Chlorin dimers

At low concentrations of chlorine, dimeric nitrosoalkanes free from chlorine are produced when alkanes are treated also with nitric oxide. Under these circumstances, molecular chlorine is first converted into atomic chlorine which attacks the alkane to form alkyl radicals and hydrogen chloride. The alkyl radicals, in turn, form nitrosoalkanes with nitric oxide. This reaction is most effectively carried out when the ultraviolet radiation is between 380 and 420 mp. [43, 56],... 

In several wood-preserving facilities, other wood preservatives such as creosote and chromate-copper—arsenate (CCA) have been used in addition to PCP (e.g., Lamar Glaser, 1994 Mueller et al., 1991a Mahaffey et al., 1991). Environmental contamination by chemical mixtures is likely in these sites. When PCP has been dissolved in an organic carrier such as oil, soil is also contaminated with the solvent (Trudell et al., 1994 Lamar Dietrich, 1990). Chlorinated dimeric impurities in technical CP formulations are also found in contaminated soil. Design of successful bioremediation must address the effects of other chemicals on CP biodegradation. 

The effect of PCDDs, PCDFs, and PCDDs on CP-degrading microorganisms in soil has not been systematically studied. These compounds do not biodegrade and do not seem to inhibit CP bioremediation (Valo Salkinoja-Salonen, 1986 McBain et al., 1995). The treatment of soils contaminated simultaneously with PAHs and chlorinated dimeric compounds by white-rot fungi could be potentially advantageous since the peroxidase enzymes oxidize all these chemicals (e.g. Valli et al., 1992 Gold et al., 1994 Lamar Glaser, 1994). 

Chlorinated dimeric impurities such as PCDDs and PCDFs are frequently present in contaminated sites. These impurities are very toxic and recalcitrant towards biodegradation and, thus, make the completion of site decontamination very difficult. 

Polychlorinated by-products are also formed, as well as chlorinated dimers (chlorinated vinyicydohexene) and butadiene oligomers. After the removal of these secondary derivatives, the mixture of the three dichlorobutene isomers is sent to the cyanation stage. 

The a-chloro-)S-oxosulfenyl chloride (321) on treatment with dipivaloylmethane and sodium ethoxide affords the intermediate a-ketothione (322) by reductive elimination of chlorine. Dimerization to (323) is spontaneous (Scheme 48) <77ACS(B)890>. 

B. Chlorin Dimers with Carbon-Carbon Linkages. 201... 

Although a considerable amount of work has been published on porphyrin dimers with ether, ester and carbon-carbon linkages, there are only a few reports dealing with the preparation of chlorin dimers and their utility as long-wavelength photosensitizers. A few of them 321-324 are shown in Scheme 67.2 ... 

B. CHLORIN DIMERS WITH CARBON-CARBON LINKAGES... 

Ando et al. 292,293 sported a series of chlorin dimers 341 and trimers 342 joined by amide bonds and found that among such oligomers, dimer 341 (Scheme 71) did show good tumor uptake and selectivity compared with the hematoporphyrin derivative (HpD). As part of their effort to improve the in vivo antitumor activity of chlorin-based photosensitizers, Pandey et extended this approach for the preparation of a series of amide-linked symmetrical and unsynunetrical chlorin dimers 345-347 (Scheme 72). For the preparation of unsymmeuical dimo 349, methyl pheophorfoide a was reacted with 1,3-propanediamine and the intermediate amide 345 was isolated in 80% yield. Reaction of 348 with H2(HPPH) afforded the unsymme-ttical dimer in 70% yield, and was found to be effective in... 

Scheme 69. Chlorin dimers from Wc-dihydroxy bacteriochlorins.

Scheme 71. Amide-linked chlorin dimer and trimer. OH...

Fig. 20 Mendeleev periodic table, displaying horizontal autoreactive elements (i.e., chlorine dimer) in respective periods (1, 2, 3...) penultimate to the vertical column of non-autoreactive noble gases. Far right column displays ideal theoretical, shell-saturated PAMAM dendrimers (G = 1, 2, 3,...) as heuristic non-autoreactive nanoscale analogs of inert, noble gas elements. In the case where G = 2, shell-saturated dendrimer structure is equivalent to argon at the atomic level...

