Trichloramine
NCl3
[10025-85-1] · Cl3N · Trichloramine · (MW 120.36)
(reactive N-haloamine for the amination of aromatics,1 tertiary chlorides,2 and tertiary hydrocarbons;3 also for chlorination of alkenes4 and organoboranes5)
Alternate Name: nitrogen trichloride.
Physical Data: mp <-40 °C; bp <71 °C; explodes at ca. 95 °C; d 1.653 g cm-3.
Solubility: insol cold H2O; sol toluene, methylene chloride, o-dichlorobenzene; decomposes in hot H2O.
Preparative Methods: not commercially available; prepared from calcium hypochlorite, ammonium chloride, and hydrochloric acid in methylene chloride-water, followed by separation of the organic phase, drying, and storage in solution at 0-5 °C or below.6,7
Analysis of Reagent Purity: determination of positive chlorine can be carried out iodometrically.6,7
Handling, Storage, and Precautions: toxic and may explode, especially on heating or when concentrated. Dilute, cold solutions of NCl3 in various organic solvents are stable for several days.6 Store under inert atmosphere. Use only behind a safety shield in an efficient fume hood.
Amination of Aromatics.
The reaction of benzene and derivatives with NCl3 and Aluminum Chloride in organic solvents can be a useful preparation for meta-substituted amines. However, yields are only moderate, and mixtures of isomers are often obtained. Arenes include mono-7-9 and dialkylbenzenes,9,10 halobenzenes,11 biphenyl, and naphthalene.1 With trichloroamine/AlCl3, the conversions of toluene to m-toluidine (eq 1) and of 1,3-dimethylbenzene to 3,5-dimethylaniline (eq 2) in moderate yields have been observed.
An addition-elimination mechanism involving a chloroarenium intermediate has been proposed for the amination reactions (eq 3).10
Amination of halobenzenes and halotoluenes with trichloramine/AlCl3 proceeds by two competing processes in moderate yields.11 For example, fluorobenzene gives predominantly m-fluoroaniline and p-chloroaniline (eq 4). It has been proposed that the former is produced by a substitution (addition-elimination) mechanism, while the latter is formed by a pathway involving nucleophilic displacement of halide in a chloroarenium cation by a nitrogen containing nucleophile (eq 5).
Amination of biphenyl gives 3-aminobiphenyl (eq 6) and amination of naphthalene gives a mixture of 1- and 2-amino derivatives in low yields.1
Amination of Alkanes.
The trichloramine/AlCl3 system has also been used for the amination of monocyclic12,13 bicyclic,13,14 and tricyclic3,15 alkanes. C5-C8 cycloalkanes and their mono- and dimethyl derivatives are aminated in good yields.13 Methylcyclohexane12,16 and methylcyclopentane13 are converted to 1-amino-1-methylcycloalkanes on treatment with trichloramine/AlCl3 (eq 7). Treatment of decalin and hydrindane with the trichloroamine/AlCl3 system affords cis-9-aminodecalin (eq 8) and cis-8-aminohydrindane, respectively, in good yields.13
The trichloroamine/AlCl3 amination route provides a simple one-step method of obtaining aminoadamantanes in high yield (eq 9).3,15 Diamantane17 can also be efficiently aminated in this fashion. When hydrocarbons which do not contain a tertiary hydrogen are subjected to reaction with NCl3/AlCl3, cationic rearrangements and fragmentations are observed.18
Amination of Alkyl-Substituted Aromatics.
Various monoalkyl substituted arenes have been aminated on the alkyl side chain to form t-benzylamines in the system trichloroamine/AlCl3/t-butyl bromide (an efficient additive).19-21 p-Alkyl and p-haloisopropylbenzenes give the corresponding aminated products in high yields (eq 10).
Tertiary Amines from Chlorides.
