N-halo

A process for the commercial synthesis of -phenylene diisocyanate using terephthalamide [3010-82-0] as a precursor and involving N-halo intermediates has been studied extensively (21). The synthesis of 1,4-diisocyanatocyclohexane from terephthaUc acid [100-21-0] also involves a nitrene intermediate (22). 

TABLE 6. Oxidation of sulphides to sulphoxides, R1R2SO, using N-halo compounds... 

Treatment with sodium hypochlorite or hypobromite converts primary amines into N-halo- or N,N-dihaloamines. Secondary amines can be converted to N-halo secondary amines. Similar reactions can be carried out on unsubstituted and N-substituted amides and on sulfonamides. With unsubstituted amides the N-halo-gen product is seldom isolated but usually rearranges (see 18-13) however, N-halo-N-alkyl amides and N-halo imides are quite stable. The important reagent NBS is made in this manner. N-Halogenation has also been accomplished with other reagents, (e.g., sodium bromite NaBr02) benzyltrimethylammonium tribromide (PhCH2NMe3 Br3"), and NCS. The mechanisms of these reactions involve attack by a positive halogen and are probably similar to those of 12-47 and 12-49.N-Fluorination can be accomplished by direct treatment of amines °° or... 

HI, or Cdl2 iodofluorination with mixtures of AgF and U and mixtures of N-bromo amides in anhydrous HF give bromofluorination. Bromo-, iodo-, and chlorofluorination have also been achieved by treatment of the substrate with a solution of Br2,12, or an N-halo amide in polyhydrogen fluoride-pyridine while... 

The groups R2N and Cl can be added directly to alkenes, allenes, conjugated dienes, and alkynes, by treatment with dialkyl-V-chloroamines and acids. " These are free-radical additions, with initial attack by the R2NH- radical ion. " N-Halo amides (RCONHX) add RCONH and X to double bonds under the influence of UV light or chromous chloride. " Amines add to allenes in the presence of a palladium catalyst. ... 

The first step is an example of 12-52 and intermediate N-halo amides (69) have been isolated. In the second step, 69 lose a proton to the base. Compound 69 are acidic because of the presence of two electron-withdrawing groups (acyl and halo) on the nitrogen. It is possible that the third step is actually two steps loss of bromide to... 

Rearrangement of N-halo-N-acyl aromatic amines (Orton)... 

Alkyl hypochlorites and N-halo amides add to isocyanides to give, after hydrolysis, carbamates and N-acylureas (ureides), respectively.806... 

A similar reaction has been carried out on N-halo amides, which give y-lactones 612... 

Barton Beckwith Goosen/. Chem. Soc. 1965, 181 Petterson Wambsgans/. Am. Chem. Soc. 1964,86, 1648 Neale Marcus Schepers J. Am. Chem. Soc. 1966,88, 3051. For a review of N-halo amide rearrangements, see Neale Synthesis 1971, 1-15. 

See R. S. Neale, N. L. Marcus, Journal of Organic Chemistry 1969, 34, 1808 for related reactions of N-halo-cyano compounds. A radical process is discussed. 

Halogen-substituted olefins may be obtained from hydrazones by the action of N-halo compounds.3 26 3 27 cf 3 28,37 2 (Chloro compounds of this type may also be made by the direct action of phosphorous pentachloride on the ketone, e.g. ref. 329, 330.)... 

Reactions at n-halo sulfides with silyl enolates... 

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