium salt in presence of cuprous cyanide or copper powder as catalyst.
This reaction is a special case of Sandmeyer reaction or Gattermann reaction.
This method cannot be used for the preparation of alkyl cyanides. The reason being that alkane diazonium salts are very unstable even at low temperature (273 – 278 K) and hence cannot be easily prepared.
3. From acid amides
Alkyl and aryl cyanides can also be prepared by dehydration of primary amides with phosphorus pentachloride (PCl5), phosphorus oxychloride (POCl3), phosphorus pentoxide (P2O5), thionyl chloride (SOCl2) etc. For example,
In this reaction, ammonium salts of carboxylic acids can be used instead of amides. Thus,
4. From aldoxime
Both alkyl and aryl cyanides can also be prepared by dehydration of aldoximes with phosphorus pentoxide (P2O5) or acetic anhydride. For example,
1. From primary amines
Alkyl and aryl isocyanides can be easily prepared by carbylamine reaction. It consists of heating a mixture primary amine (aliphatic or aromatic) , chloroform and alcoholic potash.
6. From Grignard reagent
Alkyl cyanides can also be prepared by the action of Grignard reagents on cyanogen chloride (Cl-CN)
This method is particularly useful for the preparation of tertiary alkyl cyanides.
Physical properties
1. Physical state, colour and odour : The lower alkyl cyanides and isocyanides are colourless liquids but the higher members are crystalline solids. Alkyl cyanides have generally pleasant odours but alkyl isocyanides have very unpleasant odours.
2. Boiling points : Both -CN and -N C groups are highly polar. As a result, they have strong intermolecular dipole-dipole interactions and hence have higher boiling points than the alkyl halides of comparable molecular masses.
For example,
Compound | Molecular mass | Boiling point (K) |
CH3CN | 41 | 355.5 |
CH3NC | 41 | 332 |
CH3Cl | 50.5 | 249.3 |
Alkyl isocyanides usually have lower boiling points than their corresponding alkyl cyanides. This is due to the reason that alkyl isocyanides have lower dipole moments (~ 3 D) as compared to those of alkyl cyanides ( ~ 4 D).
3. Solubility : The lower alkyl cyanides are soluble in water in which they form hydrogen bonds.
However, as the size of the alkyl group increases, the solubility decreases due to increase in size of the hydrocarbon portion of the molecule. For example, acetonitrile is miscible with water , propiononitrile is fairly soluble but higher members are practically insoluble. Hower, all cyanides are highly soluble in organic solvents.
Alkyl isocyanides , are insoluble in water . This is due to the reason that nitrogen atom does not have a lone pair of electrons and cannot form H-bonds.
Chemical properties
1. Hydrolysis
(a) Complete hydrolysis : On boiling with an aqueous mineral acid or alkali, nitriles are completely hydrolysed to give the corresponding carboxylic acids and ammonia. The hydrolysis occurs with the intermediate formation of an amide.
(b) Partial hydrolysis : The hydrolysis of alkyl cyanides can be stopped at the amide stage by shaking with the alkyl cyanide with cold conc. HCl or by dissolving the alkyl cyanide in con. H2SO4 and then pouring it into water. Thus,
Isocyanides , on the other hand , are hydrolysed by dilute acids , but not by alkalies to form primary amine and formic acid.
Explanation
The negative charge present on carbon atom in isocyanides initially attracts electrophiles (i.e, H+) but repels nucleophiles (OH- ion). As a result, isocyanides are hydrolysed only by acids but not by alkalies.
Once a proton gets attached to the negatively charged carbon atom, the tendency of this carbon to attract a nucleophile increases due to the presence of a positive charge on the nitrogen atom and thus facilitates hydrolysis as shown below :
2. Reduction
(a) Complete reduction : The carbon – nitrogen triple bond of nitriles can be completely reduced to yield the corresponding primary amine. The reduction is carried out either catalytically by H2 in presence of Ni, Pt as catalyst or chemically by using either LiAlH4 or Na and alcohohol (Mendius reaction)
Isocyanides on complete reduction gives secondary amines, i.e., N-methylamines.
