Chromatography vapor phase

Both vapor-phase chromatography and high performance Hquid chromatography, along with nuclear magnetic resonance spectroscopy, have been used for isomer and composition analysis. 

For the higher alkoxy groups, standard carbon and hydrogen analysis may be used, although careful sample preparation is required because of the ease of hydrolysis. Quantitative vapor-phase chromatography of alcohol Hberated during hydrolysis may also be used, but care must be taken in this case to ensure that hydrolysis is complete before the estimation is carried out. 

Fractions were analyzed by vapor-phase chromatography (column 0.3 X 120 cm., 20% SE-52 on Chromosorb P 60/80, 130°, helium flow rate of 60 ml./min.). Retention times of 1.9 minutes for dicyclopentadiene and 4.6 minutes for the 7,7 dichlorobicyclo[3.2.0]hept-2-en-6-one were found. 

The methylenecyclohexane was analyzed by vapor-phase chromatography and found to be better than 99% pure. 

A. J. P. Martin, Private Communication, Symposium on Vapor Phase Chromatography, London (1956). 

Additional evidence that a dynamic equilibrium exists between an enamine, N-hemiacetal, and aminal has been presented by Marchese (41). It should be noted that no acid catalysts were used in the reactions of aldehydes and amines discussed thus far. The piperidino enamine of 2-ethylhexanal (0.125 mole), morpholine (0.375 mole), and p-toluene-sulfonic acid (1.25 x 10 mole) diluted with benzene to 500 ml were refluxed for 5 hr. At the end of this time the enamine mixture was analyzed by vapor-phase chromatography, which revealed that exchange of the amino residue had occurred in a ratio of eight morpholine to one piperidine. Marchese proposed a scheme [Eqs. (4), (5) and (6)] to account for these... 

The piperidine, pyrrolidine, and morpholine enamines of cyclohexanone substituted in the 3-position by methyl, phenyl, and l-butyl have been prepared (49). The complexity of the NMR spectra in the ethylenic hydrogen region indicated a mixture of isomeric enamines. Estimation of the per cent of each isomer by examination of the NMR spectra was not possible, nor were the isomeric enamines separable by vapor-phase chromatography. 

The purity of the product was checked by vapor phase chromatography on a polyethylene glycol on Teflon column at 72°, 15 p.s.i., and a flow rate of 102 ml. of helium per minute. The sample appeared to be homogeneous, but, since the amine tails badly on the column, it is not possible to detect the presence of a small amount of water (less than 3%). 

The product is analyzed by vapor phase chromatography using a 6-ft., f-in. O.D. copper tube, packed with 5% Bentone-34 (Wilkins Instrument Co.) and 0.5% XF-1150 (General Electric Silicone Products) on Diatoport-S (80-100 mesh) (F and M Co.) flow rate of helium 60 ml./min., oven temperature 85°. This column separates m-cymene (retention time 12 minutes) from />-cymene (retention time 10 minutes) but does not resolve the ortho isomer. The purity of the distilled w-cymene is above 98%. 

Essentially the same procedure may be used to produce mixtures of cyclodimers from isoprene,4 1,3-cyclopentadiene,4 and 1,3-cyclohexadiene.7 Separation of all products is somewhat difficult in most cases but has always been possible by preparative vapor phase chromatography. Despite the problems that may be involved in separation of desired products in some instances, photocyclization frequently is the method of choice for preparation of 1,2-dialkenylcyclobutanes if they can be made major products of photoreactions. Starting materials are readily available, and the preparations are easily carried out on the scale described. There is little doubt that the method is the best for preparation of trans-1,2-divinyleyclob u tane. 

In the distillation residue (5.7-6.3 g.) remain other byproducts, presumably l,l-dimethallyl-2-propanone, 3-methallyl-2,4-pentanedione, and 3,3-dimethallyl-2,4-pentanedione (indicated by vapor phase chromatography). The checkers carried out v.p.c. analyses using an 8-ft. column of 5% silicone oil XE-60 on Diatoport S at 100° for analysis of the distillate and 175° for analysis of the residue. 

However, if the azepine is C-monosubstituted, e.g. 14, or unsymmetrically substituted, then two isomeric 2-azabicycloheptadienes, e. g. 15 and 16, may result corresponding to electrocyclic ring closure involving C2-C5 or C4-C7 of the azepine ring. In practice, the ratio of the two isomers formed (which may be separated by vapor phase chromatography) varies with the position of the substituent.236 In contrast, irradiation of methyl 2,5-di-tm-butyl-l//-azepine-l-carboxylatein methanol yields only methyl 3,5-di-tert-bulyl-2-azabicycIo[3.2.0]hepta-3,6-diene-2-carboxylate (81 %).70... 

Piperidine obtained from Eastman Kodak was fractionated through a 90-cm. column packed with glass helices, and the fraction distilling at 105° was used for this work. This material contained approximately 0.36 wt.% of pyridine as indicated by vapor phase chromatography and ultraviolet analysis. 

