In situ derivatisation

This is the first example of a reaction for which the presence of a chelating ligand was observed to facilitate rather than retard metal-catalysed epoxidation (Gao et al., 1987). It was found that the use of molecular sieves greatly improves this process by removing minute amounts of water present in the reaction medium. Water was found to deactivate the catalyst. All these developments led to an improved catalytic version that allows a five-fold increased substrate concentration relative to the stoichiometric method. Sensitive water-soluble, optically active glycidols can be prepared in an efficient manner by an in situ derivatisation. This epoxidation method appears to be competitive with enzyme-catalysed processes and was applied in 1981 for the commercial production of the gypsy moth pheromone, (-1-) disparlure, used for insect control (Eqn. (25)). 

In situ derivatisation and supercritical fluid extraction have been applied to the determination of butyl and phenyltin compounds in soils [43]. 

Let us turn now to the other coupling partner, aldehyde 58 it was synthesised by the pathway shown in Scheme 17.18. The first step was a Sharpless catalytic asymmetric epoxidation on ( )-crotyl alcohol with the oxidant derived from (—)-diethyl tartrate. An in situ derivatisation with r-butyldiphenylsilylchloride was then performed. The desired epoxide 59 was readily isolated in 76% overall yield after chromatography. Treatment of 59 with 2-lithio-l,3-dithiane in THF and 1,3-dimethyl-3,4,5,6-tetrahydro-2(l/7)-pyrimidinone (DMPU also known as N,N-... 

M.T. Sng and W.F. Ng, In-situ derivatisation of degradation products of chemical warfare agents in water by solid-phase microextraction and gas chromatographic-mass spectrometric analysis, J. Chromatogr. A, 832, 173-182 (1999). 

Ferreha, A.M.C., Moder, M., Laespada, M.E.F. GC-MS determination of parabens, triclosan and methyl triclosan in water by in situ derivatisation and stir-bar sorptive extraction. Anal. Bioanal. Chem. 399, 945-953 (2011)... 

Carrillo, J.D. and Tena, M.T. (2007). Determination of ethylphenols in wine by in situ derivatisation and headspace solid-phase microextraction gas chromatography mass spectrometry, Anal. Bioanal. Chem., 387, 2547-2558. 

Thermally-assisted hydrolysis and methylation Although GC separation facilitates identification of the pyrolysate, it prevents detection of certain pyrolysis products, notably polar and high-boiling compounds, which contain particularly useful diagnostic information about the structure of a material. In conventional GC this problem may be remedied by derivatisation of the polar compounds externally or by co-injection to give compounds which may be efficiently separated. Similarly, in order to realise the full potential of on-line PyGC high-temperature in situ derivatisation reactions may be carried out. 

Zimmermann, T, Ensigner, W.J., and Schmidt, T.C. (2004) In situ derivatisation/solid-phase microextraction Determination of polar aromatic amines. Anal. Chem., 76, 1028-1038. 

Principles and Characteristics Many of the planar chromatography methods rely on fluorescence detection to achieve the required identification limits exploitation of sensitive and selective derivatisation reactions is of considerable importance. Most TLC scanning densitometers can be operated in the fluorescence mode and are able to record in situ excitation spectra of TLC... 

The application of these perfluoroalkyl-derivatised ligands in FBS catalysis (see below) relies upon the generation, often in situ, of transition metal complexes. However, the potential impact of these perfluoroalkyl substituents is unknown, and there have been a growing number of publications directed towards identifying any physical or chemical consequences of these substitutions. Most importantly,... 

Non-chemical derivatisation has been employed for the detection of photoionisable species. The effluent is passed through a quartz tube where it is irradiated with ultraviolet light and the photoionised products passed to the conductivity detector [64,65]. Krull has reported the detection of the active components, typically organonitro derivatives, of a large number of explosives and drugs by in situ LC decomposition [66]. 

Note the absence of phosphoric acid in this sample. This method can also be used to analyse mixtures of alkylether phosphates. The advantage of this method over standard chromatographic procedures is that the phosphorus analysis can be carried out in situ there is no need to extract and subsequently derivatise the surfactants. 

A review has appeared on the synthesis and reactivity of (sUylamino) and (silyl-anilino)phosphines. The S5mthesis, derivatisation and coordination behaviour of the morpholine (69) and piperazine (70) derivatives have been described. They are formed from the appropriate amine with diphenylchlorophosphine, and both react with sulfur or selenium to give the chalcogenide, whilst reaction of (69) with paraformaldehyde leads to insertion of methylene into the P N bond to give the phosphine oxide. The reaction between ethylenediamine and diphenylchlorophosphine can lead to the bis-, tris- and tetrakis(diphenylphosphino)ethylene-diamines, depending upon the stoichiometry. The first two are oxidised in situ whist the latter, (71), is stable. A nickel complex of (71) has been shown to be active as a catalyst for ethylene pol5nnerisation. ... 

Three types of chiral auxiliary are widely used. Chiral derivatising agents (CDAs)[ l form diastereomers while chiral solvating agents (CSAs)t l and chiral lanthanide shift reagents (CLSRs)t l form diastereomeric complexes in situ with the substrate enantiomers. 

Recently self-recognition derivatisation has been carried out in situ —an approach which combines the convenience of a CS A with the A8 magnitude advantage of a CDA. A racemic alcohol is derivatised with... 

There are often problems encountered in the isolation of low molecular weight epoxy-alcohols such as the parent compound glycidol, due to their water solubility. Such difficulties can be avoided by derivatisation in situ as the p-toluenesulphonate or p-nitrobenzenesulphonate ester and this procedure is illustrated in the application of the Sharpless oxidation to prepare (-)-propranolol described in section 7.4.2. 

Chromatographic derivatisation reagent for nitrosamines. Powerful oxidant. Prepd. in situ. 

The examples described in this section 10.6.1 constituted the first report ever of ill situ reaction-extraction work involving foodstuffs. We had reported earlier on a related approach in a different field, namely a derivatisation-extraction procedure whereby phenols and methylated phenols were acetylated-extracted from environmental matrices in a one-step MAP procedure (15). The latter procedure, however, was performed under much harsher conditions that could not be used with foodstuffs where the potential of creating artefacts is a prime concern. This approach of one-pot, multiple-step procedures opens the avenue to numerous applications of direct interest to the food analysts and are especially versatile and valuable when using microwave-assisted extraction performed in open-vessel systems. This, along with solvent-less extraction (such as MAP gas-phase applications ) is believed... 

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