A- iodine

A second a-hydrogen may also be replaced by halogen. In some cases it may be difficult to obtain the mo o-halogenated product. a-Fluorinated or a-iodinated carboxylic acids cannot be prepared by this method. 

The preparation of a-iodocarboxylic acids is of particular interest, since iodide is a better leaving group as is chloride or bromide. A similar a-iodination with a phosphorus trihalide as catalyst is not known. However the iodination can be achieved in the presence of chlorosulfonic acid mechanistically the intermediate formation of a ketene 10 by dehydration of the carboxylic acid is assumed ... 

Self-Test C.1A What ions are (a) iodine and (b) aluminum likely to form ... 

Which substance in each of the following pairs would you expect to have the higher standard molar entropy at 298 K Explain your reasoning, (a) Iodine vapor or bromine vapor ... 

Identify the oxidation number of the halogen atoms in (a) iodine heptafluoride (b) sodium periodate (c) hypobromous acid (d) sodium chlorite. 

A number of other methods exist for the a halogenation of carboxylic acids or their derivatives. Acyl halides can be a brominated or chlorinated by use of NBS or NCS and HBr or HCl. The latter is an ionic, not a free-radical halogenation (see 14-2). Direct iodination of carboxylic acids has been achieved with I2—Cu acetate in HOAc. " ° Acyl chlorides can be a iodinated with I2 and a trace of HI. Carboxylic esters can be a halogenated by conversion to their enolate ions with lithium A-isopropylcyclohexylamide in THF and treatment of this solution at -78°C with... 

Gatley SJ, Gilford AN, Volkow ND, Lan R, Makriyannis A. Iodine-123 labeled AM251 a radioiodinated ligand which binds in vivo to the mouse brain CB1 cannabinoid receptor. Eur J Pharmacol 1996 307 301-308. 

Alkynylstannanes yield Z-vinylstannanes stereoselectively, when treated with zirconocene hydrochoride. This can be easily followed by other substitution processes, such a-iodination of the vinylstannane, as shown in reaction 22278. 

Experiments—Dissolve 0-02 g. of cholic acid in 0-5 c.c. of alcohol and add to the solution 1 c.c. of 0-1 A-iodine solution. On cautious dilution with water the blue crystalline iodine compound of cholic acid, comparable to starch iodide, separates. 

Selected examples of a-iodination of a.ji-unsaturated carbonyl compounds and activated methylene groups... 

Fig. 11. Relation between thermo-emf Q and conductivity. Plot Q = C — (kje log e) log a. iodine/phthalocyanine Q TCNE/phthalocyanine Q o-chloranil/poly-N-vinylcarbazolc...

Analogous a-bromination- and a-iodination- of carboxylic acids have been... 

Fig. 29. Exciting frequency (v0) dependence of the resonance Raman spectra of a iodinated PVA films soaked in a iodine solution (5 x 10 3 mol/1). (a) 514.5 nm, (b) 488.0 nro...

Fig. 21a and b. H NMR spectra of a iodine-terminated propylene oligomer (Mn = 630) and b HC1-terminated propylene oligomer. Chemical shifts are in ppm down-field from TMS... 

On alkylation of 2-(aminomethyl)oxazolines (42) and (43), stereochemical induction is evident for the tertiary carbamates (43), but not the tertiary amines (42) this is apparently a consequence of prior complexation of the carbamate carbonyl group to the base and kinetic preference for ( )-enolate formation on deprotonation 47 4-Alkenylamides (44) having a /1-cliiral centre have been found to undergo syn-selective a-iodination with iodine to give syn-a-iodoalkcnamidcs, via an intermediate... 

Alkenylamides (44) having a /i-chiral centre have been found to undergo syn-selective a-iodination with iodine to give syn - z-i odoa I kcnam i dcs, via an intermediate... 

Fig. 16. Three dimension STM images showing the basic steps of the tip induced Ullmann reaction. Two adsorbed iodobenzene molecules at the lower terrace of the Cu(lll) step-edge (a). Iodine is abstracted from the molecules by injecting tunneling electrons (b). Iodine atoms (small) and phenyl molecules (large) are further separated by lateral manipulation (c). The iodine atom located between the two phenyls is removed onto the lower terrace to clear the path between the two phenyls (d). The phenyl molecule at the left side is moved close to the right phenyl and then 500 meV voltage pulses are supplied by the STM-tip to form a biphenyl molecule (e). [Image parameters +100 mV, 0.53 nA 70 x 30 A2] [3],...

Figure 23.4 Form of the experimental phase diagram for two normal substances (a) iodine (l2) and (b) carbon dioxide (C02).

---