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Model Experiments on the Phytotoxicity of Halogenated Hydrocarbons.

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Model Experiments on the Phytotoxicity of
Halogenated Hydrocarbons
By Gernot Grimmer and Werner Schmidt*
The proposals put forward thus far to explain the causes
of the recent damage to forests are not totally satisfactory.“] The forest damage that has occurred, to an increasing
extent, during the last ten years in areas having clean air,
especially at higher elevations with intense sunlight, has
not been reproduced in the laboratory, either by exposure
to SO, or by treatment with NO,.121There is also considerable evidence that ozone is not a primary cause.[31Besides
microbes and insects, air-borne, anthropogenic photooxidants have been recently suggested as a source of the observed damage done to conifers, which is revealed by premature aging and loss of needles.l4I
Independently, Frank1” and Schenck‘61 recently suggested that halogenated hydrocarbons, upon exposure to
light, might specifically damage the photosynthetic apparatus of conifers. In view of the large amounts of halogenated hydrocarbons produced annually (Table l), their ubiquity, their persistence, and their good solubility in the cuticle layer of conifers, this hypothesis deserves closer scrutiny. Frank and Frank”’ were able to show, for example,
that, upon treatment of a white pine with gaseous tri- and
tetrachloroethylene and simultaneous irradiation with a
high-pressure mercury lamp, the needles facing the light
source turned yellow. In the extracts of such artificially
aged needles, the amount of p-carotene and chlorophyll a
had significantly decreased, as was the case for the extracts
of “naturally” aged needles (HPLC). On the other hand,
new products appeared, which were not found in the extracts of undamaged needles and which were not characterized further. They are possibly degradation products of
these pigments. It is still unclear whether sunlight
(1> 285 nm) is able to activate halogenated hydrocarbons
in vivo, since these compounds absorb at very short wavelengths (lmzsx
< 230 nm). We report here model experiments
on 0-carotene, which plays an important role as ‘Oz scavenger in all photosynthetically active organisms.[’’
M, air-saturated solution of pIrradiation of a 1.6 x
carotene in cyclohexane with simulated sunlightl’l results
in slow photodegradation (half-life
= 540 s) with loss of
the conjugated double bond system (no absorption above
2 10 nm). This photodegradation is presumably the result
[*I
Dr. habil. W. Schmidt, Prof. Dr. G. Grimmer
Biochemisches Institut f u r Umweltcarcinogene
Sieker Landstrasse 19, D-2070 Ahrensburg (FRG)
808
0 VCH Verlag.rgesellsrhafl mbH. 0-6940 Weinheim. 1986
of radical ally1 oxidation with 302and ene reaction with
lo2;it can be retarded by flushing the cuvettes with argon
and degassing the solutions (four freeze-thaw cycles at
2 x l o p 6 mbar) but not completely suppressed.[91
Irradiation in the presence of a 150-fold molar excess of
halogenated hydrocarbon, under the same conditions,
leads, in the case of alkyl and aryl chlorides, to a significantly faster and, in the case of bromides and iodides, to a
dramatically faster bleaching (Table 1). The chloroethylenes, which are important on account of the large
amounts produced industrially and their good solubility,
fall in the middle. This degradation can be inhibited
neither by flushing with argon nor by degassing; even 1,4diazabicyclo[2.2.2]octane,a good scavenger of loz,has no
significant effect. If the short-wavelength component of
the light (L1280 nrn) is eliminated by the use of normal
glass instead of quartz cuvettes, then the bleaching is retarded (tl,2= 1600 s) both in the absence and presence of a
150-fold excess of tetrachloroethylene. Moreover, selective
irradiation in the long-wavelength absorption band
= 454 nm) of p-carotene in the absence and presence
of tetrachloroethylene has no effect on the stability of the
pigment.
Table 1. Half-lives,
of the photodegradation [8] of I)-carotene in cyclohexane (1.6 x lo-.’ mol/L) in the presence of a 150-fold molar excess of halogenated hydrocarbons as well as the boiling points, long-wavelength absorption maxima in cyclohexane, distribution coefficients for olive oil/air
[lo], worldwide production [ I I], and tropospheric life-times, r,,? [12].
