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Electrolytic Desulfurization of 2-Mercapto Carboxylic Acids and the Corresponding Disulfides.

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t
(CH3)3C
The product 4,4-di-tert-butyl-3-methyl-4H-l,2-oxazete
2oxide (2) is the first derivative of the new system 4H-1.2oxazete. It was isolated in quantitative yield when a solution
of ( I ) in ethanol, after having been allowed to stand overnight, was evaporated down and the residue recrystallized
from ethanol.
The structure of ( 2 ) , which melts at 85 "C and sublimes with
spontaneous cyclization at 50 OC/lO-3 torr, is proved by the
following findings: C,H,N analysis; molecular weight (calc.
199; found 205, osmometrically); N M R spectrum (in
CDC13, 8 scale), 2 singlets at 1.2 and 2.1 ppm with relative
areas 6:l; IR spectrum (in Cc14). strong band a t 1698 cm-1
in the stretching vibration region of C = N bonds in
rings; UV spectrum, sharp band (half width 27 nm) at
222 nm, E = 7 . 4 ~lo3 (nitrones have similar UV spectra) 121.
On catalytic hydrogenation (room temperature; atmospheric
pressure, Raney Ni, dioxane) the oxazete (2) slowly absorbs
1 molecular equivalent of hydrogen. The hydrogenation
sublimes at 6OoC/10-2 torr) is
product (3) (m.p.
characterized by the following data: C,H,N analysis; N M R
spectrum (in CDC13). four singlets at 1.1, 2.1, 5.0, 8.9 ppm
with relative areas 18:3:1:1 (the signal at 8.9 ppm shows the
characteristic broadening of oxime protons); I R spectrum
in (CCl4), two bands at 3594 and 3459 cm-1 in the 0 - H
stretching region. Like other a-hydroxy oximes [31, compound
(3) forms a Cu2+ complex. The hydrogenation occurs as for
isoxazoline N-oxides 141.
The kinetics of the isomerization (1) -f (2) was studied
in several solvents by measuring the decrease in extinction
of the UV band of (I) at 345 nm. In all cases, the reaction was
clearly of the first order. The velocity increases with increasing
polarity of the solvent; half-reaction times are 140 h in nhexane, 70 h in diethyl ether, 2 h in ethanol. Solid ( I )
isomerizes to (2) within several weeks.
The unusua1 cyclization must be due to the strong steric
hindrance by the four substituents around the C=C bond.
In compound ( I ) this hindrance is avoided by rotation
around the C=C bond; in (2) this angle of twist amounts
formally to 90". A similar strong rotation is observed also
in the anion radical of ( I ) [*I.
Compound (2) is stable to heat up to at least 100 "C and can
be considered as a new example of stabilization of small rings
by tert-butyl groups (51.
Received: June 27, 1968
[Z 816 IE]
German version: Angew. Chem. 80. 666 (1968)
[*I Dr.
A. Berndt
Institut fur Organische Chemie der Universitat
355 Marburg, Bahnhofstr. 7 (Germany)
[I] A . Berndt, Tetrahedron, in press.
[2] J. Thesing and W. Sirrenberg, Chem. Ber. 91, 1978 (1958).
[3] F. Feigl, G. Sicher, and 0. Singer, Ber. dtsch. chem. Ges. 58,
2294 (1925).
[41 A. Dornow and G.Wiehler, Liebigs Ann. Chem. 578, 113
(1952).
[5] S.S.Rechtand F.D. Creene, J.Amer. chem. Soc.89,6761(1967).
.
the aqueous solution salts of the composition MC404.2 HzO
(M = Ca, Mn, Fe, Co, Ni, Cu, or Zn). According to the
temperature at which precipitation occurred and the excess
of potassium squarate used we obtained three compounds
that were readily distinguishable by X-rays. The pure cubic
modification, of composition MCz04.2 HzO is formed when
a 0.5 M metal salt solution is precipitated at the boiling point
by a three-fold excess of 0.5 M potassium squarate and the
precipitate is heated under reflux in the mother liquor for a
further three hours. When isolated and dried over KOH in
vacuo the dihydrate shows remarkable thermal stability; loss
of the two molecules of water is observed therrnogravimetrically only between 200 and 260 'C.
Indexing of the Guinier photographs (internal standard:
KCI) yields a simple cubic unit cell containing three formula
units MC404.2 HzO.
1
cOc404.2 HzO
NiC404.2 Hz0
1
Q
(A)
8.16
8.06
1
1
1
d y (g/cm3)
I
1.87
1.93
(g/cm3)
1.90
1.97
The reflectance spectra of the powdered substances are
typical of octahedral coordinated cobalt and nickel compounds, with absorption maxima (in cm-1; sh = shoulder) at:
COc404.2 H20: 7800, 11400 sh, 16000 sh, 19600, 21500 sh
NiC404.2 H20: 8600, 13300, 15200, 21 500 sh, 25300.
