Potassium reineckate

This actinometer, an aqueous solution of K[Cr(NH3)2(SCN 4] (Reinecke s salt), is based on the photoaquation reaction  

The number of photons are determined from the SCN released. These ions are complexed by addition of iron(III) nitrate 

This photoreaction has been extensively studied [14] in the spectral region 315-750 nm. The quantum yield (4 = 0.29 0.03 at 296 K and pH = 5.3-5.5) does not significantly depend on the wavelength, but is dependent on the temperature and on pH (that should be in the 5.3-5.5 range). The absorbance of the actinometric solution ( 0.05 M) is almost complete up to 600 nm (fab 0.95) for 1 cm optical path, but rapidly decreases at longer wavelength (Fig. 4.7). 

Since the aquation reaction occurs also thermally, the same analytical analysis has to be performed on the actinometric solution kept in the dark and compared to the irradiated one. 

Procedure—Ammonium reineckate is a commercial product and can be easily transformed in the potassium salt following [14]. In the experiments, saturated solutions ( 0,05 M), freshly prepared and filtered, must be used [14]. An aliquot both of the irradiated solution and of the same solution taken in the dark has to be added to a grater volume (at least 4 1) of 0.10 M Fe(N03)3 in 0.50 M HCIO4. The difference in absorbance between irradiated and dark solutions, 4A(450), is measured at 450 nm. To calculate the photon flux of the incident light the following equation is used  

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Potassium reineckate [34430-73-4] M 357.5. Crystd from KNO3 soln, then from warm water [Adamson J Am Chem 5oc 80 3183 1958]. 

The potassium reineckate actinometer developed by Wegner and Adamson (26), in 1966, represent the first actinometer for long-wavelength visible radiation. It is based on a photoinduced ligand exchange in a chromium (111) complex, i.e.. 

Two typical reactions which are used in chemical actinometry, are the photoreactions of iron oxalate (Parker s solution) [7,121] and of potassium Reinecke s salt [122]. In both cases, photochemistry and analysis are sepa-... 

T. Christensen, A. Werner and G. Richter, A. Werner and J. L. Klein, and P. Pfeiffer and M. Tilgner. The compounds include (1) the acid and its monohydrate or dihyrate (2) sodium (3) potassium—Reinecke s salt—and (4) its complex with potassium iodide ... 

Scheme 10.15 Photoinitiation of the polymerization of ethyl 2-cyanoacrylate by potassium reineckate [57].

It is noteworthy that only in the case of dehydroquinolizidine derivatives does monomethylation produce the N-alkylated product. The formation of dialkylated products can be explained by a disproportionation reaction of the monoalkylated immonium salt caused by either the basicity of the starting enamine or some base added to the reaction mixture (most often potassium carbonate) and subsequent alkylation of the monoalkylated enamine. Reinecke and Kray 113) try to explain the different behavior of zJ -dehydroquinolizidine and zJ -dehydroquinolizidine derivatives by the difference in energies of N- and C-alkylation transition states because of the presence of I strain. 

In the complex [Co(NH3)6]Cl3, the cation is [Co(NH3)6]3+, and it is named first. The coordinated ammonia molecules are named as ammine, with the number of them being indicated by the prefix hexa. Therefore, the name for the compound is hexaamminecobalt(III) chloride. There are no spaces in the name of the cation. [Co(NH3)5C1]C12 has five NH3 molecules and one CN coordinated to Co3+. Following the rules just listed leads to the name pentaamminechlorocobalt(III) chloride. Potassium hexacyanoferrate(III) is K3[Fe(CN)6j. Reinecke s salt, NH4[Cr(NCS)4(NH3)2], would be named as ammonium diamminetetrathiocyanatochro mate (III). In Magnus s green salt, [Pt(NH3)4][PtCl4], both cation and anion are complexes. The name of the complex is tetraammineplatinum(II) tetrachloroplatinate(II). The compound [Co(en)3](N03)3 is named as tris(ethylenediamine)cobalt(III) nitrate. 

