Tetrabutylammonium carboxylates

Anionic polymerization of pivalolactone with the polystyrene anion produced only homopolymer mixtures, but the polystyrene carboxylate anion was able to give a block copolymer336. The block efficiency depends on catalyst ratio and conversion because the initiation step is slow compared with propagation337. Tough and elastic films were obtained by graft copolymerization or block copolymerization of pivalolactone onto elastomers containing tetrabutylammonium carboxylate groups338,339. ... 

Table 6 Acyloxyl radical adducts formed in the oxidation of tetrabutylammonium carboxylates and PBN [3] by Ph4POsvCl6 in dichloromethane at 20°C. ...

It should be noted that this reaction is a special case of solid-liquid catalysis, because the anionic species, solubilized by the catalyst, is both reactant and substrate. Also of importance is the fact that because the tetrabutylammonium salt is used in catalytic quantities, the concentration of active species (the tetrabutylammonium carboxylate) remains very low throughout the reaction, which is therefore conducted in high dilution conditions. As expected, the yields are excellent. Another type of PTC is the triphase catalysis, having as a peculiar feature, the catalyst immobilized on a polymer (solid phase), which is in contact with the aqueous and organic phases containing the reactant and the substrate, respectively. This method presents the major advantage of avoiding the problem of catalyst and product separation. Various macrolides have been synthesized by this procedure. 

In a previous paper the formation of a clathrate-like hydrate by a series of tetrabutylammonium carboxylates ((n-C4H9) N00CR) with a saturated alkyl group in the carboxylate anion was confirmed from the solid-liquid phase diagrams and these hydrates were classified into three groups, I, II, and III, on the basis of the hydration numbers. 

The homogeneous reaction of tetrabutylammonium carboxylates (ion pair extraction) with methyl iodide in a two-phase system consisting of aqueous base and dichloromethane has also been reported. In most cases where the carboxylic acid was monobasic, excellent to quantitative yields of ester were observed. It was also noted that the esterification was insensitive to steric hindrance in the acid component under these conditions (see Eq. 6.4) [10]. 

If one of the species is anionic and we need to transport it to the organic phase, then a phase-transfer catalyst may be employed. Consider the example of benzyl penicillin where the reaction between phenyl acetic acid and the penicillin carboxylate ion, with penicillin amidase as a catalyst, is relevant, and which at pH 4.5 - 5.0 is shifted in the desired direction. Here a catalyst like tetrabutylammonium halide works, and with chloroform as a solvent 60% yield can be realized in contrast to a yield of only 5 - 10 % in water. 

The mesogenic units with methylenic spacers were prepared by reacting the sodium salt of either 4-methoxy-4 -hydroxybiphenyl or 4-phenylphenol with a bromoester in DMF at 82° C for at least 4 hours in the presence of tetrabutylammonium hydrogen sulfate (TBAH) as phase transfer catalyst. In this way, ethyl 4-(4-oxybi-phenyl)butyrate, ethyl 4-(4-methoxy-4 -oxybiphenyl)butyrate, ethyl 4-(4-oxybiphenyl)valerate, ethyl 4-(4-methoxy-4 -oxybiphenyl)-valerate, n-propyl 4-(4-oxybiphenyl)undecanoate and n-propyl 4-(4-methoxy-4 -oxybiphenyl)undecanoate were obtained. These esters were hydrolyzed with base and acidified to obtain the carboxylic acids. The corresponding potassium carboxylates were obtained by reaction with approximately stoichiometric amounts of potassium hydroxide. Experimental details of these syntheses were described elsewhere (27). 

Oxazolines have also been obtained from aziridines and carboxylic imidazolides via iV-acylaziridinesJ1271 Isomerization of the Af-acylaziridines can be achieved by heating with a catalytic amount of tetrabutylammonium iodide or bromide. The transformation can be carried out as a one-pot reaction in quantitative yield (solvents THF, CHC13, benzene) with a wide spectrum of substituents R (R = H, alkyl, c-C6Hi i, C6H5,3-pyridyl). 

In a quite different approach, shown in Scheme 204, cycloaddition of nitrile 1232 to trimethylsilyldiazomethane provides silylated triazole 1233, isolated in 75% yield. Treatment with tetrabutylammonium fluoride removes the trimethylsilyl group and simultaneously the silyl protection of the carboxylic group to afford 4-substituted triazole derivative 1234 in 81% yield <2003PEN699>. 

Example ion-pair liquid chromatography of amino acids. Amino acids are zwitterions. The amino group can form an ion-pair with an alkanesulfonate ion (such as octanesulfonate), and the carboxyl group can form an ion-pair with a tetrabutylammonium ion, depending on the pH of the solution. 

