Ionic ammonium cation

Miscellaneous Compounds. Among simple ionic salts cerium(III) acetate [17829-82-2] as commercially prepared, has lV2 H2O, has a moderate (- 100 g/L) aqueous solubiUty that decreases with increased temperature, and is an attractive precursor to the oxide. Cerous sulfate [13454-94-9] can be made in a wide range of hydrated forms and has solubiUty behavior comparable to that of the acetate. Many double sulfates having alkaU metal and/or ammonium cations, and varying degrees of aqueous solubiUty are known. Cerium(III) phosphate [13454-71 -2] being equivalent to mona2ite, is very stable. 

Ion-ion tautomerism Functional groups with a mobile hydrogen atom present in the ammonium cation can result in one more type of tautomerism, as in the case of /3-oxyethyl(triethyl)ammonium 1,3,2,5-dioxaborataphosphorinane (128) (88IZV155). In this case the equilibrium between two ionic forms (acyclic and cyclic) has been observed [Eq. (94)]. 

At low pH (acidic solution), an amino acid will exist as the protonated ammonium cation, and at high pH (basic solution) as the aminocarboxylate anion. The intermediate zwitterion form will predominate at pHs between these extremes. The uncharged amino acid has no real existence at any pH. It is ironic that we are so familiar with the terminology amino acid, yet such a structure has no real existence Amino acids are ionic compounds, solids with a high melting point. 

Heretofore, ionic liquids incorporating the 1,3-dialkylimidazolium cation have been preferred as they interact weakly with the anions and are more thermally stable than the quaternary ammonium cations. Recently, the physical properties of 1,2,3,4-tetraalkylimidazolium- and 1,3-dialkylimidazolium-containing ionic liquids in combination with various hydrophobic and hydrophilic anions have been systematically investigated (36,41). The melting point, thermal stability, density, viscosity, and other physical properties have been correlated with alkyl chain length of the imidazolium cation and the nature of the anion. The anion mainly determines water miscibility and has the most dramatic effect on the properties. An increase in the alkyl chain length of the cations from butyl to octyl, for example, increases the hydrophobicity and viscosity of the ionic liquid, whereas densities and surface tension values decrease, as expected. 

In another example, RuCl2(PPh3)3 in [BMIMjCl was shown to be a much less active catalyst than this complex in the ionic liquids [R4N]C1 or [R4N]OH for the aerobic oxidation of alcohol (199). The weaker association of the bulky tetraalkyl-ammonium cation than the planar [BMIM] cation with the anion appears to be the principal reason for the difference. 

This generalized structure was mimicked by a very simplified artificial molecule 1. The hydrophilic core part 2 was substituted simply by an oligoether carboxylate anion. The carboxylate may act as the polar ionic head group outside the membrane and the ether part of the molecule may be located in the interior part of the membrane to make an ion-conducting pathway. The molecular lengths were adjusted to fit the lipid monolayer in an extended or a helical conformation, with n being 2 or 3 in 1. The hydrophobic exterior was substituted by dioctadecyldimethyl-ammonium cation, which was ion-paired with the carboxylate. 

Ionic hquids are low melting organic salts that are liquids at ambient temperature. They typically contain quaternary ammonium cations such as l-butyl-3-methylimida-zolium- or N-butylpyridinium- with inorganic anions, such as tetrachloroaluminate or tetrafluoroborate (Chauvin and Helene, 1995 Freemantle, 1998). Melting points for these materials can be near -100°C, and the liquids are often thermally stable at temperatures approaching 200°C. 

PCH materials offer new opportunities for the rational design of heterogeneous catalyst systems, because the pore size distributions are in the supermicropore to small mesopore range (14-25A) and chemical functionality (e.g., acidity) can be introduced by adjusting the composition of the layered silicate host. The approach to designing PCH materials is based on the use of intercalated quaternary ammonium cations and neutral amines as co-surfactants to direct the interlamellar hydrolysis and condensation polymerization of neutral inorganic precursor (for example, tetraethylorthosilicate, TEOS) within the galleries of an ionic lamellar solid. 

With these anthracene-linked dimeric cinchona-PTCs, the Najera group investigated the counterion effect in asymmetric alkylation of 1 by exchanging the classical chloride or bromide anion with tetrafluoroborate (BF4 ) or hexafluorophosphate (PF6-) anions (Scheme 4.10) [17]. They anticipated that both tetrafluoroborate and hexafluorophosphate could form less-tight ionic pairs than chloride or bromide, thus allowing a more easy and rapid complexation of the chiral ammonium cation with the enolate of 1, and therefore driving to a higher enantioselectivity. However, when... 

The effect of the quaternary ammonium cations is quite complex because the smaller cations depress the freezing point more because the halide salts of the smaller cations also have a higher freezing point the net result is that all of the eutectic mixtures will have reasonably similar freezing points. Hence the cation is observed to have little effect on the absolute freezing point of the eutectic-based ionic liquids. 

It has recently been shown that the same principle can be applied to deep eutectic solvents by using small quaternary ammonium cations such as ethylammonium and fluorinated hydrogen bond donors such as trifluoroacetamide. However, there is only a limited benefit that can be achieved using this approach as the physical parameters cannot be varied totally independently of one another. For example there will be an optimum ion size too small and the lattice energy will increase the surface tension, too large and the ionic mobility will be impeded. 

The chains are attached to positively charged ammonium cations and, despite the reverse ionic character of the head groups that form the pore (compare 41-43 with Figure IS), the observed cation selectivity suggests that the inner membrane structure and not the charged head group determines ion selectivity. 

The resulting compound, NH4C1, is an ionic-bonded salt. The salts ammonium cation (NH4+) is held together by covalent bonds, one of which formed when a hydrogen ion united with the pair of unshared electrons on the nitrogen atom. Keep in mind that three of the nitrogen-hydrogen bonds in ammonia formed as ordinary covalent bonds, in which each element contributed one electron,... 

The electrodeposition of lithium has been studied in some N(CF3S02)J ionic liquids consisting of the aliphatic and aUcycUc ammonium cations [98-100]. Since these ammonium cations are more stable against lithium metal than alkylated imi-dazolium cations, the reversible deposition and dissolution of lithium metal are reported to be possible in these ionic liquids. 

Figure 14.6 Typical cations and anion of an ionic liquid with an ammonium cation, (a) N-Methyl-N-propyipiperidinium cation (PP13) (b) trimethylpropylammonium cation (TMPA) (c) bisftrifluoromethane suifonyl)imide anion (TFSI).

Although several telechelic polymers of 1,3-dioxolane have been prepared by cationic polymerization, their application is limited due to their susceptibility to acid-catalyzed hydrolysis and/or depolymerization. By termination of living mono- and difunctional poly(l,3-dioxolane) with amines or phosphines, polymers containing one or two stable ionic (ammonium, phosphonium) end groups has been prepared [129,274],... 

A solid consisting of oppositely charged ions is called an ionic solid, or (often) a salt. Ionic solids can consist of simple ions, as in sodium chloride, or of polyatomic (many-atom) ions, as in ammonium nitrate (NH4N03), which contains ammonium cations (NH4+) and nitrate anions (N03 ). The ball-and-stick models of these ions are shown in Fig. 2.20. 

Figure 12 Concentration of particle mass (panel a) and of major ionic species (panels a and b) in sub-2.5-p,m diameter particles in Atlanta, Georgia during August 18-27, 1999. Panel (c) compares equivalent concentration of anions (sulfate plus nitrate) to that of the ammonium cation. The left axis shows the molar concentrations the right axis shows mass concentration of ammonium. Time resolution of the measurements is 4 min, with a sample taken...

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