Cases chlorine

Treatment of a-thiocyanatoketones at low temperature with dry hydrogen chloride in ether solution gives satisfactory yields of 2-chloro-thiazole derivatives (188). The use of phosphorus pentachloride leads to the same results, but in this case chlorination can also occur at the 5-position (Scheme 97) (18, 68). 

The common oxidants are ozone, hydrogen peroxide, H2O, catalyzed usually with ferrous iron, Fe , and ia some cases chlorine dioxide and uv light. Advanced oxidation systems iaclude H2O2 + uv ozone + uv and H2O2, ozone, and uv. Depending on the appHcation, the oxidation can be complete to end products as in a contaminated groundwater or partial to degradable intermediate products as in a process wastewater. 

In all cases, chlorine dioxide is produced at the point of use either from sodium chlorite or sodium chlorate. Production volume can be accurately estimated from total sodium chlorate consumption for chemical pulp bleaching because this use accounts for greater than 95% of all chlorine dioxide production. 

Our own earlier work on the chlorination of toluene had been subject to similar constraints. In this case, chlorination with ferf-butyl hypochlorite had proved to be advantageous. In the presence of silica gel as catalyst the yield of chlorotoluenes was quantitative but the regioselectivity was more or less statistical (ref. 8). However, the use of proton-exchanged zeolite X allowed the production of chlorotoluenes with a para-selectivity of more than 90 % (Fig. 4) (ref. 9). No HCl is generated in this process since the by-product is tert-butanol, and there is no inhibition of the catalyst. Indeed, the catalyst can be reused if necessary. 

Naming bases is a little more straightforward. For a base name, chemists just use the name of the chemical compound. They do the same thing for the salts that are produced when acids and bases react with one another. The salt sodium chloride (NaCl), for example, is named for the two elements that are present in the salt—sodium and chlorine. The only rule is to change the ending for the name of the nonmetal (in this case, chlorine) to -ide, giving us the name sodium chloride. 

Compressed oxygen, and fresh and recycled ethylene, are heated, mixed, and then passed through a reactor with fixed beds of catalyst— silver oxide deposited on alumina pellets. In recent years the catalyst has been improved by the addition of promoters and inhibitors. (Promoters—in this case compounds of alkali or alkaline rare earth metals—enhance the activity of the catalyst inhibitors—in this case chlorine compounds—chloroethane, or vinyl chloride, reduce its rate of activity decline.)... 

Figures 4.42 and 4.43 show the absorption spectra of nitrosyl chloride (C1NO) and nitryl chloride (C1N02), respectively (Roehl et al., 1992 Ganske et al., 1992), and Tables 4.35 and 4.36 list the recommended room temperature absorption cross sections (DeMore et al., 1997). In both cases, chlorine atoms are produced with unit quantum yield ...

In many cases chlorine is used as a mule 10 a linal product which contains no chlorine For instance propylene oxide has traditionally been manufactured by the chlornhydrin process. Modem technology permits abandoning this route in favor of direct oxidalion. thus eliminating a need for chlorine. 

The reaction with silver nitrate serves to determine the presence of chlorides both gravimetrically volumetrically in the former case, chlorine is weighed as AgCl in the latter, the vol of std AgNC>3 soln reqd for complete pptn of the chloride present in a known vol of soln is detd (Refs 2 4) (See also Refs 2a, 6 7)... 

Rapid side-chain chlorination of toluene proceeds in the dark with sulphuryl chloride in the presence of benzoyl peroxide (0.001-0.005 mol per mol of S02C12) as catalyst (Expt 6.27). With an excess of sulphuryl chloride, benzylidene chloride is formed, but in this case chlorination does not proceed beyond this stage. 

On the contrary, when methylphenyldichlorosilane is chlorinated with chlorine in the presence of electrophilic catalysts (e.g. metals or their halo-genides), only the phenyl radical is chlorinated, while the methal radical is untouched. In this case chlorination develops in the following way ... 

