Monochloride

Potassium iodide prepared as described has been used in a very careful study of the absolute accuracy of the poten-tiometric iodide-silver titration,2 by comparing it directly against pure silver. The ratio KI Ag found in this way agreed to within 0.02 per cent with the theoretical ratio. This small deviation is to be attributed to a slight absorption of iodide ions by the silver iodide at the potentiometric end point and not to an impurity in the potassium iodide. 

Iodine monochloride has been prepared by leading chlorine over solid iodine and distilling the crude product. Despite improvements to obtain a more nearly pure product, this method remains a tedious and time-consuming process. 

Approximately 300 ml. of liquid chlorine is led directly from a cylinder of chlorine (commercial) into a tared 500-ml. flask cooled with a mixture of solid carbon dioxide and ether. A weighed quantity of solid iodine, roughly one-half of the molar equivalent of the chlorine in the flask, is added. The equivalence may vary rather widely, but the weight should be accurate. After the addition of iodine, the contents of the flask congeal to a solid. The flask is 

One or two recrystallizations usually suffice to obtain the pure iodine monochloride. In this connection, the word crystallization implies the gradual cooling of liquid iodine monochloride until approximately 80 per cent of it has solidified, then decanting off the portion that still remains liquid. 

The purity of iodine monochloride prepared in the foregoing manner is attested, first, by its freezing point of 27.19° as compared to 27.20° as found by Stortenbecker2,3 and second, by chemical analysis1 (the variation from the theoretical composition was never more than 0.2 per cent, generally within 0.1 per cent), and, third by the constancy 

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Aluminium monochloride, AlCl, is formed at very high temp eratures from AICI3 and Al. The reaction is reversed on cooling. 

Selenium monochloride, Se2Cl2 m.p. —85 C 130°C (decomp.). Reddish liquid, a good chlorinating agent (CI2 plus Se). 

Sulphur monochloride, S2CI2, m.p. —80 C, b.p. I38"C. Yellow liquid hydrolysed by water to SO2, HCl and S. Lower halides S CIj (jt up to 5) are formed S2CI2 plus H2 at a hot surface with freezing of products. S2CI2 is used in the rubber industry as a solvent for S. 

The aluminium monochloride vapour is unstable when cooled and disproportionates (p.77) below 1100 K thus ... 

Iodine monochloride, formed when iodine reacts with the iodate(V) ion in the presence of an excess of concentrated hydrochloric acid. 

Amino-3 5-diiodobenzoic acid. In a 2 litre beaker, provided with a mechanical stirrer, dissolve 10 g. of pure p-aminobenzoic acid, m.p. 192° (Section IX,5) in 450 ml. of warm (75°) 12 -5 per cent, hydrochloric acid. Add a solution of 48 g. of iodine monochloride (1) in 40 ml. of 25 per cent, hydrochloric acid and stir the mixture for one minute during this time a yellow precipitate commences to appear. Dilute the reaction mixtiue with 1 litre of water whereupon a copious precipitate is deposited. Raise the temperature of the well-stirred mixture gradually and maintain it at 90° for 15 minutes. Allow to cool to room tempera-tiue, filter, wash thoroughly with water and dry in the air the yield of crude acid is 24 g. Purify the product by dissolving it in dilute sodium hydroxide solution and precipitate with dilute hydrochloric acid the yield of air-dried 4-amino-3 5-diiodobenzoic acid, m.p. >350°, is 23 g. 

Iodine monochlorlde may be prepared as follows. Pass dry chlorine into 127 g. of iodine contained in a 125 ml. distilling flask until the weight has increased by 34-6 g. The chlorine should be led in at or below the surface of the iodine whilst the flask is gently shaken it is essential to have an excess of iodine. Distil the iodine chloride in an ordinary distillation apparatus use a filter flask, protected from atmospheric moisture by a calcium chloride (or cotton wool) guard tube, as a receiver. Collect the fraction b.p. 97-105° the jdeld is 140 g. Preserve the iodine monochloride in a dry, glass-stoppered bottle. 

Since iodine monochloride attacks cork and rubber, the use of an all-glass apparatus is recommended. If it should come into contact with the skin, an elective antidote is dilute hydrochloric acid (1 1). 

This simplified method gives 2-aminothiazole in good yield (50 to 70%) (311, 330), Other reactants can replace iodine, for example, chlorine, bromine, sulfuryl chloride, chlorosulfonic acid, or sulfur monochloride also give good results. 

The percentages cited in the preceding equation reflect the composition of the monochloride fraction of the product mixture rather than the isolated yield of each component... 

Photochemical chlorination of 2 2 4 trimethylpentane gives four isomenc monochlorides... 

Photochemical chlorination of pentane gave a mixture of three isomenc monochlorides The pnncipal monochlonde constituted 46% of the total and the remaining 54% was approximately a 1 1 mixture of the other two isomers Write structural formulas for the three monochlonde iso mers and specify which one was formed in greatest amount (Recall that a secondary hydrogen is abstracted three times faster by a chlonne atom than a pnmary hydrogen)... 

Under conditions of photochemical chlorination (CH3)3CCH2C(CH3)3 gave a mixture of two monochlorides in a 4 1 ratio The structures of these two products were assigned on the basis of their SnI hydrolysis rates in aqueous ethanol The major product (compound A) underwent hydrolysis much more slowly than the minor one (compound B) Deduce the structures of com pounds A and B... 

Iodine monochloride Aluminum foil, organic matter, metal sulfides, phosphorus, potassium, rubber, sodium... 

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. 

