Tetraline, autoxidation

Tetralyl hydroperoxide was isolated as the product of tetralin autoxidation... 

Two very curious but heretofore unexplained phenomena relate to the interaction of reduced polyoxometalates with O2 and are addressed by our experiments described right below. The first involves the lack of oxygenated products seen in the photochemical functionalization of heptacyclotetradecane (HCTD) in the presence of O2 by Christina Prosser-McCartha. The second involves two observations by Neumann and Levin, namely, the suppression of tetralin autoxidation and the clean conversion of a-terpinene to p-cymene in the presence of O2 without formation of oxygenated products. 

The rate of tetralin autoxidation in the aqueous colloid is not dramatically higher than it is in aqueous solution. The increased rate can be explained simply by the ability of the styrene-acrylate and styrene-methacrylate copolymers to absorb tetralin, increasing the reactant concentration near the catalytic sites. The exact environment at the active sites is iDcely important to catalytic activity, since latexes with the same copolymer composition had different activities, but the contribution of surface composition has not been explored systematically yet. 

Aqueous dispersions of charged copolymer latexes are active supports of cobalt catalysts for autoxidations of tetralin by cobalt-pyridine complexes and of 2,6-di-rm-butylphenol and 1-decanethiol by CoPcTs. Since these reactants are insoluble in water, a simple explanation of the catalytic activity is that the organic polymer serves to solubilize the reactants in the phase that contains the cobalt catalyst. All three reactions have initial rates that are independent of substrate concentration, as determined by absorption of dioxygen from a gas buret. All three reactions appear to proceed by different mechanisms. Tetralin autoxidation is a free radical chain process promoted by the CoPy complex, whereas the CoPcTs reactions are not free radical chain processes. The thiol autoxidation is reported to involve hydrogen peroxide, whereas the 2,6-di-re/t-butylphenol autoxidation apparently does not. 

Fig. 3. Chemiluminescence of Tetralin Autoxidation (after Mendenhall and Nathan [6]).

Autoxidation may in some cases be of preparative use thus reference has already been made to the large-scale production of phenol+ acetone by the acid-catalysed rearrangement of the hydroperoxide from 2-phenylpropane (cumene, p. 128). Another example involves the hydroperoxide (94) obtained by the air oxidation at 70° of tetrahydro-naphthalene (tetralin) the action of base then yields the ketone (a-tetralone, 95), and reductive fission of the 0—0 linkage the alcohol (a-tetralol, 96) ... 

Recent detailed studies on autoxidation reactions have been published for tetralin 44-46) cumene and ethylbenzene 46,47) methyl oleate 48,49) and benzaldehyde 50h... 

Aryl phosphites inhibit the initiated oxidation of hydrocarbons and polymers by breaking chains on the reaction with peroxyl radicals (see Table 17.3). The low values of the inhibition coefficient / for aryl phosphites are explained by their capacity for chain autoxidation [14]. Quantitative investigations of the inhibited oxidation of tetralin and cumene at 338 K showed that with increasing concentration of phosphite /rises tending to 1 [27]. 

Table III. Collected Rate Constants (in Mole"1 sec."1) for Autoxidation of Cumene and Tetralin...

Table IV. Effect of Tetralin Hydroperoxide on Autoxidation of Cumene at 30°C.

Figure 1. Effect of Tetralin hydroperoxide on autoxidation of cumene at 30°C.

Table V. Effect of Cumene Hydroperoxide on Autoxidation of Tetralin at 30°C.

This difficulty has now been overcome. Howard, Schwalm, and Ingold (24) show that the rate constant for reaction of any alkylperoxy radical with any hydrocarbon can be determined (by the sector method) by carrying out the autoxidation of the hydrocarbon in the presence of >0.1 M hydroperoxide corresponding to the chosen radical. All the absolute propagation and termination constants for the co-oxidation of cumene and Tetralin were thus determined. Our Tetralin-cumene work suggests that their results agree well with the best we have been able to get... 

The present paper reports the results of a kinetic study of the inhibition of the azobisisobutyronitrile-initiated autoxidation of cumene at 60 °C. and of Tetralin at 70 °C. by zinc diisopropyl dithiophosphate, undertaken to test the validity of the chain-breaking inhibition mechanism proposed above. In addition, the effectiveness of several metal dialkyl dithiophosphates as antioxidants in the autoxidation of squalane... 

From these results, it is clear that neither Equation A nor B represents the kinetics of the zinc diisopropyl dithiophosphate-inhibited autoxi-dation of cumene or Tetralin. This does not immediately indicate that the mechanism in Scheme 1 is wrong since it is highly idealized and takes no account of possible side reactions. A similar situation occurs in the inhibition of hydrocarbon autoxidation by phenols (AH), for which a basic mechanism similar to that in Scheme 1 is accepted. Termination occurs via Reactions 7 and 8 instead of Reactions 5 and 6. 

When a slow steady-state autoxidation of a suitable hydrocarbon is disturbed by adding either a small amount of inhibitor or initiatory a new stationary state is established in a short time. The change in velocity during the non-steady state can be followed with sensitive manometric apparatus. With the aid of integrated equations describing the nonsteady state the individual rate constants of the autoxidation reaction can be derived from the results. Scope and limitations of this method are discussed. Results obtained for cumene, cyclohexene, and Tetralin agree with literature data. 

