Methyl chromatography

More information has appeared concerning the nature of the side reactions, such as acetoxylation, which occur when certain methylated aromatic hydrocarbons are treated with mixtures prepared from nitric acid and acetic anhydride. Blackstock, Fischer, Richards, Vaughan and Wright have provided excellent evidence in support of a suggested ( 5.3.5) addition-elimination route towards 3,4-dimethylphenyl acetate in the reaction of o-xylene. Two intermediates were isolated, both of which gave rise to 3,4-dimethylphenyl acetate in aqueous acidic media and when subjected to vapour phase chromatography. One was positively identified, by ultraviolet, infra-red, n.m.r., and mass spectrometric studies, as the compound (l). The other was less stable and less well identified, but could be (ll). 

A solution of benzyl indole-5-carboxylate(1.0g, 3.98 mmol) and methyl 4-(bro-momethyl)-3-methoxybenzoate (2.06 g, 7.97 mmol) in dry DMF (10 ml) was heated at 80°C for 24 h. The reaction solution was cooled, poured into water (100 ml) and the product extracted with EtOAc (3 x 75 ml). The extract was washed with water and brine and dried over MgSO, . The product was obtained by evaporation of the solvent and purified by chromatography on silica gel using 1 4 EtOAc/hexane for elution. The yield was 1.11 g (32%) and some of the indole (30%) was recovered unreacted. 

Bromo-3-iodo-l-(4-methylphenylsulfonyl)indole (0.476 g, 1.00 mmol), methyl acrylate (0.108 g, 1.25 mmol), EtjN (0.127 g, 1.25 mmol) and Pd(OAc)2 (11 mg, 0.050 mmol) were mixed in a tube, purged with argon and the tube was sealed and heated to 100°C for 1 h. After cooling, it was opened and mixed with CH2CI2 (50 ml). The solution was washed with water and dried (Na SOJ. The residue was purified by chromatography on silica using 1 3 benzene-hexane for elution. The yield was 0.350 g (81%). 

To a stirred ice-cold solution of ethyl 3,6-dihydro-5-hydroxy-8-methyl-6-(phenylsulfonyl)benzo[l,2-b 4,3-b ]dipyrrole-l-carboxylate (368 mg, 0.85 mmol) in TEA (3ml) was added EtjSiH (1.5 ml), After 15 min the solution was allowed to come to room temperature and stirred for an additional 2h. The solution was evaporated in vacuo and the residue dissolved in CH2CI2 (10 ml), washed.with aq. NaHCOj and dried over MgS04. The solution was mixed with AcjO (1ml) and CH2C12 (1ml) and kept at room temperature for 2 h. The reaction mixture was evaporated and the residue purified by chromatography on silica gel using CHjClj-EtOAc (3 1) for elution. The product (271 mg) was obtained in 71 % yield. 

A solution of l-methylpyrano[4,3-b]indol-3-one (1 mmol) and methyl vinyl ketone (5 ml) in toluene (5 ml) containing 5% Pd/C (40 mg) was heated for 48 h in a sealed tube at 110°C. The reaction mixture was evaporated in vacuo and the residue purified by silica gel chromatography to give the product in 80% yield. 

Specifications and Analytical Methods. Vinyl ethers are usually specified as 98% minimum purity, as determined by gas chromatography. The principal impurities are the parent alcohols, limited to 1.0% maximum for methyl vinyl ether and 0.5% maximum for ethyl vinyl ether. Water (by Kad-Fischer titration) ranges from 0.1% maximum for methyl vinyl ether to 0.5% maximum for ethyl vinyl ether. Acetaldehyde ranges from 0.1% maximum in ethyl vinyl ether to 0.5% maximum in butyl vinyl ether. 

Analytical and Test Methods. Potentiometic titration is an analytical method for cyanoacetic acid. Methyl and ethyl cyanoacetates are usually analyzed by gas chromatography usiag the same equipment as for the malonates but with a higher column and iajector temperatures, namely 150 and 200°C, respectively. 

Gas—hquid chromatography is used extensively to determine the naphthalene content of mixtures. Naphthalene can be separated easily from thionaphthene, the methyl- and dimethylnaphthalenes, and other aromatics. Analysis of the various other impurities may require the use of high resolution capillary columns. 

Methoxy-l-methylethyl alkyl peroxides (1, X = OR , R = R = R" =, methyl R = decyl, undecyl, pentadecyl, 2-octyl) are Hquids that have been isolated using flash chromatography (131). Peroxyester derivatives (R = cyl) have also been prepared (131). 

Polymeric -peroxides (3) from hydrogen peroxide and lower carbon ketones have been separated by paper or column chromatography and have been characterized by conversion to the bis(p-(nitro)peroxybenzoates). Oligomeric peroxides (3, R = methyl, R = ethyl, n = 1-4) from methyl ethyl ketone have been separated and interconverted by suitable treatment with ketone and hydrogen peroxide (44). 

