Chlorinating reagents

Phosphoms trichloride, PCl, is a clear, volatile Hquid having a pungent, irritating odor. Principal reactions of PCl, an excellent chlorination reagent for various hydrocarbons, are summarized in Figure 3. 

Uses. The largest usage of PCl is to produce phosphonic acid, H PO, which in reaction with iminodiacetic acid and formaldehyde forms a glyphosate intermediate that is decarboxymethylated to glyphosate, an effective nonselective herbicide (see Herbicides). Phosphoms trichloride is also a convenient chlorinating reagent for producing various acyl and alkyl chlorides. 

The chloride of triflic acid (trifluoromethanesulfonyl chloride) is an effective sulfonylating agent Like triflic anhydride, it usually reacts with alcohols and other nucleophiles with the formation of the corresponding derivatives of tnflic acid [69] However, in some reactions, it acts as a chlorinating reagent [98] The reactions of tnfluoromethanesulfonyl chloride with 1,3-dicarbonyl compounds or some carboxylic esters in the presence of a base result m the formation of chlonnated products in high yields (equation 49)... 

The first kinetic study used chloromethyl methyl ether as chlorinating reagent and acetic acid as solvent, viz. reaction (188)381... 

Another reducing agent relevant to chlorination reactions is sulfur dioxide. When the material to be chlorinated contains calcium oxide, it is advantageous to convert it to calcium sulfate rather than to calcium chloride. The advantages are less chlorine consumption and easy disposal of calcium sulfate (which is water-insoluble). The chlorination of scheelite is an important example of the use of the sulfur dioxide chlorine reagent ... 

Several B-haloborazines have been prepared by photochemical reactions. B-monochloroborazine was prepared photochemically by Oertel and Porter using a number of chlorinating reagents (HCl, CH3a, CHa3, HSO3CI). Other synthetic methods reported for this compound and for B-monobromoborazine involve the for-... 

Dialkyl and diaryl ditellurides are easily converted into the corresponding tellurium trichlorides by means of the fission of the Te-Te bond by a chlorinating reagent. This route is very suitable for the preparation of the alkyl derivatives in view of the easy accessibility of dialkyl ditellurides via the alkylation of sodium ditelluride (see Section 3.2.1). 

The chlorination of tellurides is more conveniently done by using, instead of chlorine (gaseous or dissolved in solvents), chlorinating reagents such as sulphuryl or thionyl chloride (Uke the chlorinolysis of ditellurides, see Section 3.5.2). 

The nature of the chlorinated reagent is crucial for promoting the Kharasch addition reaction (Equation 8.11). The results showed that carbon tetrachloride could be added to various olefins in a regioselective way. Under these reaction conditions, no polymerization products were detected. In contrast, when chloroform was used as the halide source the methyl methacrylate and styrene conversions reached only 33% and 40% with the best performing system (VIII), and a significant fraction of polymers was observed [61]. 

Bromofluorination of dodec-2-ene, styrene, and methyl undec-10-enoate are carried out using similar conditions but using l,3-dibromo-5,5-dimethylhydantoin instead of A-halosuc-cinimide however, chlorofluorination with A-chlorosuccinimide as a chlorinating reagent is not successful at all and starting alkenes are recovered unchanged.336... 

In contrast, reactions of esters of unsaturated acids with the sulfur tetrafluoride/hydrogen fluoride/chlorine reagent result in formal addition of C1F across the C = C bond to formchloro-fluoroalkanoic acid esters. The Markovnikov-type addition occurs in reactions with methacrylic and but-2-enoic esters to give 3-chloro-2-fluoro esters, e.g. 17, while from acrylic esters anti-Markovnikov products, 2-chloro-3-fluoro esters, e.g. 16, are formed.242... 

Nanocrystalline MgO and CaO with high surface area are able to absorb large amounts of chlorine, which undergo dissociative chemisorption. These can serve as rather selective, catalytic alkane chlorination reagents, which suggests that trapped Cl atoms are involved in the reaction.295 Liquid-phase low-temperature chlorination of alkanes is also possible in the presence of various alkenes as inductors and AIBN [azobis(isobutyronitrile)] 296... 

