2- -iodobenzene

Iodobenzene boils at 188° (corrected). The yield should be about 20 grams. 

Equip a 500 ml. three-necked flask with a reflux condenser, a mercury-sealed mechanical stirrer and separator 7 funnel, and support it on a water bath. Attach an absorption device (Fig. II, 8, 1, c) to the top of the condenser (1). Place 134 g. (152 ml.) of A.R. benzene and 127 g. of iodine in the flask, and heat the water bath to about 50° add 92 ml. of fuming nitric acid, sp. gr. 1-50, slowly from the separatory funnel during 30 minutes. Oxides of nitrogen are evolved in quantity. The temperature rises slowly without the application of heat until the mixture boils gently. When all the nitric acid has been introduced, reflux the mixture gently for 15 minutes. If iodine is still present, add more nitric acid to the warm solution until the pimple colour (due to iodine) changes to brownish-red. 

In a i-l. three-neck flask fitted with a mechanical stirrer, reflux condenser and separatory funnel, are placed 381 g. (1.5 moles) of iodine and 400 g. (5.1 moles) of benzene. The mixture is heated to about 50° on a water bath and 275 cc. of nitric acid (sp. gr. 1.50) is added slowly from the separatory funnel the time required for the addition should be about one and one-quarter hours. A copious evolution of oxides of nitrogen takes place, and the gases are carried off from the upper end of the condenser to an open window or hood. The reaction proceeds smoothly (Note 1) and the temperature rises slowly without the application of heat until the mixture boils gendy. When all of the nitric acid has been added, the solution is refluxed for about fifteen minutes. If iodine still remains, more nitric acid should be added slowly to the warm solution until the purple color of the iodine has been discharged and the solution becomes brownish red. 

The lower reddish oily layer is separated, mixed with an equal volume of 10 per cent sodium hydroxide solution and steam distilled from a 2-1. flask until no more oil passes over. Towards the end of the distillation a yellow solid begins to collect in the receiver this consists of nitro compounds, which are removed by vigorously stirring the oil for about three hours with 20 cc. of concentrated hydrochloric acid, 300 cc. of water and 200 g. of iron filings in a 2-1. flask connected with a reflux condenser. 

The mixture is allowed to cool and is then filtered. The filtrate is rendered distinctly acid to congo red with hydrochloric acid and again distilled with steam. The oil so obtained is separated and distilled under normal pressure with the use of a fractionating column (Note 2). The fraction boiling at 180-1900 is redistilled and the pure compound is collected at 184-186°. The yield is 523-531 g. (86-87 per cent of the theoretical amount) (Note 3). 

The reaction proceeds smoothly without stirring however, the time of addition is decreased somewhat by stirring. Ordinary rubber stoppers may be used although they are somewhat attacked, this is not sufficiently serious to warrant any special apparatus. In very large runs it may be desirable to use stoppers made from asbestos paper and water glass (Org. Syn. 5, 9). Rubber stoppers have been used in a run five times the size of that described. 

A good separation is obtained by means of a 500-cc. modified Claisen flask (Org. Syn. 1, 40) without the use of diminished pressure. 

CfiH5NH2 + NaN02 + 2HCI - CaH5N2Cl + 2H2O + NaCl CeHsNsCl + KI - Cc,H5I + N2 + KC1 

In a 3- or 5-gallon stoneware crock are placed 950 cc. (1130 g., 11.7 moles) of concentrated hydrochloric acid (sp. gr. 1.19), 950 cc. of water, 200 g. (196 cc., 2.15 moles) of aniline, and 2 kg. of ice (Note x). The mixture is agitated by a mechanical stirrer, and, as soon as the temperature drops below 50, a chilled solution of 156 g. (2.26 moles) of sodium nitrite in a measured volume (700-1000 cc.) of water is introduced fairly rapidly from a separatory funnel, the stem of which projects below the surface of the reaction mixture. The addition should not be fast enough to cause the temperature to rise to io° or to cause evolution of oxides of nitrogen. The last 5 per cent of the nitrite solution is added more slowly, and the reaction mixture is tested with starch-iodide paper at intervals until an excess of nitrous acid is indicated. 

If more ice is used a portion remains unmelted after the diazotization is completed. 

If a good separation has been made not more than 1-2 g. of iodobenzene is lost with the upper layer. 

An appreciable amount of iodobenzene is retained by the solid calcium chloride. By treating the spent drying agent with water 8-12 g. of iodobenzene can be recovered. 

---

Kung C Y, Chang B-Y, Kittrell C, Johnson B R and Kinsey J L 1993 Continuously scanned resonant Raman excitation profiles for iodobenzene excited in the B continuum J. Phys. Chem. 97 2228-35... 

