Lead dihalides

In the environment the lead dihalide undergoes oxidation-reduction by sunlight to elemental lead and halogen, both of which are serious pollutants. 

Hal = F, Cl, Br, I), a solid state reaction between germanium sulfide and suitable lead dihalides at ca 570 K was used304-306. The observed IEs, corresponding to ionizations from the valence shell MOs, are presented in Table 11. 

Molecular dimensions are those given by Sutton (,5). Vibrational frequencies are estimated by comparison with the corresponding values for Hgl2(g) (4) and with the lead dihalide series (4). The electronic ground state is assumed to be A... 

Addition to the Double Bond. Chlorine, bromine, and iodine react with aHyl chloride at temperatures below the inception of the substitution reaction to produce the 1,2,3-trihaLides. High temperature halogenation by a free-radical mechanism leads to unsaturated dihalides CH2=CHCHC1X. Hypochlorous and hypobromous acids add to form glycerol dihalohydrins, principally the 2,3-dihalo isomer. Dehydrohalogenation with alkah to epicbl orobydrin [106-89-8] is ofgreat industrial importance. 

Hydrogen hahdes normally add to form 1,2-dihaLides, though an abnormal addition of hydrogen bromide is known, leading to 3-bromo-l-chloropropane [109-70-6], the reaction is beUeved to proceed by a free-radical mechanism. Water can be added by treatment with sulfuric acid at ambient or lower temperatures, followed by dilution with water. The product is l-chloro-2-propanol [127-00-4]. 

The chemistry of alkynes is dominated by electrophilic addition reactions, similar to those of alkenes. Alkynes react with HBr and HC1 to yield vinylic halides and with Br2 and Cl2 to yield 1,2-dihalides (vicinal dihalides). Alkynes can be hydrated by reaction with aqueous sulfuric acid in the presence of mercury(ll) catalyst. The reaction leads to an intermediate enol that immediately isomerizes to yield a ketone tautomer. Since the addition reaction occurs with Markovnikov regiochemistry, a methyl ketone is produced from a terminal alkyne. Alternatively, hydroboration/oxidation of a terminal alkyne yields an aldehyde. 

Kumakov s test (1893) is generally applicable to cis- and trans-ammine dihalides. Addition of thiourea (tu, (H2N)2CS) to the cA-complex leads to successive replacement of all the ligands (Figure 3.29) here the lability of the Pt—Cl bond (see section 3.8.9) causes substitution of a chloride. 

The reaction of cobaltocene with organoboron dihalides RBX2 (R = Me, Ph and X = Cl, Br mainly) and boron trihalides (BC13, BBr3) leads essentially to three types of (boratabenzene) cobalt complexes, 19,20, and 21 (7,57). CoCp2 plays a dual role in part it acts as a reductant, in part it... 

The dihalides of tin and lead behave as ionic metal compounds, and they will not be discussed further. 

The dihalides of tin and lead are so very well known that it is unnecessary to summarize the extensive chemical knowledge of these compounds. The chemistry of divalent tin and lead has been reviewed several times recently 132 A few points that are relevant to the material already discussed will be made. 

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