Pentafluorobenzyl esters

Lee et al. [187] developed a multi-residue method with a low detection limit for 10 commonly used acid herbicides in non saline waters. The herbicides were Dicamba, MCPA, 2,4-DP, 2,3,6-TBA, 2,4-D, Silvex, 2,4,5-T, MCPB, 2,4,5-DB and Picloram. The method used solvent extraction and the formation of pentafluorobenzyl esters. The derivatives were quantified by capillary column gas chromatography with electron capture detection. The detection limit was 0.05pg L. Recoveries of herbicides from spiked Ontario lake water (0.5-1.Opg L 1) were 73-108% except for Picloram recovery which was 59% at 0.1 pg L 1. 

Agemian and Chau [190] have reported a method for determining low levels of 4-chloro-2-methylphenoxyacetic acid and 4-(4-chloro-2-methylphenoxy)-butyric acid in non saline and waste waters by derivatisation with pentafluorobenzyl bromide. The increased sensitivity of the pentafluorobenzyl esters of these two herbicides over the 2-chloroethyl methyl esters as well as their longer retention times make pentafluoro-benzyl bromide the preferred reagent. 

Acrylic acid Tri-w-phosphine -oxide Electron capture Acid converted to pentafluorobenzyl ester — [230]... 

Figure 11. GC/MS/MS/MRM chromatograms showing the detection of alkyl MPAs, spiked into human urine at 1 ng/ml, as pentafluorobenzyl esters using NICI and a benchtop ion trap instrument...

Kawahara [156] introduced pentafluorobenzyl esters, prepared by the following procedure. A mixture of four acids (0.8 mg of each) was dissolved in 100 ml of acetone, and 250 mg (25-fold excess) of a-bromo-2,3,4,5,6-pentafluorotoluene and 50 mg (10-fold excess of potassium carbonate were added (it can be replaced with an ethanolic solution of potassium hydroxide). After refluxing for 3 h, the mixture was diluted with 500 ml of diethyl ether and 20 ml of ethyl acetate, washed with 10 ml of water and dried with 8 g of anhydrous sodium sulphate. After filtration, the sulphate and the filter were washed with 50 ml of diethyl ether, the solvent was removed and the residue was dried at 40°C and 50 mmHg it was further dissolved in 100 ml of -hexane and, after an additional 100-fold dilution, 6 /il were injected. The ECD response to pentafluorobenzoate was almost the same as that to aldrin. A method for the preparation of p-substituted benzyl esters of lower monocarboxylic acids on the micro-scale [157] is based on the same reaction scheme. A 10-pl volume of an ethanolic solution of carboxylic acids (ca. 1 pg/pl)... 

De Beer et al. [501] reported an extensive comparative study of the chromatographic behaviour of methyl esters and pentafluorobenzyl esters of these substances. They correlated retention data (Kovats retention indices) on nine stationary phases with the structure of the derivatives and with the polarity of the stationary phases with the aim of utilizing these dependences for identification purposes. However, much more significant is the better separation obtained with pentafluorobenzyl esters and the possibility of increasing the sensitivity of the analysis. 

Anticholinergics, such as atropine and oxyphenonium bromide, which are esters of carboxylic acids, were analysed in plasma and urine as pentafluorobenzyl esters [541,542], The method involves ion-pair extraction of the material under analysis, hydrolysis of esters and derivatization of the acid moiety. The minimal detectable amount was found to be 0.15 pg with the use of an ECD. 

The dipeptides can also be transformed into d3,do-l-l-acyl-dipeptides (with a mixture of do and dg acetic anhydride (1 1) in methanol). Free carboxyl groups are esterified into pentafluorobenzyl esters (with fluorobenzyl bromide in acetonitrile and... 

Lee, H.-B., T.E. Peart, and J.M. Carron. 1990. Gas chromatographic and mass spectrometric determination of some resin and fatty acids in pulpmill effluents as their pentafluorobenzyl ester derivatives.. Chromatogr. 498 367-379. 

For the determination of alkyl- and arylmercaptans, reaction with acrylonitrile followed by analysis of unreacted excess has been recommended [135]. Atkinson and Natoli [171] proposed an indirect catalytic method. The determination of tertiary and secondary thiols has been discussed [172]. Kawahara [173] proposes to detect trace amounts of mercaptans in the form of pentafluorobenzyl esters prepared from a-bromo-... 

Higher esters with boron trifluoride 15 2.4.10 Pentafluorobenzyl esters 21... 

