Boffis - 11-5-2014 at 17:54
The Preparation of Diaminoglyoxime from Dithiooxamide
In Axt's work on Diaminoglyoxime and Diaminofurazan (SM Prepublication) he references a paper (1) concerning a complex energetic heterocyclic in which
the preparation of diaminoglyoxime from rubeanic acid (dithiooxamide) is described. Given that rubeanic acid can be prepared by reacting cyanogen and
hydrogen sulphide gases in the presence of a little water and alcohol (2) or by passing hydrogen sulphide into a solution of copper sulphate just
decolourised with sodium or potassium cyanide (3) I thought it fruitful to compare this alternative route into these compounds with the glyoxal route
of Axt. While the second route to rubeanic acid is not amateur friendly due to the requirement for large quantities of alkali cyanide the former route
is; provide due care is exercised in handling the highly toxic gases and a suitably designed set of glassware is used (this is currently "work in
progress"). The idea of using cyanogen to prepare dithiooxamide occurred to me after reading a thread on SM concerning the preparation of cuprous
cyanide from readily obtainable ferrocyanides. Cuprous cyanide reacts with ferric chloride solution to give cyanogen gas (4) and this is reacted with
excess hydrogen sulphide in a large flask containing a little, vigorously stirred, water or diluted alcohol.
The work described below is concerned with my experiments into the preparation of diaminoglyoxime from rubeanic acid.
Experiment 1
5g of rubeanic acid was dispersed into 25ml of water and 5.78g of hydroxylammonium chloride added; the orange slurry was placed in a 150ml round
bottom flask in heating mantle with a built in magnetic stirrer and a PTFE stirrer bar (15mm) placed in the flask. 33.5ml of 10% sodium hydroxide
solution was added rapidly. A faint smell of hydrogen sulphide was soon detectable, to prevent the escape of the gas a reflux condenser was added to
the flask and a take-off point added to the top of the condenser with a rubber pipe leading to a Dreschel bottle containing 70ml of 10% NaOH solution
as a scrubber. The slurry was stirred and warmed slowly to reflux and then gently refluxed until no further hydrogen sulphide was released (about 2
hrs.). At this point the flask content comprises an orange yellow, cloudy solution; 0.2g of decolourizing charcoal (BDH brand) was added and the
solution reheated for a few minutes. The solution was allowed to cool to about 60 C and then filtered at the pump. The clear brownish orange filtrate
slowly became cloudy again as it cooled and only deposited crystals after standing for several hours at room temperature (14 C). The coarse bladed
crystals were rinsed with ice cold water and then recrystallized from about 35ml of boiling water after the addition of 0.1g of decolouring charcoal
and filtering; a slight cloudiness appeared before the product crystallised. On cooling pale brownish yellow blades of diaminoglyoxime were deposited,
they were rinsed with a little cold water and dried; yield 2.309g (46%). This material does not appear as pure as the product prepared from glyoxal as
tiny brownish inclusion are visible under the microscope. Further attempts to purify this material are in hand.
Experiment 1 showing the set up with the dreschel gas washing bottle
Experiment 1 after 2 hrs refluxing not the insoluble material (sulphur?)
Experiment 2
This experiment differed from the previous only in the sequence of reagent addition. 5.79g of hydroxylammonium chloride was dissolved in 25ml of water
and the added drop wise to a solution of 5g of rubeanic acid in 33.5ml of 10% sodium hydroxide solution in a 150ml round bottom flask. Once the
addition was complete it was refluxed as before. After the initial charcoal treatment the solution was deep orange yellow and on cooling and standing
for 24 hours gave no crystalline product at all. The solution was evaporated down to half its original volume on water bath and cooled but still gave
no crystals. A few drops were tested with ammonical nickel acetate solution and gave only a small amount of almost black precipitate (nickel
sulphide?) but no terracotta coloured nickel diaminoglyoximate. It appears that no diaminoglyoxime was formed in the procedure.
This second experiment was a total failure possibly because the warm alkali rapidly hydrolyses the rubeanic acid before it can react with the
hydroxylamine. It is intended to try further experiments using free hydroxylamine solution and to dissolve the rubeanic acid in alcohol in order to
create a homogeneous reaction mixture with the strongly alkaline conditions.
Conclusion
While the reaction works the yield is low and the reaction susceptible to conditions, however, Gunasekaran & Boyer report yields of 85% for their
procedure so further work to seems worthwhile. Work on a safe synthesis of rubeanic acid from cuprous cyanide is also in progress.
1) Gunasekaran & Boyer; 1993; Dense Energetic Compounds of C, H, N & O atoms III -
5-(4-Nitro-(1,2,5-oxadiazolyl-5H-(1,2,3)-triazole-(4,5-c)(1,2,5)oxadiazole; Heteroatom Chem. 4 (5) pp521-524
2) H E Williams; Cyanogen Compounds Their Chemistry Detection and Estimation; 2nd Ed, 1947; p14
3) J. Formánek; Beitrag zur Kenntniss des Rubeanwasserstoffs; Berichte 1889, v22 pp2655-2656
4) G. Jacquemin; Preparation du cyanogene; Ann. de Chim. et de Phys.; 1885, ser6, vol 6 p140-144