Dialkyl peroxides, 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... 

Dialkyl peroxides (continued) colorimetry, 707-8 flame ionization detection, 708 NMR spectroscopy, 708 titration methods, 707 UV-visible spectrophotometry, 707-8 enthalpies of reactions, 153-4 graft polymerization initiation, 706 hydroperoxide determination, 685 peroxide transfer synthesis, 824-5 stmctural characterization, 708-16 electrochemical analysis, 715-16 electron diffraction, 713 mass spectrometry, 714 NMR spectroscopy, 709-11 thermal analysis, 714-15 vibrational spectra, 713-14 X-ray crystallography, 711-13 synthesis... 

Br > OTs > Cl, are observed, as are the expected stereoselectivity and inversion at the carbon center. In DMF, the final product is the dialkyl peroxide. The peroxy radical (ROO-), which is produced in the primary step and has been detected by spin trapping, is an oxidant that is readily reduced by 02 - to form the peroxy anion (R00 ). Because the latter can oxygenate Me2SO to its sulfone, the main product in this solvent is the alcohol (ROH) rather than the diaUcyl peroxide. 

Peroxide-forming solvents and reagents should be dated at the time they are first opened, and should be either discarded or tested for peroxides within a fixed period of time after their first use. Peroxides can be detected with Nal/AcOH, though dialkyl peroxides may need treatment with concentrated HCl or 50% H2SO4 before detection with iodide is possible. A commercially available test paper, which contains a peroxidase, can detect hydroperoxides and dialkyl peroxides, as well as oxidizing anions, in organic and aqueous solvents. 

The reaction of alkoxy radicals with triethyl phosphite apparently is sufficiently rapid to swamp out their known rapid conversion to alcohols or ketones, since such products were not detected. It would be interesting to know whether unsymmetrical or less sterically hindered dialkyl peroxides could be induced to interact via a polar mechanism. 

In principle, termination of two alkoxy radicals would give a peroxide cross-link, where as termination of an alkoxy radical with an alkyl radical would give an ether cross-link. It is very difficult to get direct experimental evidence for either of these reactions, since both dialkyl peroxides and ethers are difficult to detect however, there is no doubt that chain scission is dominant in saturated hydrocarbon polymers. 

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