Pure anhydrous aluminium chloride is a white solid at room temperature. It is composed of double molecules in which a chlorine atom attached to one aluminium atom donates a pair of electrons to the neighbouring aluminium atom thus giving each aluminium the electronic configuration of a noble gas. By doing so each aluminium takes up an approximately tetrahedral arrangement (p. 41). It is not surprising that electron pair donors are able to split the dimer to form adducts, and ether, for example, forms the adduct. 

Halides. Gold(III) chloride [13453-07-1] can be prepared directiy from the elements at 200°C (167). It exists as the chlotine-bridged dimer, Au2Clg ia both the soHd and gas phases under an atmospheric pressure of chlorine at temperatures below 254°C. Above this temperature ia a chlorine atmosphere or at lower temperatures ia an iaert atmosphere, it decomposes first to AuCl [10294-29-8] and then to gold. The monochloride is only metastable at room temperature and slowly disproportionates to gold(0) and gold(III) chloride. The disproportionation is much more rapid ia water both for AuCl and the complex chloride, [AuCy, formed by iateraction with metal chlorides ia solution. 

Rhenium Halides and Halide Complexes. Rhenium reacts with chlorine at ca 600°C to produce rheniumpentachloride [39368-69-9], Re2Cl2Q, a volatile species that is dimeric via bridging hahde groups. Rhenium reacts with elemental bromine in a similar fashion, but the metal is unreactive toward iodine. The compounds ReCl, ReBr [36753-03-4], and Rel [59301-47-2] can be prepared by careful evaporation of a solution of HReO and HX. Substantiation in a modem laboratory would be desirable. Lower oxidation state hahdes (Re X ) are also prepared from the pentavalent or tetravalent compounds by thermal decomposition or chemical reduction. 

The fluorinated titanocycle related to (28) is not obtained from C H CMUCgF. Photolysis of CP2T1X2 always gives first scission of a Cp—Tibond. In a chlorinated solvent, the place vacated by Cp is assumed by Cl. In the absence of some donor, the radical dimerizes (298—299). 

The reddish brown pentachloride, uranium pentachloride [13470-21 -8], UCl, has been prepared in a similar fashion to UCl [10026-10-5] by reduction—chlorination of UO [1344-58-7] under flowing CCl, but at a lower temperature. Another synthetic approach which has been used is the oxidation of UCl by CI2. The pentachloride has been stmcturaHy characterized and consists of an edge-sharing bioctahedral dimer, U2CI2Q. The pentachloride decomposes in H2O and acid, is soluble in anhydrous alcohols, and insoluble in benzene and ethers. 

Many reagents are able to chlorinate aromatic pyrazole derivatives chlorine-water, chlorine in carbon tetrachloride, hypochlorous acid, chlorine in acetic acid (one of the best experimental procedures), hydrochloric acid and hydrogen peroxide in acetic acid, sulfuryl chloride (another useful procedure), etc. iV-Unsubstituted pyrazoles are often used as silver salts. When methyl groups are present they are sometimes chlorinated yielding CCI3 groups. Formation of dimers and trimers (308 R = C1) has also been observed. 

Fig. 1. Examples of temperature dependence of the rate constant for the reactions in which the low-temperature rate-constant limit has been observed 1. hydrogen transfer in the excited singlet state of the molecule represented by (6.16) 2. molecular reorientation in methane crystal 3. internal rotation of CHj group in radical (6.25) 4. inversion of radical (6.40) 5. hydrogen transfer in halved molecule (6.16) 6. isomerization of molecule (6.17) in excited triplet state 7. tautomerization in the ground state of 7-azoindole dimer (6.1) 8. polymerization of formaldehyde in reaction (6.44) 9. limiting stage (6.45) of (a) chain hydrobromination, (b) chlorination and (c) bromination of ethylene 10. isomerization of radical (6.18) 11. abstraction of H atom by methyl radical from methanol matrix [reaction (6.19)] 12. radical pair isomerization in dimethylglyoxime crystals [Toriyama et al. 1977].

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