Diazomethane is a useful reagent for the one-carbon homologation of

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Of course, the reagent must be prepared and used in a well-ventilated hood, preferably behind a blast shield.

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A one-step method for preparation of

The greatest value of HPLC is for volatile components (short chain fatty acids), forpreparative scale separations or for studying isotopically labelled fatty acids.

A typical procedure is to add a yellow solution of diazomethane to the carboxylic acid in portions.

Handling, Storage, and Precautions: diazomethane as well as the precursors for its synthesis can present several safety hazards, and must be used with great care. The reagent itself is highly toxic and irritating. It is a sensitizer, and long term exposure can lead to symptoms similar to asthma. It can also detonate unexpectedly, especially when in contact with rough surfaces, or on crystallization. It is therefore essential that any glassware used in handling diazomethane be fire polished and not contain any scratches or ground glass joints. Furthermore, contact with certain metal ions can also cause explosions. Therefore metal salts such as , , or must not be used to dry solutions of the reagent. The recommended drying agent is potassium hydroxide. Strong light is also known to initiate detonation. The reagent is usually generated immediately prior to use and is not stored for extended periods of time. Of course, the reagent must be prepared and used in a well-ventilated hood, preferably behind a blast shield. The precursors used to generate diazomethane are irritants and in some cases mutagens and suspected carcinogens, and care should be exercised in their handling as well.

1. TITLE AND DESCRIPTION OF EXPERIMENT OR PROCESS:

The various reagents each have their advantages and disadvantages, as discussed below. The original procedure for the synthesis of diazomethane involved the use of , and similar procedures are still in use today. An advantage of using this reagent is that solutions of diazomethane can be prepared without distillation, thus avoiding the most dangerous operation in other preparations of diazomethane. For small scale preparations (1 mmol or less) which do not contain any alcohol, a kit is available utilizing MNNG which produces distilled diazomethane in a closed environment. Furthermore, MNNG is a stable compound and has a shelf life of many years. For larger scale preparations, kits are available for the synthesis of up to 300 mmol of diazomethane using as the precursor. The shelf life of (about 1–2 years), however, is shorter than that of MNNG. Furthermore, the common procedure using produces an ethereal solution of diazomethane which contains ethanol; however, it can be modified to produce an alcohol-free solution. Typical preparations of diazomethane involve the slow addition of base to a heterogeneous aqueous ether mixture containing the precursor. The precursor reacts with the base to liberate diazomethane which partitions into the ether layer and is concomitantly distilled with the ether to provide an ethereal solution of diazomethane. Due to the potentially explosive nature of diazomethane, the chemist is advised to carefully follow the exact procedure given for a particular preparation. Furthermore, since diazomethane has been reported to explode upon contact with ground glass, apparatus which do not contain ground glass should be used. All of the kits previously mentioned avoid the use of ground glass.

After addition of a drop of triethylamine (about 1.5 equivalents), the solvent isevaporated and the residue is converted to phenacyl esters as explained before.

Diazomethane has also been used in the preparation of

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Preparative Methods: diazomethane is usually prepared by the decomposition of various derivatives of N-methyl-N-nitrosoamines. Numerous methods of preparation have been described, but the most common and most frequently employed are those which utilize N-Methyl-N-nitroso-p-toluenesulfonamide (Diazald®; ), 1-Methyl-3-nitro-1-nitrosoguanidine (MNNG, ), or .

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on the synthesis of diazomethane cautions against ..

Other procedures are reported, the most efficient but also the mostsophisticated used methylated extracts analyzed by gas chromatography coupled with massspectrometry ().

Procedure:

Free diacids are extracted using the classical Folch's procedure but after theaddition of 0.1 volume of 0.1 N H2SO4.

Diazomethane is the chemical ..

Using a novel Fouriertransform infrared spectroscopic method, the lower limit of trans quantificationwas shown to be about 5% of total fat.


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Analysis of Reagent Purity: diazomethane is titrated by adding a known quantity of to an aliquot of the solution such that the solution is colorless and excess remains. Water is then added, and the amount of remaining is back-titrated with NaOH solution. The difference between the amount of acid added and the amount remaining reveals the amount of active diazomethane present in the aliquot.

Diazomethane distillations must use a blast shield that protects ..

After evaporation, a mixture containing about 50%of each isomer with a yield of about 92% is obtained.

A separation of the two conjugated isomers may be obtained using the ability oflipases produced by the fungus to selectively hydrolyze thecis-9,trans-11-18:2 methyl ester ().

A general cis-trans isomerization of polyunsaturated fatty acids may be obtainedusing p-toluenesulfinic acid has been described ().

It must be noticed that infrared methodologies was developed for the rapidquantification of the total trans fatty acid levels in oils and fats (overviewin ).

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Solubility: diazomethane is most often used as prepared in ether, or in ether containing a small amount of ethanol. It is less frequently prepared and used in other solvents such as dichloromethane.

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