(Hive Bee)
11-23-00 05:15
No 70465
      Another route to nitrostyrenes
(Rated as: excellent)

OK, this one uses AgNO2, Et3N and prefers water-free solvents & working under N2, so it's not exactly for the garage-cooks. Am curious if it is possible to use NaNO2.

Tet. Lett. 26, 9, 1193, 1985:

In connection with the search of a more efficient synthesis of 2,3,5-trimethoxyamphetamine, for use as a drug standard, we have found that nitryl iodide is a particular effective general reagent for the nitration of substituted styrenes. beta-nitrostyrenes are generally prepared by direct nitration of stryenes or by condensation of the aldehyde with nitroethane; reduction of the beta-nitrostyrenes gives the amphetamine. Nitration of styrene by tetranitromethane is difficult and yields vary greatly. Nitration reagents such as HgCl2-NaNo2[3) lead to varying degrees of ring nitration as well as the intended reaction at the double bond.

Nitryl iodide is generated in situ by the reaction of silver nitrite with iodine. First reported by Birchenbath in 1932[4], this reaction was virtually disregared until 1964. Its synthetic utility and the mild conditions of its application were initially described by Hassner et al[5]. [...]

The mechanism of the reaction was examined in detail by Hassner. Nitril iodide underwent regioselective addition to styrene to form the iodonitro compound which upon treatment with base generated the beta-nitrostyrene. However, contrary to Hassners claim, we have found that the use of excess iodine does not improve the yield. We deduce that poor yield is attributable to degradation of the unstable iodonitro intermediate which is sensitive to moisture and oxygen. In some instances, hydroxynitro compounds and nitroketone could be detected. However, good yields of beta-nitrostyrene could be consistenly assured by treatment of the crude addition product with triethylamine, immediately following the disappearance of the styrene substrate, as judged by TLC monitoring of the course of the reaction.

The solubility of the beta-nitrostyrene product in the reaction medium is a major factor affecting the yield realized: beta-nitrostyrenes whch are relatively insoluble in the reaction medium co-precipitate with the reagent, forming a solid cake which inhibits further reaction. in such a circumstance, changing to a more suitable solvent such as THF is necessary to ensure a respectable yield. I2 (1016 mg, 4 mMol) and AgNO2 (616 mg, 4 mMol) were stirred in anhydrous ether (20 ml) ar r.t. under nitrogen for 45 min. Beta-methylstyrene (236 mg, 2mMol) and pyridine (632 mg, 8 mMol) in ether were added, and the mixture was stirred at rt for 3.5 h.; after this time the yellow solid was removed by filtration. The filtrate as treated with 0.5 ml Et3N and evaporated to dryness. The residue was the treated with Et3N (1 mL) in CH2Cl2 (1 mL) at rt for 1h. The resulting solution was evaporated to dryness, the residue was dissolved in Ch2Cl2, washed with 5% aqeous NaHSO3, 5% aqeous HCl, saturated aqeous NaHCO3 and water, dried over Na2SO4, and solvent removed under reduced pressure to give a dark brown liquid. This material was chromotographed on silica and eluted with 8% ether/hexane to give the pure product (249 mg, 76.4%).

starting material:         solvent       yield
2,4,5-trimethoxystyrene    ether         80.3%
p-methoxybenzene           THF           81.8%
isosafrole                 THF           69.8%
5-propenylbenzene          THF           53.0%
beta-methylstyrene         ether         76.4%
styrene                    ether         45.3%

[3] JACS, 100, 6294, 1978
[4] Berichte, 1339, 1932
[5] JOC, 34, 2328,1969

(Chief Bee)
04-19-04 12:58
No 501645
      Nitration of Alkenes to Nitroalkenes
(Rated as: excellent)

An Improved Method for the Preparation of Nitroalkenes from Alkenes
D. Ghosh & D.E. Nichols
Synthesis 195-197 (1996) (../rhodium/chemistry /nitryliodide.ptc.html)

Nitration of cyclic conjugated olefins was achieved in a one-pot procedure using nitryl iodide generated in situ from iodine and potassium nitrite complexed with 18-crown-6 in tetrahydrofuran under sonication/stirring, followed by treatment of the unstable iodo nitro compound with base. The yield of the nitro compound varied from 52 to 90%.
____ ___ __ _

A New Method for Nitration of Alkenes to ,-Unsaturated Nitroalkenes
Jih Ru Hwu, Keh-Loong Chen and Sarkkarai Ananthan
J. Chem. Soc., Chem. Commun., 1425-1426 (1994) (../rhodium/pdf /alkene.nitration.can-nitrite.pdf)

,-Unsaturated nitroalkenes were synthesized in 54-99% yields by sonication of a chloroform solution containing the corresponding alkenes, NaNO2 (10 equiv.), Ce(NH4)2(NO3)6 (2.0 equiv.), and acetic acid (12 equiv.) in a sealed tube at 25-73C.

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