Peroxy compounds, detection

Methods for detecting whether peroxy compound have been used for cross-linking elastomers have been reviewed. An important application of dialkyl peroxides is as initiators of cross-linking and graft polymerization processes. The success of both processes depends on the ability of the peroxide to produce free radicals and the ability of the free radicals for H-abstraction from a relevant donor substrate. A method for evaluating this ability consists of inducing thermal decomposition of the peroxide dissolved in a mixture of cyclohexane and MSD (225). The free radical X" derived from the... 

Benzyl alcohol [100-51-6] M 107.2, f.p. -15.3°, b 205.5 , 93°/10mm, d 0.981, n 1.54033. Usually purified by careful fractional distn at reduced pressure in the absence of air. Benzaldehyde, if present, can be detected by UV absorption at 283nm. Also purified by shaking with aq KOH and extracting with peroxide-free ethyl ether. After washing with water, the extract was treated with satd NaHS sol, filtered, washed and dried with CaO and distd under reduced pressure [Mathews JACS 48 562 7926]. Peroxy compounds can be removed by shaking with a soln of Fe(II) followed by washing the alcohol layer with distd water and fractionally distd. 

To isolate acidic products which were not found by gas chromatographic analysis, the crude products were treated by ordinary methods, but only small amounts of viscous brownish red liquid products were obtained, and no adipic acid was isolated. Isolation of cyclohexene oxide was unsuccessful, however gas chromatographic analysis based on the two columns showed clearly the presence of cyclohexene oxide. Gaseous products included ethylene, 1,3-butadiene, carbon dioxide, and an unidentified C4 hydrocarbon in the ratio of 12 6 3 1. Trace amounts of other gaseous hydrocarbons were also detected, and any gaseous peroxy compound was not detected. These hydrocarbons were considered to be decomposition products of activated cyclohexene. 

Maura, G, Rinaldi, G. Detection of traces of transition metals by peroxy compounds and sorption on a chelating resin. Anal. Chim. Acta 53, 466 (1971)... 

When oxygen was bubbled through a boilhig solution of colupulone in an aqueous buffer solution (pH 5-5) cohulupone (44 R = Pr ) and four new products were isolated. These were the C3 -exo and -endo epimers of tricyclo-oxycolupulone (TCOC) (54) and tricyclo-peroxycolupulone (55). These compounds, which are not bitter, accounted for 80% of the p-acid. The peroxy compounds (55) were formed first and the alcohols (54) on further heating but neither is very soluble. They were not detected in beer [44]. 

The following tests can detect most (but not all) peroxy compounds, including all hydroperoxides ... 

Kharash and coworkers first proposed a hydroperoxysulphide intermediate in the formation of jS-sulphinyl alcohols in the co-oxidation of thiols with olefins. This was later confirmed by detection of peroxy compounds in the reaction mixture. Further studies led to the isolation of several hydroperoxysulphides when aromatic thiols were oxidized at low temperatures ""... 

As peroxy compounds differ from one another in solubility, it is obvious that several solvent systems are necessary for their separation. The following solvent systems have been found suitable (49—51) dimethylformamide/ /hexane to benzene ethylene glycol/hexane formamide/hexane -butanol-ethanol-water (45 5 50) or (10 10 1). For detection, sensitive down to 1 pg, the following sprays have been recommended (a) 0.1% p-amino-dimethylaniline hydrochloride and (b) a mixture of 3 ml of glacial acetic acid, 2 ml of a saturated potassium iodide solution, and 5 ml of starch solution. For the chromatography of organic peroxides on thin layers see (52, 53). 

Mention should be made of studies of slow, controlled combustion of alkanes, where formation of oxetanes can be detected. For example, oxetane is observed during combustion of propane, while 2-f-butyl-3-methyloxetane and 2-isopropyl-3,3-dimethyloxetane are observed from combustion of isooctane. While the yields are extremely low, the presence of these compounds, along with the other products found, have provided evidence for the mechanism of combustion. The oxetanes are believed to result from rearrangement of peroxy radicals in the radical chain process (equation 114) (70MI51300,73MI51301). 

Peroxytitanium species have been detected during the production of hydrogen peroxide from organic hydroperoxides and Ti(SO)4)2- Alkaline earth peroxy-titanates, e.g. Ca3[Ti(02)4(0H)2]H20, have been prepared by the addition of Ca(N03)2 to a solution of titanium hydroxide in ammoniacal hydrogen peroxide the composition and structures of the compounds were established by thermal analysis i.r. and n.m.r. spectroscopy, and X-ray diffraction, their thermal stabilities decrease in the series Ba > Sr > Ca. 

A similar approach was used for the optical detection of phenolic compounds and hydrogen peroxide, using CdTe QDs-enzyme hybrids. For this, mercaptosucdnic add-capped CdTe QDs were first synthesized, after which the horseradish peroxi-dasephenolic compounds by H2O2 to quinone products resulted in an efficient quenching of QD luminescence [197]. 

Careful attempts to detect hydroperoxides and peroxynitrates, expected products of the reactions of the hydroxycyclohexadienylperoxy radicals with HO2 and NO2, respectively, were unsuccessful. This has been taken, in conjunction with work on the effect of NOx on the kinetics and products of the aromatic compound oxidation, as an indication that such peroxy radicals are very short-lived. It has been suggested, therefore, that the peroxy radicals are not able to oxidise NO as is the case for alkane and alkene atmospheric oxidation. 

---