Diazomethane

About: Diazomethane is a research topic. Over the lifetime, 2546 publications have been published within this topic receiving 34107 citations. The topic is also known as: Azimethylene & Azomethylene.

A Recyclable Ru-Based Metathesis Catalyst

Abstract: A Ru carbene (8, Scheme 2) that contains an internal metal−oxygen chelate is an active metathesis catalyst and is readily obtained by the sequential treatment of Cl2Ru(PPh3)3 with (2-isopropoxyphenyl)diazomethane and PCy3 This Ru-carbene complex offers excellent stability to air and moisture and can be recycled in high yield by silica gel column chromatography The structures of this and related complexes have been unambiguously established by NMR and single-crystal X-ray diffraction studies

Evaluating acid and base catalysts in the methylation of milk and rumen fatty acids with special emphasis on conjugated dienes and total trans fatty acids

Abstract: Milk analysis is receiving increased attention. Milk contains conjugated octadecadienoic acids (18∶2) purported to be anticarcinogenic, low levels of essential fatty acids, and trans fatty acids that increase when essential fatty acids are increased in dairy rations. Milk and rumen fatty acid methyl esters (FAME) were prepared using several acid-(HCl, BF3, acetyl chloride, H2SO4) or base-catalysts (NaOCH3, tetramethylguanidine, diazomethane), or combinations thereof. All acid-catalyzed procedures resulted in decreased cis/trans (Δ9c, 11t-18∶2) and increased trans/trans (Δ9t, 11t-18∶2) conjugated dienes and the production of allylic methoxy artifacts. The methoxy artifacts were identified by gas-liquid chromatography (GLC)-mass spectroscopy. The base-catalyzed procedures gave no isomerization of conjugated dienes and no methoxy artifacts, but they did not transesterify N-acyl lipids such as sphingomyelin, and NaOCH3 did not methylate free fatty acids. In addition, reaction with tetramethylguanidine coextracted material with hexane that interfered with the determination of the short-chain FAME by GLC. Acid-catalyzed methylation resulted in the loss of about 12% total conjugated dienes, 42% recovery of the Δ9c,11t-18∶2 isomer, a fourfold increase in Δ9t,11t-18∶2, and the formation of methoxy artifacts, compared with the base-catalyzed reactions. Total milk FAME showed significant infrared (IR) absorption due to conjugated dienes at 985 and 948 cm−1. The IR determination of total trans content of milk FAME was not fully satisfactory because the 966 cm−1trans band overlapped with the conjugated diene bands. IR accuracy was limited by the fact that the absorptivity of methyl elaidate, used as calibration standard, was different from those of the other minor trans fatty acids (e.g., dienes) found in milk. In addition, acid-catalyzed reactions produced interfering material that absorbed extensively in the trans IR region. No single method or combination of methods could adequately prepare FAME from all lipid classes in milk or rumen lipids, and not affect the conjugated dienes. The best compromise for milk fatty acids was obtained with NaOCH3 followed by HCl or BF3, or diazomethane followed by NaOCH3, being aware that sphingomyelins are ignored. For rumen samples, the best method was diazomethane followed by NaOCH3.

Preparation of ester derivatives of fatty acids for chromatographic analysis

Abstract: A. Introduction B. Acid-Catalysed Esterification and Transesterification 1. General mechanism 2. Methanolic hydrogen chloride 3. Methanolic sulfuric acid 4. Boron trifluoride-methanol 5. Other acidic catalysts C. Base-Catalysed Transesterification 1. General mechanism 2. Sodium and potassium methoxide catalysts 3. Organic base catalysis D. Diazomethane and Related Reagents 1. Diazomethane and methyl ester preparation 2. Preparation of UV-absorbing and other derivatives E. Pyrolysis of Tetramethylammonium Salts of Fatty acids for the Preparation of Methyl Esters F. Preparation of Esters and Amides via Activated Fatty Acids 1. Acid halides 2. Fatty acid anhydrides 3. Imidazolides 4. Other coupling reagents G. Reaction of Alkyl or Aryl Halides with a Base 1. Derivatives for gas chromatography 2. Phenacyl esters and other derivatives for high-performance liquid chromatography H. Alternative Methods for the Preparation of Esters, Amides and Other Fatty Acid Derivatives 1. Dimethylsulfate with dicyclohexylamine 2. Preparation of esters with alkyl formamide derivatives 3. Trimethylsilyl esters 4. Preparation of pyrrolidides from esters 5. Preparation of hydroxamic acid and related derivatives 6. Reaction with Grignard reagents I. Special Cases 1. Short-chain fatty acids 2. Fatty acids with unusual structures 3. Sphingolipids and other N-acyl lipids 4. Sterol esters 5. Selective esterification of free fatty acids in the presence of other lipids J. Preparation of Esters in the Presence of Adsorbents for Thin-Layer Chromatography K. Simultaneous Extraction from Tissues and Transesterification L. Artefacts of Esterification Procedures M. The Choice of Reagents a Summary

Hydroxyl Radical-scavenging Effects of Spices and Scavengers from Brown Mustard (Brassica nigra)

Abstract: The effects of methanol extracts of 51 spices on ·OH scavenging were studied in detail. 2-Deoxyribose oxidation and sodium benzoic acid hydroxylation methods were used for detecting the scavenging activity of ·OH. Mustard varieties, thyme, oregano, clove, and allspice all exhibited strong ·OH-scavenging activity. In particular, 3 varieties of mustard had above 90% ·OH-scavenging activity with a 1 μg/ml concentration of their extracts. The ·OH scavenger of Brassica nigra (brown mustard) was isolated and purified by XAD-2 column chromatography and preparative HPLC, and was identified as a 3,5-dimethoxy-4-hydroxycinnamic acid methyl ester by MS, ‘H-NMR, and 13C-NMR. The 3,5-dimethoxy-4-hydroxycinnamic acid methyl ester was prepared by methylating of sinapic acid with diazomethane.