Benzotriazole can be chlorinated at the N(l) position by NaOCl (85H(23)2225). 1-Chlorobenzotriazole - a rather stable crystalline compound that has found application in organic synthesis as a selective chlorinating reagent and mild oxidant. A-Fluorination of benzotriazole with cesium fluoroxysulfate gives 1-fluorobenzotriazole in 25% yield (91T7447). 

Similarly to AVal derivatives, ALeu methyl ester was prepared from Leu methyl ester in 90% yield using terf-butyl hypochlorite as the chlorinating reagent and DBU as the base for dehydrochlorination. A number of peptides have been prepared using this approach.124-2X1 The other method reported by Shin et al.1841 involves a one-pot procedure using N-carboxy-Z-a, 3-didehydroleucine anhydride 61 (ALeu-NCA) to give 62 (Scheme 21) 129 841 a ANCA can also be used to prepare Alle derivatives.1841... 

This compound is a useful chlorinating reagent, and although relatively stable, its purification by distillation is not normally attempted. Primary and secondary hypochlorites readily explode when exposed to light, and even in the absence of light rapid decomposition occurs at room temperature. t-Butyl hypochlorite may be prepared by the interaction of t-butyl alcohol, sodium hydroxide and chlorine at low temperature, which must be carefully controlled during the reaction... 

Remove chlorinating reagents by evaporation, followed by co-evaporating with toluene and diethyl ether. 

The direct enantioselective a-chlorination of aldehydes leads to important intermediates 27 in organic synthesis (Scheme 2.34). This reaction was developed independently by two groups MacMillan et al. applied the salt of the imidazolidinone 3g as the catalyst, as i-proline was found to be a poor catalyst for this reaction (Scheme 2.34) [26a]. Various chlorinating reagents were tested, and the per-chlorinated quinone 28 was found to provide the best enantioselectivity. It was... 

The other development for the direct enantioselective a-chlorination of aldehydes was reported by the present authors, and was seen to differ from the first approach in several ways. For example, the catalysts used for the a-chlorination reaction were the C2-symmetric (2R,5R)-diphenylpyrrolidine 3h and i-proline amide 3i, while the electrophilic chlorinating reagent was N-chlorosuccinimide (NCS) 29 (Scheme 2.34) [26b]. Both chiral amines were effective catalysts for the a-chlorination reaction, and the optically active products 27 were obtained in high yields the use of catalyst 3h provided generally higher enantiomeric excess (81-97% ee) than 3i (70-95% ee). 

S02C12) acts as a chlorinating reagent. Here, the chlorination of tert-butylbenzene is shown. 

On account of its low chlorine potential178 (pJ cp = 4.85 at 250)11 40 is a stronger chlorinating reagent in water than either chloramine-T or V-chlorosuccinimide.174 Methanolysis of 40 yields 1 and methyl hypochlorite.174 An earlier report122 and references179 on formation of N-methylsaccharin (8) in this reaction should be revised. 

Trichloromedianesulfonyl chloride has also been used as a chlorination reagent for alkanes, but this reaction requires a peroxide initiation step (equation 80). ... 

Indok synthesis. Gassman and van Bergen have used a modification of the above-mentioned procedure for synthesis of 2-substituted indoles from anilines. The aniline IS treated as above with a chlorinating reagent at — 65° and then an equivalent of methyl-thio-2-propanone at the same temperature. An equivalent of a base (usually triethyl-amine) is added. Workup affords the indole derivative (2) in 60-70% yield. The thio-methyl group is removed with Raney nickel (>70% yield). The keto sulfide can be varied thus nse of methyl phenacyl sulfide [CH3SCH2C(=0)C5H5]4 in the synthesis leads to 2-phenylindoles. 

Other chlorinating reagents that have also been used are indicated in the table. 

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