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Pyridine is used as a polar, basic, low-reactive solvent, for example in Knoevenagel condensations. [24] [107] It is especially suitable for the dehalogenation, where it acts as the base for the elimination reaction. In esterifications and acylations, pyridine activates the carboxylic acid chlorides and anhydrides.
Basic aromatic compounds get protonated and form aromatic cations (e.g. pyridinium) under acidic conditions. Typical examples of basic aromatic rings are pyridine or quinoline. Several rings contain basic as well as non-basic nitrogen atoms, e.g. imidazole and purine.
It is the conjugate acid of pyridine. Many related cations are known involving substituted pyridines, e.g. picolines, lutidines, collidines. They are prepared by treating pyridine with acids. [3] As pyridine is often used as an organic base in chemical reactions, pyridinium salts are produced in many acid-base reactions.
Structure of CrO(O 2) 2 (pyridine).Hydrogen atoms bonded to carbon atoms are omitted. Color code: Cr = gray, C= black, H = white, O= red, N = blue. Chromium(VI) oxide peroxide is formed by the addition of acidified hydrogen peroxide solutions to solutions of metal chromates or dichromates, such as sodium chromate or potassium dichromate.
With a pK a of 5.25 for its conjugate acid, pyridine is about 15x less basic than imidazole. 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]
The handling of this chemical may incur notable safety precautions. It is highly recommend that you seek the Material Safety Datasheet for this chemical from a reliable source such as eChemPortal, and follow its directions.
In fact, the addition of acid (H+) or hydroxide (OH-) acts to attenuate protodeboronation by shifting the speciation away from the reactive zwitterion. It is important to note that not all basic heteroaromatic boronic acids are reactive through a zwitterionic intermediate. Scheme for the speciation of 2-pyridine boronic acid in aqueous solution
A Lewis base is also a Brønsted–Lowry base, but a Lewis acid does not need to be a Brønsted–Lowry acid. The classification into hard and soft acids and bases ( HSAB theory ) followed in 1963. The strength of Lewis acid-base interactions, as measured by the standard enthalpy of formation of an adduct can be predicted by the Drago–Wayland ...