Carboxidation

Kabum-jodid, n. potassium iodide, -jodidlo-sung, /. potassium iodide solution, -jodid-st ke, /. potassium iodide starch, -jodid-starkepapier, n. potassium iodide starch paper, -kobaltnitrit, n. potassium cobalti-nitrite. -kohlenoxyd,n. potassium carboxide, potassium hexacarbonyl. -nitrat, n. potassium nitrate. 

Kohlenozyd, n, carbon monoxide, -eisen, n. iron carbonyl, -gas, n. carbon monoxide gas. -hamoglobin, n. compound of carbon monoxide with hemoglobin, -kalium, n. potassium carboxide, potassium hexacar-bonyl. -knallgas, n, explosive mixture of carbon monoxide and oxygen, -nickel, n. nickel carbonyl. 

Potential mutagenic danger DDT, dichlorvos, sulfallat, triallat, carboxide, trifluraline... 

Since the carbonyl groups are formed by oxidation, this reaction type was called carboxidation [83, 172]. In particular cases, depending on the main carbonyl product (ketone or aldehyde), one may call the reaction more specifically, that is, ketonization or aldehydization. ... 

Below we give an overview of carboxidation results published for alkenes of various types [168, 173-175],... 

Carboxidation of linear alkenes is presented in Table 7.8 [173]. The location of the C=C bond and configuration of intermediate oxadiazoline complex are two important parameters with these substrates. For terminal alkenes, the complex may have configuration I and II (Figure 7.4). Complex I has the oxygen bound to the first carbon atom, and its decomposition leads to an aldehyde. Complex II has the oxygen bound to the second carbon atom, and its decomposition leads to a ketone. However, decomposition of the latter complex may occur also in a different way, involving... 

Based on the product distribution, one may calculate the contribution of cleavage route to the total rate of carboxidation [173]. For the terminal alkenes, the cleavage... 

The carboxidation of internal 2-butene and 2-pentene proceeds with a much smaller cleavage (8%), yielding the ketones as major products. The reason for this difference in the behavior of terminal and internal alkenes is unclear. One may relate it to dissipation of the energy evolved at the oxidative attack to the double bond. The efficiency of this process maybe higher for the more remote position of the double bond from the end of the molecule. However, the cleavage contribution for the ethylene is as low (7%) as that for the internal alkenes, which undermines the idea. 

Carboxidation of 1,5-cyclooctadiene also leads to the formation of mono- and diketones. However, in this case there is no deactivation effect of the C=0 group, so that the diketone fraction (13%) is dose to the statistical value. This is probably explained by a more distant location of the double bonds from each other in the latter diene. 

In addition to the cyclodienes discussed above, the carboxidation of 1,3-cyclohex-adiene having conjugated double bonds was also tested. In this case, the reaction is strongly complicated by the Diels-Alder side reaction. The main part of the diene is consumed by the dimerization process, and only 25-30% is involved in the oxidation, yielding cyclic ketones. 

Table 7.10 presents results for this alkenetype. Carboxidation of norbornylene (entry 1) leads to the formation of both a ketone and an aldehyde in approximately equal amounts, indicating that a significant cleavage of the double bonds occurs. There is also a set of other reaction products as a consequence of the bond cleavage. 

To test the effect of a heteroatom, Starokon et al. [175] studied three five-membered heterocycles with a similar molecular structure, containing the oxygen (2,5-dihy-drofuran), nitrogen (3-pyrrole) and sulfur (butadiene sulfone). Only the oxygen-containing cycle was carboxidized selectively, while the others showed a strong tendency towards side reactions resulting in a set of unidentified products. 

In contrast, the carboxidation of 2,5-dihydrofuran (entry 2) and 4,7-dihydro-l,3-dioxepin (entry 4), having a more distant location of the double bonds, proceeds with minor cleavage, leading in both cases to formation of the corresponding ketones with 94% selectivity. 

In conclusion, we can say that the liquid-phase carboxidation of alkanes can be applied to various substrates, induding linear, cyclic, heterocydic alkenes and their derivatives, yielding the corresponding ketones and aldehydes with selectivities in many cases of >90%. 

