PdCl2 is used in some electrochemical sensors present within common CO detectors found in homes, and such replacement sensors can be bought
seperately:
That would be bullshit. If you want PdCl2, make it from Pd bullion bought at market price from e.g. ebay.
PdCl2 is often much more expensive than the palladium it contains, so it always pays off to make it from the metal.obsessed_chemist - 13-7-2007 at 13:07
^ Yes, but ebay isn't exactly otc, and neither is palladium bullion. Plus, I'd rather not chlorinate palladium in my apartment if I don't have to,
especially if only small quantities are needed. But I see your point.
[Edited on 7/13/2007 by obsessed_chemist]garage chemist - 13-7-2007 at 13:22
PdCl2 is not made by chlorination of palladium.
Pd is dissolved in HNO3, then the solution is evaporated several times with HCl until all nitrate has been removed, and lastly the resulting H2PdCl4
is thermally decomposed to PdCl2 (although it would be more sensible to leave it as H2PdCl4 since this readily dissolves in water, in contrast to
PdCl2 which needs refluxing with HCl in order to revert it to H2PdCl4 which then dissolves in the water).leu - 13-7-2007 at 15:44
Quote:
PdCl2 is not made by chlorination of palladium.
It seems that reliable sources differ on this:
From Brauer's: Palladium (II) Chloride
The anhydrous salt is prepared by heating loose palladium sponge (contained in a porcelain boat set in a glass tube) to a dull red heat in a stream of
Cl2. According to Krustinsons, the decomposition pressure of PdCl2 reaches 1 atm. at 738 degrees C.
By dissolving finely divided Pd in conc. HCl through which Cl2 is bubbled, one obtains a solution in which both H2PdCl4 and H2PdCl6 can be detected.
Concentrating the solution also yields a residue of PdCl2.
PdCl2 Solution for the Detection of CO
Winkler gives the following method for preparing this solution. Pure Pd (0.2 g.) is dissolved with gentle heating in about 10 ml. of aqua regia. The
solution Is evaporated to dryness in a 50-ml. porcelain dish placed on a steam bath. The residue is dissolved in 10 ml. of 20% hydrochloric acid and
the solution is again evaporated to dryness; this last procedure is repeated three times. The resulting residue, which is now completely nitrate-free,
is mixed with 2 g. of KBr and dissolved (gentle heating) in 10 ml. of 1 N HCl. After dilution to about 150 ml. with water, a few particles of pumice
and 1 ml. of alcohol are added to the solution. which is then boiled for about 10 minutes in an Erlenmeyer flask in order to reduce any Pd (M) not
decomposed during the drying to Pd (H) and to drive off the excess alcohol. After cooling. 2.5 g. of CH3COONa . 3 H2O is dissolved In the liquid. The
solution Is filtered through a small wad of cotton wool and diluted to 200 ml. with the water used for washing the cotton wool. The clear,
reddish-brown liquid, which contains 0.1% palladium. is stable when stored in a flask provided with a ground-glass stopper. To be on the safe side, It
Is best to filter the solution before use; It should be stored In the dark.
REFERENCES:
J. Krustinsons. Z. Elektrochem. 44, 537 (1938); L. Winkler. Z. Anal. Chem.100, 321 (1935); 97, 18 (1934); also describes analytical methods for
detecting CO with PdCI2 solutions. Explicit directions for the preparation of palladium catalysts using PdCI2 are given by R. Mozingo in Organic
Syntheses, collective vol. III, p. 685 (Wiley, New York, 1955).
