Synthesis of 2 bromomethyl tetrahydrofuran, in this section
As an alternative, phenacyl esters 23 can be prepared under mild conditions by reaction of phenacyl bromide 22 and a fatty acid in the presence of triethylamine in acetone solution Scheme 14 [ 36, ]. In addition, fatty acid chlorides have been prepared under gentle conditions by reacting an acid with triphenylphosphine and carbon tetrachloride [ ].
For example, 9-anthryldiazomethane in diethyl ether, methanol, ethyl acetate or acetone solution gave good yields of anthrylmethyl esters in some hands [ 26,, ], but others have preferred alternative methods see Section G. Reaction of fatty acids with a Grignard reagent, ethyl magnesium bromide Preparation of esters by reaction of acids with chloroformates.
In some of these applications, samples were hydrolysed to the free acids prior to esterification, although it is now realized that the same catalysts can effect transesterification directly see Section C.
For example, propanol, butanol or 2-chloroethanol may be used, but great care is still necessary. Losses occurring during refluxing of solutions can be avoided by carrying out the reaction in a sealed vessel or using procedures that work satisfactorily at room temperature.
Again, each step is reversible and in the presence of a large excess of the alcohol, the equilibrium point of the reaction is displaced so that the Synthesis of 2 bromomethyl tetrahydrofuran is almost entirely the required ester 6.
The reagent is generally prepared in ethereal solution by the action of alkali on a nitrosamide, e. Although Klopfenstein [ ] could not confirm the suggested explanations for artefact formation, he confirmed the existence of Synthesis of 2 bromomethyl tetrahydrofuran problem.
Methods requiring hydrolysis prior to esterification are not recommended. In the latter circumstance, traces of water adsorbed to glassware, in solvents or in the atmosphere can be especially troublesome with many otherwise reliable procedures.
Diazomethane and methyl ester preparation Diazomethane 11 reacts rapidly with unesterified fatty acids to give methyl esters Scheme 6but does not effect transesterification of other lipids see also Section I. The use of chloroformates for derivatization has been reviewed by Husek [ ].
Preparation of esters with alkyl formamide derivatives Carboxylic acids react with alkyl formates in dimethylformamide solution to give esters in good yield, and the method was used to prepare a variety of different esters [ ]. Ethyl esters can be prepared in a similar way. Preparation of esters with 2-bromomethylpyridinium iodide 20 as the coupling agent.
Others carried out the reaction in a solution of acetonitrile, the alcohol and pyridine , though other basic catalysts, such as 3-picoline, N-methylpiperidine and dimethylaminopyridine appeared to be preferable [ ].
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Fatty acids with unusual structures If the appropriate precautions are taken, most of the methods described above can be used to esterify unsaturated fatty acids with two to six methylene-interrupted double bonds without causing stereomutation or double bond migration, i. Similar methodology has been used for the synthesis of simple amide derivatives, such as those of p-methoxyaniline [ ], naphthylamine [ ], 9-aminophenanthrene [ ] and aniline [ ].
Morrison and Smith [ ] showed that the reagent could be used to transesterify most lipid classes inert solvent must again be added to effect solution of simple lipidsalthough in general longer reaction times are necessary than with free fatty acids.
Also, unlike acidic catalysts, it will not liberate aldehydes from plasmalogens. Dimethylsulfate with dicyclohexylamine Methyl esters can be prepared from unesterified fatty acids in a basic medium by heating them with dimethylsulfate in the presence of dicyclohexylamine for 15 to 60 minutes [ ].
Longer reaction times are required as the molecular weight of the alcohol is increased. The various procedures are discussed with reference to the preparation of methyl esters from the more common C14 to C22 fatty acids mainly, in the free state or bound to lipids by ester or amide bonds.
Similarly, benzyl esters have been prepared by reaction of potassium carboxylates with benzyl bromide and catalysed by a crown ether in acetonitrile solution [ ]. In this instance, the hydroxyl groups of the 2-hydroxy fatty acids present were methylated simultaneously see also Section I.
Methoxyphenacyl [ ], bromophenacyl [ ], naphthacyl [ 64,79, ], methylanthryl [ ], Persona 3 portable dating fuuka [ ], 4-bromomethylmethoxycoumarin [ 87,, ], 4-bromomethylacetoxy-coumarin  and other [ , ] esters have been prepared in the same way.
Klopfenstein [ ] established that artefact formation was much less of a problem with boron trichloride in methanol, and others [ 40 ] have shown that it does not cause disruption of cyclopropane fatty acids see Section I.
The stability of the reagent was studied by Kishimoto and Radin [ ], who found that half the titratable acid was lost at room temperature in six weeks, presumably by reaction between the acid and methanol to give methyl chloride and water. Hydrocarbon solvents, such as hexane, pentane or light petroleum gave better recoveries than did diethyl ether or benzene.
The initial step is Vienna va dating of the acid to give an oxonium ion 1which can undergo an exchange reaction with an alcohol to give the intermediate 2and this in turn can lose a proton to become an ester 3.
Thionyl chloride will react much more quickly, and though it can cause isomerization of double bonds if used carelessly, this is not a problem if the reaction time is confined to 1 minute [ ].
Acetone is unsuitable also.