Aliquat, reagents

The use of cesium fluoride is limited because of its cost and its availability as a truly anhydrous reagent. Its use with 18-crown-6 shows a 5 times higher rate for the formation of benzyl fluoride from benzyl bromide when compared with cesium fluonde or potassium fluoride supported on calcium fluoride [21] Either cesium fluoride or potassium fluoride supported on calcium fluoride (Procedures 5a and 5b, p 194) provides about a twofold improvement over either unsupported alkali metal fluoride [55, 69], Cesium fluoride and Aliquat 336 convert benzyl bromide to the fluoride in 94% yield. Using tetrabuty lammonium fluoride in place of Aliquat... 

Pt-catalyzed hydration of various aliphatic and aromatic alkynes under phase transfer conditions in (CH2C1)2/H20 in the presence of Aliquat 336 led to either a Markovnikov product, mixtures of two ketones, or ketones with the carbonyl group positioned away from the bulky side.72 In the absence of the phase transfer reagent, Aliquat 336, hardly any reaction took place. Recently, a hydrophobic, low-loading and alkylated polystyrene-supported sulfonic acid (LL-ALPS-SO3H) has also been developed for the hydration of terminal alkynes in pure water, leading to ketones as the product.73 Under microwave irradiation, the hydration of terminal arylalkynes was reported to proceed in superheated water (200°C) without any catalysts.74... 

Potassium acetate, for example, can be readily alkylated by the use of an equivalent amount of an alkylating reagent (for example, an alkyl halide) in the presence of the phase-transfer catalyst Aliquat 336 (10 mol%) (Scheme 4.7) [16]. Yields are always near quantitative within a few minutes of microwave irradiation, irrespective of the chain length and the nature of the leaving group. This procedure has been scaled-up from 50 mmol to 2 mol scale in a large batch reactor [17]. 

Seductive animation. The limited solubility of NaBH3CN restricts its use to aprotic, ethereal solvents. Tetrabulylammonium cyanoborohydride or NaBHjCN in combination with Aliquat 336 can be used in most common organic solvents. Either reagent is useful for reductive amination of aldehydes or ketones. 

A stock Pb standard must first be prepared. Place reagent-grade Pb chloride in an oven at approximately 100°C for a few hours. Accurately weigh 0.3355 g of this salt and dissolve in 200 ml of a 10% v/v solution of Aliquat 336 in a 250 ml volumetric flask. Dilute to the mark with 10% v/v Aliquat 336 solution. This standard contains 1000 pg ml-1 Pb. Store in a darkened bottle, tightly stoppered. 

Wittig-Horner reaction. The reagent reacts with a wide range of aldehydes, aliphatic, aromatic, and a,P-unsaturated, in the presence of a base to form (E)-a-methyl-a, -unsaturated esters stereoselectively. The reaction can be carried out either with potassium t-butoxide in DMF or with K,COj in QH /HjO and Aliquat 336 as phase-transfer agent. 

Another commonly used extraction reagent for metal ions is diethylhexyl phosphoric acid (DEHPA) [55,56]. See Figure 12.3c. In this case a pH gradient must exist over the membrane, so the acceptor is kept more acidic than the donor (typically pH 1 and pH 3, respectively). Speciation of different chromium species (chromate and chromium ion) has been performed by the combination of two membrane extraction systems, one working with DEHPA for extraction of Cr + and the other with Aliquat-336 for extraction of the chromate anions [51]. Using the same principles, also organic compounds, such as amino acids [57] and polyamines [58], can be extracted. 

Scheme 12.10 Synthesis of 10,11-didehydro-quinine and -quinidine. Reagents and conditions (a) Br2, CCI4, 0°C, 2h (b) Et3N, CHCI3, rt, 14h (c) KOH, aliquat 336, THF, rt, 20h.

The presence of the sulphonic acid group in the azo reagents makes these and their complexes soluble in aqueous solutions. These complexes can be extracted in the presence of Aliquat 336 or tetrahexylammonium iodide in chloroform [36]. 

As with EDTA (Complexone III), DCTA ( Complexone IV) has also been used as a spectrophotometric reagent for chromium [13,14,17,31,32]. The Cr(III)-DCTA complexes have been extracted with chloroform solutions of Aliquat 336 [13,14]. 

Many other reagents have been used for determining iron, e.g., sulphosalieylic acid [106-109], ferron (7-iodo-8-hydroxyquinoline-5-sulphonic acid) (e = 4.0-10 at 610 nm) [110], Tiron [111,115], HTTA [116,117], pyrocatechol [118], phenylfluorone (in presence of Triton X-100 [119], morin (in the presence of a surfactant e = 6.3-10 ) [120-122], Alizarin S (extraction with Aliquat 336 in CHCI3] [123], Purpurin [124,125], salicylates[126,127], 2,2 -diquinoxalyl [128], sulphanilic acid in the presence of a surfactant [129], haematoxylin [130], and hydroxamic acid derivatives [13,14,131,132]. 

Thorium is one of the few multivalent metals [others are Au(III), Ce(IV), U(VI), and Cr(VI)] which are extractable as nitrate complexes from nitric acid solutions [25-28]. The extractants used include TBP in CCI4 [26,29], TOPO in cyclohexane, toluene or xylene [25,30,31], and triphenylarsine oxide in CHCI3 [27]. Other reagents used for extraction of the nitrate complex of thorium include dibutyl dithiophosphate in various organic solvents [32], dibutyl sulphoxide in xylene [28], and bis(2-butoxyethyl) ether [33].The liquid anion-exchanger Aliquat 336 in xylene [34] and a solution of tertiary ammonium salt (Hyamine) in dichloroethane [35] have been also proposed for extraction of Th. The presence of Li, Na, or A1 nitrate improves the extraction of thorium. Sulphate, phosphate, and tartrate do not interfere, but fluoride must be masked, e.g., by aluminium. Thorium has been separated from U and Pu with the use of Alamine 336 and TOPO (in xylene or cyclohexane) [36]. 

The use of chelating reagents (LIX and Kelex series), which are commercially available for solvent extraction, has been reviewed by Ashbrook 490). High-molecular-weight amines (Aliquat, Alamine, and Adogen series) are also in commercial use. The use of Aliquat-336 in the extraction of thorium 491) from spring waters has recently been reported 492). 

Stearyltrimethyl-ammonium chloride Benzyltrimethyl-, Benzyltriethyl-ammonium chloride, Aliquat 336 Crystal violet Girard reagent T Pyridiniiim ethiodide Me NBr Br PhMeoNHaL... 

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