(b) Partial reduction - Stephen’s reduction : When an ethereal solution of nitrile is reduced with hydrogen chloride gas and stannous chloride at room temperature, imine hydrochloride is precipitated. This upon hydrolysis with boiling H2O gives aldehydes. For example,
3. Reaction with Grignard reagent
Grignard reagents add to nitriles giving intermediate imine salts which upon hydrolysis give ketones.
Uses
1. Conversion of alkyl halides into alkyl cyanides provides a useful method for stepping up the series.
2. Aryl cyanides are useful intermediates in organic synthesis because it can be easily converted into amines, aldehydes, amides, carboxylic acids etc as shown below :
3. Some cyanides such as acetonitrile is widely used as solvents.
4. Acrylonitrile (CH2=CHCN) is used in the manufacture of nitrile rubbers and textiles.
Problems
16. How will you prepare :
(a) acetaldehyde from methyl cyanide
(b) methyl cyanide from acetic acid
(c) 1-aminopentane from n-hexanenitrile
(d) benzonitrile from aniline.
17. An organic compound A (C3H5N) on boiling with alkali gives ammonia and sodium salt of an acid B (C3H6O2) . A on reduction gives C (C3H9N) which with nitrous acid gives D (C3H8O) . Give the structural formulae of A, B, C and D.
18. An organic compound A having molecular formula C2H3N on reduction gave another compound B. Upon treatment with nitrous acid, B gave ethyl alcohol and on warming with chloroform and alcoholic KOH , it formed an offensive smelling compound C. Identify A, B and C. Write the equations involved.
Some commercially important compounds
Acrylonitrile
It can be commercially prepared by any one of the following methods :
(i) From acetylene : By catalytic addition of hydrogen cyanide to acetylene.
(ii) From ethylene
(iii) Ammonoxidation of propylene : It is the most important and widely used method for the manufacture of acrylonitrile. A mixture of ammonia and propylene is made to react with compressed air at 673 – 723 K in presence of bismuth phosphomolybdate deposited on silica gel as catalyst.
Uses
1. It is widely used in the manufacture acrylic fibres (PAN) , nitrile rubbers(co-polymer of 1,3-butadiene and acrylonitrile), SAN resin (co-polymer of styrene and acrylonitrile) and ABS resin ( copolymer of acrylonitrile, butadiene and styrene).
2. Acrylonitrile is also used in the manufacture of hexamethylene diamine which is used in the manufacture of nylon -66.
3. Polyacrylonitrile is also used in the manufacture of carbon fibres.
DIAZONIUM SALTS
Arenediazonium salts were discovered by John Peter Greiss in 1858. They have the general formula , Ar+N2X- where Ar- stands for the aryl group and X may be any anion such as Cl-, Br, NO3-, HSO4-, BF4-, etc.
Aliphatic diazonium salts are also known but they are highly unstable. They rapidly decompose even at low temperatures forming carbocations and nitrogen gas.
Therefore we shall discuss the chemistry and synthetic applications of arenediazonium salts only particularly with reference to benzenediazonium chloride.
Nomenclature
Diazonium salts are named by adding the suffix diazonium to the name of the aromatic compound followed by the name of anion. For example,
Preparation of Diazonium salts
Aromatic diazonium salts are prepared treating an ice-cold solution of aromatic primary amine in excess of mineral acid like HCl or H2SO4 with an ice cold solution of sodium nitrite dissolved in water. The temperature is maintained between 0 - 5°C because most of diazonium salts decompose at higher temperature.
The diazonium salt so formed remains in solution. Since the diazonium salts are unstable and explosive substances, they are not isolated in solid form but are used directly in solution.
For example, benzene diazonium chloride is prepared by treating an ice-cold solution of aniline in hydrochloric acid with an ice-cold solution of sodium nitrite at about 273 K. The reaction of converting aromatic primary amine to diazonium salt is called diazotisation.
Stability of Diazonium salts
Aromatic diazonium salts are much more stable than aliphatic diazonium salts due to the dispersal of the positive charge over the benzene ring as shown below.
