Triphenylcarbonium ion was photolyzed with visible light in various acidic media. In 72% aqueous sulfuric acid, bis-µ,p'-diphenylmethylbiphenyl (3), p-diphenylcarbinol-p'-diphenylmethylbiphenyl (5), and bis-µdiphenylcarbinolbiphenyl (4) were formed, each in about 20% yield. Mechanistic investigations indicate that this dimerization involves interaction of an excited, triplet tritylcarbonium ion with a ground-state tritylcarbonium ion. Dimerization was suppressed by increasing the acidity of the medium, and in 96% sulfuric acid the only product obtained was 9-phenylfluoren-9-ol (formed in 60 % yield). In the presence of acetic acid and lower concentrations of sulfuric acid, the excited triplet tritylcarbonium again plays a role, cyclizing to the 9-phenylfluorenyl system or oxidizing the solvent forming trityl radical, which then reacts further. In 3 % sulfuric acidacetic acid the products were 21 % triphenylmethane, 22% 9-phenylfluorene, 17% bis-9-phenylfluorenyl peroxide, and 10% benzophenone. In 3 % sulfuric acid-16 % tolueneacetic acid the products were 20% of a mixture of 9phenylfluorene and triphenylmethane, 45% 1,1,1,2-tetraphenylethane, and 11 % 9-benzyl-9-phenylfluorene. In the presence of oxygen, photolysis of the tritylcarbonium ion in 3% sulfuric acid-acetic acid yielded 37% benzophenone, 28% 2,2-diphenylmethylenedioxybenzene, and 11% of the novel peroxide acetate 17. Under still more weakly acidic conditions the aldehyde acetate 18 was formed. In 30 % sulfuric acid-acetic acid, diphenyl-ptritylphenylcarbinol was formed in 30% yield, along with 12% 5, while in 60% sulfuric acid-acetic acid the only product isolated was 4.

decomposition of solutions of 7 in organic solvents after 1 week at room temperature. Since the rearrangement of the less stable esters from other isoxazolium salts is subject to basic catalysis,218 it is also noteworthy that the N-t-butyl enol esters are not highly sensitive to base. l 4 However, these results do not establish whether the t-butyl substituent merely causes rearrangement to be extremely slow or if the enol esters are thermodynamically favored relative to the rearrangement products.The potential utility of the new esters as acylating agents was tested in a reaction of 8 with benzylamine. Equivalents of the reactants were combined in various organic solvents, and, in each case, the solvent was removed under reduced pressure the next day. Separation of the freely water-soluble by-product 9 from the residue with a few small portions of water left better than 98 % yield of pure carbobenzoxyglycylbenzylamide in each test.(14) For example, 8 was recovered in better than 90% yield after 24 hr in dry 2-picoline, (15) A portion of this investigation was carried out during the tenure of a predoctoral fellowship from the National Sir:Although the visible and ultraviolet spectra of various carbocationic species have been duly recorded and theoretically treated, the question of product formation from excited carbonium ions has been neglected. In pursuing a program concerned with photolysis of charged carbon species, we have examined the nature of the substances formed during ultraviolet irradiation of tropylium (I), triphenylcyclopropenium (11), and triphenylcarbonium (111) ions, the first carbocationic cases investigated from the standpoint of product develop-mentS2 In the first case (I), photogeneration of the [3.2.0] valence bond isomer Ia of the aromatic system "Dewar tropylium ion") apparently controls the over-all reaction course. In the other systems coupling emerges as an important p r o c e s~;~ however, depending on solvent and other factors, additional modes of reaction are also observed.aqueous sulfuric-acid for 10 min with a Hanovia 450-W high-pressure lamp (Vycor filter), 4 2 z of the tropylium ion4 (fluoroborate salt, A, , , 217 and 273 r n~)~ was consumed, giving rise to (1) For a review, see S. F. Mason, Quart. Rev. (London), 15, 335 (1961). (2) We have been able to locate in the literature only one possible prior example, the observation that 9-phenylfluorene was isolated after trityl perchlorate had lain on a desk top for 15 days [H. Dauben, Jr., J. Org. Chem., 25, 1442 (1960)J. (3) Coupling phenomena have also been encountered in anionic types: E. E. van Tamelen, J. I. Brauman, and L. E. Ellis, J. Am. Chem. SOC., 87, 4964 (1965); 89, 5073 (1967). After irradiation in 5 (4) W. von E. Doering and L. H. Knox, ibid., 76, 3203 (1954).I Ia n'v 58% yield (based on unrecovered starting material) of bicycl0[3.2.0]hepta-3,6-dien-2-01 (IV) and the corresponding ether V, colorless liquids interconvertible in dark reactions. Verification of structural assignments made initially by ir, uv, and nmr methods...

Scientific Research for its generous support of this research.(2) (a) M. Kasha, J. Chem. Phys., 20, 71 (1952); (b) M. Kasha,

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going this reaction, especially since in this system no fluorescence could be observed.3 The homolysis of VI to VII would be expected on the basis of findings that diaryl peroxides are stable only at very low temperatures, decomposing upon warming to aryloxy radicals.8•9The conversion of VII to VIII is analogous to the known conversion of triphenylmethoxy radical to the more stable diphenylphenoxymethyl radical,10 while the four-membered peroxide IX would be expected by precedent11-14 to cleave to the keto aldehyde.It has not yet been determined whether singlet oxygen is produced in this system. However, preliminary results indicate that the excited triplet carbonium ion is quenched by oxygen to an extent greater than can be accounted for by the formation of the peroxide-derived products.