Amines, quaternary ions

The reactions are catalyzed by tertiary amines, quaternary ammonium salts, metal salts, and basic ion-exchange resins. The products are difficult to purify and generally contain low concentrations of acryhc acid and some diester which should be kept to a minimum since its presence leads to product instabihty and to polymer cross-linking. 

The nitro alcohols available in commercial quantities are manufactured by the condensation of nitroparaffins with formaldehyde [50-00-0]. These condensations are equiUbrium reactions, and potential exists for the formation of polymeric materials. Therefore, reaction conditions, eg, reaction time, temperature, mole ratio of the reactants, catalyst level, and catalyst removal, must be carefully controlled in order to obtain the desired nitro alcohol in good yield (6). Paraformaldehyde can be used in place of aqueous formaldehyde. A wide variety of basic catalysts, including amines, quaternary ammonium hydroxides, and inorganic hydroxides and carbonates, can be used. After completion of the reaction, the reaction mixture must be made acidic, either by addition of mineral acid or by removal of base by an ion-exchange resin in order to prevent reversal of the reaction during the isolation of the nitro alcohol (see Ion exchange). 

New synthetic procedures used to crystallize VPI-5 are described. Mixtures of amines and quaternary ions are utilized to crystalize pure VPI-5. A low cost, high yield preparation involves the use of triisopropanol amine and tetramethylammonium hydroxide. Some samples of VPI-5 can be transformed into AIPO4-8 upon certain calcination conditions. Extensive washings of the aforementioned, as-synthesized VPI-5 yields a product which does not transform into AIPO4-8. 

The VPI-5 samples prepared using TBA show greater thermal stability than those synthesized with DPA (ref. 3). Also, the TBA synthesized VPI-5 is stable in its mother liquor while the DPA synthesized VPI-5 is not (refs. 4, 5). The differences in stability are not due to pH variations between TBA and DPA mother liquors. Thus, the quaternary ion appears to assist the crystallization process in some manner that is not possible with an amine. Unfortunately, TBAOH is very expensive compared to most amines. 

Priimiry amines Secondary amines Ternary amines Quaternary ammonium ion... 

Berberine Phenyl ethyl ami nes,neuroleptic amines,quaternary ammonium compounds Analysis in coptis species Separation by reversed-phase ion-pair HPLC... 

Certain higher esters (hydroxyethyl and 2-hydroxypropyl acrylates) are also obtained by the reaction of ethyfene oxide with acrylic acid in the presence of catalysts based on tertiary amines, quaternary ammonium salts, ion exchange resins, etc. 

An anion exchange resin is a polymer containing amine (quaternary ammonium) groups as an integral part of the polymer lattice and an equivalent amount of anions such as chloride, hydroxide, and sulfate ions. 

In the field of cation analysis, ion-pair chromatography is an alternative method for the separation of all types of amines. While short-chain aliphatic amines (C1-C3), alkanolamines, and some smaller aromatic amines [44] are much easier separated on modern cation exchangers, ion-pair chromatographic applications have been developed for the separation of structurally isomeric amines, quaternary ammoniimi compounds as well as arylalkylamines, barbiturates, and alkaloids. 

Many glycosylamines exhibit mutarotation which may be due to the establishment of an equilibrium between the a- and jS-isomers and the corresponding Schiff base or possibly to a partial hydrolysis (id, 62 dP, Pa,6). The mechanism outlined necessitates the presence of a hydrogen atom attached to the nitrogen atom, i.e., the aglycon amine must be a primary amine. However, the observed mutarotation of the corresponding derivatives of secondary amines may be ascribed to the formation of an intermediate quaternary ion R2N+=CH—(CHOH)4—CH2OH. 

More recently, Normant and coworkers have reported catalysis of the reaction between potassium acetate and benzyl chloride in acetonitrile by polyamines in a two phase system [28]. It seems likely that the catalytic activity reported by Normant et al. is related to the earlier alkylations discussed above. The authors state in their communication, however, their finding that ... quaternary ammonium salts corresponding to the diamines do not activate anions under the experimental conditions used. . In the reaction referred to here, it seems likely that the diamines are playing a dual role. The diamines are probably assisting in the solubilization of the solid (and relatively insoluble) potassium acetate by chelation of the potassium cation and the homogeneous reaction is then probably catalyzed by the quaternary ion formed in situ. That the catalytic activity of the amine depends on the hardness of the cation (the harder the cation, the less catalytic activity) [28] seems to accord with this interpretation although lattice energy differences cannot be discounted. 

