Silica phases scale-like

The limitations of standard reversed-phase materials have been partially overcome by introducing modem, specially deactivated hydrocarbon-silica pha.ses ]126]. the hydrocarbonaceous phases immobilized on alumina or zirconia support ]127] and the polymeric materials ]128]. Using the latter two types of stationary phase materials one can determine the HPLC capacity factors at acidic, neutral and alkaline conditions. This way a universal, continuous chromatographic hydrophobicity scale can be constructed like the standard log P scale ] 129]. 

Pyridine was first isolated, like pyrrole, from bone pyrolysates the name is constrncted from the Greek for fire, pyr , and the suffix idine , which was at the time being used for all aromatic bases - phenetidine, toluidine, etc. Pyridine and its simple alkyl derivatives were for a long time produced by isolation from coal tar, in which they occur in quantity. In recent years this source has been displaced by synthetic processes pyridine itself, for example, can be produced on a commercial scale in 60-70% yields by the gas-phase high-temperatnre interaction of crotonaldehyde, formaldehyde, steam, air and ammonia over a silica-alumina catalyst. Processes for the manufacture of alkyl-pyridines involve reaction of acetylenes and nitriles over a cobalt catalyst. 

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