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Facile Synthesis of Racemic Cysteine.

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COMMUNICATIONS
Procedure
Facile Synthesis of Racemic Cysteine
By Jiirgen Martens, Heribert Offermanns, and
Paul Scherberich'"
Until now racemic cysteine has only been synthetically
accessible via expensive multi-step syntheses['].
In the course of our investigations on the synthesis of
natural and unnatural amino acids['] and amino acid deriv a t i v e ~ [we
~ ] have now found a facile and efficient synthesis for DL-cysteine hydrochloride . H 2 0 (3). The key intermediate, 2,2-dimethyl-3-thiazoline ( I ) , can be obtained in
92% yield in a one-pot reaction from chloroacetaldehyde,
sodium hydrogen sulfide, ammonia and acetone. This
reaction is based on the fundamental studies of Asznger et
a1.[4~.
( I ) : 350 mg of a 45% aqueous soIution of chloroacetaldehyde (2.0 mol) is added between 0 and 1O"C, over 45 min,
to a suspension of sodium hydrogen sulfide (135 g, 2.4
mol) in acetone (450 mL, 6.1 mol), 235 g water, and ammonia
(93 g, 5.5 mol). After 25 min at 5- 1O"C, the organic and
aqueous phases are separated. Fractional distillation of the
organic phase (88--89"C/100 mbar) gives 106 g (1) (92%)
as a colorless liquid.
(2): Hydrocyanic acid (50 mL, 1.3 mol) is added over 60
min to a stirred solution of ( I ) (I15 g, 1 mol) in 100 mL
methanol at 5-10°C. After 30 min at 15-20°C, the solution of (2) obtained is directly further reacted.
(3): A solution of (2), as prepared above, is dropped over
60 min into 1000 mL (ca. 11 mol) conc. hydrochloric acid
at 20-30°C. After 3 h stirring at 40-50°C the mixture is
diluted with 600 mL water, the methanol and acetone distilled off, the resulting solution refluxed for 4-5 h, clarified with activated charcoal and the solvent removed. Ammonium chloride, which does not dissolve upon digestion
of the residue in 400 mL methanol, is filtered off. The
methanolic filtrate is evaporated to dryness and the residue recrystallized from 20% hydrochloric acid ; (3) forms
thick colorless crystals. The latter are suction-filtered,
washed with cold 20% hydrochloric acid, and dried in a
fluidized bed dryer at 20--40°C. 122.9 g (70%) of (3) is
obtained from two crystallization fractions; the product is
found to be pure by thin layer chromatography.
Received: December 5, 1980 [Z 797 IE]
German version: Angew. Chem. 93. 680 (1981)
CAS Registry numbers: (I), 66692-88-4; (%)-(2), 78249-03-3; (DL)-(3/ . HCI,
10318-18-0; acetone, 67-64-1 ; chloraldehyde, 107-20-0; sodium hydrogen
sulfide, 16721-80-5
111 J . P. Greenstein. M . Winitz: Chemistry of the Amino Acids, Vol. 3, Wiley,
New York 1961, p. 1892.
121 W. M . Weigeri, H . Offermanns, P. Sckerbericli. Angew. Chem. 87, 372
(1975); Angew. Chem. Int. Ed. Engl. 14. 330 (1975).
131 A . Kleemann, B. Lekmann, J. Martens, Angew. Chem. 91, 858 (1979); Angew. Chem. Int. Ed. Engl. 18. 797 (1979); A . Kkemann, W. Leuchienberger. J . Martens, H . Weigel. ibid. 92. 640 (1980); 19. 627 (1980).
(41 F. Asinger. H . Offermanns, Angew. Chem. 79. 953 (1967); Angew. Chem.
Int. Ed. Engl. 6, 907 (1967); M . Thiel, F. Asinger, K . Schrniedel. Justus
Liebigs Ann. Chem. 611. I21 (1958).
151 The isolated intermediates and i 3 j gave correct elemental analysis and
spectroscopic data.
Anhydrous hydrocyanic acid adds to the azomethine
group of ( I ) to give the 2,2-dimethylthiazolidine-4-carbonitrile (2) in almost quantitative yield.
New Tungsten-Iridium Dinuclear Complexes
Containing Cyclopentadienyl and Hydrido Bridges
The crude thiazolidine (2) can be directly further
reacted. Using aqueous hydrochloric acid, the desired (3) is
obtained in 709'0 yield (relative to ( I ) ) in a one-pot reacti
By Paul S. Pregosin, Antonio Togni, and
Luigi M. VenanziL'l
We have previously shown that neutral monomeric hydrido complexes of platinum(ir)""l and iridium(riI)['blreact
with cationic species to form dimeric complexes containing one or more bridging hydrido ligands.
As an extension of this work we report here the new dinuclear complex (la) obtained by reacting (2) with (3a).
["I Prof. Dr.
[*I Dr. J. Martens, Dr. H. Offermanns, Dr. P. Scherberich
Degussa A G
Postfach 2644, D-6000 F r a n k f u d M a i n (Germany)
668
0 Verlag Chemie GmbH. 6940 Weinheim. 1981
L. M. Venanzi, Dr. P. S . Pregosin, A. Togni (Ciba-GeigyFellow)
Laboratorium fur Anorganische Chemie
ETH-Zentrum, Universitatstrasse 6, CH-8092 Zurich (Switzerland)
0570-0833/81/0808-0668 $02.50/0
Angew. Chem. Int. Ed. Engl. 20 (198t) No. 8
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