Dimeric quaternary ammonium salts

Scheme 4.2 General synthetic scheme for cinchona-derived dimeric quaternary ammonium salts, (a) bis(Bromomethyl)-linkers (0.5 equiv.), EtOH-DMF-CHCI3 (5 6 2), r.t. or reflux, (b) Allyl bromide or benzyl bromide (6.0 equiv.), 50% KOH (10.0 equiv.), CH2CI2, r.t.

Slow, except in presence of alkalis products formed are complex polymeric quaternary ammonium salts dimerizes fairly rapidly in water. 

Cyanuric chloride reacts vigorously and exothermically with DMF after a deceptively long induction period. The 1 1 adduct initially formed decomposes above 60° C with evolution of carbon dioxide and formation of a dimeric unsaturated quaternary ammonium salt. Dimethylformamide is appreciably basic and is not a suitable solvent for acyl halides. 

Alkynes react with haloethenes [38] to yield but-l-en-3-ynes (55-80%), when the reaction is catalysed by Cu(I) and Pd(0) in the presence of a quaternary ammonium salt. The formation of pent-l-en-4-ynes, obtained from the Cu(I)-catalysed reaction of equimolar amounts of alk-l-ynes and allyl halides, has greater applicability and versatility when conducted in the presence of a phase-transfer catalyst [39, 40] although, under strongly basic conditions, 5-arylpent-l-en-4-ynes isomerize. Symmetrical 1,3-diynes are produced by the catalysed dimerization of terminal alkynes in the presence of Pd(0) and a catalytic amount of allyl bromide [41]. No reaction occurs in the absence of the allyl bromide, and an increased amount of the bromide also significantly reduces the yield of the diyne with concomitant formation of an endiyene. The reaction probably involves the initial allylation of the ethnyl carbanion and subsequent displacement of the allyl group by a second ethynyl carbanion on the Pd(0) complex. 

Cathodic reduction of ammonium salts RR 3N+ in aprotic media, e.g., DMF, yields dimers R-R, for e.g., R=benzyl, fluorenyl, in moderate yields (15-30%) s03l Free radicals are assumed as intermediates, as inactive dimers were obtained from optically active ammonium salts RR 3N+. This rules out a conceivable S t2 reaction between cathodically generated R and RR 3N+ as products with partially inverted configuration should be obtained this way. Reduction of quaternary ammonium salts R4N+ in hexamethylphosphortriamide yields hydrocarbons RH and olefins RH(-H2) as main products and dimers R-R as minor side products, whose formation is rationalized by assuming radicals R as intermediates... 

The effect of the quaternary ammonium salt depends also on the substrate and on the electrode material [38]. Addition of tetraethylammonium salts thus sharply increases the yield of dimer product from acrylonitrile, has little effect upon the hydrodimerization of methyl acrylate, and does not affect the hydrodimerization of mesityl oxide. 

It has been shown by studies of the electroreduction of acrylonitrile at Pb, Ni, and Pt cathodes in the presence of quaternary ammonium salts that the yield of adiponitrile depends on the electrode material, with little dependence on cathode potential. On a Pb cathode the yield of adiponitrile was found to be almost independent of quaternary ammonium salt concentration, whilst on a Ni cathode the yield increased with increasing concentration of quaternary salt. The yield of adiponitrile, when a Pt cathode was used, was low and this led to the conclusion that atomic H2 plays a part in the mechanism. The ratio V2/v (dimerization/propionitrile rates) from their common... 

Classification Quaternary ammonium salt Empirical C43H92N2O 2CI Uses Antistat in cosmetics conditioner for hair and skin, perms, mousses emulsifier Trade Name Synonyms M-Quat Dimer 18 [BASF http //www.basf.com]... 

Synonyms Dimer acid bis (N-amidopropyi-N,N-dimethyi, N-benzyi ammonium chioride) Classification Quaternary ammonium salt Empirical C62H102N4O4 Cl Properties Liq., aromatic odor sol. in water m.w. 995 dens. 0.975 pH 3-6 (5% aq.) Cationic Uses Antistat in cosmetics conditioner in hair care, skin care Quaternium-70... 

The derivatization of IPDI is easier to accomplish because of the different reactivities of the two isocyanate groups in the molecule. For example, preferential dimerization of the primary isocyanate group is observed in the trialkylphosphine-catalyzed reaction (46). Trimerization of IPDI in the presence of quaternary ammonium salts affords mainly the isocyanurate trimer (47). Attempted biuret formation from IPDI and Na2S04 IOH2O gives a mixture of ureas and biurets (48). A biuret derivative is also obtained from IPDI and HDA (49). 

The formation of aldehyde cyanohydrin esters has been achieved under phase transfer catalytic conditions in which the two liquid phases are aqueous sodium or potassium cyanide and a methylene chloride solution of an aromatic aldehyde and an acid chloride. Both quaternary ammonium salts and 18-crown-6 are effective catalysts in this reaction. The formation of aldehyde cyanohydrin esters according to equation 7.7 probably occurs by a mechanism similar to that proposed for the formation of benzoyl cyanide dimers (see Eq. 7.5) [3, 22]. Accordingly, cyanide anion adds to the aldehyde carbonyl group to yield an alkoxide anion which in turn is acylated by the acid chloride. 

