qashimalik - 12-3-2004 at 10:12
can someone tell me the preparation of lead thiocyanate???
chemoleo - 12-3-2004 at 10:54
Isn't this some weak primary?? In that case it should be in the Energetic Mat. Section.
If so, I would be happy to hear some data about it - despite searching I never found much about it.
Later edit: No, it is not a primary, but yet added to certain types of blasting caps, i.e. those containing Pb-azide.
As to the Synthesis- you need to find out whether Pb(SCN)2 is insoluble in H2O. If it is (which is likely), it should be easy to prepare it - mix
Pb(Ac)2 (aq) with KSCN in stoichiometric amounts, and hope for a precipitate 
[Edited on 4-12-2004 by chemoleo]
chemoleo - 12-3-2004 at 14:32
Ok I had a look at Roempp.
It says it is a colourless non-smelling powder, density 3.82. It decomposes at 190 deg C (how fast is the decomposition? 
), and is slightly soluble in water --->>> THE PRECIPITATION REACTION WOULD
WORK!
It also mentions it is produced just like how I described.
Apparently it is used in saftey matches, and firing caps (blasting caps?)
Does anyone know more?
Mephisto - 13-3-2004 at 16:12
There is a detailed prescription of its synthesis in Brauer [1]. But it's not difficult to figure it out by oneself. Nevertheless, here it is:
[color=darkgreen]For 90 g Pb(SCN)2 you had to add a solution of 90 g KSCN in 840 ml distilled water with continuously stirring to a second
solution of 150 g Pb(NO3)2 1500 ml distilled water. Put the mixed solution to the freezer to complete the crystallization. Filter out the crystals and
wash them with some parts of cold water. After drying, you will have 90 g lead thiocyanate.[/color]
[1] German handbook: Brauer, Handbuch der Präparativen Anorganischen Chemie Vol 1-3, Stuttgart; Ferdinand Enke, 1975 - BTW: It's on the
ftp.
Another lead thiocyanate synth
Elroy - 4-12-2004 at 11:25
I have no idea why anyone would want to make lead thiocyanate, other than the joyous thrill of watching ppt fall out of solution But here's another way to make it simply if other materials cannot bee
obtained. I found this on a photographer's forum online. Alas, I don't have the ref., but here's what I do have (formula copied
verbatim from source). Hope this helps.
ammonium thiocyanate 0.2 oz
water to make 8.25 oz
lead acetate 0.1 oz
boiling water to make 8.25 oz
dense ppt will settle as lead thiocyanate.
It didn't say, but I assume one would prepare each of the two solutions separately, and add one to the other. After cooling, filter and dry.
(keep the crystals. The liquid is ammonium acetate and water). Use distilled water throughout.
I have not done this, but it makes sense to me. Pb(SCN)2 is soluble in 200 parts cold water and 50 parts boiling water, and is obviously
poisonous. The amount of water in the above rxn is below these thresholds, but I would chill the combined solutions to ensure complete precipitation
(not in the 'fridge!) in an ice bath after addition. I don't know if fumes are a factor, so assume they are and ventilate.
As for the reagents, where to get? Last I saw, lead acetate is a watched substance so if purchasing as such, buy only what you need. It seems
to me (speculation here) that combining lead peices with acetic acid would produce lead acetate. I'm going to try this unless I learn otherwise.
Lead acetate is alo poisonous. Lead acetate, unless labelled anhydrous, comes as the trihydrate and as such is soluble in water. If it is old,
improperly stored, or otherwise exposed to air for lengthy periods, it absorbs CO2 and becomes incompletely soluble in H2O.
Ammonium thiocyanate is not on any watched list I have and is available through common suppliers. It appears to be used in photography.
Now, more speculation. I am curious to know whether one could use something other than lead acetate. Consult a table of the Activity Series of
the Elements and you see 14 possibilities. Only I don't know where the ammonium ion would fit here. I'm thtumped. Anyone?
Also, any idea what a good recrystallization solvent would be for lead thiocyanate? I imagine some ammonium acetate will be present as an
impurity. I'm reluctant to experiment with different solvents on a poisonous compound like this one. Maybee just washing filtered crystals with
cold dH2O would work well enough. Never know till ya try.
