Ether autooxidation

A -dien-3-ol ethers gives rise to 6-substituted A" -3-ketones. 6-Hydroxy-A" -3-ketones can be obtained also by autooxidation.Structural changes in the steroid molecule may strongly affect the stability of 3-alkyl-A -ethers. Thus 11 j5-hydroxyl and 9a-fluorine substituents greatly increase the lability of the enol ether/ while halogens at C-6 stabilize this system to autooxidation and acid hydrolysis. 

Vinylidene Chloride CH2=CC12. Monomer forms unstable peroxides by autooxidation therefore, no oxidg agents or w Air Vap Monomer In Air 7.0 to 16.0% > Ambient > Ambient Inhibitor—Methyl Ether of Hy droquino ne (100 ppm) Transport store under. inert gas in a cool, dry place. No sparks -18.0 570 Self-polymerizing, easily copolymerizes with with Acrylates Styrene. Polymerization catalyzed by light or w... 

Most ethers react slowly with oxygen by a radical process called autooxidation to form hydroperoxides and peroxides. 

The slow spontaneous oxidation of compounds in the presence of oxygen is termed autoxidation (autooxidation). This radical process is responsible for a variety of transformations, such as the drying of paints and varnishes, the development of rancidity in foodstuff fats and oils, the perishing of rabber, air oxidation of aldehydes to acids, and the formation of peroxides in ethers. 

A bottle that you thought contained pure diethyl ether actually has autooxidized to 10% diethyl ether hydroperoxide. What is the temperature if the contents of the bottle suddenly react to chemical equilibrium At what hydroperoxide concentration would the temperature not exceed 100°C Assume that the heat of decomposition of the hydroperoxide is 30 kcal/mole. 

At this stage it may be worth conjecturing as to why some calorimetric smdies of peroxides and hydroperoxides are seemingly unreliable. Recall that an ether that has been left standing too long autooxidizes to a peroxide, which then has a tendency to explode on heating or when shocked. In an experimental combustion process, this same tendency to explode may result in incomplete combustion with attendant carbon build-up. If so, there are thermodynamically ill-defined and irreproducible products that increase the variability and uncertainty in the measurements and essentially invalidate the results derived . 

Phenanthroline in the presence of heavy metals acts as an activator of the polymerization of vinyl compounds558,559 and other olefins.560-564 It also assists the dimerization of olefins in the presence of titanium catalysts.565,566 It enhances the metal catalyzed oxidation of ascorbic acid567 and dimethyl sulfoxide.568 On the other hand, on its own it can inhibit several polymerization processes.545,569 It also stabilizes butadiene and isoprene and prevents their dimerization.570 It prevents peroxide formation in ether,571 inhibits the vinylation of alcohol572 and stabilizes cumyl chloride.573 It accelerates the vulcanization of diene rubbers574 and copolymers.575 1,10-Phenanthroline catalyzes the autooxidation of linoleic and ascorbic acids in the absence of metals.567... 

Reactions that take place via radical intermediates are occasionally also begun by radical initiators, which are present unintentionally. Examples are the autooxidation of ethers (see later Figure 1.28) or one of the ways in which ozone is decomposed in the upper stratosphere. This decomposition is initiated by, among other things, the fluorochlorohydrocarbons (FCHCs), which have risen up there and form chlorine radicals under the influence of the short-wave UV light from the sun (Figure 1.10). They function as initiating radicals for the decomposition of ozone, which takes place via a radical chain. However, this does not involve a radical substitution reaction. 

Organic peroxo compounds are also obtained by autooxidation of ethers, unsaturated hydrocarbons, and other organic materials on exposure to air. A free-radical chain reaction is initiated almost certainly by radicals generated by the interaction of oxygen and traces of metals such as copper, cobalt, or iron. The attack on specific reactive C—H bonds by a radical X" gives first R, then hydroperoxides, which can react further ... 

Molecular oxygen can also oxidize a variety of organic compounds, including hydrocarbons, aldehydes, amines, ethers and ketones. These autooxidation reactions can be used to make a variety of small molecules and a number of industrial processes rely on the controlled oxidation of organics using molecular oxygen (often with a metal catalyst). Examples include the formation of phenol and acetone from cumene (isopropylbenzene) and cyclohexanone from cyclohexane. Phenol is a popular starting material for a number... 

Also potentially hazardous are compounds that undergo autooxidation to form organic hydroperoxides and/or peroxides when exposed to the oxygen in air (see Table 3.12). Especially dangerous are ether bottles that have evaporated to dryness. A peroxide present as a contaminant in a reagent or solvent can be very hazardous and change the course of a planned reaction. Autoxidation of organic materials (solvents and otho" liquids are most frequently of primary concern) proceeds by a free-radical chain mechanism. For the substrate R—H, the chain is initiated by ultraviolet... 

Uses food preservative antioxidant for foods (margarine, peanut butter, etc.), cosmetics and pharmaceutic creams, fats, oils, flavorings, ethers, emulsions, waxes, and transformer oils packaging material used to inhibit autooxidation of paraldehyde and similar substances that develop peroxides in the presence of oxygen A... 

FIGURE 1.14 (a) Structures of some commonly used peroxide-forming ethers, (b) Scheme for the autooxidative production of a peroxide, (c) The structure of a peroxide-resistant ether. 

Many organic compounds, such as ethers, are particularly susceptible to autooxidation. For example, consider the reaction between diethyl ether and oxygen to form a... 

Draw the propagation steps that achieve the autooxidation of diethyl ether to form a hydroperoxide ... 

Recall from Section 11.9 that ethers undergo autooxidation in the presence of atmospheric oxygen to form hydroperoxides ... 

Except at very low oxygen pressures, the first step [equation (5.185)] is, as usual, rate determining. The reaction is accelerated by E and — / substituents (e.g., aryl, methyl) but especially strongly by — substituents, in particular alkoxyl. Ethers therefore autooxidize very easily indeed, giving hydroperoxides, which are often dangerously explosive. Numerous explosions have occurred through the distillation of ethers from which the peroxides had not first been removed. Another example is chloroform, which autooxidizes rather easily to phosgene. 

Since phosgene is very toxic, a small amount of alcohol is usually added to chloroform to act as an inhibitor of the autooxidation. The easy oxidation of pure chloroform shows, incidentally, that the guiding principle in these cases is not one of simple nucleophilicity. Indeed, the hydrogen atom in chloroform is especially positive, due to the inductive effect of the three -h / chlorine atoms. Chloroform can consequently form hydrogen bonds with donors such as ethers and it also reacts easily with bases to form the CCI3 ion. 

As seen in Section 11.9, diethyl ether undergoes autooxidation to give the following hydroperoxide ... 

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