-
Halogenated
hydrocarbon
Br2HC-CHBr2
C12C=CCI-CCI=CC12
C6HSBr
BrH2C-CH2Br
CeH,I
CH,I
CIHC=CCIZ
c12C=cCl~
H,C=CC12
CCI,
C2HSBr
1,2,4-CoH?CI,
n-CzH,Br
Cl2HC-CHCI2
H,C-CCI,
CoHsCl
CHClz
CI F2C-CFCI:
CHrC12
CIH2C-CHrCI
B.p.
[s] [ T I
,
I
,,,.,,
[nm]
Distrib.
coeff
Production
[tlyear]
227
251
271
214
9 I88 ca.280
I 2 42
257
27 87
211
720
> 1000000
30121
211
1900
>1000000
40 32
207
[b]
49 77 ca. 207
360
1000000
63 38
211
66 214
286 >100000[a]
72 71 ca. 208
20000
85 147
212
13000
92 75
360
600000
211
3800
104 132
271
400
169 61 ca. 205
300000
214 46 i 200
1%
400000
216 40 Cd.206
229 83 ca.207
450
5000000[b]
3 237
4 215
7 156
8 132
~
~
r,.:
[dl
-
22
64
17
-
6
8
-
422
32
-
788
24
109
-
120
73
[a] Extrapolated on the basis of data for monochloro-, o-dichloro-, and mdichlorobenzene. [b] Precursors in the production of polyvinyl chloride and
its copolymers.
If the concentration of tetrachloroethylene is decreased,
then the bleaching is retarded, but even for a molar ratio of
tetrachloroethylene to 0-carotene of 1 to 66, the bleaching
takes place twice as fast as in the absence of tetrachloroethylene. These results are indicative of a radical chain
reaction. The photochemical sensitivity of b-carotene toward anthropogenic halogenated hydrocarbons provides
possible support for the validity of the Frank-Schenck hy-
0570-0833/86/0909-0808 $ 02.50/0
Angew. Chem. Int. Ed. Engl. 2s (1986) No. 9
pothesis.lih1 The wavelength dependence of the quantum
yields and the structures of the photoproducts remain to be
elucidated.
Received: March 19, 1986;
revised: June 19, 1986 [Z 1706 IE]
German version: Angew. Chem. 98 (1986) 807
[I] “Classical” damage from industrial smoke has been known since the
last century.
[2] N. Overrein, H. M. Seip, A. Tollan: Acidprecip;tation-effects on forest
a n d f k h , Fagrapport 19/80, Oslo 1981, p 9 ; J. S. Amthor, Enuiron. Pollut 3 6 A (1984) l ; B. Prinz, G. H. M. Krause, H. Stratmann, LIS-Report
28.Londesanstult .fir Immissionsschutz des Landes Nordrhein- Westfalen.
Esren 1982.
(31 M. Ashmore, N. Bell, J. Rutter, Ambio 14 (1985) 81.
141 Seminar at the Kernforschungsanlage Jiilich: The effect of atmospheric
pollution on forests and forest soils, December 2-4, 1985.
[5] H. Frank, Nachr. Chem. Tech. Lab. 32 (1984) 298; H . Frank, W. Frank,
Notumrssenschajren 72 (1985) 139; H. Frank, Eur. Photochem. Assoc.
N e d 1985. No. 23/24, p. 7; H. Frank, W. Frank, Nachr. Chem. Tech.
Lab. 34 (1986) 15.
[6] G. 0. Schenck, VDI-Nachr. 39 (1985) No. 13, p. I I ; Eur. Photochem.
Asso(.. Newd. 1985, No. 23/24, p. 15; lecture at the annual meeting of
the Fachgruppe Photochemie der GDCh, Siegen, November 20-22,
1985.
[7] M. Calvin. Nature (London) 176 (1955) 12 I I ; H. Claes, T. 0. M. Nakayama. Z.Naturlorsch. B 14 (1959) 746; J . Feierabend, Z . Naturfor.sch. C 3 9
(1984) 450; E . L. Schrott, Pure Appl. Chem. 57 (1985) 729.
