Carbonyl group formation

ATR spectra show that oxygen groups are located at the surface to the depth of 0.6 /l m. Kinetic curves of carbonyl groups formation in different experimental conditions are shown in Fig.4. 

Figure 4. Kinetics of carbonyl group formation at 1714 cm- in polypropylene samples (0) and ( ) ozone and UV light (L2) (4) and (A) ozone only (0) and ( ) ATR spectra (A) and (A) transmission spectra.

Changes in the number of free amino residues alter the modified proteins susceptibility to proteolysis. Albumin chlorination and /V-chloramine formation decreases susceptibility to trypsin digestion. Removing of chloramine residues by treatment with thiosulfate shows that chlorination alters albumin properties by a biphasic mode the reversible chlorination and removal of chloramine moieties markedly increases albumin susceptibility to proteolysis, whereas chlorination produces the irreversible loss of amino moieties and carbonyl group formation effects decrease in albumin susceptibility to trypsin digestion. The effect is related to the number of lost amino residues. A similar relationship was observed for IgG. Fibrinogen and protamine, on the other hand, did not show dependence between chlorination and proneness to trypsin proteolysis (06). 

Carbon monoxide, evolution from cellulose on beating, 428, 429 Carbonylation, of alkyl balides, 61 Carbonyl groups, formation from cellulose on heating, 426, 428, 435 Carboxyl groups, formation from cellulose on beating, 426, 427, 435 Cardenolides, synthesis of 1,2-cis-, 267 Cellobiose, /8-, mutarotation of, 23 Cellulase, 376 Cellulose... 

The rearrangement of acetals of 2-haloalkyl aryl ketones is a well-documented process yielding esters of 2-arylalkanoic acids by 1,2-aryl shift (equation 7). The mechanism of this rearrangement is reminiscent of other semipinacol rearrangements. Loss of the halogen (usually assisted by Lewis acid), yields a carbocation (4), which then undergoes a 1,2-aryl shift with carbonyl group formation. 

As it is visible from Fig. 1, the selectivity towards COL increased with conversion. This was most clearly observed in non-reduced catalysts. Previously [23], it was demonstrated that in the liquid-phase hydrogenation of a similar molecule (e.g. crotonaldehyde), there was a clear increase of the selectivity as a function of conversion. This kinetic pattern did not obey the general behavior characteristic for parallel-consecutive reactions, thus calling for the introduction [23] of the reaction-induced formation of active sites. One can thus speculate that, also in cinnamaldehyde hydrogenation, during the reaction there is in situ formation of sites responsible for the hydrogenation of the carbonyl group (formation of unsaturated alcohol). 

A broad peak at 3200-3500 cm appears as a result of hydroxy/ hydroperoxide group formation. The peak at 1720 cm- emerges and it can be attributed to the formation of carbonyl groups. Formation of these bands is characteristic for the photo-oxidation of both polystyrene (15,23) and polyester (14) samples. 

The mechanism of carbonyl group formation in the main chain of the polymer is not entirely elucidated. The following are some of the suggested mechanisms. 

Depending on the substitution of the pyrazol-3-one ring, oxidation can lead to pyrazol-3-one radicals, carbonyl group formation on the ring or oxidative coupling. 

In a more detailed view of the mechanism of the Wittig reaction, it has been shown that, after the carbanionic center adds to the carbonyl group, formation of a 4-membered ring with a P-C bond, an oxaphosphetane derivative (4.49), occurs. Such heterocycles are unstable when P is in the pentacoordinate state, but they can be detected by NMR spectroscopy at low temperatures. Their decomposition takes place by ejecting triphenylphosphine oxide (Scheme 4.50). 

Figure 10.52 shows that addition of the plasticizer decreased dehydrochlorination rate of PVC. Crosslinking rate was reduced with the presence of plasticizers. Also, the carbonyl group formation was slower in the presence of a plasticizer. Comparison of data presented by the same authors for the effect of radiation above and below 290 nm stresses importance of wavelength selection on the results obtained. When studies were conducted with an unfiltered mercury lamp, presence of phthalates increased the carbonyl group formation. 

Figure 15.8 Carbonyl group formation (a), vinyl group formation (b), and crystallinity (c), as a function of exposure time for neat HDPE and WF/HDPE samples [60].

Thermo-oxidative studies have also been reported on polyisoprenes and on natural rubber. In the latter case, the effect of relative molecular weight on thermo-oxidation as evidenced by carbonyl group formation was investigated. A mechanism for formation of isoprene during thermal degradation of natural rubber has been proposed. It involves a cyclic intermediate. 

At temperatures between 120 and 160 °C, there is a relationship between oxygen absorption and carbonyl group formation. Moreover, there is a relationship between end groups and thermal-oxidative stability. Here, the initial rate of oxidation increases with the concentration of carboxyl end groups. Alkaline amino end groups, however, increase the induction period of oxidation and thus lead to improved resistance. 

For non-transparent or non-translucent specimens, the relative humidity of the interfacial climate on an irradiated surface can be decisive for photo-chemical aging. Tests with PE-HD packaging showed clear influence of relative humidity on molecular weight reduction and carbonyl group formation. Figure 1.32 [87]. 

The photooxidation mechanism occurs via free radical mechanism with formation of polymer peroxy and alkoxy radicals and hydroperoxide and carbonyl groups. Formation of these groups was confirmed from IR spectra. 

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