Novel Photo-oxidation o
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and Sanae H
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Department 01 Textile Science， Mukogawa Women's University， Nishinomiya 663
Photo-oxidation of aromatic hydrocarbons having an active methylene group in the presence of Fe(血 inacetonitrile afforded ketones， alcohols， and acetamides. One electron transfer mechanism from the aromatics to Fe(渡)was suggested for this photoreaction.
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Photo-oxid討ion of organic substrates in the
presence of metallic ion， especially ferric ion has been of recent interest from both mechanistic and synthetic aspects.
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long rangc elcctron transfer mechanism has bεen suggested for the photoreacti -on of olefins with Fe(m) under th号oxygenatmoシ phere to giveα-chloroketones1• Photolysis o f 1 I 3， 4 aromatic ethers伽 and aliphatic alcohols"" with Fe(m
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has also b告enelucidated from the viewpoint of electron transfer. However， little is known about the photo-oxidation of aromatic hydrocarbons having an active methylene group with metallic ion through el邑ctrontransf号r. In this respect， phot臼 -chlorinations of toluene with FeC13' and l-methyl -naphthalene with FeCl3 on alumina6 were reported. We now report a novel photo-oxidation of diph叩 ylmethane derivatives in the presence of ferric ion.E
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Materials. Substituted diphenylmeth証口君s were Substituted benzhydryl alcohols wer日 obt証ined by the NaBH4-reduction of the corresponding benzo phenones. Substituted N -benzhydrylacetamides were obtained by Ritter reaction of substituted benzhydrols in acetonitrile in the presence of sulfuric acid7. Diphenylmethane 1a， benzhydryl alcohol 2a， and substitut号d benzophenones were commercially available Jrradiation 01 Diphenylmethane Derivatives in the Presence 01 Ferric Jon. Typical procedure was as follows. An acetonitrile solution of diphenylmeth -ane la (0.9 mmol)and ferric chlorid号 hexahydrate (or ferric nitrate nonahydrate) (2.8 mmol) was irradiat号d with a high pressure mercury lamp (400¥九T)through a pyrex filter for about 6h in air The solution， which changed from yellow to pale yellow by irradiation (white precipitates of ferrous ion were sometimes observed)， was washed with water and extracted with chloroform¥
1
0 ml x2). The extracts werεconcentrat巴d carefully by arot呈tory evaporator.Instead of ac巴tonitrile as a
solvent， 10% aqueo叫s acetonitrile， 10% aq ueous
DMSO， nitromethane， and acetic acid were also synthesized by Friedel-Crafts alkylation of benzen日 employed.
with substituted benzyl chloride in the pr巴S告nceof a Product Analyses and Product Distributions. The
catalytic amount of anhydrous aluminium chloride. products were separated by column chromatography on silica gel， using hexane-b告nzene-ethylacetate
*
潔滋化学研究室長 as a εluent and were identified by comparison of -43ーIrradiation of 1 a in the pres己nceof ferric nitrate afforded benzophenone 2a口 93% yield， togeth己r with benzhydrol 3a (3%) and N -benzhydrylac巴tam -ide 4a (4%) as minor products‘Substituted diph巴nyl methane derivatives similarly gave the corresponding k巴tones，alcohols，品目damides. No reactions occurred in the dark.Thεse results concerning the direct photo-oxidation of active methylene groups wer告
summarized in Table 1， togethεr with some relative rates of the reaction(kH= 1).As shown in Table 1， electron releasing substituents， in generaL百nhanced
the reaction rate and caused an increasing yi日ld of
the ketones， wh邑r日aselectron withdrawing substitャ
uents and ortho ones caused rather lowering of the reactivities，註lthoughadditional irradiation showed an increase in the yiεld even in these cas己S The product yields also exhibited remarkable solvent d告pendence (Table 2) In acetonitrile th巴 highest selectivity for the oxidation was observ号d (this is presumably the result of high solubility of t(
m
巻(1989)Results and Discussion
