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Monothioformic Acid.

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oxobutyric acid (2) gives a 70% yield of a mixture of ( 3 )
and ( 4 ) , both of which we obtained pure in 10% yield by
one separation on a cellulose column. UV, ORD, CD, and
fluorescence spectra, as well as chromatographic and electrophoretic comparison, revealed no difference between
the natural and the synthetic materials.
(5). R = O H
(6). R = NH,
(7). R = H
(8). R = COzH
(9). R = O H
(10). R = COzH
Molecular-weight determinations in an ultracentrifuge
gave values around 430$-5%, as were found also by
Sugiura and G0toC4].Spectral comparison with dimeric
xanthopterin derivatives had led first"] to constitutions
involving direct C-C linkage of two pterin rings at the 7
positions, but such structures were ruled out by the products obtained on alkaline hydrolysis of (3) and ( 4 ) . On
treatment with 1% ammonia solution drosopterin and
isodrosopterin gave a large number of hydrolysis products,
among which xanthopterin (S), 6-aminopterin ( 6 ) , pterin
(7), pterin-6-carboxylic acid (8), 7,8-dihydroxanthopterin
( 9 ) , and 7,8-dihydropterin-6-carboxylicacid (10) could
be identified by chromatographic comparisons and by
determination of remission spectra. In addition, a yellowfluorescing degradation product was found whose UV
spectrum was related to that of sepiapterinr6].0.1 N NaOH
or 4% Na,CO, solution degraded ( 3 ) and ( 4 ) to the same
products, except for ( 4 ) .
Elemental analyses of crystalline drosopterin and isodrosopterin gave molecular formulas C, 5H,oNlo06which,
according to NMR spectra, must refer to stable dihydrates
of the molecule C1,H,,N,,O4; however, we have not yet
succeeded in effecting dehydration without decomposition.
NMR spectra of (3) and ( 4 ) are not very informative and
are difficult to interpret, but from the spectra in
[D,]DMSO, CFJOOH, and conc. H,SO, it can be
deduced that no methyl or methine group is present. Catalytic hydrogenation of ( 3 ) and ( 4 ) with Pt/H, causes
decoloration and absorption of 2 equivalents of hydrogen,
yielding products that have UV spectra characteristic of
The synthesis of drosopterin and isodrosopterin certainly
involve a two-fold Michael addition of the methyl group
of 2-hydroxy-3-oxobutyric acid to the azomethine function
of ( I ) since the latter is readily accessible to nucleophilic
attack[*], and this is followed by dehydrogenation and
decarboxylation. This synthetic pathway together with
the facts given above strongly suggest structure (11).
Compounds (3) and ( 4 ) are not merely isomeric, but,
contrary to earlier suppositions[91,are clearly shown to be
Angew. Chem. internal. Edit. / Vol. I 0 (1971) / No. 6
enantiomers by the ORDrlO1and CD spectra, which are
symmetrical about the zero line. The very large optical
activities of the two optical antipodes are due to an inherent-
ly dissymmetric chromophore, which in turn results from
non-planarity of the two 7,8-dihydropterin rings caused
by steric hindrance. The hindrance to free rotation around
the C-C single bond at positions 6 is, as shown by a model,
due mainly to the neighboring methylene groups, and the
steric effects are so great that it has not yet been possible
to interconvert (3) and (4) by thermal isomerization. So
far as we know, the red eye pigments drosopterin and isodrosopterin thus constitute a new class of atropisomeric
natural pigments.
Received: March 22,1971 [Z 401 IE]
German version: Angew. Chem. 83,440 (1971)
[I] M . Hscontini in W Pfleiderer and E. C. Taylor: Pteridine Chemistry.
Pergamon Press, New York, 1964, p. 267, and references therein.
[ 2 ] W Pfleeiderer, Angew. Chem. 75, 1008 (1963); Angew. Chem. internat. Edit. 3, 114 (1964).
[3] H . S. Forrest and S. N a w a in [I], p. 281. S. Nawa and H . S . Forrest,
Nat. Inst. Genetics Ann. Report 13, 23 (1962).
141 K . Sugiura and M . Goto, Tetrahedron Lett. 1970,4059.
[5] W Pfleiderer in K . Iwai, M . Akino, M . Goto, and Y lwanami: Chemistry and Biology of Pteridines. Internat. Acad. Printing Co., Tokyo
1970, p. 7.
