Loss during conversion

Energy loss during conversion to radiant heat... 

The characteristics of the supported Pt catalysts used in this study are compiled in Table 1. The activity of the catalysts during a typical time-on-stream experiment are shown in Fig 1. While Pt/ZrOj catalyst showed high stability (less than 5% loss in conversion during 180 hours time on stream), Pt/y-AljO, lost all catalytic activity after 3 hours and Pt/Ti02 deactivated gradually during 40 hours. The supports alone were catalytically inactive. 

Under reflux conditions on a small scale in acetonitrile, the reaction was complete only after 24 h (entry 1). In a microwave reactor at 150°C, 86% isolated yield was achieved after 20 min reaction time (entry 2). Running the same reaction in DMSO or DMF at 150°C gave complete conversion of starting material, but because of losses during work-up, isolated yield was lower (entries 3 and 4). For scale-up trials, the Voyager SF was used, and the reaction was performed at 180°C for 20 min... 

Acyl azides (see Section 2.13) The acyl-azide method of coupling is unique for two reasons. First, it is the only case in which the immediate precursor of the activated form of the peptide is not the parent acid. The starting material is the peptide ester that is obtained from the amino acid ester by usual chain assembly (Figure 2.25, path A). Second, it is the only method that just about guarantees production of a peptide that is enantiomerically pure, provided scrupulous attention is paid to details of procedure. There is no danger for loss of chirality during conversion of the ester to the hydrazide and then the azide, but care must be taken to avoid contact of... 

Conversely, too few interactions with the surface may lead to loss during hybridization and washing steps. This is why the covalent attachment of oligonucleotides at their 3 or 5 terminus has the advantage, but modified oligonucleotides and slide chemistries can be expensive. 

It is noteworthy that in practice even the reverse of the above may occur. Often it is necessary to analyse compounds that are too volatile. Significant losses during the preliminary treatment of the sample (e.g., extraction, removal of the solvent), due to this volatility, may introduce errors into the quantitative evaluation. Analysis of volatile carboxylic acids in biological samples is an example. Conversion of these compounds into less volatile derivatives is therefore advantageous from the viewpoint of both GC proper and preliminary isolation of the compounds and sample treatment. 

Several experiments have provided information concerning the mechanism of formation of 12 from 11, and all evidence is consistent with intramolecular loss of dinitrogen from the diazoalkane adduct. Observation by spectrophotometry of an isosbestic point at 554 nm. during conversion of 11a to 12a demonstrated not only the cleanness of the reaction but also the absence of any appreciable concentration of an intermediate. Heating a benzene solution containing either a mixture of 11a and (C5HitMe)2Mo2(C0)it (eq. 32) or 11a and lid (eq. 33) yielded only the direct products no cross... 

For instance, an isolated yield is always lower than the actual conversion due to losses during work-up. 

By the end of 2004 ring-opening polymerisation in ionic liquids has been reported in only one paper, using complexes 35a, 35b or 36 as catalysts.[33] A biphasic system comprised of [C4CiCiim][PF6] and toluene in a 1 4 ratio was used to minimise catalyst loss during product isolation and the polymer could be obtained almost quantitatively by simple decantation. The activity of ionic liquid solutions of 35a drop markedly after the first cycle and become inactive in the third cycle, whereas 35b and 36 could be used for three and five cycles, respectively, with very good conversions, as shown in Scheme 7.5. 

Sampling. Concentrations of carbon in archaeological materials range from very large in charcoal to less than 1% in metals, foundry slags, and pottery. The size of the sample needed for analysis, thus, depends on the nature of the material as well as its age. The analytical procedure used to isolate the carbon may result in significant losses during extraction and chemical conversion. Samples should always be taken in sufficient quantity for replicate determinations and comparison with control specimens. 

Polyacrylonitrile (PAN) precursor fibers are more expensive than rayon. Nevertheless, PAN is more commonly used because the carbon fiber yield is about double that from rayon. Pitch-based carbon fibers are also important, because, potentially pitch is perhaps the cheapest raw material. Table 8.2 shows that carbon yield is highest from the mesophase pitch. The reader is cautioned that this is true only if we exclude the losses during the mesophase conversion step. If, however, one compares the overall carbon fiber yield from raw pitch to that from PAN, then the yield from PAN is higher. In any event, the carbon fiber yield or precursor weight loss is a very important factor in the economics of processing. 

Isothermal dehydrations of single crystals (about 1 mm ) of the hexahydrate [111] in vacuum between 213 and 243 K gave or-time curves for conversion to the trihydrate with no induction period and a constant rate of water loss during a large fraction of reaction. The rate of dehydration decreased linearly with the prevailing pressure of water (contrasting with the behaviour of many other hydrates) attributed to the occurrence of the reverse reaction. The activation energy for conversion of... 

A systematic error will occur if the method used to determine the response, y, underestimates or overestimates the true response. A well known example of this is that an isolated yield is always lower than the actual conversion due to losses during work-up. Other examples are when chromatographic methods are used to determine the composition of a reaction mixture and it is assumed that isomeric compounds will have the same detector response, which may not be exactly true different batches of chemicals may contain impurities which causes a systematic variation in yield. 

The temperature of samples taken at different locations in the packed bed was sometimes as high as 393 K, so a certain amount of methanol vapour was flashed off and consequently the measured molar concentrations of the organic compounds were higher than in the reactor. On the basis of Eq. 1 and 2 we still obtain the correct hydrogen conversions, automatically compensated for the evaporation loss during sampling. 

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