Toluene quality standards

Toluene is marketed mostly as nitration and industrial grades. The generally accepted quality standards for the grades are given by ASTM D841 and D.162, respectively. 

As noted before, the most significant refinery emissions were airborne. For those options that involved a change in emissions affecting air quality, impacts were modeled using standard air dispersion techniques. Exposure estimates were developed for three classes of chemicals (1) benzene, toluene, ethylbenzene and xylene (BTEX), (2) other chemicals reported in the refinery s TRI submissions, and (3) criteria pollutants (SO2, NO2, PMjo, and CO). Similar modeling techniques were used for all three classes. The project focused on the impact of benzene emissions, since benzene turned out to be the chemical species of greatest concern relative to other releases. 

As even the optimized hydrogenation conditions gave rise to not more than 89% enantioselectivity it became very important to find an efficient purification procedure which would allow the enrichment of the desired (-(-enantiomer. A rapid screening of several weak and strong acids led to an acceptable solution. The acetates of both the racemate 11 as well as the (-)-enantiomer 12 are readily crystalline salts but the acetate of the desired (S)-enantiomer is less soluble in toluene at 0°C than that of the racemate by a factor of 10. Thus it could be crystallized in overall yield of 84%, content 99.1%, 98.9% ee. Finally it was noticed that traces of iridium (70-200 ppm) in the acetate salt hindered the following reaction in the synthetic sequence, by leading to decomposition of the formic acid (used as for-mylation reagent). A treatment of the octahydroisoquinoline solution with charcoal prior to precipitation of the acetate salt lowers the Ir content to 20-40 ppm. This new quality can then be formylated without problems under the standard conditions. 

Make up thin layer plates as described above. Chromatograph the standards and the unknown(s) in toluene and locate the spots by iodine staining. Calculate the R( values and hence determine which of the five standard compounds the unknown(s) contain. Confirm your conclusions by running a further chromatogram using the unknown mixture as one spot and the suspected mixture as a second spot. (The Rf values may vary with the quality of the TLC plate and hence comparisons between the unknown and the standard must finally be made on the same plate.)... 

The most popular solvent for monolayer deposition is ethanol. Other solvents, such as water, hexane, toluene, THF, dichloromethane, acetonitrile and DMF, can also be used without affecting the stmeture of the resultant monolayer. However, the monolayers prepared using long-chain alkanes as solvents (e.g. hexadecane) did not form high quality layers, probably because the monolayer is contaminated with the solvent molecules . Hexadecanethiol was also reported to give monolayers with poorer conductivity blocking properties when deposited from DCM as compared to the standard deposition from the ethanol solution . To ensure that the monolayer is not contaminated by coadsorption of adventitious impurities, only highest purity solvents should be used. 

Liquid scintillators, used in the experiment, were of standard commercial quality, such as Aqualuma Plus, Rialuma and Lumagel (Lumac Systems AG, Basel, Switzerland), and Triton - X 100 toluene scintillators prepared according to Patterson and Green (Patterson, 1965). Scintillation vials were from the same company as the liquid scintillators (Milli -6 / Milli-20 glass and polyethelene). 

The major important quality criteria for benzene, toluene and xylenes are summarized in Table 4.13.The specifications in various countries are covered by comparable national standards (ASTM, DIN, BSS etc.). 

Fig. 6.16. Intrinsic viscosity [ij] as function of the molar mass for poly(styrene) (PS) of low average molar mass in different solvents.The slope of the [rjl-M-relationship in this molar mass range is independent of the solvent quality. (Data for benzene from [65], for toluene at T=0 C from [66], for toluene at 25 C from [111], cyclohexane at 34.5 C from [64] c/s-decaline at 25 C from [63] and THF at 30 C as a courtesy from PSS Polymer Standards Service, Mainz, Germany...

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