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Direct Conversion of Aromatic Nitro Compounds into Isothiocyanates.

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pentane mixture (1 5 ) and is obtained in the form of leaflets
on removal of the solvent (yield 8-9 g).
A solution of ( 5 ) (917 g) in CC14 (7ml) is irradiated under
nitrogen in a glass ampoule at -2OOC for 15-20 h. The
contents of the ampoule are chromatographed on silica gel
(30 g) and eluted with pentane (500ml). Evaporation to
dryness leaves 578 mg of crystals from which compound (6)
(534 mg, 82%) is obtained by sublimation at 30 torr (bath
temperature 75 “C); compound (7) (44 mg, 7 %) remains
behind as residue.
Received: June 30, 1969
[Z 59 IE]
German version: Angew. Chem. 81, 750 (1969)
[ * ] Prof. Dr. R. Criegee and Dipl.-Chem. R. Huber
Institut fur Organische Chemie der Universitat
75 Karlsruhe, Richard-Willstatter-Allee (Germany)
[l] W. C. Solomon, L . A. Due, and D. W. Schultz, J. org. Chemistry 31, 1551 (1966).
[21 The best yield is obtained when a mixture of the dichloro and
dibromo compounds is used.
[3] Prepared by K. 0.Scherer and T . J. Meyers [J. Amer. chem.
SOC.90, 6253 (1968)] by another method.
[4] (5) can be obtained directly from the mixture of ( 3 ) and 14)
because ( 4 ) does not react with ozone under the above conditions.
[ 5 ] P. R . Story, W. H. Morrison, T. K . Hall, J . C. Farine, and
E. E. Bishop, Tetrahedron Letters 1968, 3291; R. P. Story, T. K .
Hall, W. H . Morrison, and J. C. Farine, ibid. 1968, 5397.
Direct Conversion of Aromatic Nitro
Compounds into Isothiocyanates
The conversion of aromatic nitro compounds into isothiocyanates by method a) is accompanied by concomitant
formation of anilines in varying amounts. This undesired
side reaction is more favored by phenoxides than it is by
alkoxides. The formation of anilines is arrested or at least
reduced to insignificant levels, and both conversions and
yields are increased, when aryl sulfides are employed as base
(method b). The aryl sulfides are oxidized predominantly to
disulfides, which were isolated. Similar but slightly reduced
conversions and yields are achieved when the nitro compounds are treated in CS2 with a sodium aryl trithiocarbonate, e.g. m-CH3-C&4SC(S)SNa, formed from sodium mtolyI sulfide and carbon disulfide. Nearly complete conversion
of the nitro compounds takes place under the conditions of
method c); however, the formation of anilines is not controlled so effectively as in method b).
Extension of the reaction (method b) to aromatic dinitro
compounds, e.g. m-dinitrobenzene, gave 3-nitrophenyl isothiocyanate and small amounts of m-phenylene diisothiocyanate. Aliphatic nitro compounds d o not react satisfactorily under the above conditions.
m-Tolyl isothiocyanate (method b )
A 300-ml stirring autoclave was charged with 13.7 g of mnitrotoluene, 7.3 g of sodium m-toiyl sulfide, and 50 ml of
carbon disulfide. The mixture was heated at 16OoC for 3
hours. The crude reaction product was distributed between
100 ml of ether and 75 ml of cold water. The organic layer
was dried with CaCIZ and distilled over a spinning band
column. Yield 9 g of m-tolyl isothiocyanate (87% based on
71 % conversion of m-nitrotoluene).
By G. Ottmann and E. Kober[*l
Isothiocyanates (2) could previously be synthesized from
nitro compounds ( I ) only by reduction to the amines and
reaction of the latter with, e.g., carbon disulfide and a heavy
metal salt or with thiophosgene[l].
We have now been able to accomplish the direct conversion
of aromatic nitro compounds (nitrobenzene, dinitrobenzene,
and their derivatives) into isothiocyanates by reaction with
carbon disulfide or carbonyl sulfide in presence of selected
bases.
The reaction is best performed by heating the nitro compound in an autoclave with a) carbon disulfide and alkali
metal alkoxide or phenoxide, b) carbon disulfide and an alkyl
or aryl sulfide, or c) carbonyl sulfide and an aryl sulfide.
Optimum results are obtained at a reaction temperature of
between 150 and 17OoC, and by employing carbon disulfide
(methods a and b) or carbonyl sulfide (method c) as both
reactant and solvent. In other solvents, such as benzene,
toluene, benzonitrile, o-dichlorobenzene, carbon tetrachloride, or 1,1,2-trichloro-1,2,2-trifluoroethane,the reactions result in conversions and yields lower than those reported in the Table.
RNOz
+
RNCS
___
Meth.
R
___
a
b
b
b
b
b
a
b
b
C
a
b
C
a
b
760
Conversion
of (1) ( %)
66
34
50
73
93
53
50
71
59
99
41
50
96
80
74
50
58
51
61
73
77
66
87
75
55
81
88
53
58
84
Received: June 10, 1969
[Z 65 IE]
German version: Angew. Chem. 8/, 782 (1969)
[**I and Dr. E. H. Kober [***I
Olin Mathieson Chemical Corporation
Research Center
275 Winchester Ave.,
New Haven, Connecticut 06504 (USA)
[**I New address:
Dr. Kurt Herberts & Co.,
56 Wuppertal-Barmen, Christbusch 25 (Germany)
[***I New address:
NITROCHEMIE GmbH
8261 Aschan bei Kraiburg/Inn (Germany)
[I] Houben- Weyl-Miiller: Methoden der organischen Chemie.
Thieme, Stuttgart 1955, Volume IX.
[*] Dr. G . Ottmann
The Carbene/Carbenoid Problem[**I
By M . Schlosser and G . Heinzr*J
Competitive experiments may afford definitive information
about unisolable intermediates in reaction sequences [I]. If a
short-lived species S is really the product-forming agent and
can be formed from two different starting materials A and B,
any reaction products C + D are formed in the same proportions independently of whether the postulated intermediate is derived from A or from B:
A
I
S*C+D
B
f
In connection with the problem whether “free” carbenes
(here C6H5-CH)
or “carbenoids” (carbene-metal salt
adducts, here C6H5-CHLiX) add to olefins, giving cyclopropane derivatives [21, we have treated the benzyl halides
(Iu)-(Id) with butyllithium in the presence of cyclohexene
(2), then measuring the proportions in which the products
syn- and anti-7-phenylnorcarane are formed in four solvents
(Fig. 1).
Angew. Chem. internat. Edit.
1 Voi. 8 (1969) J No. I 0
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compounds, direct, nitra, aromatic, isothiocyanate, conversion
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