General Method for the Preparation of l-Organyl-2-(l-phenyl-2-fluorocyclobut-l-en-3 l one)7o-carboranes, a) A sample of I0 ml conc. H~SO 4 was added to 0.01 mole (IIIa)-(IIlc) and stirred for 1 h at 100~ and for an additional 1 h at II0~ The reaction mixture was poured onto ice and extracted with ether. The extract was dried over MgSO~. Ether was re- moved and ketones (IVa)-(IVc) were isolated.

b) a mixture of i0 ml freshly distilled CH~CO2H and 0.02 mole (CF~CO2)2Hg was added to 0.01 mole (IIIc). The mixture was heated for 2 h at 50~ CF~CO2H was removed in vacuum and 15 ml ether and 15 ml 10% aq. NaHCO~ were added to the residue. The ethereal layer was separated and dried over MgSO 4. Ether was removed to give 1.56 g (45%) (IV).

l-Methyli2-(2-phenyl-3-fluoro-2-buten-4-al)-o-carborane (Va). A solution of 3 mmoles (IVa) in 5 ml abs. ether was added to 6 mmoles AIH2CI in 20 ml abs. ether and stirred for 1 h at 20~ Then, i0 ml 10% hydrochloric acid was added and the organic layer was sepa- rated and dried over MgSO~. Ether was evaporated to give 0.4 g (40%) l-methyl-2-(2-phenyl- 3-fluoro-2-buten-4-al)-o-carborane (Va), mp 144-145~ (from ethanol). IR spectrum (~, cm-~): 1640 (C=C), 1690 (CH=O). PMR spectrum (6, ppm): 2.10 s (3H), 3.60 s (2H), 7.45 m (5H), 9.32 d (IH). 19F NMR spectrum (6, ppm): 43.6 d, JHF 19.6 Hz. Found: C 48.72; H 6.49. C~2H21BIoFO. Calculated: C 48.75; H 6.56; F 4.79%. DNPH of (Va), mp 265~ Found: N 10.91%. Calculated: N 11.19%.

CONCLUSION

I. The reaction of l-organyl-2-1ithi~m-o-carboranes with l-phenyl-3,3,4-trifluoro-4- chloro-l-butene gave l-organyl-2-(l-phenyl-2,3,3-trifluoro-l-cyclobutene)-o-carboranes. The hydrolysis of these o-carboranes leads to l-organyl-2-(l-phenyl-2-fluoro-l-cyclobuten-3-one) - o-carboranes.

2. An unusual cleavage of the cyclobutene ring was found upon the action of AIH2CI on l-methyl-2-(l-phenyl-2-fluoro-l-cyclobuten-3-one)-o-carborane with the formation of 1-methyl- 2-(2-phenyl-3-fluoro-2-buten-4-al)-o-carborane.

i. 2. 3.

LITERATURE CITED

V. N. Lebedev and L. I. Zakharkin, Izv. Akad. Nauk SSSR, Set. Khim., 190 (1970). V. N. Lebedev and L. I. Zakharkin, Zh. Obshch. Khim., 558 (1972). K. Magarajan, M. J. Cagetio, and J. D. Roberts, J. Am. Chem. Soc., 86, 449 (1964).

DIRECT PHOTOLYSIS OF ACETYL BENZOYL PEROXIDE AND BENZOYL PEROXIDE

Ya. N. Malkin, S. V. Rykov, UDC 541.124:541.141.7:547.582.3 and E. V. Skakovskii

Aromatic acyl peroxides are initiators of free radical reactions but the mechanism of their photodissociation leading to the formation of radicals has not yet been clarified. The quantitative characteristics of the decomposition reaction and the relationship between the peroxide structure and the efficiency of this process are unknown. In the present work, we determined the quantum yields of the photodissociation of benzoyl peroxide (BP), acetyl benzoyl peroxide (ABP) and perbenzoic acid (PBA) in nonpolar solvents by the action of light at 313 and 250-230 nm.

Thequantum yields for the photodecomposition of the starting peroxide (~) were deter- mined upon irradiation in standard quartz cells using a DRSh-500 lamp (the band at 313 nm was separated using a combination of the ZhS-3, UFS-5 and BS-4 light filters and the light at 230-250 nm was separated using a chlorine filter). The fraction of absorbed light was found actinometrically [i]. The lamp output was 2.38.10 Is quanta/sec at 254 nm and 1.06"i0 i5 quanta/see at 300 nm. The spectral distribution of the incident light was given in our previ- ous work [i]. The amount of unreacted peroxide was found iodometrically by titration with

Institute of Chemical Physics, Academy of Sciences of the USSR, Moscow. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2815-2817, December, 1986. Original article submitted March 27, 1986.

0568-5230/86/3512-2581512.50 ~ 1987 Plenum Publishing Corporation 2581

Fig. i. Transformations of the dependence of the photo- decomposition quantum yield on [E] for light at 313 nm in heptane: i) PBA, 2) BP, 3) ABP.

