Ethers pentafluorobenzyl

Saltar and Paasivirta [155] have described a method for the analysis in soils of MCPA (4-chloro-2-methyl phenoxy acetic acid) and two of its main metabolites, 4-chloro-o-cresol and 6-chloromethyl catechol by gas chromatography of their pentafluorobenzyl derivatives (Fig. 9.12). After derivitization of the residue extract, a clean-up procedure was applied. The best recoveries of compounds from soil were obtained when the extraction was performed by shaking with ether-acetone-heptane-hexane (2 1 1 1) from acidified soil and when the clean-up was done by thin layer chromatography (Table 9.17). Detection limits were in the range 20-25ng absolute. 

McCallum NK. 1986. Specific method for the analysis of low-molecular-weight phenols using pentafluorobenzyl ethers. Lower Hutt, New Zealand Department of Science and Industrial Research. 

A GLC method for the determination of benzoic acid to concentrations as little as 10 ng/mL in plasma and urine was described by Sioufi and Pommier [42]. After addition of an internal standard (3-phenylpropionic acid), benzoic acid was extracted at acidic pH into diethyl ether, whereupon both compounds were derivatized with pentafluorobenzyl... 

Chloro-2-methyl- phenoxyacetic acid Dichloromethane extraction Extracts esterified with 2,3,4,5,6-pentafluorobenzyl bromide, petroleum ether extract analysed by gas chromatography, limit of detection 0.5 - 2 pg/kg [403]... 

Davis, B., Crown ether catalyzed derivatization of carboxylic acids and phenols with pentafluorobenzyl bromide for electron capture gas chromatography, Anal. Chem., 49, 832, 1977. 

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)... 

Pentazocine, cyclazocine and related drugs, prior to analysis, were converted into pentafluorobenzyl ethers [543,544] or TMS derivatives [545]. The former make the determination of pentazocine possible at concentrations down to 1 ng/ml in human plasma. The method involves a several step extraction. 

Kawahara (51) found that he could identify spilled asphalts by making the pentafluorobenzyl thioethers and ethers from traces of mer-captans and phenols in asphalts, and separating them by gas chromatography, using an electron capture detector to obtain the distinctive chromatograms. 

In the case where liquid chromatography is not available, acidic herbicides need to be derivatized because they can dissociate in water and are not usually volatile to be analyzed by gas chromatography. The basic methods used for chlorophenoxy acid herbicides are esterification, silylation, and alkylation, as described in a recent exhaustive review.The derivatization step is performed after preconcentration and cleanup. The step consists of the formation of esters and ethers from the carboxyl and phenol groups of the acidic herbicides. A lot of reagents and chemical mechanisms can be used to perform derivatization reactions. The most employed derivatization reagents are diazomethane, methyliodide, trimethylsulfonium (or anilinium) hydroxide, bis (trimethylsilyl) trifluoroacetamide (BSTFA), pentafluorobenzyl bromide, and anhydride acetate. It should be noted that explosive and hazardous diazomethane was replaced by safer agents. Authors also underline that surface water generally contains humic substances, which can interfere with the derivatization reaction. ... 

The characterization of the product of RCS targeting of plasmalogens led to several methods that were developed to both purify and quantify a-halofatty aldehyde. For example, thin-layer chromatography with silica gel G as a solid phase and petroleum ether/ethyl ether/acetic acid (90/10/1) separates a-chlorofatty aldehydes (/f =0.46) and a-bromofatty aldehydes (Rf= 0.58) (Albert et al. 2001, 2002). The confirmation of the structure of 2-chlorohexadecanal and 2-bromohexadecanal using GC-MS following derivatization to its pentafluorobenzyl oxime also proved to be an extremely... 

The acids (5 pmol of each) are dissolved in 100 ml of acetone and 250 mg of pentafluorobenzyl bromide (NB this is a strong lachrymalor, so appropriate precautions should be taken), and 50 mg of potassium bicarbonate are added. The mixture is refluxed for 3 hours and then 500 ml of ether and 200 ml of ethyl acetate are added. The combined solution is briefly washed with 10 ml of ether-saturated water and dried over sodium sulphate before evaporation to dryness. The residue is taken up in 100 ml of hexane containing 1% each of acetone and ether [94]. This widely quoted procedure is readily scaled down a much smaller-scale version has been described for the drug flurbiprofen [95]. 

Pentafluorobenzyl bromide 2.16.3 Preparation of pentafluorobenzyl ethers and esters for ECD-GLC and MS analysis N-alkylalion of barbiturates 11381 and sulfonamides 1126] ... 

CAUTION Pentafluorobenzyl bromide is a strong lachrymator and should be handled with appropriate precautions for routine work, a stock solution of the reagent in acetone (1 50, w/v) may be prepared [127], An alternative reagent for the purposes just described is hexafluorobenzene. Under the conditions of procedure 2.6, it readily converted free hydroxyl groups into pentafluorophenyl ethers [130],... 

Herbicides may be determined by specific extraction, esterification, and gas chromatographic conditions. Aqueous samples are extracted with diethyl ether and then esterified with either diazomethane or pentafluorobenzyl bromide. The derivatives are determined by GC with an electron capture detector. Compound identifications should be supported by GC-MS for the qualitative confirmation. Alkaline hydrolysis and subsequent solvent wash removes many chlorinated hydrocarbons and phthalates that might otherwise interfere with the electron capture analysis. 

Most derivatizations for gas chromatography are esterifications or etherifications. For example, analytes containing carboxyl groups are often converted into methyl [156], [161], pentafluorobenzyl [255]-[258], or triethyl esters [259]-[261], Analytes containing acidic hydroxyl groups (phenols, chlorophenols, glycol ethers) or amino groups (e.g.. aniline) can be derivatized with such per-fluorinated compounds as heptafluorobutyric anhydride, pentafluoropropionic anhydride [169], or pentafluorobenzoyl chloride [262]. 

Thioaldehyde-mediated nucleophilic addition Si wafers (1) 2-(4-bromophenyl) ethanamine (2) monofunctional amino end capped poly(ethylene glycol) methyl ether (3) (4-bromophenyl) methanethiol with DIPEA (4) o-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine hydro-chloride Xmax = 355 nm 1 h, RT, (l)-4 3) dichloromethane, (4) acetonitrile yes ToF-SIMS [PAU 13a]... 

Jacob P, Wilson M, Benowitz NL. Determination of phenolic metabolites of polycyclic aromatic hydrocarbons in human urine as their pentafluorobenzyl ether derivatives using liquid chromatography-tandem mass spectrometry. Anal Chem 2007 79(2) 587-98. 

Electrophilic substitution of the hydrogen in 2//-heptafluoronaphthalene can be effected with oleum [-> NapF SOjH (Napp = 1,3,4,5,6,7,8-hepta-fluoronaphthyl)], chlorosulphonic acid (-> Napp-SOaCl), and bromine, bis(chloromethyl) ether, or 2,3,4,5,6-pentafluorobenzyl chloride in chlorosulphonic acid [ —> Napp Br, Napp-CHgCI, and Napp-CHj CjFj, respectively (the last of these can also be obtained from Napp-CHsCl and C FbH in... 

---