From Mellor's:
J. J. Berzelius prepared palladium dichloride or palladous chloride, by evaporating to dryness a solution. of palladium in
aqua regia, and dehydrating the residue by a gentle heat. L. R. von Fellenberg obtained the chloride, as a rose-red sublimate, and a garnet-red mass,
by heating palladium sulphide in a current of chlorine; and E. H. Keiser and M. B. Breed obtained it as a sublimate by heating spongy palladium to
dull redness in chlorine; the anhydrous chloride can be distilled at a low red-heat in a current of chlorine when it yields a sublimate of
deliquescent, dark red, acicular crystals. N. W. Fischer obtained a solution. of the chloride by exposing palladium to hydrochloric acid and air; the
process of dissolution is then a slow one. If chlorine is passed into hydrochloric acid in contact with palladium, the metal dissolves quickly to form
the dichloride; and if nitric acid is added to the hydrochloric acid, some palladous nitrate is formed. By evaporating the hydrochloric acid solution
over quicklime, the chloride is obtained in reddish-brown, prismatic crystals, which, if free from nitric acid, remain dry. L. N. Vauquelin found that
when palladium is dissolved in aqua regia, and the nitric acid removed by repeated evaporation with hydrochloric acid, there remains a
brownish-yellow, crystalline mass, which, according to the analyses of R. J. Kane, is the dihydrate, PdCI2-2H2O.
The dichloride obtained by dehydrating the dihydrate is a browniish-black mass; the sublimed salt appears as rose-red, or dark red, acicular crystals;
the unsublimed salt is a garnet-red crystalline mass. The dihydrate forms reddish-brown, prismatic crystals. V. M. Goldschmidt said that the crystals
are probably rhombohedral. L. Pauling discussed the structure. E. H. Keiser and M. B. Breed gave 2.5 for the sp. gr; and G. Beck, 4.00 for the sp. gr.
at 18 degrees and 44 for the mol. vol. J. J. Berzelius observed that the anhydrous salt fuses without decomposition when gently heated in a glass
vessel; when fused in a platinum vesed, it acquires a bluish-green colour by taking up platinum chloride. When.strongly heated, chlorine and palladium
are formed. F. Puche found that the dissociation begins at 600 degrees, and attains one atmosphere of pressure at 920 degrees.
References: J. J. Berzelius, Pogg. Ann., 13, 454 (1828); Schweigger's Jour, 7, 66 (1813); L. R. von Fellenberg, Pogg. Ann., 50, 61 (1840); E. H.
Keiser and M. B. Breed, Chem. News, 69, 197, 211 (1894), N. W. Fischer, Schweigger's Jour., 51,197 (1827), Pogg. Ann. 9, 256 (1827); 10, 607 (1827);
L. N. Vauquelin, Ann. Chim. Phys., (1), 88, 167 (1813), R. J. Kane, Phil. Trans., 132,275 (1842); V. M. Goldschmidt, Skrift. Norske Akad. Oslo, 5
(1925); L. Pauling, Proc. Nat. Acad. 15, 709 ( (1929); Puche, Compt. Rend. 200, 1206 (1935)
Interestinly, the aqua regia method appears to be the very first method, and from the above, it can be seen that oxidation methods not using chlorine
gas or nitric acid proceed very slowly, though IMHO if violent agitation under pressure quicker results should be attained.
From Chemical Abstracts: Electrochemical solution of palladium in hydrochloric acid. A. I. Vol'fson, A. I. Ryazanov, and G. D. Chigrinova. Zhur.
Vsesoyuz. Khim. Obshchestva im. D. I. Mendeleeva 5 , 712(1960).-Powdered Palladium, placed on a graphite plate-type anode, was electrochemically.
dissolved in a cell with a diaphragm. The current efficiency in I0 N HCI at 25-32 degrees with an anodic current density of 6.25 amp./sq. dm was 96%
over 11.5 hrs. The resulting solution. contained 342 g. PdCl2./L Increasing the temperature of the electrolyte to 55-60 degrees lowered 71 to 95.2%
over 14 hours., giving a solution. containing. 420 g. PdCl2/L. Increasing current density. to 12.5 amp./sq. dm., at 24-36 degrees, reduced the current
efficency to 68.7%, giving a solution. containing. 491 g. PdCl2/L. in 12.75 hrs. The decrease in current efficnecy was ascribed to the passivation of
the anode by solutionns. containing. 330-340 g. PdCl/L. A solution. contg.332 g. PdCl2/L. was obtained with current efficiency of 99.5% over 10
hrs.with 6 N HCI in the anolyte and IO N KCI in the catholyte at 25-32 degrees. Palladium was not deposited on the cathode in any of the experiments.
