Halogenation: When primary and secondary nitroalkanes react with a halogen in the presence of a base, -halogenation occurs. Secondary nitroalkanes form pseudonitroles; which are blue in color. the blue color is probably due to the presence of the nitroso group).
Electrophilic substitution reactions: It takes place at the meta- position and drastic conditions are required to do so
Electrophilic attack: Thus, an electrophile that wants to attack at the most electron-rich position(s) will attack the meta position and not the ortho and para positions. The nucleophile that wants to attack at the most electron-deficient position(s) will attack the ortho and para positions and not at the meta positions.
Nucleophilic substitution reactions a. Aromatic Nucleophilic substitution
Second Step: Elimination Step: The ring undergoes rearomatization with the loss of the Leaving Group. The nature of the Leaving Group also has little influence on the course of the reaction.
Reduction
Reduction in alkaline medium: Reduction of nitro group in alkaline medium first forms nitrosobenzene and phenylhydroxylamine. Selective reduction of nitro group: In the presence of other reducible groups such as - CH = CH2 or - CHO etc.
From phenol: When phenol is treated with concentrated nitric acid in the presence of conc
Picric acid is used in electric batteries, leather industry, dyes, pigments, inks, paints, colored glass production, textile mordants, as a laboratory reagent, in matches and explosives.
Picrates: Are charge-transfer complexes of picric acid
The efficiency of phase transfer catalysis is influenced by the size of the groups bound to the phase transfer catalyst, its lipophilicity, and that of the counterion. Phase transfer catalysis is especially useful for carrying out reactions between anions (and certain neutral molecules such as H2O2 and transition metal complexes such as RhCl3) and organic substrates. The name phase transfer catalysis does what it says on the tin: the catalyst acts as a shuttling agent by extracting the anion or neutral compound from the aqueous (or solid) phase into the organic reaction phase (or interfacial region) where the anion or neutral compound resides . can react freely with the organic reactant already in the organic phase.
This mechanism is called the "extraction mechanism" of phase transfer catalysis and is shown in Figure 1. Some Reactions: There are hundreds of commercial applications of Phase Transfer Catalysis and they were commercialized because of the competitive advantages they really offer.
Thiolation (Methyl Mercaptan)
Oxidation (Hypochlorite)
Cyanation
Michael Addition
Chiral Alkylation
Like ammonia, primary, secondary and tertiary amines have a lone pair of electrons on the nitrogen atom and are thus basic in character. This can be explained in terms of an inductive electron-donating effect of the alkyl groups. Alkyl groups, with their electron-donating effect, increase the electron density of nitrogen and thus make the nitrogen's lone pair more readily available for donation to acids.
The difference in basicity between primary, secondary and tertiary aliphatic amines is due to a combination of salience and polar factors. In gas phase: Among primary, secondary and tertiary aliphatic amines, the number of electron-donating alkyl groups is maximum in tertiary amines and minimum in primary amines.
In gas phase: Among primary, secondary and tertiary aliphatic amines, the number of electron donating alkyl groups are maximum in tertiary amines and minimum in primary amines
Aniline and anilinium ion contain the benzene ring and are therefore hybrids of the Kekule structure I and II, and III and IV respectively. Guanidine is a very strong base: Although delocalization of the lone pair generally reduces the basicity of amines, a dramatic example of the opposite effect is found in the compound guanidine (pKa = 13.6). A solution of the nitro compound in alcohol is shaken with finely divided nickel or platinum under hydrogen gas.
Made by adding hydrochloric acid to a mixture of the nitro compound and a metal, usually granulated tin. The crude amine is generally contaminated with some unreduced nitro compound from which it can be separated by taking advantage of the basic properties of the amine; the amine is soluble in aqueous mineral acid and the nitro compound is not.
By ammonolysis: Alkyl halides react with alcoholic ammonia to form amines. The reactivity of various halides in this reaction is as follows
The reduction of aromatic nitro compounds is by far the most useful method for preparing amines because it uses readily available starting materials and produces the most important class of amines, namely primary aromatic amines. These amines can be converted into aromatic diazonium salts, which are among the most versatile class of organic compounds known. Reduction of alkyl cyanides: When alkyl or aryl cyanides are reduced with H2/Ni or LiAlH4.
Synthesis via reduction of nitriles has the special property of increasing the length of a carbon chain, producing a primary amine that has one more carbon atom than the alkyl halide from which the nitrile was prepared. Displacement of halogen by NH3 gives the amine salt, from which the free amine can be liberated by treatment with hydroxide ion.
Reductive amination of aldehydes and ketones
Finally, the tertiary amine can attack the alkyl halide to form a compound with the formula R4N+X–, which is called a quaternary ammonium salt. Reaction involves reduction of an intermediate compound (an imine, RCH = NH or R2C = NH) containing a carbon-nitrogen double bond. Reductive amination has been used successfully with a wide variety of aldehydes and ketones, both aliphatic and aromatic.
This is because during reductive amination, the aldehyde or ketone can react not only with ammonia, but also with the primary amine that has already been formed, thus yielding a certain amount of secondary amine. However, the tendency for the reaction to proceed beyond the desired stage can be quite limited by the ratios of reactants used.
Gabriel's phthalimide synthesis: Gabriel's phthalimide synthesis is used to prepare pure primary aliphatic amines and thus provides an indirect method of carrying on the transformation
Step (2): is the abstraction of a proton (hydrogen ion) attached to the nitrogen, by the hydroxide ion, assisted by the presence of the electron-withdrawing bromine, which increases the acidity of the amide. Stereochemistry at the migrating group in the Hofmann rearrangement: The rearrangement proceeds with complete conservation of configuration around the chiral center of the migrating group. The nitrogen takes the same relative position of the chiral carbon that was originally occupied by the carbonyl carbon.
