Oxidisable unsaturation

Potassium permanganate (KMn04) oxidises unsaturated secondary alcohols at the point of unsaturation. However, KMn04 supported on bentonite clay oxidises the hydroxyl group in preference to the alkene (e.g. equation 4.26) [122]. Unsaturated primary alcohols give virtually no reaction and allylic alcohols are oxidised much more readily than non-allylic ones. 

It has been shown that Hpid hydroperoxides are easily decomposed to form free radicals that accelerate autoxidation reaction. Hydroperoxides can also oxidise unsaturated fatty acids by nonradical mechanisms, as mentioned in the secondary reaction of oxidised Kpids. Also, hydrogen peroxide, which arises naturally in... 

Typical solvent based resins used for this type of coating are alkyd resins, which contain oxidisable unsaturation. During the drying process, the solvent evaporates and the unsaturation oxidises using atmospheric oxygen to cure and crosslink the film. This leads to solvent insolubility, film integrity and durability. 

Oxidation, (a) Unsaturation test. Dissolve about o-i g. of cinnamic acid or of a soluble cinnamate in about 5 ml. of 10% NajCOg solution. To the cold solution add 1% aqueous KMn04 drop by drop. Immediate decolorisation denotes unsaturation. (Note. Many easily oxidisable substances, e.g.y formic acid, acetaldehyde, etc.y also rapidly decolorise alkaline permanganate. Cinnamates, however, do not reduce Fehling s solution.)... 

Styrene undergoes many reactions of an unsaturated compound, such as addition, and of an aromatic compound, such as substitution (2,8). It reacts with various oxidising agents to form styrene oxide, ben2aldehyde, benzoic acid, and other oxygenated compounds. It reacts with benzene on an acidic catalyst to form diphenylethane. Further dehydrogenation of styrene to phenylacetylene is unfavorable even at the high temperature of 600°C, but a concentration of about 50 ppm of phenylacetylene is usually seen in the commercial styrene product. 

Exhaustive Methylation. As in the lobeline group it is the diketo-bases, lelobanines (p. 30) in the lelobine series and lobinanines (p. 31) in the lobinine group, which give methiodides amenable to this mode of degradation. They are decomposed by alkali yielding an unsaturated neutral oil, which is hydrogenated and then, if necessary, oxidised to the saturated open chain diketone, e.g., see under lelobanine. 

Chromic acid adsorbed on silica gel (Cr03 Si02 = 3 10) is a mild and safe reagent to oxidise saturated or unsaturated alcohols in carbon tetrachloride to the corresponding aldehydes. 

Cholesterol C27H45OH, an unsaturated secondary alcohol, contains the same ring system as the bile acids and is closely related to them genetically. Pseudocholestane, indeed, which is a stereoisomer of the parent hydrocarbon of cholesterol, cholestane, can be oxidised to cholanic acid by chromic acid with elimination of acetone (Windaus). 

The oxidation of alcohols to carbonyl compounds has been studied by several authors and a variety of methods have been used. Papers concerned vith such oxidations are illustrated (Scheme 3.26). Good results have been obtained using pyridinium chlor-ochromate (PCC) adsorbed onto silica gel for the selective oxidation of unsaturated substrates e.g. terpene [135] and furanyl derivatives [136]. Steroidal homoallylic alcohols can be converted to the corresponding 4-ene-3,6-diones using tetrapropylammo-nium per-ruthenate (TPAP) in catalytic amounts [137]. In this case, the oxidising agent is N-methyl morpholine N-oxide (NMO). 

Each turn of the P-oxidation spiral splits off a molecule of acetyl-CoA. The process involves four enzymes catalysing, in turn, an oxidation (to form a double bond), a hydration, another oxidation (forming a ketone from a secondary alcohol) and the transfer of an acetyl group to coenzyme A (Figure 7.12). The process of P-oxidation operates as a multienzyme complex in which the intermediates are passed from one enzyme to the next, i.e. there are no free intermediates. The number of molecules of ATP generated from the oxidation of one molecule of the long-chain fatty acid pal-mitate (C18) is given in Table 7.4. Unsaturated fatty acids are also oxidised by the P-oxidation process but require modification before they enter the process (Appendix 7.3). 

Allylic P-unsaturated,alcohols (geraniol, 3-phenyl-2-propenol) were efficiently oxidised to the aldehydes by fran.y-Ru(0)2(TMP)/(lutidine-iV-oxide)/CgHg [586]. As fran.y-Ru(0)2(TMP)/(Cl2pyN0)/CgHy24h it oxidised cyclohexanol to cyclohexanone [587]. 

RuCl/TMP), as RuCl2(TMP)/(Cl2pyNO)/CDCl3, oxidised alkenes RCHj=CH to the aldehydes RCH CHO. Oxidation of 1,3-dienes gave the unsaturated aldehyde -thus 1-phenyl-l,3-butadiene gave the p, y-unsaturated aldehyde 4-phenylbut-3-enal (styrylacetaldehyde) RuClj(TDCPP) also effected these reactions [584],... 

RuCl2(TDCPP) as RuClj(TDCPP)/(CljpyNO)/CDCl3 oxidised terminal alkenes RCH3=CH to the aldehydes RCH CHO 1,3-dienes gave the unsaturated aldehydes RuCljtTMP) was also effective as a catalyst [584]. 

---