TNS reagent

Toluidino-2-naphthalene sulfonic acid (TNS reagent) cholesterol [180] phospho- and glycolipids [181] neutral lipids [182]... 

As is evident from the patterns in Figure 3-2, the sulfuric acid (char) spray will detect all organic carbon-containing lipids whereas the phosphorus spray will detect only phospholipid phosphorus-containing lipids. In addition to these sprays, of course, the TNS reagent will react with all lipids and is very effective in locating various types of compounds on a plate. 

If an examination of the chemical nature of the products is desired, then an aliquot of the reaction mixture can be subjected to thin-layer chromatography on silica gel G plates. In a solvent system of chloroform-methanol-water (65 35 7, v/v), the liberated fatty acids will migrate to an Rf near 0.90, the unreacted substrate to an Rf near 0.42, and the lysophosphatidylcholine to an Rf near 0.18. These compounds can be visualized by spraying the plate with TNS reagent (see Chapter 3) and then exposing to ultraviolet light. The... 

It is also possible to use more powerful reagents to nitrate thiazoles for example, 2-methylthiazole has been nitrated using nitronium tetrafluorobo-rate and the complex nitrogen dioxide-boron tn fluoride (240). The overall yield is about 50 to 60%. 

Much better known are the fluonnatedphosphoranes, which have been widely used m the Wittig reaction for the preparation of fluoroolefms Difluoromethylena tion reactions have been effected by using a variety of conditions Treatment of dibromodifluoromethane with two equivalents of tns(dimethylammo)phosphine m carefully dried tnglyme yields a solution of bromodifluoromethylphosphonium broomide, which very effectively converts ketones to difluoromethylene derivatives A more sensitive reagent is prepared by the addihon of two equivalents of the phosphine to the reaction mixture of fluorohalomethane and a carbonyl compound [39, 40] (equation 40) (Table 14)... 

Perfluorovinyl iodides readily undergo stereospecific coupling with the tn-fluoroinethylcopper solution [224] (equation 151) prepared from dibromodifluo-romethane [210] With longer-chain perfluoroalkylcopper reagents, the coupling reaction is accompanied by some exchange processes [225] (equation 152)... 

Cyclic and acyclic silyl enol ethers can be nitrated with tetranitromethane to give ct-nitro ketones in 64-96% yield fEqs. 2.42 and 2.43. " The mechanism involves the electron transfer from the silyl enol ether to tetranitromethane. A fast homolydc conphng of the resultant cadon radical of silyl enol ether with NO leads tn ct-nitro ketones. Tetranitromethane is a neutral reagent it is commercially available or readdy prepared. " ... 

It can be advantageous to heat the chromatogram to 160 °C for 15 min before tn ing with nitrous fumes and to place it in the reagent chamber while still hot [1]. Heat to 260°C has even been recommended for the purpose of reducing the fluorescent ba ground [14], whereby the layer is previously immersed in 1 percent Ludox solut (silicic acid sol) to increase its stability [2]. The fluorescence of the substances deter usually remains stable for at least 2 weeks [2]. 

In the synthesis of polypeptides with biological activity on a crosslinked polymer support as pioneered by Merrifield (1 2) a strict control of the amino acid sequence requires that each of the consecutive reactions should go virtually to completion. Thus, for the preparation of a polypeptide with 60 amino acid residues, even an average conversion of 99% would contaminate the product with an unacceptable amount of "defect chains". Yet, it has been observed (13) that with a large excess of an amino acid reagent —Tn the solution reacting with a polymer-bound polypeptide, the reaction kinetics deviate significantly from the expected exponential approach to quantitative conversion, indicating that the reactive sites on the polymer are not equally reactive. 

Alkyl silyl ethers are cleaved by a variety of reagents Whether the silicon-oxygen or the carbon-oxygen bond is cleaved depends on the nature of the reagent used Treatment of alkoxysilanes with electrophilic reagents like antimony tn-fluonde, 40% hydrofluoric acid, or a boron tnfluonde-ether complex results in the cleavage of the silicon-oxygen bond to form mono-, di-, and tnfluorosiloxanes or silanes [19, 20, 21] (equations 18-20)... 

All other reagents (Tns, glycine, urea, methanol) are reagent grade. 

Nucleophilic Reagents. Tn contrast to electrophilic reactions, nucleophiles attack positively charged, even carbons in the chain. The reactions lead to the exchanging of substituents or terminal residues. Thus. SR and OR groups, or halogen atoms can be exchanged by other suitable nucleophiles. 

B 4. Describe how you would prepare a 0.20 M Tns-HCl buffer of pH 8.0. The only Tris reagent you have available is Tris base. What other reagent do you need and how would you use it to prepare the solution ... 

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