In situ Chlorination

The first (inconclusive) work bearing on the synthesis of element 104 was published by the Dubna group in 1964. However, the crucial Dubna evidence (1969-70) for the production of element 104 by bombardment of 94PU with loNe came after the development of a sophisticated method for rapid in situ chlorination of the product atoms followed by their gas-chromatographic separation on an atom-by-atom basis. This was a heroic enterprise which combined cyclotron nuclear physics and chemical separations. As we have seen, the actinide series of elements ends with 103 Lr. The next element should be in Group 4 of the transition elements, i.e. a heavier congenor of Ti, Zr and Hf. As such it would be expected to have a chloride... 

Figure 5.5. In situ chlorinator for the generation of hafnium chloride.

The electrolyte is made by in situ chlorination of vanadium to vanadium dichloride in a molten salt bath. Higher valent chlorides are difficult to retain in the bath and thus are not preferred. The molten bath, which is formed by sodium chloride or an equimolar mixture of potassium chloride-sodium chloride or of potassium chloride-lithium chloride or of sodium chloride-calcium chloride, is contained in a graphite crucible. The crucible also serves as an anode. Electrolysis is conducted at a temperature about 50 °C above the melting point of the salt bath, using an iron or a molybdenum cathode and a cathode current density of 25 to 75 A dnT2. The overall electrochemical deposition reaction involves the formation and the discharge of the divalent ionic species, V2+ ... 

For chlorination we graduated from hypochlorite tanks to in situ chlorine generation by electrochemical means, a major improvement indeed, which we highly recommend. However, we have had more than our share of problems with the chlorine generator we used. 

If one does not have the possibility of using different sources for different elements, one may feed the source with compounds more volatile than the elements. Chlorides, fluorides, and oxides, in particular, are useful feed materials. Unfortunately, some compounds, which are otherwise suitable, tend to undergo thermal decomposition in the source and therefore have to be eliminated. Others, such as some chlorides, are extremely sensitive to water and hence converted under normal experimental conditions into their non-volatile oxides. To overcome this difficulty, the CCI4 method was developed. With it the desired element is stored as an oxide in a rather hot zone near the inlet of the ion source. By passing CCI4 over the oxide an in situ chlorination takes place and the resulting chloride is immediately swept in-... 

This reaction has been modified by the in situ chlorination of sulfone using CCI4 as a chlorination reagent. In addition, the sulfones have been mixed with powdered KOH and AI2O3 to improve the extrusion of S02. The reaction is also extended to a solid-phase supported condition (e.g., resin). ... 

Sanda K, Rigal L, Gaset A (1992) Optimisation of the synthesis of 5-chloromethyl-2-furancarboxaldehyde from D-fructose dehydration and in-situ chlorination of 5-hydroxymethyl-2-furancarboxaldehyde. J Chem Technol Biotechnol 55 139-145... 

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). 

Basic oxides of metals such as Co, Mn, Fe, and Cu catalyze the decomposition of chlorate by lowering the decomposition temperature. Consequendy, less fuel is needed and the reaction continues at a lower temperature. Cobalt metal, which forms the basic oxide in situ, lowers the decomposition of pure sodium chlorate from 478 to 280°C while serving as fuel (6,7). Composition of a cobalt-fueled system, compared with an iron-fueled system, is 90 wt % NaClO, 4 wt % Co, and 6 wt % glass fiber vs 86% NaClO, 4% Fe, 6% glass fiber, and 4% BaO. Initiation of the former is at 270°C, compared to 370°C for the iron-fueled candle. Cobalt hydroxide produces a more pronounced lowering of the decomposition temperature than the metal alone, although the water produced by decomposition of the hydroxide to form the oxide is thought to increase chlorine contaminate levels. Alkaline earths and transition-metal ferrates also have catalytic activity and improve chlorine retention (8). 

