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When the acidic proton is replaced by alkyl, the compounds are called N-alkylpyridinium. A simple representative is N -methylpyridinium ( [C 5 H 5 NCH 3 ] + ). These pyridinium intermediates have been used as electrophiles in synthetic organic chemistry to build dearomatized congeners called dihydropyridines, as demonstrated in one example from ...
Pyridine is a weak pi-acceptor ligand. Trends in the M-N distances for complexes of the type [MCl 2 (py) 4] 2+ reveal an anticorrelation with d-electron count. [2] Few low-valent metal complexes of pyridines are known. The role of pyridine as a Lewis base extends also to main group chemistry.
For example, carbon monoxide is a very weak Brønsted–Lowry base but it forms a strong adduct with BF 3. In another comparison of Lewis and Brønsted–Lowry acidity by Brown and Kanner, [ 19 ] 2,6-di- t -butylpyridine reacts to form the hydrochloride salt with HCl but does not react with BF 3 .
In organic synthesis, PPTS is used as a weakly acidic catalyst, providing an organic soluble source of pyridinium (C 5 H 5 NH +) ions. For example, PPTS is used to deprotect silyl ethers or tetrahydropyranyl ethers when a substrate is unstable to stronger acid catalysts.
Its Lewis base properties are discussed in the ECW model. Its relative donor strength toward a series of acids, versus other Lewis bases, can be illustrated by C-B plots . [ 106 ] [ 107 ] One example is the sulfur trioxide pyridine complex (melting point 175 °C), which is a sulfation agent used to convert alcohols to sulfate esters .
An example of a weak base is ammonia. It does not contain hydroxide ions, but it reacts with water to produce ammonium ions and hydroxide ions. [4] The position of equilibrium varies from base to base when a weak base reacts with water. The further to the left it is, the weaker the base. [5]
Containing a pyridinium ion, pyridinium chloride has a pK a of approximately 5, slightly more acidic than that of typical amines. This is due to the hybridization of the nitrogen: the nitrogen is sp 2 hybridized and more electronegative than those nitrogens in ammonium cations, which are sp 3 hybridized. Hence they are stronger acids than ...
Pyridinium chlorochromate in a vial. Pyridinium chlorochromate (PCC) is a yellow-orange salt with the formula [C 5 H 5 NH] + [CrO 3 Cl] −. It is a reagent in organic synthesis used primarily for oxidation of alcohols to form carbonyls. A variety of related compounds are known with similar reactivity.