Pyridines alkyl groups

Alkyl sulfonates are derivatives of sulfonic acids m which the proton of the hydroxyl group is replaced by an alkyl group They are prepared by treating an alcohol with the appropriate sulfonyl chloride usually m the presence of pyridine... 

Carbon Substituents. Alkyl groups at positions 2 and 4 of a pyridine ring are more reactive than either those at the 3-position of a pyridine ring or those attached to a benzene ring. Carbanions can be formed readily at alkyl carbons attached at the 2- and 4-positions. This increased chemical reactivity has been used to form 2- and 4-(phenylpropyl)pyridines, eg, 4-(3-phenylpropyl)pyridine [2057-49-0] (21) (24). 

In general, pyridazine can be compared with pyridine. It is completely miscible with water and alcohols, as the lone electron pairs on nitrogen atoms are involved in formation of hydrogen bonds with hydroxylic solvents, benzene and ether. Pyridazine is insoluble in ligroin and cyclohexane. The solubility of pyridazine derivatives containing OH, SH and NH2 groups decreases, while alkyl groups increase the solubility. Table 1 lists some physical properties of pyridazine. 

Few other reactions of series of substituted pyridines have been investigated extensively. Dondoni, Modena, and Todesco have measured the rate of N-oxidation of a limited series of pyridines and found a good correlation with normal u-values with a p-value of — 2.23. The A-alkylation of pyridines with alkyl iodides in nitrobenzene has been studied by Brown and Cahn and by Clarke and Rothwell. Unfortunately, the only data available are for the parent compound and for alkyl derivatives, and, since the a-values for the various alkyl groups in a given position are substantially constant, this leaves a correlation of only three independent points. However, the rates of A-alkylation of the j8- and y-alkyl derivatives are so nearly equal that it appears as if no correlation existed. Clarke and Rothwell have also studied the alkylation with allyl bromide in nitromethane at various temperatures, and in this case a more extensive series is available. The authors state that no overall Hammett correlation is obtained however, the j8-substituted derivatives fall on one straight line and the y-derivatives on another one with a different slope. The data are shown in Fig. 2. The line for the j8-compounds, p = — 2.53 0.31, r = 0.95, is seen not to be very good the line for the y-derivatives, p = — 1.42 0.06, r = 0.99, is much more satisfactory. It does not seem likely that the discrepancy is due to the intervention of resonance effects, since in this case one would expect the correlation for the y-derivatives to be poorer than that for the j8-analogs. More extensive studies with a wider variety of substituents would seem very desirable. 

Treatment of a 3-aminotriazolopyridine with acid gave the imidazopyridine 242 (81T1787), also obtained from the 3-nitro derivative by catalytic reduction (83AHC79). Quaternary salts derived from compound 2, when treated with tri-ethylamine and subsequently heated give 2-pyridylcyanamides 243 or 2-(oxazol-l-yl)pyridines 244 depending on the alkyl group (86H(24)2563) the ylides are presumably intermediates (see also Section IV.I). 

Relatively few pyridines with substituents other than alkyl groups have so far been examined, and with some of these the reaction has been carried out only in the presence of added solvent. A comparison of the reactivities of these pyridines is therefore difficult. It has, however, been established that the presence of benzoyl groups in the 3- and 4-positions causes a very marked drop in the yields of the corresponding 2,2 -bipyridines. The 3- and 4-benzylpyridines were found to be more reactive but even in the absence of solvent, and in vacuo, 4-benzylpyridine gave only about one-third of the yield of the 2,2 -bipyridine compared with pyridine itself. Ethyl nicotinate in the absence of solvent and under vacuum -- gave a similar yield of biaryl but 4-phenylpyridine was found to be less reactive. 

Some characteristic ions in the mass spectra of quinolines include m/z 102, 128, 156, and so on. Again, as in alkyl pyridines, RCN is lost if the alkyl group is attached to the carbon atom adjacent to the nitrogen atom. 

Brown and McDonald (1966) provided another type of kinetic evidence for these size relationships by determining secondary kinetic isotope effects in reactions of pyridine-4-pyridines with alkyl iodides. For example, the isotopic rate ratio in the reaction between 4-(methyl-d3)-pyridine and methyl iodide at 25-0 C in nitrobenzene solution was determined to be kjyfk = l-OOl, while that in the corresponding reaction with 2,6-(dimethyl-d6)-pyridine was 1-095. (Brown and McDonald (1966) estimate an uncertainty of 1% in the k jk values.) Furthermore, the isotopic rate ratio in the case of the 2-(methyl-d3)-compound increased from 1 030 to 1-073 as the alkyl group in the alkyl iodide was changed from methyl to isopropyl, i.e. the isotope effect increased with increasing steric requirements of the alkyl iodide. 

The encapsulated complex with bulky alkyl groups was more active than the complex without alkyl groups. The catalytic activity increases on the addition of axial ligands as pyridine N-oxide, and the highest enantiomeric excess, 88%, was also achieved in the presence of the pyridine N-oxide. 

Akiba, K.-y., Matsuoka, H., and Wada, M., Regiospecific introduction of alkyl groups into 4-position of pyridine — novel synthesis of 4-substituted py-... 

Kinetics of the reaction of diazodiphenylmethane (92) in a wide range of alcohols with pyridine and pyridine-A -oxide 3- and 4-carboxylic acids (84)-(87), 4-substituted benzoic acids (88)," cw -substituted cinnamic acids (89), 2-(4-phenyl-substituted)cyclohex-l-enyl carboxylic acids (90), and 4 -substituted-biphenyl-2-carboxylic acids (91)" have been reported. Comparison of the new results for 4-substituted benzoic acids with the published results of data for 3-substituted benzoic acids was made, " and it was concluded that the most important solvent property influencing the rate of reaction appears to be the polarity of the alkyl group expressed as Taft s polar constant a. Transmission coefficients in the cinnamic acids (89) were compared with those in the bicyclic acids (90) and... 

The position of the alkyl group on the pyridine ring is very important. 4-Alkylpyridines react readily and much like alkylbenzenes, whereas... 

For sulfamides with larger alkyl groups (C3 to Cg) the following j)rocedure is preferred. To a stirred mixture of 135 g. (1.00 mol( ) of sulfuryl chloride and 500 ml. of chloroform is added, dropwise and with cooling to —10° to —5°, a solution of 316 g. ( (.00 moles) of pyridine in 400 ml. of chloroform followed by, with cooling to —5° to 0°, a solution of 2.5 moles of alkylamine in 600 ml. of chloroform. After addition is complete the mixture is stirred for 30 minutes at room temperature and then evap-ora(,( d under reduced pressure to a thick brown liquid, to wbic li aqueous 2M hydrochloric acid is added until the pyridine dissolves. On cooling of the acidic solution the crystalline MiiHaiMidc precipitates and is filtered. Any dissolved sulfamide limy be recovered by extraction of the filtrate with ether. Tb( crude product may be purified by recrystallization from bd )), cf.hanol. 

Transalkylation involves the transfer of alkyl groups between aromatic nuclei, usually in the presence of strong Lewis acids. Heredy and Neuworth used this reaction to "depolymerize" coal. As a result of the reaction of coal with BF3 and phenol, the solubility of coal in phenol or pyridine increased substantially. Various modifications of this reaction have since been reported . Transall lation reactions in the presence of trifluoromethane sulfonic acid and aromatic hydrocarbons have recently been used by Benjamin et al. and Farcasiu et al. to identify structural features in coals and heavy petroleum ends, respectively. 

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