Iodobenzene, as usually prepared, is a very pale yellow liquid of b.p. 188°, and d, 1 83. The freshly distilled pure liquid i colourless, but soon redevelops the yellow colour on exposure to light. Iodobenzene is insoluble in water. 

The iodine atom in iodobenzene (unlike that in the corresponding aliphatic compounds) is very resistant to the action of alkalis, potassium cyanide, silver nitrite, etc. This firm attachment of the iodine atom to the benzene ring is typical of aromatic halides generally, although in suitably substituted nitio-compounds, such as chloro-2,4-dinitrobenzene, the halogen atom does possess an increased reactivity (p. 262). 

Iodobenzene Dichloride C6H3ICI2, lodosobenzene, CsHsIO, and lodoxybenzene, CgH. IOi. 

When iodobenzene in chloroform solution is treated with chlorine, the iodine... 

When lodosobenzene is boiled with water, interaction occurs with the formation of one equivalent of iodobenzene and one of iodoxybenzene ... 

Alternatively, if it is not desired to collect the iodobenzene, the iodosobenzene can be added to about 150 ml. of water contained in an open beaker or conical flask, and the mixture gently boiled until a clear solution is obtained and the pale yellow colour has disappeared. On cooling the iodoxybenzene rapidly separates. 

To the cold solution, add about 2 ml. of 10% potassium iodide solution. A brisk effervescence of nitrogen occurs, and iodobenzene separates, usually as drops so small that in spite of their density they float on the surface. 

Meanwhile, during the cooling of the cuprous chloride solution, prepare a solution of benzenediazonium chloride by dissolving 20 ml. (20-5 g.) of aniline in a mixture of 50 ml. of concentrated hydrochloric acid and 50 ml. of water, and after cooling to 5°, adding slowly a solution of 17 g. of sodium nitrite in 40 ml. of water. Observe carefully the general conditions for diazotisation given in the preparation of iodobenzene (p. 184). 

Methyl iodide, ethyl bromide and iodide, higher alpihatic halides chloroform, iodoform, carbon tetrachloride chlorobenzene, bromobenzene, iodobenzene benzyl chloride. 

Halogen, Chloral hydrate, sodium chloroacetate, chlorobenzene, />-chlorophenol, dichlorhydrin, bromobenzene, iodobenzene. 

Physical Properties. All heavier than, and insoluble in water. All liquids, except iodoform, CHI3, which is a yellow crystalline solid with a characteristic odour. The remainder are colourless liquids when pure ethyl iodide, CjHjI, and iodobenzene, CjHgl, are, however, usually yellow or even brown in colour. Methyl iodide, CH3I, ethyl bromide, CgH Br, ethyl iodide, chloroform, CHCI3, and carbon tetrachloride, CCI4, have sweetish odours, that of chloroform being particularly characteristic. 

Chlorobenzene, CjHjCl, bromobenzene, CgHgBr, and iodobenzene possess aromatic odours. Benzyl chloride, CgHjCHgCl, has a sharp irritating odour and is lachrymatory. 

Bromobenzene, iodobenzene and benzyl chloride behave somewhat similarly. The />-nitro-derivatives of the first two compounds frequently crystallise out even before pouring into water p-nitrobenzyl chloride usually remains as an oil for several minutes before solidifying. 

It is convenient to describe here certain polyvalent iodine compounds, formed by such substances as iodobenzene and p-iodotoluene. lodobenzeue in chloroform solution reacts readily with chlorine to form iodobenzene dlchlorlde (phenyl iododichloride) (I) ... 

Iodosobenzene undergoes a slow change on keeping this change can be accelerated by heat and consists in a disproportionation to iodoxybenzene (III) and iodobenzene ... 

In practice, the iodoaobenzene is steam distilled pure iodobenzene is thus removed as formed. 

Fit up a 1 -litre round-bottomed flask for steam distillation (Fig. II, 40,1) and place in it 22 g. of iodosobenzene (Section IV.25) made into a thin paste with water (1). Steam distil until almost all the iodobenzene has been removed (about 9 g.) cool the residue in the flask at once, filter the white solid with suction and dry in the air. Wash it with a little chloroform, filter with suction, and dry in the air upon filter paper. The yield is 10-5 g. It may be recrystallised from 800-900 ml. of water, lodoxybenzene melts with explosive decomposition at 237°,... 