All these faults can be largely eliminated by chlorinating ferrosilicon in a medium of melted salts. In this case, chlorination should be started in a melt of sodium chloride (or an equimolar mixture of sodium and potassium chlorides). Then the iron chlorides which form alongside with SiCl4, are held in the melt in the form of complexes with chlorides of alkaline metals (NaFeCLt and KFeCl4). After the concentration of Fe in the melt reaches 45-50% (equivalent to FeCfi), the new portions of ferrosilicon are supplemented with a corresponding quantity of sodium chloride (or an equimolar... 

Chlorination is also an important step in the synthesis of oxygenated aromatic compounds. In this case, chlorination takes place at alkyl groups attached to the rings and is conducted in the absence of iron. The use of UV light... 

The actual application of the method is best illustrated by dealing with a particular atom, in this case chlorine. For the chlorine atom N = Ny = 2 and N =l, and on substituting these values in equation 16 it is seen that gat = gz, hence... 

Obviously, when the desired product contains a chlorine atom, the use of chlorine can be avoided only by replacing the product. However, in many cases chlorine is a reagent that does not appear in the product, and its use can be circumvented. How remarkably simple the solution can be, once the problem has been identified, is illustrated by the manufacture of a family of sulfenamides that are used as rubber additives. 

In special cases, chlorination is brought about by replacement of a sulfonic group by chlorine. This reaction is particularly important with anthraquinone compounds, but it is also known in the benzene series (see page 236). 

The reaction of furancarboxylic acids with sulfur tetrafluoride leads to the corresponding trifluoromethyl-substituted furans in good yields (see examples in Table 6). A number of furancarboxylic acids, mainly furan-2-carboxylic acids, and furan-2,5- and -3,4-dicarboxylic acids, show a different behavior. Here highly fluorinated dihydrofurans, e g. 25, are formed. This class of compounds is also obtained with the reagent system sulfur tetrafluoride/hydrogen fluoridc/chlorine or sulfur tetrafluoride/hydrogen fluoride/sulfuryl chloride. In some cases chlorine-containing products are found. 

Fluorinated plastics are thermoplastic paraffinic polymers where the hydrogen has been replaced by fluorine and, in some cases, chlorine. 

The submitter states that a number of aromatic mono-and dinitriles have been prepared by this procedure vvith slight or no modification in the temperature. The reaction mixtures were usually worked up by the acetone-ammonia method described in Note 6. Among the compounds prepared by this method are o-nitrobenzonitrile, o-bromobenzonitrile, w-methoxy-benzonitrile, 4,4 -dicyanodiphenylsulfone, 4,4 -dicyanostilbene, a,7-di-(4-cyanophenoxy)propane. With the last, a temperature of 185 190° for 20 minutes gave the best results. The yields before purification ranged between 75% and 95% and after purification between 63% and 79%. Aliphatic acids give low yields of the corresponding nitriles and, in some cases, chlorinated by-products. 

Another example for the bioisosteric equivalence of aromatic bulky polar substituents (in this case chlorine) and ortho difluorination is a second generation analog of the anti-HIV drug Efavirenz. The difluoro analog acts as a reverse transcriptase inhibitor with a different pattern of resistance [62] (Scheme 4.29). 

It is not known whether polychloroalkanes can be absorbed on zeolites if that is the case, chlorination on zeolites can be used for selective introduction of one or two additional Cl atoms into terminal groups of the carbon chain. 

Addition of fluorine to a C=C bond is different from that of the other halogens in one important respect the heat of reaction exceeds the dissociation energy of an aliphatic C-C bond (80 kcl/mole) quite appreciably. Addition and substitution reactions of fluorine are so exothermic that most organic substances burn or explode if brought into direct contact without special arrangements.15 Addition of F2 to olefins has no preparative importance 48 in the aromatic series addition and substitution result simultaneously. In electrophilic addition, i.e., in most cases, chlorine reacts faster than bromine with olefins, but in nucleophilic addition bromine reacts faster than chlorine.16... 

Greenberg and Moffatt also examined the reaction of I vvith ribonucleosides in particular, a protected form of uridine (9). In this case, chlorine is introduced... 

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