Alternatively the instability of diazonium salts is due to their tendency to to eliminate an exceptionally stable molecule of nitrogen to form carbocations, i.e.,
Since phenyl (or aryl ) carbocation is much less stable than alkyl carbocations, therefore aromatic diazonium salts have much lower tendency to eliminate nitrogen than aliphatic diazonium salts. In other words, aromatic diazonium salts are much more stable than aliphatic diazonium salts.
Physical properties
The general physical properties of diazonium salts are :
1. Diazonium salts are generally colourless, crystalline solids.
2. They are readily soluble in water but less soluble in alcohol.
3. They are unstable and explode in dry state. Therefore they are generally used in solution state.
4. Their aqueous solutions are neutral to litmus and conduct electricity due to the presence of ions.
Chemical properties of Diazonium salts
The diazonium salts give the following types of reactions :
1. Substitution reactions : In substitution or replacement reactions, nitrogen of the diazonium salts is lost as N2 and different groups are introduced in its place. Some important displacement reactions are :
(i) Replacement by –OH group : When an aqueous solution of diazonium salt is boiled or steam distilled , it gives phenols, therefore, diazo group is replaced by –OH group.
(ii) Replacement by hydrogen : When diazonium salt is treated with hypophosphorus acid, benzene is obtained.
(iii) Replacement by chlorine or bromine – Sandmeyer reaction : Aryl chlorides and bromides can be easily prepared by treating a cold aqueous solution of arenediazonium salt with a solution of cuprous chloride in hydrochloric acid , or cuprous bromide in hydrobromic acid . This reaction is called Sandmeyer reaction and gives aryl halides in 60 – 80% yield.
When diazonium salt solution is warmed with copper powder and corresponding halogen acid, the respective halogen is introduced. The reaction is a modified form of Sandmeyer reaction and is known as Gattermann reaction.
(iv) Replacement by iodo group : When aqueous solution of benzene diazonium salt is warmed with excess of potassium iodide, aryl iodide is formed.
(v) Replacement by Fluorine – Balz-Schiemann reaction
When an aqueous solution of a diazonium salt is treated with fluoboric acid (HBF4) , diazonium fluoborate gets precipitated. It is filtered and dried. Unlike other diazonium salts, diazonium fluoborates are fairly stable compounds. When dry diazonium fluoborate is heated, it decomposes to produce aryl fluoride and boron trifluoride.
(vi) Replacement by cyano group : When benzene diazonium salt is treated with cuprous cyanide, cynobenzene is formed.
(vii) Replacement by nitro group : Nitrobenzene is prepared by decomposing diazonium fluoborate with aqueous NaNO2 in the presence of copper powder.
(viii) Replacement by thio (-SH) group : When diazonium salt is treated with potassium hydrosulphide, thiophenol is produced.
2. Reactions in which nitrogen is retained
(a) Reduction to arylhydrazines
Arenediazonium salts upon reduction give good yield of arylhydrazines. The reduction can be brought about by a number of reagents such as SnCl2-HCl, sodium sulphite, sodium hydrosulphite and even electrolytically.
If, however, vigorous reducing agents such as Zn/HCl is used, product is an aromatic amine.
(b) Coupling reactions
Bezene diazonium chloride couples with electron rich aromatic compounds like phenol and aniline to give diazo compounds. The azo compounds contain –N=N – bond and the reaction is called coupling reaction.
Coupling occurs para to hydroxy or amino group. All azo compounds are strongly coloured and are used as dyes.
Methyl orange
Methyl orange is an important dye obtained by coupling the diazonium salt of sulphanilic acid with N,N-dimethylaniline.
Uses
Diazonium salts are highly useful intermediates in the synthesis of a large number of aromatic compounds especially the aryl halides in pure states as given below.
1,2,3-Tribromo benzene which is not formed in pure state by direct bromination of benzene, is obtained by the following sequence of reactions staring from p-nitroaniline. Here , use is made of the orientation effect of –NO2 and –NH2 groups. These groups are removed afterwards to obtain the final product.
