Hydroperoxides as initiators

PBMA with PMMA 255.257 PF. with PMAN 257 PMAN with PS- 257 cumene hydroperoxide, as initiator 92 cumy I dilhiobcrzoulc see ditliioberzome R A FT agents... 

Mo containing Y zeolites were also tested for cyclohexene oxidation with oxygen as oxidant and t-butyl hydroperoxide as initiator [86]. In this case the selectivity for cyclohexene oxide was maximum 50%, 2-cyclohexene-l-ol and 2-cyclohexene-l-one being the main side products. The proposed reaction scheme involves a free radical chain mechanism with intermediate formation of cyclohexenyl hydroperoxide. Coordination of the hydroperoxide to Mo + in the zeolite and oxygen transfer from the resulting complex to cyclohexene is believed to be the major step for formation of cyclohexene oxide under these conditions. 

Materials. Poly (olefin sulfone)s were prepared by copolymerization of liquid mixtures of sulfur dioxide and the appropriate olefin using tert.-butyl hydroperoxide as initiator in the temperature range from —80 to 0°C. The poly (amino acid)s were obtained from Sigma Chemical Co. and used without further purification. The poly (olefin) s were provided by Mr. O. Delatycki and Dr. T. N. Bowmer and were prepared under controlled conditions. The aromatic polysulfones were prepared and purified by Mr. J. Hedrick. The purity of all polymers was checked by H and 13C NMR. 

Peroxide end groups can also be formed by polymerization of a monomer in the presence of ferf-butyl hydroperoxide as initiator and small quantities of a copper-II salt, e. g. copper octoate 128). The reaction scheme is ... 

Oil-acrylate hybrid-emulsions were formed using the fatty-acid hydroperoxides as initiator system for the miniemulsion polymerization of acrylate. The initiation took place at the droplet interface and resulted in the formation of triglycide modified polyacrylate molecules which act as compatibili-... 

Heterogeneous, radically initiated, sulphochlorination at 15 °C of low, medium and high density compression molded PE films, using SOjCl/Cl in CCl with methylethyl ketone hydroperoxide as initiator, yields copolymers that contain blocks of pure PE and blocks of sulphochlorinated-PE. 

Another example is the polymerization of acrylic acid in supercritical carbon dioxide (20 wt %) with t-butyl hydroperoxide as initiator [24]. The effect of initiator concentration (2 to 6%), temperature (160 to 350 °C) and pressure (185 to 320 bar) have been reported. The polymerization was conducted at 250 °C and 310 bar. Contrary to conventional free radical polymerizations, in these polymerizations, it is reported that the initiator amount does not influence the molecular weight, even though in the absence of the initiator polymerization would not proceed. No explanation for this observation has been provided. Also, at a given temperature, molecular weight was found to decrease with pressure. For example, at 160 °C weight average molecular weight decreased from about 80,000 to 45,000 upon increase of the pressure from 185 to 250 bar while polydispersity was reduced from about 10 to 7. This behavior is somewhat similar to the... 

Also obtained (poor yield) by oxidation of 2-tert-butyl-4-ethyl-6-methylphenol. The oxidation was carried out by bubbling air at 80-100° into a solution of 2-tert-butyl-4-ethyl-6-methylphenol in cumene containing cobalt phthalate and cumene hydroperoxide as initiator (4%) [3486],... 

Hydroperoxides are more widely used as initiators in low temperature appHcations (at or below room temperature) where transition-metal (M) salts are employed as activators. The activation reaction involves electron-transfer (redox) mechanisms ... 

Thermally induced homolytic decomposition of peroxides and hydroperoxides to free radicals (eqs. 2—4) increases the rate of oxidation. Decomposition to nonradical species removes hydroperoxides as potential sources of oxidation initiators. Most peroxide decomposers are derived from divalent sulfur and trivalent phosphoms. 

Many types of peroxides (R-O-O-R) are known. Those in common use as initiators include diacyl peroxides (36), pcroxydicarbonatcs (37), peroxyesters (38), dialkyl peroxides (39), hydroperoxides (40), and inorganic peroxides [e.g. persulfate (41)1, Multifunctional and polymeric initiators with peroxide linkages are discussed in Sections 3.3.3 and 6.3.2.1. 

The common initiators of this class are f-alkyl derivatives, for example, t-butyl hydroperoxide (59), Aamyl hydroperoxide (60), cumene hydroperoxide (61), and a range of peroxyketals (62). Hydroperoxides formed by hydrocarbon autoxidation have also been used as initiators of polymerization. 

