Photochemical aquation

Table 7.1. Comparison of the S- and N- Linkage Isomers from Thermal and Photochemical Aquation of Co(CN)jX in the Presence of SCN"...

The trans-acidochloro complexes were prepared from the aquochloro complex, which was generated in solution by the photochemical aquation of the dichloro complex. Typical of this method of preparation is the procedure described here for the synthesis of the chlorobromo salt. 

A study of the thermal and photochemical aquation of the fra j-[Cr(en)2ClF]+ ion is reported. The results of the thermal aquation are in line with those of another group discussed previously (Table 13), involving the formation of some [Cr(en)-(enH)(OH2)FCl]2+ as well as ra/w-[Cr(en)2(OH2)F] + ion in acidic solution. The results of the photoaquation involve loss of chloride ion to give mainly cw -[Cr(en)2) (0H2)F] + ion, reportedly in violation of Adamson s second rule. Some trans-[Cr(en)2(OHa)F]2+ion and unidentate 1,2-diaminoethane complex are also formed. The ease with which ligands are lost upon photoaquation is observed to decrease in the order NH8>H20>C1 NCS >F (and NH3>Br >F ), whereas a simple interpretation of Adamson s second rule would predict NH3>NCS>H20>F > Cl >Br as the expected order. ... 

Photochemical aquation of hexachlorotechnetate(IV) has been reviewed.Chloride substitution by thiocyanate, to give [Tc(NCS)6], is... 

Photochemical aquation of the [Rh(NH3)6Cl] + cation results mainly in replacement of chloride, with only a little replacement of ammonia, by water. For [Rh(NH3)gBr] + loss of bromide and loss of water are of comparable importance, whereas [Rh(NH3)5l] + photoaquates predominantly (>90%) by ammonia loss. Two photochemically excited states are proposed. These, from comparisons of the results of irradiation in the presence and in the absence of biacetyl, must both be triplet states. rra 5 -[Rh(NH3)4l2]+, like [Rh(NH3)6-I] +, gives ranj-[Rh(NH3)4(OH2)2] + as the principal product of photoaquation. This stereospecifidty suggests that the excited state in each case is a... 

It is well established that important photochemical reactions are mediated by humic material in the aquatic environment (Zepp et al. 1981a,b), and that these are particularly signihcant for hydrophobic contaminants. Partial reductive dechlorination of the persistent insecticide mirex associated with... 

Collectively, these examples illustrate the diversity of transformations of xenobiotics that are photochemically induced in aquatic and terrestrial systems. Photochemical reactions in the troposphere are extremely important in determining the fate and persistence of not only xenobiotics but also of naturally occurring compounds. A few illustrations are given as introduction ... 

Zepp RG, GL Baugham, PA Scholtzhauer (1981a) Comparison of photochemical behaviour of various humic substances in water. I. Sunlight induced reactions of aquatic pollutants photosensitized by humic substances. Chemo sphere 10 109-117. 

McClure, J.w. "Secondary Constituents of Aquatic Angio-sperms"in Photochemical Phylogeny, J.B. Harborne... 

Photo-oxidation or reduction is often found if the complex is irradiated in the charge-transfer bands (see above) photo-oxidation of the metal occurring if the transition is M - -L. Thus the photochemical generation from Ir(IV)Cl6 of a species active in forcing filaments of E. coli may well involve the photoreduction of Ir(IV) to Ir(III) since the intense bands in the visible spectrum of Ir(IV)Clcharge-transfer bands. A report has appeared of the photo-aquation of IrCl -(43). 

The rate of photolytic transformations in aquatic systems also depends on the intensity and spectral distribution of light in the medium (24). Light intensity decreases exponentially with depth. This fact, known as the Beer-Lambert law, can be stated mathematically as d(Eo)/dZ = -K(Eo), where Eo = photon scalar irradiance (photons/cm2/sec), Z = depth (m), and K = diffuse attenuation coefficient for irradiance (/m). The product of light intensity, chemical absorptivity, and reaction quantum yield, when integrated across the solar spectrum, yields a pseudo-first-order photochemical transformation rate constant. 

These synthetic pyrethroids mimic natural counterparts, of which the most important is pyrethrin 1 (10.265). Unfortunately, the natural products lack the photochemical and hydrolytic stability necessary for use as wool insect-resist agents. The synthetic products have the required stability, yet retain the low mammalian toxicity and low environmental retention of the natural products. Permethrin, however, is toxic to aquatic life and is therefore subject to increasingly severe discharge limits. There is some evidence that permethrin is less effective against larvae of a certain beetle. This can be compensated for by using a combination of permethrin with the hexahydropyrimidine derivative 10.264. Some possible alternative pyrethroids have been mentioned [517] as development products (10.266-10.269). 

Smith RC, Prezelin BB, Baker KS, Bidigare RR, Boucher NP, Coley T, Karentz D, MacIntyre S, Matlick HA, Menzies D, Ondrusek M, Wan Z, Waters KJ (1992) Ozone depletion ultraviolet radiation and phytoplankton biology in Antarctic waters. Science 255 952-959 Sommaruga R, Psenner R (1997) Ultraviolet radiation in a high mountain lake of the Austrian Alps air and underwater measurements. Photochem Photobiol 65 957-963 Swanson AK, Druehl LD (2002) Induction, exudation and the UV protective role of kelp phlorotannins. Aquat Bot 73 241-253... 

Endrin ketone may react with photochemically generated hydroxyl radicals in the atmosphere, with an estimated half-life of 1.5 days (SRC 1995a). Available estimated physical/chemical properties of endrin ketone indicate that this compound will not volatilize from water however, significant bioconcentration in aquatic organisms may occur. In soils and sediments, endrin ketone is predicted to be virtually immobile however, detection of endrin ketone in groundwater and leachate samples at some hazardous waste sites suggests limited mobility of endrin ketone in certain soils (HazDat 1996). No other information could be found in the available literature on the environmental fate of endrin ketone in water, sediment, or soil. 

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