1)Physical Properties
The melting and/or boiling points of a number of peroxides are listed in the Appendix. Melting above 100C is usually accompanied by decomposition,
and melting points may vary with the rate of heating. Equally unreliable are boiling points for most, since distillation without decomposition
requires such low pressures that gauge readings are inaccurate.
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Spectra
1. Infrared
The infrared spectra of alkyl peroxides are chiefly useful for detecting the presence or absence of impurities, such as the structurally related
alcohols, hydroperoxides, aldehydes, or ketones. The presence of a weak to moderately strong absorption in the 820-860 /cm region (C-O-O-) coupled
with the absence of O-H or C=O absorption may be confirmatory evidence of dialkyl peroxide structure but does not constitute strong proof. Monitoring
the disappearance of this band has been used for kinetic studies, however.
2. Ultraviolet
Like other peroxides, dialkyl peroxides exhibit weak absorption starting at 300-320 nm and gradually increasing at lower wavelengths. Published
spectra of ethyl, t-butyl, and cumyl peroxide are typical, the latter showing aromatic absorption imposed on that from O-O.
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Determination of Active Oxygen
A mixture of 10 ml concentrated hydrochloric acid and 10 ml of chloroform is boiled for 10 min. The peroxide is then added in a solution of 10 ml
chloroform and 10 ml isopropanol. Approximately 1 millimole peroxide is used. Then a solution of 1 g potassium iodide in 2 ml of water is added, and
the mixture boiled for 10 min. After heating, 100 ml of water is added, and the cooled solution is titrated with 0.1N thiosulfate solution. A 1-ml
volume of titrant solution corresponds to 1/40 millimole of dimeric ketone peroxide or 1/60 millimole of trimeric ketone peroxide. Blanks are
required.
The reduction of the peroxide bond by iodine in glacial acetic acid proceeds slowly; dimeric ketone peroxides are reduced faster then the trimeric
ones. With sodium iodide in glacial acetic acid at 20C, 50% of dimeric acetone peroxide is reduced in 50 min. Trimeric acetone peroxide and trimeric
cyclohexanone peroxide, in contrast, yield hardly any iodine under the same reaction conditions. A similar difference is found in catalytic
hydrogenation with palladium black in glacial acetic acid. The following decreasing order of hydrogentation rate points to the importance of steric
effects (blocking of the O-O groups) : dimeric dipropyl ketone peroxide > dimeric benzyl methyl ketone peroxide > dimeric methyl propyl ketone
peroxide > dimeric methyl t-butyl ketone peroxide > dimeric diethyl ketone peroxide > dimeric dimethyl ketone peroxide > dimeric methyl
ethyl ketone peroxide > dimeric bromoacetone peroxide >> Trimeric dimethyl ketone peroxide > Trimeric methyl isobutyl ketone peroxide =
Trimeric methyl isopropyl ketone peroxide > Trimeric diethyl ketone peroxide. |
This has nothing to do with methods of
synthesis, just that one can determine the active oxygen of a peroxide species relatively easily and this can help differentiate and compare peroxides
to one another, I mentioned the DPPP thread because comparing the active oxygen of the theoretical DPPP molecule with TCAP would have given different
noteable results without the effort of using instrumental analysis, this thread was just so that people at home had some method to compare the active
oxygen content of one peroxide to another. The other information was just interesting.