Hydrocarbon chain oxidation

The traditional chain oxidation with chain propagation via the reaction RO/ + RH occurs at a sufficiently elevated temperature when chain propagation is more rapid than chain termination (see earlier discussion). The main molecular product of this reaction is hydroperoxide. When tertiary peroxyl radicals react more rapidly in the reaction R02 + R02 with formation of alkoxyl radicals than in the reaction R02 + RH, the mechanism of oxidation changes. Alkoxyl radicals are very reactive. They react with parent hydrocarbon and alcohols formed as primary products of hydrocarbon chain oxidation. As we see, alkoxyl radicals decompose with production of carbonyl compounds. The activation energy of their decomposition is higher than the reaction with hydrocarbons (see earlier discussion). As a result, heating of the system leads to conditions when the alkoxyl radical decomposition occurs more rapidly than the abstraction of the hydrogen atom from the hydrocarbon. The new chain mechanism of the hydrocarbon oxidation occurs under such conditions, with chain... 

Oxidation of carbon side-chains has resulted in the synthesis of dithiazolyl ketone (82) and thiazolyl phenyl ketone (83). The hydrocarbon chain can also be dehydrogenated in acetic acid in the presence of... 

The basic flow sheet for the flotation-concentration of nonsulfide minerals is essentially the same as that for treating sulfides but the family of reagents used is different. The reagents utilized for nonsulfide mineral concentrations by flotation are usually fatty acids or their salts (RCOOH, RCOOM), sulfonates (RSO M), sulfates (RSO M), where M is usually Na or K, and R represents a linear, branched, or cycHc hydrocarbon chain and amines [R2N(R)3]A where R and R are hydrocarbon chains and A is an anion such as Cl or Br . Collectors for most nonsulfides can be selected on the basis of their isoelectric points. Thus at pH > pH p cationic surfactants are suitable collectors whereas at lower pH values anion-type collectors are selected as illustrated in Figure 10 (28). Figure 13 shows an iron ore flotation flow sheet as a representative of high volume oxide flotation practice. 

Stmctures with the widest temperature range of demonstrated stabiUty have fluorine in the gamma position relative to siUcon (or further removed), as in CF2CH2CH2SiIlR R. Longer hydrocarbon chains, with or without hetero atoms, are feasible, but oxidative stabiUty is compromised and such materials are generally disfavored. Poly(3,3,3-trifluoropropyl)methylsiloxane [26702-40-9] demonstrates this stmctural principle. This polymer is one key member of the industrially important family of fluorosiUcone materials. 

Phosphorus—Carbon Bond. The P—C bond is 0.184—0.194-nm long and has an energy of ca 272 kj/mol (65 kcal/mol). It is one of the more stable bonds formed by phosphoms, resistant to both hydrolysis and oxidation (7,8). Unlike the phosphoms—halogen or phosphoms—oxygen bonds, the P—C linkage is inert to exchange. A phosphoms atom connected to carbon behaves similarly to another carbon atom in a hydrocarbon chain. 

Free-radical chain inhibitors are of considerable economic importance. The term antioxidant is commonly appUed to inhibitors that retard the free-radical chain oxidations, termed autoxidations, that can cause relatively rapid deterioration of many commercial materials derived from organic molecules, including foodstuffs, petroleum products, and plastics. The chain mechanism for autoxidation of hydrocarbons is ... 

Whereas catabolism is fundamentally an oxidative process, anabolism is, by its contrasting nature, reductive. The biosynthesis of the complex constituents of the cell begins at the level of intermediates derived from the degradative pathways of catabolism or, less commonly, biosynthesis begins with oxidized substances available in the inanimate environment, such as carbon dioxide. When the hydrocarbon chains of fatty acids are assembled from acetyl-CoA units, activated hydrogens are needed to reduce the carbonyl (C=0) carbon of acetyl-CoA into a —CHg— at every other position along the chain. When glucose is... 

