1 -Ethyl-4- pyridinium iodide

DMII = N,N-dimethyl imidazohum iodide DEII = N,N-diethyl imidazohum iodide BMII = N-butyl-N-methyl imidazohum iodide [Etpy]I = N-ethyl pyridinium iodide [pyMe]I = N-methyl pyridinium iodide MTOPI = methyl trioctyl phosphonium iodide [BusPMe] = methyl tributyl phosphonium iodide. 

As in the earlier examinations, the amount of methyl iodide detected in the purged product was still averaged ca. 0.3 wt.%. However, unlike the earher ran with [MePy]I, we took a close look at the effluent from the operation with l,2-dimethyl-5-ethyl-pyridinium iodide ([DMEpy] ). All the product was distilled overhead leaving a residue that upon examination by NMR contained a ca. 3 1 acetate [DMEpyratio. Closer examination by NMR revealed that only about 3% of [DMEpy]l in the overhead distillate had been dealkylated to 2-methyl-5-ethyl pyridium hydroiodide. 

In addition to compounds quoted by Lyle and Anderson," the following quaternary salts have recently been reduced with sodium borohydride ethiodides of pyridine and its homologs, methiodides of 3-ethylpyridine, 4-ethylpyridine, 2-methyl-5-ethylpyridine, and 3-methyl-4-ethylpyridine,102 and the methiodide of 2-benzyl-4-methylpyridine.103 Reductions (NaBH4) of l,2-dimethyl-5-ethyl-pyridinium iodide and l,3-dimethyl-4-ethylpyridinium iodide afford as principal products those 3-piperideines (94, 95) which carry the maximum number of substituents on the double bond, presumably due to hyperconjugation.102... 

Fig. 2. The effect of substituents in the 4-position on the methyl resonance of the A -ethyl group of 4-substituted 7V-ethyl pyridinium iodides recorded at 25°C. (From Biellman and Callot. )...

Dimethoxyacetophenone (48.0 mmol) was heated in 20 mL pyridine until a clear solution was obtained. Crystalline iodine (17.4 g, 57.0 mmol) was added portionwise, and the resulting solution was refluxed for 1 h and then cooled to room temperature. The brownish precipitate was Altered off and successively washed with absolute pyridine (3x15 mL) to give 9.29 g l-[2-(2,6-dimethoxyphenyl)-2-oxo-ethyl]-pyridinium iodide as a pale yellow solid, in a yield of 50%, m.p. 201-203°C (water). 

Cl5H1sBrN20, N-(2-Pyridylacetomethylene)-4-bromoaniline, 39B, 184 Cl5H15IN2O, 4-Cyano-N (2-(p-methoxyphenyl)ethyl)pyridinium iodide, 34B, 135... 

Other Names 2-[p-(Dimethylamino)styryl]-l-ethyl-pyridinium iodide Pyridinium, 2-[2-[4-(dimethylamino) phenyl]ethenyl]-l-ethyl-, iodide Pyridinium, 2-[p-(di-methylamino)styryl]-1-ethyl-, iodide 2-[4-(Dimethyla-mino)styryl]-l-ethylpyridinium iodide D 426 DASPEI NK 557 Pinaflavol... 

Anyles are another class of dyes successfully studied by polarization IR spectroscopy of oriented colloids. N,N-Diethyl-N -[(Z)-phenyl(pyridin-4-yl)methylidene]benzene-1,4-diamine and its N-ethyl pyridinium iodide (Figure 6.23) wiU be presented next. 

Pyridinium iodide, l-ethyl-4-methoxycarbonyl-UV spectrum, 2, 127 Pyridinium iodide, 1-methyl-decomposition, 2, 300 Pyridinium iodide, 6-pterinylmethyl-synthesis, 3, 312... 

Kosower made the first use of this phenomenon for measuring solvent polarity. The model process is the absorption transition of l-ethyl-4-carbomethoxy-pyridinium iodide, 7 ... 

Z values are obtained from Eq. (8-76) for solvents having Z in the approximate range 63-86. In more polar solvents the CT band is obscured by the pyridinium ion ring absorption, and in nonpolar solvents l-ethyl-4-carbomethoxy-pyridinium iodide is insoluble. By using the more soluble pyridine-1-oxide as a secondary standard and obtaining an empirical equation between Z and the transition energy for pyridine-1-oxide, it is possible to measure the Z values of nonpolar solvents. The value for water must be estimated indirectly from correlations with other quantities. Table 8-15 gives Z values for numerous solvents. 