The values of the ligand field parameters Dq and the Racah
parameters B are collected in the annexed table, where the
corresponding values for the hexaaquo complexes 121 are
given (in parentheses) for comparison.
NiC404.2 HzO
The metal ion is bound to two water molecules and chelated
to two squarate ions; it is assumed from the size and symmetry of the unit cell that the two water molecules are in cispositions.
I
Received: June 10, 1968
[Z 818 IE]
German version: Angew. Chem. 80, 664 (1968)
[*I Dr. A. Ludi and Prof. Dr. P. Schindler
Institut fur anorganische, analytische und physikalische
Chemie der Universitat
CH-3000 Bern, Freiestr. 3 (Switzerland)
[**I We thank the Schweizerischer Nationalfonds for financial
support.
[l] R. West and H.Y. Niu, J. Amer. chem. SOC.85, 2589 (1963).
[2] H . L. Schlafer and G. Gliemann: Einfuhrung in die Ligandenfeldtheorie. Akademische Verlagsgesellschaft, Frankfurt/Main
1967, p. 86.
Electrolytic Desulfurization of 2-Mercapto
Carboxylic Acids and the Corresponding DisuEdes
By P. Rambacher and S. Make[*]
Unit Cells and Absorption Spectra of the Cubic
Squarates of Cobalt and Nickel [**I
By A. Ludi and P. Schindler[*]
On treatment of bivalent metal ions with potassium squarate
(squarate anion = C4O$--, the anion of squaric acid, 3,4dihydroxy-3-butene-l.2-dione). West et al. 111 obtained from
638
Electrolytic reduction of cystine o n tinned electrodes or o n
copperrxl leads to a n almost quantitative yield of cysteine
without detectable evolution of hydrogen sulfide. However,
in attempts to reduce isocystine [2,2'-dithiodi-(3-aminopropionic acid)] to 3-amino-2-mercaptopropionic
acid in the
same way reduction was accompanied from the beginning by
evolution of hydrogen sulfide, which ceased only when all
Angew. Chem. internat. Edit. I Vol. 7 (1968) I No. 8
the sulfur had been removed. A similar evolution of hydrogen
sulfide was also observed when isocysteine was used. The
only further reduction product isolated was p-alanine in the
form of its benzoyl derivative. This reductive exchange of
sulfur for hydrogen occurs also with other 2-mercapto
carboxylic acids and their derivatives. For instance, mercaptoacetic acid gives acetic acid, and 2-mercaptopropionic
acid gives propionic acid. Desulfurizations of this kind were
previously known only for reactions on Raney nickel [2J.
Experimentid:
Isocystine (12 gj was dissolved in a mixture of concentrated
hydrochloric acid (12 ml) and water (200 ml) and reduced
electrolytically at 2 A and 5 V at a copper cathode (current
density 6 A!dm*). Graphite in hydrochloric acid served as
anode, and was separated from the cathode chamber by a
diaphragm. The transient SH reaction of the solution disappeared after 4 h, during which time hydrogen sulfide was
continuously evolved. The solution was concentrated and
7.1 g of benzoyl-P-alanine (m.p. 133OC) were isolated on
benzoylation.
Isocysteine hydrochloride (4 g) was treated similarly.
After 2.5 h a t 1 A (current density 3 Aidrn2) benzoylation
afforded 3 g of benzoyl-@-alanine.
4 8 mmoles of hydrogen sulfide were evolved from 50 mmoles
(4.6 g) of mercaptoacetic acid at a copper cathode (8 A/cm2)
within 8 h; it was trapped in cadmium acetate solution and
determined iodometrically. 2 g of acetic acid were determined
by gas chromatography of the cathode liquid.
Analogous treatment of 50 mmoles (5.3 g) of 2-mercaptopropionic acid gave 47.8 mmoles of hydrogen sulfide and
2.3 g of propionic acid (determined by gas chromatography).
Double irradiation of A results in some simplification of B,
and D collapses t o a sharp singlet. Resonance A becomes a
doublet when B is irradiated, and C changes to a broad
singlet. The contour of B changes when C is irradiated, and
irradiation of D causes A to collapse t o a doublet, with some
sharpening of resonance C.
Clearly, these N M R data d o not correspond t o those found
with the familiar complexes X - C ~ H ~ M ( C O
(M) ~= Fe, Ru),
even in their fixed configurationc21. In particular, the couplings between HA and HD, and between H B and H c , indicating one hydrogen coupling t o two other identical hydrogen atoms in each case, severely restrict the possible structures of this complex.
We propose the novel structure ( I ) for this complex, i n
which the hydrocarbon is bonded to the Os(CO), group by
both a r-ally1 system and by a metal-carbon D bond, with the
C8H8 assuming a boat configuration. The deshielding effect
of the vinylic systems on the protons HB of the =ally1 group
causes H c t o be at higher field than HB. The bands in the
infrared spectrum at 1640 (vc,~) and at 775 cm-1 (cis-C-C)
lend support t o this structure.