With some alkenes, carboxidation can be successfully performed also in the gas phase [172, 178]. 

The macromolecules of many polymers include C=C bonds and therefore can be considered as alkene analogs. This gives rise to the idea of applying the carboxidation approach to polymers. It was expected to open up a new way for their chemical modification so as to improve the adhesion and other physicochemical properties. 

As in the case of alkenes, the carboxidation of PE may also include the cleavage of C=C bond. However, the decrease of P E macromolecule by one carbon atom does not... 

Figure 7.6 IR spectra of carboxidized polyethylene in the vibration region of C=0 and C=C bonds (1) parent sample (2) after carboxidation at 503 K (3) after carboxidation at 523 K.

Unlike PE, many polymers have ahigh concentration of the internal C=C bonds. The carboxidation of such materials led to quite unexpected results. This can be illustrated by the carboxidation of cis- 1,4-polybutadiene rubber (poly-BD) studied in detail by Dubkov et al. [180], The concentration of C=C bonds in this rubber is 250 bonds per 1000 carbon atoms. Possible oxygen content in the poly-BD can reach up to 23 wt%, if all C=C bonds are transformed into the C=0 groups. 

Similar to internal alkenes, carboxidation of the rubber involves intermediate formation of an oxadiazoline cycle (Figure 7.7). Decomposition of the cycle without cleavage of the C=C bond (route 1) is accompanied by the formation of a ketone and does not lead to change in the molecular weight. Decomposition with cleavage (route 2) leads to fragmentation of the macromolecule with the formation of two smaller fragments a linear aldehyde R2-CH2-CHO and a carbene R -CH2-CH , which further isomerizes into the terminal alkene Rj-CH=CH2. 

An estimation based on NMR data showed that the route 1 comprises 95% and route 2 only 5% of the total carboxidation rate. These data are dose to the carboxidation results of 2-butene, for which the non-deavage route was found to be 92% and cleavage route 8% [173]. However, in distinction to the individual alkene, where the cleavage route only slightly decreases the selectivity for ketone, in the case of poly-BD, as we shall see below, this route may have dramatic consequences even at a 5% contribution. 

Figure 7.8 MWD curves of carboxidized poly-BD samples. The numbers of the curves correspond to the sample numbers in Table 7.12.

The carboxidation degree exhibits a dramatic effect on the consistency of the resulting samples. At the introduction of small amounts of oxygen (0.2-0.8 wt%), the rubber retained its consistency, but became sticky. At an oxygen content of 1.6 wt%, the material became fluid and lost the ability to retain its shape. At oxygen contents of 5.0 wt% or more, the samples turned into a bright viscous liquid. 

For the most oxygenated sample, the carboxidation reaction may be presented by (7.19), having huge stoichiometric coefficients compared to conventional chemical reactions ... 

Carboxidation of the poly-BD and other rubbers by nitrous oxide opens a simple and effective way for preparing polyketones with a regulated oxygen content and molecular weight. The presence of C=0 and C=C groups provides additional opportunities for application and modification of the material. 

Of special interest is a new type reaction discovered with N20 direct oxidation of alkenes to carbonyl compounds, called carboxidation. Beside various individual alkenes, carboxidation can be applied effectively to unsaturated polymers, opening up a way for the preparation of new materials. Reactions of this type should receive special attention from the catalytic community, since currently they are conducted in a thermally. This oxidation area is waiting for the beneficial arrival of catalysis to provide better control of the activity and selectivity. 

SYNS BELL MINE BIOCALC CALCIUM DIHYDROXIDE CALCIUM HYDRATE CALCIUM HYDROXIDE (ACGIH, OSHA) CALVIT CARBOXIDE O HYDRATED LIME KALKHYDRATE O KEMIKAL O UMBUX UME MILK LIME WATER MILK OF LIME SLAKED UME... 

Thermal stabilities of the polyoxides, -alkoxides, -aroxides and -carboxides (67), 70), (72), (73) were examined In general, the stability is not enhanced drastically when comparing the polymers with low molecular model compounds. 10% weight loss in air occurs at 710-770 K. Investigations on electrical conductivity are more important. 

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