The checkers used a 10-mm. x 0.76-m. Nester spinning band still and obtained material having 1.4620 that could not be purified by redistillation. Analysis by vapor-phase chromatography (silicone gum rubber, 20% w/w on firebrick, 120-cm. x 6-mm. outside diameter column at 125°) showed this material to be 95% methyl butadienoate contaminated by small amounts of two other materials. 

Cycloheptatriene containing 9% toluene is available from the Shell Chemical Company, New York. Less pure cycloheptatriene, obtained by pyrolysis of bicycloheptadiene followed by a crude distillation, has been used successfully in this preparation. The quantity of the tropilidene/toluene mixture is adjusted in accord with its purity as estimated by vapor-phase chromatography on didecyl phthalate. 

Trans-4-Octene oxide 1885 (1.2 mmol), then hexamethyldisilane 857 (1.8 mmol) in 5 mL HMPA, are added, at 65 °C under argon, to 0.2 mmol potassium methox-ide in 10 mL anhydrous HMPA. After 3 h stirring at 65 °C and cooHng to room temperature saturated aqueous NaCl solution is added to the reaction mixture, which is then extracted with pentane. The pentane extracts are combined and dried with Na2S04 and analyzed by vapor phase chromatography (VPC) to reveal the formation of 99% cis 4-octene 1887 [103] (Scheme 12.71). 

The product contains less than 10% of lower-boiling impurities determined (by the checkers) by vapor-phase chromatography with a column packed with 15% XF-1150 on Chromo-... 

The distilled product is 99% pure by vapor-phase chromatography. 

The purity of the 1,1-diphenylpentane is attested by vapor-phase chromatography on a 5-ft. column of 10% Apiezon L on Celite at 200°. 

Tetramethyl-l,3-cyclobutanedione is available from Eastman Organic Chemicals. It melts at 115-116° and is typically 99% pure by vapor-phase chromatography. 

The isomerization is usually complete in 5 hours and can easily be followed by vapor-phase chromatography. Heating periods up to 20 hours are not detrimental. The only failure among numerous preparations occurred when tetramethyl-1,3-cyclobutanedione contaminated with 4% of isobutyric acid was used. In case of partial conversion after 5 hours, additional increments (0.5 g.) of aluminum chloride should be added to complete the reaction. 

This material should be at least 98% pure by vapor-phase chromatography (SE-30 column at 180-200°). It usually crystallizes if stored in a refrigerator. Unreacted hexamethylbenzene, present if insufficient oxidant is used, can best be removed by column chromatography on alumina with pentane as eluant. 

Gas chromatography (GC) can also be referred to as vapor-phase chromatography (VPC) and even gas—liquid chromatography (GLC). Usually the technique, the instrument, and the chart recording of the data are all called GC ... 

Let s start with two components, A and B again, and follow their path through an adsorption column. Well, if A and B are different, they are going to stick on the adsorbant to different degrees and spend more or less time flying in the carrier gas. Eventually, one will get ahead of the other. Aha Separation—Just like column and thin-layer chromatography. Only here the samples are vaporized, and it s called vapor-phase chromatography (VPC). 

The ability to recover monolayers and subject them to meaningful analysis has become practical only in recent years because of the development of new methods of trace analysis. High-performance liquid chromatography and vapor phase chromatography allow separation and identification of such small quantities (54a). Attenuated total reflectance techniques for infrared analysis (56) and field desorption mass spectrometry (68) have been applied to the trans-... 

The exact proportion of unsaturated acetate varies slightly but is typically 10-15% as determined by vapor-phase chromatography. 

Vapor-phase chromatography shows no detectable impurities under conditions where <1% of isomeric material would be easily visible. A melting point of 108-109° has been reported. ... 

Purity was checked by analytical vapor phase chromatography (98-99%). This product can be used for most reactions without further purification. If further purification is desired, 2-bromonaphthalene can be recrystallized from aqueous methanol (95% recovery) to give a product melting at 53 55°. 

The product is readily analyzed by vapor phase chromatography. Since the only impurity is o-xylene (conversions range from 80% to 100%), the percentage of reduction product was... 

If all the pentane is removed before pyrolysis, the bicyclo [2.1.0]pentane shows no impurities on vapor phase chromatography with a 20% Dow 710 on 50/60 U Anaprep column. Analysis by n.m.r. also revealed the absence of any traces of cyclo-pentene in the spectrum consisting of three complex multiplets at 0.3-0.8, 1.1-1.7, and 1.9-2.4 p.p.m. (downfield from internal tetramethylsilane reference). 

Vapor Phase Chromatography. This is accomplished by constructing or buying complicated and expensive equipment. Although this method is very effective, it is superseded by the simple, inexpensive and effective column chromatography. 

Aryl derivatives of dibenzothiophene are generally described as being thermally stable up to 400° and are therefore of use as heat-transfer media, dielectric or hydraulic fluids, lubricants, and stationary phases for vapor-phase chromatography. 3-Phenyldibenzothiophene 5,5-dioxide is capable of detecting X, y, or corpuscular radiation when incorporated in photographic film. ... 

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