A quantitative study of alkyl radical reactions by kinetic spectroscopy. IV. The flash photolysis of azopropanes

✍ Scribed by Hiroyuki Adachi; Norman Basco

• Publisher: John Wiley and Sons
• Year: 1981
• Tongue: English
• Weight: 855 KB
• Volume: 13
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550130404

✦ Synopsis

T h e flash photolysis of azo-n-propane and of azoisopropane has been studied by kinetic spectroscopy. Transient absorption spectra in the region of 220-260 nm have been assigned to the n-propyl and isopropyl radicals. For the n-propyl radical, cmax = 744 f 39 limo1 cm a t 245 nm and the rate constants for the mutual reactions were measured to he k , = (1.0 f 0.1) X 1Oln I/mol sec (Combination) and k d = (1.9 f 0.2) X loy I/mol sec (disproportionation). For the isopropyl radical, cmax = 1280 f 110 I/mol cm a t 238 nm, with k , = ( i . 7 f 1.6) X loy I/mol sec and k d = (5.0 f 1.2) X loy h o l sec.

T h e rate constant for the dissociation of the vibrationally excited triplet state of the azopropanes into radicals was measured from the variation in the quantum yield of radicals with pressure. For azo-n-propane k i = (6.6 f 1.3) X 10' sec-I, and for azoisopropane k z = (1.6 f 0.4) X lo8 sec-I. Collisional deactivation of the vibrationally excited singlet and triplet states was found to occur on every collision for n-pentane; hut nitrogen and argon were inefficient with a rate constant of 1.1 X 10") I/mol sec.

Spectra observed in the region of 220-260 and 370-400 nm are attributed to the cis isomers of the parent trans-azopropanes. These are formed, as permanent products, in increasing amounts a s the pressure is increased.

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