Pyridinium compounds, — chloride

Fig. 10.8 A where the R substituents are alkyl or heterocyclic radicals to give compounds such as cetyltrimethylammonium bromide (cetrimide), cetylpyridinium chloride and benzalkonium chloride. Inspection of the stmctures of these compounds (Fig. 10.8B) indicates the requirement for good antimicrobial activily of having a chain length in the range Cg to Cig in at least one of the R substituents. In the pyridinium compounds (Fig. 10.8C) three of the four covalent links may be satisfied by the nitrogen in a pyridine ring. Polymeric quaternary ammonium salts such as polyquatemium 1 are finding increasing use as preservatives.

Wright KA, RB Cain (1972) Microbial metabolism of pyridinium compounds. Metabolism of 4-carboxy-l-methylpyridinium chloride, a photolytic product of paraquat. Biochem J 128 543-559. 

A class of acylpyridinium salts that has been investigated quantitatively is the carbamoyl pyridinium compounds. Diphenylcarbamoyl-pyridinium chloride was synthesised in 1907277. l-(N,N-Dimethylcarbamoyl)-pyridinium chloride (XLVI) was found by Johnson and Rumon278 to decompose to its component parts in non-hydroxylic solvents, dielectric constants from 5 to 95, viz. 

Use is made, for example, of cetyldimethylbenzylammonium chloride and pyridinium compounds of the type... 

The 2-halo-substituted benzimidazoles, then, more or less readily react with ammonia, amines and hydrazines (80AHC 27)241,70AHC(12)103,74CRV279), It is likely that the formation of the 2-pyridinium compound (123) when cycloheptimidazolin-2(l//)-one reacts with phosphoryl chloride in pyridine occurs via the 2-chloro intermediate (Scheme 56). The sulfur function of benzimidazole-2-sulfonic acid can be displaced by amino or alkylamino groups. 

A great advance was made by the introduction of pyridinium compounds containing a long-chain aliphatic radical which could be split off on heat curing. The earliest of this range of products was Velan PF which is stearo-amido-methyl pyridinium chloride, (C17H35.CO.NH.CH2.N) 0, con-... 

Other methods for the synthesis of l,4-dihydro-l,2,4,5-tetrazines 9 which can be explained by intermediate formation of nitrile imines 8 are the photolysis of 1,2,3-triazoles 2181 and sydnones 3,182 reaction of tetrazoles 4180 with tosyl chloride, elimination of pyridine from the pyridinium compounds 5,189-190 of hydrogen chloride from the hydrazonic acid chlorides 1 s.3-i88 or elimination 0f sulfinate from the a-sulfonyl hydrazone 7.189... 

Fluoropolymers are also used as mixtures with nonfluorinated water repellents [145]. De Marco et al. [146] found that the combination of a fluoropolymer and a pyridinium-type water repellent on cotton has a synergistic effect, resulting in long-lasting resistanee to rain and durability to laundering. A patent to the U.S. Department of the Army [20] claims repellent compositions comprising >1 % of a pyridinium compound, for example, stearoyloxymethylpyridinium chloride, and 0.5% of a mixed fluorocarbon polymer, a copolymer of l, liT,2, 2 -perfluo-roalkane methacrylates and poly(octyl methacrylate). 

After evaporation of the solvent, the solid residue consists of 5-(2-chlorobenzyl)-thieno[3,2-cl -pyridinium chloride which melts at 166°C (derivative n°30). This compound is taken up into a solution comprising ethanol (300 ml) and water (100 ml). Sodium borohydride (NaBH4) (20 g) is added portionwise to the solution maintained at room temperature. The reaction medium is maintained under constant stirring during 1 2 hours and is then evaporated. The residue is taken up into water and made acidic with concentrated hydrochloric acid to destroy the excess reducing agent. The mixture is then made alkaline with ammonia and extracted with ether. The ether solution is washed with water, dried and evaporated. The oily residue is dissolved in isopropanol (50 ml) and hydrochloric acid in ethanol solution is then added thereto. 

In an attempt to study the behavior and chemistry of coal in ionic liquids, 1,2-diphenylethane was chosen as a model compound and its reaction in acidic pyri-dinium chloroaluminate(III) melts ([PyHjCl/AlCb was investigated [69]. At 40 °C, 1,2-diphenylethane undergoes a series of alkylation and dealkylation reactions to give a mixture of products. Some of the products are shown in Scheme 5.1-40. Newman also investigated the reactions of 1,2-diphenylethane with acylating agents such as acetyl chloride or acetic anhydride in the pyridinium ionic liquid [70] and with alcohols such as isopropanol [71]. 

There are some problems associated with the use of functional derivatives of carboxylic acids. Long-chain acid anhydrides are not commercially available, and one half of the acylation reagent is not utilized. Acyl chlorides require the use of tertiary base catalysts, whose double role has been explained before. Some of the intermediate acyl ammonium compounds formed are, however, insoluble in the solvent system. Examples include RCO - N+EtsCL in LiCl/DMAc, where RCO refers to the propionyl, hexanoyl, and stearoyl moiety, respectively. Hexanoyl- and stearoyl-pyridinium chlorides are also insoluble in the same solvent system [185]. 

Xb was utilized in the elaboration of the hydrindan XIII and subsequently compound XIV. We expected that Xa could be converted to XIII in the same manner as was in the Sih synthesis. This was confirmed in practice (Scheme II). Oxidation of 569 mg (2.68 mmol) of Xa with pyridinium chlorochromate in methylene chloride furnished 532 mg (94%) of enone Ila (7,21). Treatment of 130 mg of Xa witlj a slight excess of Jones reagent (3,22) afforded 126 mg (98%) of Ila. Allylic brominatlon of Ila with a 20% excess of N-bromosuccinimide (NBS) in refluxing carbon tetrachloride provided Xlla in 98% yield. 

The reaction of 196 with phenyl chlorocarbene 198 illustrates the synthesis of indolizines by cyclization of pyridinium ylides (Scheme 7). Cyclization of ylide rotamer 199 generates the intermediate product 200, which undergoes elimination of chloride to provide compound 201 <2005EJ01532>. 

The less important positive CCAs are metal-free cationic molecules, such as the black dye nigrosine and the colorless quaternary compound cetyl pyridinium chloride.35,36... 

There is nothing unusual about the acidic behavior of ammonium salts. In fact, any protonated amine can function as a proton donor. Because of this, many amine salts have been used as acids in synthetic reactions. If the chlorides are used, the amine salts are known as amine hydrochlorides. One of the earliest amine hydrochlorides studied with regard to its behavior as an acid is pyridine hydrochloride (pyridinium chloride), C5H5NH+C1. In the molten state, this compound undergoes many reactions of the type just shown. 

Many years ago, L. F. Audrieth studied numerous reactions of amine hydrochloride salts. These compounds contain a cation that is a protonated amine that can function as a proton donor. Consequently, the molten salts are acidic and they undergo many reactions in which they function as acids. This behavior is also characteristic of ammonium chloride as well as pyridine hydrochloride (or pyridinium... 

However, based on the following evidence, a question has been raised about the assumed Sn2 character of the displacement reaction.78 The reaction of 2,3,4,l, 3, 4 -hexa-0-benzoylsucrose 6,6 -bis(chlorosulfate) (44) with pyridinium chloride in chloroform for 4 h at 55° gave 2,3,4,l, 3, 4 -hexa-0-benzoyl-6,6 -dichloro-6,6 -dideoxy-sucrose (54) in 96% yield. When compound 44 was heated under reflux with butanone alone, compound 54 (35%) was the only iso-... 

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