Phase transfer processes rely on the catalytic effect of quaternary onium or crown type compounds to solubilize in organic solutions otherwise insoluble anionic nucleophiles and bases. The solubility of the ion pairs depends on lipophilic solvation of the ammonium or phosphonium cations or crown ether complexes and the associated anions (except for small amounts of water) are relatively less solvated. Because the anions are remote from the cationic charge and are relatively solvation free they are quite reactive. Their increased reactivity and solubility in nonpolar media allows numerous reactions to be conducted in organic solvents at or near room temperature. Both liquid-liquid and solid-liquid phase transfer processes are known the former ordinarily utilize quaternary ion catalysts whereas the latter have ordinarily utilized crowns or cryptates. Crowns and cryptates can be used in liquid-liquid processes, but fewer successful examples of quaternary ion catalysis of solid-liquid processes are available. In most of the cases where amines are reported to catalyze phase transfer reactions, in situ quat formation has either been demonstrated or can be presumed. 

Makosza has argued that the proton transfer occurs at the interface, and that the remainder of the reaction sequence occurs in the bulk organic phase [9]. He has drawn attention to the following facts. First, hydroxide is a harder ion than either trichloromethide or chloride and the latter two would tend to pair with the soft quaternary ion rather than the former. As a consequence, the base concentration in the organic phase should be low. In addition, numerous examples of isotopic (C-D for C-H) exchange are known for weak carbon acids. These exchange reactions are frequently accomplished under biphasic conditions in the absence of a phase transfer catalyst. Finally, the observation that tertiary amines are effective catalysts for the dichlorocarbene... 

Table 6.1. Quaternary ion and amine catalyzed ester formation...

The catalytic activity could be due to the coordination and enhanced solubilization of potassium acetate by the amine or it could be due to in situ quaternary ion formation (or both). Although the authors rule out the latter as a mechanism of catalysis, it seems unlikely that there is no component of this mechanism operating. 

Not only will crown ethers, quaternary ions, and amines catalyze the esterification reaction, but cryptates are also effective in this application. Potassium carboxylates react in good yield with a variety of alkyl halides in the presence of a catalytic amount of [2.2.2]-cryptafe to yield the corresponding esters [28]. The results are summarized in Table 6.9. 

Amines as Catalysts. Some reports have appeared on the use of amines as catalysts in PTC nucleophilic substitution methods. For example, the preparation of alkyl thiocyanates or nitriles from alkyl bromides in two-phase systems may be assisted by a variety of primary, secondary, or tertiary amines as alternatives to quaternary ions. Efficient catalysis seems to require a sterically unhindered amino group with relatively high basicity (J.e. t-alkyl and aromatic amines are not fully efficient), and a total number of carbon atoms in the amine of greater than six to achieve good phase distribution of the catalysts. A similar study on the alkylation of benzyl methyl ketone reached the same conclusions, and from various observations e.g. that the reaction displayed an induction period at low catalyst concentration) it was postulated that initial alkylation of the amine by the alkylating agent (usually a halide) was essential to provide quaternary ions as the actual catalyst,... 

Displacement of a tertiary amine from a quaternary (eq. lb) iavolves the attack of a nucleophile on the a-carbon of a quaternary and usually competes with the Hoffman elimination (173). The counterion greatiy iafluences the course of this reaction. For example, the reaction of propyltrimethylammonium ion with hydroxide ion yields 19% methanol and 81% propylene, whereas the reaction with phenoxide ion yields 65% methoxybenzene and 15% propylene (174). 

The Jordi quaternary amine phase has been developed to perform ion chromatographic applications and also can be used in a GPC mode to block... 

The amination of 2-chloropyridine-A-oxide (53) with potassium amide in liquid ammonia yielded a mixture of 2-(55) and 3-amino-pyridine-A-oxide (56) in 5-10% total yield.This rearrangement might be explained by an aryne mechanism involving 2,3-pyridyne-A-oxide (54). Since the structure of 56, with its quaternary nitrogen atom, is more analogous to that of 3-methoxybenzyne (39) than to that of 2,3-pyridyne (26), an orientation effect directing the amide ion to C-3 can be expected here. 

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