Quinoline basicity

It is not clear why a basic quinoline system dissolves more quartz than a basic aqueous system, especially since potassium hydroxide is not readily soluble in quinoline. Attempts to dissolve potassium hydroxide in quinoline result in a dense milky suspension. The suspension may contain the active agent, perhaps a quaternary organic salt, that serves as a better hydroxyl source than solid potassium hydroxide in water. Practical grade quinoline was used for these experiments, and this may contain enough water for dissociation. 

Finally, Reactions 9, 10, and 11 (see Figure 4) illustrate the reduction of carboxyl and ester groups on a quinoline system. These groups are reduced in high yields to the basic quinoline some C—C cleavage is also observed, as found earlier (17). In our opinion, Compounds 9 and 10 represent the most likely precursors of quinolines present in the neutral fractions of the heavy gas oils and residuals. The basicity of the heterocyclic N is sharply reduced by the a-substituted acid or ester, as demon-... 

The historical importance and utility of quinine was known in the medical practice for a long time as a potent antipyretic in addition to its remarkable effect against the malarial fever. The basic quinoline nucleus, present in the quinine molecule, contributes to antipyretic activity to a certain extent. Therefore, an attempt was made to synthesize a number of quinoline derivatives which might exhibit better antipyretic activity. 

On acetylation it gives acetanilide. Nitrated with some decomposition to a mixture of 2-and 4-nitroanilines. It is basic and gives water-soluble salts with mineral acids. Heating aniline sulphate at 190 C gives sulphanilic add. When heated with alkyl chlorides or aliphatic alcohols mono- and di-alkyl derivatives are obtained, e.g. dimethylaniline. Treatment with trichloroethylene gives phenylglycine. With glycerol and sulphuric acid (Skraup s reaction) quinoline is obtained, while quinaldine can be prepared by the reaction between aniline, paraldehyde and hydrochloric acid. 

Crude oils contain nitrogen compounds in the form of basic substances such as quinoline, isoquinoline, and pyridine, or neutral materials such as pyrrole, indole, and carbazole. 

The presence of certain substituents e.g., the amino group) may markedly affect the solubibty and other properties of the sulphonic acid or carboxylic acid. Thus such sulphonic acids as the aminobenzenesul-phonic acids, pyridine- and quinoline-sulphonic acids exist in the form of inner salts or zwitter-ions that result from the interaction of the basic amino group and the acidic sulphonic acid. Sulphanilic acid, for example, is more accurately represented by formula (I) than by formula (II) ... 

Because of these difficulties, special mechanisms were proposed for the 4-nitrations of 2,6-lutidine i-oxide and quinoline i-oxide, and for the nitration of the weakly basic anilines.However, recent remeasurements of the temperature coefficient of Hq, and use of the new values in the above calculations reconciles experimental and calculated activation parameters and so removes difficulties in the way of accepting the mechanisms of nitration as involving the very small equilibrium concentrations of the free bases. Despite this resolution of the difficulty some problems about these reactions do remain, especially when the very short life times of the molecules of unprotonated amines in nitration solutions are considered... 

The easier elimination of pyridine compared to quinoline-4 may be related to the pK value of 4-methylthiazole, which is between those of lepidine and 2-picoline (25. 55). This reaction explains also why a neutrodimethine cyanine is obtained with such good yields when reacting together a quaternary salt, ketomethylene, and o-ester in a basic medium. As the reaction proceeds, the trimethine cyanine is attacked by the ketomethylene. The resulting 2-methyl quaternary salt is transformed into trimethine cyanine, consuming the totality of the ketomethylene (1, p. 512 661). The mesosubstituted neutrodimethine cyanine is practically pure. 

As early as 1889 Walker (320), using samples of thiazole, 2,4-dimethylthiazoie, pyridine, and 2,6-dimethylpyridine obtained from Hantzsch s laboratory, measured the electrical conductivity of their chlorhydrates and compared them with those of salts of other weak bases, especially quinoline and 2-methylquinoline. He observed the following order of decreasing proton affinity (basicity) quinaldine>2,6-dimethyl-pyridine>quinoline>pyridine>2,4-dimethylthiazole> thiazole, and concluded that the replacement of a nuclear H-atom by a methyl group enhanced the basicity of the aza-aromatic substrates. 

Although only ppm levels of nitrogen are found in the mid-distillates, both neutral and basic nitrogen compounds have been isolated and identified in fractions boiling below 345°C (12). Pyrroles and indoles account for about two-thirds of the nitrogen. The remaining nitrogen is found in the basic pyridine and quinoline compounds. Most of these compounds are alkylated. 

