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Derivatization Reactions in Trace Chemical Analysis
Published in Pradyot Patnaik, Handbook of Environmental Analysis, 2017
Also carboxylic acids can be converted into their esters by Fisher esterification reactions with alcohols using a mineral acid catalyst, such as HCl or H2SO4. An alternative catalyst is a Lewis acid, such as BF3, dissolved in methanol to convert the lower carboxylic acids and fatty acids into their methyl esters for GC analysis. Methyl esters can also be prepared by reacting carboxylic acids with diazomethane, CH2N2, instead of methanol. Diazomethane is an unstable substance which can explode at high temperature and is also toxic. The reaction however is smooth and goes to completion. Diazomethane should be freshly generated and the apparatus to make this substance is commercially available. The esterification reaction of carboxylic acid with diazomethane is shown below: RCOOH+CH2N2→RCOOCH3+N2
Chemical Conversion Process for Biodiesel Production
Published in Jay J. Cheng, Biomass to Renewable Energy Processes, 2017
Notice that the CH2N2 appears to insert itself between the O and the H of the O–H bond (Reaction 9.3). The high reactivity of diazomethane arises from the fact that it possesses an exceedingly reactive leaving group, the nitrogen molecule (N2). A nucleophilic substitution reaction on the protonated diazomethane molecule transfers a methyl group to the oxygen atom of the carboxylic acid, while liberating a very stable product (N2 gas). This process is very favorable energetically, owing to the great stability of N2.
Low and High LET Degradation Studies of Metal-Loaded Organic Phase Ligands in the ALSEP Process
Published in Solvent Extraction and Ion Exchange, 2023
Christian G. Bustillos, Randy O. Ngelale, Mikael Nilsson
A Hewlett-Packard 5890 Gas Chromatograph using a flame-ionization detector, equipped with a 30-m DB 5 ms column (Agilent Technologies, Santa Clara, California, USA), and an associated Hewlett-Packard Controller 7673 A integrator was utilized to determine the concentration of HEH[EHP] and T2EHDGA after irradiation. Irradiated samples were diluted 1:150 in hexane, and triphenyl phosphate was added to each diluted sample to function as an internal standard to monitor the performance and consistency of the GC. A derivatization agent, diazomethane, was also added to each diluted solution in order to add a methyl group to acidic compounds, which could be retained by silica within the GC column. Diazomethane was prepared within a diazomethane generator kit (Sigma Aldrich) using diazald (99%, Sigma Aldrich), Carbitol (99%, Sigma-Aldrich), and potassium hydroxide (Fisher Scientific).
Atmospheric chemistry of diazomethane – an experimental and theoretical study
Published in Molecular Physics, 2020
Simen Gjelseth Antonsen, Arne Joakim C. Bunkan, Tomas Mikoviny, Claus J. Nielsen, Yngve Stenstrøm, Armin Wisthaler, Erika Zardin
Diazomethane was prepared in mmol scale by adding excess 50% aqueous KOH to solid nitrosomethylurea. Nitrosomethylurea was synthesised from methylamine and urea as described by Arndt, [13] with some modifications. Diazomethane is reported to be explosive and all safety measures should be taken accordingly [14]. Methylamine hydrochloride (5.0 g, 0.075 mol) was dissolved in water (50 mL). Urea (15 g, 0.25 mol) was added. The mixture was heated to reflux for 3 h, then cooled to room temperature. Sodium nitrite (5.5 g, 0.075 mol) was added and allowed to dissolve at room temperature. The mixture was cooled to 0°C and poured into a beaker containing ice (30 g) and sulphuric acid (5.0 g, 0.050 mol). Nitrosomethylurea precipitates as fluffy, slightly yellow crystals, which is filtered with suction. The precipitate is washed with cold water (10 mL), and the solid is dried in desiccator over night to give nitrosomethylurea (5.2 g, 0.050 mol).