Attempts to achieve selective oxidations of hydrocarbons or other compounds when the desired site of attack is remote from an activating functional group are faced with several difficulties. With powerful transition-metal oxidants, the initial oxidation products are almost always more susceptible to oxidation than the starting material. When a hydrocarbon is oxidized, it is likely to be oxidized to a carboxylic acid, with chain cleavage by successive oxidation of alcohol and carbonyl intermediates. There are a few circumstances under which oxidations of hydrocarbons can be synthetically useful processes. One group involves catalytic industrial processes. Much effort has been expended on the development of selective catalytic oxidation processes and several have economic importance. We focus on several reactions that are used on a laboratory scale. 

A similar mechanism of chain oxidation of olefinic hydrocarbons was observed experimentally by Bolland and Gee [53] in 1946 after a detailed study of the kinetics of the oxidation of nonsaturated compounds. Miller and Mayo [54] studied the oxidation of styrene and found that this reaction is in essence the chain copolymerization of styrene and dioxygen with production of polymeric peroxide. Rust [55] observed dihydroperoxide formation in his study of the oxidation of branched aliphatic hydrocarbons and treated this fact as the result of intramolecular isomerization of peroxyl radicals. 

Chain oxidation of hydrocarbons occurs by the following elementary steps [2,3,10-15] ... 

Mechanism III. When the temperature is sufficiently high for the prompt decomposition of the alkoxyl radical, the chain oxidation of the hydrocarbon in the gas phase includes the following steps ... 

Ozone initiates the chain oxidation of hydrocarbons in the gas [117] and the liquid phases [118]. 

In the oxidized hydrocarbon, hydroperoxides break down via three routes. First, they undergo homolytic reactions with the hydrocarbon and the products of its oxidation to form free radicals. When the oxidation of RH is chain-like, these reactions do not decrease [ROOH]. Second, the hydroperoxides interact with the radicals R , RO , and R02. In this case, ROOH is consumed by a chain mechanism. Third, hydroperoxides can heterolytically react with the products of hydrocarbon oxidation. Let us consider two of the most typical kinetic schemes of the hydroperoxide behavior in the oxidized hydrocarbon. The description of 17 different schemes of chain oxidation with different mechanisms of chain termination and intermediate product decomposition can be found in a monograph by Emanuel et al. [3]. 

In the later stages, the oxidation of hydrocarbons is often self-inhibited due to the accumulation of such oxidation products that retard chain oxidation. Each hydrocarbon has the individual peculiarities of oxidation including the mechanism of self-inhibition. A few of such main peculiarities will be mentioned here [3,56]. 

The chain mechanism is complicated when two hydrocarbons are oxidized simultaneously. Russell and Williamson [1,2] performed the first experiments on the co-oxidation of hydrocarbons with ethers. The theory of these reactions is close to that for the reaction of free radical copolymerization [3] and was developed by several researchers [4-9], When one hydrocarbon R H is oxidized in the liquid phase at a sufficiently high dioxygen pressure chain propagation is limited only by one reaction, namely, R OO + R H. For the co-oxidation of two hydrocarbons R1 and R2H, four propagation reactions are important, viz,... 

Catalysis by nitroxyl radicals in hydrocarbon oxidation was discovered and studied recently [82-89], The introduction of /V-hydroxyphthalimide into oxidized alkylaromatic hydrocarbon was found to accelerate the oxidation. The formation of the stable phthalimide-/V-oxyl (PINO) radical was evidenced by the EPR method [90]. The following kinetic scheme was put forward to explain the accelerating effect of PINO on the chain oxidation of hydrocarbons [82-84]. 

Alcohols, like hydrocarbons, are oxidized by the chain mechanism. The composition of the molecular products of oxidation indicates that oxidation involves first the alcohol group and the neighboring C—H bond. This bond is broken more readily than the C—H bond of the corresponding hydrocarbon, since the unpaired electron of the formed hydroxyalkyl radical interacts with the p electrons of the oxygen atom. 

---