Tetraalkylammonium halides

When reacted with tetraalkylammonium halides, hydrated [Me2Sn(IV)], [Bu2Sn(IV)]2-",2 [Ph2Sn(IV)]2-", 5 and [EtPhSn(lV)]2-",2 ester derivatives of 2,6-pyridinedicarboxylic acid yield tetraalkylammonium diorganohalogeno(2,6-pyr-idinedicarboxylato)stannates. Both classes of compounds exhibit high in vitro antitumor activity. 

One difference in behavior between the hydrophilic alkali halides and hydrophobic solutes like the larger tetraalkylammonium halides in water is expressed by the enthalpy. The enthalpies of solution of the larger tetraalkylammonium halides in water are more exothermic than those of the corresponding alkali halides but in other solvents, e.g., several amides, propylene carbonate (PC), and dimethylsulfoxide (DMSO), the reverse is true. Generally, this phenomenon is attributed to an enhanced hydrogen bonding in the highly structured solvent water in the vicinity of the tetraalkylammonium ions (hydrophobic hydration) (i). This idea is substantiated by the absence of the effect in solvents like N,N-dimethylformamide (DMF), PC, and DMSO (2), where specific structural effects are not present in the pure solvents. 

Quaternary ammonium salts of heterocyclic compounds have been used in liquid-liquid phase-transfer syntheses. When these compounds are achiral, they show a behavior very similar to that of other quaternary ammonium salts. For example, 2-dialkylamino-l-alkylpyridinium tetrafluoroborates have been used by Tanaka and Mukayama282 in the alkylation of active methylene compounds PhCH2CN, PhCH(Et)CN, and PhCH(Me)COPh. However, comparative studies of the efficiency of the catalysts show that alkylpyridinium bromides283 or N-alkyl-Af-benzyl-piperidinium chloride284 have a smaller catalytic activity compared to tetraalkylammonium halides. McIntosh285 has described the preparation of azapropellane salts 186 as potential chiral phase transfer catalysts. 

The tetraalkylammonium halides formed by complete alkylation of amines are ionic compounds that resemble alkali-metal salts. When silver oxide is used to precipitate the halide ion, tetraalkylammonium halides are converted to tetraalkylammonium hydroxides, which are strongly basic substances similar to sodium or potassium hydroxide ... 

Cyclic pentacoordinate plumbyl anions were synthesized by the oxidative addition of tetraalkylammonium halides to a dithiolatoplumbole (equation 63)79. An X-ray structure analysis of the adduct revealed a monocyclic anionic geometry. 

Falcone and Wood179) have reported enthalpies of dilution in NMA for a large series of alkali metal halides as well as for a number of tetraalkylammonium halides (all measurements at 35 °C). These heats were expressed as excess enthalpies180,181) and values of the excess free energies calculated from the previously mentioned osmotic coefficients allowed calculation of the excess entropies. 

Table VI-3. Excess enthalpies (kJ mol ) of tetraalkylammonium halides in watet and in NMA...

Simple 2,2-dibutyl-l,3,2-dioxastannolanes form solid complexes of monomer units with certain nucleophiles, such as pyridine and dimethyl sulfoxide, that have 1 1 stoichiometry and pentacoordinate tin atoms.62 Such complexes are less stable for more-substituted stannylene acetals, such as those derived from carbohydrates.62 Unfortunately, the precise structures of these complexes have not yet been defined. Addition of nucleophiles to solutions of stannylene acetals in nonpolar solvents has been found to markedly increase the rates of reaction with electrophiles,63 and transient complexes of this type are likely intermediates. Similar rate enhancements were observed in reactions of tributylstannyl ethers.57 Tetrabu-tylammonium iodide was the nucleophile used first,57 but a wide variety of nucleophiles has been used subsequently tetraalkylammonium halides, jV-methylimidazole,18 and cesium fluoride64,65 have been used the most. Such nucleophilic solvents as N,N-dimethylformamide and ethers probably also act as added nucleophiles. As well as increasing the rates of reaction, in certain cases the added nucleophiles reverse the regioselectivity from that observed in nonpolar solvents.18,19... 

The nitrogen ylides (3.60) are formed as intermediates in the Sommelet rearrangement ". The method is used for the conversion of the tetraalkylammonium halides 3.59 (having hydrogen in an a-position to N) into tertiary aromatic amines 3.61 (Scheme 3.25). 

There are some other methods that might be envisioned that could lead to OMS and OL materials. One obvious direction would be to use structure directors or templates that are similar to those used in zeolite synthesi such as tetraalkylammonium halides. Unfortunately, we have observed that such structure directors and templates react with KMn04 and get oxidized to C02- Another seemingly obvious route would be electrochemical syntheses. Some research has been done in this area, however, it is difficult to synthesize a sizeable amount of material such as with controlled potential electrolysis. In addition, some early work showed the generation of amorphous materials that after inital formation can be heated to form spinel phases without apparently going through the OMS/OL phases. 

Solutions of alkali metals in ammonia have been the best studied, but other metals and other solvents give similar results. The alkaline earth metals except- beryllium form similar solutions readily, but upon evaporation a solid ammoniate," MINI-lj),. is formed. Lanthanide elements with stable + 2 oxidation states (europium, ytterbium) also form solutions. Cathodic reduction of solutions of aluminum iodide, beryllium chloride, and tetraalkylammonium halides yields blue solutions, presumably containing Al, 3e Be", 2e and R4N, e respectively. Other solvents such as various amines, ethers, and hexamethylphosphoramide have been investigated and show some propensity to form this type of solution. Although none does so as readily as ammonia, stabilization of the cation by complexation results in typical blue solutions... 

A reaction of haloforms with a base, which generates dihalocarbenes (a-elimination) and their addition to alkenes is an efficient method for the preparation of 1,1-dihalocyclopropanes, with the exception of 1,1-difluoro derivatives (Houben-Weyl, Vol.E19b, pp 1464-1466). When chlorodifluoromethane and an alkene are treated with methyllithium, potassium tcrt-butox-ide, powdered sodium hydroxide in tetraglyme or a concentrated aqueous solution of alkali metal hydroxide and a phase-transfer catalyst, the expected 1,1-difluorocyclopropanes are formed in low yields. Comparable low yields of these products result, if dichlorodi-fluoromethane and an alkene are treated with methyllithium. " The main products formed are those that result from reaction of difluorocarbene (carbenoid), and its precursor, with the base or the solvent present in the system (for examples, see refs 10-12). Therefore, the reaction of chlorodifluoromethane with base and an alkene lacks preparative value. The difficulties mentioned above are circumvented in the method using chlorodifluoromethane, oxirane (or chloromethyloxirane), with tetraalkylammonium halide as a catalyst and an alkene (Houben-eyl, Vol. 4/3, p 380 and Vol. E19b, pp 1468-1469). 

No reaction is observed between the benzyl or allyl halides and the stannylenes, even in warm benzene in which these derivatives are apparently polymers. However, these ethers can be prepared in good yields in refluxing benzene in the presence of catalytic quantities of tetraalkylammonium halides and this is... 

A variety of tetraalkylammonium salts may be precipitated from an aqueous solution of the crude potassium salt, K2[Fe4(CO)13], by the addition of an aqueous solution of a tetraalkylammonium halide. 

---