自然科学編 lH-NMR with authentic samples. lH-NMR spectra were obtained on a Hitachi孔600. The similar proc吋ureswere p巴rformedfor other diphenylmeth anεderivatives The product distributions w告redetermined by the internal standard m母thodby GLC (column; DEGS 5% on Celite 545 [80…100 meshl， 2m). GLC was carried out on a Shimadzu GC-6A gas chromatograph equipped with a hydrogen flame det巴ctor
Competitive Reaction Rate. The reactivities of diphenylmethane derivatives w告rεdeterminedby the
competitive reaction method of substitut巴ddiphenyト
methane and unsubstituted one by GLC according to the following eq uation
武Jtlï川女子大学紀~
kx/kH=OOg [Dxl i-log [DHh )/Oog [DHli-log fDHh) where [Dxl and [D封
1
are concentrations of X(Y)substituted and unsubstituted diphenylmethanes，
respectively‘Subscripts and t express initial tim号 証nd reaction time. These relative rates
obtained from average of threεindepεndent runs. were
Product Yield (%) from Photo山oxidationof 1 in CH3CN
a1 Table 1 Re.lrate 5.9 2.4 0.48 0.17 0.72 Product Yield (%) 3 4 3 (5)d1 4(2) 6 12
o
3 31 10 29 7 (14)同 13 (29)e) 12 7o
(11)e) 10 12(3) e) roo-ooTo
2 93 (62) 34 96 29 63 23 (62)e) 21 (48)e) 81 55 11 (75)e) 16 28(71)e) Y X Starting Material la A B A A A A B A A A 日 H H H H H p-Me o-Me p-Cl o-Cl Ib F U A U ρ v -p.-Br H P-COCH3 H p-NOz H f g h B B p-Cl -44ー p-Cl a) Determined by GLC after irradiation for 6 h. b) Method A; F日(N03h・9HzO B; FeCb・6HzO c) Obtained form the competitive reaction with la. d) Irradiation for 3 h. e) Irr在diationfor 12 h.Photo…oxidation of Aromatic Hydrocarbons in the Presenc告ofF号rriclon (Seguchi . Hirota) X -C6H4 -CH2C6H4 -Y
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X -C6H4-C…C6H4-Y+Xー
C6H4-CH-C6H4-Y+ 1a-jScheme
1 1 1F
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1
1
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CH3CN0
O H 2a-j X-C6H4-CH-C6H4-Y NHCOCH3 4a-j 3a-j Fe(m)， and while in ac芭tic acid a considerable amount of benzhydryl証cetate(5%) 5 was obtained in addition to 2 and 3. Table 2 Solvent Effect of Product Yields (%) in the Photo叩oxidationof la.") From a mechanistic viewpoint. qu在日titative 3+ ，~ 2+ analyses of Fe"' and Fe"' were performed in the Yield (%) course of irradiation. As a result. the extent of the photo -oxidation of 1 a proceeded depending on the 3+ ~ 2+ reduction of Fe"' to Fe"' . This fact indicates that a primary process of the interesting photoreaction is 3+ electron transfer from an organic substrate to Fe ltis unlikely that the reaction proceeds by a radical generated from one electron transfer from the 3十 5. 6 counter-anion to Fe"' "." because the replace -ment of th日nitrateion by other anions. Cl . caused the similar photoreaction (Table1).although the Solvent Methodbl 10%aq DMSO A 8 CH3N02 A B CH3COOH A 8 products yield depend日d markedly on th告 anion a) lrradiation for 24 h used. lt was confirmed individually that the ketones b) Corresponding to Table 1 were photochemically derived from the correspond -ing在lcohols with己ase under our conditions; for 2a 3a 5a 45 9 15 3 29 3 12。
39 3 10 10 6 26examples. 3a. 3b. and 3c afforded 2a， 2b， and 2c in acetic acid afforded the corresponding acetate 87%. 95%. and 68% yields. respectively. Thus the instead of the amide (Table 2). The two experimen -oxidation products in Table 1 should be deriv号dfrom tal results may demonstrate intervention of the the following Scheme 2， taking into account that a carbocation 1十inthe course of the photo-oxidation primary process involves a cation radical formation. Particularly， detection of a small amount of N -alkylacetamide obtained by Ritter addition of a (Scheme 2)ー
Acknowledgement
carbocation to acetonitrile followed by hydration We thank Prof. A. Sera (Kobe University) for his might support this reaction schemel. ln addition.(i) helpful discussions and Miss A. Yamamoto forthe irradiation of 1 a in acetonitrile-water system invaluable assistance. This work was supported by a (90・10v/v) significantly depressed the formation of Grant-in-Aid for Sci告ntific Research from the
N -alkylacetamide. and (ii) th芭 irradi証tionof la抗 Ministryof Education. Scienc号andCulture
-45-武庫川女子大学紀婆 自 然 科 学 編 第37巻(1989) Fe3今 Fe 2 + 附 F=e3+ Fe2+ + Ph-CH2-Ph-X