Methyl methacrylate can also be polymerized by radiation using either a cobalt-60 source or accelerated electrons at dose rates up to 3 megarads/sec. The activation energy for the electron beam polymerization is about 7.0kcal/ mole (Ref 12). Radical polymerization can also occur using diisocyanates or hydroperoxides as the initiating species (Ref 15)... 

Under certain conditions the hydroperoxide (90) itself breaks down to radicals, RO + OH which can act as initiators, and the autoxida-... 

Kinetics based on the idea of spreading is formally based on the model of development of an infectious disease among human population [59,60]. The formalism of chemical kinetics, however, should be treated with a care as a similar equation can be derived from the homogeneous model assuming bimolecular decomposition of hydroperoxides as an initiating event. 

G. Geuskens, D. Baeyens Volant, G. Delaunois, Q. Lu Vinh, W. Piret, and C. David, Photo oxidation of Polymers II. The Sensitized Decomposition of Hydroperoxides as the Main Path for Initiation of the Photo oxidation of Polystyrene Irradiated at 253.7 nm, Eur. Polym. J., 14, 299 303 (1978). 

The experiments on emulsion cumene oxidation with AIBN as initiator proved that oxidation proceeds via the chain mechanism inside hydrocarbon drops [17]. The presence of an aqueous phase and surfactants compounds does not change the rate constants of chain propagation and termination the ratio (fcp(2fct)-1/2 = const in homogeneous and emulsion oxidation (see Chapter 2). Experiments on emulsion cumene oxidation with cumyl hydroperoxide as the single initiator evidenced that the main reason for acceleration of emulsion oxidation versus homogeneous oxidation is the rapid decomposition of hydroperoxide on the surface of the hydrocarbon and water drops. Therefore, the increase in the aqueous phase and introduction of surfactants accelerate cumene oxidation. 

Compounds of transition metals (Mn, Cu, Fe, Co, Ce) are well known as catalysts for the oxidation of hydrocarbons and aldehydes (see Chapter 10). They accelerate oxidation by destroying hydroperoxides and initiating the formation of free radicals. Salts and complexes containing transition metals in a lower-valence state react rapidly with peroxyl radicals and so when these compounds are added to a hydrocarbon prior to its oxidation an induction period arises [48]. Chain termination occurs stoichiometrically (f 1) and stops when the metal passes to a higher-valence state due to oxidation. On the addition of an initiator or hydroperoxide, the induction period disappears. 

Acidic products (S02, H2S04, RS02H, RS03H) break hydroperoxides into molecular products, thereby inhibiting autoinitiation. At the same time, they act as initiators by breaking hydroperoxide with the formation of free radicals. 

Invented in Germany during World War II by H. Hock and S. Lang in the course of developing cumene hydroperoxide for initiating the polymerization of butadiene-styrene mixtures. After the war the process was developed by the Distillers Company in England and Allied Chemical Corporation in the United States. Since 1954 this has been the main commercial process for the production of phenol and acetone. By 1987, 97 percent of the phenol made in the United States was produced via this route. In 1990, both resorcinol and hydro-quinone were produced commercially by this route as well. See also Cumox. 

Olefin epoxidation is an important industrial domain. The general approach of SOMC in this large area was to understand better the elementary steps of this reaction catalyzed by silica-supported titanium complexes, to identify precisely reaction intermediates and to explain catalyst deachvahon and titanium lixiviation that take place in the industrial Shell SMPO (styrene monomer propylene oxide) process [73]. (=SiO) Ti(OCap)4 (OCap=OR, OSiRs, OR R = hydrocarbyl) supported on MCM-41 have been evaluated as catalysts for 1-octene epoxidation by tert-butyl hydroperoxide (TBHP). Initial activity, selechvity and chemical evolution have been followed. In all cases the major product is 1,2-epoxyoctane, the diol corresponding to hydrolysis never being detected. 

Also among the oxidants that add oxygen at carbon-carbon double bonds is singlet oxygen.121 For most alkenes, this reaction proceeds with the specific removal of an allylic hydrogen and shift of the double bond to provide an allylic hydroperoxide as the initial product. 

Epoxidation of olefins over Mo containing Y zeolites was studied by Lunsford et al. [86-90]. Molybdenum introduced in ultrastable Y zeolite through reaction with Mo(C0)g or M0CI5, shows a high initial activity for epoxidation of propylene with t-butyl hydroperoxide as oxidant and 1,2-dichloroethane as solvent [88]. The reaction is proposed to proceed via the formation of a Mo +-t-butyl hydroperoxide complex and subsequent oxygen transfer from the complex to propylene. The catalyst suffers however from fast deactivation caused by intrazeolitic polymerization of propylene oxide and resulting blocking of the active sites. 

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