Quenching, radical formation, and disproportionation in the photoreduction of 4-carboxybenzophenone by 4-carboxybenzhydrol, hydrazine, and hydrazinium ion

Journal Article · Wed Dec 02 00:00:00 EST 1981 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00414a047· OSTI ID:5886209

Inbar, S; Linschitz, H; Cohen, S G

Laser flash and steady irradiation studies have been carried out on the 4-carboxybenzophenone (CB)-4-carboxy-benzhydrol (CBH/sub 2/) and CB-hydrazine systems over the pH range 5.8 to 12. In reaction with CBH/sub 2/, CB triplet is quenched in part by the carboxylate, k/sub q/ approx. = 4 x 10/sup 6/ M/sup -1/s/sup -1/; total reaction, k/sub 4/ = 3.0 x 10/sup 7/ M/sup -1/s/sup -1/ leads to the ketyl radical CBH, phi = 1.7. Absorption spectra were recorded for CB triplet, lambda/sub max/ = 535 nm (epsilon = 6600 M/sup -1/ cm/sup -1/), for CBH, lambda/sub max/ = 570 nm (epsilon = 5500), and for the radical anion CB/sup -/, lambda/sub max/ = 660 nm (epsilon = 8100). The pKa ofCBH was determined, 8.2. Rate constants were determined: for combination of CBH to pinacol, 2k/sub 6/ = 1.8 x 10/sup 9/ M/sup -1/s/sup -1/; for reactions of CBH with CB/sup -/, k/sub 7/ = 1.1 x 10/sup 9/ M/sup -1/s/sup -1/; for disproportionation of 2CB/sup -/, 2k/sub 8/ = 9.8 x 10/sup 6/ M/sup -1/s/sup -1/. Factors to convert observed yields of photoreduction by hydrazine to yields of ketyl radical leading to pinacol and hydrol were determined from effects of pH on quantum yields of reduction of CB by CBH/sub 2/. Reduction of CB triplet by neutral hydrazine occurs with k/sub ir/ = 6.8 x 10/sup 8/ M/sup -1/s/sup -1/, forming ketyl radical with phi = 1.0, measured relative to the CBH/sub 2/ reaction. The reaction with protonated hydrazine is slower, k'/sub ir/ = 4.4 x 10/sup 6/ M/sup -1/s/sup -1/. Computer simulation, using the measured rate constants, pK/sub a/ and primary yields, and literature constants for pure hydrazine systems, leads to calculated reduction yields very similar to the observed values, with phi/sub ketyl/ approx. = 0.0 for reaction of triplet with protonated hydrazine, and ratios of rate constants for ketyl-hydrazyl disproportionations appropriately close to unity.

• Research Organization: Brandeis Univ., Waltham, MA
• DOE Contract Number: EY-76-S-02-3117
• OSTI ID: 5886209
• Journal Information: J. Am. Chem. Soc.; (United States), Vol. 103:24
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
HYDRAZINE
PHOTOCHEMICAL REACTIONS
KETONES
ABSORPTION SPECTRA
AROMATICS
CHEMICAL REACTION KINETICS
COMPUTERIZED SIMULATION
PH VALUE
REDUCTION
SCINTILLATION QUENCHING
TRIPLETS
CHEMICAL REACTIONS
KINETICS
MULTIPLETS
NITROGEN COMPOUNDS
ORGANIC COMPOUNDS
REACTION KINETICS
SIMULATION
SPECTRA
400500* - Photochemistry