Saturation of Double Bonds

In contrast to heterogeneous metal catalysts, the chlororhodium complex is not sensitive to sulfur poisoning,thus allowing the saturation of double bonds in the presence of mercapto functions. 

Irreversible complex forma- [21] tion or saturation of double bonds detection by IR... 

Namely, if the double bond was saturated ( ) simultaneously when it formed, the retardation of the development of conjugated polymer structure might be expected. We chose the reduction with diimide (NH=NH) for the saturation of double bond. Thus, p-toluenesulfonyl hydrazide (PSH) was used which acts as a diimide source under the condition (130-150°C) of PVC-processing. 

Reduction reactions mediated by microorganisms may include the reduction of nitro bonds, sulfoxide reduction, and reductive dehalogenation. Reduction of the nitro group to amine involves the intermediate formation of nitrase and hydroxy amino groups. Selected reductive reactions may involve the saturation of double bonds, reduction of aldehydes to alcohols or ketones to secondary alcohols, or of certain metals. The main reductive processes in the subsurface environment have been discussed earlier in this chapter. 

Saturation of double bonds can also be achieved by catalytic transfer of hydrogen [74, 76], Styrene was quantitatively reduced to ethylbenzene by 1,4-cyclohexadiene in the presence of iodine under ultraviolet irradiation [76], and /ru j-stilbene to 1,2-diphenylethane in 90% yield by refluxing for 46 hours with cyclohexene in the presence of palladium on charcoal [74],... 

Most of the functional groups obtained in this work have very high absorption coefficients comparatively with the parent functions and this technique can also be usefull to improve their detection in polymer matrix. From this point of view, reactions as saturation of double bonds or oxidation of NH group into nitroxyl radical can allow to follow these groups in situ along typical reactions as the ageing. 

It is not known whether hydrogenation in the presence of catalyst (see Support Protocol) causes side reactions other than the saturation of double bonds. Therefore, this method should only be used if the accurate quantitation of lipid classes cannot be achieved using the Basic Protocol or Alternate Protocol. 

Of more interest than the saturation of double bonds is the hydrodimerization reaction (Chapter 21) sodium amalgam hydrodimerizations of a, -unsaturated ketones were reported early [28], and the product distribution resembled that obtained from direct electrolytic reduction (Chap. 10). 

The P-2 Ni(B) is an effective catalyst for the saturation of double bonds.68> With this catalyst, terminal alkenes are hydrogenated with greater than 95% selectivity in the presence of di- and tri-substituted olefins in ethanol solution at room temperature and atmospheric pressure.69 Solvent Effect... 

When aqueous solutions (buffered or unbuffered) are used (and their pH adjusted to a desired process), electrolytic reactions afford hydrogenations at cathodes and oxidations of the diverse functional groups at anodes. In other words, cathodic saturation of double bonds or carbonyl groups is, in principle, achievable under these conditions, while alcohols are anod-ically transformed into ketones or acids. Additionally, catalytic hydrogenations can also be performed in acidic electrolytes at... 

Out-of-cage reaction leading to the saturation of double bonds (b). Competitively to photo-Fries rearrangement, some -CH2-R radicals formed by direct 0-CH2 scission may add to the double bonds provoking the loss of conjugation. It is indeed well know that radicals can directly add on unsaturations [32]. 

Finally, an example using baker s yeast as the catalyst for the hydrogenation of butenoate shows that in the case of carboxylic acids yeast may also mediate the saturation of double bonds. The products of these reactions are used as key intermediates for the synthesis of optically pure l- or D-armcntomycin79. 

Transfer hydrogenation. Saturation of double bonds in the presence of Pd/C shows selectivity correlating with steric hindrance. Semihydrogenation of alkynes with this system is reported. 

Since the process of saturation of double bonds is not usually carried to completion, as already pointed out earlier, the control of the process to produce specific hydrogenated oil stocks is relatively complex. There are three main aspects which require consideration (1) selection of process conditions, (2) hydrogenation end point control, and (3) hydrogenation selectivity and isomer formation during the process. 

Atactic 1,4-polybutadiene and syndiotactic 1,2-polybutadiene can be hydrogenated at 100°C and 50 bar pressure of hydrogen with a soluble catalyst [(Ph)3-P]3RhQ[. Complete saturation of double bonds results [52]. Butadiene aciylMiitrile copolymers can also be hydrogenated quantitatively with... 

A specific application of biphasic hydrogenations is the saturation of double bonds in biological membranes (104,105). The membranes within or arovmd the cells and organelles contain a large proportion of polar lipids, providing the bilayer structure. The fluidity of these membranes is largely determined by the... 

The main purpose of hydrogenation is bleaching and increasing the stability of HRs [186]. The process aims the saturation of double bonds that are easily oxi-dizable and possess chromophoric properties. 

Z. Combos, K. Barabas, F. Job and L. Vigh Lipid saturation induced microviscosity increase has no effect on the reducibility of flash-oxidized Cytochrome in pea thylakoids. Plant.Physiol. (1988) 335-337 B. Szalontai, M. Droppa, L. Vigh, F. Job, and G. Horvath Selectivity of homogeneous catalytic hydrogenation in saturation of double bonds of lipids in chloroplast lamellae, Photobiochem.Photobiophys. (1986) 233-240... 

We have carried out a series of experiments In which the lipid composition of the photosynthetic membrane has been altered by the homogeneous catalytic hydrogenation of the unsaturated fatty acid residues of membrane lipids. Ordering state of lipids was not a linear function of the degree of unsaturation. Decrease of the double bonds beyond about 75% resulted only In a measurable Increase of the orientational order. Progressive saturation of double bonds primarily Inhibited electron transport between the photosystems, followed by the Inhibition of electron flow around PS II. Our results underlined the functional Importance of the presence of polyunsaturated fatty acyl chains, but the hypothesis, that the level of mlcrovlscoslty in the hydrophobic core regulates the electron flow via controlling the rate of diffusion of mobile electron carriers has not been confirmed experimentally. 

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