Dimethylformamide reducing property

Divalent chromium salts show very strong reducing properties. They are prepared by reduction of chromium(III) compounds with zinc [187] or a zinc-copper couple and form dark blue solutions extremely sensitive to air. Most frequently used salts are chromous chloride [7SS], chromous sulfate [189], and less often chromous acetate. Reductions of organic compounds are carried out in homogeneous solutions in aqueous methanol [190], acetone [191], acetic acid [192], dimethylformamide [193] or tetrahydrofuran [194] (Procedure 37, p. 214). 

The recent introduction of non-aqueous media extends the applicability of CE. Different selectivity, enhanced efficiency, reduced analysis time, lower Joule heating, and better solubility or stability of some compounds in organic solvent than in water are the main reasons for the success of non-aqueous capillary electrophoresis (NACE). Several solvent properties must be considered in selecting the appropriate separation medium (see Chapter 2) dielectric constant, viscosity, dissociation constant, polarity, autoprotolysis constant, electrical conductivity, volatility, and solvation ability. Commonly used solvents in NACE separations include acetonitrile (ACN) short-chain alcohols such as methanol (MeOH), ethanol (EtOH), isopropanol (i-PrOH) amides [formamide (FA), N-methylformamide (NMF), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA)] and dimethylsulfoxide (DMSO). Since NACE—UV may present a lack of sensitivity due to the strong UV absorbance of some solvents at low wavelengths (e.g., formamides), the on-line coupling of NACE... 

The ideal solvent for electrochemical studies should satisfy a number of requirements. In addition to the properties required for any good solvent for organic chemistry, such as a high solvating power and a low reactivity towards common intermediates, solvents for electrochemical use should be difficult to oxidise or reduce in the potential range of interest. Traditionally, the recommended potential limits are +3 V (versus the SCE) for oxidations and —3 V for reductions. Also, the solvent should have a dielectric constant higher than about 10 in order to ensure that the supporting electrolyte is well dissociated. Commonly used solvents are acetonitrile (MeCN) and dichloromethane for oxidations, and MeCN, N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) for reductions. 

Physicochemical properties of so-called Fe " " and Fe° porphyrins have been reviewed by Reed who pointed out a possibility of partial migration of the reducing equivalents to the macrocycle. Vibrations of the porphyrin are expected to reflect the extent of delocalization of the reducing equivalents. The RR spectra of mono- and di-anions of Zn(TPP) and VO(EP) were reported by Ksenofontova et al. and Yamaguchi et al. and appreciable low frequency shifts of RR bands compared with those of neutral porphyrins were pointed out. Contrary to it, Srivatsa et al. did not find any difference between the RR spectra of Fe(TPP) and [Fe(TPP)] both in DMF (DMF dimethylformamide). 

Such a technique is very useful, for example to study the spectroscopic (absorption and emission) properties of metal complexes in unusual oxidation states, non reachable by means of the traditional synthetic routes [3]. In this regard Fig. 9.1 shows the absorption spectra of the [Ru(bpy)3] complex and of its [Ru(bpy)3], [Ru(bpy)3], and [Ru(bpy)3] reduced species obtained in dimethylformamide at 232 K by electrolysis at suitable potential values [4]. 

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