I hope this post helps somebody, 'cause so many strangers have helped me in my lusty thirst for knowledge I could cry.
[Edited on 4-12-2004 by Elroy]
Esplosivo - 5-12-2004 at 00:59
Tried the synth of thiocyanate just now - had nothing better to do. Mixed some lead nitrate with KSCN in roughly stoichiometric quantities. A white
ppt. formed, and the solution turned somewhat reddish brown (might be iron (III) impurities - not sure). I did this only with small quantities. Is
anyone sure if this rxn can work out also with lead ethanoate instead of lead nitrate? Lead ethanoate can be produced cheaply and in good amounts
quite easily. I know lead ethanoate can be converted easily into lead nitrate but that would 'waste' nitric acid sort of. Thanks for the
help.
Edit: Left to stand, ignorantly, in sunlight. Turned yellowish. Just found out that it photodecomposes.
After warming some of the sample a greyish substance was formed soluble in hot dilute nitric acid - most probably the Pb(SCN)<sub>2</sub>
decomposes to lead and oxides of sulfur and carbon, together with nitrogen and maybe some NO<sub>x</sub>. Decomposition was not explosive,
although deflagration did occur. Note that my product was wet and in small quantities (I have heated less than 1g of sample).
[Edited on 5-12-2004 by Esplosivo]
Similar route, but as a byproduct
roXefeller - 23-12-2020 at 19:54
I was looking to produce guanidine nitrate a different way after the condensation reaction failed (from a defective thermometer). Guanidine
thiocyanate is a reagent in biology labs, for protein folding I think. Anyway the guanidinium is more reactive than lead as a result of the amine
orbitals. Likewise the thiocyanate group is less reactive than nitrate ions because of the electron withdrawing effect of three oxygen atoms. Just
as KSCN can participate because potassium is more reactive than lead, almost everything can replace lead, but the real need is something more reactive
than thiocyanate. Which the nitrate does in spades. I almost bought guanidine hydrochloride but I think it is more electronegative than nitrate. I
would appreciate some advice on quantifying that using the constituent pauling electronegativities.
Anyway, using lead nitrate solution that was leftover from producing lead dioxide, I measured out 10mL in a cylinder. It weighed 12.82g. Based on
the low concentration and high molecular weight, I was satisfied in the approximation that 2.82g lead nitrate were present. Stoichiometry says 2x118g
guanidine thiocyanate + 331.2g lead nitrate react to form 2x122g guanidine nitrate + 323.2g lead thiocyanate. Then 2.009g guanidine nitrate are
needed and will produce 2.078g guanidine nitrate and 2.752g lead thiocyanate.
The reaction proceeded without much energy. Heavy precipitation formed. I added distilled water to make 40mL total and allowed for settling. I
filtered off a white precip and set the filtrate on the hotplate with stirring until it boiled to ~5mL. Guanidine nitrate is very soluble at
boiling. Then allowed to cool slowly with stirring. A white/light yellow cake formed. It weighed 2.62g. I expect 0.553g/100mL of lead thiocyanate
to ride along, 0.22g. I also saw a little precipitation pass the filter before the boiling. The precipitate in the filter is still drying but will
probably be at 2.2g when dry. I'll report back if something different occurs.
I'm going to check solubility with methanol to see if I can separate the products better.
Edit: The precipitate is weighing out near 2.7g, which is near the theoretic weight expected. Maybe not much went into solution from the high
solubility of the guanidine nitrate salt. I think the error lies in the assumed quantity of lead nitrate in the original solution. It may have
displaced around a half or quarter gram of water. If so, then it would end up in the evaporate, unreacted. I have 8mL evaporating right now to weigh
the dry mass.
[Edited on 24-12-2020 by roXefeller]
Edit2: 8mL evaporated to 2.65g lead nitrate at the rate of 0.33g/mL. This made a 0.49g excess in the original reaction and brings the final numbers
closer to predictiins 2.62-0.49=2.13g compared to 2.078g. Lead thiocyanate was probably the remaining weight.
[Edited on 24-12-2020 by roXefeller]