Phase-transfer catalysis with cinchona alkaloid derivatives is a very active area within the field of organocatalysis, as indicated in quite recent reviews [98c, 112]. In terms of structure, the quaternary ammonium salts can be varied in a straightforward manner by changing the structure of the benzylic compound used for the alkylation of the nitrogen atom of the quinuclidine moiety. In addition, dimeric and trimeric quaternary ammonium salts of cinchona alkaloids have been prepared [112] and applied successfully in catalysis, as exemplified in Scheme 6.55 for the epoxidation of 2,4-diarylenones [117]. 

The production of adiponitrile (intermediate in the production of nylon 66) via electrosynthesis is an important industrial process. It also is a good example of how electrogenerated hydrogen atoms [H ] induce the dimerization and oligerimization of terminal olefins. In this process a solution that contains acrylonitrile and a quaternary ammonium salt is circulated through a cathode compartment with a lead electrode. A dilute solution of sulfuric acid is circulated through an anode compartment with a lead-alloy electrode. An ion-exchange membrane separates the two compartments ... 

Figure 12.7 Dimeric and trimeric cinchona-derived quaternary ammonium salt phase-transfer catalysts.

Other research groups also devoted their efforts toward the design and synthesis of new polymeric cinchona-based quaternary ammonium salts. Najera et al. [59] developed the catalyst 29 which incorporates a 9,10-dimethylanthracenyl bridge as a spacer, whereas Siva and Murugan [60] prepared the dimeric cinchonidinium salts 30 using a cyclic tetraamine spacer. Both catalysts exhibited good performance in the asymmetric benzylation of N-(diphenyhnethylene) glycine tert-butyl ester. 

Aromatic and aliphatic thiols are oxidized by quaternary ammonium dichromate salts to disulphides (8, 13]. Yields are very good, even with the oxidative dimerization of diethyl phosphorothiolothionate to the corresponding disulphide (79%). 

Monoetherification of polyols.12 Monobenzylation and monoallylation of polyols can be conducted conveniently under mild conditions by conversion to the stannylene derivative (dimeric) by di-n-butyltin oxide (5, 189 9, 141). The stannylene is then treated with benzyl bromide or allyl bromide and tetra-n-butylammonium iodide (1 equiv.) in benzene. The same conditions can be used to prepare monomethoxymethyl ethers. Quaternary ammonium bromides are less efficient catalysts than the iodides. These salts also accelerate reaction of stannylenes with acid anhydrides. The mechanism for this activation is not clear it may involve coordination of I" to tin. 

The alkaloid content of curare is from 4% to 7%. The most important constituent in menispermaceous curare is the bis-benzyltetrahydroisoquinoline alkaloid (+)-tubocurarine (Figure 6.48). This is a monoquaternary ammonium salt, and is water soluble. Other main alkaloids include non-quaternary dimeric structures, e.g. isochondrodendrine and curine (bebeerine) (Figure 6.48), which appear to be derived from two molecules of (R)-N-methylcoclaurine, with the former also displaying a different coupling mode. The constituents in loganiaceous curare (from calabash curare, i.e. Strychnos toxifera) are even more complex, and a series of 12 quaternary dimeric strychnine-like alkaloids has been identified, e.g. C-toxiferine (toxiferine-1) (see page 359). 

Whatever metal is used, homogeneous processes suffer from high cost resulting from the consumption of the catalyst, whether recycled or not. This is why two-phase catalytic processes have been developed such as hydroformylation catalyzed by rhodium complexes, which are dissolved in water thanks to hydrophilic phosphines (cf. Section 3.1.1.1) [17]. Due to the sensitivity of most dimerization catalysts to proton-active or coordinating solvents, the use of non-aqueous ionic liquids (NAILs) as catalyst solvents has been proposed. These media are typically mixtures of quaternary ammonium or phosphonium salts, such as 1,3-dialkylimi-dazolium chloride, with aluminum trichloride (cf. Section 3.1.1.2.2). They prove to be superb solvents for cationic active species such as the cationic nickel complexes which are the active species of olefin dimerization [18, 19]. The dimers. 

Cinchona ammonium salt and 2,6-napthylsulfonate. ° In 2009, the novel chiral polymer 14c (henzylation, 86% enantiomeric excess), involving dimeric chiral quaternary ammonium repeating units internally connected hy two C(9)-OH groups prepared from dihalide via a repeated Williamson ether synthesis, was developed by the same research group. ... 

Though these alkaloids are not truly composed of two identical monomeric units, they are popularly named dimers or dimeric alkaloids. We prefer to avoid this incorrect nomenclature and would like to encourage the use of the more adequate binary terminology. In another consideration of nomenclature, we describe quaternary salts derived from an imine functionality as imonium salts, in accord with the descriptor for other onium salts (ammonium, oxonium, etc.), rather than by the frequently used iminium terminology. This nomenclature was suggested earlier (/). 

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