IS] 450-W xenon lamp (Osram, type XBO), filtered through a 60-mm thick
layer of water to remove IR radiation, 10-mm quartz cuvette with 2.5-mL
volume. distance from the xenon lamp 175 mm. According to the information supplied by the manufacturer, the lamp provides a small amount
of UV-A, which is not present in sunlight (Dr. F. Lochner. Munich, private communication).
[9] In degassed solutions, an 0,-independent photodegradation pathway
may iilso occur. It is also conceivable that traces of autooxidation products i n the oxidation-sensitive 8-carotene could lead to photochemically
induced degradation via a radical chain reaction.
[lo] A Sato. T. Nakajima, Arch. Enuir. Health 34 (1979) 69.
[ I I ] IARC Monogr. Eual. Carcinog. Risk Chem. Man 20. IARC, Lyon 1979;
F. R. Atri: Chlorierte Kohlenwasserstoffe in der Umwelt I . Gustav-Fischer-Verlag, Stuttgart 1985; G. McConnel, D. M. Ferguson, C. R. Pearson,
Endearwur (dt,rch. Ausgabe) 34 (1975) 13.
[I21 Calculated from the measured rates of degradation by OH radicals: H.
Ciisten, L. Klasinc, D. Maric, J . Atmos. Chem. 2 (1984) 83; H . Giisten,
L. Klasinc, Naturwi.ssenschaften 73 (1986) 129.
1-Thia-2-cyclooctyne- A Strained Cycloalkyne with
Polarized Triple Bond**
By Herbert Meier,* Evaggelia Stavridou, and
Christiane Storek
Dedicated to Professor Leopold Horner
on the occasion of his 75th birthday
Very few representatives of strained heterocyclic alkynes
have so far been reported in the
We have
now been able to synthesize the first molecule of this type,
namely I-thia-2-cyclooctyne 4, whose triple bond is polarized by the heteroatom immediately adjacent to it. A preparative entry to 4 was accomplished by thermal fragmentation of the heterocycle 3 , which was obtained in good
yields from the ketone lC4I via the semicarbazone 2. Although the E-isomer dominates, the ring-closure reaction
with selenous acid leads regioselectively to the 1,2,3-selenadiazole 3 (Scheme 1).
[*I
[**I
Prof. Dr. H. Meier, DipLChem. E. Stavridou, DipLChem. C . Storek
lnstitut fur Organische Chemie der Universitat
J J -13echer-Weg 18-22, D-6500 Mainz (FRG)
Thi5 work was supported by the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie.
Angew Cliem. I n / . Ed. Engl. 25 (1986) No. 9
2 E / Z = 3 / 2
1
Scheme I . Synthesis of 4
4, an oily liquid with a characteristic odor, is hardly less
stable than cyclooctyne 5 . The crucial difference between
4 and 5 lies in the polarity of the triple bond. Aside from
the - I effect of the sulfur atom, two mutual mesomeric
effects are conceivable (Scheme 2).
Scheme 2. Possible mewmeric influence ol the S atom in 4
The charge densities on the acetylenic C-atoms, which
can be deduced from their I3C-NMR shifts, confirm the
above-mentioned mesomerism (a). The effect is strongly
reversed in its direction to that in ynol ethers. The 6-values
of C-2 and C-3 differ by ca. 25 ppm owing to the anisotropy and the polarization by the sulfur. The ‘H- and I3CN M R shifts of 4, 5 , and the much more weakly polarized
1-thia-3-cyclooctyne 6”’ compared to 4 , are given in
Scheme 3.
_
34.5
1.81 2.10
20.8
3.00
-
40.6
105.5
1.63
28.3
190
-
33.0
a
21.4
4
1.57
29.7
3.30
-
21.9
94.4
2.w
97.2
29.7
1.81 2.10
345 20.8
2.00 2.21
-
5
6
19.9
32.5
Scheme 3 Comparison o l t h e ‘ H - arid “ C - N M R shifts or the compound\ 4.
5. and 6 .
The polarity of the triple bond of 4 must confer remarkable chemical reactivity upon the molecule. Thus, on the
one hand 4 undergoes reactions that are very common to
other strained cycloalkynes, e.g. cycloaddition with tetracyclone 7 to give 8 (yield ca. 100% (80% for 3 + 8 ) , m.p.
234°C (decomp.)); on the other hand, however, it slowly
adds water, even at room temperature. The regioselectivity
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