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Chemical Methods
Published in Somenath Mitra, Pradyot Patnaik, Barbara B. Kebbekus, Environmental Chemical Analysis, 2018
Somenath Mitra, Pradyot Patnaik, Barbara B. Kebbekus
Such derivatization reactions are used for gas chromatography to convert compounds such as carboxylic acids and phenols that contain acidic hydrogen into their ester derivatives. Also alkylation reactions can be used to prepare ethers, thioethers, and thioesters. Acylation reactions involve substances containing aryl group and an active hydrogen atom converting into their esters, thioesters, and amide derivatives. For example, an amine may be converted into its amide derivative by reacting with an acid chloride shown as RR′NH + R″COCl → RR′NC(=O)R″ + HCl
Sample Preparation Techniques to Isolate and Recover Organics and Inorganics
Published in Paul R. Loconto, Trace Environmental Quantitative Analysis, 2020
Let us take a broad view of chemical derivatization in analytical chemistry. The flowchart shown in Figure 3.72 summarizes how most commercially available derivatization reagents are categorized. Silylation is the conversion of active hydrogen in a functional group to a trimethyl silyl (TMS) derivative. This was the first means to chemically convert carboxylic acids, alcohols, thiols, and primary and secondary amines to TMS esters. TMS esters are most appropriate where GC-MS is the principal determinative technique. Acylation is the conversion of active hydrogen, as is found in alcohols, phenols, thiols, and amines, into esters, thioesters, and amides by reacting organic compounds that contain these functional groups with fluorinated acid anhydrides. Heptafluorobutyrylimidazole and N-methyl-N-bis (trifluoroacetamide) are particularly effective in converting primary amines to fluorinated amides. Introduction of a perfluoroacyl moiety in the derivative leads to a significant increase in analyte sensitivity when using GC-ECD as the determinative technique. Alkylation is the conversion of active hydrogen by an alkyl or benzyl group to an ester or ether, depending upon whether the functional group in the organic compound is a carboxylic acid or alcohol or phenol, respectively. Diazomethane via in situ generation, BF3-MeOH, dimethyl formamide-dialkyl acetals, and pentafluorobenzyl bromide are commonly used derivatizing reagents. Enantiomeric purity analysis reagents form diastereomers when reacted with optically active analytes. Diastereomers are easily separated by GC. Commercially available reagents include (−) methyl chloroformate that reacts with enantio-enriched alcohols and N-TFA-L-prolyl chloride that couples with amines to form diastereomers. Chromotags are derivatizing reagents that add an ultraviolet-absorbing chromophore to an aliphatic carboxylic acid that converts the aliphatic acid to a UV-absorbing derivative to enhance sensitivity in HPLC-UV. Fluorotags convert a minimally fluorescent analyte to a highly fluorescent derivative, and hence enhance sensitivity in HPLC-FL. The reaction of aliphatic carboxylic acids with p-bromophenacyl bromide in the presence of 18-crown-6 under alkaline conditions to form a strong ultraviolet-absorbing ester, and the conversion of aliphatic carboxylic acids to highly fluorescent 4-bromomethyl-7-methoxycoumarin represent common uses of chromotags and fluorotags.153
An expedient and rapid green chemical synthesis of N-chloroacetanilides and amides using acid chlorides under metal-free neutral conditions
Published in Green Chemistry Letters and Reviews, 2018
Acetyl chloride and chloroacetyl chloride can be efficiently used for acylation reactions. The major advantage of chloroacetyl derivatives lies in their ability to be used for further functional modifications. However, the reactivity profiles of chloroacetyl chloride are less explored compared to acetyl chloride. Thus, improving the N-acylation of amino derivatives, without compromising the high reactivity of the acid chlorides to give amides, is a challenging task worth exploring.