Hydrogen-carbon bonds aminations, benzene

A substance is readily miscible with water only if it can act as a proton acceptor in a hydrogen bond, as, for example, ketones, nitriles, ethers, alcohols and amines. Such substances are also freely miscible with inert non-polar solvents such as benzene or carbon tetrachloride. The interpretation of the properties of the latter solutions is well established and there would appear to be an analogy between them and aqueous solutions. Thus,... 

Amines possess higher boiling points than non-polar compounds (of the same molecular weight), but lower boiling points than alcohols or carboxylic acids. Amines of all types can form hydrogen bonds with water. Consequently, the solubility of amines depends on size smaller amines are quite soluble in water, with borderline solubility reached at about six carbon atoms. In less polar solvents such as ether, alcohol, and benzene, amines are soluble. 

Table 10.5 lists the physical properties of the aromatic-type pyridine and the three isomeric methyl derivatives (picolines) as well as the 2-ethyl and 4-ethyl pyridine derivatives. Complete hydrogenation of the pyridine ring yields the cyclic secondary amine, piperidine, which is also listed in Table 10.5. The pyridine derivatives are medium boiling liquids with flash points in the range of 37-134°F. The substitution of a nitrogen atom for a carbon atom in the benzene ring gives the pyridine derivative with much higher Hansen polarity and hydrogen bonding values (5 = 8.8 and 5 , = 5.9) than the benzene molecule (6 = 0 and 6 = 2.0).

In addition to hydrogen halides, water is the most studied HBD in the gas phase. The structures of the complexes with water, dinitrogen, carbon monoxide, ozone, benzene, ethane, formaldehyde, formamide, 1,4-dioxane, ethylene oxide, tetrahydropyran, difluo-romethane, pyrazine, pyrimidine, pyridazine, benzonitrile, quinuclidine, ammonia, methy-lamine, trimethylamine and so on can be found in the Mogadoc database [29]. In the water-morpholine complex [30], water is hydrogen bonded to the nitrogen and not to the oxygen, as predicted by the higher HB basicity of amines than that of ethers. 

What happens to them is a hydrogenolysis—a reaction that is liable to occur under catalytic hydrogenation conditions whenever a heteroatom (in particular O or N) finds itself bonded to a carbon atom adjacent to a benzene ring, in other words with benzylic amines, alcohols or ethers. 

Amines are compounds in which a nitrogen atom is bonded to one or more carbon atoms. They can be considered as derivatives of ammonia in which one, two or three hydrogen atoms are replaced by hydrocarbon groups Ri, R2 and R3. These three groups can be acyclic or benzenic, identical or different. 

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