The iodination reaction can also be conducted with iodine monochloride in the presence of sodium acetate (240) or iodine in the presence of water or methanolic sodium acetate (241). Under these mild conditions functionalized alkenes can be transformed into the corresponding iodides. AppHcation of B-alkyl-9-BBN derivatives in the chlorination and dark bromination reactions allows better utilization of alkyl groups (235,242). An indirect stereoselective procedure for the conversion of alkynes into (H)-1-ha1o-1-alkenes is based on the mercuration reaction of boronic acids followed by in situ bromination or iodination of the intermediate mercuric salts (243). 

Indium dichlotide [13465-11 -7/, InCl, made by heating indium in hydrogen chloride or by reduction of InCl iu H2/HCI, forms colorless crystals. Indium monochloride [13465-10-6] InCl, can be formed by passing InCl vapor over heating indium. 

However, in strong hydrochloric acid, these reagents, as weU as iodic acid, oxidize iodine to iodine monochloride or to the ICl ion. 

Iodine monochloride [7790-99-0] ICl, mol wt 162.38, 78.16% I, is a black crystalline soHd or a reddish brown Hquid. SoHd ICl exists ia two crystalline modifications the a-form, as stable mby-red needles, d = 3.86 g/mL and mp 27.3°C and as metastable brownish red platelets, d = 3.66 g/mL, mp 13.9°C and bp 100°C (dec). Iodine monochloride is used as a halogenation catalyst and as an analytical reagent (Wij s solution) to determine iodine values of fats and oils (see Fats and fatty oils). ICl is prepared by direct reaction of iodine and Hquid chlorine. Aqueous solutions ate obtained by treating a suspension of iodine ia moderately strong hydrochloric acid with chlorine gas or iodic acid (118,119). 

The aHphatic iodine derivatives are usually prepared by reaction of an alcohol with hydroiodic acid or phosphoms trHodide by reaction of iodine, an alcohol, and red phosphoms addition of iodine monochloride, monobromide, or iodine to an olefin replacement reaction by heating the chlorine or bromine compound with an alkaH iodide ia a suitable solvent and the reaction of triphenyl phosphite with methyl iodide and an alcohol. The aromatic iodine derivatives are prepared by reacting iodine and the aromatic system with oxidising agents such as nitric acid, filming sulfuric acid, or mercuric oxide. 

Niobium Pent chloride. Niobium pentachloride can be prepared in a variety of ways but most easily by direct chlorination of niobium metal. The reaction takes place at 300—350°C. Chlorination of a niobium pentoxide—carbon mixture also yields the pentachloride however, generally the latter is contaminated with niobium oxide trichloride. The pentachloride is a lemon-yeUow crystalline soHd that melts to a red-orange Hquid and hydrolyzes readily to hydrochloric acid and niobic acid. It is soluble in concentrated hydrochloric and sulfuric acids, sulfur monochloride, and many organic solvents. 

The monohalide vapors are conveyed to a slightly cooler zone (700—800°C) where the reaction reverses, resulting in the condensation of pure aluminum. The monochloride process was carried to the demonstration plant stage but was abandoned because of corrosion problems (24). 

Selenium and precious metals can be removed selectively from the chlorination Hquor by reduction with sulfur dioxide. However, conditions of acidity, temperature, and a rate of reduction must be carefliUy controlled to avoid the formation of selenium monochloride, which reacts with elemental selenium already generated to form a tar-like substance. This tar gradually hardens to form an intractable mass which must be chipped from the reactor. Under proper conditions of precipitation, a selenium/precious metals product substantially free of other impurities can be obtained. Selenium can be recovered in a pure state by vacuum distillation, leaving behind a precious metals residue. 

Physical Properties. Sulfur monochloride [10025-67-9] S2CI2, is a yeUow-orange Hquid with a characteristic pungent odor. It was first discovered as a chlorination product of sulfur in 1810. Table 5 provides a Hst of the physical properties. 

Table 5. Physical and Thermodynamic Properties of Sulfur Monochloride, S2CI2...

Chemical Properties. The chemistry of the sulfur chlorides has been reviewed (141,142). Sulfur monochloride is stable at ambient temperature but undergoes exchange with dissolved sulfur at 100°C, indicating reversible dissociation. When distilled at its atmospheric boiling point, it undergoes some decomposition to the dichloride, but decomposition is avoided with distillation at ca 6.7 kPa (50 mm Hg). At above 300°C, substantial dissociation to S2 and CI2 occurs. Sulfur monochloride is noncombustible at ambient temperature, but at elevated temperatures it decomposes to chlorine and sulfur (137). The sulfur then is capable of burning to sulfur dioxide and a small proportion of sulfur trioxide. 

Sulfur monochloride is hydrolyzed at a moderate rate by water at room temperature but rapidly at higher temperatures. In the vapor state, the hydrolysis rate is slow and involves disproportionation of the primary hydrolysis products ... 

Various reducing agents, eg, hydrogen iodide, can abstract chlorine from sulfur monochloride leaving elemental sulfur ... 

Sulfur trioxide [7446-11-9] reacts with sulfur monochloride to produce pyrosulfuryl chloride [7791-27-7] CISO2OSO2CI. 

Numerous organic reactions of sulfur monochloride are of practical and commercial importance. Of particular importance is the reaction of sulfur monochloride with olefins to yield various types of addition products (142). With ethylene, the severe vesicant bis(2-chloroethyl) sulfide [505-60-2] (mustard gas) forms with elemental sulfur and polysulfides (see Chemicals IN war). Propylene reacts similarly ... 

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