ISSN 1070-4280, Russian Journal of Organic Chemistry, 2008, Vol. 44, No. 6, pp. 929–930. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © M.G. Voronkov, L.I. Belousova, A.V. Vlasov, N.N. Vlasova, 2008, published in Zhurnal Organicheskoi Khimii, 2008, Vol. 44, No. 6,
p. 936.
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COMMUNICATIONS
Synthesis of Symmetric α-Diketones
M. G. Voronkov, L. I. Belousova, A. V. Vlasov, and N. N. Vlasova
Favorskii Irkutsk Institute of Chemistry, Siberian Division, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
e-mail: Andreiwlasov@rambler.ru
Received February 14, 2008
DOI: 10.1134/S1070428008060250
The known procedure for the synthesis of aliphatic
α-diketones is fairly complex: it is based on reaction of
ketones of the RCOCH2R series with isoamyl nitrite or
p-nitroso-N,N-dimethylaniline [1], followed by hydrol-
ysis of the resulting compounds with mineral acids.
α-Diketones can also be prepared by oxidation of the
corresponding hydroxy compounds or their derivatives
[2, 3]. For example, the synthesis of symmetric α-di-
ketones by oxidation of bis-trimethylsilyl ethers
derived from enediols with bromine in aprotic solvents
was reported [4].
acyl chlorides [7] or by exchange reaction of the
simplest acyl iodide, i.e., acetyl iodide, with carboxylic
acids [8].
A 50-ml quartz flask equipped with a reflux con-
denser and protected from atmospheric moisture was
charged with a solution of 17.0 g of acetyl iodide in
10 ml of toluene, and the solution was irradiated with
an OKN-11 mercury lamp over a period of 55 h. When
the reaction was complete, the mixture was filtered
from the precipitate of crystalline iodine, and the fil-
trate was distilled under reduced pressure. Yield of
biaceyl (I) 4.0 g (93%), bp 88–90°C; published data
[1]: bp 88°C. The IR spectrum of the product coin-
cided with that of an authentic sample. Found, %:
C 55.02; H 6.67. C4H6O2. Calculated, %: C 55.81;
H 7.02.
We have developed a simple and effective proce-
dure for the synthesis of symmetric α-diketones on the
basis of photochemical dissociation of acyl iodides. It
is known [5] that acyl iodides RCOI readily undergo
homolytic dissociation of the C–I band; this process
partially occurs even on exposure to daylight. How-
ever, the product expected to be formed via recombina-
tion of acetyl radical, biacetyl MeCOCOMe, was not
detected previously in the photolysis of acetyl iodide;
this was rationalized in term of a short lifetime of
MeCO· (~10–11 s) [6].
Likewise, a solution of 17.5 g of benzoyl iodide in
8 ml of toluene was irradiated with UV light over
a period of 20 h. The solvent and a part of iodine were
distilled off. The remaining iodine was removed from
the crystalline product under reduced pressure. Yield
of benzil (II) 7.1 g (88.4%), mp 95°C; published data
[1]: mp 95–96°C. The IR spectrum of the product coin-
cided with that of an authentic sample. Found, %:
C 79.52; H 5.06. C14H10O2. Calculated, %: C 79.98;
H 4.79.
On the other hand, we have found that photo-
chemical dissociation of acyl iodides RCOI in toluene
(which is known to act as triplet sensitizer) gives the
corresponding symmetric α-diketones RCOCOR in
40–95% yield.
A solution of 9 g of isobutyryl iodide [8] in 8 ml of
toluene was irradiated with UV light over a period of
20 h. The mixture was subjected to distillation under
reduced pressure, and the product was treated with
copper powder to remove elemental iodine. Yield of
The importance of the proposed procedure for the
synthesis of α-diketones from the preparative view-
point follows from accessibility of initial acyl iodides
which are readily obtained from the corresponding
α-diketone III 1.3 g (40.6 %), bp 140–145°C, nD20
=
hν
2RCOI
RCOCOR
1.5310. IR spectrum: ν 1705 cm–1 (C=O). Found, %:
C 67.00; H 9.88. C8H14O2. Calculated, %: C 67.57;
H 9.92.
I–III
I, R = Me; II, R = Ph; III, R = Me2CH.
929