Boron trifluoride-Methanol

Alkylating reagents such as boron trifluoride-methanol, sulfuric acid-methanol, methanol-hydrochloric acid and methyl iodine-sodium hydride do not react efficiently with pyrithiobac. Trimethylsilyldiazomethane may be used for the methyl-ation of pyrithiobac. 

Pyrimidinylidenemalonate (1653) was converted into the isopropyli-dene derivative (1654) in 70% yield by treatment with the boron trifluoride methanol complex in methylene chloride and then with 2,2-dimethoxypro-pane (87TL2821). 

Methyl esters may be prepared by reaction of the aromatic carboxylic acid with diazomethane (cf. Section 4.2.25, p. 433) or, more conveniently, by reaction with a boron trifluoride-methanol reagent. The latter procedure is illustrated by the preparation of methyl m-chlorobenzoate and dimethyl terephthalate (Expt 6.164). t-Butyl esters may be prepared by conversion of the acid into an N-acylimidazole by reaction with N,N -carbonyldiimidazole, followed by reaction with t-butyl alcohol in the presence of DBU62 (Expt 6.165). 

Place 9.4 g (0.06 mol) of m-chlorobenzoic acid and 66 ml (0.12 mol) of boron trifluoride-methanol complex (14% w/v of BF3 Section 4.2.8, p. 421) in a 250-ml round-bottomed flask. Heat the mixture under reflux on an oil bath for 2 hours, cool and pour into about 250 ml of saturated sodium hydrogen carbonate solution. Extract the organic product with three 50 ml portions of ether, dry the ethereal extract over magnesium sulphate and evaporate on a rotary evaporator. Distil the residue under reduced pressure and collect the methyl m-chlorobenzoate as a colourless liquid of b.p. 63 °C/3mmHg the yield is 9.3 g (91%). 

The addition of methanolic alkali or boron trifluoride methanol [97,99] as a modifier has been recommended for the extraction of polycyclic aromatic hydrocarbons from soils containing a high proportion of humic acids. 

Fatty acid analysis of a fat is nowadays a relatively routine analytical operation. After methylation of the fat using reaction with boron trifluoride/methanol, boron trichloride/methanol, methanolic hydrogen chloride solution, diazomethane or, if free fatty acids are not present, alkaline catalysts such as sodium methoxide/methanol, the prepared methyl esters are then analysed by GC on a polar column such as CpSil 88, BPX70 or SP2340. The high polarity of the column is necessary to separate the saturated and unsaturated fatty acids fully. The fatty acid composition of a milk fat sample is thus relatively easily obtained, and was therefore one of the first techniques investigated for authentication purposes. 

Acid-catalyzed procedures typically are either boron trifluoride/methanol (BF3/ CH3OH) or hydrochloric acid/methanol (HCI/CH3OH). Many analysts use sulfuric acid instead of hydrochloric acid. Acid-catalyzed procedures are used for free fatty acids, phospholipids, or triacylglycerols, often at elevated temperatures. Although the procedures are relatively efficient at production of methyl esters, there will be some isomerization of some cis-, trans-isomers to the trans-Ztrans-isomers (136). This isomerization can be reduced by using lower temperatures, for instance 60 °C, for HCI/CH3OH or room temperature for BF3/CH3OH (137). However, under these milder conditions, some phospholipids may not be esterified (137). In addition, methoxy adducts may be formed and hydroxy fatty acids may produce artifacts. 

Amino-3-formylpyrazine in boron trifluoride-methanol complex at room temperature gave 2-amino-3-dimethoxymethylpyrazine (1075), and 2-amino-... 

Isomerization of alkylbenzenes [1, 73, before Boron trifluoride-Methanol], Pearson et al.1 give full details for use of a liquid mixture of the two reagents for effecting isomerization of p-cymene to m-cymene at —78°. Anhydrous hydrogen fluoride is... 

Intramolecular cyclisations have been used for a variety of complex anisole derivatives. Thus, 2-methoxycarbonylindole with butyrolactone or a 2-alkylbutyrolactone in the presence of NaOMe gave a derivative which after decarboxyiation and oxidation with PCC resulted in 4-(2 -indolyl)-4-oxobutanal, or the corresponding alkyl analogue. 4-Methoxycarbazole was then obtained for the parent compound by treatment of the aldehyde with boron trifluoride/methanol at ambient temperature (ref.78) with yields generally in the range 61-83%. 