It is of interest that complex ( I ) isomerizes on gentle warming in solution to an orange-yellow complex (2),m.p. 90.5 "C,
which shows vco at 2072 (s), 2001 (s), and 1989 (s) cm-1
(cyclohexane, and which shows a single resonance at 4.78 7
(CDCI3). Complex (2) is evidently analogous to the now
well-known iron [31 and ruthenium [21 cyclooctatetraene
complexes, and the ease of isomerization is convincing
evidence that the hydrocarbon iigand in complex ( 1 ) has a
similar carbon skeleton to that in complex (2).
Received: June 28, 1968
[Z 820 IEI
German version: Angew. Chem. 80, 664 (1968)
[*I Dr. P. Rambacher and S. Make
Forschungslaboratorium des Werkes Pharmazell der
Aschaffenburger Zellstoffwerke AG
8201 Redenfelden (Germany)
[11 P . Rambacher, German Pat. 1024518 (Nov. 29, 1955),
Aschaffenburger Zellstoffwerke; Chem. Zbl. 1958, 11952.
[Z] R . Schrofer in W. Foerst: Neuere Methoden der Praparativen
Organischen Chemie. 4th Edit., Verlag Chemie, Weinheim 1963,
Vol. 1 , p. 88.
o,x-C8H8Os(CO),, an UnusuaI CycIooctatetraeneTransition Metal Complex
By M. I . Bruce, M . Cooke, and M. Green [ *I
Ultraviolet irradiation of dodecacarbonyltriosmium and
cyclooctatetraene in benzene (room temperature, 72 h) affords a pale yellow crystalline complex (I), m.p. 69 "C, of
molecular formula C11H~o@S(found: mol. wt. 380.00792;
calc. for CllH8031920s: mol. wt. 380.00906). The parent ion
shows stepwise loss of three carbonyl groups, and the infrared
spectrum shows three bands at 2079.5 (s), 2008 (s), and
1995.5 (s) cm-1 (cyclohexane), characteristic of the YCO for
a n M(C0)3 group. Other bands occur at 1640 (m), 1350 (m),
877 (m), 814 (m). 775 (s), and 708 (m) cm-1 (CS2).
The IH-NMR spectrum at room temperature (100 and 220
MHzLll) remains unchanged o n cooling to -14OoC, and
shows four absorptions (A, B, C, D; see Table).
Table
1. 'H-NMR spectrum of ( I ) at 100 and
Resonance
I
;cc14)
I
220 MHz.
Multiplicity and
A
4.0
2
B
C
D
4.9
5.2
4
7.45
1
1
Double doublet;
JAB = 6.5, J ~ =
D 4.5
Assyrnetric complex multiplet
Broad triplet; JBC = 9.5
Triplet; JAD = 4.5
Angew. Chem. internat. Edit. 1 VoI. 7 (1968) No. 8
As expected, the 1,2 motion of the Os(CO), moiety around
the ring is slower in complex (2) than that found in the iron
and ruthenium complexes, as evidenced by the resolution of
the IH-NMR spectrum a t higher temperatures.
Complex ( I ) is not reformed from (2) either thermally or by
ultraviolet irradiation. We suggest that the formation of ( I )
results from fragmentation of a n initially formed complex
between cyclooctatetraene and the Os3 cluster, perhaps anaC Oboth
) ~ of
logous t o ( C B H & R U ~ ( C OC41
) ~ or C ~ H ~ F ~ Z ([51,
which have been shown t o contain n-ally1 systems.
__-__
Received: May 3, 1968
[Z 822 IE]
German version: Angew. Chem. 80, 662 (1967)
[*] Dr. M. I. Bruce, M. Cooke, and Dr. M. Green
Department of Inorganic Chemistry
The University
Bristol 8 (England)
[I] We thank Dr. J . Becconsull for the 220 MHz 1H-NMR
spectra.
121 F. A . L. Anet, H. D. Kaesz, A . Maasbol, and S . Winstein,
J. Amer. chem. SOC.89,2489 (1967); M. I. Bruce, M. Cooke, and
M . Green, J. organometallic Chem. 13, 227 (1968); W . K. Bratton, F. A . Cotton, A . Duvison, A . Musco, and J . W. FaNer, Proc.
nat. Acad. Sci. USA 58, 1324 (1967).
[31 T. A. Munueland F. G. A . Stone, J. Amer. chem. SOC.82,366
(1960); M. D. Rausch, and G. N . Schrauzer, Chem. and Ind. 1959,
957; A. Nakamura and N. Hagihara, Bull. chem. SOC.Japan 32,
880 (1959).
I41 M. J . Bennett, F. A . Cotton, and P. Legtdins, J. Amer. chem.
SOC.89, 6791 (1967).
I51 E. B. Fleischer, A . L. Stone, R . B. K . Dewar, S. D. Wright,
C. E. Keller, and R. Petfit, J. Amer. chem. SOC. 88, 3158 (1966).
639
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acid, carboxylic, desulfurization, electrolytic, mercapto, disulfide, corresponding
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