Quaternary ammonium salts, solubilizers

Another catalytic system which has been successfully applied to the autoxidation of substituted toluenes involves the combination of Co/Br" with a quaternary ammonium salt as a phase transfer catalyst (ref. 20). For example, cobalt(II) chloride in combination with certain tetraalkylammonium bromides or tetraalkylphosphonium bromides afforded benzoic acid in 92 % yield from toluene at 135-160 °C and 15 bar (Fig. 19). It should be noted that this system does not require the use of acetic acid as solvent. The function of the phase transfer catalyst is presumably to solubilize the cobalt in the ArCH3 solvent via the formation of Q + [CoBr]. ... 

Early procedures used stoichiometric amounts of the quaternary ammonium catalyst to solubilize the preformed sodium or potassium salts of the active methylene compounds (prepared under anhydrous conditions) in the organic medium. Subsequently, liquidrliquid two-phase procedures using catalytic amounts of the quaternary ammonium salts were developed, and solidrliquid two-phase conditions have been used to improve yields. In some cases, only the solidrliquid two-phase procedures are effective. 

In a different approach to those described in earlier sections, quaternary ammonium salts are used to solubilize hydrogenation catalysts either in the organic substrate or... 

Solvent polymeric membranes that incorporate quaternary ammonium salt anion-exchangers, such as tri-n-octylpro-pylammonium chloride decanol, are used to construct CP-selective electrodes in clinical analyzers. Although by far the most common method for measuring CP in clinical laboratories, these electrodes have been described to suffer from membrane instability and lot-to-lot inconsistency in selectivity to other anions. " Anions that tend to be problematic are other halides and organic anions, such as SCN", which can be particularly problematic because of their ability to solubilize in the polymeric organic membrane of these electrodes. 

The quaternization of amines to the quaternary ammonium salt has proved a very useful method of converting the soft amine base to the pH insensitive quaternary ammonium salt. The amine is reacted with an appropriate measure of an alkyliodide as first described by Menshutkin (106). This reaction was systematically examined by Arcus and Hall in the 1960s as a means of quaternizing preformed polymers (107), and has emerged as a method of choice. For example, thwarted in our efforts to solubilize a high molecular weight... 

Solubilization of Solid Salt by Quaternary Ammonium Salts... 

Another method to solubilize organometallic compounds in water is the incorporation of quaternary ammonium salts (Figure 10). A characteristic member of this group is the AMPHOS ([Ph2P-(CH2)2-NMe3] CU) 18, which could be prepared from Ph2P-(CH2)2-NMe provided the phosphorus atom is protected by oxidation or coordination to a transition-metal center before forming the ammonium salt. ... 

Surfactants are also used in many pharmaceutical formulations, e.g. to prepare suspensions or emulsions of insoluble drugs, or as solubilizers (in the micelles) for many compounds for application as injectables or enhancement of the drug efficacy. Many surfactants are also used as germicides or antibacterials (e.g. the cationic quaternary ammonium salts). 

Further investigation of phase transfer catalysis, a phenomenon where quaternary ammonium salts catalyse reactions in aqueous-organic two-phase systems, has confirmed that the function of the ammonium ion is to solubilize the reagent/substrate in the organic phase. The use of phase transfer catalysis in the alkylation of weak acids such as diethyl malonate has been described other examples - - of this phenomenon are cited above. 

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. 

Phenols have been phosphorylated under phase transfer conditions in the presence of a nucleophilic catalyst [31, 32]. The reaction of 4-nitrophenol with dimeth-oxythiophosphoryl chloride is ordinarily slow and leads to a mixture of the desired methyl parathion and hydrolysis products. Addition of N-methylimidazole enhanced the rate but the best results were obtained when both the imidazole and a quaternary ammonium salt (TBAB) were used at the same time. The co-catalysis was accounted for in terms of nucleophilic activation of the acylating agent by imidazole and solubilization of the phenoxide by ion pairing with the quaternary ion. The overall transformation is formulated in equation 6.13. 

Use as a Nucleophile. The rate of nucleophilic substitution of 1,3-dichloropropane with potassium acetate in a range of polar solvents has been studied and correlates with the solubility of the salt. Quaternary ammonium salts (e.g., triethyl ammonium chloride, TEAC) catalyze these nucleophilic reactions by solubilizing the acetate anion. The relative rates of nucleophilic substitution of variously substituted 2-chloroethyl compounds with KOAc in DME and TEAC/MeCN solutions have a Unear free-energy relationships with the Taft substituent constant, a, showing that these reactions proceed through nucleophilic attack of acetate on RCH2CH2CI (eq 1). ... 

These normally contain anionic and nonionic surfactants, builders (such as sodium tripolyphosphate, acrylate polymers or copolymers, or sodium carbonate), ion exchangers (such as polyacrylic acid or zeolite), corrosion inhibitor (sodium silicate), processing aids, antiredeposition agent (such as sodium carboxymethylcellulose), whitener or optical brightener (stilbene derivative), dye, and perfume. They may also contain bleach (sodium perborate or percarbonate), enzymes (a protease and/or an amylase), foam suppressor, filler/processing aid (sodium sulfate), fabric softener (quaternary ammonium salt immobilized on a clay), and solubilizer. The surfactant concentration of a heavy duty powder is in... 

In order to avoid the necessity of adding a quaternary ammonium compound to solubilize the organotin derivative, a number of new, anionic, tributyltin salts of the type (RsR P)" (BuaSnClt) , where R = Ri = "Bu or Ph R = Ph, R = Bz, were prepared (440, 536). Although these contain discrete, trigonal, bipyrEimidal tributyldichloro-stannate anions (440), their solubility in water was found to be very low. 

It is worth mentioning at this point that according to Normant et al. (1975) simple polyamines such as tetramethylethylenediamine (TMEDA) are even more active than [2.2.2]-cryptand in the benzylation of acetates in acetonitrile under liquid-solid conditions. These authors suggested that the activity was due to salt solubilization by cation complexation and not to formation of a quaternary ammonium ion since the latter showed no activity. This statement, however, is not in line with the results of Cote and Bauer (1977), who were unable to detect any interaction between K+ and TMEDA in acetonitrile. Furthermore, Vander Zwan and Hartner (1978) found Aliquat 336 (tricaprylylmethylammonium chloride) to be almost as effective as TMEDA in this reaction (Table 30). It might well be, however, that in amine-catalysed benzylation reactions the quaternary salt formed in situ acts both as a reactant and as a phase-transfer catalyst, since Dou et al. (1977) have shown that the benzyltriethylammonium ion is a powerful benzylation agent. 

The example chosen here is that of quaternary ammonium cations (Q ). During the last 10 years, their salts have enjoyed extensive use as phase transfer catalysts(50). In the presence of Q" ", anions A are solubilized into the organic phase while retaining high nucleophilic activity in non polar solvents. In practice the best results are achieved with S3nnmetrical ammonium ions NR in which the alkyl chains R have at least four carbon atoms(51). Hence, our study has focussed on such symmetrical cations Q . 

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