D, 2,4,5-T, Silvex.) are converted into their methyl esters by treatment with boron trifluoride-methanol or diazomethane following extraction with ether. If present in the form... 

Morrison, W.R., and Smith, LM. (1964) Preparation of Fatty Acid Methyl Esters and Dimethylacetals from Lipids with Boron Trifluoride-Methanol, J. Lipid Res. 5,600-608. 

Methyl esters with boron trifluoride/methanol... 

On the other hand, free fatty acids can be methylated by acid-catalyzed procedures provided that the reaction time is kept short. For example, mild boron trifluo-ride-methanol or sulfuric acid (l%)-methanol reagents can be employed provided that scrupulous attention is paid to detail (2) in particular, freshly prepared reagent and the minimum reaction time are essential. For example, free fatty acids are fully methylated with boron trifluoride-methanol in 10 min at ambient temperature [or with sulfuric acid-methanol (1%) at 50°C for up to 1 h]. A phase-transfer catalyzed method employs basic conditions and can be used on a small scale, although the reaction does not always go to completion (2). However, trimethylsilyl-diazomethane, which is often recommended for free acids, can produce artifacts (8). 

Lipids were extracted from plasma, red blood cells, and rod outer segments with chloroform methanol (2 1). Phospholipids were fractionated by two dimensional thin layer chromatography (Anderson et al., 1969) and methyl esters were prepared with boron trifluoride-methanol (Morrison and Smith, 1964). Aliquots of the total lipid from plasma and of RBC were directly methylated as were small pieces of adipose tissue. Gas liquid chromatography was carried out on a Varian Model 2100 series gas chromatograph (Anderson et al.y 1970). 

Boron trichloride in methanol does not appear to have been much used for transesterification of lipids, but Is almost as effective as boron trifluoride-methanol and does not appear to bring about the same unwanted side reactions [129,485]. 

Oxidative ozonolysis became a more attractive technique when Ackman and colleagues [12,826] demonstrated that ozonolysis could be carried out in a solution of 7 % boron trifluoride-methanol reagent in such a way that acid ozonolysis products were formed, with a minimum of secondary reaction, and they were then methylated in a one-pot reaction. The reaction is carried out as follows ... 

Cyclopropane fatty acids behave as normal saturated fatty acids on silver ion chromatography, but react with bromine and so can be distinguished by this means [128]. They form methoxy-derivatives with boron trifluoride-methanol reagent [610], and they are converted to methyl-branched fatty acids by vigorous catalytic hydrogenation [571]. Both types of derivative can be characterized by mass spectrometry. 

Epoxy fatty acids (as the methyl esters) give El mass spectra which are not easily interpreted in terms of the position of the oxygen atom (especially when double bonds are also present), although it is possible with some effort if suitable model compounds are available [116,473,481]. It is generally recommended that the epoxide be isomerised to a mixture of keto compounds [473], or that the ring should be opened with boron trifluoride-methanol reagent to a mixture of methoxy-hydroxy derivatives [481,833] or with lithium aluminium hydride to hydroxy derivatives followed by trimethylsilylation [940], for identification by GC-MS. MS was used to study the incorporation of into the oxirane ring of 9,10-epoxyoctadecanoic acid in wheat tissues [488]. If derivatization is undesirable, more useful spectra are obtained with chemical ionisation [474,717]. 

Boron trifluoride/methanol (12%-14%, w/v) is a widely used acid catalyst, but it should be noted that the use of old reagent or solutions that are too concentrated can result in production of artifacts and loss of PUFA (Christie, 1989, 2003) The official methods, American Oil Chemists Society (A(X S) method Ce lb-89 (American Oil Chemists Society, 2005) and AO AC method 991.39 (AOAC, 1995), for analysis of marine oils use 0.5 M sodium hydroxide to hydrolyze the sample to release FFA that are then reacted with boron trifluoride/methanol. 

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