Base decomposition of dichromate

Abstract

The rate of decomposition of dichromate, Cr2O72-, to form chromate, CrO42-, is very dependent upon the choice of cation, and its concentration. At a total ionic strength of 1.0 mol l-1 and at 25.0°C, the second-order rate constant decreases in the order Ca2+ (2600 mol-1 l. s-1) >> K+ + (960) > Na+ (920) >Li+ (700)>> bistet2+ (410) >> Me4N+ (125) >> Et4N+ (35) where bistet2+ is the N,N,N,N',N',N'-hexamethylethylene-1,2-diammonium ion. In the presence of sodium chloride the second-order rate constant increases as the ionic strength increases (200 and 1900 mol-1 l. s-1 at ionic strengths of 0 and 2.7 mol l-1 respectively), whereas in tetramethylammonium chloride a maximum is reached at intermediate ionic strengths. The equilibrium between dichromate and hydrogen chromate is shifted towards the dichromate side in the presence of tetraalkylammonium ions, and towards the hydrogen chromate side in the presence of calcium ion.

UV−Vis Spectroscopic Determination of the Dissociation Constant of Bichromate from 160 to 400 °C

“…[25][26][27][28][29] Hexavalent chromium appears to be an ideal candidate for direct spectrophotometric study without an indicator, since all the Cr-(VI) species absorb light in the UV and visible regions. 32 This method [33][34][35][36][37][38][39][40][41][42][43][44] and others [45][46][47][48][49][50][51] have been used to study acid-base equilibria of Cr(VI) at 20 °C or slightly elevated temperatures. However, the potentiometric study by Palmer and co-workers 50 is the only high-temperature study (to 175 °C) of Cr(VI) equilibria.…”

“…UV−vis spectroscopy is limited to equilibria involving species containing appropriate chromophores. , Recently, stable pH indicators have been developed for temperatures up to 400 °C. − Hexavalent chromium appears to be an ideal candidate for direct spectrophotometric study without an indicator, since all the Cr(VI) species absorb light in the UV and visible regions − and others − have been used to study acid−base equilibria of Cr(VI) at 20 °C or slightly elevated temperatures. However, the potentiometric study by Palmer and co-workers 50 is the only high-temperature study (to 175 °C) of Cr(VI) equilibria.…”

C1‐(C84‐C2(11))(CF3)12: Trifluoromethylation Yields Structural Proof of a Minor C84 Cage and Reveals a Principle of Higher Fullerene Reactivity

“…26, 27 (This is consistent with the observation that substituents do not add to THJs (the two exceptions cited above notwithstanding), and THJs are the least pyramidal C atoms in HHFs.) The tendency of substituents to add to large‐ θ p C atoms appears to be valid for cycloadditions and other 1,2 additions, but it is not valid for ribbons of 1,4 additions, which are common for CF 3 groups3, 18, 19 or large “non‐cycloadduct” groups 28. 29 Another HHF principle is needed.…”