Quaternization reactions

In principle, the quaternization reactions are extremely simple the amine (or phosphine) is mixed with the desired haloalkane, and the mixture is then stirred and heated. The following section refers to the quaternization of l-alkylimidazoles, as these are the most common starting materials. The general techniques are similar, however, for other amines such as pyridine [9], isoquinoline [10], 1,8-diazabi-cyclo[5,4,0]-7-undecene [11], 1-methylpyrrolidine [12], and trialkylamines [13], as... 

The quaternization reaction should be carried out either in a system that has been degassed and sealed under nitrogen, or else under a flow of inert gas such as nitrogen. Furthermore the reaction temperature should be kept as low as possible (no more that ca. 80 °C for Cl salts, and lower for Br and F salts). 

Other more complex linear block co-, ter- and quarterpolymers, such as ABC, ABCD, ABABA can be prepared using the previously mentioned methods. An important tool in the synthesis of block copolymers involves the use of post-polymerization chemical modification reactions. These reactions must be performed under mild conditions to avoid chain scission, crosslinking, or degradation, but facile enough to give quantitative conversions. Hydrogenation, hydrolysis, hydrosilylation and quaternization reactions are among the most important post-polymerization reactions used for the preparation of block copolymers. 

Kinetic studies on the quaternization reaction of pentamethylpyridine (154A, Scheme 64) and its deuterated congener suggest that there may be an equilibium between this aromatic pyridine and its valence isomer, pentamethyl-Dewar-pyridine (154B). It is known that such valence isomers are stabilized by steric factors such as encountered in pentamethylpyridine.194195 On determining conductometrically the initial rate of quaternization with methyl iodide for polymethylpyridines in acetone, it was found that all but one followed clean bimolecular kinetics. Pen-... 

Fields et al. found one example of an alkene, 1,1-dimorpholino-ethylene, which did not give the expected cycloaddition product, the 12,12-dimorpholino-6,ll-dihydro-6,ll-ethanoacridizinium ion (10). They conjectured that the l-(2-pyridyl)-2-morpholinonaphthalene (12) isolated had been formed via the expected adduct (10) which had undergone loss of morpholine to form the enamine (11) which could undergo ring opening (via a retro-quaternization reaction) followed by loss of a proton to yield (12). 

We tried a different approach to create a supported chloroaluminate IL on silica to be used for the toluene carbonylation reaction. A functionalized silica (2-(2-pyridyl)ethyl-functionalized silica gel (Sigma Aldrich 53,798-5) was reacted with one equivalent of n-propyl chloride in toluene (0.2 M) for 12 h at 140 °C to form the quaternary ammonium chloride." The pyridyl concentration on the silica was 1.3 mmol/g silica per the vendor. Prior to reaction with the -propyl chloride, the solid was evacuated at 150 °C for 1 h. The supernatant liquid was decanted, then the solid was evacuated at room temperature overnight. A small portion of this solid was examined by C-MAS-NMR to determine how well the quaternization reaction had occurred. The spectra of the sample before and after treatment with the -propyl chloride were compared to show the same peaks in both samples 1.42, 12.22, 29.87, 47.81, 110.5, 120.8, 134.9, 147.4, and 163.5 ppm however, the treated sample showed the peak at 110.5 ppm grew after the treatment confirming the success of the quaternization reaction. This... 

IX. Obtaining Relative Rate Constants for Quaternization Reactions by... 

An intriguing question then arises. Can evidence of the effects of pair-pair interactions be found in the solution chemistry of heterocyclic compounds in which electron transfer is not involved Although some unusual reactivity patterns have been observed in quaternization reactions, it is not obvious that the explanation lies with pair-pair interactions. 

Fio. 1. Bronsted plot for azoles reacting with methylating agents in quaternization reactions. Pyridine is the reference substrate. 1, 1-methylimidazole 2, 1-methylbenzimidazole 3, thiazole 4, 1-methylpyrazole 5, 2-methylindazole 6, benzo-thiazole 7, oxazole 8, 1-methylindazole 9, benzoxazole 10, 2,1-benzisothiazole 11, isothiazole 12, 2,1-benzisoxazole 13, isoxazole and 14, 1,2-benzisoxazole. 

Sections VI,A, B, D, and E give information about indazoles, oxazole, benzoxazole, isoxazole, benzisoxazoles, isothiazole, benziso-thiazoles, and benzothiazole. In addition, Sections II and VI,F,1 refer to quaternization reactions of isoxazole and benzisothiazoles, respectively. 

Emphasis is placed on simply substituted free bases. The problems of conformational equilibria in /V-alkylpiperidinium salts and N-quaternization reactions and the relationships of these to conformational equilibria in the free bases are not covered, since this area is a large one requiring separate treatment. In other relevant previous reviews, the topics include heterocyclic conformational analysis,3-7 interactions in azacyclic systems,8 the conformational analysis of piperidine,9 hexahydropyrimidines,10,11 hexahydropyri-dazines,12 quinolizidines,13 the conformational analysis of bi- and polycyclic... 

Naphthyridine chemistry has been well reviewed by Allen1 (up to 1947), and by Weiss and Hauser2 (up to 1958). It has also been considered incidentally by Duffin8 (quaternization reactions) and by Campbell4 in The Chemistry of Carbon Compounds. ... 

These final diversity elements were spatially encoded, i.e., the resin pools are kept separated and assayed separately, to allow for identification of the final monomers without the need for a further chemical encoding step. As a result no further pooling was necessary after the quaternization reaction and we were able to tailor the most favorable reaction conditions for incorporation of the required alkylating agents in each reaction. 

Derivatizing the neutral sample molecules to form ionic species enhances their secondary ion yield. Derivatization of the neutral sample molecules can often be accomplished by simply adding acid or base to the sample solution, or through the chemical modification of specific functional groups of the molecules, e.g., quaternization reactions [20, 89]. 

An alternative approach to the reaction conditions described above employs microwave irradiation for the quaternization reaction of 1-methylimidazole with various haloalkanes and l,reaction times (minutes instead of hours) and scaling up this technology to an industrial scale can easily be achieved. 

The trisquaternary salt (product of equation 6) is a pale purple powder which can be isolated by addition of dioxane to the ethanol-water mixture followed by filtration. In cases where the isolation of the salt is desired, better yields can be obtained by carrying out the quaternization reaction in dioxane solution. Isolation is then accomplished by addition of ethyl ether and filtration. Preliminary experiments in which laboratory animals were injected with solutions of the crude salt indicated a high degree of toxicity. 

Thiazoles readily undergo AT-alkylation by alkyl halides or tosylates (Menshutkin reaction). The sensitivity of this SN2 quaternization reaction to the molecular environment of the nitrogen atom has been used to evaluate, in a quantitative way, steric and electronic effects of ring substituents. The electronic effect of alkyl substituents (unperturbed by any steric effect) may be evaluated from the rate constants for the reaction of 5-alkylthiazoles with methyl iodide (in nitrobenzene at 30 °C) Table 19 shows that introducing a methyl group at the 5-position corresponds to an acceleration of the rate by a factor of 2 but that each addition of a methyl ramification to the 5-alkyl group enhances the rate only by a factor of 1.1. The data in Table 19 fit well with a Hammett-Taft equation (3) ... 

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