Carbon iodine

The USA Military Specification (Ref 8) contains the following chemical criteria and requirements (1) As2Os by sodium thiosulfate—iodine titration 99.0% min, (2) As203 by carbonate-iodine titration 0.05% max, (3) Cl as AgCl turbidity 0.005% max, (4) heavy metals as PbS turbidity 0.010% max, (5) Fe as a Fe(CNS)3. 9KCNS.4H20 red coloration 0,010% max and (6) nitrate as an indigo carmen blue coloration which persists for over 5 mins... 

Hydrogen peroxide Carbon Iodine heptafluoride Carbon Iodine(V) oxide Non-metals MRH 6.19/15... 

Another domino radical cyclization approach, which allows construction of the B- and E-rings of the alkaloid ( )-aspidospermidine (3-46), has been described by the same group [25]. Transformation of the iodoazide 3-44 into the tetracycle 3-45 was accomplished in 40 % yield by selective attack at the carbon-iodine bond in the... 

The important observation is that all of the isotope effects are large and inverse. Therefore, the transition states in these reactions must be very crowded, i.e. the Ca—H(D) out-of-plane bending vibrations in the transition state must be high energy (Poirier et al., 1994). As a result, these workers concluded that nitrogen-a-carbon bond formation is more advanced than a-carbon-iodine bond rupture in the transition state. It is interesting, however, that in spite of the small secondary a-deuterium KIEs, these authors concluded that the N—C bond formation is only approximately 30% complete in the transition state. 

Photolysis of the carbon-iodine bond in iodo-perfluoroalkyl compounds has been employed to enable the formation of the corresponding pefluoroalkyl radical [37]. Different perfluorinated alkyl chains can thus be covalently bound to the CNT. Interestingly, the authors reported that no change in solubility of the nanotubes was noted after the perfluoro-alkylation. 

Tertiary alkyl halides are easier to reduce than secondary alkyl halides, which are easier to reduce than primary alkyl halides. Carbon-iodine bonds are easier to reduce than carbon-bromine bonds, which are easier to reduce than carbon-chlorine bonds [1-3]. 

Recently, a reductive magnesium insertion into a carbon-iodine bond of a / -iodo-a-ketoester has been described. The preparation of the iodomagnesium enolate 17 derived from an a-ketoester is the first preparation of such metallic species in this series. It was obtained from the reaction between the /1-iodo-a-ketoester precursor 16 and magnesium. In this case, the form of the metal is critical and magnesium powder with a large surface area is necessary (equation 6). 

Let us now look at some examples to illustrate what we have discussed so far to get a feeling of how structural moieties influence the mechanisms, and to see some rates of nucleophilic substitution reactions of halogenated hydrocarbons in the environment. Table 13.6 summarizes the (neutral) hydrolysis half-lives of various mono-halogenated compounds at 25°C. We can see that, as anticipated, for a given type of compound, the carbon-bromine and carbon-iodine bonds hydrolyze fastest, about 1-2 orders of magnitude faster than the carbon-chlorine bond. Furthermore, we note that for the compounds of interest to us, SN1 or SN2 hydrolysis of carbon-fluorine bonds is likely to be too slow to be of great environmental significance. 

The last example represents a fairly rare elimination of hydrogen fluoride in preference to hydrogen chloride, a reaction that deserves a more detailed discussion A comparison of bond dissociation energies of carbon-halogen bonds shows that the carbon-fluorine bond is much stronger than the carbon-chlorine, carbon-bromine, and carbon-iodine bonds 108-116, 83 5, 70, and 56 kcal/mol, respec-... 

Because the by-product of the coupling is a strong acid, bases are usually added to die reaction mixture to scavenge it. For example, 4-iodobromobenzene can be coupled with methyl acrylate to give the 4-bromocinnamate ester in >68% yield. This reaction takes advantage of the faster oxidative addition to the carbon-iodine bond to give a single product. 

Basically two types of reactions can be used for iodinations electrophilic- or nucleophilic iodination at a unsaturated carbon. Iodine attached to a saturated carbon atom is labile and is readily substituted by nucleophiles. For the same reason, radiopharmaceuticals which are labelled at a saturated carbon atom, are quickly metabolised in vivo. 

Thus, while cyclization occurred to the tune of overall 45%, almost half of it proceeded with loss of C21-C22 stereochemistry. A radical process through homolytic cleavage of the carbon-iodine bond and subsequent isomerization of the vinyl radical could be responsible (vide supra), possibly initiated by electron transfer from Ni(I) in the mixture. 78 Nevertheless, a third approach to strychnine had been developed. Having accomplished such and one author s graduate career... 

The mechanism of this reaction shows that excitation of the substrate gave an n,n triplet state, but this excited state was unable to dissociate the carbon-iodine bond. This was demonstrated by showing that the n,n triplet state, when sensitized by chrysene, did not produce coupling products. Probably, the reaction occurred in an excited a,a triplet state mainly localized on the carbon-iodine bond, and the interaction between this triplet state and aromatic compounds led to homolytic cleavage of the C-I bond with the formation of both a 5-thienyl radical and a complex between the aromatic compound and the halogen atom. The formation of this complex was demonstrated by the presence of a short-lived transient with Amax = 510 nm, showing a second-order decay kinetics and a half-life of ca. 0.4 (is in laser flash photolysis. The thienyl radical thus formed... 

Ultrafast molecular elimination of iodine from IF2C-CF2I has been studied using the velocity map ion imaging technique in combination with femtosecond pump-probe laser excitation.51 By varying the femtosecond delay between pump and probe pulse, it has been found that elimination of molecular iodine is a concerted process, although the two carbon-iodine bonds are not broken synchronously. 

Dichlorine oxide Carbon, or Oxidisable materials Fluorine Non-metals Hydrogen peroxide Carbon Iodine heptafluoride Carbon Iodine(V) oxide Non-metals Nitrogen oxide Non-metals Nitrogen trifluoride Charcoal Oxygen difluoride Non-metals Oxygen (Liquid) Charcoal Ozone Charcoal, Potassium iodide... 

---