Some Commercially important compounds
1. Aniline : It is one of the important of all the amines. It is manufactured by the reduction of nitrobenzene using :
(a) iron –fillings and hydrochloric acid.
(b) Catalytic hydrogenation.
Catalytic hydrogenation of nitro group takes place smoothly with hydrogen gas in presence of finely divided nickel or platinum as catalyst.
2. N, N-Dimethylaniline (DMA) : It is used as a raw material in the preparation of a number of azodyes, for example, methyl orange, crystal violet, malachite green etc. It couples readily to give p-azo derivatives. DMA is prepared by methylation of aniline with bromomethane.
3. Hexamethylenediamine : It is used as a raw material in the production of terylene.
4. Novocain : It is also called procaine and is used as a local anaesthetic. It was developed in 1905 and contains a primary and tertiary amino groups.
A number of nitrogen containing compounds which act as bases occur in nature. These are known as alkaloids. In these compounds, nitrogen may be present in the form of primary, secondary and tertiary amino group. Most of the alkaloids produce striking physiological effect. Caffeine – a central nervous system stimulant , occurs in tea leaves, coffe bean, and cola nut, nictin (present in tobacco plant), atropine (present in Atropa belladonna) and cocaine (present in Erythroxylum coca) are some examples of alkaloids. In small doses , nictine acts as stimulant , but in larger doses , it causes depression, nausea and vomitting. Atropine is an intense poison. In 0.5 – 1% concentration, it is used to dilate the pupil of the eye in ophthalmic examinations. In small doses, cocaine decreases fatigue and increases metal activity. Prolonged use of cocaine leads to physical addiction and to periods of deep depression.
A large number of medically and biologically important compounds are amines. A few examples are given as follows :
Adrenaline : Adrenaline , a hormone released into the blood stream when an animal senses danger. It causes an increase in blood pressure and a widening of passages of the lungs. All, these effects prepare the animal to fight or to flee.
Amphetamine is a neurotransmitter in the brain. Abnormalities in the level of dopamine cause many psychological disorders. Dopamine also plays an important role in regulation and control of movement, motivation and cognition.
Two important nitrogen containing explosives are trinitrotoluene (TNT) and glyceryl trinitrate. Trinitrotoluene is prepared by treating toluene with a mixture of nitric acid and sulphuric acid . Glyceryl trinitrate is an explosive component of dynamite which is prepared by treating glycerol with concentrated nitric acid.
QUESTIONS
1. Give the structures for the following compounds :
(a) TNT (d) Azoxybenzene
(b) picric acid (e) Benzenediazonium chloride
(c) p-Nitrotoluene (f) Sulphanilic acid
2. Why do nitro compounds have higher boiling points than the hydrocarbons having almost same molecular mass ?
3. How do you prepare p-nitroaniline from aniline ?
4. Explain what happens when aniline reacts with a mixture of sulphuric acid and nitric acid ?
5. How is nitrobenzene converted to aniline under neutral conditions ?
6. Explain why does nitrobenzene on nitration with nitric acid and sulphuric acid form only m-dinitrobenzene ?
7. How will you prepare 1-Nitropropene-1 from acetaldehyde ?
8. How can you convert 2-Nitropropane to acetone ?
9. Explain why is nucleophilic substitution of p-nitrochlorobenzene easier than that of chlorobenzene ?
10. Write structures for the following compounds :
(a) Butyronitrile (b) Phenylacetonitrile (c) Propylcarbylamine.
11. Why is acetonitrile preferred as a solvent for running organic reactions ?
12. Explain the role of mineral acid in the reaction of a carbonyl compound with aq. KCN ?
13. How is it that a ketone reacts with Grignard reagent to form tertiary alcohol but in a reaction of a nitrile with Grignard reagent , a ketone is formed ?
