Tetra-Alkylammonium HydroxIDE

Finally, we have discovered that the use of a tetra-alkylammonium hydroxide dramatically increases the paraselectivity of the reaction in aqueous media. Our initial results are listed in Table 2 (ref. 12). 

Table 2. Increase of paraselectivity by the use of tetra-alkylammonium hydroxides.

We have discovered that the use of tetra-alkylammonium hydroxide in place of sodium hydroxide increases dramatically the paraselectivity of the condensation between guaiacol and glyoxylic acid in aqueous media. The other advantages are the possibility to increase the productivity, increasing initial concentration, with a lower ratio of base. The new conditions for condensation can be used for other 2 alloxyphenols for example 2 ethoxyphenol. 

Figure 13.7.1 Variation of the rate of reduction of chromate (0.2 mM) in the presence of different tetra-alkylammonium hydroxides (R4NOH) at —0.75 V vs. SCE and 25°C. (Me, methyl Et, ethyl Pr, propyl Bu, butyl). [From L. Gierst, J. Tondeur, R. Comelissen, and F. Lamy, J. Electroanal Chem., 10, 397 (1965), with permission.]...

One effective method of pre-determining the type of zeolite structure that will be formed is the use of template molecules of the appropriate size. Using bulky tetra-alkylammonium hydroxides rather than alkali metal hydroxides to increase the pH gives more open structures. For example, if a short-chain alkyl trimethylammonium surfactant (detergent), C6Hi3N+(CH3)3, is used in the reaction mixture, this provides a template of a suitable size for the formation of the medium-pore zeolite ZSM-5 (Zeolite Synthesized by Mobil, number 5). 

Potentiometric titrations of aqueous solutions of PGA with some alkali hydroxides LiOH,NaOH,KOH)a.ni. tetra-n-alkylammonium hydroxides, e.g. (C/Zj) AO//and (C Hg) NOH, were performed in three parallel determinations... 

Alkylation of P-dicarbonyl compounds and p-keto esters occurs preferentially on the carbon atom, whereas acylation produces the 0-acyl derivatives (see Chapter 3). There are indications that C- and 0-alkylated products are produced with simple haloalkanes and benzyl halides, but only C-alkylated derivatives are formed with propargyl and allyl halides [e.g. 90]. Di-C-alkylation frequently occurs and it has been reported that the use of tetra-alkylammonium 2-oxopyrrolidinyl salts are more effective catalysts (in place of aqueous sodium hydroxide and quaternary ammonium salt) for selective (-90%) mono-C-alkylation of p-dicarbonyl compounds [91]. 

Retention of solutes and selectivity can be controlled by adjusting the type and concentration of the ion-pair reagent added and by selection of the type and concentration of the organic solvent in the mobile phase (135,168). The ion pair reagents most commonly used are tetra-alkylammonium salts such as cetrimide (155,156,177) and tetra-n-butylammonium (TBA). The TBA reagent can be used as TBA phosphate (159,184), TBA chloride (221), TBA hydrogen sulfate (188,189), or TBA hydroxide (168,175,183). 

The complex hydrate structure, 1.67 choline hydroxide-tetra-n-propyl-ammonium fluoride 30-33H2O (space group = R-3, a = 12.533, c = 90.525 A) was discovered by Udachin and Ripmeester (1999b). It should be noted that the tetra-n-propylammonium salt will not form a hydrate on its own (Dyadin et al., 1988), even though other tetra-alkylammonium salts will form a variety of hydrate structures. Similar to structures II, H, and IV, this complex structure consists of stacked sequences of layers, CABBCAABCCABBCAAB. That is,... 

Other anions may be transferred into organic phases by tetra-alkylammonium phase-transfer catalysts. For example, sodium cyanide (NaCN) is not soluble in most organic solvents, but the cyanide ion ( CN) can be used as a nucleophile in organic solvents under phase-transfer conditions, as shown here. Like the hydroxide ion, cyanide is a stronger nucleophile in the organic phase because it is not solvated by water molecules. 

As an alternative to the potassium salt, tertiary amines and tetra-alkylammonium salts have been used instead. The acids, e.g. the dried residue from a serum extraction, are treated with an acetonitrile solution of pentafluorobenzyl chloride and di-isopropylethylamine, in a 3 1 molar ratio, at 40 °C for 5 minutes. The reaction mixture is blown dry with nitrogen if necessary the esterification may be repeated (96). lndole-3-acetic acid was similarly esterified, but using acetone as solvent and N-ethylpiperidine as the cation and reaction for 45 minutes at 60 °C [97). Tetrabutylammonium hydrogen sulphate (0.1 mmol) was converted to the hydroxide with sodium hydroxide (0.2 mmol) and added to the dried acids in a serum extract with 1 ml of methylene chloride and 20 pi of pentafluorobenzyl bromide. The mixture was vigorously shaken for 30 minutes and blown down to dryness with nitrogen, and the esters were extracted into hexane for HPLC [98,99). 

Method using Base and a Substituted Halogenomethane. The influence of catalyst anions (as their tetrabutylammonium salts) and cations (as chlorides or bromides) on the generation of dichlorocarbene from chloroform-sodium hydroxide has been studied under standard conditions by determining the yield of dichloronorcarane produced from the addition of the carbene to cyclohexene. The presence of olefin appears to be necessary since in its absence only very slow decomposition of the trichloromethyl anion occurs. Dehmlow has also devised a new procedure for phase-transfer-catalysed cyclopropanation. Treatment of an alkene (or cycloalkene) with sodium trichloroacetate and a tetra-alkylammonium salt in chloroform without... 

In some instances tetra-alkylammonium ions possess some specific properties. Thus in the solutions of cyclo-octatetraene no reduction waves were observed in the presence of ammonium nitrate or sodium hydroxide, but well developed waves were obtained at —1-5 V in the presence of tetramethylammonium ions. 

Much higher amounts of organic solvents are required for the elution of tetra-alkylammonium compounds, which are used as reagents in ion-pair chromatography of anions. If the analysis times are kept constant, an amount of 60 mL/ L acetonitrile suffices to elute tetramethylammonium hydroxide at a hexanesulfonic acid concentration of c = 1 mmol/L (Fig. 6-29), 280 mL/L is needed for the elution of tetrapropylammonium ions, and 480 mL/L for the even more... 

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