Electrochemical method for preparation of salts. A. I. Ryazanov, G. D. Chigrinova, and A. I. Vol'fson. U.S.S.R. 138,922. Appl. July 28, 1939.
PdCl2,TeCI4,and BiCI3 are obtained by anodic dissolution. of the respective metals in HCI in an electrolytic bath with 3 chambers. To intensify the
process, the metals are used as powders and placed on graphite plate-type electrodes, provided with perforations for elimination of the salt solution.
Electrochenucal solution of palladium in hydrochloric acid. A. 1. Vli'fson, A. I. Ryazanov, and G. D. Chigrinova. Zhur. Priklad. Khim 34, 173-6
(1961).-To develop, a commercial. electrochernical. process for the production of PdCl2 the anodic solution. of Palladium. powder and solid, in HCI
was studied in a cell without a diaphragm. The powder was placed on a horizontal graphite anode. The solubility of Palladium in HCI at 20 degrees
increased from 46.0 g./L. in 0..3 N HCI to 902.0 g./L. in 11 N HCL The anode potential was at the lowest electronegativity value in 6 N HCl
Electrolysis of palladium anode in 6 and I0 N HCl (S - 542.0 and 810.0 g/L., with cathodic current.densities of 12.5-50 and anodic current.densities.
of 6.25-25 amp./sq. dm. at 25 degrees produced solutions with concentration of 350 g/L. with a current efficiency of 90.2%.Increasing current density.
from 7.5 to 12.5 and 25 amp./sq. .dm.. in I0 N HCI lowered current efficiency from 90.2 to 71.2 and 66.6% and p,from350 to250 and 47.2g./L. In 6 N HCl
on electrolysis with current density of-6.25 amp./sq. dm., current efficiency of- 100%, and concentration 55.4 g/L.using the duration of electrolysis
from 1 to 12.5 hours.in 10 N HCl with current density of 7.5 amp./sq. dm. lowered current efficiency from 100 to 90.2% and increased concentration
from 20 to 350 g/L. Pallaium deposited on the Platinum cathode formed a slime which contaminated the electrolyte.
Also, this abstract gives a thermochemical method of production.
Chloridation of platinum metals with ammonium chloride. O. E. Zvyagintsev and L. D. Plaksina. Izvest. Sektora Platiny i Drugikh Blagorod. Metal. Inst.
Obshchei i Neorg. Khim., Akad. Nauk S.S.S.R. No. 24, 121-8(1949).- Platinum
and Palladium were chloridated with NH4Cl 1:2 at 250-400 degrees C.The reaction is more effective when metals are finely divided and in the presence
of Fe and Cu but not Ni. Excess NH4Cl gave no advantage. Chloridation dropped sharply at temps. above 450 degrees. Palladium is chloridized more
easily than Platinum.
[Edited on 14-7-2007 by leu]Nick F - 17-7-2007 at 06:05
It can be made by chlorination of the metal, or via the nitrate, but I would imagine that direct chlorination would give a nicer product. I hope
iamthewaffler will not mind me pointing out that he sells it at a very reasonable price, if he has any left....Fleaker - 17-7-2007 at 09:19
He sells most everything at a reasonable price, and nicely packaged too.BromicAcid - 17-7-2007 at 15:14
Palladium is over the counter. Many coin shops now carry the canadian $50 coin, one troy ounce of palladium metal at 99.95% (Could be 99.5% I forget
which). It's just as over the counter as going to a hydroponics shop to get HNO<sub>3</sub> or a beauty supply store to get >10%
H<sub>2</sub>O<sub>2</sub>.