Methyl ester-HFB derivatives have been employed in prostaglandin analysis by GC-MS [140], but most applications employ methyl ester—silyl derivatives (see Section 3) or mixed pentafluorobenzyl ester derivatives for NICI (Section 5, below). 

Steam distillation of biphenyl and 2-hydroxybiphenyl has been used to isolate the preservatives prior to analysis by GC. Simultaneous analysis of biphenyl, 2-hydroxybiphenyl, and thiabendazole in an organic extract from homogenized citrus fruits has been achieved with a column packed with FFAP as stationary phase. However, thiabendazole has commonly been converted into the methyl ester or pentafluorobenzyl ester before GC analysis. LC methods are also used for the determination of thiabendazole. 

We have made standard curves by injecting 50 up till 12 000 picograms pentafluorobenzyl-ester or -oxime into the gas chromatograph. Within this range, the response was linear. 

Collins and coworkers [35] have also exploited the use of Ti(Oi-Pr) as an additive in the context of a total synthesis effort to prepare longithorone C (67 Scheme 12.20). The macrocycUzation of the pentafluorobenzyl ester 65 was investigated using the Blechert catalyst 68 [36]. While the use of Ti(Oi-Pr)4 increased the yield of the final product, the successful macrocyclization of the pentafluorobenzyl ester 65 additionally benefitted from the presence of several structural features, including the use of a relay RCM strategy and having one of the side chains be present as a cis-olefin. Treatment of the pentafluorophenyl benzyl ester 65 (10 mol%) with catalyst 68 in CH2CI2 afforded the product 66 in 39% isolated yield. 

More recently we have measured the turnover rate of lAA in tomato shoots after different incubation times, as part of a study of lAA biosynthesis in that tissue. lAA was supplied to the surface of the youngest leaf, 1 cm or longer, of excised shoots from twenty, 4-week-old tomato plants, as a 10 /xl drop (2 1 1, ethanol propan-2-ol H2O) containing 3711 Bq pH]IAA (1.11 GBq//xmol). Uptake was allowed for 2 h, surface radioactivity was then removed by several washes with 50% aqueous propan-2-ol followed with water, and the plants equilibrated for 1 h. After 0,4,10 or 20 h incubation in continuous light, lAA was extracted, purified, derivatised to form the pentafluorobenzyl ester [10] and the specific activity measured by liquid scintillation counting and GC-ecd. The purity and identity of selected samples was confirmed by combined GC-MS. 

Methodologies to produce reactive SAMs, such as inter-chain anhydrides, have been adapted to forming patterns of SAMs with pCP (45-47). Monolithic films of SAMs containing reactive pentafluorobenzyl esters were converted into patterned amides by using a stamp containing a primary amine. In the areas of contact, the amine reacts with the activated surface to form a patterned amide. Printing of benzenesul-fonamide was detected by binding cabonic anhydrase (CA) to the sulfonamide-derivatized SAM. Benzenesul-fonamide binds to CA with a dissociation constant of less than 10 M. Similarly, the stamp can be treated with poly(ethylene imine) (PEI) to transfer a pattern of amide-coupled PEI, where the pendant, unreacted amines of PEI can be used for subsequent nucleophilic reactions. This procedure can introduce patterned biotin... 

Retinoic acid and other retinoid carboxylic acids, however, can be readily converted to derivatives that are suitable for gas chromatography. Many of these applications have used mass spectrometry for detection (see below). Diazomethane is used, at room temperature, to prepare the methyl esters without apparent isomerization. Pentafluorobenzyl esters of retinoic acid and its analogs have also been prepared for GC-MS (280) or HPLC-MS (281). Deuterated analogs of retinoic acid or other retinoid carboxylic acids have been used as internal standards, with mass spectrometric detection (88,282) (reviewed by Napoli [283] and by De Leenheer and Lambert [89]). The pentafluorobenzyl ester of a synthetic retinoid, Ro 13-7410, was analyzed by column switching the peak of interest from a SE54 colunm was cut to an OV 240 column, with subsequent detection by negative ion chemical ionization mass spectrometry (280). 

Netting, A.G. Duffleld, A.M. Pentafluorobenzyl esters as derivatives for the semi-preparative high-performance liquid chromatography of fatty acids, J.Chromatogr., 1983,257,174-179. [derivatization SPE normal phase stearic acid oleic acid linoleic acid linolenic acid]... 

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