The Z scale developed by Kosowct and Mohammad [48,49] is based by the chaige-transfer absorption of Af-ethyl methoxycarbonyl) pyridinium iodide molecule. The wavelength of maximum adsorption (A in nm) is measured and the energy (kcal/mol) of this transition becomes the actual polarity measured for a given solvent (Equation 4.17) ... 

In another approach to the estimation of solvent polarities the effect of a solvent on the absorbance maximum in the visible-ultraviolet region of the charge-transfer band of a salt such as 1 -ethyl-4-carbomethoxy pyridinium iodide is measured 147). A shift of the maximum to shorter wavelengths occurs as solvent polarity increases. The wavelength, expressed in kcal, is called the Z value of the solvent. This method provides a simple and rapid measure of solvent polarity at the molecular level. 

A striking example is the negatively solvatochromic effect observed for l-ethyl-4-(methoxycarbonyl)pyridinium iodide, the UV/Vis spectra of which in a variety of solvents are shown in Fig. 6-3 [65-67]. The longest-wavelength band of the ground-state ion-... 

Kosower [5, 55] has taken the longest-wavelength intermolecular charge-transfer (CT) transition of l-ethyl-4-(methoxycarbonyl)pyridinium iodide as a model process. It exhibits a marked negative solvatochromism cf. the formula of this dye and its UV/Vis... 

Z values are both temperature- and pressure-dependent. The CT absorption band of substituted pyridinium halides is shifted hypsochromically as the temperature of the solution is decreased [59]. Thus, Z values decrease with increasing temperature due to a lowering of the solute/solvent interactions at the higher temperature. Furthermore, it has been shown that the CT absorption band of l-ethyl-4-(methoxycarbonyl)-pyridinium iodide is shifted bathochromically for solutions in methanol and ethanol with increasing pressure (up to 1920 bar), while for other solvents such as acetone and A, A -dimethylformamide it is shifted hypsochromically [60]. Except for the lower alcohols, the bulk solvent polarity generally increases with pressure [60]. 

Ethyl-2,6-bis[4-(pyrrolidin-1 -yl)styryl]pyridinium iodide C3,H36lN3 = 577.6 CAS—3784-99-4... 

The pure l-ethyl-4-carbomethoxypyridinyl radical 4") was isolated by distillation from the mixture produced by sodimn amalgam reduction of the corresponding pyridinium iodide Flash photolysis of 4 l also yielded the pyridinyl... 

Evaluation of solvent-sensitive properties requires well-defined referena i ran eis. A macroscopic parameter, dielectric constant, does not always give interpretable correlations of data. The first microscopic measure of solvent polarity, the Y-value, based on the solvolysis rate of t-butyl chloride, is particularly valuable for correlating solvolysis rates. Y-values are tedious to measure, somewhat complicated in physical basis, and characterizable for a limited number of solvents. The Z-value, based on the charge-transfer electronic transition of l-ethyl-4-carbomethoxy-pyridinium iodide , is easy to measure and had a readily understandable physical origin. However, non-polar solvent Z-values are difficult to obtain b use of low salt solubility. The Et(30)-value , is based on an intramolecular charge-transfer transition in a pyridinium phenol b ne which dissolves in almost all solvents. We have used the Er(30)-value in the studies of ANS derivatives as the measure of solvent polarity. Solvent polarity is what is measured by a particular technique and may refer to different summations of molecular properties in different cases. For this reason, only simple reference processes should be used to derive solvent parameters. 

Beichardt (1965). Molar trmisition energies from the visible spectrum of pyridinium N-phenol betaines in solvents. Dimroth et al. (1963). Molar transition energies from spectrum of l-ethyl-4-methoxycarbonyl pyridinium iodide (Koso rer, 1958). From rates of Sj l solvolyses of alkyl halides and tosylates (Grunwald and Winstein, 1948). From ratio of endo to exo products in the Siels-Alder addition of cyclopentadiene to... 

The Z scale is based on the strong solvatochromism of the l-ethyl-4-(methoxycarbonyl)pyridinium iodide ion-pair (4) and defined by the position (in kcal mol ) of the maximum of its first absorption band, which has marked intermolecular charge-transfer connotations according to Scheme IV (the excited state of the chromophore is much less... 

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