[6] M . Hscontini and E. Mohlmann, Helv. Chim. Acta 42, 836 (1959).
[7] A . Bobst and M . Kiscontini, Helv. Chim. Acta 49, 875 (1966).
[S] H.C. Wood, 7: Rowan, and A. Stuart in [I], p. 267; A . Stuart,
H . C. S . Wood, and D. Duncan, J. Chem. SOC.1966, 285.
[9] M . Escontini and P . Karrer, Helv. Chim. Acta 40,968 (1957).
[lo] K . Sugiura, M . Goto, and S. Nawa. Tetrahedron Lett. 1969, 2963.
By Gerhard Gattow and RudolfEngZerr*I
The existence of monothioformic acid HCOSH has been
signaled in the literature['].-The free acid is formed on
treatment of Na[HCOS] or KCHCOS] (prepared by
hydrolysis of phenyl formate with NaHS or KHS) with
18% HCl and it can be distilled from the solution in a
vacuum at - 5 "C.
The pale yellowish acid (m. p. - 68 1"C, d i 0 = 1.34 50.02
g/ml, n~O=1.4880f0.0005, K , = 9 x
in H,O), which
polymerizes to [HCOSHIx even at 30°C, is very readily
soluble in CHCl, and CH,Cl, but less so in water.
[HCOSH], dissolves almost only in aqueous sodium
hydroxide and then with partial disproportionation to
[HCO,]- and [HCS,]-[31. In the mass spectrum of
[HCOSH], there appear, besides the molecular ion at
m/e = 62, the disproportionation products at m/e =46
(HCOOH) and 78 (HCSSH)[41in the ratio 1:1, together
with small amounts of [HCOSH], but no trimeric unitr4'.
p] Prof. Dr. G. Gattow and Dip1.-Chem. R. Engler
Institut fur Anorganische Chernie und Kernchemie der Universitat
65 Mainz, Joh.-Joachim-Becher-Weg 24 (Germany)
Aqueous solutions of the [HCOSI- ion and of the monomeric acid show visible and UV absorptions at 211 and
247nm and additionally at 223nm respectively. The
'H-NMR spectrum[51of HCOSH contains two singlets
at 6,-,=10.18
and 6,-,=4.66ppm. The singlet in the
'H-NMR spectrum of the [HCOSl- ion [measured in
D,O against sodium 2,2,3,3-tetradeuterio-3-(trimethylsilyl)propionate] at 6 = 10.64 ppm fits well into the series
of ions [HCOOI- at 6=8.42ppm and [HCSSI- at
6= 12.22 p ~ m [ ~ ] .
IR spectrum of [HCOSl- : 2810 (m), 1610 (m), 1525 (s),
1352 (m), 946 (m), 844 (s)cm- lL6].IR spectrum of HCOSH:
3310 (w), 2850 (m), 2540 (m), 1661 (s), 1339 (m), 1235 (w),
1160(w), 1055 (w),946(s),727 (~),692(s),and666(s)cm-''~~.
From the UV and 'H-NMR spectra it can be seen that
HCOSH exists preferentially in the thiol form; only the
weak bands in the IR spectrum at 3310 (0-H) and 1235
(C=S) cm-' indicate very small amounts of acid in the
hydroxy form. This is in accord with results obtained in
the study of monothioacetic
Both S- and 0-esters of HCOSH can be prepared: the
S-methyl ester is formed on reaction of Na[HCOS] with
methyl iodide, and the 0-ester on reaction of methyl
orthoformate and H,S in the presence of ZnC1, and
hydroquinone[']. 'H-Nh4R spectrum of HCO(SCH,) :
6,H=10.12 and 6,,=2.34ppm;
of HCS(OCH,): 6,,
=9.66 and 6,,,=4.02 ppm.
Received: March 26,1971 [Z 406 IE]
German version: Angew. Chem. 83,444 (1971)
[I] Part 49 of Cha1cogenocarbonates.-Part 48: G. Gattow and M.
Dr4ger, Z. Anorg. Allg. Chem. in press.
[2] M . !I Auger, C. R. Acad. Sci. Paris 139,798 (1904).
