Model compound conversion

Fig. 34. Reactions with ox3 en of some model compounds conversion-time curves obtained by VPC analysis (III,a) = ( ) HD = (o) DMHD = ( ) NB = )...

Lee and Sumimoto [47] suggested that peroxide-bleached mechanical pulps yellow readily because the hydroquinones they contain are leucochromophores, which may be subsequently oxidized further to colored compounds. In particular they showed that peroxide treatment of phenolic stilbene (XIII), which was formed from phenylcoumaran (XII) by mechanochemical action, gave rise to a labile hyd-roquinone that was easily oxidized by air to an intensely colored stilbenequinone (XIV) (Figure 12.4). It should be noted that these conclusions were based on experiments with model compounds. Conversely, Zhu et al. [48] found that mechanochemical action had no significant effect on the photosensitivity of mechanical pulps. 

Table 11 Model compound conversion data 410 C, 1 atm., 1.0-1.1 WHSV, 20 min. reaction intervals HZSM-5 in Si02/Al203...

The goals of this catalyst screening project are to gain insight into the conversion of biomass pyrolysis products with a variety of catalysts and under a range of conditions. Three topics will be discussed here catalyst and parameter screening, MBMS estimation of yield, and model compound conversion. 

AijAT-dicyclohexylcarhodiimide (DCC) also leads to essentially quantitative conversion of amic acids to isoimides, rather than imides (30,31). Combinations of trifluoroacetic anhydride—triethjlarnine and ethyl chi oroform a te—triethyl amine also result in high yields of isoimides (30). A kinetic study on model compounds has revealed that isoimides and imides are formed via a mixed anhydride intermediate (12) that is formed by the acylation of the carboxylic group of amic acid (8). 

In thioamidation the nitrile groups of PAN have a much higher reactivity than those of the corresponding model compounds. This fact is explained by the specific character of the polymeric nature of PAN and by the mutual influence of adjacent groups. As it is seen from the data presented in Fig. 4, the highest reaction rate and conversion level, as compared with low-molecular nitriles, is observed in the thioamidation of PAN. 

Initiator efficiency in terms of conversions and molecular weights were similar for model compounds and polymerizations. The influence of chlorine and bromine-containing counterions on polymerization was similar to that found in model study. 

Hydrogenation reactions, particularly for the manufacture of fine chemicals, prevail in the research of three-phase processes. Examples are hydrogenation of citral (selectivity > 80% [86-88]) and 2-butyne-l,4-diol (conversion > 80% and selectivity > 97% [89]). Eor Pt/ACE the yield to n-sorbitol in hydrogenation of D-glucose exceeded 99.5% [90]. Water denitrification via hydrogenation of nitrites and nitrates was extensively studied using fiber-based catalysts [91-95]. An attempt to use fiber-structured catalysts for wet air oxidation of organics (4-nitrophenol as a model compound) in water was successful. TOC removal up to 90% was achieved [96]. 

Catalyst Model Compound Model Compound to Glucose Ratio (mole ratio) Glucose Conversion (mol%) HMF Yield (mol%) Other ( mol%)... 

Figure 46.3. Experiment A, molar composition of products of glucose conversion after 3h, 100°C reaction (includes control - with no model compounds, and competitive reactions with 1 1 and 1 2 model compound to glucose molar ratios).

Conversion of chloromethylated polymers to our second target system, aminomethylated polymers, was approached In several different ways. Two of the approaches, which were used successfully to convert model compound 11 to the desired amlnomethyl products failed when applied to the polymer system. The first of these, the Delepine reaction, appeared to be the most reasonable and economical, but only Insoluble, apparently crosslinked products could be Isolated. 

Figure 1. Summary of results for coal and selected model compounds in some strongly basic conversion systems. Arrows indicate that significant conversion to reduced products was observed. The X ed arrows indicate that no reduction was observed.

Ganguly, T. Pal, S. K. 2006. Photoinduced electron transfer research to build model compounds of artificial photosynthesis and solar energy conversion. J. Chinese Chem. Soc. 53 219-226. 

The conversion of the monofunctional adducts into bifunctional lesions depends drastically on the structure of the Pt drug. Obviously, Pt compounds exhibiting trans geometry form different bisadducts than cisplatin and hence, a different spectrum of antitumor activity is expected. Mechanistically, the formation and possible isomerization of bisadducts are not well understood. The assumption that hydrolysis of the second leaving group controls the formation of bisadduct may be an oversimplification. Studies with model compounds as well as with oligonucleotides have indicated that a certain nucleobase may be a powerful nucleophile toward Pt(II) if spatially in a correct position. Unfortunately, our knowledge on these interactions is at present very limited. 

The ability of peptides CBPOl-GBP 18 to modulate pyridoxamine-mediated transamination was determined by the conversion of pyruvic acid to alanine in both the absence and presence of copper(II) ion, which would be coordinated by the transamination intermediates [32]. In the absence of copper(II) ion,peptide CBP13 showed up to a 5.6-fold increase in alanine production relative to a pyridoxamine model compound and peptide CBP14 produced alanine with a 27% ee of the 1-enantiomer. In the presence of copper(II) ion, peptide CBP13 again showed the greatest increase in product production, with a 31.7-fold increase in alanine production relative to the pyridoxamine model compound. Peptide CBPIO showed optical induction for D-alanine with a 37% ee. 

In order to assess whether intramolecular cooperativity could occur within the dendrimeric [Co(salen)]catalyst the HKR of racemic l-cyclohexyl-l,2-ethenoxide was studied at low catalyst concentrations (2xl0 " M). Under these conditions the monomeric [Co(salen)] complex showed no conversion at all, while the dendritic [G2]-[Co(salen)]catalyst gave an impressive enantiomeric excess of 98% ee of the epoxide at 50% conversion. Further catalytic studies for the HKR with 1,2-hexen-oxide revealed that the dendritic catalysts are significantly more active than a dimeric model compound. However, the [Gl]-complex represents already the maximum (100%) in relative rate per Go-salen unit, which was lower for higher generations [G2] (66%) and [G3] (45%). 

Question 3. Where do the increased aromatics come firom The most probable answer. Large increases in aromatics were observed in some cases, which are probably due to naphthalene adduction. Conversion from aliphatics is unlikely. The evidence comes from FT-IR, NMR, FIMS and the model compound studies which show that naphthalene adduction occurs. 

For the present discussion, a number of these conversions are of relevance. Phenolic dimeric model compounds of the 0-1, 0-0-4 and phenyl coumaran type are degraded via Ca-arene cleavage yielding methoxy-... 

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