Analytical methods iaclude thin-layer chromatography (69), gas chromatography (70), and specific methods for determining amine oxides ia detergeats (71) and foods (72). Nuclear magnetic resonance (73—75) and mass spectrometry (76) have also been used. A frequentiy used procedure for iadustrial amine oxides (77) iavolves titratioa with hydrochloric acid before and after conversion of the amine to the quaternary ammonium salt by reaction with methyl iodide. A simple, rapid quaHty control procedure has been developed for the deterrniaation of amine oxide and unreacted tertiary amine (78). 

Instmmental methods of analysis provide information about the specific composition and purity of the amines. QuaUtative information about the identity of the product (functional groups present) and quantitative analysis (amount of various components such as nitrile, amide, acid, and deterruination of unsaturation) can be obtained by infrared analysis. Gas chromatography (gc), with a Hquid phase of either Apiezon grease or Carbowax, and high performance Hquid chromatography (hplc), using siHca columns and solvent systems such as isooctane, methyl tert-huty ether, tetrahydrofuran, and methanol, are used for quantitative analysis of fatty amine mixtures. Nuclear magnetic resonance spectroscopy (nmr), both proton ( H) and carbon-13 ( C), which can be used for quaHtative and quantitative analysis, is an important method used to analyze fatty amines (8,81). 

Specifications and Analytical Methods. The purity of l-methyl-2-pyrrobdinone is determined by gas chromatography and is specified as 99.5 wt % minimum. Maximum moisture content is specified as 0.05 wt % by ir spectroscopy. 

Several properties of the filler are important to the compounder (279). Properties that are frequentiy reported by fumed sihca manufacturers include the acidity of the filler, nitrogen adsorption, oil absorption, and particle size distribution (280,281). The adsorption techniques provide a measure of the surface area of the filler, whereas oil absorption is an indication of the stmcture of the filler (282). Measurement of the sdanol concentration is critical, and some techniques that are commonly used in the industry to estimate this parameter are the methyl red absorption and methanol wettabihty (273,274,277) tests. Other techniques include various spectroscopies, such as diffuse reflectance infrared spectroscopy (drift), inverse gas chromatography (igc), photoacoustic ir, nmr, Raman, and surface forces apparatus (277,283—290). 

Trace impurities present in commercial benzoic acid include methyl diphenyls and phthaHc acids. The concentration and presence of these impurities vary by product grade and by manufacturer. Gas chromatography and high pressure Hquid chromatography are useful for determining the concentrations of those impurities. 

The most widely used method of analysis for methyl chloride is gas chromatography. A capillary column medium that does a very good job in separating most chlorinated hydrocarbons is methyl siUcone or methyl (5% phenyl) siUcone. The detector of choice is a flame ionisation detector. Typical molar response factors for the chlorinated methanes are methyl chloride, 2.05 methylene chloride, 2.2 chloroform, 2.8 carbon tetrachloride, 3.1, where methane is defined as having a molar response factor of 2.00. Most two-carbon chlorinated hydrocarbons have a molar response factor of about 1.0 on the same basis. 

There is no specific color or other reaction by which methyl chloride can be detected or identified. QuaUty testing of methyl chloride for appearance, water content, acidity, nonvolatile residue, residual odor, methanol, and acetone is routinely done by production laboratories. Water content is determined with Kad Fischer reagent using the apparatus by Kieselbach (55). Acidity is determined by titration with alcohoHc sodium hydroxide solution. The nonvolatile residue, consisting of oil or waxy material, is determined by evaporating a sample of the methyl chloride at room temperature. The residue is examined after evaporation for the presence of odor. Methanol and acetone content are determined by gas chromatography. 

Cyclopentadiene oligomers up to octamers can be effectively analy2ed and quantified by supercritical fluid chromatography using a chemically bonded methyl siUcone capillary column. 

Thin-layer chromatography (76,77) has been used for the estimation of the amounts of dimer, trimer, and monomer ia methyl esters. Both this method and paper chromatography are characterized by lack of precision (78,79) (see Chromatography). 

Oils are mixtures of mixed esters with different fatty acids distributed among the ester molecules. Generally, identification of specific esters is not attempted instead the oils are characterized by analysis of the fatty acid composition (8,9). The principal methods have been gas—Hquid and high performance Hquid chromatographic separation of the methyl esters of the fatty acids obtained by transesterification of the oils. Mass spectrometry and nmr are used to identify the individual esters. It has been reported that the free fatty acids obtained by hydrolysis can be separated with equal accuracy by high performance Hquid chromatography (10). A review of the identification and deterrnination of the various mixed triglycerides is available (11). 

Diaziridines also show slow nitrogen inversion, and carbon-substituted compounds can be resolved into enantiomers, which typically racemize slowly at room temperature (when Af-substituted with alkyl and/or hydrogen). For example, l-methyl-3-benzyl-3-methyl-diaziridine in tetrachloroethylene showed a half-life at 70 °C of 431 min (69AG(E)212). Preparative resolution has been done both by classical methods, using chiral partners in salts (77DOK(232)108l), and by chromatography on triacetyl cellulose (Section 5.08.2.3.1). 

STUDY OF CONDITIONS FOR DETERMINATION OF TIAMETOXAM METHYL BY THE METHOD OF THIN LAYER CHROMATOGRAPHY... 

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