When simple tertiary alkyl chlorides are exposed to NCl3 and AlCl3 in methylene chloride at -10 °C, varying yields of the corresponding amines can be obtained. t-Pentyl chloride under these conditions provides t-pentylamine in 82% yield (eq 11), while t-octylamine is obtained in 35% yield from the corresponding chloride.2
Primary and secondary halides give isomeric amines resulting from skeletal rearrangement, as well as aziridines (eqs 12-14). Mechanistic details of this reaction have been reported.22
Vicinal Dichlorides from Alkenes.
The reaction of NCl3 with a variety of mono- and disubstituted alkenes, both cyclic and acyclic, affords the corresponding 1,2-dichlorides in high yield. For example, cyclopentene with NCl3 at 0 °C gives trans-1,2-dichlorocyclopentane in 89% yield (eq 15).4
These transformations tend to be high yielding and the products formed are generally simple to purify. In comparison with other reagents commonly used for chlorination of alkenes (Sulfuryl Chloride, Chlorine, Phosphorus(V) Chloride),4,23 NCl3 usually gives fewer byproducts such as allylic chlorides. However, this method fails in the case of trisubstituted alkenes, as well as for styrene.
Conversion of Organoboranes to Alkyl Chlorides.
Trialkylboranes can be oxidized to the corresponding alkyl chlorides with NCl3 in methylene chloride at 0 °C.5,24 Yields range from 66-94% overall from the alkene (eq 16).
Other reagents (PCl5, SO2Cl2, N,N-Dichlorourethane) known to chlorinate organoboranes are usually considerably less efficient.
Other Reactions.
Fluorocyclohexane is obtained in 45% yield from cyclohexene in the presence of NCl3 and Boron Trifluoride.25
1. Kovacic, P.; Harrison, A. K. JOC 1967, 32, 207.
2. Kovacic, P.; Lowery, M. K. JOC 1969, 34, 911.
3. Kovacic, P.; Roskos, P. D. JACS 1969, 91, 6457.
4. Field, K. W.; Kovacic, P. JOC 1971, 36, 3566.
5. Brown, H. C.; De Lue, N. R. T 1988, 44, 2785.
6. Kovacic, P.; Chaudhary, S. S. OSC 1973, 5, 35.
7. Kovacic, P.; Goralski, C. T.; Hiller, J. J., Jr.; Levisky, J. A.; Lange, R. M. JACS 1965, 87, 1262.
8. Strand, J. W.; Kovacic, P. JACS 1973, 95, 2977.
9. Kovacic, P.; Levisky, J. A.; Goralski, O. T. JACS 1966, 88, 100.
10. Kovacic, P.; Field, K. W.; Roskos, P. D.; Scalzi, F. V. JOC 1967, 32, 585.
11. Kovacic, P.; Gormish, J. F. JACS 1966, 88, 3819.
12. Kovacic, P.; Chaudhary, S. S. T 1967, 23, 3563.
13. Field, K. W.; Kovacic, P.; Herskovitz, T. JOC 1970, 35, 2146.
14. Kovacic, P.; Lowery, M. K.; Roskos, P. D. T 1970, 26, 529.
15. Kovacic, P.; Roskos, P. D. TL 1968, 5833.
16. Kovacic, P.; Chaudhary, S. S. OS 1968, 48, 4.
17. Cahill, P. A. TL 1990, 31, 5417.
18. Wnuk, T. A.; Chaudhary, S. S.; Kovacic, P. JACS 1976, 98, 5678.
19. Kovacic, P.; Hopper, R. J. T 1967, 23, 3965.
21. Kovacic, P.; Gormish, J. F.; Hopper, R. J.; Knapczyk, J. W. JOC 1968, 33, 4515.
22. Kovacic, P.; Lowery, M. K. CC 1966, 651.
23. (a) Field, K. W.; Kovacic, P. S 1969, 135. (b) Strand, J. W.; Kovacic, P. SC 1972, 129.
24. Brown, H. C.; De Lue, N. R. JOM 1977, 135, C57.
25. Heasley, G. E.; Janes, J. M.; Stark, S. R.; Robinson, B. L. TL 1985, 26, 1811.
Ender K. Erdik
Ankara University, Turkey
Howard Sard
Organix, Woburn, MA, USA