. g g g

Z,Yg

I/ x Z

o o ~ [ f

Z # 6 I/[fl] .ig~Z liters/mole

TABLE i. Quantum Yields for Cleavage of the O-O Bond (~o-o) of Peroxides at 22~ for Light at 313 and 230-250 nm

Compound

ABP BP PBA

Solvent

CTHta C7Hts CTHi~

3i3 :Ilm

0.12 0.'12 0:t4

(PO--O

230--250 -rim Compound

0 32 0.42

- PBA

Solvent

C6Hs C~H6 C6Hs

3t3 rim

r

230--250 11111

0,12 I - oAa 0 , t 2

an ethanolic solution of KI. The iodine liberated was measured spectrophotometrically.

The quantum yield for the photodecomposition of all three peroxides increases with in- creasing initial concentration of the peroxide and with increasing energy of the exciting light (Fig. i, Table i). The concentration dependence of the photodecomposition may be a conse- quence of a photoinduced chain reaction or a bimolecular interaction. However, at ABP less than 0.005 mole/liter and at BP less than 0.002 mole/liter, neither O2 nor added styrene affect the photodecomposition quantum yield for the photodecomposition at 313 nm. Above these con- centrations, a decrease in ~ is observed with increasing concentration of the free radical traps.

In our opinion, free radical decomposition reactions for peroxide concentrations less than 0.002 mole/liter in heptane do not make a significant contribution to the overall trans- formation of the peroxide.

The increase in with increasing concentration is thus due to a bimoiecular interaction of the peroxide in the electronically excited state witha ground state molecule (perhaps, from the triplet excimer as proposed by Leborgeois et al. [2]).

We propose the following scheme for the reaction proceeding uponthe photoirradiation of a heptane solution of ABP in heptane at 313 nm:

I] § h'~ ~ $1 (1)

S1 -+ r l (2)

s~ -~ n (so) ( 3 )

$1 ---+ RCO~ (4)

T~ -f- II ..~ 2RC02 (5)

T~ -~ H (So) ( 6 )

TI q- H --> 2II

2582

==~_=

where H and n(S 0) are the peroxide molecule in the ground state, RCO 2 are the primary photo- lysis products (benzoyloxy radicals), and S I and T l are the peroxide molecules in the S I and T I states. Then, the quantum yield for decomposition of the peroxide ~ is

or

2k4[H] = ~o-o + ~r k5 + (h + k~) [HI

k6

k5 i+k7 (~ -- ~~176 -- It4 [H] (2T~) 4 2*T

(7)

(8)

where ~o-o = k~/(k~ § k 2 + k 3) is the quantum yield for cleavage of the O-O bond from the S I state and ~T = kl/(k ~ + k= + k~) is the quantum yield for intercombinational conversion; [HI is the peroxide concentration.

The lack of effect of 02 on the quantum yield for the photodecomposition at infinite dilution indicates that the lifetime of the T I state of ABP cannot be longer than 20 nsec and, thus, k 4 is not less than 9"109 liters/mole'sec.

Figure i shows that Eq. (7) holds only for sufficiently dilute solutions (up to 0.002 mole/liter). Above these concentrations, increases with increasing concentration more rap- idly. This occurs, as proposed above, due to an increase in the contribution of a radical chain decomposition process.

Analysis of the dependence for ~ on [H] plotted as (~--~o-o) -I vs. [~]-z permits evalua- tion of the value of ~T from the y-intercept. Assuming that k~ ~ k~ (Joe., the major path- way for the conversion of the triplet excimer is the formation of peroxy radicals), ~T = 0.04 • 0.02 for all three acyl peroxides. In our opinion, ~T characterizes the intercombi- national conversion in the C~H~C(O)O0 fragment which is common for all three molecules.

Analysis of Fig. i indicates that with increasing peroxide concentration, the value for increases toward ~o-o �9 Thus, we take the photodecomposition quantum yields at "infinite

dilution" (<i0 -s mole/liter) as ~o-o. We note that if all three peroxides are seen as mole- cules, in which the right-hand part of the molecule is altered with an unchanged benzoyl group, ~o-o does not change upon change in the second chromophore. This indicates that the photodissociation process occurs entirely in the aromatic portion of the molecule, C~HsC(O)O0 , and depends only slightly on the structure of the remaining part of the molecule.

CONCLUSION

The quantum yields were found for the photodissociation of the 0-0 bond for acyl perox- ides (0.12-0.14). In the framework of our assumptions, the increase in ~ with increasing peroxide concentration may be related to conversion of the triplet excimer.

i .

2.

LITERATURE CITED

Sh. Ruziev, Ya. N. Malkin, and V. A. Kuz'min, Izv. Akad. Nauk SSSR, Ser. Khim., 537 (1986). P. Leborgeois, R. Arnaud, and J. Lemair, J. Chim. Phys., 1633 (1972).

2583