After stirring for a short period, the clear and almost colorless solution is treated with potassium chloride and potassium 2,5-dihydroxyphenylthiosulfate (Ar-S-SO3K) begins to precipitate.Colorless solution? Anyone who has followed this procedure and can second the patent's information that the solution becomes colorless prior to KCl addition? I have tried it three times, and the color always remains a rusty brown/red.
And now some
bad news. Reading throug the chemical literature for no obvious reason (certainly not with the intenstion to try ALEPH), I stumbled on the following article:
Kinetics of the reaction of p-benzoquinone with sodium thiosulfate. Y Ogata et al. JACS 90(13) (1968) 3469-3472
(
https://www.thevespiary.org/rhodium/Rhodium/pdf/25-dihydroxyphenylthiosulfate.pdf). It contains some information on the reaction kinetics, and why exactly Shulgin reduces the thiosulfate reaction mixture volume before he saturates it with KCl solution.
[...]
Kinetics - Aqueous solution of p-benzoauinone and of sodium thiosulfate containing acetate buffer in separate flasks were thermostated at a definite temperature. The reaction was started by mixing the two solutions followed by a nimble transfer into a thermostated quartz cell for the UV spectrometry. The unreacted quinone was estimated directly from the optical density at 246 mu, where molecular extinction coefficients of p-benzoquinone, hydroquinone thiosulfate, and thiosulfate are 22000, 2700 and 488 respectively. The concentration of the quinone was determined by the difference method, since absorbances at 246 mu are proportional to their concentrations.
The kinetic reactions were conducted in the presence of excess thiosulfate. The obtained pseudo-first-order rate constant holds good constancy over 90% conversion. Since the rate constants thus obtained were found to be porportional to the initial concentration of sodium thiosulfate, the present reaction was observed to follow second-order-kinetics with respect to both reactants.
Reaction procedure - p-Benzoquinone (2.2 g, 0.02 mol) in 240 mL of water and sodium thiosulfate (5.0 g, 0.02 mol) in 100 mL of water were mixed in the presence of acetate buffer at pH 3.2.
The yellow color of the quinone faded out soon after the mixing and then the color of the reaction mixture changed to light brown. The solution was condensed by evaporation under reduced pressure up to ca 15 mL and salting out by addition of KCl (3 g) resulted in the precipitation of potassium hydroquinone thiosulfate. Triplicate recrystallization from water gave ca 0.8 g (15% yield) of fine crystals, mp 225-250°C. Anal. calcd for C6H5O5S2K: C, 27.68; H, 1.94. Found: C, 27.57; H, 2.01.
The IR spectrum of the salt, determined by Nujol paste method, shows peaks at 635, 832, 870, 1035, 1245, and 1660-2000 cm^-1 characteristic of SO, two adjacent ring H, one isolated ring H, SO2, phenolic OH and 1,2,4-trisubstituted ring H, respectively. The UV spectrum in water shows a peak at 313.5 mu (e 4190).
The yield of hydroquinone thiosulfate at pH 2-5, however, is quantitative on the basis of direct spectrophotometry in UV cell instead of isolation of the product. The yield was significantly reduced at pH above 5, e.g. ca 60% at pH 5.6. The main by-product, isolated from the ether extract, was found to be hydroquinone on the basis of IR and UV spectra, but the analysis for all other products was not carried out because of the complexity of products due to the further reaction of hydroquinone and benzoquinone.[...]
I guess the German patent should state that the color upon addition of the benzoquinone/AcOH mixture is colorless, but that the FINAL color is a rusty red/light brown. At least, this article mentions it like this, and it also is what I usually see.
Also, the K salt is too soluble in water to make it precipitating quantitatively. Such a shame... Shulgin reduced the reaction mixture volume and saturates it with a satd. salt solution (according to the drawings, I think he used NaCl). If you do not reduce the volume, you can wave your pretty yields goodbye (in the 30s instead of in the 60s%). I also tried to reduce the volume of the K-salt filtrate, but this gave, off course, alot of KCl as well. I don't think it is worth the extra work to reduce the filtrate's volume as well.