Hydrocarbon Concentration. The steady rate of hydrocarbon oxidation is exactly first order with respect to hydrocarbon concentration, but it tends to be independent of this concentration below l.OAf (Figure 4). The cobalt-catalyzed autoxidation of Tetralin (6) and ethylbenzene at 0.05M cobalt in the absence of bromide is exactly second order with respect to hydrocarbon concentration. 

Similarly, cobalt(ll)-pyridine (CoPy) complexes bound to copolymers of styrene and acrylic or methacrylic acid, cross-linked with divinylbenzene, catalyze the autoxidation of tetralin dispersed in water at 50°C and 1 bar.45 The rate of oxidation with the colloidal CoPy catalyst was twice as fast as with homogeneous CoPy and nine times as fast as with cobalt(II) acetate in acetic acid. 

In recent years much emphasis has been placed on studies of co-oxidations, since they can provide quantitative data about fundamental processes (such as the relative reactivities of peroxy radicals toward various hydrocarbons48-50), which are difficult to obtain by other methods. Co-oxidations are also quite important from a practical viewpoint since it is possible to utilize the alkylperoxy intermediates for additional oxidation processes instead of wasting this active oxygen. That the addition of a second substrate to an autoxidation reaction can produce dramatic effects is illustrated by Russell s observation51 that the presence of 3 mole % of tetralin reduced the rate of cumene oxidation by two-thirds, despite the fact that tetralin itself is oxidized 10 times faster than cumene. The retardation is due to the higher rate of termination of the secondary tetralyl-peroxy radicals compared to the tertiary cumylperoxy radicals (see above). 

Small but significant effects of solvent polarity were found in the autoxidation of a variety of alkenes and aralkyl hydrocarbons [216-220] (styrene [216, 218, 219], ethyl methyl ketone [217], cyclohexene [218], cumene [218, 219], tetralin [219], etc.). An extensive study on solvent effects in the azobisisobutyronitrile (AIBN)-initiated oxidation of tetralin in a great variety of solvents and binary solvent mixtures was made by Kamiya et al. [220],... 

Peroxidase catalyzed the oxidative polymerization of fluorinated phenols to give fluorine-containing polymers.46 During the polymerization, elimination of fluorine atom partly took place to give the polymer with a complicated structure. Antioxidant effects of the enzymatically synthesized polyphenols were evaluated.47 The autoxidation of tetralin was significantly suppressed in the presence of the polyphenols. 

The reactions of phosphites with peroxy radicals continue to attract attention because of the use of phosphites as anti-oxidants. The autoxidation of a variety of hydrocarbons, e.g. tetralin, cumene, styrene, and cyclohexane, is inhibited by zinc dialkyldithiophosphates (60). In order to assess the reactivity... 

If there is a CH2 or a CH group in a-position to an aromatic system, it is attacked preferentially by oxygen with formation of a substituted benzyl hydroperoxide, 317 examples being tetralin, ind ne, fluorene, cumene, p-xylene, and ethylbenzene. Temperatures required for autoxidation of such compounds are lower than for alkanes. 

Autoxidation of ethers is very important since the peroxides formed are often the cause of violent explosions for details see Rieche s review.328 Peroxide-containing ethers, particularly diethyl ether, tetrahydrofuran, diisopropyl ether, and dioxan are sources of great danger since violent explosions can result on distillation. Moreover, petrol, light petroleum, decalin, xylene, cumene, and tetralin may all also contain peroxides. 

Isopropylbenzene peroxide is a liquid comparatively stable to heat, decomposition beginning to ser in at 165-175°C. The following peroxides also are described p-menthane-hydroperoxide, diphenyl-methane-hydroperoxide, autoxidation of indene, and cleavage of tetralin-peroxide. ... 

Thus, 1 seems to be a true catalyst rather then a new kind of free radical initiator. This behavior is in contrast to the behavior of related manganese complexes. For example, Mn(II) carboxylates are known to decompose CHP during autoxidation of cumene l dinuclear Mn(III) complexes decompose tetralin hydroperoxide during oxidation of tetralin (an inner-sphere Mn-alkyl hydroperoxide intermediate has been proposed) trinuclear, carboxylate and oxo-bridged complexes containing Mn(II) were found to decompose CHP during the catalyzed oxidation of cumene. 

The known examples of catalytic oxygenations involve substrates that undergo relatively facile autoxidation to hydroperoxides often even without an added catalyst. For example tetraline is converted to a-tetralone in the presence of ClFeTPP at 25 °C [96]. CoTTP catalyzes the oxidation of 2,5-dihydrofuran to 2-hydrofuran-5-one and 2-hydrofuran-5-ol in ethyl acetate at 30 C [97]. Furan and 2,3-dihydrofuran were also oxidized but the products were not determined. Tetraline and cumene did not react. The kinetics of autoxidation were interpreted in terms of chain initiation by the dioxygen adduct of CoTTP ... 

Autoxidation of Tetralin. The interfacial technique has also been applied to foe autoxidation of tetralin (Lim et al, submitted to J, Phys, Chem,). The reaction is... 

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