Derivatization reactions

Knapp, D.R., Handbook of Analytical Derivatization Reactions, Wiley, New York, 1979. 

Side-Chain Derivatization. Reaction of thiophene with aqueous formaldehyde solution in concentrated hydrochloric acid gives 2-chloromethylthiophene [765-50-4]. This relatively unstable, lachrymatory material has been used as a commercial source of further derivatives such as 2-thiopheneacetonitrile [20893-30-5] and 2-thiopheneacetic acid [1918-77-0] (24). Similar derivatives can be obtained by peroxide, or light-catalyzed (25) halogenation of methylthiophenes, eg, Ai-bromosuccinimide/benzoylperoxide on 2-, and 3-methylthiophenes gives the corresponding bromomethylthiophenes. 

Liquid Ghromatography/Mass Spectrometry. Increased use of Hquid chromatography/mass spectrometry (Ic/ms) for stmctural identification and trace analysis has become apparent. Thermospray Ic/ms has been used to identify by-products in phenyl isocyanate precolumn derivatization reactions (74). Five compounds resulting from the reaction of phenyUsocyanate and the reaction medium were identified two from a reaction between phenyl isocyanate and methanol, two from the reaction between phenyl isocyanate and water, and one from the polymerisation of phenyl isocyanate. There were also two reports of derivatisation to enhance either the response or stmctural information from thermospray Ic/ms for linoleic acid hpoxygenase metabohtes (75) and for cortisol (76). 

The MW of the TBDMS derivatives of PTH-AAs can be calculated using the following formula MW = R + 191 + n(114), where n is the number of TBDMS groups. Arginine loses NH3 during, or prior to, the derivatization reaction. Thus, the characteristic loss of 57 Daltons (C4H9) from the TBDMS derivative occurs at M - 74 (57 + 17). 

Several solvent systems dissolve cellulose, a process that may, or may not lead to cellulose derivative formation. Both types of solvent systems will be considered, although the important derivatizing reaction employed in the... 

The examples that are treated below are those sequences where all steps - except the last — are preparations for a color or fluorescence derivatization reaction which is carried out in the last step, i. e. they can be regarded as a sort of selective in situ pretreatment for a final detection reaction. Such reaction sequences are frequently necessary because all the reagents cannot be mixed together in a single solvent, or because it is necessary to dry, heat or irradiate with UV light between the individual reaction steps. The detection of aromatics by the reaction sequence nitration — reduction — diazotization - couple to form an azo dye is an example of this type (Fig 21). 

A derivatization technique is commonly applied to an agrochemical with certain reactive functional groups (e.g., carboxylic acid, amine, phenol) to make the compound amenable to either gas chromatography (GC) or LC analysis. An in-depth discussion of derivatization reactions used in the analysis of agrochemicals is beyond the scope of this article. For more information on this topic, the reader is referred to Knapp. °... 

D.R. Knapp, Handbook of Derivatization Reactions, WUey, New York (1979). 

To the residual M.A3 and M.A4 sample obtained from above are added 1 mL of 0.5 M triethylamine in benzene solution and 0.1 mL of trifluoroacetic anhydride, and the reaction mixture is shaken under tightly sealed conditions at 40 °C for 30 min. After the derivatization reaction, 0.05 mL of triethylamine is added to each reaction mixture, and the reaction mixture is concentrated with a rotary evaporator below 45 °C. 

Prechromatographic derivatization reactions re usually favored when it is desired to modify the properties of the sample to enhance stability during measurement (i.e., minimize oxidative and catalytic degradation, etc.), to improve the extraction efficiency of the substance during sample cleanup, to improve the chromatographic resolution, or to simplify the optimization of the reaction conditions [698-702]. As both pre- and postchromatographic methods enhance the sensitivity and selectivity of the detection process a choice between the two methods will usually depend on the chemistry involved, ease of optimization, and which method best overcomes matrix and reagent interferences. 

The reagents and conditions used for derivatization. reactions are so varied that no attempt at a comprehensive coverage can be presented here.. Only general reactions, common reagents, and a few typical applications will be discussed. V Extensive compilations of methods and conditions can be found in references [435-441]. Subject reviews covering trialkylsilyl... 

The diazoalkanes are toxic substances and aay explode on contact with rough surfaces. Consequently, aany workers prefer not to sake large quantities of these aaterials when only snail quantities are needed for derivatization reactions. Sinple aicro-diazoalkane generators capable of rapidly preparing snail quantities of the reagents, as required, are coaaercially available [499-501]. 

The limitations of derivatization are that derivatization reactions only approach completion and never attain it, that the conditions of derivatization sometimes cause degradation, and that even very similar compounds are derivatized to different extents. Use of derivatization, therefore, requires a careful study of recovery of known components. A limitation common to the use of specialized detectors and derivatization is the response factor problem. The detector responds to different compounds to a greater or lesser extent. Measurement of correction factors to account for this is one of the most time-consuming aspects of analysis. 

Take, as an example of an optimization problem, a derivatization reaction A + B —> C in which it is desired to maximize the yield. The rate of formation of C might be dependent on pH, temperature, the concentrations of A and B, and the time allowed for the reaction to take place. A reasonable first step would be to perform an analysis of the reaction rate at fixed pH (say, pH 7), concentration, and temperature (say, 50°C) to estimate the time required for the reaction to reach completion. It is useful to follow the reaction well... 

G. Lunn, L. Hellwig and A. Cecchini, Handbook of Derivatization Reactions of HPLC, John Wiley Sons, Inc., New York, NY (1998). 

Identification of Products from Polyolefin Oxidation by Derivatization Reactions... 

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