Strongly basic antibiotics may be precipitated by formation of the coloured reineckate salt which may then be determined spectrophotometri-cally 65. Bickfordl66 dissolved the precipitated neomycin reineckate in acetone and has successfully used this procedure to assay neomycin extracted from topical formulations. Roushdi et al 73 preferred to oxidise the precipitate with potassium permanganate and then colorimetrically estimate the chromate produced with diphenylcarbazide. 

This result may be substituted into Eq. 15-40 to calculate Oir(A). Classical actinometers that are used in this way include the potassium ferrioxalate actinometer that can be employed both in the uv and visible spectral region the Reinecke s salt actinometer (visible region), and the ort/io-nitrobenzaldehyde actinometer (uv region). For further description of these actinometers we refer to the literature (e.g., Leifer, 1988, pp. 148-151). 

If potassium dichromate is used instead of the ammonium salt, approximately an equal weight of a mixture of the potassium and ammonium salts of the reineckate anion ia obtained. The free solid acid may be readily made by decomposing the barium salt with sulfuric add followed by ether extraction. 

Reinecke salt has been prepared by adding either potassium dichromate2 or ammonium dichromate ia to fused ammonium thiocyanate. 

Reinecke compared the effects of two bases, potassium hydroxide and triethylamine, on the dehalogenation of dichlormethyl-substituted cyclohexanones over 10% Pd-C in methanol.207 Dehalogenation of 4-dichloromethyl-4-methylcyclohexanone proceeded smoothly in the presence of potassium hydroxide to give primarily 4,4-di-methylcyclohexanone, while in the presence of triethylamine, in addition to 4,4-dimethylcyclohexanone and a little partially dechlorinated material, an approximately equal amount of stereoisomeric 4-dichloromethyl-4-methylcyclohexanols was isolated. Since the dichloro alcohols were rapidly dehalgenated to 4,4-dimethylcyclo-hexanol in the presence of potassium hydroxide, the inertia of the chlorine atoms in the dichloro alcohols was considered to be due to the presence of triethylamine (eq. 13.112). 

The nickel complex, Ni ( 5115)2, has been made by the action of the Grignard reagent on nickel (II) acetylacetonate (217) or from potassium cyclopentadienyl and the ammine [Ni(NHs)el (S N)2 in liquid ammonia (58). It forms dark emerald-green crystals which sublime at 80-90° and which, when heated in nitrogen, melt, with decomposition and the formation of a nickel mirror, at 173-174°. It is only slowly oxidized in air, and cold water neither attacks nor dissolves it it is, however, readily soluble in organic liquids. Oxidation of the compound yields an orange-yellow solution containing the ion [Ni( 5H5)2]+, which is stable for a short period in weakly acidic media, and which may be precipitated as the reineckate or tetraphenylborate. 

For preparative purposes, purifications based on the precipitation of alkaloids are sometimes employed. A crude extract of the alkaloids is made with aqueous acid, subsequently the alkaloids are precipitated with reagents such as Mayer s reagent (IM mercury chloride in potassium iodide) or Reinecke s salt (5% ammonium reineckate in 30% acetic acid) at pH 2, or picric acid (saturated aqueous solution) at pH 5-6. After collection of the precipitate by filtration or centrifugation, the precipitate is dissolved in an organic solvent (acetone-methanol-water 6 2 1). The complexing group is then removed by means of an anion exchanger (Jordan and Scheuer 1965 Verpoorte and Baerheim Svendsen 1976). This method is particularly suited for the purification of quaternary alkaloids. 

The formula of silicotungstic acid is Si02, I2WO3, 26H2O. It is used as a precipitating reagent of alkaloids. Reinecke s salt exhibits the formula NH4[Cr(NH3)2-(SCN)4]H2. It is the ammonium diamminetetracyanatochromate(III). Actually, the potassium salt is known as Reinecke s salt. It is a precipitant of primary and secondary amines and of some amino acids. 

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