photolytic cleavage of a CꢀCl bond, and subsequent
reactions of the resulting halomethane radicals with O2
finally generate carbon oxides with eliminations of Cl2 and
HCl via formation ofCOCl2 (Scheme 1).6,13 Since COCl2 is
soluble in organic solvents, 13C NMR spectroscopy of a
CDCl3 solution, which had been exposed to the gas
including photodecomposed products of chloroform for
1.0 h at 0 °C, actually showed only a strong singlet signal at
δ = 143.22 ppm, originating from COCl2 (Figure S1). On
the other hand, the resulting photodecomposed CHCl3
solution after exposure to UV light contained not only the
above volatile products but also CꢀC coupled products.
Solid C2Cl6 could actually be isolated in 0.1% yield from
the remaining chloroform solution after exposure to light
for 1.0 h and subsequent washing of the solution with
water. C2Cl6 may form through a radical coupling reaction
of trichloromethyl radicals, generated in the course of
photodecomposition reactions (Scheme 1). The observed
photodecomposition of chloroform also occurred under
flowing natural air, containing moisture, or in the presence
of a little amount of ethanol, which has been used as a
stabilizer in commercially available chloroform.9
Table 1. Syntheses of Organochlorine Compounds, HCl Salt of
Amine, Ureas, and Carbonates with Photodecomposed Chloro-
forma
With the above experimental results for photodecompo-
sition of chloroform in mind, we then demonstrated some
possible organic reactions for the reactive photodecom-
posed products of Cl2, HCl, and COCl2 with appropriate
reaction substrates. These photodecomposed products,
especially COCl2, are extremely toxic, but following pro-
cedures developed in this study will allow their application
into a variety of reactions without hazardous handling,
expensive experimental settings, or otherwise harsh condi-
tions. As illustrated in Figure 1, the reactions can be
demonstrated ina pseudoclosed system, where the reaction
substrate dissolved in organic solvents is exposed to the
photodecomposed chloroform gas, prepared by photoir-
radiation under flowing O2. The unreacted photodecom-
posed products, after passing through the reaction system,
must be trapped and neutralized by water containing
NaHCO3 at the terminal of the reaction system. With this
system, when 8.3 mmol of anisole, dissolved in 15 mL of
chloroform, was exposed for 1 h to the photodecomposed
chloroform/O2 gas at rt, 4-chloroanisole was obtained in
90% isolated yield (Table 1, entry 1). Anthracene also
underwent chlorination to give 9,10-dichloroanthracene in
97% yield (entry 2). Here, Cl2 included in the photode-
composed products may allow the observed chlorination
reaction.14 On the other hand, amines dissolved in metha-
nol, whose solvent allows dissolution of polar species and
decomposition of COCl2,15 provided their HCl salts
a Reactions were carried out with 0.6ꢀ8.3 mmol of substrates in
15 mL of organic solvent upon exposure to the photodecomposed chloro-
form gas for 0.5ꢀ1.0 h at rt. b Isolated yields are given.
quantitatively upon exposure to the gas. For example, a
methanol solution of cyclohexylamine provided its HCl
salt in 99% yield after the reaction for 1 h (entry 3). How-
ever, interestingly, cyclohexylamine dissolved in chloro-
form upon exposure to the gas gave not only the HCl salt
but also 1,3-dicyclohexylurea in 19% isolated yield, which
most likely formed through the reaction of the amine with
COCl2 (entry 4-I).16 In order to trap HCl, which may
prevent substitution reactions of the amine to COCl2,
5 equiv amounts of triethylamine (TEA) were added into
the solution, and then, the yield was dramatically increased
to 99% yield (entry 4-II). Aniline also converted to the
corresponding ureas in the solution containing 5 equiv of
TEA in 76% yield (entry 5). These reactions described
above also occurred under flowing natural air instead of
O2 gas in analogous high yields, but no reactions were
observed without photoirradiation.
(11) Russel, R. B.; Edwards, O. L.; Raymonda, W. J. J. Am. Chem.
Soc. 1973, 95, 2129–2133.
(12) The volatilization loss was evaluated from the decrease in weight
of 40 mL of chloroform in the cylindrical flask by bubbling with O2
(50 mL/min) for 1 h, where the lamp, wrapped with aluminum foil,
illuminated in the quartz glass jacket fixed in the flask.
(13) McGivern, W. S.; Kim, H.; Francisco, J. S.; North, S. W.
J. Phys. Chem. A 2004, 108, 7247–7252.
(14) Watson, W. D. J. Org. Chem. 1982, 47, 5270–5276.
(15) Phosgene is known to give chloroformic esters through reactions
with alcohols: Saunders, J. H.; Slocombe, R. J.; Hardy, E. E. J. Am.
Chem. Soc. 1951, 73, 3796–3797.
(16) (a) Turner, W. R.; Werbel, L. M. J. Med. Chem. 1985, 28, 1728–
1740. (b) Izdebski, J.; Pawlak, D. Synthesis 1989, 423–425.
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Org. Lett., Vol. 14, No. 13, 2012