Quarternary ammonia salts: Some recent applications in organic synthesis

Abstract

Some recent applications in organic synthesisMost undergraduate organic textbooks give only a passing reference to the unique class of compounds called quaternary ammonium salts. They are often referred to merely as the final products of exhaustive alkylation of primary amines. A student may get the erroneous impression that they are of no particular use in chemistry and that, being ionic, they are all soluble in water. Many textbooks make unqualified statements about their thermal stability.In the last ten years there has been a great upsurge of interest in the chemistry of quaternary ammonium salts. As a result, a number of interesting applications of molten quaternary ammonium salts have resulted (1-5). More recently, Starks reported that a small amount of quaternary ammonium salt added to certain two-phase organic reaction mixtures would catalyze these reactions to a remarkable extent (6). This phenomenon of phase-transfer catalysis has spurred considerable study in the United States, Europe, and Japan as evidenced by the large number of papers published in this area during the past four years.Part of the attractiveness of this area of research stems from the fact that it is within the scope and reach of most institutions where undergraduate research in chemistry is encouraged. No expensive and sophisticated instruments are required, and most of the chemicals needed are relatively inexpensive. Quaternary Ammonium SaltsQuaternary ammonium salts are compounds of the general formula R4N+X_ where R is alkyl, aryl, or aralkyl group and X is any anion. The R groups could be identical or different.These organic salts are ionic compounds which are made from primary, secondary or tertiary amines and an appropriate alkyl halide, sulfate, or some other similar compound carrying an excellent leaving group. Synthesis from a primary amine involves treatment with an excess of alkyl halide in methanol, acetonitrile, ethyl acetate, or benzene solution in the presence of a mild base. The last alkylation step is recognized as the Menshutkin reactionMany of these salts are crystalline solids at room temperature and are stable at their melting points for short periods of time. Low-melting salts may not crystallize easily at room temperature and a few salts are liquids at laboratory temperature (6-9). Their melting points depend on molecular weight, symmetry of the cation, and the nature of the anion. Thermal stability is related to the nucleophilicity of the anion. Strongly nucleophilic anions promote reverse Menschutkin reaction. Elimination products will also be obtained if the tertiary amine formed in the reverse Menschutkin reaction is not promptly removed from the reaction mixture. Hygroscopic properties vary in poorly defined fashion.Low-molecular weight salts up to Cg-salts are highly soluble in water, but beyond that the solubility in water decreases rapidly. However, incorporation of ether linkages in one or more of the alkyl groups tends to increase the solubility in water remarkably. Quaternary ammonium salts are gener...

Insights into Free Volume Variations across Ion-Exchange Membranes upon Mixed Solvents Uptake by Small and Ultrasmall Angle Neutron Scattering

“…These results suggest that the CEX solvent uptake is due mostly to the swelling of the microstructure by the solvent molecules resulting from the London–van der Waals interactions . However, in the case of AEX, the affinity of quaternary ammonium groups (anion-exchange groups) to organic solvents is particularly high which leads to the observed increase in solvent uptake . Unlike Nafion type membranes, the cluster-type structure of the IEMs results from cross-linked hydrocarbon backbone polymer chains with functional ionic groups grafted across short side chains. , While the swelling of Nafion membranes is limited by the polymer chain elastic energy, the swelling of the hydrocarbon-based Selemion and hybrid IEMs are limited by the degree of cross-linking of the IEX and to the nature of the solvent …”

Application des conditions de réaction par transfert de phase à la synthèse d'amino-éthers dérivés du trans phénoxy-2 cyclohexanol

“…Ainsi le test de Winter appliquC au composC l,, en vue de dCterminer son activitC antiinflammatoire potentielle, rCvkle une activitC du m&me ordre de grandeur que celle de l'lndomtthacine utilisCe cornme substance de rtfkrence.' Nous avons rCalist la synthkse de type Williamson des Cthers 1, d'une part par rCaction dans le xylkne a reflux entre l'alcoolate de sodium du trans phCnoxy-2 cyclohexanol et l'amine tertiaire halogCnte aliphatique (schtma 2), et d'autre 1. RCvision reque le 16 octobre 1985.…”

A Solvent-Free Base Liberation of a Tertiary Aminoalkyl Halide by Flow Chemistry

“…The reaction takes place under even mild storage conditions and is the reason for the limited shelf life of the free base 1. 11,12 Due to the number of processes relying on a key raw material, with limited shelf life, the manufacturing approach to 1 has been reconsidered to simplify the production planning and execution. It is obvious that the production setup would benefit from harmonization of the processes; however, the benefits of producing both solutions from a scaled-up batch distillation were perceived to be minimal even if the different APIs were produced simultaneously.…”

“…From a chemical reaction engineering perspective, the reaction can be described as a competitive-consecutive reaction. The reaction takes place under even mild storage conditions and is the reason for the limited shelf life of the free base 1 . , …”