Quaternary ammonium salts hydration

Girard s reagent T is carbohydrazidomethyltrimethylammonium chloride (I) and is prepared by the reaction of the quaternary ammonium salt formed from ethyl chloroacetate and trimethylamine with hydrazine hydrate in alco-hoUc solution ... 

Low sulfate selectivity of the ion-selective electrodes (ISE) based on lipophilic quaternary ammonium salts (QAS) is usually explained by unfavorable ratio of sulfate hydration and solvation energies. We have been shown that another reason does exist as well namely, low efficiency of sulfate-QAS cation interaction caused by steric hindrance for simultaneous approach of two QAS cations, containing four long-chain hydrocarbon substituents, to sulfate ion. 

The hydration number (the number of water molecules intimately associated with the salt) of the quaternary ammonium salt is very dependent upon the anion. The change in the order of reactivity is thus believed to be due to the hydration of the anion the highly hydrated chloride and cyanide ions are less reactive than expected, and the poorly hydrated iodide fares better under phase transfer conditions than in homogeneous reactions. Methanol may specifically solvate the anions via hydrogen bonding, and this effect is responsible for the low reactivity of more polar nucleophiles in that solvent. 

A slow non-competing liquid/liquid reaction with no catalyst present gave only 78 % O-alkylation. Thus the active site of the lipophilic phosphonium ion catalysts appears to be aprotic, just as in analogous phase transfer catalyzed alkylations with soluble quaternary ammonium salts 60), Regen 78) argued that the onium ion sites of both the 17% and the 52% RS tri-n-butylphosphonium ion catalysts 1 are hydrated, on the basis of measurements of water contents of the resins in chloride form. Mon-tanari has reported measurements that showed only 3.0-3.8 mols of water per chloride ion in similar 25 % RS catalysts 74). He argued that such small hydration levels do not constitute an aqueous environment for the displacement reactions. No measurements of the water content of catalysts containing phenoxide or 2-naphthoxide ions have been reported. 

A typical water soluble Shell-type AA is a quaternary ammonium salt (QAS), in which two or three of the four ammonium branches are short (e.g., a butyl compound that might be a candidate for inclusion within hydrate cavities ) and one or two branch(es) are much longer (e.g., C8 to Cl8) so that it might be soluble within the oil phase. The mechanism of AAs is uncertain at this time, but some educated guesses can be given, which evolve from the chemical structure of AAs. 

These were developed in an endeavor to expand the range of metals that could be incorporated into an ionic liquid. The presence of waters of hydration decreases the melting point of metal salts because it decreases the lattice energy. Hence, as Figure 2.4 shows, hydrated salts should be more likely to form mixtures with quaternary ammonium salts that are liquid at ambient temperature than anhydrous salts. Table 2.5 shows a list of some of the metal salts that have been made into ionic liquids with choline chloride and the freezing point of a lChCl 2metal salt mixture. 

In the higher hydrates of the quaternary ammonium salts, the cations are the guest species and the water and anions form the anionic host lattice. In the recently discovered strong add hydrates such as HC104 6H20 [767], the anions are the guests in a cationic water lattice. 

Fowler DL, Loebenstein WV, Pall DB, Kraus CA (1940) Some unusual hydrates of quaternary ammonium salts. J Am Chem Soc 62 1140-1144... 

McMullan RK, Jeffrey GA (1959) Hydrates of the tetra-n-butyl and tetra-i-amyl quaternary ammonium salts. J Chem Phys 31 1231-1234... 

Most potentiometric anion-selective electrodes are based on anion exchangers such as quaternary ammonium salts. The selectivity pattern of these sensors correlates with anion lipophilicity. Highly hydrated anions such as fluoride, bicarbonate and chloride are difficult to monitor due to significant interference from more lipophilic anions like perchlorate, salicylate and nitrate which may be present in the analyzed sample. The anions can be classified according to their lipophilicity resulting in the classical Hofmeister series (ClOi > SCN > salicylate > I > NOJ > Br >... 

Simple monoalkyl quaternary ammonium salts have been shown to inhibit formation of gas hydrates of the type that block gas and oil pipelines and equipment. For the most part, in order to be effective the salts must have at least two C4-C6 alkyl groups on the quaternary head-group. Such head-groups appear to fit well within the nascent gas hydrate crystal and, by a mechanism that is not yet totally understood, inhibit further growth of such crystals. 

Quaternary ammonium salts containing hydroxyl or ether functions in the shorter groups attached to the head-group are can also be used as hydrate inhibitors. Ethoxylated alkyldiamines are another class of cationic hydrate inhibitor that has been patented recently. In all of the above cases, cationic hydrate inhibitors appear to work best when used in combination with other additives. 

A remarkable variation of the type-I clathrate superstructure is associated with the formation of semiclathrates in the Ge-P-Q (Q = Se, Te) systems [34, 35]. The term semiclathrate was first introduced for hydrates of quaternary ammonium salts, which show general structural and physical properties of normal clathrates but in addition feature a single hydrogen bond between host and guest substructures [50]. Up to now quite a number of semiclathrates-hydrates have been reported in the literature [51] compared to a very limited number of inorganic semiclathrates, which are exclusively cationic semiclathrates. 

Park S, Lee S, Lee Y, Seo Y (2013) CO2 Capture from simulated fuel gas mixtures using semiclathrate hydrates formed by quaternary ammonium salts. Environ Sci Technol 47(13) 7571-7577... 

---