Side product, high-boiling

Only trace amounts of side-chain chlorinated products are formed with suitably active catalysts. It is usually desirable to remove reactive chlorides prior to fractionation in order to niinimi2e the risk of equipment corrosion. The separation of o- and -chlorotoluenes by fractionation requires a high efficiency, isomer-separation column. The small amount of y -chlorotoluene formed in the chlorination cannot be separated by fractionation and remains in the -isomer fraction. The toluene feed should be essentially free of paraffinic impurities that may produce high boiling residues that foul heat-transfer surfaces. Trace water contamination has no effect on product composition. Steel can be used as constmction material for catalyst systems containing iron. However, glass-lined equipment is usually preferred and must be used with other catalyst systems. 

The findings from the evacuation experiment confirmed the interpretation that the observed slight deactivation over time was not due to catalyst decomposition, as an accompanying decrease in activity and selectivity otherwise would have been observed. Instead, we expected the formation of aldol products 2-ethyl-hexanal and 2-ethyl-hexanol to be of relevance, as traces of these high boiling side products were observed at particular high conversions. 

C). Of course, in some cases, such as the hydrogenation of soft oils to yield components suitable for incorporation into margarine, the products decompose before their boiling points (even under reduced pressure) so that distillation is not a practical method for separation of the catalyst in such cases. Distillation is also impossible in the case of reactions giving high-boiling side products that would steadily build up in concentration if they were not removed. 

Indeed, the Na-HMPA route consistently provided the cleanest products and has been the only synthesis to provide solutions of Na3[M(CO)4]. It is often important to use solutions rather than slurries of trianion salts to minimize the formation of side products during the reactions of these materials with electrophiles. Until recently, product separation from the viscous and high-boiling HMPA has always been a problem (and remains so in some cases). For example, addition of excess THF to solutions of Na3[M(CO)4] in HMPA invariably resulted in the formation of sticky solids that contained HMPA and did not analyze satisfactorily (14). But recently, it was discovered that addition of these HMPA solutions to excess liquid ammonia resulted in practically quantitative precipitation of tan to pale yellow brown solids, which provided satisfactory elemental analyses of unsolvated Na3[M(CO)4] (M = Mn, Re). Virtually all impurities remained in the HMPA-NHj filtrate [Eqs. (4) and (5)]. 

Benzoic acid in the vapor is removed from the rectification column as a side stream. The high-boiling by-products leave the column as a residue. The benzoic acid is suitable for hydrogenation without any further purification264. 

A small amount of side-chain fluorination was observed [274], Benzyl fluoride was formed in about the same extent as the meta isomer. Small amounts of difluoro-toluenes and trifluorotoluenes as well as some unidentified high-boiling compounds were also found [274]. Additional products were not detected [308],... 

In addition to the hydroformylation reactions, side reactions of the product alcohols and aldehydes occur to form heavy ends, particularly at higher reaction temperatures, and usually account for 9% of the product distribution. Industrial reactors usually start using high boiling solvents, but after a while these heavy ends become the solvents. 

The separation of catalyst and product by distillation causes some disintegration of the complex catalyst, leading to finely divided metal which in turn tends to induce side reactions of the product and has to be recovered [185]. The addition of high-boiling oxygen-containing compounds, such as diphenyl ether or dibenzyl ether, is claimed to have a beneficial effect [180], as well as the presence of unreacted olefin (6) [181, 186] or of a carboxylic acid [187]. 

Besides methanol formation, side reactions also occur, forming high molecular weight alcohols, dimethyl ether, carbonyl compounds, and methane. Because of the numerous side products formed, these compounds are divided into two groups, called the low-boiling and high-boiling compounds. No methane forms in die converter [31]. 

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