2- Alkylpyridinium salts, oxidation

On 100% acrylic materials the quaternary ammonium retarders are used almost exclusively. Other types have been evaluated, however. For example, saturated alkylamines (RNH2 R = C10, C12, C14 and C16 hydrophobes) were found to be just as effective as the quaternary types although other factors, such as aqueous solubility at the optimal dyebath pH and resistance to subsequent discoloration, favour the quaternary compounds [34]- On the other hand, bis (hydroxyethyl) coco amine (12.10) had relatively little effect and the amphoteric carboxymethyldimethylcocoamine (12.11) none at all, although dimethyl-cocoamine oxide (12.12) was quite an effective retarder [34]- Other cationic compounds used [43,44] have included alkylpyridinium salts, imidazoles and imidazolinium salts, alkyldiamines, alkylpolyamines, as well as sulphonium and phosphonium derivatives. 

A number of other routes are available for the syntheses of diquaternary salts of 4,4 -bipyridines. One method that has been extensively studied involves reaction of a 1-alkylpyridinium salt with sodium amalgam (or sodium in liquid ammonia) to form the 1,1 -dialkyl-1,1, 4,4 -tetrahydro-bipyridine, which is readily oxidized to the corresponding l,l -dialkyl diquaternary salt. This reaction is analogous to the synthesis of 4,4 -bipyridine by the action of sodium on pyridine, followed by oxidation of the intermediate tetrahydrobipyridine. " The reduction may be achieved electrolytically or by reaction with zinc or magnesium. Various oxidizing agents have been used to assist the conversion to the di-quaternary Another synthesis of diquaternary salts of... 

Oxidation of N-alkylpyridinium salts to the 2-pyridones (157) is an old, high-yield process that utilizes a mediator, usually potassium ferricyanide (Scheme 51).216-218 Selectivity for the 2-position was quite high. Iron anodes, an economic and readily machined electrode material, in basic electrolyte are satisfactory. Large variations in current density did not affect the yield. The... 

The hydroxy adducts can be oxidized into the Sn products. Indeed, the oxidative hydroxylation of Al-alkylpyridinium salts into pyridones is a well-known Sn transformation, as illustrated by the reaction of 3-methoxycarbonyl-l-methylpyridinium iodide with the hydroxide ion in the presence of potassium ferricyanide, affording the corresponding l-methyl-6-pyridone (Scheme 37) [2, 11, 139]. 

Acceptor-CH-substituted pyridinium-N-betaines 15 (accessible in situ by deprotonation of the corresponding N-alkylpyridinium salts 14) undergo 1,3-dipolar cycloaddition with activated alkynes and alkenes as dipolarophiles. With alkynes, the cycloadducts (16/19) dehydrogenate spontaneously to indolizines, which are either of the 1,2,3-trisubstituted type 17 or (indicating a regioselective cycloaddition) of the 1,3-disubstituted type 18. With olefinic substrates, the presence of an oxidant for additional dehydrogenation of the primary cycloadduct (20 -> 17) is required [219] ... 

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