Pyridinium hydrochloride

Pyridinium 1-dicyanomethylide neutron diffraction, 2, 116 (80AX(B)1807) Pyridinium hydrochloride X-ray, 2, 110 <62AX427>... 

Pyridinium hydrobromide dibromide reactions, 2, 34 Pyridinium hydrochloride structure, 2, 109... 

The above-mentioned results indicate the additive effect of protons. Actually, a catalytic process is formed by protonation of the metal-oxygen bond instead of silylation. 2,6-Lutidine hydrochloride or 2,4,6-collidine hydrochloride serves as a proton source in the Cp2TiCl2-catalyzed pinacol coupling of aromatic aldehydes in the presence of Mn as the stoichiometric reduc-tant [30]. Considering the pKa values, pyridinium hydrochlorides are likely to be an appropriate proton source. Protonation of the titanium-bound oxygen atom permits regeneration of the active catalyst. High diastereoselectivity is attained by this fast protonation. Furthermore, pyridine derivatives can be recovered simply by acid-base extraction or distillation. 

Several acids salts have been proposed to replace tetrazole as the activator of phosphoroamidite coupling with alcohols. The most popular are benzimida-zolium [20a], imidazolium [20b], AT-methylimidazolium [20c], AT-methylani-line [20h] trifiates, pyridinium hydrochloride [20d,e], hydrobromide [20e], tetrafluorborate [20f], trifluoroacetate [20g] and 2,4,6-collidine trifiuoroac-etate [20i]. 

The triethylamine hydrochloride formed in step (a) serves as an activator in step (b) for the reaction with an alcohol (ROH) providing the phosphite containing the desired protecting group. Acetonitrile proved to be a better solvent for this reaction than dichloromethane. It was found that activation by pyridinium hydrochloride was faster but led to formation of dinucleoside phosphite. 

During this time, pyridinium hydrochloride precipitates from the solution as white needles. 

A very large number of complexes of pyridines and quinolines with all the halogens and interhalogen compounds are known, and as they have been enumerated elsewhere (74HQ14-S2)407,77HC(32-1)319) just a few examples are illustrated (Scheme 14). Treatment of pyridine with chlorine or bromine in the presence of aluminum chloride yields 4-pyridylpyridinium salts (equation 29), but rather curiously the action of iodine chloride on pyridinium hydrochloride at 250 °C produces the 2-isomer (51 equation 30). 

Chlorohydrins. F.poxides can be cleaved to frotw-chlorohydrins with pyridinium hydrochloride in chloroform or pyridine. The reagent also cleaves a-cyclopropyl ketones to mixtures of y-chloro ketones obtained by the two possible modes of cyclo-propyl ring fission.2... 

The polymerisation of several unsubstituted aldosyl fluorides1 under mildly acidic conditions has been briefly described.in Treatment of the aldosyl fluorides with pyridinium hydrochloride or hydrofluoride under diminished pressure gave good yields (see Table III) of nondialyzable, polymeric material. 

If pyridinium hydrochloride is present, configuration is inverted (15). Explain. 

PCC is usually prepared using the description of Corey and Suggs,189 although other procedures have been reported.190,191 Agarwal et al. published that preparing PCC by addition of CrC>3 over a pyridinium hydrochloride solution avoids the handling of poisonous chromyl chloride.192... 

The oxidation of primary alcohols to aldehydes also suffers from the problem of overoxidation of the aldehyde to a carboxylic acid. Mild methods capable of stopping die oxidation at the aldehyde oxidation level are required if aldehydes are to be obtained. The most common and effective reagent for this purpose is pyridinium chlorochromate (PCC), produced by the reaction of pyridinium hydrochloride with chromium trioxide. This reagent is soluble in dichloromethane and smoothly oxidizes primary alcohols to aldehydes in high yields. Because of die mild, neutral reaction conditions and the use of stoichiomettic amounts of oxidant, the aldehyde product is not oxidized further. 

When pyridinium hydrochloride was treated at 250°C with iodine monochloride in the presence of aluminium chloride, a 2-pyridylpyridinium salt was formed. Both 1 1 and 1 2 complexes formed when iodine monochloride or iodine reacted with pyridine (80AJC1743). Formation constants for the charge-transfer complexes between iodine and pyridine (and pico-lines) have been measured [84JCS(P2)731], and solvent effects on the... 

To a solution of 56.6 g (0.25 mol) of anthralin in 1750 ml of absolute toluene and 27.3 ml of pyridine, 31.5 ml (0.3 mol) of butyryl chloride was added with stirring over 30 min at room temperature. The reaction mixture was then heated to 85°C for 1 hour. After this mixture had recooled to room temperature, 27.3 ml of pyridine and 31.5 ml of butyryl chloride were again added. The suspension obtained was then heated to 85-90°C for 1 hour. The precipitated pyridinium hydrochloride was eliminated by filtration then washed with toluene. The toluene filtrates were concentrated to around 500 ml under reduced pressure, washed several times with water then dried over magnesium sulfate. The product was then fractionated by chromatography on... 

Piers and co-workers have shown that pyridine-stabilized borabenzenes 76 (R = H, Me, Pr1) react with cationic Bronsted acids such as pyridinium hydrochloride to produce the boronium ions 77 and 78 in 1 1 ratio. Protonation occurs at C-2 and C-4, respectively, followed by addition of pyridine at electrophilic boron <2005CC2480>. 

Alditols [405] and amino sugars [406] have been analysed by GC—MS as combined methyl ether—acetyl derivatives. Acetylation was performed with acetic anhydride in pyridine, as follows. A 0.15-ml volume of re-distilled dry pyridine was added to 0.5 ml of 1.5 A acidic methanolysate containing 0.025—2.5 pmol of amino sugars. The apparent pH of the methanolic pyridinium hydrochloride varied in the range 4—5. Acetic anhydride (0.1 ml) was added and the mixture was stirred thoroughly and allowed to stand at room temperature for 30 min. Evaporation to dryness was performed in vacuum over solid KOH with subsequent vacuum drying for 4 h over P20s. SE-30 was used as the stationary phase. 

There does not appear to be any reliable information on the isomerization reactions of chloroaminocyclotetraphosphazenes. Lehr (281) claims to have observed the isomerization of 2-trans-6- and 2-trans-4-N4P4(NMe2)2Cl6 derivatives to the corresponding cis compounds in the presence of pyridinium hydrochloride in chloroform. Details of the experimental procedures and the evidence for the structural assignments have not been stated. 

The phenolic functions are deprotected under rather drastic conditions, by analogy with methods defined previously for the cleavage of aryl methyl ethers.14 Treatment of dianisylphenanthroline 4 with pyridinium hydrochloride at 210°C affords 2,9-di(p-phenol)-l,10-phenanthroline 5 quantitatively (Scheme 9.4). 

Hexaethoxycyclotriphosphazatriene may be prepared by the slow addition of dry ethanol to a cold, stirred solution of hexachlorocyclotriphosphazatriene (1,3,5,2,4,6-triazatri-phosphorine 2,2,4,4,6,6-hexachloride phosphonitrile chloride, cyclic trimer) in dry pyridine. The reaction mixture is worked up by the addition of an excess of dry diethyl ether and filtration of the precipitated pyridinium hydrochloride. The solvents are then removed from the washed and dried solution and the product is purified by vacuum distillation. 

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