The following give abnormal results when treated with chlorosulphonio acid alone, preferably at 50° for 30-60 minutes —fluobenzene (4 4 -difluorodiplienyl-sulphone, m.p. 98°) j iodobenzene (4 4 -di-iododiphenylsulplione, m.p. 202°) o-diclilorobenzene (3 4 3. -4 -tetrachlorodiphenylsulphone, m.p. 176°) and o-dibromobenzene (3 4 3 4 -tetrabromodiphenylsulphone, m.p. 176-177°). The resulting sulphones may be crystallised from glacial acetic acid, benzene or alcohol, and are satisfactory for identification of the original aryl halide. In some cases sulphones accompany the sulphonyl chloride they are readily separated from the final sulphonamide by their insolubility in cold 6N sodium hydroxide solution the sulphonamides dissolve readily and are reprecipitated by 6iV hydrochloric acid. 

When an aqueous solution of phenyldiazonium chloride or of p-tolyl-diazonium hydrogen sulphate is treated with an equivalent of potassium iodide and warmed on a water bath, iodobenzene or />-iodotoluene is formed in good 3deld ... 

The iodobenzene is conveniently distilled under reduced pressure and the fraction b.p. 77- 80°/20 mm. or 63-64°/8 mm. collected. The product has a higher degree of purity than that obtained directly from benzene (Section IV,21). 

Under conditions in which benzene and its homologues were nitrated at the zeroth-order rate, the reactions of the halogenobenzenes ([aromatic] = c. o-1 mol 1 ) obeyed no simple kinetic law. The reactions of fluorobenzene and iodobenzene initially followed the same rates as that of benzene but, as the concentration of the aromatic was depleted by the progress of the reaction, the rate deviated to a dependence on the first power of the concentration of aromatic. The same situation was observed with chloro- andjbromo-benzene, but these compounds could not maintain a zeroth-order dependence as easily as the other halogenobenzenes, and the first-order character of the reaction was more marked. 

More typically its reactions showed an intermediacy of kinetic order like that observed with fluorobenzene or iodobenzene in nitromethane. 

As a typical example, the catalytic reaction of iodobenzene with methyl acrylate to afford methyl cinnamate (18) is explained by the sequences illustrated for the oxidative addition, insertion, and /3-elimination reactions. 

Chlorobenzene reacts with alkenes with bimetallic catalyses of Ni and Pd. Chlorobenzene is converted in situ into iodobenzene (14) by the Ni-cataiyzed reaction of Nal at 140 "C. NiBr2, rather than the Ni(0) complex, is found to be a good catalyst. Then the Pd-catalyzed reaction of the iodobenzene with acrylate takes place) 15]. 

The reaction of iodobenzene with acrylate is a good synthetic method for the cinnamate 17[7]. In the competitive reaction of acrylate with a mixture of 0-and /i-iodoanisoles (18 and 19), the o-methoxycinnamate 20 was obtained selectively owing to the molecular recognition by interlamellar montmorillonite ethylsilyldiphenylphosphine (L) as a heterogenized homogeneous catalyst used as a ligand[28]. 

The coupling of 1,8-diiodonaphthalene (25) with acenaphthylene (26) affords acenaphth[l,2-a]acenaphthylene (27). It should be noted that the reaction involves unusual trans elimination of H—Pd—1[32], This tetrasubstituted double bond in 11 reacts further with iodobenzene to give the [4, 3, 3]propellane 28 in 72%. This unusual reaction may be accelerated by strain activation, although it took 14 days[33]. 

Vinyl acetate reacts with the alkenyl triflate 65 at the /3-carbon to give the 1-acetoxy-1,3-diene 66[68]. However, the reaction of vinyl acetate with 5-iodo-pyrimidine affords 5-vinylpyrimidine with elimination of the acetoxy group[69]. Also stilbene (67) was obtained by the reaction of an excess of vinyl acetate with iodobenzene when interlamellar montmorillonite ethylsilyl-diphenylphosphine (L) palladium chloride was used as an active catalyst[70]. Commonly used PdCl2(Ph3P)2 does not give stilbene. 

The reaction of the o-iodophenol 275 with an alkylallene affords the bcnzo-furan derivative 276[184], Similarly, the reactions of the 6-hydroxyallenes 277 and 279 with iodobenzene afford the tetrahydrofurans 278 and 280. Under a CO atmosphere, CO insertion takes place before the insertion of the allenyl bond, and a benzoyl group, rather than a phenyl group, attacks the allene carbon to give 280. Reaction of iodobenzene with 4,5-hexadienoic acid (281) affords the furanone derivative 282[185]. 

Allenes also react with aryl and alkenyl halides, or triflates, and the 7r-allyl-palladium intermediates are trapped with carbon nucleophiles. The formation of 283 with malonate is an example[186]. The steroid skeleton 287 has been constructed by two-step reactions of allene with the enol trillate 284, followed by trapping with 2-methyl-l,3-cyclopentanedione (285) to give 286[187]. The inter- and intramolecular reactions of dimethyl 2,3-butenylmalonate (288) with iodobenzene afford the 3-cyclopentenedicarboxylate 289 as a main product) 188]. 

---