Reactive separation, derivatization

To get a complex set of substituents by direct derivatization of benzotriazole is not feasible. In such situations, it is better to have all the substituents in place first and later construct the heterocyclic ring. High reactivity of anilines and their well-developed chemistry makes them good stating materials. In an example shown in Scheme 215, acetanilide 1288 is nitrated to afford nitro derivative 1289 in 73% yield. Catalytic reduction of the nitro group provides methyl 4-acetylamino-3-amino-5-chloro-2-methoxybenzoate 1290 in 96% yield. Nitrosation of compound 1290 in diluted sulfuric acid leads to intermediate 1291, which without separation is heated to be converted to 7-chloro-4-methoxy-l//-benzotriazole-5-carboxylic acid 1292, isolated in 64% yield <2002CPB941>. 

Functionalized polymers are of interest in a variety of applications including but not limited to fire retardants, selective sorption resins, chromatography media, controlled release devices and phase transfer catalysts. This research has been conducted in an effort to functionalize a polymer with a variety of different reactive sites for use in membrane applications. These membranes are to be used for the specific separation and removal of metal ions of interest. A porous support was used to obtain membranes of a specified thickness with the desired mechanical stability. The monomer employed in this study was vinylbenzyl chloride, and it was lightly crosslinked with divinylbenzene in a photopolymerization. Specific ligands incorporated into the membrane film include dimethyl phosphonate esters, isopropyl phosphonate esters, phosphonic acid, and triethyl ammonium chloride groups. Most of the functionalization reactions were conducted with the solid membrane and liquid reactants, however, the vinylbenzyl chloride monomer was transformed to vinylbenzyl triethyl ammonium chloride prior to polymerization in some cases. The reaction conditions and analysis tools for uniformly derivatizing the crosslinked vinylbenzyl chloride / divinyl benzene films are presented in detail. 

For trace analysis it is common to include in a derivatization step the formation of a derivative that not only aids the desired chromatographic or separation factors, but also provides sensitivity to one or another of the specific detectors available. It is common to use a halogen-substituted derivatizing reagent to provide simultaneously decreased polarity or reactivity, better chromatographic separation, and more selective, sensitive detection using electron capture. Thus, for example, trichloroacetic anhydride is used to form acetate derivatives instead of using acetic anhydride. 

Ellman s reagent has been used not only for the determination of sulfhydryls in proteins and other molecules, but also as a precolumn derivatization reagent for the separation of thiol compounds by HPLC (Kuwata et al., 1982), in the study of thiol-dependent enzymes (Masamune etal., 1989 Tsukamoto and Wakil, 1988 Alvear et al., 1989), and to create sulfhydryl-reactive chromatography supports for the coupling of affinity ligands (Jayabaskaran etal., 1987). Another important use of the compound... 

Sample Derivatization. Hie derivatization of nutmeg constituents described by Harvey (7) is designed to increase the volatility and stability of the components so that they can be separated in the gas chromatograph. With direct probe introduction, MS/MS is usually able to deal with samples of lower volatility hence, derivatization is not required. Direct probe temperatures reach as high as 400° C, vaporizing many samples directly into the vacuum of the mass spectrometer source. Derivatization is used in MS/MS for the somewhat different purpose of inparting a specific chemical reactivity to the analyte. 

Colorometric procedures involving reaction of aldehydes with hydrazines, semicarbazide, or piperidine/nitroprusside solutions are also non-specific and lack sensitivity (15, 35, 36). Schmidt et al. (33) have proposed an HPLC method for analyzing the 2,4-dinitrophenylhydrazone (DNPH) derivatives of specific aldehydes. This procedure allows for a number of ddehydes to be separated and measured simultaneously, however, HPLC methods in general suffer from poor resolving power and may have low sensitivity (37). In addition, hydrazine derivatizations are often performed under acidic conditions for maximal reactivity these conditions would not provide quantitative information on total aldehyde content. 

In another approach, reactive monodisperse porous poly(chloromethylstyrene-co-styrene-co-divinylbenzene) beads have been employed for the preparation of chiral HPLC packings. Thus, reactive chloromethyl groups were derivatized to yield amino functionalized beads onto which both rt-basic and rt-acidic type chiral. selectors, (/ )- -(l-naphthyl)ethylamine and (/ )-A -(3.5-dinitrobenzoyl)phenylglycine, respectively, were attached. The resulting chiral particles were chromatographically tested for the enantioseparation of model SAs. Despite the presence of strongly competitive it-TT-binding sites of the styrenic support these chirally modified beads afforded baseline separations for 2,2,2-trifluoro-l-(9-anthryl) ethanol and Af-(3.5-dinitro-benzoyl) leucine enantiomers, respectively [369. ... 

As mentioned above, fhe second PASP strategy for purifying a crude reaction mixture after a synfhesis is to separate fhe desired product by selective covalent derivatization with a functionalized resin followed by filtration and rinsing. After fhe formation of the product in solution, it reacts selectively wifh a solid support while impurities and unreacted substrate remain in solution and are washed away. This resin-capture concept has been demonstrated in fhe context of fhe Ugi four-component condensation [51]. After the condensation, fhe reactivity of fhe enam-ide allowed fhe specific reaction with Wang resin under anhydrous acidic conditions. The resin was washed wifh methanol and dichloromefhane and fhe subsequent cleavage was performed with trifluoroacetic add in dichloromefhane. The final carboxyhc adds were characterized without further purification and were found to be > 95 % pure. 

Derivatization Chemical reaction to improve separation or detection Treatment of active hydrogen functional group with electrophilic reagent Small volumes of reactive derivatization reagents... 

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