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Deutsche Gold- Und Silber-scheideanstalt Vormals Roessler

Kurt Gunther

Gunter Giesselmann

Jurgen Martens

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Maren Schickedanz

Alkylisothiocyanic acid esters having the formula R--N.dbd.C.dbd.S can be prepared by reacting N-alkyldithiocarbamates with hydrogen peroxide in aqueous phase at 95.degree. to 130.degree. C. The aqueous solution of N-alkyldithiocarbamate is reacted with a 20 to 40% by weight aqueous solution of hydrogen peroxide in a volumetric ratio of 1 to 0.8 to 1 while maintaining a pH of 1.5 to 4.5. The solutions are preferably sprayed into a reactor, at which time the alkylisothiocyanate formed distills off in vapor form and an aqueous phase containing the byproducts collects in the reactor. The method is capable of significantly increasing the space-time yield because much less sulfur is formed in comparison to the previously known method, which takes place at pH 5 to 9, thereby minimizing the shutdown times previously required for cleaning the reactor.

Method of preparing alkylisothiocyanic acid esters

Thin-layer chromatography is employed to separate enantiomers of the general formula, ##STR1## in which C* represents an asymmetric center and the substituents R.sup.1, R.sup.2, and R.sup.3 are such that they supply the structural element ##STR2## for .alpha.-amino- or .alpha.-iminocarboxylic acids, particularly the well-known .alpha.-amino- or .alpha.-iminocarboxylic or for derivatives of such carboxylic acids, either of which contains no free thiol groups. In the thin-layer chromatographic separation operation a TLC plate is used which is coated with silica gel hydrophobicized by a silane derivative and which is further impregnated with an ionic compound of a divalent transition metal and a chiral selector. The mobile phase employed is a ternary mixture of a water-miscible alkanol, such as methanol, water, and acetonitrile, or a quaternary mixture of the latter ternary mixture to which a water-miscible cyclic ether, such as tetrahydrofuran, has been added.

Thin-layer chromatographic method for the separation of enantiomers

Methyl isocyanate is prepared by reacting an alkali cyanate with dimethyl sulfate in the presence of an alkaline earth metal oxide and in an inert organic liquid. There can also be present an alkali metal or alkaline earth metal salt.

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Erlensee, Germany

Kurt Gunther