The ready insertion of carbon monoxide into furanylpalladium complexes is impressively demonstrated by the reaction depicted in 6.63. The iodofiirane derivative was reacted with carbon monoxide in the presence of tetrabutylammonium chloride. Following an aqueous workup the appropriate carboxylic acid was isolated in good yield (6.63.).94 It is worth pointing out, that due to the mildness of the reaction conditions the Heck coupling of the olefin moiety could be excluded. 

In another type of oxidative decarboxylation, arylacetic acids can be oxidized to aldehydes with one less carbon (ArCH2COOH — ArCHO) by tetrabutylammonium periodate. 23l< Simple aliphatic carboxylic acids were converted to nitriles with one less carbon (RCH2COOH — RC=N) by treatment with trifluoroacetic anhydride and NaNCU in FjCCOOH.239 See also 4-39. 

This method has been extended to heterocycles bearing a hydroxymethyl-substituted nitrogen. Thus, ethyl l-(hydroxymethyl)pyrazole-4-carboxylate (10) is converted into ethyl 1-(fluoromethyl)pyrazole-4-carboxylate (11) in 76% yield with cesium fluoride/methanesulfonyl fluoride/18-crown-6 system.167 Potassium fluoride did not react at all and tetrabutylammonium fluoride leads to decomposition and formation of coupling products. 

The electrochemical behavior of malonyl-a-aminopyridines 661 was investigated by Gullu et al. in acetonitrile or a mixture of trifluoroacetic acid and dichloromethane containing tetrabutylammonium tetrafluoro-borate or triethylammonium trifluoroacetate in a water-jacketed, two-compartment glass cell equipped with a platinum disk anode at 1.50 V (Ag/ Ag+) and a carbon-rod secondary electrode (91T675). Controlled potential anodic oxidation of 661 afforded labile coupled carboxylic acids 662 (R2 = COOH), which easily decarboxylated to compounds 662 (R2 = H) under the work-up conditions. Sometimes, the carboxylic acid 662 (R2 = COOH) could be isolated or when the reaction mixture was treated with methanol, methyl ester 662 (R = H, R1 = Bu, R2 = COOMe) was obtained in 40% yield. 

Crossed aldol reaction between an aromatic aldehyde and the TMS enolate of another aldehyde proceeds smoothly in wet or dry DMF using a lithium carboxylate as Lewis base catalyst.158 One-pot conversion to 1,3-diols using sodium borohydride as reductant gives up to 87% yield. A similar report, using tetrabutylammonium phe-nolates as Lewis bases, is diaslereoselective.159... 

A solution of 72.08 g (0.19 mol) of 5-bromo-l-pentanyl acetate in 1.4 L of MeOH was treated with 38 mL of a 1.0 molar solution of tetrabutylammonium hydroxide and the mixture was stirred at room temperature for 3.0 h, 3.0 mL of AcOH was added and the solution was evaporated at 35°C. The residue was dissolved in 400 mL of EtOAc and the solution was washed with saturated NaHC03, brine, dried, and evaporated to give 60.45 g (94% yield) of the intermediate hydroxy ester (an analytical sample may be obtained by crystallization from 70% EtOAc in hexane, m.p. 58-61°C. A stirred solution of 60.25 g of the hydroxyester in 700 mL of EtOAc was cooled to 5°C and treated with 75.5 mL (3 equiv.) of triethylamine and 32.6 mL (2.35 equiv.) of methanesulfonyl chloride. The mixture was stirred at 6°C for 2.0 h, transferred to a separatory funnel and washed sequentially with water, 2 N HCI, and brine. Concentration of the EtOAc to ca. 300 mL and dilution cooled to 0°C and treated with 75.5 mL (3 equiv.) of triethylamine and 32.6 mL (2.35 equiv.) of methanesulfonyl chloride. The mixture was stirred at 6°C for 2.0 h transferred to a separatory funnel and washed sequentially with water, 2 N HCI, and brine. Concentration of the EtOAc to ca. 300 mL and dilution with 250 mL of hexane led to crystallization (0°C, 18 h). The product was collected by filtration and washed with some cold hexane - EtOAc (1 1) to give 66 g (84% yield) of methyl (R,S)-6-acetyl-3,4-dihydro-7-[5-[(methylsufonyl)oxy]pentyloxy]-2H-l-benzopyran-2-carboxylate m.p. 73-76°C. 

Quaternary amines, e.g., tetramethylammo-nium, tetrabutylammonium, and palmityl-trimethylammonium ions For strong and weak acids, sulfonated dyes, carboxylic acids... 

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