The piC values of polymethine dyes depend on terminal group basicity (64) thus the protonation abHity diminishes if the basic properties of the residues decrease, passing from benzimidazole, quinoline, benzothiazole, to indolenine. On the other hand, the piC of higher homologues increases with chain lengthening. The rate constant of protonation is sensitive to other features, for example, substituents and rings in the chain and steric hindrance for short-chain dyes. 

Polymers. Quinoline and its derivatives may be added to or incorporated in polymers to introduce ion-exchange properties (see Ion exchange). For example, phenol—formaldehyde polymers have been treated with quinoline, quinaldine, or lepidine (81) (see Phenolic resins). Resins with variable basic exchange capacities have been prepared by treating Amherlites with 2-methylquinoline (82). 

Polymers containing 8-hydroxyquinoline appear to be selective adsorbents for tungsten in alkaline brines (95). In the presence of tartrate and citrate, quinaldic acid [93-10-7] allows the separation of zinc from gallium and indium (96). Either of these compounds can selectively separate lead and zinc from oxide ores as complexes (97). It is also possible to separate by extraction micro quantities of rhenium(VII), using quinoline in basic solution (98). The... 

Of the total tar bases in U.K. coke-oven and CVR tars, pyridine makes up about 2%, 2-methyl pyridine 1.5%, 3- and 4-methylpyridines about 2%, and ethylpyridine and dimethylpyridines 6%. Primary bases, anilines and methylanilines, account for about 2% of the bases in coke-oven and CVR tars and 3.5% of the bases in low temperature tars. The main basic components in coke-oven tars are quinoline (16—20% of the total), isoquinoline (4—5%), and methyl quinolines. These dicycHc bases are less prominent in CVR and low temperature tars, in which only a minority of the basic constituents have been identified. 

Phenols. Phenols are unreactive toward chloroformates at room temperature and at elevated temperatures the yields of carbonates are relatively poor (< 10%) in the absence of catalysis. Many catalysts have been claimed in the patent Hterature that lead to high yields of carbonates from phenol and chloroformates. The use of catalyst is even more essential in the reaction of phenols and aryl chloroformates. Among the catalysts claimed are amphoteric metals or thek haUdes (16), magnesium haUdes (17), magnesium or manganese (18), secondary or tertiary amines such as imidazole (19), pyridine, quinoline, picoline (20—22), heterocycHc basic compounds (23) and carbonamides, thiocarbonamides, phosphoroamides, and sulfonamides (24). 

Reactions involving quinoline hydrazide derivatives have been noted in the pyridazino-[4,3-c]- (64MI21500), -[4,5-f ]- (31M(58)238) and -[4,5-c]-quinoline (71CB3341) series, whilst the double cyclization of (358) to the pyridazino[4,5-f ]quinoline (359) (80CPB3457) and related cyclizations in the same series (80H(14)267) are of a basically similar type. A lone cyclization of this type from cinnoline intermediates involves the o-acetonylcarboxamide type formation of the pyridine ring to give the pyrido[3,4-c]cinnoline (360) (76JCS(Pl)592). 

Friedel-Crafts acylation, 2, 322 Quinoline, methyl-basicity, 2, 172 NMR, 2, 120 radical cations... 

Dried with Linde type 5A molecular sieves or Na2S04 and fractionally distd at reduced pressure. Alternatively, it was refluxed with, and distd from, BaO. Also purified by fractional crystn from the melt and distd from zinc dust. Converted to its phosphate (m 135°) or picrate (m 223°), which were purified by crystn and the free base recovered and distd. [Packer, Vaughn and Wong J Am Chem Soc 80 905 1958.] The procedure for purifying via the picrate comprises the addition of quinoline to picric acid dissolved in the minimum volume of 95% EtOH to yield yellow crystals which are washed with EtOH and air dried before recrystn from acetonitrile. The crystals are dissolved in dimethyl sulfoxide (previously dried over 4A molecular sieves) and passed through a basic alumina column, on which picric acid is adsorbed. The free base in the effluent is extracted with n-pentane and distd under vacuum. Traces of solvent are removed by vapour phase chromatography. [Mooman and Anton J Phys Chem 80 2243 1976.]... 

In one process the naphtha fraction boiling between 160 and 180°C is washed with caustic soda to remove the acids and then with suilphuric acid to remove basic constituents such as pyridine and quinoline. The naphtha is then frozen to remove naphthalene, and agitated with sulphuric acid, then with caustic soda and finally with water. Concentrated sulphuric acid is then run into the purified naphtha at a temperature below 0°C. The reaction is stopped by addition of water after 5-10 minutes, any sediment is removed, and the solution is neutralised and then washed with water. Residual naphtha is distilled off under vacuum, leaving behind the resin, which is run into trays for cooling. 

---