[3] G. Gattow, M. Drager, and R. Engler, Naturwissenschaften 58, 53
141 G . Gattow and R. Engler, Naturwissenschaften 58, 53 (1971).
[ S ] 60 MHz; measured in DCCI, against TMS as internal standard.
[6] s = strong, m = medium, w = weak.
[7] R. Mecke and H . Spiesecke, Chem. Ber. 89, 1110 (1956).
[ 8 ] R. Mayer and H. Berthold, Z. Chem. 3,310 (1963); Chem. Ber. 96,
3096 (1963).
Br, +AgNCO
( I ) +AgBr
Carbonyl isocyanate is formed as by-product, in proportions increasing as the temperature is raised; at 250°C it
is the main product.
Bromine isocyanate in the solid state (below - 60°C) forms
yellow crystals that melt to a brown unstable liquid that
dimerizes to crystalline (2) very rapidly. In this, (I) differs
from chlorine isocyanate which dimerizes under these
conditions to the cyclic 1,3-di~hlorouretidinedione~~~.
is characterized, not only by this ready polymerization but
also by extreme sensitivity to moisture; the cyanic acid
formed on hydrolysis can be detected by IR spectroscopy.
Purification of (I) is accompanied by great losses because
its volatility is comparable with that of cyanic acid and of
bromine [HCNO 2 (I) 2 Br2] and because liquid (1) is
unstable, so that (I) has in fact not been obtained completely free from bromine.
The IR spectrum of (1) (condensed on a KBr disk cooled
in liquid N,) showed bands in the 4OOO--400 cm-' region
at 3440m, 2256s, 2164vs, 2120ms, 1289ms, 690ms,
566 s, and 473 m an-'. Molecular weight (mass-spectrometric): 122.
A column (length 15 cm,0 2 cm) of a finely ground (24 h)
mixture of AgNCO (prepared according tdS1;4o.g) and
roasted quartz powder (20g) is pre-heated for 12 h at
200°C; gaseous bromine (taken from a trap cooled at
-45°C) is passed at 1torr in a dynamic vacuum through
this column while it is heated at 150°C. The~reaction
products are condensed at -196°C. (I) can be largely
purified by several fractional recondensations in the temperature range -45 to -85 "C.
Received: January 27,1971 [Z 414 IE]
German version: Angew. Chem. 83,445(1971)
L. Birckenbach and M . Linhard, Ber. Dt. Chem. Ges.62,2261(1929);
63, 2528 (1930).
[2] E. Nachbaur and W Gottardi, Mh. Chem. 97,115 (1966).
[3] L. Birckenbach and M.Linhard, Ber. Dt. Chem. Ges. 63,2544 (1930).
141 W Gottardi and D. Henn, Mh. Chem. 101,264 (1970).
[5] W Gottardi, Mh. Chem. 102,264 (1971).
Bromine Isocyanate
By Waidemar Gottardi[*]
Birckenbach and Linhard"] failed to obtain bromine isocyanate (1) by treating silver isocyanate with bromine in
ethyl chloride at -8O"C, obtaining instead the acyclic
dimer, N,N-dibromocarbamoyl isocyanate (2).
Since monomeric chlorine isocyanate''' and iodine isocyanater3' can be prepared it appeared that it should be
possible to synthesize (I) if the reaction conditions were
chosen so as largely to exclude dimerization. This can be
done by reaction of gaseous Br, with AgNCO at 150°C
and condensation of the resulting (I) at -196°C.
[*I Dr. W. Gottardi
Institut fur Anorganische und Analytische Chemie der Universitat
A 6 0 2 0 Innsbruck, Innrain 52a (Austria)
Trisboranephosphite and Tetrakisboranephosphate
By Erwin Mayer"]
Oxyacids of non-metals and their ions show a surprising
chemical resemblance. to compounds in which the oxygen
is replaced by an isoelectronic BH, group[']. Boranecarbonyl, H,BCO, and the boranecarbonate ion,
[H3BCO2I2-, react similarly to CO, and CO:-. Of the
analogs of phosphorus-oxygen ions, the bisboranephosphite ion (I) which is isoelectronic with hypophosphite is
already known[2-41:
p] Dr. E. Mayer
Institut fur Anorganische und Analytische Chemie der Universilt
A 4 0 2 0 Innsbruck, Innrain 52a (Austria)
Angew. Chem. internat. Edit. / Vol. 10 (1971) / N o . 6
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