14. How will you convert acetonitrile to propiononitrile ?
15. How does an isocyanide react with an electrophile and a nucleophile at the same isocyanide carbon ? Give an example.
16. How will you convert benzonitrile to acetophenone ?
17. Draw the structures of (a) N-Isopropylaniline (b) p-Toludine (c) t-butylamine.
18. Arrange the following sets in order of their basic strength :
(a) Ethylamine, ammonia, triethylamine
(b) Aniline, p-nitroaniline, p-toludine
19. How will you prepare a pure sample of simple primary amine from a primary alkyl halide ?
20. How will you convert an alkyl halide into a primary amine having one more carbon than the alkyl halide used ?
21. How can a carboxylic acid be converted to an amine having one carbon atom less than the carboxylic acid used ?
22. Explain the observed Kb order :
(C2H5)2NH > (C2H5)3N > C2H5NH2
in aqueous solution.
23. Why are amines less acidic than comparable alcohols ?
24. Why are primary amines higher boiling than teriary amines ?
25. Why are aromatic amines weaker bases than aliphatic amines ?
26. How can you find out whether a given amine is a primary amine ? Write chemical reaction involved in the test you perform.
27. How can you separate a mixture of primary, secondary and tertiary amines ? Write chemical reactions involved in the process.
28. How do aromatic and aliphatic tertiary amines react with nitrous acid ?
29. How do aliphatic primary and secondary amines react with nitrous acid ?
30. Explain how does the presence and absence of hydrogen on N of amines affect the modes of their reactions with nitrous acid ?
31. How will you prepare ethylamine from acetaldehyde ?
32. Amino group is o,p-orienting for aromatic electrophilic substitution. Why does aniline on nitration gives a substantial amunt of m-nitroaniline ?
33. Why does bromination of aniline , even under very mild conditions give 2,3,5-tribromoaniline instantaneously ?
34. How can you convert aniline to iddobenzene ?
35. How can you get benzonitrile from aniline ?
36. How is an amide more acidic than an amine ?
37. Draw structures, name according to IUPAC and indicate primary, secondary and tertiary amine :
(i) Eight isomeric amines of formula C4H11N
(ii) Five isomers of amines of formula C7H9N that contain a benzene ring.
38. Account for the following :
(i) Alkane nitrites are higher boiling than the corresponding alkyl halides.
(ii) Tertiary nitroalkanes cannot tautomersise to aci-form.
39. What happens when ethyl amine reacts with :
(i) acetyl chloride
(ii) nitrous acid
(iii) chloroform and alcoholic KOH
40. How do the following pairs of compounds react ? Give proper conditions and equation.
41. What happens when the following react ?
(i) Ethyl amine + dil nitrous acid
(ii) Potassium phthalimide + Ethyl bromide
(iii) Benzamide + Bromine + KOH
(iv) Ethylamine treated with chloroform in presence of ethanolic KOH.
(v) Tin and HCl reacts on nitrobenzene.
42. What happens when :
(i) an alkyl halide reacts with AgNO2 and the product is reduced .
(ii) ethylamine reacts with excess of methyl iodide.
(iii) Aniline is diazotised and the product is reacted with phenol.
43. What happens when :
(i) an alkyl halide is reacted with AgCN and the product hydrolysed.
(ii) Aniline is diazotised and the product is reacted with phenol.
(iii) Methylamine reacts with chloroform and KOH.
44. Explain why aniline is converted into acetanilde before nitration
45. Compare the basic character of ethylamine with that of ammonia.
46. Secondary amines are more basic than primary amines. Account for it.
47. Compare the basic strength of an aliphatic aminbe, aromatic amine and ammonia.
48. Explain the following about CH3NH2.
(i) Its boiling point is less than that of methanol.
(ii) It is a stronger base than ammonia.
49. Suggest a convenient method for separating aniline,N-methyl aniline, toluene and phenol, present together in a mixture. Distillation is not to be used.
50. Illustrate the following with an example.
(a) Ambident nucleophile (b) ammonolysis
(c) Gabriel’s synthesis (d) Hofmann reaction
(e) Acylation (f) Zwitter ion
(g) Hinsberg test (h) Diazotisation
(i) Sandmeyer reaction (j) Coupling reaction.