Tetrahedron ~~~~~~~ ~~.52, pp. 53aq-5392, lq68. Yergmon Press. Printed in Great Britain-

THE PHOTOOXIDATION OF 14METHYLANTHRAQUINONE AND ~+ETHYLACETOPHENOE

Peter Yates, A. C. Mackay, and F. X. carneau

Lash Miller Chemical Laboratories, University of Toronto, Toronto, Canada

(Received in USA 8 July 1968; received in UK for Publication 17 September 1968)

It has been found that photooxidation of a number of c-methylaryl

ketones qivcs nroducts in which the methvl qrouy, is converted to a

carboxvlic acid aroup or becomes the carhonvl qrouv of a lactonc ring. Such

vroducts have been obtained from anthraquinone, l,&naphthoauinone,

xanthone, and acetonhenone derivatives. We report here on the cases of

1-methylanthraquinone and c-methylacetophenone.

Exposure of a 0.1% solution of i-methylanthraquinone (I) in benzene to

sunliqht in the presence of air for 6 days gave anthracuinone-1-carboxylic

acid (II) (54%) (1) and anthraquinone (III) (9%). A third comoound was

shown to be present bv a stronq band at 5.6 u in the infrared spectrum

(CHCl3) of the benzene-soluble fraction of the crude product. This comnound

r*as obtained as the ma-jar oroduct (60%) when a 1% solution of I in benzene

nresaturated with oxyqen was irradiated in Pyrex with a 450-w. Hanovia

medium-pressure mercury arc lame and a C.E. 270-w. sunlamp. It was isolated

hv removal of other comnonents of the crude reaction product with hot acetic

acid: crvstallization of the insoluble residue from nitrobenzene qave

colorless crystals, m.p. 3Q4-306°, X pax (Nujol) 5.65, 6.nr), 6.31 u. It was

assiqned the molecular formula CaoHlbO6 on the basis of elemental analytical

and mass snectral data: the neak with highest m/e (apart from isotopic

satellites), which was also the base peak, appeared at 235 and was considered

to arise bv fraqmentation of the molecule into two fragments oc equal mass

(metastahln Peak at -118). It was shown to be the dilactone IV by direct

comnarison with a sample, m.v. 304-306O [lit. (2) 28ZZ"l, prepared bv

oxidation of the lcctonc v with boilinq nitrobenzonc (1,3).

5389

5390 No.52

I, R -CH3 SZUI, R=CHO

It, R =C02H XI, R=CPH5

III, R=ii XX, R =COCH, 0

I4

@lJ pp @$ OR

9, R-H

X, R=COCH3

XL X - H2

lx, x=0

m

Studies by Yanq (4) and Ullman (5) and coworkers suuqest that photo-

oxidation of I proceeds via photoenolization to VI qqhich is converted in turn

to the oeroxide VII and the aldehyde VIII. Photoenolization of VITI to the

ketene IX followed by intramolecular attack of the hydroxvl qrouw at the

ketene group would sive the lactone V or its ketonic tautomer (6). Facile

oxidation of either tautomer to the dilactone IV finds ample orecedent in

the case of analoqous lactones (2,7). Oxidation of VIII or IX could also

account for the formation of the carhoxylic acid I, while photodecarbonvlation

of VIII could lead to anthraauinone. The followinq evidence corroborating

the occurrence of these processes has heen obtained: (a) irradiation of I

in methanol-d/benzene in the absence of oxvuen led to the incorporation of

deuterium into the nethvl uroun (8) (h) irradiation

in the presence of air qave, inter al., the aldehvde --

lactons X (c) irradiation of VIII in benzene in the

of I in acetic anhydride

vIII (9) and the

presence of air save

No.52 5391

the dilactone IV (d) photooxidation of 1-ethylanthraquinone (XI) gave

1-acetvlanthraquinone (XII) (e) photooxidation of 2-methylanthraquinone and

2-ethvlanthraauinone to qive anthraquinone-2-carboxylic acid and 2-acetyl-

anthraquinone, respectively, occurred very much more slowlv than did the

ohotooxidation of I and XI.

XIII, RICH,

XSZII, R=CHO

Irradiation of g-methplacetophenone (XIII) in acetic anhydride in the

presence of air qave 3-methylohthalida (XIV). In this case it was found

possible to isolate the intermediate peroxide XV, the analog of the postulated

intermediate VII, by irradiation of XIII in benzene in the presence of

oxygen: further irradiation of XV in either benzene or acetic anhydride gave

XIV. The structure of XV is assiqned on the basis of spectroscopic data

[a (CHCl,) 1.65 (s, 3H), 4.0 (broad, cont. deeendent, lR), 4.83 and 5.36

(AR, J = 15.5 Hz, 2H), 7.33 (m)J and of the demonstration that the compound

is not the hvdroneroxide XVI, m.p. 88-!39.5", which was orepared by an

independent route. The intermediacv of the aldehvde, XVII, analoaous to VIII,

is suqqested by the observation that this aldehvde, obtained by treatment of

XV under acidic conditions, is converted to XIV'on irradiation in benzene in

the nresence of air. The isolation of XIV in this case, rather than a

bimolecular product analoqous to IV, must reflect the greater susceptibility

to oxidation of the monolactone in the anthraauinone series.

We thank the National Research Council of Canada and the donors of the

Petroleum Research F!and administered by the American Chemical Societv for

support of this research.

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REFERENCES

Cf. A. Eckert, Ber. W, 313 (1325). -

R. Scholl and H .-D. Wallenstein, Ber. 69, 593 (1936): R. Scholl and

F. Renner, Ber. 62, 1278 (1929).

The possibility that the photochemical nroduct was lactone V, which was

oxidized to IV durinq the crvstallisation of the crude product from

nitrobenzene, was excluded bv comparison of the properties of the product

prior to crystallization with those of IV and V.

N. C. Yanq and C. Rivas, J. Am. Chem. Sot. 13, 2213 (1961). __

K. R. Huffman, M. Lay, and E. F. Ullman, J. Am. Chem. Sot. 87, 5417

(1965): IV. A. Henderson, Jr., and E. F. Ullman, J. Am. Chem. Sot. a,

5424 (1965).

Evidence for the occurrence of such a process in-the case of the ohoto-

reaction of g-phth.alaldehyde has very recentlv been reoortcd by

S. P. Pap-as and J..E. Blackwell, Jr., Tetrahedron Letters, 3337 (1968).

Cf. H. H. Wasserman, T.-C. Liu, and E. R. Wasserman, J. Am. Chem. Sot.

75, 2056 (1953); P. Yates and T. J. Clark, Tetrahedron Letters, 435

(1961).

Cf. Reference 4: we thank Professor N. C. Yanq, Universitv of Chicago,

for providinq us witn further details of his deuterium-exchange

experiments.

Identified bv comparison with a sample preoared by treatment of

l-(hromomethvl)anthraauinone with dimethvl sulfoxide and collidine.