In SN1-like mechanism, the migrating group will wait for departure of the leaving group before moving. This reaction is one of the four reactions involving the rearrangement of acyl nitrenes to isocyanates.
Other methods of preparation
Loss Route: A hydroxamic acid derivative (RCONHOH) is made by reacting an ester with a hydroxyl amine. Curtius route: An acyl azide (RCON3) is prepared in one of two ways. i) Reaction of an acyl chloride with sodium azide, or (ii) Reaction of an ester with excess. Schmidt route: A variant of the Curtius procedure in which a carboxylic acid is heated with hydrozoic acid (HN3) and an acid catalyst.
With certain reagents, the actual product obtained may vary depending on the class of the amines. Here too, the first step is the nucleophilic attack; it's just that what happens in the end depends on how much hydrogen the nitrogen carries, that is, on the class of the amine.
Alkylation: (Reaction with alkyl halides) : Both aliphatic and aromatic amines react with alkyl halides to form amines of higher classes
All three classes of amines contain nitrogen that carries a nonshared covalent pair. The tendency of nitrogen to share this pair of electrons underlies the entire chemical behavior of amines: their basicity, their actions as nucleophiles - in both aliphatic and acyl substitution - and the extremely high reactivity of aromatic rings containing amino substituted amino groups or groups. Reaction with metal ions: lower aliphatic amines form coordination complexes with metal ions such as Ag+ and Cu2+.
Alkylation: (Reaction with alkyl halides) : Both aliphatic and aromatic amines react with alkyl halides to form amines of higher classes. Reaction with aldehydes and ketones; Primary amines react with aliphatic and aromatic aldehydes or ketones to form imines known as Schiff's bases.
Reaction with aldehydes and ketones; Primary amines react with aliphatic and aromatic aldehydes or ketones to form imines known as Schiff's bases
Conversion into amides
In this test, amine is treated with benzenesulfonyl chloride in the presence of cold aqueous sodium hydroxide (NaOH). Primary amines produce N-alkylsulfonamide, which contains acidic hydrogen and therefore dissolves in a sodium hydroxide (NaOH) solution to form the soluble sodium salt. This is because nucleophilic attack on a trigonal acyl carbon is relatively unimpeded; it involves the temporary attachment of the fourth group, the nucleophilic reagent.
Nucleophilic attack on tetrahedral sulfonyl sulfur is relatively hindered; it concerns the temporary attachment of the fifth group. Also, the tetrahedral carbon of the acyl intermediate uses the allowed number of electrons; although sulfur can potentially use more than eight electrons in covalent bonding, this is a less stable system than the octet.
Ring substitution in aromatic amines
Electron withdrawal of oxygen by the carbonyl group makes the nitrogen in an amide a much poorer source of electrons than the nitrogen in an amine. To obtain monosubstituted products, the phenyl ring of aniline is deactivated by acetylation of the -NH2 group. Furthermore, the amine is converted in the strongly acidic nitration medium to the anilinium ion; thus, substitution is controlled not by the group, but by the group, which, because of its positive charge and –I effect (electron withdrawing), directs much of the substitution to the meta position.
Sulfanilic acid is a salt, but a rather special kind, called a dipolar ion (sometimes called zwitterions, from German, Zwitter, hermaphrodite). It is the product of the reaction between an acidic group and a basic group that are part of the same molecule.
Reactions with nitrous acid
Primary aliphatic and aromatic amines react with chloroform in the presence of an alcoholic solution of potassium hydroxide to give offensive (foul) smelling isocyanides (or carbylamines). This neutral electrophile attacks the electron-rich nitrogen of amino, followed by the elimination of two HCl molecules to form the foul-smelling isocyanide. Primary aliphatic and aromatic amines react with CS2 in the presence of HgCl2 to give alkyl isothiocyanates.
Primary and secondary (both aliphatic and aromatic) amines react with a Grignard reagent to form alkanes. Strong oxidation of primary aromatic amines with potassium dichromate and sulfuric acid leads to the formation of quinones.
Hofmann’s elimination from quaternary ammonium salts
Amines are converted to quaternary ammonium salts by treatment with excess methyl iodide.
Simple amines are easily converted to the necessary 4º-ammonium salts by exhaustive
When a given alkyl group has two different sets of beta-hydrogens available to the elimination process, the major product is often the alkene isomer having the less substituted double bond
A mixture of primary, secondary, and tertiary amines is treated with benzene sulfonyl chloride in the presence of excess aqueous sodium hydroxide (or potassium hydroxide) solution. The amine is treated with benzene sulfonyl chloride in the presence of an excess of aqueous sodium hydroxide (or potassium hydroxide). In this test, the compound is heated with chloroform in the presence of an alcoholic solution of potassium hydroxide.
The diazonium salt is simply left to stand in the presence of the hypophosphorous acid; Alternatively, when diazonium salts are heated with halogen acids in the presence of Cu, the diazonium group is replaced by halogen.
When The Substitution Is Nucleophilic
- On phenol: A phenol is appreciably acidic; in aqueous solutions it exists in equilibrium with phenoxide ion
Replacement of diazonium group by nitro group: diazonium salts form nitro compounds when heated with sodium nitrite in the presence of copper oxide. Replacement of Diazonium Group by Thiol Group: Diazonium salts on reaction with H2S form thiophenol by SN1 reaction. Replacement of Diazonium Group by - NCO or - NCS Group: When diazonium salts are reduced with KNCO or KNCS they form phenylisocyanate and phenylthioisocyanate.
There are few reactions of diazonium salts in which both nitrogen atoms are retained. Reaction with alkali: On treatment with NaOH, diazonium salts are converted first to diazohydroxides and then to sodium diazotes which exhibit geometric isomerism due to the presence of - N = N.