Several commercial grades are available fine crystals of 99 to 100% purity, large crystals, pressed lumps, rods, and granular material. Double-Decomposition Methods. Double-decomposition processes all iavolve the reaction of sodium chloride, the cheapest chlorine source, with an ammonium salt. The latter may be suppHed directiy, or generated in situ by the reaction of ammonia and a supplementary iagredient. Ammonium chloride and a sodium salt are formed. The sodium salt is typically less soluble and is separated at higher temperatures ammonium chloride is recovered from the filtrate by cooling. 

In two proposed alternative processes, the chlorine is replaced in the hypochlorination reaction by hypochlorous acid [7790-92-3] HOCl, or tert-huty hypochlorite. In the first, a concentrated (>10% by weight) aqueous solution of hypochlorous acid, substantially free of chloride, chlorate, and alkah metal ions, is contacted with propylene to produce propylene chlorohydrin (113). The likely mechanism of reaction is the same as that for chlorine, as chlorine is generated in situ through the equiUbrium of chlorine and hypochlorous acid (109). 

Aerobic, Anaerobic, and Combined Systems. The vast majority of in situ bioremediations ate conducted under aerobic conditions because most organics can be degraded aerobically and more rapidly than under anaerobic conditions. Some synthetic chemicals are highly resistant to aerobic biodegradation, such as highly oxidized, chlorinated hydrocarbons and polynuclear aromatic hydrocarbons (PAHs). Examples of such compounds are tetrachloroethylene, TCE, benzo(a)pyrene [50-32-8] PCBs, and pesticides. 

Chlorine gas is usually used, but electrolysis of alkaline salt solutions in which chlorine is generated in situ is also possible and may become more important in the future. The final pH of solutions to be sold or stored is always adjusted above 11 to maximize stabiUty. The salt is usually not removed. However, when the starting solution contains more than 20.5% sodium hydroxide some salt precipitates as it is formed. This precipitate is removed by filtration to make 12—15% NaOCl solutions with about one-half of the normal amount of salt. Small amounts of such solutions are sold for special purposes. Solutions with practically no salt can be made by reaction of high purity hypochlorous acid with metal hydroxides. 

Stable A/-chloro compounds are formed by reaction of hypochlorous acid and appropriate N—H compounds. For example, HOCl, formed in situ via chlorine hydrolysis, converts di- or trisodium cyanurates to dichloro- and trichloroiso-cyanuric acids, respectively (114). Chloroisocyanurates can also be prepared from isocyanuric acid or monosodium cyanurate and preformed HOCl (115—117). Hydrolysis of chloroisocyanurates provide HOCl for use in swimming pool disinfection and in bleaching appHcations. 

Hypochlorous acid, preformed or generated in situ from chlorine and water, is employed in the manufacture of chlorohydrins (qv) from olefins, en route to epoxides, and in the production of chloramines (qv), especially chloroisocyanurates from cyanuric acid (see Cyanuric and isocyanuric acids). 

Uses. Chloric acid is formed in situ by reaction of sodium chlorate and a strong acid during chlorine dioxide production. Stoichiometric amounts... 

The chlorination of benzene can theoretically produce 12 different chlorobenzenes. With the exception of 1,3-dichlorobenzene, 1,3,5-trichlorobenzene, and 1,2,3,5-tetrachlorobenzene, all of the compounds are produced readily by chlorinating benzene in the presence of a Friedel-Crafts catalyst (see Friedel-CRAFTS reactions). The usual catalyst is ferric chloride either as such or generated in situ by exposing a large surface of iron to the Hquid being chlorinated. With the exception of hexachlorobenzene, each compound can be further chlorinated therefore, the finished product is always a mixture of chlorobenzenes. Refined products are obtained by distillation and crystallization. 

TCCA can also be prepared by reaction of performed or in situ generated HOCl with CA slurry (23). Chlorine monoxide can also be used to prepare TCCA from finely powdered CA (24). 

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